Post by: old guy on 31/08/2012 17:51:10
(Incoming muons having a longer than expected "lifespan" does not make Earth's atmosphere thinner (contracted), except "for a muon," not actually thinner)
SR theorists claim that from a frame of reference flying by Earth at near light speed ('c') Earth's diameter as measured in the direction of the fly-by would be contracted, making Earth a very oblate spheroid rather than the near sphere established by Earth science. Further, they claim that the effect is not just a distortion (appearance only) but that Earth is in fact flattened (like the subatomic particles) "for that frame of reference" and that "there is no preferred frame of reference," so that measurement (flattened shape of earth) is "equally valid."
What say you SR experts here?
Post by: imatfaal on 31/08/2012 18:09:37
Welcome to the forum by the way.
Then nightly sings the staring owl,
Tu-whit;
Tu-who, a merry note
Love's Labour's Lost
Post by: lightarrow on 31/08/2012 19:28:33
Special relativity (SR) theory has a part called length contraction. There is evidence for it on subatomic scale in particle accelerators, but none that I know of on large scale.1. Definition of lenght between two points of an object: measure the simultaneous position of the two points and make the difference.
(Incoming muons having a longer than expected "lifespan" does not make Earth's atmosphere thinner (contracted), except "for a muon," not actually thinner)
SR theorists claim that from a frame of reference flying by Earth at near light speed ('c') Earth's diameter as measured in the direction of the fly-by would be contracted, making Earth a very oblate spheroid rather than the near sphere established by Earth science. Further, they claim that the effect is not just a distortion (appearance only) but that Earth is in fact flattened (like the subatomic particles) "for that frame of reference" and that "there is no preferred frame of reference," so that measurement (flattened shape of earth) is "equally valid."
What say you SR experts here?
2. In SR simultaneity is frame-dependent (= if two spatially separated events are simultaneous in a frame, they are not in a frame which is moving with respect to the first).
1. + 2. = ...
Post by: old guy on 31/08/2012 20:29:20
Surely SR's length contraction theory is not claiming that earth's atmosphere depth and diameter varies with how they are measured or how they would be observed from a muon's or the high speed ship's frames of reference. Right?
Post by: yor_on on 31/08/2012 22:36:41
Post by: old guy on 01/09/2012 03:01:29
It actually is defined just the way you doubt :) As belonging to your 'local clock and ruler'. And that local clock will always fit that local ruler just the same, and the definer of how that come to be is 'c', lights speed in a vacuum. The question then becomes if this contraction is a illusion or a reality. As far as I can see it's a reality, not a illusion. The contraction logically follows from the stipulation that lights speed in a vacuum constantly is the same, no matter from where you measure it. If you assume that 'time' is a illusion you then will have to do the same with 'distance' as they are complementary phenomena, meaning that what A measure for B may be a slower 'time', but from B:s side his time will be the same as always although the distance measured is 'contracted'. So to invalidate it one will have to redefine 'c' as a variable instead of a constant.Thanks, yor_on. This leaves me wondering if SR recognizes a "natural world" or whether measurement from different frames, measuring the same object differently creates many different versions of reality for the same natural object. Or does SR deny that there are "natural objects" which exist independent of measurement?
Also I wonder how the well documented slowing down of clocks' rates of timekeeping at increased velocities makes distances shrink (like earth's diameter), I mean, other than the concept that time dilation and length contraction are reciprocal functions in the math.
Post by: yor_on on 01/09/2012 03:44:43
Assume you are on that rocket.
Do you expect your time to slow down?
Read Tolstoy collected works in a second?
Or do you expect yourself (uniformly moving, just to make it more precise) to find your time to behave as usual?
If you expect that, how will you explain that you cover a distance in so much less time than what is possible from that definition of 'time as usual'?
To assume that 'time' really slows down is wrong, as proven by NIST in their gravitaiona time dilation experiments.
What is left?
Contractions.
As for a object being the 'same' relativity, loosely speaking now and depending on how strict you want to be, states that 'locally', using your own ruler and your own wrist watch, nothing change for you. Doesn't matter how fast you go as measured relative something else, or what mass you are on. Everything stays the same for you.
But, yeah, it's weird.
Post by: yor_on on 01/09/2012 04:06:53
Accelerations are something that does not need another frame of reference to be defined. At least not macroscopically, we all know in our body when we accelerate. Although you can still question what make us know, do we need a 'universe' filled with mass for experiencing a acceleration or will it exist in a 'empty space' too?
=
The 'empty space' here must then be defined relative the smallest constituent making sense in physics, and as our definitions stops making sense somewhere around Plank scale you can then assume that for this question to have a validity you will have to refer it to that scale. What that also, and all as I see it, state is that as long as we keep above Planck scale you must have several frames of reference acting relative each other, meaning that ones body indeed consists of both time dilations as well as LorentzFitzGerald contractions. Now, if we use this definition then what creates the feeling must be a result of those different 'frames' acting relative each other and so we have defined a acceleration as a result of frames of reference acting relative each other, bound to matter (particles).
And if this solution lose its coherence around Plank scale, what we will find instead will be Quantum mechanics.
=
what such a definition fail to to account for is how matter at rest with each other can experience 'gravity' though. We all experience it, no matter if we move relative Earth or not. And in Einsteins terms a uniform acceleration becomes the equivalent of a 'gravity'. So, using frames of reference, how do I define Earths gravity?
Post by: old guy on 01/09/2012 18:40:00
Imatfaal said:
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From the rest frame of the ship it is completely valid. From the lab on earth we can predict with accuracy what the ship would observe and it matches what the ship's crew do observe.
Does “valid” for the ship mean that ‘flattened’ ( having a contracted diameter) is a valid description of Earth? How can that be? You didn’t address my confusion in this regard in reply to your answer above:
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What I am still confused about however is the difference between the phrases (edited)... "for the ship flying by Earth” (its diameter is contracted) and its actual diameter(s) (polar a bit shorter than equatorial) as well known and documented by Earth science.
I do understand that the Lorentz formula can accurately translate or transform the observation of a contracted diameter (from the near ‘c’ frame) back to the nearly spherical shape as measured from at rest with Earth’s frame.
Lightarrow said:
Quote
1. Definition of lenght between two points of an object: measure the simultaneous position of the two points and make the difference.
2. In SR simultaneity is frame-dependent (= if two spatially separated events are simultaneous in a frame, they are not in a frame which is moving with respect to the first).
Regarding #1: This would seem to yield the familiar earth science measurements of earth, say as from in orbit, at rest with Earth.
Regarding #2: I don’t understand how the relativity of simultaneity addresses the question of a length contracted Earth diameter or my statement, “Surely SR's length contraction theory is not claiming that earth's atmosphere depth and diameter varies with how they are measured.”
Yor_on’s first reply included the statement, “...If you assume that 'time' is a illusion you then will have to do the same with 'distance'...”
As my reply indicated, I’m ok with “time” being the concept required for all movement, and that clocks ‘tick’ more slowly the faster they move, called “time dilation” though “time” need not be an entity of any kind which “dilates.”
Further, I still don’t see how a slower ‘ticking” clock, say onboard a ship flying at near ‘c’ makes the distance it travels or the objects it measures shorter.
I will give an illustration. The Alpha Centauri complex (AC) is 4.37 light years away from Earth. It takes light from AC 4.37 (edit) years to reach Earth, and no “thing” with mass can travel that fast.
A ship traveling at near ‘c’ velocity from here to there must, therefore take longer than 4.37 years to get there, even though the onboard clock will have slowed down and recorded much less than 4 years passing. Yet Earth will have orbited the Sun (the "year" standard) much more than 4 times during the ship’s journey to AC. So, even though “for the ship” much less than 4 years will have passed, the distance between Earth and AC will not have contracted to way less than 4 light years. The ship’s journey obviously will not make Earth and AC move closer together.
I hope these more specific questions and the above example will be addressed, or this thread will be buried in more questions than answers to the title subject. Thanks.
Post by: David Cooper on 01/09/2012 20:49:38
Does “valid” for the ship mean that ‘flattened’ ( having a contracted diameter) is a valid description of Earth? How can that be?
It's best to think of things only being fully valid when viewed from their own frame of reference - any other frame will appear distorted.
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A ship traveling at near ‘c’ velocity from here to there must, therefore take longer than 4.37 years to get there, even though the onboard clock will have slowed down and recorded much less than 4 years passing. Yet Earth will have orbited the Sun (the "year" standard) much more than 4 times during the ship’s journey to AC. So, even though “for the ship” much less than 4 years will have passed, the distance between Earth and AC will not have contracted to way less than 4 light years. The ship’s journey obviously will not make Earth and AC move closer together.
If we imagine the ship travelling at 86.6% the speed of light, that speed conveniently slows its clocks to half the normal speed and contracts the ship to half its normal length. From the point of view of the ship though, its length is normal and so is the rate its clocks are running at, but it sees everything else around it as having slowed clocks and being contracted in the direction in which it all appears to be moving in relative to the ship, and that includes the distance between AC and the Earth. Visually, the Earth will actually appear to be further away, but once an adjustment is made for the light received from it being emitted when the Earth was much further away (bear in mind that the Earth appears to be rushing towards the ship at 86.6% the speed of light), it will be calculated that the Earth is only about two lightyears away from AC. Once the ship has reached the Earth and stops there, the distance to AC will suddenly appear to be over four lightyears again. The distance measured depends entirely on the speed you're travelling at at the time.
Post by: old guy on 01/09/2012 21:55:41
"The distance measured depends entirely on the speed you're travelling at at the time."
This must be a quick 'pass by' in reply to your last sentence.(More when I find "time.") I think I understand your post clearly. It seems to insist that AC and Earth are, in reality, closer together than 4+ light years as the ship travels between them.
(Ref: My statement above: "The ship’s journey obviously will not make Earth and AC move closer together."
Do you think there are no natural objects with intrinsic properties or distances between established by gravity as they were formed in space? All the cosmos depends on how it is observed? Is this not relativity's version of classical subjective idealism, with 'frame of reference' as the abstract, virtual "subject."
Post by: yor_on on 02/09/2012 04:31:45
What you are asking about is if your senses can lie to you, right?
As relativity state that the geometry we see can change with relative motion, not only accelerations.
And there is one more question hidden in that, if it is so that the geometry change it must do so relative some 'constant' if it have a proportionality, and it has, if it didn't no Lorentz transformations should be applicable.
The first question is very easy to answer. Sure, your senses lie to you, your brain does the same evaluating them and interpreting the environment you live in. People like to think that they know what happens, but the brain has all kind of strategies for simplifying and choosing a preference of interpretation.
Then we come to a experiment, does that lie too? Well, assuming you have made it very strict and simple to follow that question will be answered if it is 'repeatable' or not. Relativity has been tested over a hundred years, and the beautiful experiments NIST has made is to my eyes very convincing.
Post by: yor_on on 02/09/2012 04:47:24
But choosing that you can now, possibly, assume that any 'contraction' should be a illusion. But, what you've just done is to invalidate all measurements you make yourself, on that ship. What science builds on is 'repeatable experiments' done 'locally' in a similar, or 'same', environment. You've just invalidated them making this conclusion.
Post by: old guy on 02/09/2012 18:02:56
Quote
Do you think there are no natural objects with intrinsic properties or distances between established by gravity as they were formed in space? All the cosmos depends on how it is observed? Is this not relativity's version of classical subjective idealism, with 'frame of reference' as the abstract, virtual "subject."
I understand that "for the ship" time (its clock) has slowed down. I understand that what the ship observes appears shortened. The question is, does Earth's diameter or the distance to AC (in the "real world") vary with how it is observed? I think the answer is "no." And the question still remains, Is there any empirical evidence for large scale length contraction?
Saying that length contraction is the mathematical reciprocal of time dilation does no constitute empirical evidence for large scale length contraction.
David Cooper said:
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If we imagine the ship travelling at 86.6% the speed of light, that speed conveniently slows its clocks to half the normal speed and contracts the ship to half its normal length.
I get that its clock will have slowed to half speed. This slowing of clocks at higher velocities has been empirically verified. However, the ship is a solid object. It would require a tremendous force to squeeze the ship to half its normal length, (and it would be crushed in the process), and I am sure that "length contraction" is not claiming to be such a force. Likewise for the astronomically verified distance between Earth and AC. A ship observing the distance to have contracted is not the same as the two bodies actually becoming closer together in space.
The rest will remain "window dressing" until these questions are answered.
Post by: yor_on on 02/09/2012 19:15:58
To get away from a contraction you will have to introduce a 'slower time' existing at both frames of reference, 'Earths and the muon. And that is just not true, as proofed by NIST:s experiments on Earth. We all walk through time dilations without noticing, and even when being at rest relative Earth.
Einstein called 'time' a dimension, and that seems to catch it pretty well. The time and the room is entwined into one expression becoming SpaceTime.
=
Why it not can be a 'force' seems pretty simple to me, assuming length contractions, what would the force be for 'moving' a universe one light year closer? Than it was when you where at rest with Earth before accelerating. And is that force reciprocal to the energy you expended accelerating?
Post by: lightarrow on 02/09/2012 20:10:45
In my post you had the answer: simultaneity is frame-dependent. If you are still with respect to Earth, every Earth's dimension has a value, in your frame of reference; if you are moving with resperct to Earth, those dimensions are different, as measured in that new frame of reference (because of #).
Lightarrow said:Quote1. Definition of lenght between two points of an object: measure the simultaneous position of the two points and make the difference.
2. In SR simultaneity is frame-dependent (= if two spatially separated events are simultaneous in a frame, they are not in a frame which is moving with respect to the first).
Regarding #1: This would seem to yield the familiar earth science measurements of earth, say as from in orbit, at rest with Earth.
Regarding #2: I don’t understand how the relativity of simultaneity addresses the question of a length contracted Earth diameter or my statement, “Surely SR's length contraction theory is not claiming that earth's atmosphere depth and diameter varies with how they are measured.”
In relativity you *cannot* say: "the lenght is 2 metres", you have to say: "the lenght is 2 metres as measured in this specific frame of reference".
Post by: David Cooper on 02/09/2012 22:57:05
Do you think there are no natural objects with intrinsic properties or distances between established by gravity as they were formed in space? All the cosmos depends on how it is observed? Is this not relativity's version of classical subjective idealism, with 'frame of reference' as the abstract, virtual "subject."
You can look at things in two different ways. If there is a preferred frame of reference, then anything stationary in that frame will be undistorted in shape and everything moving through that frame would genuinely be contracted in the direction of travel, but you wouldn't be able to identify the preferred frame. If there is no preferred frame, then you can look at things differently and decide that everything is fundamentally undistorted, but that anything moving relative to it will appear to be contracted in its direction of travel. With a preferred frame, all the distances would be fixed, but they'd be impossible to pin actual values on as you wouldn't know if they've been contracted or not. Without a preferred frame, the distances between things can be measured accurately within the frame in which they're stationary, and that would arguably be the truest measurement. Einstein appears to offer a spacetime in which the contractions are not real - things appear to contract, but they're really just reorienting themselves in spacetime such that they appear shortened from other frames because part of their length is taking up part of the time dimension.
Is there any empirical evidence for large scale length contraction?
I don't know if anything with more than one component that can be seen clearly enough has ever moved fast enough to detect the contraction, but I don't think there's any reason to doubt that it does happen. The reason for this is the Michelson Morley experiment. We know that we can move the MM apparatus in any direction and at any speed without affecting how long it takes light to complete the journey along both arms. The arm which is pointing in the direction of travel would need to contract to make this possible if there is a preferred frame of reference, whereas with Einstein's theory there is no real contraction at all, but just the appearance of contraction when viewed from other frames.
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...the ship is a solid object. It would require a tremendous force to squeeze the ship to half its normal length, (and it would be crushed in the process), and I am sure that "length contraction" is not claiming to be such a force.
With Einstein there is no real contraction, and therefore no issue. With Lorentz (and a preferred frame of reference) there is, but there's no crushing force involved. Imagine a room inside a space ship with a lamp in the middle of it. When the ship moves fast, the light has further to go to catch up with the leading wall of the room after it's been emitted from the lamp, and less far to go to reach the trailing wall which is rushing towards the lamp. This would lead you to expect the light to spread out more by the time it has reached the leading wall and to illuminate it less brightly as a result, whereas the rear wall would be brighter than it should be. That doesn't happen though, because the lamp will throw more light forwards than backwards. You can imagine why this happens if you work out what would happen to light being emitted sideways from the lamp and then reflected forwards or backwards by a flat mirror - because the light will take longer to reach some parts of the mirror than others, the mirror will actually act as if it is curved, concentrating light forwards or spreading it out more behind. The same kind of thing happens with lenses, so your eyes act as telephoto lenses when looking backwards and as wide-angle lenses when looking forwards. The end result of all this is that the front and rear walls remain equally well lit and appear to be the same distance from the lamp as they would if the ship wasn't moving, though only if the ship is contracted in the direction of travel.
If you now imagine forces being emitted and received in the same way as light, you can imagine them being concentrated forwards and spread out behind, and that means the atoms in molecules will attempt to maintain their separations and naturally sit closer together in the direction of travel at the points where the forces balance out for them, so there is no crushing force involved - just adjustments to maintain balance. Einstein simply sidesteps all of this by rotating the object in spacetime to get rid of all the distortions.
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Likewise for the astronomically verified distance between Earth and AC. A ship observing the distance to have contracted is not the same as the two bodies actually becoming closer together in space.
They aren't becoming closer in space, just measured as appearing to be closer together in some frames of reference than others. It's exactly the same as judging a space ship flying past as being contracted in length - you will judge it's true length by eliminating the contraction. Whether it is actually contracted while moving fast relative to you isn't particularly important to you, and the same will apply to any stars racing past - you'll see them squashed too and automatically think that to get their real measurements you need to remove the contraction, so you'd automatically do the same with the distance between those stars as well and remove the contraction from it which your movement is introducing.
But you're still going to wonder how all the different distances between two stars depending on the speed you move past them can be valid at the same time, and the answer is in the way that things rotate into the time dimension. When you travel fast, you and the stars are at a different angles in spacetime, so while the distance between the stars appears to reduce, it's compensating by taking up more space in the time dimension (and reducing the amount of time dimension left over to control the passage of time for it, or for you, depending on which frame is taking up more of the time dimension than the other, though of course that leads into more difficult questions).
Post by: old guy on 03/09/2012 21:12:53
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Einstein appears to offer a spacetime in which the contractions are not real - things appear to contract, but they're really just reorienting themselves in spacetime such that they appear shortened from other frames because part of their length is taking up part of the time dimension.(Yes, I got your PM.)
... with Einstein's theory there is no real contraction at all, but just the appearance of contraction when viewed from other frames.
This makes sense to me and fits with the idea that length contraction is an appearance of shortened objects and distances due to extremely high velocivity. This goes back to my question in reply #3 about the difference between ..."for the ship flying by Earth (its diameter is contracted) and... its actual diameter(s)...as well known and documented by Earth science.
I agree with your statement:
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Without a preferred frame, the distances between things can be measured accurately within the frame in which they're stationary, and that would arguably be the truest measurement.
But lightarrow said:
Quote
If you are still with respect to Earth, every Earth's dimension has a value, in your frame of reference; if you are moving with resperct to Earth, those dimensions are different, as measured in that new frame of reference (because of #).
In relativity you *cannot* say: "the lenght is 2 metres", you have to say: "the lenght is 2 metres as measured in this specific frame of reference".
Does this claim that Earth changes shape as it is measured from different frames of reference? This, of course, is impossible and has never been empirically observed. So the claim seems to be that there are no actual objects with intrinsic properties (or distances between them) independent of how they are observed/measured?
Here is another “reality check” against large scale length contraction:
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
Lightarrow, please address this challenge and the “earth changing shapes (diameters)" challenge. Thanks.
Post by: yor_on on 03/09/2012 21:37:22
To speak of it as wandering of in 'time' isn't that clarifying to me David :) And to say that Einstein saw contractions as a illusion needs at least a citation from him. There are two views, some accept that time dilations exist, it's hard avoiding that, but adhere to that a LorentzFitzGerald contraction is a 'optical illusion', others as me expect it to be real, meaning true from the frame of reference finding/measuring it.
Let us assume that it really would be time ticking 'slow' in the muon-Spaceships 'inertial frame' (being in uniform motion), that will naturally include all decay and all 'change', including all 'force carriers' aka photons and 'virtual photons', add infinitum. What we now do is to introduce a 'variable speed of light' in where the constant 'c' has to adapt to the local frame of reference. That as it indeed will present a 'clock' for all natural processes assuming 'virtual photons', although we don't even need to do that. Just assume that the muon-ship has a device for measuring the speed of the light before leaving it, to then cross space to be received on Earth, aka a two way mirror sending that light of.
So let us assume that you ('inertial frame' Earth) really can see that other, uniformly moving frames light , and that you too let that light 'bounce' between two mirrors, just to measure that lights speed. Can you expect the measurement to come out as 'c'? And if assuming that light to have changed its speed somewhere? To 'fit' our notion of 'c' on Earth, where would that be? And what would should I call that light changing its speed, a acceleration/deceleration maybe? And a variable?
The whole idea of contractions relative time dilations is that it is a symmetry as I see it, that's also why you can use a 'light clock' to illustrate it. If it was a illusion those light clock examples in where you have a contraction 'compensating' the time dilation by necessity would have to be wrong.
"Suppose we observe a body A to rest in space relative to our reference system. Let another body impinge on it, causing it to deform slightly as the force of impact is transmitted throughout, also setting A in motion relative to us. Such motion and deformations involve physical causes, yet they may well be described kinematically. Next consider a body B resting in free space relative to us,and now let us just begin to glide sideways away from it until we achieve a constant inertial speed. In Newton’s framework we say that B now seems to move away from us, and we call that a kinematical effect. In Einstein’s framework, we say that the body moves away relative to us and that its length is shortened relative to us, and we call those effects kinematical.
Einstein expected that the effect is identical to what would transpire if instead B were moving away from us at the same rate. For example, if a rocket accelerates near the Earth, and we are inside that rocket, then relative to us the Earth now should have a narrower length. Yet nobody will claim that thus something happened to all the molecules that constitute the Earth. The way we describe their cohesion relative to our rocket may change, but we would not say that there is any material change in the Earthly molecules partly because no such change happened relative to all other systems. By contrast, certain common changes in the configuration of molecules on a body are material changes, which might be observed from any system. Special relativity takes the effects of relative motion as fully reciprocal regardless of which system is regarded as oving. Thus observers on Earth would judge, instead, that the rocket is moving and contracted. Neither contraction is more real than the other, and neither is an optical illusion. Relativity of length means just that any two points on a given body are separated not by one universal length but by indefinitely many lengths."
A.A. Martinez / Studies in History and Philosophy of Modern Physics 38 (2007) 209–215 213
As for Einstein I found this citation.
In 1911 Vladimir Varićak asserted that length contraction is "real" according to Lorentz, while it is "apparent or subjective" according to Einstein. Einstein replied:
The author unjustifiably stated a difference of Lorentz's view and that of mine concerning the physical facts. The question as to whether the Lorentz contraction really exists or not is misleading. It doesn't "really" exist, in so far as it doesn't exist for a comoving observer; though it "really" exists, i.e. in such a way that it could be demonstrated in principle by physical means by a non-comoving observer.[15]
—Albert Einstein, 1911
Post by: David Cooper on 03/09/2012 21:56:30
But lightarrow said:QuoteIf you are still with respect to Earth, every Earth's dimension has a value, in your frame of reference; if you are moving with resperct to Earth, those dimensions are different, as measured in that new frame of reference (because of #).
In relativity you *cannot* say: "the lenght is 2 metres", you have to say: "the lenght is 2 metres as measured in this specific frame of reference".
Does this claim that Earth changes shape as it is measured from different frames of reference? This, of course, is impossible and has never been empirically observed. So the claim seems to be that there are no actual objects with intrinsic properties (or distances between them) independent of how they are observed/measured?
I suspect you're talking at cross purposes here. I don't think Lightarrow was suggesting that the size of anything changes as it's viewed from different frames, but that it is measured as having different sizes from within different frames. X has a constant size, but the measurements vary according to how you're moving relative to X when you measure X. Those measurements are only relevant in the frame in which they are made.
Quote
Here is another “reality check” against large scale length contraction:
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
If the 10.1m cargo bay is open at both ends such that the alien ship can fly through it, it will fit completely inside it for a moment, so in that sense it really is only ten metres long, but if you accelerate the shuttle up to the same speed as the alien ship and then try to capture it, it will then stick out of the cargo bay at both ends.
Post by: David Cooper on 03/09/2012 23:28:45
David, "Einstein appears to offer a spacetime in which the contractions are not real - things appear to contract, but they're really just reorienting themselves in spacetime such that they appear shortened from other frames because part of their length is taking up part of the time dimension."
To speak of it as wandering of in 'time' isn't that clarifying to me David :)
It isn't just wandering - it's a very precise rotation which enables objects to maintain their shape while appearing to be contracted when judged from other frames.
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And to say that Einstein saw contractions as a illusion needs at least a citation from him. There are two views, some accept that time dilations exist, it's hard avoiding that, but adhere to that a LorentzFitzGerald contraction is a 'optical illusion', others as me expect it to be real, meaning true from the frame of reference finding/measuring it.
I wouldn't cite anything from Einstein - almost everything he says is worded in such a way that it's easy to misinterpret. It's better to go by other people's explanations of SR as a guide to what Einstein meant, but that opens you up to stating things about what Einstein thought that may not match up to what he actually thought, so it's easy to get it wrong. My judgement is that he saw contraction as both real and an illusion. It's real within the frame you're observing as moving, contracted object from, but it's only when you're in the same frame as the object that its real shape is revealed. The contraction is real in observational terms, but the object is not really contracted.
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Let us assume that it really would be time ticking 'slow' in the muon-Spaceships 'inertial frame' (being in uniform motion), that will naturally include all decay and all 'change', including all 'force carriers' aka photons and 'virtual photons', add infinitum. What we now do is to introduce a 'variable speed of light' in where the constant 'c' has to adapt to the local frame of reference. That as it indeed will present a 'clock' for all natural processes assuming 'virtual photons', although we don't even need to do that. Just assume that the muon-ship has a device for measuring the speed of the light before leaving it, to then cross space to be received on Earth, aka a two way mirror sending that light of.
So let us assume that you ('inertial frame' Earth) really can see that other, uniformly moving frames light , and that you too let that light 'bounce' between two mirrors, just to measure that lights speed. Can you expect the measurement to come out as 'c'? And if assuming that light to have changed its speed somewhere? To 'fit' our notion of 'c' on Earth, where would that be? And what would should I call that light changing its speed, a acceleration/deceleration maybe? And a variable?
I don't know what point you're trying to make here. If you're analysing a moving thing, you will assume that light is travelling at the speed it does in your own frame, thereby measuring different values of the speed of light relative to that moving object depending on which way the light's going, but it will always be going at c in your frame. If you're measuring the speed of light while travelling with the moving object, you will then measure it as being c and regard it as being higher or lower than c relative to other frames. There appear to be contradictions there, but they may disappear when you account for the realignment of things in spacetime - it's hard to visualise so I don't know.
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The whole idea of contractions relative time dilations is that it is a symmetry as I see it, that's also why you can use a 'light clock' to illustrate it. If it was a illusion those light clock examples in where you have a contraction 'compensating' the time dilation by necessity would have to be wrong.
A light clock is no different from either arm of the Michelson Morley experiment, so it will be contracted or appear to be contracted if it's aligned with the direction of travel. Lorentz would have said that it is actually contracted if it is aligned with the direction of travel, but Einstein would perhaps have said you can consider it to be contracted if it's in a frame different from the one you're viewing it from and not contracted if you're moving with it - both are correct views, but the contradiction can be dealt with by considering the uncontracted version to be the superior one. There are different kinds of validity involved in this - the measurements are all valid for the frame they're made from, but if you want the real shape of anything you would want to measure it from its own frame.
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"Suppose we observe a body A to rest in space relative to our reference system. Let another body impinge on it, causing it to deform slightly as the force of impact is transmitted throughout, also setting A in motion relative to us. Such motion and deformations involve physical causes, yet they may well be described kinematically. Next consider a body B resting in free space relative to us,and now let us just begin to glide sideways away from it until we achieve a constant inertial speed. In Newton’s framework we say that B now seems to move away from us, and we call that a kinematical effect. In Einstein’s framework, we say that the body moves away relative to us and that its length is shortened relative to us, and we call those effects kinematical.
[By the way, no one should be misled by deformations caused by impacts and decelerations - they are temporary and go away when the force is no longer being applied. The contractions caused by relative movement have nothing to do with that.]
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Einstein expected that the effect is identical to what would transpire if instead B were moving away from us at the same rate. For example, if a rocket accelerates near the Earth, and we are inside that rocket, then relative to us the Earth now should have a narrower length. Yet nobody will claim that thus something happened to all the molecules that constitute the Earth. The way we describe their cohesion relative to our rocket may change, but we would not say that there is any material change in the Earthly molecules partly because no such change happened relative to all other systems. By contrast, certain common changes in the configuration of molecules on a body are material changes, which might be observed from any system. Special relativity takes the effects of relative motion as fully reciprocal regardless of which system is regarded as oving. Thus observers on Earth would judge, instead, that the rocket is moving and contracted. Neither contraction is more real than the other, and neither is an optical illusion. Relativity of length means just that any two points on a given body are separated not by one universal length but by indefinitely many lengths."
A.A. Martinez / Studies in History and Philosophy of Modern Physics 38 (2007) 209–215 213
What that appears to be saying is that all the measurements are valid and that there is no most correct measurement that can be made (e.g. by measuring from the same frame as the thing you're measuring). That would mean that there is an infinite range of equally valid measurements for the size of any object or the distance between any two points, and changing the frame from which you make the measurement simply gives you access to a different version of that length - you aren't changing the shape of it, but merely changing your viewpoint on it.
Even so, that appears to me to be just one interpretation of what Einstein thought. It's clear that there is a maximum measurement for the length of anything, and that measurement shows up when you measure the object from the same frame. I'd be surprised if Einstein didn't consider that to have greater validity.
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As for Einstein I found this citation.
In 1911 Vladimir Varićak asserted that length contraction is "real" according to Lorentz, while it is "apparent or subjective" according to Einstein. Einstein replied:
The author unjustifiably stated a difference of Lorentz's view and that of mine concerning the physical facts. The question as to whether the Lorentz contraction really exists or not is misleading. It doesn't "really" exist, in so far as it doesn't exist for a comoving observer; though it "really" exists, i.e. in such a way that it could be demonstrated in principle by physical means by a non-comoving observer.[15]
—Albert Einstein, 1911
That's typical of Einstein - it leaves it open.
Post by: yor_on on 04/09/2012 00:15:31
As for my example I was referring to how you would like to see it from the muon's side if there was no contraction to be seen, as I discussed earlier too btw. Assuming no contraction it being a 'illusion' you only have time dilations left, and then assuming ( as they say:) that 'time' indeed goes slow 'objectively' not only as seen from Earth measuring, but really goes sloow in the muon frame locally, although unobservable from the muon's side, the rest I wrote follow, using two-way mirrors to measure a speed. And reasoning it out from such a premise becomes something of a logical fallacy to me.
Because there is never any change of your time/ruler locally, only between frames of reference.
==
But yes, in a way I agree David. I think he found himself rather uncomfortable acknowledging it as a fact. It, in a much more definite way introduce 'frames of reference' as something 'real'. The idea of 'time' and 'the arrow' as a 'illusion' is easier to handle than varying lengths depending on your relative motion mass energy etc, aka comparisons between 'frames of reference' (SpaceTime positions). He wanted one cosmos and one 'reality', and if this was a fact?
People still find this idea deeply uncomfortable I think.
Post by: yor_on on 04/09/2012 01:20:59
Post by: old guy on 04/09/2012 19:36:25
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The contraction is real in observational terms, but the object is not really contracted.
In other worlds, just to be clear, large scale length contraction is an illusion, if “the object is not really contracted.”
That is what I’ve been saying (with no replies directly to my points) about Earth’s diameter, the distance to Alpha Centauri, and the length of the alien probe... all staying the same regardless of how they are variously observed/measured.
Obviously earth’s diameter does not shrink, as measured from a near ‘c’ fly by. Obviously Earth and AC do not move closer together as measured from a near ‘c’ ship flying between them (even though its clock will slow down.) Obviously an alien probe, measured as 10 meters long as it approaches Earth at near ‘c’ will not fit into a 10 meter cargo bay, because its “contracted length” is an illusion. As the shuttle pulls alongside the probe, in the same frame at rest with the probe, its actual length will be found to be much longer than its “contracted length” as seen from Earth.
Comments to the points above, the point of this thread, anyone?
Btw, David, I agree with you on the following, with one vital point of exception: (my bold)
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That would mean that there is an infinite range of equally valid measurements for the size of any object or the distance between any two points, and changing the frame from which you make the measurement simply gives you access to a different version of that length - you aren't changing the shape of it, but merely changing your viewpoint on it.
... It's clear that there is a maximum measurement for the length of anything, and that measurement shows up when you measure the object from the same frame. I'd be surprised if Einstein didn't consider that to have greater validity.
It is clear that measuring something from the same frame, at rest with the object, yields the valid and correct measure. I think that the dictum "there is no preferred frame of reference" is in blatant denial of what science already knows for sure about Earth's diameter, the distance to AC, the distance to the Sun, etc. They don't change with how one looks at them.
If objects like Earth have intrinsic shape independent of “your viewpoint” then there is a “valid” shape (both polar and equatorial diameters are well documented to a high degree of precision), and other measurements from all different varieties of viewpoint are not “equally valid."
yor_on said:
And so a contraction becomes a observer dependent fact, not illusion. And that's what Einstein himself say too.
I think that length contraction as an “observer dependent fact” is an oxymoron. A very oblate spheroid might be "observer dependent" but it is not a factual description of Earth.
Post by: David Cooper on 04/09/2012 20:06:11
David Cooper:QuoteThe contraction is real in observational terms, but the object is not really contracted.
In other worlds, just to be clear, large scale length contraction is an illusion, if “the object is not really contracted.”
That is what I’ve been saying (with no replies directly to my points) about Earth’s diameter, the distance to Alpha Centauri, and the length of the alien probe... all staying the same regardless of how they are variously observed/measured.
Yes - we're all pretty much agreed now (I think) that the objects don't change, but that the measurements do, and where there's always going to be room for disagreement is in how we describe the differences in measurements. I think it's valid to refer to the contracted lengths as being illusions, and it's also valid to refer to them as being real because they are real measurements, but also because they are, if Einstein's theory is correct, genuine lengths of the things being measured - lengths which only show up when viewed from other frames.
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It is clear that measuring something from the same frame, at rest with the object, yields the valid and correct measure. I think that the dictum "there is no preferred frame of reference" is in blatant denial of what science already knows for sure about Earth's diameter, the distance to AC, the distance to the Sun, etc. They don't change with how one looks at them.
But a preferred frame of reference would not orbit around the sun with the Earth, nor with the sun around the Milky Way, so a preferred frame of reference would actually render just about everything genuinely contracted in it's direction of travel through that frame, and more so depending on its speed relative to that frame.
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If objects like Earth have intrinsic shape independent of “your viewpoint” then there is a “valid” shape (both polar and equatorial diameters are well documented to a high degree of precision), and other measurements from all different varieties of viewpoint are not “equally valid."
There are different kinds of validity. If the alien space ship is flying through a shuttle's cargo bay it may fit inside it completely for an instant, so it's apparent length of ten metres is a valid measurement of it for that situation. If you then try to keep it in the cargo bay, it will then stick out at the ends and the measurement won't seem so valid after all. In one way it's valid, and in another way it isn't, but the apparent contradiction is in the flexible way that language is being used to describe the situation, so there is no actual contradiction in valid = not valid because they're not the same kind of valid - each one depends on its own conditions, and the conditions don't match up.
Post by: lightarrow on 04/09/2012 20:26:04
"Without a preferred frame" and "within the frame in which..." are mutually contradictory. You always have to specify a frame of reference, it *doesn't exist* a "lenght" independent of it.
I agree with your statement:QuoteWithout a preferred frame, the distances between things can be measured accurately within the frame in which they're stationary, and that would arguably be the truest measurement.
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But lightarrow said:Certainly. In a frame of reference which is still with respect of our planet, the Earth is sphericalQuoteIf you are still with respect to Earth, every Earth's dimension has a value, in your frame of reference; if you are moving with resperct to Earth, those dimensions are different, as measured in that new frame of reference (because of #).
In relativity you *cannot* say: "the lenght is 2 metres", you have to say: "the lenght is 2 metres as measured in this specific frame of reference".
Does this claim that Earth changes shape as it is measured from different frames of reference?
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This, of course, is impossible and has never been empirically observed.You're wrong for both assertion. Maybe you still haven't totally grasped what "measure of lenght" means, read again my first post. A measure of lenght *is* frame-dependent, and so is, as consequence, an object's shape.
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So the claim seems to be that there are no actual objects with intrinsic properties (or distances between them) independent of how they are observed/measured?Define "actual".
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Here is another “reality check” against large scale length contraction:http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/polebarn.html
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?
There are an infinity of relativity "paradoxes". Of course they are not real paradoxes, after an accurate analysis of the problem's physics.
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... A very practical test of “actual length” vs “contracted length.”I have solved these problems tens of times, you simply have to remember the definition of lenght I gave you in my first post:"...simultaneously measured..."
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
Lightarrow, please address this challenge and the “earth changing shapes (diameters)" challenge. Thanks.
Post by: lightarrow on 04/09/2012 20:29:43
Yes - we're all pretty much agreed now (I think) that the objects don't change, but that the measurements do,Two contradictory statements, put in this way. Physics concerns measures; if an object's measure changes, then the object changes.
Unless you intended something else...
Post by: yor_on on 04/09/2012 23:12:28
No we haven't David, agreed that is. I will stand by it is frame related (observer dependent) and as 'real' as can be, from the frame measuring.
Post by: lightarrow on 05/09/2012 13:29:46
heh :)At least you agree with me [:)]
No we haven't David, agreed that is. I will stand by it is frame related (observer dependent) and as 'real' as can be, from the frame measuring.
Post by: yor_on on 05/09/2012 15:33:11
So we are, let's see here? 2 against 2 sort of :)
A mirror of the discussion elsewhere too methinks?
Or maybe 3 doubting, 2 finding it true.
It all depends on what faith one has in Einsteins predictions and field equations. Saw someone write somewhere that he 'guessed' at them. That's not true, he wrestled with finding the right type of equations for years, but he already 'knew' that they had to fit, because he could see the implications in his mind.
Math is terribly hard and there's such a lot of it.
Post by: old guy on 05/09/2012 18:29:07
Lightarrow said:
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Physics concerns measures; if an object's measure changes, then the object changes.
(Also):You always have to specify a frame of reference, it *doesn't exist* a "lenght" independent of it.
This claims that things have no length (shape, etc.) on their own, intrinsically, independent of measurement.
Me:
"Does this claim that Earth changes shape as it is measured from different frames of reference?"
Lightarrow:
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Certainly. In a frame of reference which is still with respect of our planet, the Earth is spherical...; in another, moving, frame, it's not (and of course every human being is flattened too). Where is the problem?
The "problem" is that, "in the real world" Earth does not change shape with every different possible measurement of it. It is in fact nearly spherical. As I said: "This, of course, is impossible and has never been empirically observed." (A flattened Earth, for instance.)
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You're wrong for both assertion. Maybe you still haven't totally grasped what "measure of lenght" means, read again my first post. A measure of lenght *is* frame-dependent, and so is, as consequence, an object's shape.
I grasped it just fine. You are wrong to assert that an object's shape (like Earth) depends on how it is observed/measured, as if it had no reality, no intrinsic properties of its own.
Say 1000 ships pass by Earth going 1000 different (but near 'c') velocities, all going in 1000 different directions. Does Earth change into 1000 different shapes with its diameter contracting variously in all those directions? Of course not!
This goes directly to the difference between relativity's version of subjective idealism and realism.
As I asked David in post 10 and refer the same questions to you:
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Do you think there are no natural objects with intrinsic properties or distances between established by gravity as they were formed in space? All the cosmos depends on how it is observed? Is this not relativity's version of classical subjective idealism, with 'frame of reference' as the abstract, virtual "subject."
Wiki on Realism (my bold):
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In philosophy, Realism, or Realist or Realistic, are terms that describe manifestations of philosophical realism, the belief that reality exists independently of observers."Observers" here in the context of this thread includes abstract points of view, all possible "frames of reference... no living "subject" required.
You asked me to define "actual." That would be that "reality exists independently of observers."
Earth is actually nearly spherical. AC is actually 4.37 light years from Earth. The distance to the Sun is actually about 93 million miles, which would not change if it were measured by a ship flying by very fast. The probe in my example is not actually 10 meters long, as observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)
Post by: David Cooper on 05/09/2012 20:05:54
Yes - we're all pretty much agreed now (I think) that the objects don't change, but that the measurements do,Two contradictory statements, put in this way. Physics concerns measures; if an object's measure changes, then the object changes.
Unless you intended something else...
Are you actually saying that the object physically changes as you look at it from different frames?
heh :)
No we haven't David, agreed that is. I will stand by it is frame related (observer dependent) and as 'real' as can be, from the frame measuring.
Same question for you: are you actually saying that the object physically changes as you look at it from different frames?
I don't know if this is a real disagreement or simply an interpretation issue.
Say 1000 ships pass by Earth going 1000 different (but near 'c') velocities, all going in 1000 different directions. Does Earth change into 1000 different shapes with its diameter contracting variously in all those directions? Of course not!
Einstein's SR does not require anyone to believe in something with those particular contradictions in it. It simply isn't necessary to believe that things are physically changed in shape by being observed from different frames, so you don't need to spend any more of your time attacking positions which aren't essential to SR.
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Earth is actually nearly spherical. AC is actually 4.37 light years from Earth. The distance to the Sun is actually about 93 million miles, which would not change if it were measured by a ship flying by very fast. The probe in my example is not actually 10 meters long, as observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)
Sort of, but it isn't that simple. If Einstein's SR is correct, then what you have said is right in the sense that these are the maximised sizes and distances of things, but it is still true that a 20m long object can fit in a 10.1m long container for a moment if the object is moving through the container at 0.866c.
Interestingly, if Lorentz's view of the universe is true, it actually leads to similar problems with deciding what the real shapes of things are. All things would be contracted in their direction of travel through the preferred frame, but their true shapes would still arguably be the shapes they would have if they weren't moving (which are also the shapes they appear to have if you're moving along with them).
Post by: yor_on on 05/09/2012 20:29:55
Post by: flr on 05/09/2012 22:05:27
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Yep, it's frame dependent.And that means the observed object changes its shape as the observer changes its (say inertial) frame of reference?
Post by: old guy on 06/09/2012 00:08:37
I "ditto" that. Also...QuoteYep, it's frame dependent.And that means the observed object changes its shape as the observer changes its (say inertial) frame of reference?
JP:
“You do have to be capable of separating events in space and in time for movement to have any meaning.”
You do. I don’t. Things move around, on all scales, regardless of human capability for “separating events.” Everything in the universe moves. We say that “time elapses” when things move. I agree. But that does not make time an entity of any kind which can “dilate.”
It’s just that clocks run slower after being accelerated to higher speeds. (Probably human bodies “age” more slowly too.)
The coalescence of “time” and “space” was Minkowski’s invention, and then Einstein subscribed.
There was no mention of the ontology of what either space or time was supposed to BE when the ‘fabric of spacetime” (both non-entities woven toghether) was invented.
it was just a coordinate system on a 4-D graph. (3-D space "interwoven" with "time.")
Just passing by. Back tomorrow.
Ps:
Me:
“ The probe in my example is not actually 10 meters long, as observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)”
David Cooper:
“Sort of, but it isn't that simple. If Einstein's SR is correct, then what you have said is right in the sense that these are the maximised sizes and distances of things, but it is still true that a 20m long object can fit in a 10.1m long container for a moment if the object is moving through the container at 0.866c.”
If Einstein is not correct then it is not true that "a 20m long object can fit in a 10.1m long container for a moment if the object is moving through the container at 0.866c.”
Btw, it's my probe retrieval project and I say that a 10 meter cargo bay can not contain a probe "measured to be 10 meters" from earth in the specifics of the case I laid out. I'll give you the .1 meter for easy fit if the probe were actually
10 meters long... which it is not in the "experiment" I devised.
Now can we get back to the real issues I have raised in this thread?
Post by: damocles on 06/09/2012 00:57:28
It is quite true that in special relativity there is no inertial frame of reference that is privileged over any other as far as observations are concerned, it is also a fact, and one that is not inconsistent, that
when considering the intrinsic properties of any object there is a preferred or privileged frame of reference, and that is the inertial frame of its own motion
So, if we are wanting to measure the size, or the shape, or the density of the Earth, we must put ourselves in a stationary motion relative to the Earth (or, alternatively, make an inference and a calculation to what the result of a measurement would have been in such a frame). Of course, the fact that the Earth is not in an inertial state of motion takes us into the muddier waters of general relativity, but fortunately not in a way that affects the measurements we make at the precision we can currently make them. The foregoing is the reason why we can regard the "rest mass" of an object as one of its intrinsic properties, but not its inertial mass.
Post by: flr on 06/09/2012 03:50:27
The time dilation was experimentally proved, but length contraction was only assumed to obey the invariance of "c".
I understood the time dilation in seconds from that photon clock imaginary experiment.
However I still cannot picture the length contraction in a nice intuitive way.
This is the closest I could get to Lorentz contraction: I force myself to accepting that the lengths and therefore the shape of objects, as observed from various frames, are not intrinsic properties of objects but rather relationships between observer and the measured object. Seeing lengths as relationships between frames rather than an absolute property of the measured object, I can then digest that they could change with changing the frame of reference. But then we can always ask: "are these relationships the real lengths or apparent" - and ... here we go again .....
I cannot really understand why and how the space of a muon is different from mine (staying on Earth) in such a way that the muon somehow finds a path of only 1 meter to travel through what for me is 50 km layer of atmosphere.
Post by: CPT ArkAngel on 06/09/2012 03:54:51
Post by: damocles on 06/09/2012 04:02:41
As far as I know, there is no direct experimental proof of length contraction.
The time dilation was experimentally proved, but length contraction was only assumed to obey the invariance of "c".
I understood the time dilation in seconds from that photon clock imaginary experiment.
However I still cannot picture the length contraction in a nice intuitive way.
This is the closest I could get to Lorentz contraction: I force myself to accepting that the lengths and therefore the shape of objects, as observed from various frames, are not intrinsic properties of objects but rather relationships between observer and the measured object. Seeing lengths as relationships between frames rather than an absolute property of the measured object, I can then digest that they could change with changing the frame of reference. But then we can always ask: "are these relationships the real lengths or apparent" - and ... here we go again .....
I cannot really understand why and how the space of a muon is different from mine (staying on Earth) in such a way that the muon somehow finds a path of only 1 meter to travel through what for me is 50 km layer of atmosphere.
So the sort of thing I was saying in my previous post is that the "measured length" of an object (like the Earth's atmosphere) -- is not an intrinsic property of that object -- but its "rest length" is. As far as the muon travelling through the atmosphere is concerned, there will be no inappropriate change in the physics of its interaction with the atmosphere because the relativistic decrease in the length of path will be matched by a relativistic increase in the number density of atmospheric molecules, and the relativistic increase in the observed mass of each molecule (which operates quite separately to the increase in number density) will produce an exact match with the physics we observe from an Earth-stationary frame.
Post by: flr on 06/09/2012 07:47:14
So the sort of thing I was saying in my previous post is that the "measured length" of an object (like the Earth's atmosphere) -- is not an intrinsic property of that object -- but its "rest length" is.
The only way the moun can get from upper atmosphere to Earth surface while experiencing so little "proper time", is to travel 1 meter of distance of what in Earth frame is 50Km of distance.
So the contraction from muon frame (and hence the distorted non-spherical shape that he sees it) appear to me to be as real as it gets. If so, why the length and shape as perceived from co-moving frame would be 'more special' to give the 'intrinsic length' and 'intrinsic shape' of the object?
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As far as the muon travelling through the atmosphere is concerned, there will be no inappropriate change in the physics of its interaction with the atmosphere because the relativistic decrease in the length of path will be matched by a relativistic increase in the number density of atmospheric molecules, and the relativistic increase in the observed mass of each molecule (which operates quite separately to the increase in number density) will produce an exact match with the physics we observe from an Earth-stationary frame.
Based on these kinds of arguments I feel tempted to see the length contraction as a "geometrical mirage" (i.e. apparent rather than real).
Yet somehow the muon finds a path of 1 meter distance to travel what for the Earth observer is 50km distance, and this is real thing since the muon does not decay enough.
......I guess I really can't figure how the length contraction works.... Ironically, understanding the time dilation was so easy.....
Post by: old guy on 06/09/2012 17:52:58
In particles accelerators like the LHC, there is proofs that particles are flattened in the velocity direction.Yes. That is why my title specifies "large scale length contraction."
In an accelerator, the subatomic particles (little bundles of energy) are accelerated to near 'c' by extremely powerful force exerted on micro-sized energy packets. It is not hard to see why they would flatten out, becoming "pancaked."
However, there is no evidence that this effect is transferable to large scale. A "frame of reference" flying by Earth at near 'c' will not exert any force on Earth, and Earth will certainly not become "pancaked" as a result, even though the image of Earth observed from such a frame may well appear "pancaked."
The trick is to clearly sort out the intrinsic properties of Earth as a solid, massive, nearly spherical planet from the extrinsic effects of the above frame's high velocity relative to Earth as it observes and measures the planet.
Edit; Ps, fir,
The fact that muons at high speed entering the atmosphere "live longer" than would be expected without "time dilation" does not automatically mean that they travel a shorter distance than the well known depth of the atmosphere. The mathematically reciprocal functions theorized between "time dilation" and "length contraction" do not make "things" or distances "in the real world" shrink. (Realism)
Edit #2:
Damocles:
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...when considering the intrinsic properties of any object there is a preferred or privileged frame of reference, and that is the inertial frame of its own motionYes! Thank you.
Post by: yor_on on 07/09/2012 06:20:52
And to be locally at the same SpaceTime 'spot' you better be 'at rest' with it. Otherwise it can't be a 'local solution' in relativity. I usually argue from 'superimposing' aka 'photons', if one want to define a 'exact same' SpaceTime position. Because then there can be no doubt of what I see as being 'at rest', or a 'microscopic definition' of 'locality' as, and as Imatfaal pointed out, we have HUP cloaking the process long before that. But for macroscopic definitions we can't use that, can we? :)
And yeah, it seems you agree with me in that most people can accept 'time/the arrow' as plastic, but when it comes to LorentzFitzGerald contractions, most feel being 'put upon' by us crazy relativists :) And it's so hard to prove experimentally in a convincing way.
Post by: hubble_bubble on 07/09/2012 07:29:36
Post by: hubble_bubble on 07/09/2012 07:33:54
Post by: imatfaal on 07/09/2012 18:23:04
It is clear that many of you regard Special Relativity and/or its implications as a convenient fiction - that discussion can continue in the New Theories section. In the main physics forum we endeavour to answer simple questions (and sometimes very complicated ones) with mainstream answers from accepted physics.
This thread is rapidly descending into a melange of arguments from personal incredulity and ignorance of the subject and that is against the ethos of this Q&A forum.
Please steer clear of statements that are based on "what you reckon to be true", "that which is blindingly obvious", and "simple common sense" Much to the chagrin of many people - physics works on mathematics, modelling, predictions, and experimentation; not on intuition, philosophical truths, nor everyday notions of the way of the world.
It is clear that we have not travelled past earth at relativistic velocities - if that is the only proof that is acceptable then the theory will have to stand as it currently does. However special relativity is mathematically intricate, self-contained and non-contradictory - if length contraction did not occur on the largest scales (as numerous posters are suggesting) then the whole theory would be mathematically bankrupt; you cannot just take out length contraction from the model - it is entirely integral. Special Relativity theory is incredibly accurate and is tested continuously (satellite timing is the most well known example) - whilst every test that we can come up with (and some amazing brains are trying desperately and would love to find the first flaw - it's a guaranteed trip to Oslo) is passed by Special relativity we are not going to jettison the theory without good reason. one thing that is not a good reason is when non-physicists create gedankan and and are philosophically disinclined to accept the predictions that arise!
Post by: yor_on on 07/09/2012 18:24:11
Post by: old guy on 07/09/2012 18:45:51
Please address this, my summary statement before you close the thread:
Quote
The trick is to clearly sort out the intrinsic properties of Earth as a solid, massive, nearly spherical planet from the extrinsic effects of the above frame's high velocity relative to Earth as it observes and measures the planet.
Is there no place anymore in science to question "accepted ideas?"
Ps: I intended to move the recent "length contraction" posts from the "Does time exist" thread, but will cancel that given the immanent threat of censorship of free thinking here.
Post by: imatfaal on 07/09/2012 18:58:26
imatfaal,
Please address this, my summary statement before you close the thread:QuoteThe trick is to clearly sort out the intrinsic properties of Earth as a solid, massive, nearly spherical planet from the extrinsic effects of the above frame's high velocity relative to Earth as it observes and measures the planet.
Is there no place anymore in science to question "accepted ideas?"
Ps: I intended to move the recent "length contraction" posts from the "Does time exist" thread, but will cancel that given the immanent threat of censorship of free thinking here.
Old Guy
Please drop the accusations of censorship - they really grate. Especially immanent ones - I can assure you I am neither divine nor purely an act of the mind (well to the best of my knowledge) .
Yes there are plenty of ways to question accepted ideas. Arguments from incredulity and naked disbelief are not included - most especially on the main fora. post as much as you like in New Theories - just keep the main fora to Science Q&A
To answer your last point - you are privileging your notions (and the common and nature notions of humanity) over the scientific method. It has be shown countless times that ideas of intrinsic nature, of an immutable realism, of absolute time and space etc are useful, practically universal, easy to accept, and wrong. Perhaps once you have shown (in New Theories please) why earth has an intrinsic nature outside the laws of physics - then we can start afresh.
Post by: old guy on 07/09/2012 19:13:46
Quote
Please drop the accusations of censorship - they really grate. Especially immanent ones - I can assure you I am neither divine nor purely an act of the mind (well to the best of my knowledge) .
Sorry; I obviously meant "imminent" as in "impending" or "about to happen.
But you didn't address the intrinsic vs extrinsic issue as I requested at all, and it would be the solution to the whole shebang if addressed.
And it is in fact censorship if the opinion that Earth stays nearly spherical is not only rejected by the authority of mainstream SR but not allowed in a discussion of it.
Post by: imatfaal on 07/09/2012 19:30:14
Post by: David Cooper on 07/09/2012 20:19:16
The idea of absolutes in time and space, of a universal reference frame, of immutability have been shown to be incorrect.
They haven't all been shown to be incorrect, but length contraction certainly must happen in one way or another, as has been demonstrated by the Michelson Morley experiment. Anyone who wants to deny length contraction would really be better off joining the Einstein camp rather than attacking it, because SR at least provides a way for the contraction to be apparent rather than actual, even if it then leads to endless arguments about whether the contraction then counts as an illusion or not.
Post by: flr on 07/09/2012 21:11:34
You have decided - on the basis of zero evidence - that earth has an essential, absolute shape that forms part of a natual universal truth;
To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths.
Why should not some real object have a form of itself? Why an object cannot be something by itself?
the products of special relativity threaten your preconceptions therefore you reject the proven science and embrace your intuitionsIt is not that I reject proven science, actually I really want to get there but myself and in my own way.
In this process I asked myself many of the questions you have seen in this thread or in other related threads.
I hope @imatfaal will not close this topic. Why should be closed? Isn't special relativity an interesting topic?
Post by: flr on 07/09/2012 21:22:01
.. SR at least provides a way for the contraction to be apparent rather than actual.
To me looks quite "actual", otherwise how could muon decay so little while passing through atmosphere? The little decay of muon is quite actual and not apparent. Note that In muon frame it has to travel a smaller distance that the observer on Earth measure.
Post by: JP on 07/09/2012 21:30:07
To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths.
Why should not some real object have a form of itself? Why an object cannot be something by itself?
That's a good point, flr. The problem is that intuition only works when you're so familiar with something that it becomes intuitive! It can also be very misleading in science, since many effects are counterintuitive. A far better guide in science is logic. Once you know something is true (by observing or measuring it), you can logically figure out its consequences.
That's the case in special relativity. Length contraction is very counterintuitive, but we know that the speed of light is constant for all observers from experiments. Once you know that's true, you can logically work through the consequences, and find that lengths have to contract. Our intuition fails because we hardly ever experience relativistic effects in daily life. You can definitely train your intuition by studying something thoroughly, but it takes a lot of effort to actually learn a subject so well that it becomes intuitive, especially when its as abstract as relativity theory.
Post by: old guy on 08/09/2012 00:07:44
Post by: damocles on 08/09/2012 00:27:07
SR does not rob an object of its intrinsic properties.
The properties that we measure and ascribe to an everyday object: its mass, size and shape, are its intrinsic properties. The Earth is an oblate spheroid of revolution, with minor radius 6353 km and major radius 6379 km, and mass 5.98 E 24 kg. Those are absolute and immutable properties.
If a traveller moving at speeds where SR effects exceed the precision of measurement makes observation of the Earth's properties, then s/he will observe a set of properties different to this, and different to those observed by another such observer moving at a different speed and direction. But none of this directly reflects the Earth, which can blissfully retain its intrinsic properties.
When we refer to such observations, it is quite usual to use the term "rest mass". Perhaps the logic of the situation would become clearer if we were also to use terms like "rest shape" for the other intrinsic properties of an object.
If, however, the Earth interacts with another object moving at such speeds, then the interaction will, from the point of view of the other object, be determined by the "distorted" properties of the Earth, as measured in its own reference frame. From an Earthbound point of view, though, the interaction will be governed by the intrinsic properties of the Earth and the "distorted" properties of the other object as observed from the Earthbound frame of reference. And the mathematical detail of the SR formulation will ensure that both observers will get the same result when the actual consequences of the interaction are calculated -- relative to the particular frame of each observer, of course.
The other laws of physics are likely to ensure that neither of these observers is still around to make the actual measurements, of course [;D]
Post by: yor_on on 08/09/2012 15:37:52
This particular thread was so interesting to me, because for such a long time I tried to train my intuition to see the length contraction. And I visited this forum (and some others) specifically because I could find some line of thinking different from text-book, and some freedom of users to express whatever they wanted.You have decided - on the basis of zero evidence - that earth has an essential, absolute shape that forms part of a natual universal truth;
To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths.
Why should not some real object have a form of itself? Why an object cannot be something by itself?the products of special relativity threaten your preconceptions therefore you reject the proven science and embrace your intuitionsIt is not that I reject proven science, actually I really want to get there but myself and in my own way.
In this process I asked myself many of the questions you have seen in this thread or in other related threads.
I hope @imatfaal will not close this topic. Why should be closed? Isn't special relativity an interesting topic?
It's no illusion friend :) And I like the way you think btw, but neither will you ever see it locally. The only way a length contraction can be expressed is in a measurement between 'frames of reference'. If you use what I call 'locality' as your guiding principle OG is right. A object has the form you find it to have being at rest with it and the proofs for that is simple. Just become 'at rest' relative whatever you want to measure. Damocles hit the nail spot on with that one.
To further the discussion :) All of this has to do with what you think you observe. A 'whole undivided SpaceTime', or 'frames of reference' mediated by and through 'radiation'. Using your own unique frame you can define yourself and your closest environment as, loosely speaking again :) unchanging, aka 'invariant', no matter where you are or how 'fast' you go.
I believe in 'frames of reference' and 'locality', and there you will find things to have a consistency. Using a 'undivided SpaceTime the concept becomes trickier to me in that, what we have, still must relate to those 'frames of reference' 'joining it up'. Then defining it as 'one reality', the degrees of freedom we find it to have (dimensions) becomes 'unbreakable definitions´, defining a 'bubble' of sorts called SpaceTime. It's not like that to me, SpaceTime is a (very) partial 'bit' of something more/less, and it all coexists. What we see use radiation.
=
Can you see what I mean there? That when we find those length contractions contradict common sense. we all assume that 'one SpaceTime to bind us all'? ahem. If we let locality define a SpaceTime it will use frames of reference, radiations constant, 'gravity/mass', 'energy'. And we can leave the 'space' as it is, 'empty', at least classically, locally definable as 'invariant' too. Our problems arise with our preconceptions of how 'things always have been, and always must be'. Those change with knowledge, but each generation somehow still presume that their 'level' defines 'what is', don't they :)
When it comes to the question of 'motion' as uniform/accelerations?
That's tricky, but in locality all (uniform) motion must by definition become relative. Although we still have that constant frame radiation binding together 'locality', to measure a 'motion' against, using lights blue/red shifts. Accelerations will then be equivalent to 'gravity' as I think.
===
Sorry, I write too slow, and my brain seems to assume that my fingers have brains of their own, as I keep missing those letters and small binding words. Also, you can always polish it a bit, can't you ::))
=
And OG, please stop being so hard on the mods. It's definitely not easy being one, and? I find Imatfaal a quite good one.
Post by: David Cooper on 08/09/2012 19:50:56
.. SR at least provides a way for the contraction to be apparent rather than actual.
To me looks quite "actual", otherwise how could muon decay so little while passing through atmosphere? The little decay of muon is quite actual and not apparent. Note that In muon frame it has to travel a smaller distance that the observer on Earth measure.
That's a different aspect of it - it travels further through our frame, but it itself appears to be (or is) shortened in length. You're now talking about it travelling further in our frame due to time dilation making it longer-lived in our frame. To make sense of it without SR, the internal mechanical mechanisms of the muon would have to be slowed down by its movement through the fabric of space such that it lasts longer. Alternatively, to make sense of that in SR you have to eliminate all ideas of Newtonian time such that the most genuine length of time for the muon to last is the one as measured in its own frame, while in any other frames where the measurement is different it will appear to last for longer than that.
What this means is that both the shape and time are probably best measured from the same frame as the thing being measured, while other frames may contract the apparent length in one direction and extend the apparent lifespan of the thing in question. But we're always trying to describe things in terms which shouldn't be applied to a universe with Newtonian time removed from it. If we attempt to remove Newtonian time properly, everything in the universe ends up being effectively simultaneous (because you end up with an eternal block universe) and there is no longer any speed of anything - not even a speed of light. Time is transformed into a kind of distance instead, and the future was never generated out of the past in cause-and-effect order.
Those are the necessary consequences of removing Newtonian time, and I hope there's no one here who wants to have their cake and eat it by smuggling a Newtonian time back in by the back door to try to make SR sound more compatible with common sense, because it won't fit.
Post by: lightarrow on 08/09/2012 23:24:47
Lightarrow said:When you say "in the real world" you are actually saying "in the Earth's frame of reference".QuotePhysics concerns measures; if an object's measure changes, then the object changes.
(Also):You always have to specify a frame of reference, it *doesn't exist* a "lenght" independent of it.
This claims that things have no length (shape, etc.) on their own, intrinsically, independent of measurement.
Me:
"Does this claim that Earth changes shape as it is measured from different frames of reference?"
Lightarrow:QuoteCertainly. In a frame of reference which is still with respect of our planet, the Earth is spherical...; in another, moving, frame, it's not (and of course every human being is flattened too). Where is the problem?
The "problem" is that, "in the real world" Earth does not change shape with every different possible measurement of it. It is in fact nearly spherical. As I said: "This, of course, is impossible and has never been empirically observed." (A flattened Earth, for instance.)
Do you want to postulate the existence of a preferred frame of reference in relativity (that is, the "proper" frame, which in this case is the Earth frame )? Then you should explain how could Einstein base his theory on the fact that a preferred frame doesn't exist.
Quote
See up. You are still talking of the Earth's shape in a preferred one of the frames.QuoteYou're wrong for both assertion. Maybe you still haven't totally grasped what "measure of lenght" means, read again my first post. A measure of lenght *is* frame-dependent, and so is, as consequence, an object's shape.
I grasped it just fine. You are wrong to assert that an object's shape (like Earth) depends on how it is observed/measured, as if it had no reality, no intrinsic properties of its own.
Say 1000 ships pass by Earth going 1000 different (but near 'c') velocities, all going in 1000 different directions. Does Earth change into 1000 different shapes with its diameter contracting variously in all those directions? Of course not!
Quote
Wiki on Realism (my bold):In all of those cases we refer to distances and dimensions in the "proper" frame, because is the simpler one; but is it always possible to find such a frame?QuoteIn philosophy, Realism, or Realist or Realistic, are terms that describe manifestations of philosophical realism, the belief that reality exists independently of observers."Observers" here in the context of this thread includes abstract points of view, all possible "frames of reference... no living "subject" required.
You asked me to define "actual." That would be that "reality exists independently of observers."
Earth is actually nearly spherical. AC is actually 4.37 light years from Earth. The distance to the Sun is actually about 93 million miles, which would not change if it were measured by a ship flying by very fast. The probe in my example is not actually 10 meters long, as observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)
Imagine a massive neutron star, which is composed of two concentric parts spinning along a same axis but in opposite directions, so that the outer edges of these parts are moving at relativistic speeds.
1. Which would be the measured radius of the star?
2. Which would be its "intrinsic" radius?
Post by: damocles on 08/09/2012 23:55:39
Quote
Imagine a massive neutron star, which is composed of two concentric parts spinning along a samr axis but in opposite directions, so that the outer bords of these parts are moving at relativistic speeds.
1. Which would be the measured radius of the star?
2. Which would be its "intrinsic" radius?
We would have to imagine something a little different to that, because in SR length contraction operates only in the direction of motion, and rotation only describes motion perpendicular to the radius. So the intrinsic radius would be easily and unambiguously determined in an inertial frame that is stationary relative to the centre-of-mass of the neutron star.
Nevertheless it is possible to think of an "intrinsic" property that is ill-defined for a complex object -- in fact such properties are legion. What is the rest mass of the solar system? If we try to measure it in the frame of the centre-of-mass of the solar system, the orbital motion of each of the planets would ascribe to it a mass slightly greater than its own rest mass. So we are faced either with an object that has a mass somewhat greater than the sum of the parts or a mass that cannot be directly measured.
For a physicist, this creates a contradiction and a crisis, that can only be ultimately resolved with a denial that anything has "intrinsic" properties. For a chemist, though, there is no problem. We are forever ascribing an "intrinsic" weight to an atom which (for quite different reasons) is quite significantly different to the sum of masses of its protons, neutrons, and electrons.
Even in a Newtonian universe, the solar system does not have a shape. The concept of "intrinsic" properties does not collapse as a result. A house or a raindrop still has an intrinsic shape. In the chemist's world an object may or may not have a particular intrinsic property. A benzene molecule has an intrinsic shape, a butane molecule does not.
Post by: flr on 09/09/2012 02:31:58
A benzene molecule has an intrinsic shape, a butane molecule does not.
Note that, although in benzene is no free rotation of some chemical group(at room T), the benzene also changes its [instantaneous] shape (on fs time-scale) due to all sort of vibrations/deformations. But that has nothing to do with Lorentz contraction.
Post by: damocles on 09/09/2012 09:10:47
Post by: lightarrow on 09/09/2012 11:56:02
From Lightarrow:Yes, you're right. Then we could substitute "radius" with "circumference", even if this quantity it's not so immediate to measure...QuoteImagine a massive neutron star, which is composed of two concentric parts spinning along a samr axis but in opposite directions, so that the outer bords of these parts are moving at relativistic speeds.
1. Which would be the measured radius of the star?
2. Which would be its "intrinsic" radius?
We would have to imagine something a little different to that, because in SR length contraction operates only in the direction of motion, and rotation only describes motion perpendicular to the radius. So the intrinsic radius would be easily and unambiguously determined in an inertial frame that is stationary relative to the centre-of-mass of the neutron star.
Quote
Nevertheless it is possible to think of an "intrinsic" property that is ill-defined for a complex object -- in fact such properties are legion. What is the rest mass of the solar system? If we try to measure it in the frame of the centre-of-mass of the solar system, the orbital motion of each of the planets would ascribe to it a mass slightly greater than its own rest mass. So we are faced either with an object that has a mass somewhat greater than the sum of the parts or a mass that cannot be directly measured.I have written a lot of times that the term "rest mass" is misleading and you have found now a perfect example of this (apart the case of a massless object as a photon).
The right concept is "invariant mass" m, and it's very easy to compute it: you find a frame of ref. where the total momentum p is zero, then m = E/c2 where E is the total energy of the system. Of course invariant mass is not additive: the solar system's mass is not the sum of the planets masses (as for an atom, as for a nucleus, as for a gas in a box).
Quote
For a physicist, this creates a contradiction and a crisis, that can only be ultimately resolved with a denial that anything has "intrinsic" properties. For a chemist, though, there is no problem. We are forever ascribing an "intrinsic" weight to an atom which (for quite different reasons) is quite significantly different to the sum of masses of its protons, neutrons, and electrons.
Even in a Newtonian universe, the solar system does not have a shape. The concept of "intrinsic" properties does not collapse as a result. A house or a raindrop still has an intrinsic shape. In the chemist's world an object may or may not have a particular intrinsic property. A benzene molecule has an intrinsic shape, a butane molecule does not.
Post by: simplified on 09/09/2012 12:14:49
Our logic should use what laws of measurement of speeds?To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths.
Why should not some real object have a form of itself? Why an object cannot be something by itself?
That's a good point, flr. The problem is that intuition only works when you're so familiar with something that it becomes intuitive! It can also be very misleading in science, since many effects are counterintuitive. A far better guide in science is logic. Once you know something is true (by observing or measuring it), you can logically figure out its consequences.
That's the case in special relativity. Length contraction is very counterintuitive, but we know that the speed of light is constant for all observers from experiments. Once you know that's true, you can logically work through the consequences, and find that lengths have to contract. Our intuition fails because we hardly ever experience relativistic effects in daily life. You can definitely train your intuition by studying something thoroughly, but it takes a lot of effort to actually learn a subject so well that it becomes intuitive, especially when its as abstract as relativity theory.
Post by: old guy on 10/09/2012 20:41:35
Quote
OK - Enough. This is a semi-official note that we either return to accepted ideas or the thread gets closed.
There have been 18 posts here since this warning. Are they all based on “accepted ideas” or are my criticisms of mainstream large scale length contraction the only ones censored?
I tried to move the discussion to “New theories,” as you demanded, but none but one joined in there, and it continues here.
I have replies to many of those posts since your warning, but I am gagged while no one else is. I need some guidance here, preferably from a moderator not so prejudiced against me.
imatfaal:
Quote
It is clear that many of you regard Special Relativity and/or its implications as a convenient fiction - This thread is rapidly descending into a melange of arguments from personal incredulity and ignorance of the subject and that is against the ethos of this Q&A forum.
No, I do not regard SR as a “convenient fiction.” You continue to intentionally misrepresent me. Clocks do slow down when accelerated to higher velocities, and adjustments to the GPS system (and other applications) compensate for the differences precisely and effectively. Yet there is still no empirical evidence for large scale length contraction, and insisting that it is a logical consequence of the math, as a reciprocal of “time dialation” still doesn’t make earth’s diameter or the distance to the sun contract.
Imatfaal From post 49:
Quote
Frame dependence, special and general relativity, and a privileging of observation, modelling, and mathematics mean that your false division into intrinsic and extrinsic is meaningless.
That division is the core of the issue, as far from "meaningless" as it gets.
Yet you have not replied to any of the very cogent arguments by others here, let alone mine, here or in “New Theories,” explaining the central relevance of the internal vs external properties distinction to the difference between actual, real, naturally occurring properties and the differences among observational effects due to differences in frames of reference.
I am bound and gagged here and need of some help from someone who is willing to address these issues on behalf of the forum admin and let me speak freely in reply.
Post by: JP on 10/09/2012 22:15:32
Hopefully I count as a less prejudiced moderator. :)
First, the moderators did discuss this as a team, and we support Imatfaal's decision.
The reason why is that this forum is primarily a science Q&A and discussion forum to answer questions and foster follow-up discussion about mainstream science. Unfortunately, if we regularly allowed posts on non-mainstream science, we would confuse the many users who come to the site to get answers in terms of the main stream!
'Mainstream' in terms of length contraction is Einstein's special relativity, which does predict length contraction. Criticisms of that idea should be kept to New Theories, as mentioned above.
As you note, the New Theories forum is not an incredibly active part of this site. This is probably because our primary purpose as a forum is science Q&A. While we're happy to accommodate non-mainstream ideas in 'New Theories', if your primary goal on the site is to discuss outside-the-mainstream ideas, then you might find it more productive to seek out another forum.
Finally, I've posted this publicly because you've posted your complaint publicly. If you don't find this a satisfactory response, please PM me or another moderator, but please do not post your response here so that this thread stays on topic.
Thanks!
JP moderator
Post by: flr on 11/09/2012 00:13:16
But how came the moun finds a shorter path in its way through atmosphere? By which mechanism its path is shorter than what I observe from Earth?
Is our universe made of multiple "realities" that are superimposed? In each such "reality" length is shorter or longer and time "flow" faster or slower?
Post by: old guy on 11/09/2012 00:28:20
Good questions, fir. I hope you get some answers. So far, I haven't.
But how came the moun finds a shorter path in its way through atmosphere? By which mechanism its path is shorter than what I observe from Earth?
Is our universe made of multiple "realities" that are superimposed? In each such "reality" length is shorter or longer and time "flow" faster or slower?
Post by: imatfaal on 11/09/2012 16:10:08
http://skullsinthestars.com/2012/09/10/relativity-ten-minutes-to-alpha-centauri/
Quote
This warping of space and time is the most shocking part of special relativity when one encounters it for the first time. It is important to note that I use words like “perceive”, “observe” and “point-of-view” to describe the changes in time and space, but these are real changes — no physical experiment or measurement of any kind will disagree with the results.
Post by: JP on 11/09/2012 17:24:12
But how came the moun finds a shorter path in its way through atmosphere? By which mechanism its path is shorter than what I observe from Earth?
Is our universe made of multiple "realities" that are superimposed? In each such "reality" length is shorter or longer and time "flow" faster or slower?
Now you're venturing into philosophy, flr. What physics can tell you, as imatfaal said, is that distance is something we measure. We know that for the same Newtonian (non-relativistic) path, from the sun to the earth, the distance measured does in fact depend on how fast the observer is moving along that path. This is what the theory of special relativity tells us and is in accordance with experiments and observations.
Science restricts itself to predicting the results of measurements, however. If you want to ask about what it means for two observers going from the sun to the earth to measure two different distances, that's getting into philosophy. Science can guide your inquiries by telling you that any philosophical interpretation you come up with has to match validated theories, but building some reality that exists beyond those theories is beyond science.
Post by: flr on 11/09/2012 17:24:49
In my opinion the invariance of "c" does not explain the length contraction and time dilation just - because they are 2 sentences with the same meaning but put in different wording.
I am not sure I found a satisfactory answer to the question: "what makes space and time be relative?" or its equivalent "what makes c be invariant?"
Instead I found in many places the argument that the invariance of c is immediately equivalent with relativity of space and time.
Post by: JP on 11/09/2012 17:32:12
I am not sure I found a satisfactory answer to the question: "what makes space and time be relative?" or its equivalent "what makes c be invariant?"
Instead I found in many places the argument that the invariance of c is immediately equivalent with relativity of space and time.
I don't think there is a satisfactory answer to why the speed of light is constant. It's a postulate of special relativity, which means we take it as a fact. We have plenty of measurements that establish it as a fact, but we don't have some deeper theory that tells us why it is. The other postulate of special relativity is that the laws of physics are the same for all observers in inertial (constant velocity) reference frames.
(See: http://en.wikipedia.org/wiki/Postulates_of_special_relativity#Postulates_of_special_relativity)
Once you take those two to be true (and we do so based on observations) then special relativity follows. You can further validate special relativity by checking its specific predictions against reality, which has also been done. So we're pretty sure it's true because the postulates have been checked, and the theory follows from those, and the theory itself has been checked.
As for why the postulates are true, we don't know. Some deeper theory may come along to explain that, or it may be something we never know. The fact that we don't know means there's plenty of future work to be done.
Post by: David Cooper on 11/09/2012 22:30:33
Here's an example of the problem:-
Quote
I don't think there is a satisfactory answer to why the speed of light is constant. It's a postulate of special relativity, which means we take it as a fact. We have plenty of measurements that establish it as a fact, but we don't have some deeper theory that tells us why it is.
So, we take something as a fact because it is a postulate of a theory. That does not make it a real fact - it's only a "fact" within a theory. This is then backed up by a claim about measurements establishing it as a fact, but there are no measurements that can be made which can do anything of the kind - the speed of light can only be measured on a round trip, thereby completely hiding any actual variation that may be there. To call things facts when they are not facts is wrong, and it's absolutely wrong to mislead the public in this way.
Special Relativity is a theory and not a fact. The things taken as facts within SR are not automatically facts outside of SR. I had to take my questions about relativity to another forum because I was not allowed to ask them here as I was daring to question Einstein's relativity. You are not supposed to be a church defending a religion here by excluding people who ask awkward questions which challenge your own beliefs. Your job is to explain theories and to word things carefully so as not to make claims which go beyond what can be justified.
On the other side we have a claim that there's no real length contraction, but ironically that could only be true in any absolute sense if Einstein's Special Relativity is true - any other way of interpreting the Michelson Morley experiment requires actual length contraction to account for the only real fact which can be measured here (that light always completes the journeys along the arms of the MM apparatus and back in the same length of time [assuming they're exactly the same length - they don't actually have to be, but that's a detail that doesn't need to be explored]).
I myself made some assertions here a while back when asking a question about the mechanism behind time dilation and was banned from posting here for ten days on the basis that I was evangelising. I could have backed up those assertions and demonstrated them all to be correct, but I wasn't allowed to. The moderators, however, are allowed to make assertions without backing them up, and they refuse to engage in any discussions which are in danger of showing them to be false - it all gets pushed into a backwater instead where they can ignore it and where no one will see it.
I've arranged for some people at a couple of radio stations to watch what happens to this post because the way it is dealt with will be very revealing to them about the nature of a certain forum which they promote through their connections with a certain person who has already failed to deal with my fully-reasonable complaints about the way I've been treated here. I want to discuss science, and science has to be open to question. If this is actually a Church of Einstein, it should say so at the top and not claim to be a science forum.
Post by: JP on 11/09/2012 22:58:01
Our scope is, as I said above, science Q&A and discussion in terms of mainstream theories. We're a site staffed mostly by volunteer moderators and provided freely to our members as a place to do just this. Your previous posts were moved because they were simply beyond the limited scope of this forum. As I mentioned to Old Guy, we're not trying to stifle your ideas--we just have a very limited scope: science Q&A and discussion in terms of mainstream science. Topics that stray too far from that are moved to the appropriate sub-fora (generally new theories for non-mainstream science).
If you are eager to discuss non-mainstream ideas, we do provide the New Theories forum for this. However, as you can see it's a small part of this forum and not our focus. If you would like an in-depth discussion of non-mainstream theories, there are other science fora on the net which are far broader in scope and content that might generate livelier discussions.
Again, due to our limited scope and time, and to keep this thread on topic, I'll be moving all further off-topic posts to the appropriate sub-fora.
Thanks,
JP moderator
Post by: David Cooper on 12/09/2012 00:31:02
Post by: yor_on on 12/09/2012 06:49:55
Post by: old guy on 12/09/2012 20:02:26
yor_on:
Quote
...but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions,...(my bold.)
There seems to be an exception made for large scale length contraction of objects as a theory with no empirical evidence to support it, since, as JP pointed out, no one has yet observed Earth, for instance, from that ubiquitous, thought-experimental near 'c' fly-by frame. But Einstein loved a good thought experiment, and I thought I presented one as a reasonable test of length contraction in reply 17.
Quote
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)Also, from my reply 34:
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
Quote
The probe in my example is not actually 10 meters long, as (it was) observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)
The above was not directly addressed here the first time around. I hope it will generate relevant replies this time.
Post by: David Cooper on 12/09/2012 20:44:31
I think it's fairly simple what the mods want. We can all soar, but that's for 'New theories', (although) it's quite hard not to put in your own interpretations in this Physics, Astronomy & Cosmology forum and we're all failable. This site was once constructed for giving people the chance to have in depth discussions, but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions, and to be perfectly strict also the math behind the reasoning. And the last demand is definitely the hardest. But that is if one want people to take one seriously, and then one probably publish elsewhere :)
There was a long argument caused by people using different interpretations of the word "real". Length contraction is absolutely real for Lorentz (though it's impossible to tell whether something's really been contracted as you can't tell if it's moving), while for Einstein it's real as a measured phenomenon. We can argue as much as we like about the degree to which Einstein considered it to be real in any other sense, but none of that makes any difference to his theory. Some people even think that objects are physically changed in shape by being observed by moving observers, and they can think that if they like, but so far as I am aware it is not a requirement of SR that you believe such a thing. It may be that Einstein considered all possible observed shapes of things as being absolutely real at the same time and that the one which maximised all its dimensions not to be superior - I haven't seen enough evidence to know what he believed on that point, but I certainly don't think it's crucially important to SR. Regarding the case where the dimensions of an object are all maximised as the real shape of that object would simply be a slightly different interpretation of a trivial detail of SR and not a new theory.
Post by: David Cooper on 12/09/2012 21:01:33
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
Is it Groundhog Day? This has already been answered. It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.
Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger. This allows you to decelerate the ship without a pile-up, and maybe it should be applied inwards from the sides of the cargo bay to avoid the force acting on one end of the ship before the other. You would close the rear door just as the end of the alien ship has entered the cargo bay (which is theoretically possible if the ship is very thin), and then you apply the force to stop the ship. The ship is completely contained in the cargo bay for a moment and is still moving at high speed, but that speed is completely removed in the next instant, thereby preventing it from crashing into the end wall. What will happen next? Well, all the atoms are too close together in the direction in which the ship was moving a moment earlier, so they will push out against each other and the ship will lengthen, either breaking its way through the wall and the door, or the ship will buckle badly in order to lengthen without exceeding the 10m space available to it.
I hope that helps.
Post by: old guy on 12/09/2012 22:03:16
No, it only confuses the experiment, as I laid it out, with your own conditions.
The rules of engagement for a thought experiment are set by its author's conditions.
You say:
Quote
It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.
I said that the shuttle pulls alongside of the probe and finds that it is way longer than the 10 meters it was measured to be from earth. Yes, it will "be too large to fit", which was my point illustrating that its "contracted length" is much shorter than its actual length, as observed from its own frame of reference "alongside" it. The bay is a standard shuttle bay, not "open at both ends" for a brief fly-through by the probe. It either will fit in a 10 meter bay or it will not.
Quote
Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger.
This is blatant obfuscation of the thought experiment as I presented it.
The project was to retrieve the probe. The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.
... And your 'evangelism' above is not helping the credibility of this thread. I expect it will be closed primarily because of your continuing rants, like about "The Church of Einstein" and such. You are hijacking this thread with your radical opinions.
I am still hoping for an intelligent replies to my experiment as I presented it.
Post by: David Cooper on 12/09/2012 23:06:27
David Cooper:"I hope that helps."
No, it only confuses the experiment, as I laid it out, with your own conditions.
The rules of engagement for a thought experiment are set by its author's conditions.
You say:QuoteIt will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.
I said that the shuttle pulls alongside of the probe and finds that it is way longer than the 10 meters it was measured to be from earth. Yes, it will "be too large to fit", which was my point illustrating that its "contracted length" is much shorter than its actual length, as observed from its own frame of reference "alongside" it. The bay is a standard shuttle bay, not "open at both ends" for a brief fly-through by the probe. It either will fit in a 10 meter bay or it will not.
I answered the question. It's up to you to interpret the results. While they were moving at different speeds, it did fit, and once they aren't, it won't.
Quote
QuoteActually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger.
This is blatant obfuscation of the thought experiment as I presented it.
The project was to retrieve the probe. The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.
It was a very clear way of looking at how things work and it will allow the shuttle to retrieve the probe.
Quote
... And your 'evangelism' above is not helping the credibility of this thread. I expect it will be closed primarily because of your continuing rants, like about "The Church of Einstein" and such. You are hijacking this thread with your radical opinions.
I am still hoping for an intelligent replies to my experiment as I presented it.
My radical opinions? I'm trying to be neutral about things, not pushing any theory forward as being correct, but making it clear where the failings of different theories lie so that people can make up their own minds, or better still, not make up their minds but continue to be open to all reasonable possibilities. I'm not interested in hijacking your thread - I'm only still posting here because I thought you were looking for help in understanding this, but you clearly aren't. You've had the answers you need from various people, but you simply reject them every time. I'm now being won over by the mods - they read you absolutely right. Goodbye.
Post by: damocles on 13/09/2012 00:32:30
Any object does have intrinsic properties. That is not a matter that hinges on any observational result -- it is a matter of definition. An intrinsic property of any object is one that is measured in or calculated to an observation in the inertial frame of reference that is stationary with respect to that object's centre-of-mass.
This definition automatically gives rise to the fact that an inertial frame of reference that is stationary with respect to the centre-of-mass of an object is a privileged frame in that it allows an observer to directly measure the object's intrinsic properties.
Both of these assertions are a matter of definition -- you cannot deny either of them unless you can establish that there is some ambiguity or indeterminacy in my definitions.
It is only through the operation of these definitions that we are able to make tables of atomic mass, Earth's shape and size, and 100,000 other intrinsic properties that are listed in the CRC Handbook of Chemistry and Physics.
It is only through the operation of these definitions that we are able to make generalizations such as "the (intrinsic) shape of any sufficiently large and plastic planet must be an oblate spheroid of revolution", and similar issues that were quite legitimately worrying old guy around posting #30 of this thread.
There is one other matter that I think needs to be cleared up:
Any idea that mentions "large scale" suggests a theory that treats large scale and sub-microscopic systems differently. If that is what is intended, then we need a smooth boundary condition at the swap-over scale. This is consistently achieved for quantum theory as a "sub-microscopic theory". I do not see how it could be for a Lorentz transformation that is well-established for sub-microscopic objects, but would become "switched off" for macroscopic ones.
Post by: JP on 13/09/2012 04:26:04
I admit this thread has so many different subjects being discussed that I haven't kept up on all of them. I tend to agree with you that a lot of properties of an object can be, and are in practice, defined in its center-of-mass rest frame. And we definitely know when something is in our inertial reference frame. It's center of mass won't be moving with respect to us, which is easy to observe.
So we can define the properties of a known object by specifying them in its rest frame, but we cannot practically redefine our definitions of measurement of length and time in such a way. If we did so, our clocks and meter sticks would have to change length to match the speed anything was moving with respect to us.
What I've also argued against is the idea that length doesn't contract simply because we can define the length of an object in its center of mass reference frame. Just as the laws of physics say a planet should be (roughly) spherical in it's COM frame, they also say it should be squashed if you're moving with respect to it. Unless you choose to completely redefine how we make measurements, you're going to measure the planet as squashed and all physical laws formulated in your reference frame are going to treat it as squashed. Of course, special relativity also allows you to formulate the laws from the planet's COM frame, in which case it's spherical and you are squashed. Neither is more correct than the other because they both describe physical reality as measured by observers.
-----------------------------------
The following isn't addressed at you, Damocles, but there's so many viewpoints being expressed in this thread that I feel I should make my point of view clear.
What I've also argued against is the introduction of extra complexity to special relativity in order to preserve some preconception about the universe. Science doesn't work that way. We can always hold an infinite number of preconceptions about the universe and introduce extra hidden variables into a model to preserve them. Obviously no one's arguing something this far out, but if I were more comfortable with unicorns causing length contraction, I could always introduce unicorns who zip about the universe shrinking our rulers with magical pony power. As long as the unicorns are undetectable by measurement, and their pony power works identically to Lorentz contraction, I can claim that my results are completely in line with observations. That doesn't this viewpoint valid science, nor does it make other viewpoints with far less absurd preconceptions valid science. Science is generally about using the simplest possible model to describe some phenomenon, not choosing the more complex model because it fits your preconceptions.
A far more real point than the unicorns is that many scientists are also deeply religious and believe that a deity or deities play an important role in the universe. Their personal view probably involves a complex theory that allows the deity to act but remain undetectable. However, they also generally realize that good science does not involve complicating a theory with undetectable variables that have no influence on measurement, so when they present their work to other scientists, they present the 'mainstream' version of the theory.
Einstein's special relativity is the mainstream scientific explanation because it is the simplest model which introduces the fewest extraneous variables and preconceptions and explains observations.
Post by: damocles on 13/09/2012 04:37:00
I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.
Post by: JP on 13/09/2012 04:44:28
I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.
Are intrinsic and extrinsic the usual technical terms used here? It's been a while since I studied special relativity, but I don't recall ever learning terms other than "rest ____" to describe properties measured in the rest frame.
Post by: damocles on 13/09/2012 04:49:55
Quote
Are intrinsic and extrinsic the usual technical terms used here? It's been a while since I studied special relativity, but I don't recall ever learning terms other than "rest ____" to describe properties measured in the rest frame.
Probably not, but their meanings are fairly clear, they are much loved of philosophers, old guy had already used the terms, and someone in the earlier posts in this thread had objected to the use of "rest ..." properties.
Post by: imatfaal on 13/09/2012 11:07:10
Post by: lightarrow on 13/09/2012 13:02:39
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be non identifiable.
Any object does have intrinsic properties. That is not a matter that hinges on any observational result -- it is a matter of definition. An intrinsic property of any object is one that is measured in or calculated to an observation in the inertial frame of reference that is stationary with respect to that object's centre-of-mass.
This definition automatically gives rise to the fact that an inertial frame of reference that is stationary with respect to the centre-of-mass of an object is a privileged frame in that it allows an observer to directly measure the object's intrinsic properties.
Post by: damocles on 13/09/2012 13:23:58
It is purely and simply a term that I chose to define and use because there were a couple of problems with "rest" properties
(1) An objection to "rest mass" that Lightarrow expressed that I did not quite understand but attempted to accommodate. He suggested "invariant" but I had my problems with that particular term because I would want to restrict that term to quantities like c0 that are genuinely the same to all observers. The rest mass is indeed the same to all observers, but only privileged observers in the rest frame can measure it directly. Others have to deduce its value from the measurements they make of a non-invariant related property.
(2) A rather more trivial, but possibly confusing ambiguity in a rest property of a complex object: The rest property should be taken as the value of a physical quantity in the frame of the centre-of-mass of the complex object, but could be confused with a very different property that would be measured if all of the parts of the complex object were brought to rest relative to one another. This particular problem seemed about to come to the fore when someone -- lightarrow? -- started talking about neutron stars with incoherent internal motions at relativistic relative speeds.
I chose the words "intrinsic" and "extrinsic" because their normal meanings in the English language seemed very apt for the flavour I was trying to give them. The dictionary definition of "intrinsic" is "belonging to a thing by its very nature". The Earth has an "intrinsic" shape because local application of the laws of physics say that the equipotential surfaces in its gravitational field will be shaped as oblate spheroids of revolution, and it is plastic enough as a planet to have its surface adopt an equipotential shape (to a very close approximation). Basically, if the Earth were an observer, the intrinsic shape of the Earth is the one that it would know it had, in spite of whatever others may observe. It is a part of the Earth's nature. The opposite of intrinsic -- extrinsic -- means something that belongs to a thing only by virtue of a relationship with an external force or object. Extrinsic properties are every bit as "real" as intrinsic ones, but they can and do vary according to different relationships with different external objects.
But these terms are not SR technical terms. They are simply English words that I have chosen that in their normal English meanings capture the character that I see operating in properties of objects under SR conditions. The meanings are also congruent with those that several philosophers give them as technical terms.
From lightarrow:
Quote
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be non identifiable.Oh, and lightarrow, i have already in an earlier post in this very long thread, pointed out that an argument that a particular object might not possess a particular intrinsic property is not an argument against intrinsic properties per se. If the monochromatic light that it emits at a particular time is a property of a star, then it did have a unique rest frame at the time it emitted it; if we can no longer determine what that frame was that does not deny its existence, and nor does the fact that the star might since have died. And if the light is regarded as a property of the photons, then it cannot be intrinsic, because the photons themselves have no rest frame.
Post by: flr on 13/09/2012 15:25:26
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be non identifiable.
Interesting point, but I have a quick question.
Let's assume there is a distant source (like our Sun) that emits harmless visible light for an Earth observer.
The observer take a relativistic ship (0.9999c) and travel toward the source. His ship screen out all radiation except those wavelengths that for the Earth frame were harmless visible light. Due to Doppler Effect the light that penetrates the ship will be now gamma-ray.
My question is: Will the observer on ship get hurt by gamma rays? Or in his ship those penetrating gamma rays (that on Earth were visible light) have the same impact as the visible light on Earth frame, i.e. they will be harmless?
Post by: JP on 13/09/2012 16:00:33
Rest properties seem a bit different, since they require a reference frame to be fixed. However, it seems at first glance that (aside from light) you could always use local measurements to figure out the required transformation into a rest frame of the measuree and then transform whatever measurements you make to that rest frame.
However, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic. Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic. It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).
Post by: JP on 13/09/2012 16:14:39
His ship screen out all radiation except those wavelengths that for the Earth frame were harmless visible light.
Due to Doppler Effect the light that penetrates the ship will be now gamma-ray.
What type of shielding are you using? Most shielding will only care about how fast the light wave peaks hit its surface, i.e. the frequency. Let's say the sun emits only one wavelength of visible light when your ship is at rest with respect to the sun. The light wave's peaks hit your shielding at a slow enough rate that they pass through the shielding.
Now you start flying really fast towards the sun. Because you're flying into the peaks, they'll start hitting your shield faster. Since your shield only cares about how fast the peaks hit it, it blocks the light and no light gets into your ship.
Post by: imatfaal on 13/09/2012 16:25:16
SR definitely has invariant quantities, which may be defined in terms of some formula entirely in terms of local measurements (in any inertial reference frame), and which turn out to be constant, no matter which reference frame is chosen.
Rest properties seem a bit different, since they require a reference frame to be fixed. However, it seems at first glance that (aside from light) you could always use local measurements to figure out the required transformation into a rest frame of the measuree and then transform whatever measurements you make to that rest frame.
However, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic. Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic. It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).
Now I am getting confused - a single photon has no invariant mass, it must be zero. Spin - yep
Post by: JP on 13/09/2012 16:37:30
I meant that having an invariant mass of zero still counts as having an invariant mass in the case of a photon, even though it has no rest frame. You can calculate it from the length of it's energy-momentum four vector in any reference frame and get zero as a result.
Post by: imatfaal on 13/09/2012 16:42:38
Post by: yor_on on 13/09/2012 18:34:10
Post by: old guy on 13/09/2012 18:52:06
I still have received no unequivocal answer to the “will it fit?” question, illustrating the difference between the intrinsic length of the probe measured from at rest with it and the extrinsic , contracted length measured from Earth’s frame.
A very brief recent summary from my post 79, edited (...) for clarity of detail:
Quote
The project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.
As I said, “I am still hoping for intelligent replies to my experiment as I presented it.”
Damocles:
Quote
The dictionary definition of "intrinsic" is "belonging to a thing by its very nature". The Earth has an "intrinsic" shape ...
So does my alien probe: its shape as it was built, obviously “at rest” with it.
Substitute “as it was originally formed by gravity” and you have the intrinsic shape of Earth.
Damocles said:
Quote
It is only through the operation of these definitions that we are able to make generalizations such as "the (intrinsic) shape of any sufficiently large and plastic planet must be an oblate spheroid of revolution", and similar issues that were quite legitimately worrying old guy around posting #30 of this thread.
The core of my “worry” as expressed in post 30:
Me:
Quote
Does this claim that Earth changes shape as it is measured from different frames of reference?Lightarrow:
Quote
Certainly. In a frame of reference which is still with respect of our planet, the Earth is spherical...; in another, moving, frame, it's not (and of course every human being is flattened too). Where is the problem?Me:
Quote
The "problem" is that, "in the real world" Earth does not change shape with every different possible measurement of it.
Damocles:
Quote
I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.(my bold)
Very contradictory! The “contracted length” of the probe or shape of Earth’s diameter is NOT the “actual” length/shape in either case.
Imatfaal:
Quote
...misconception that the length contraction is not "real" - ie that it is merely an artifact of vision/observation rather than an actual consequence of frames in relative motion.
My thought experiment illustrates what is “real” about the length of the probe as compared with the “vision/observation”/measurement of it from Earth’s frame. It “really” will not fit into a 10 meter bay!
Post by: yor_on on 13/09/2012 19:14:56
If you think of it OG. To retrieve that probe it will have to be in its so called 'rest frame'. And in that frame of reference the probe will have its 'rest properties', if you like. Assuming that the cargo bay is built to the dimensions we found the probe to have before joining up with it, becoming 'still' relative it, it will be found not to fit. The whole idea with a length contraction is that frames of reference will differ when compared, not that you will find length contractions being in the same frame of reference, 'at rest' with what you measure. As you are, approximately, on any planet.
Post by: yor_on on 13/09/2012 19:20:59
That's wrong.
=
What you can do is to assume that locally (locality) must be the preferred frame, just as the idea of 'invariant mass' have a same property assumed, no matter where it is measured. But the discussion about what is more 'real', comparisons between frames of reference, or comparisons being at rest with what you measure, is meaningless. They are both as real from the frame measuring. Instead of complaining, embrace it :)
Post by: JP on 13/09/2012 20:09:47
I still have received no unequivocal answer to the “will it fit?” question, illustrating the difference between the intrinsic length of the probe measured from at rest with it and the extrinsic , contracted length measured from Earth’s frame.
A very brief recent summary from my post 79, edited (...) for clarity of detail:QuoteThe project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.
As I said, “I am still hoping for intelligent replies to my experiment as I presented it.”
You've received plenty of replies, Old Guy. You haven't received any that you happen to like, but that's now this forum operates. :)
I think it's clear from almost every poster in this forum that the 'rest length' of the probe is longer than the 'rest length' of the cargo bay, while the measured length of the probe as it passes through the cargo bay in motion will be exactly as long as the cargo bay.
You're engaging in evangelism of your viewpoint by continually restating the same arguments without engaging in discussion. That is not acceptable on this forum.
If you do want to discuss what 'rest length' means vs. length measured in non-rest frames, there is an interesting discussion going on about that and you're welcome to engage in it, so long as you keep it a discussion.
Post by: old guy on 13/09/2012 21:28:33
This part of the thread is intended to be a sincere discussion of a (future) practical application of length contraction with each person listening to the other and replying to specific points.
As I told David Cooper, the ‘rules of engagement’ (as I understand) for a thought experiment dictate that the specific situation is taken as the author presents it.
yor_on:
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If you think of it OG. To retrieve that probe it will have to be in its so called 'rest frame'.
As I already said, the shuttle must match velocities with the probe ("come alongside") to capture it, as we well know from all “docking” procedures in space. It is still going at near ‘c’ but now the shuttle is at rest with it and therefore sees it as it is, much longer that 10 meters, not as it was observed from earth, going very fast relative to earth... i.e., “contracted.”
yor-on:
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Assuming that the cargo bay is built to the dimensions we found the probe to have before joining up with it,
I originally said that our shuttle has a 10 meter bay, as it was built. We saw the probe, from earth, as 10 meters. Will it fit in the bay? Simple. Clear. No.
yor_on
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becoming 'still' relative it, it will be found not to fit.
Exactly my point. It was not ‘actually’ 10 meters, as it was seen from earth. That “actually” means “really” is demonstrated by the fact that it is actually, really way too long to fit into the 10 meter bay.
yor_on:
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You still don't get it OG? We measure, and from there construct what is 'real'.
You are not listening. We measured the probe to be 10 meters. However, it was not “really” 10 meters, as the example has abundantly demonstrated.
I now put this experiment to rest. I do hope to hear answers to my last reply.
Post by: JP on 13/09/2012 21:42:43
Here's a question for you: would you agree that the result of the measurement of the probe from the earth's frame (where the probe is moving very rapidly) is 10 meters?
Post by: damocles on 13/09/2012 22:44:59
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However, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic. Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic. It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).
Yes I clearly goofed up here. Clearly a photon has (at least? only?) three properties that should be regarded as intrinsic, in spite of the fact that it has no "rest frame": a zero spin, a zero "rest mass", and a "vacuum speed" of c0. But the "colour as emitted" of a photon must be seen as an intrinsic property of the emitting body rather than the photon, because it is only by translation to the rest frame of the emitting body that different observers can agree on this sort of property, and it is only in this frame that the "character" of the photon can be assessed (e.g. a sodium emission line).
It seems to me (a propos of lightarrow response 87) that whether or not a particular observer finds this translation practically feasible is not particularly relevant to how the property should be regarded.
Post by: imatfaal on 13/09/2012 23:00:25
For those of you who don't mind adapting a thought-experiment... relativity is of course reciprocal; just as we can define the rest frame as the frame in which the shuttle has zero momentum, we can also define the rest frame as the frame in which the probe has zero momentum and the shuttle is approaching it at high velocity (in the opposite direction). From the rest frame of the probe we now see the shuttles cargo bay as length contracted, and the probe is no longer contracted ...and the probe would still all fit in just before destroying itself and the shuttle! The timings are very tough to reconcile, events seem to be switched, and with relativistic speeds you cannot be sure of any simultaneities without the maths; but in the end the same set of events happens - it must be the case because it is the exact same scenario.
Post by: imatfaal on 13/09/2012 23:08:24
From JP, a few posts ago in this busy threadPolarization and charge (or lack of same) are also intrinsic for a photon, and photons are spin 1 btw not spin 0 (that would be the higgs) . I would argue that these (spin, invariant mass, charge, polarization, speed) are intrinsic because they are valid from any frame of measurement - ie no frame can be postulated that can change circular polarization to linear - whereas a frame can be postulate that would red-shift/blue-shift.QuoteHowever, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic. Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic. It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).
Yes I clearly goofed up here. Clearly a photon has (at least? only?) three properties that should be regarded as intrinsic, in spite of the fact that it has no "rest frame": a zero spin, a zero "rest mass", and a "vacuum speed" of c0. But the "colour as emitted" of a photon must be seen as an intrinsic property of the emitting body rather than the photon, because it is only by translation to the rest frame of the emitting body that different observers can agree on this sort of property, and it is only in this frame that the "character" of the photon can be assessed (e.g. a sodium emission line).
It seems to me (a propos of lightarrow response 87) that whether or not a particular observer finds this translation practically feasible is not particularly relevant to how the property should be regarded.
Post by: JP on 13/09/2012 23:47:35
*states, even. I love autocorrect
Post by: damocles on 14/09/2012 00:14:20
I am going to outline a thought experiment that I think is a genuine proxy for old guy's original proposal, that will highlight some of the issues involved, and that might be critical in that it could give a different result depending whether or not OG's term "real" applies to a Lorentz contraction.
1.) Prepare a metal disk that is 20% larger in diameter than the mirror of the Hubble telescope.
2.) Tow the Hubble telescope to a location in "empty" space outside the solar system.
3.) Focus the telescope on Sirius (or another conveniently bright star), and monitor the light reaching the focal point -- our observer.
4.) Launch the disk, frisbee-wise, on a trajectory that "should" completely block off the telescope to light from Sirius, at a near-light speed.
I believe that the Lorentz contraction is "real" and that the observer should not observe an absence of Sirius light at any instant during this exercise. If, on the other hand, the Lorentz contraction is "not real", then there should be a brief period of time when Sirius is in complete eclipse.
I therefore ask OG -- is this a fair proxy for your thought experiment? Would you agree with my interpretation of the possible results of such an experiment?
And I ask the several SR experts here -- do you think that I have correctly interpreted the SR mathematical model in my belief about the conclusions?
Post by: yor_on on 14/09/2012 00:49:12
As the contraction is in the direction of spin it will 'crack', and yes, that will let light through ::))
Sorry, couldn't help that one. It's a classical example that might be feasible to test for with spinning black holes? Maybe that is? If we can 'see' them good enough that is :)
But, I do get your idea.
You think the same way as me. A frame of reference is where you are. What measurements you make in that frame will be true for you. And it doesn't matter if someone else far away have a different opinion on lengths or 'time'. That doesn't change a thing for you, inside your 'frame', if we say so.
==
And sorry OG, instead of trying to see the points made you use your opinion as some club, and on us no less :) The contraction is no illusion :)
Post by: damocles on 14/09/2012 00:55:36
Post by: yor_on on 14/09/2012 01:02:08
Post by: yor_on on 14/09/2012 01:04:17
I make lot of those myself ::))
Where's the fun if we're not allowed to make some eh, faus paux(?) whatever :) at times?
Post by: old guy on 14/09/2012 01:05:18
Old Guy, if you define "really" to mean in the rest frame then your logic holds. This isn't an accepted meaning of the term "really" in science, which is why you're getting push-back from others.
Yes, I do. I am advocating realism here as apposed to the idealism that reality is defined by observation and measurement. The question of how best to measure something is a technical question. I think it is reasonable to be "in the rest frame" with whatever science is measuring, rather than flying by the object being measured at relativistic speeds.
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Here's a question for you: would you agree that the result of the measurement of the probe from the earth's frame (where the probe is moving very rapidly) is 10 meters?
Yes. But I already said several times that the probe as measured from earth appeared to be 10 meters long. I wonder why I think no one is paying attention to what I actually say.
Post by: JP on 14/09/2012 01:12:05
I won't spoil the outcome just yet, though. :)
Post by: JP on 14/09/2012 01:15:39
Old Guy, if you define "really" to mean in the rest frame then your logic holds. This isn't an accepted meaning of the term "really" in science, which is why you're getting push-back from others.
Yes, I do. I am advocating realism here as apposed to the idealism that reality is defined by observation and measurement. The question of how best to measure something is a technical question. I think it is reasonable to be "in the rest frame" with whatever science is measuring, rather than flying by the object being measured at relativistic speeds.QuoteHere's a question for you: would you agree that the result of the measurement of the probe from the earth's frame (where the probe is moving very rapidly) is 10 meters?
Yes.
Ok, that's fair enough. It sounds like you don't disagree with the predictions of special relativity. You just disagree with the idea that we call our measurements "real" lengths. I guess that's fair, but it's why no one in special relativity uses the term "real." You can go into philosophy and argue about the definitions, but as far as science is concerned, which deals with measurements, we simply have to admit that we measure one length in the rest frame and another in the moving frame and leave it up to philosophers to argue over what's "real" or not.
Post by: yor_on on 14/09/2012 01:22:00
This is assuming a equivalence with a constant uniform acceleration relative a 'gravity', and then stretch the definition into uniform motion. The other way to see it is that a uniform motion, no matter its speed, always must present us with the same 'energy' and that only a acceleration ('gravity') will present a blue shift. But that can't be right.
==
This one is tricky on so many levels though. First of all, is gravity uniform accelerations? If it is, then mass always must be moving in some 'degree of freedom' that we can't measure. The other is using blue shifts as a definer for both uniform motion and accelerations. But assuming that blue shift must be there in a uniform (relative) motion, after your acceleration to near light speed, we do have one coherent description locally. And by 'locally' we can just as easily exchange to a 'rest frame', where you are 'at rest', meaning that you follow a geodesic.
Post by: yor_on on 14/09/2012 01:36:36
'ripples'?
I better put this in New Theories' huh :)
Post by: old guy on 14/09/2012 01:39:47
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old guy's original formulation was in terms of a fly-by and compare rather than an actual attempt at docking at relativistic speed.
To what original formulation are you referring here? The experiment in discussion here is the alien probe retrieval project with no “fly-by” involved... except the shuttle flying by the probe before it turns around and catches up.
damocles:
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I therefore ask OG -- is this a fair proxy for your thought experiment? Would you agree with my interpretation of the possible results of such an experiment?
No, and no.
But why complicate my experiment with a spinning, flying disk, asking whether it is “really” big enough to cover the Hubble lense? My scenario was an attempt to illustrate the “real” length of a probe by the simplest possible means. Maybe the more complicated you make it the more it will obscure the fact that the probe will not “really” fit in the bay.
Post by: yor_on on 14/09/2012 01:46:01
Assuming that mass is a constant uniform acceleration what is then a geodesic?
'ripples'?
I better put this in New Theories' huh :)
The point I'm struggling with here is that 'c' is a constant, but 'energy' is relative. But to define a 'speed' close to 'c' there must be a blue shift, no matter if it is measured in a acceleration or in its subsequent uniform motion. There is no other way I can come up with to define a 'speed', and, the universe needs one if 'motion' exist.
Post by: old guy on 14/09/2012 01:50:36
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Ok, that's fair enough. It sounds like you don't disagree with the predictions of special relativity. You just disagree with the idea that we call our measurements "real" lengths. I guess that's fair, but it's why no one in special relativity uses the term "real." You can go into philosophy and argue about the definitions, but as far as science is concerned, which deals with measurements, we simply have to admit that we measure one length in the rest frame and another in the moving frame and leave it up to philosophers to argue over what's "real" or not.
I think I see a glimmer of mutual understanding emerging here. I do not, in fact, disagree with the predictions of SR.
As to what is "real," what was seen from earth to be 10 meters in length ("contracted") turned out to be however much longer than 10 meters, depending on its velocity relative to earth, causing the apparent contraction.
Post by: yor_on on 14/09/2012 01:55:34
Post by: imatfaal on 14/09/2012 11:17:55
Polarization stater* are the spin states by the way.
*states, even. I love autocorrect
I wish my autocorrect had caught my classical/quantum blunder. Skitt's Law struck again
Post by: imatfaal on 14/09/2012 11:59:51
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Here is another “reality check” against large scale length contraction:This was the formulation - and I am pretty sure that no one has argued about the answer as it is uninteresting. The question doesn't make it clear that you are placing the shuttle also at rest within the rest frame of the probe - but with that condition then obviously the probe will not fit - there is no need for special relativity here.
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
it is your insistence that the contraction is only apparent, and the concomitant implication that this is an artefact, an illusion that better observation greater understanding would dispel which has lead other to postulate refined experiments that have interesting consequences. DavidC's concept of the cargo bay with open end(s) makes the experiment doable with the shuttle in a frame of high relative motion to the frame of probe. I have been told off for wrecking space shuttles (it's not as if we are using them anymore) - and Damocles managed to take it to another level by leaving the shuttles unharmed yet encompassing the objects in high relative motion.
You presented another thought-experiment regarding alpha centauri
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I will give an illustration. The Alpha Centauri complex (AC) is 4.37 light years away from Earth. It takes light from AC 4.37 (edit) years to reach Earth, and no “thing” with mass can travel that fast.
A ship traveling at near ‘c’ velocity from here to there must, therefore take longer than 4.37 years to get there, even though the onboard clock will have slowed down and recorded much less than 4 years passing. Yet Earth will have orbited the Sun (the "year" standard) much more than 4 times during the ship’s journey to AC. So, even though “for the ship” much less than 4 years will have passed, the distance between Earth and AC will not have contracted to way less than 4 light years. The ship’s journey obviously will not make Earth and AC move closer together.
I posted a link and quotes to a very interesting blog which I believe correctly showed the principles and unsettling consequences of Special relativity. Skulls in the Stars (http://skullsinthestars.com/2012/09/10/relativity-ten-minutes-to-alpha-centauri/#more-6685)
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...For a spacecraft traveling at 90% of the speed of light, the distance will only be 1.90 light-years, less than half the distance that an Earth-bound observer would measure! ...
I am completely confused as to what you want from us. If you want an admission that length contraction is illusory and in some sense not "real" - then you just won't get it (from me at least); mainly because SR deals in maths and not semantics, and secondly because I can fit the probe (very briefly) entirely within the shuttle's cargo bay.
Post by: lightarrow on 14/09/2012 13:31:56
No, the ship will be hit by gamma rays and it will become radiactive and, furthermore, the intensity of the gamma rays will be much greater than the intensity of the visible light hitting the Earth. Apart from interstellar powder, the mere presence of the CMBR (cosmic background microwave radiation) puts a serious limit to relativistic travels for this reason.Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be non identifiable.
Interesting point, but I have a quick question.
Let's assume there is a distant source (like our Sun) that emits harmless visible light for an Earth observer.
The observer take a relativistic ship (0.9999c) and travel toward the source. His ship screen out all radiation except those wavelengths that for the Earth frame were harmless visible light. Due to Doppler Effect the light that penetrates the ship will be now gamma-ray.
My question is: Will the observer on ship get hurt by gamma rays? Or in his ship those penetrating gamma rays (that on Earth were visible light) have the same impact as the visible light on Earth frame, i.e. they will be harmless?
Post by: JP on 14/09/2012 14:37:17
http://en.wikipedia.org/wiki/Length_contraction#Reality_of_Lorentz_contraction
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The question as to whether the Lorentz contraction really exists or not is misleading. It doesn't "really" exist, in so far as it doesn't exist for a comoving observer; though it "really" exists, i.e. in such a way that it could be demonstrated in principle by physical means by a non-comoving observer.
—Albert Einstein, 1911
It also goes on to point out what most of us have been stating, that argument over what is "real" only depends on terminology. If you define "real" to mean "in the rest frame" then your argument is right. If you define "real" to mean "what is measured" then your argument is wrong. In actual science, we don't use muddled terms like "real," and constrain ourselves to describing the predicted measurements, for which there is no ambiguity.
In essence, "real" matches your definition of "real" because you defined it to do so from the start.
Post by: lean bean on 14/09/2012 16:20:25
For those of you who don't mind adapting a thought-experiment... relativity is of course reciprocal; just as we can define the rest frame as the frame in which the shuttle has zero momentum, we can also define the rest frame as the frame in which the probe has zero momentum and the shuttle is approaching it at high velocity (in the opposite direction). From the rest frame of the probe we now see the shuttles cargo bay as length contracted, and the probe is no longer contracted ...and the probe would still all fit in just before destroying itself and the shuttle! The timings are very tough to reconcile, events seem to be switched, and with relativistic speeds you cannot be sure of any simultaneities without the maths; but in the end the same set of events happens - it must be the case because it is the exact same scenario.
made me think of the old pole and barn
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/polebarn.html (http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/polebarn.html)
Post by: old guy on 14/09/2012 17:57:34
There's a nice quote from Einstein on the wiki about "real" and length contraction:Good link and very relevant Einstein quote. It confirms my previous quote of him (here or in my other thread) saying that the word "real" is "meaningless" because reality depends on what science chooses to observe. (Never mind that the universe is much larger than we can observe, but remains "real" even beyond our capability for observation, as new discoveries constantly inform us.)
http://en.wikipedia.org/wiki/Length_contraction#Reality_of_Lorentz_contractionQuoteThe question as to whether the Lorentz contraction really exists or not is misleading. It doesn't "really" exist, in so far as it doesn't exist for a comoving observer; though it "really" exists, i.e. in such a way that it could be demonstrated in principle by physical means by a non-comoving observer.
—Albert Einstein, 1911
It also goes on to point out what most of us have been stating, that argument over what is "real" only depends on terminology. If you define "real" to mean "in the rest frame" then your argument is right. If you define "real" to mean "what is measured" then your argument is wrong. In actual science, we don't use muddled terms like "real," and constrain ourselves to describing the predicted measurements, for which there is no ambiguity.
In essence, "real" matches your definition of "real" because you defined it to do so from the start.
My probe example intended to put some meat on the bones of the question, "What is real?" as a practical application, once we achieve relativistic speeds in space travel, of course. (See quote below.)
The retrieval team must know the "real length" of the probe in order to send out a shuttle with a large enough cargo bay. Obviously the shuttle must "come alongside" the probe, matching velocities, at rest with the probe to capture it. (The conjectures about colliding with the probe would be the result of a very poorly planned mission!)
Our cargo bay, as stated, is 10 meters. The "contracted length" of the probe, as seen from Earth's frame appears to be 10 meters. The point of the whole exercise was that 10 meters is not the probes *real length*, so sending out the above shuttle would be very stupid, because the probe is *really* longer than 10 meters. So there is your functional definition of "What is real?"
Your link, above the Einstein quote, directly addresses the topic of this thread:
Wiki:
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In addition, even in a non-co-moving frame, direct experimental confirmations of Lorentz contraction are hard to achieve, because at the current state of technology, objects of considerable extension cannot be accelerated to relativistic speeds. And the only objects traveling with the speed required are atomic particles, yet whose spatial extensions are too small to allow a direct measurement of contraction.
The next section, however cites several “indirect confirmations.” I’ll quote the most famous/popular one and comment:
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Another example is the observed lifetime of muons in motion and thus their range of action, which is much higher than that of muons at low velocities. In the proper frame of the atmosphere, this is explained by the time dilation of the moving muons. However, in the proper frame of the muons their lifetime is unchanged, but the atmosphere is contracted so that even their small range is sufficient to reach the surface of earth.
Essentially this argues that, because of “time dilation” (their rate of decay slows down at higher velocity), these mouns “live longer” than expected of lower velocity muons, and since length contraction is the math reciprocal of time dilation, for those muons “the atmosphere is contracted."
From “the frame” of the whole picture however (earth and incoming muons) , there is no contracting of the atmosphere around each muon. “For a muon” does not change the atmospheric science of its thickness/depth.
(More later in reply to other posts as time permits, if I am so allowed.)
Post by: old guy on 14/09/2012 18:30:43
Imatfaal:
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I posted a link and quotes to a very interesting blog which I believe correctly showed the principles and unsettling consequences of Special relativity. Skulls in the Stars
I read the link and commented (post #7) in the New Theories version of this topic where I was told to go with my argument.
Post by: David Cooper on 14/09/2012 19:02:41
From the rest frame of the probe we now see the shuttles cargo bay as length contracted, and the probe is no longer contracted ...and the probe would still all fit in just before destroying itself and the shuttle! The timings are very tough to reconcile, events seem to be switched, and with relativistic speeds you cannot be sure of any simultaneities without the maths; but in the end the same set of events happens - it must be the case because it is the exact same scenario.
That's a really good point, Imatfaal, so it's worth going through carefully how it's still works out that way. The force being applied inside the shuttle to accelerate the alien ship to the same speed as the shuttle is now going to be applied unevenly from one end to the other instead of to the whole ship at once, so that means it will start by compressing the front end of the ship just before it reaches the end wall of the cargo bay, and will continue to compress the rest in the same manner, compressing the tail end just after the tail has entered the cargo bay, at which point the door is closed on a compressed ship (although most of it is already expanding again). As the atoms push out and buckle the ship (or burst it through the ends of the cargo bay), the front end of the ship will have been expanding while the tail end was still being compressed behind it, but there's no difference to the end result of the buckling or bursting even if it's sequential along the length of the ship rather than simultaneous.
-------------------------------------------------------------------
What I've also argued against is the introduction of extra complexity to special relativity in order to preserve some preconception about the universe. Science doesn't work that way. We can always hold an infinite number of preconceptions about the universe and introduce extra hidden variables into a model to preserve them. Obviously no one's arguing something this far out, but if I were more comfortable with unicorns causing length contraction, I could always introduce unicorns who zip about the universe shrinking our rulers with magical pony power. As long as the unicorns are undetectable by measurement, and their pony power works identically to Lorentz contraction, I can claim that my results are completely in line with observations. That doesn't this viewpoint valid science, nor does it make other viewpoints with far less absurd preconceptions valid science. Science is generally about using the simplest possible model to describe some phenomenon, not choosing the more complex model because it fits your preconceptions.
That is completely right - no one wants unicorns, or anything else that adds completely unnecessary components to a theory.
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Einstein's special relativity is the mainstream scientific explanation because it is the simplest model which introduces the fewest extraneous variables and preconceptions and explains observations.
I cannot see how that is the case. Einstein has a fabric of space called spacetime (which can be curved to cause gravity, but we don't even need to go there for evidence). Einstein himself spoke of the necessary role of an aether of some kind to enforce the separation between things in the universe (in terms of distance and geometry), which is something his fabric of space called spacetime does. Lorentz's theory also has a fabric of space which enforces distances and geometry, but it is three dimensional instead of four and has a Newtonian time instead of making time a special kind of space dimension. Both theories have the speed of light restricted to c through their fabric of space. Lorentz doesn't need to add anything else at all for his theory to fit the facts. Einstein doesn't either if he's only interested in the maths of measuring and predicting things. There is something extra required for Einstein's theory though, as he still has to explain the apparent pattern of cause-and-effect written throughout the universe - because he has no Newtonian time in his model, he is not able to generate effects from their apparent causes. There are long, complex chains of causation written through everything that's happened in the universe across billions of years of time, and for them to exist in that form without actually being generated in cause-and-effect order would be more than a little surprising. If you threw a sackful of grain out of a high window and the grain ended up on the ground with a complex pattern to it (perhaps forming a series of images telling a story with apparent cause-and-effect events unfolding from one picture to the next), you would be astonished [I suspect]. But that is exactly what Einstein's theory requires of the real universe, only the grain is never thrown from a window - the pattern is simply eternal and was not constructed in cause-and-effect order.
How can you be comfortable with that?
Post by: old guy on 14/09/2012 19:16:11
Quote
I am completely confused as to what you want from us. If you want an admission that length contraction is illusory and in some sense not "real" - then you just won't get it (from me at least); mainly because SR deals in maths and not semantics, and secondly because I can fit the probe (very briefly) entirely within the shuttle's cargo bay.
My argument here simply questions how "real" length contraction is. Does a fast moving ship make stars move closer together? No, but its clock will "tick" more slowly the faster it flies, and its occupants will probably age more slowly.
Do objects have shapes and lengths independent of how they are measured? Yes, there is a "real cosmos with real objects" in it, but they may well appear contracted from very fast fly-by frames.
Can you really " fit the probe (very briefly) entirely within the shuttle's cargo bay?"
No.
Let's make the velocity of the probe relative to earth specific at 86.6 % of 'c.' If the "contracted length" as measured from earth is 10 meters, as established, it will then be 20 meters in its own frame and as measured from the shuttle once it enters that frame, at rest with the probe. A 20 meter probe will not fit into a 10 meter cargo bay, period, no matter how "briefly." Sorry.
Post by: JP on 14/09/2012 21:00:52
Lorentz doesn't need to add anything else at all for his theory to fit the facts.Lorentz's theory postulates an unmeasurable reference frame, the aether. The Lorentzian theory is essentially a historic holdover from the days when scientists thought matter of some form was required to support light wave propagation. As more and more observations added up, it was found that this aether would have to be invisible and undetectable. Say what you will about anything else, but Lorentz's theory has an extra, unobservable feature, while special relativity doesn't. This is why it's been superceded by special relativity among scientists.
Quote
There is something extra required for Einstein's theory though, as he still has to explain the apparent pattern of cause-and-effect written throughout the universe - because he has no Newtonian time in his model, he is not able to generate effects from their apparent causes.I'm not sure what you mean. Can you give an example? Special relativity does respect causality--that's one of it's important features.
Post by: JP on 14/09/2012 21:23:12
Imatfaal:QuoteI am completely confused as to what you want from us. If you want an admission that length contraction is illusory and in some sense not "real" - then you just won't get it (from me at least); mainly because SR deals in maths and not semantics, and secondly because I can fit the probe (very briefly) entirely within the shuttle's cargo bay.
My argument here simply questions how "real" length contraction is. Does a fast moving ship make stars move closer together? No, but its clock will "tick" more slowly the faster it flies, and its occupants will probably age more slowly.
Do objects have shapes and lengths independent of how they are measured? Yes, there is a "real cosmos with real objects" in it, but they may well appear contracted from very fast fly-by frames.
Can you really " fit the probe (very briefly) entirely within the shuttle's cargo bay?"
No.
Let's make the velocity of the probe relative to earth specific at 86.6 % of 'c.' If the "contracted length" as measured from earth is 10 meters, as established, it will then be 20 meters in its own frame and as measured from the shuttle once it enters that frame, at rest with the probe. A 20 meter probe will not fit into a 10 meter cargo bay, period, no matter how "briefly." Sorry.
Do you really not see that your entire argument hinges on making "real" fit your definition of, and then telling us that's proof that you're right? Of course "real" matches your definition if you tell us that you're redefining it to do so!
Post by: old guy on 14/09/2012 22:07:34
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Do you really not see that your entire argument hinges on making "real" fit your definition of, and then telling us that's proof that you're right? Of course "real" matches your definition if you tell us that you're redefining it to do so!
You misunderstand me. It is not about my personal definition of "real." I speak as a "realist," not some crank trying to debunk all of SR. That is why I used the example to demonstrate a "real world application" of length contraction as a sub-theory of SR... in a future world, of course, with near 'c' space travel.
If you were on the retrieval team, you would know that the observed length of 10 meters, from earth's frame, was not its true length, in its own frame. You would not send out a shuttle with a 10 meter bay to retrieve it.
Please do not make this personal, as if I invented realism. Einstein endorsed a form of idealism when he said that there is no reality independent of observation/measurement.
If one is not allowed to disagree with that, then SR has become a realism- intolerant dogma in favor of SR's version of classical idealism.
How about you? Are you an idealist or a realist. (Rhetorical question.) Does the falling tree make a sound without an observer to hear it?
Does Earth change shapes with every possible different perspective viewing it. I can't believe that you believe that!
Post by: JP on 14/09/2012 22:12:23
We had some interesting discussions here, but unless you'd like to discuss science, I'll have to ask you again to keep it to "new theories."
Thanks!
Post by: David Cooper on 14/09/2012 23:02:45
Lorentz doesn't need to add anything else at all for his theory to fit the facts.Lorentz's theory postulates an unmeasurable reference frame, the aether. The Lorentzian theory is essentially a historic holdover from the days when scientists thought matter of some form was required to support light wave propagation. As more and more observations added up, it was found that this aether would have to be invisible and undetectable. Say what you will about anything else, but Lorentz's theory has an extra, unobservable feature, while special relativity doesn't. This is why it's been superceded by special relativity among scientists.
The unmeasurable reference frame is simply the fabric of space which restricts the speed of light within itself to c. The fact that the aether was originally regarded as something more like matter when these theories were originally being worked out does not disqualify the final form in which the fabric of space does the entire job, and having that fabric of space is not anything extra over having a fabric of space called spacetime. The difference between the two theories is really limited to the nature of time - one has Newtonian time while the other attempts to get rid of that entirely and to replace it with something which is almost identical to a space dimension.
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QuoteThere is something extra required for Einstein's theory though, as he still has to explain the apparent pattern of cause-and-effect written throughout the universe - because he has no Newtonian time in his model, he is not able to generate effects from their apparent causes.I'm not sure what you mean. Can you give an example? Special relativity does respect causality--that's one of it's important features.
Special relativity respects it in the sense that the patterns of causality are there and appear to "work", but without Newtonian time it appears to be impossible to have the causes happen before their effects, which is something they would have to do in order to cause their effects. Perhaps you can point me to a way round that.
Let me illustrate the issue clearly by taking a version of a thought experiment with a lot in common with the (incorrectly named) twins paradox. This pushes relativity to the extreme to show up the difficulty, but I'll ramp it up in stages. Let's begin with the idea of a rocket leaving a planet, reaching a high speed, then stopping after a while, turning round, returning home at a high speed and eventually arriving back at the planet. If the rocket was to travel at 0.866c both on the way out and the way back, and with a rapid turn-around which can be taken as being close enough to instantaneous that we can ignore it, a year may have ticked by for the rocket during its trip while two years have ticked by on the planet.
Now, a lot of confusion comes into things if you try to explain things in terms of clocks ticking at different rates on the planet and in the rocket, because if all frames are genuinely equal there can be no difference between the fundamental rates at which clocks tick and you can't have some ticking faster than others. This can be got round by allowing the rocket to take a shortcut into the future by travelling at a high speed and thereby at a different angle through time, so while its clock is ticking at the same rate, it's also on a different course through spacetime which allows it to get back to the planet far in the future while the planet is still only half way there - the two can still meet up because the future of the planet is already there for the rocket to interact with. The whole business of clocks ticking is actually Newtonian time, so you must actually get rid of it altogether and just have an eternal block universe where the future is linked to the past by many pathways of different time-dimension lengths. We can still imagine time ticking at constant rates along each time-dimension paths if we like and picture things taking shortcuts into a ready-built future, but you always have to be aware that in doing so you would be adding a Newtonian time to the model, and that is not part of SR.
Now let's ramp it up. Let's make the rocket faster such that it records only one second by its clock (not practically possible, but this is a thought experiment in which the details of the effects on time, distance, etc. are correct). We can now put in place a series of complex events on the planet which all feed into the next so that there's a chain of causation which couldn't be predicted in any less time, and this might involve running a computer program which could end up producing any one of billions of different results. When the rocket returns a year later it is immediately able to access the answer of the computation, even though it only took one second to get there according to its clock. Thirty million seconds' worth of processing have taken place, but from the rocket's point of view this has all happened in one second.
Ramp it up again and you could have the rocket trip timed within the rocket as a billionth of a second while a billion years have gone by on the planet. There is a ratio of events here of thirty thousand quintillion to one. It appears that you have time running thirty thousand quintillion times faster on some pathways than others, but the block universe model has a billion year's worth of future (and more) ready-built and waiting for things like the rocket to take shortcuts into. By eliminating Newtonian time altogether, the rocket doesn't actually move though - it simply is, and all of its atoms are stretched through the model like spaghetti such that they exist in all times. This is what SR does to the nature of the universe.
There is nothing in SR to account for how such a universe can be generated, so it just exists eternally without the future ever having been generated from the past and without causes having any opportunity to generate effects. As soon as you attempt to have a cause generate an effect you introduce a Newtonian kind of time back into it to provide a before and after, and then you suddenly have ratios of events like thirty thousand quintillion to one coming into play for different paths in the construction - a single clock cycle occurs in the computer on the rocket during its trip while a computer on the earth has thirty thousand quintillion of them, and because we're now trying to construct a block universe, we're necessarily working with one which doesn't have a ready-built future to allow shortcuts - the rocket has to wait for the thirty thousand quintillion sequential events on the planet to run through before its computer (the rocket's) can have its second tick.
This is where SR hits its major snag - it appears to be impossible to generate a universe without introducing a Newtonian time back into things, so what you appear to be forced to do instead is just accept that it can't be generated while at the same time accepting that the patterns of cause and effect which are written through it are just an extraordinary coincidence. Now, I'm not asking anyone to reject SR on that basis, but I do think it's absolutely fair for me to insist that people accept that SR is in no way superior to Lorentz's theory to the point that the latter can be rejected and the former treated as if it is as good as a fact. It looks to me as if Lorentz's theory is more likely to be correct than Einstein's, but I don't need to go anywhere near that far in making the point that things are in no way clear cut in favour of Einstein's SR.
If any of the above needs clarification or further explanation, please ask and I'll provide it. What I'm hoping is that someone can see some way to overturn what I've said and reveal to me that SR can eliminate this difficulty, because if mainstream science is actually right, I want to be part of it.
Post by: JP on 14/09/2012 23:21:47
Well, the history and everything else doesn't matter (I provided it because it's interesting to know where the Lorentzian model came from, IMO). What matters to scientists is which one has an extra undetectable feature and which one doesn't. At least on the count of an undetectable reference frame, the Lorentzian model has it, while special relativity doesn't. :)Lorentz doesn't need to add anything else at all for his theory to fit the facts.Lorentz's theory postulates an unmeasurable reference frame, the aether. The Lorentzian theory is essentially a historic holdover from the days when scientists thought matter of some form was required to support light wave propagation. As more and more observations added up, it was found that this aether would have to be invisible and undetectable. Say what you will about anything else, but Lorentz's theory has an extra, unobservable feature, while special relativity doesn't. This is why it's been superceded by special relativity among scientists.
The unmeasurable reference frame is simply the fabric of space which restricts the speed of light within itself to c. The fact that the aether was originally regarded as something more like matter when these theories were originally being worked out does not disqualify the final form in which the fabric of space does the entire job, and having that fabric of space is not anything extra over having a fabric of space called spacetime. The difference between the two theories is really limited to the nature of time - one has Newtonian time while the other attempts to get rid of that entirely and to replace it with something which is almost identical to a space dimension.
The rest of your post is quite long, so I'll get to that separately...
Post by: David Cooper on 14/09/2012 23:44:07
What matters to scientists is which one has an extra undetectable feature and which one doesn't. At least on the count of an undetectable reference frame, the Lorentzian model has it, while special relativity doesn't. :)
The Lorentzian model has a fabric of space which can't be detected, and Einstein's model has a fabric of space called spacetime which can't be detected either. The fabric of space in the Lorentzian model is automatically the preffered frame, so there's no extra undetectable thing tied up in it.
Post by: yor_on on 14/09/2012 23:49:58
Here is The Einstein Theory of Relativity, by H.A. Lorentz. (http://www.gutenberg.org/files/11335/11335-h/11335-h.htm) as well as 'mathpages' comments on the same. Who invented relativity? (http://mathpages.com/rr/s8-08/8-08.htm)
Post by: JP on 14/09/2012 23:52:47
What matters to scientists is which one has an extra undetectable feature and which one doesn't. At least on the count of an undetectable reference frame, the Lorentzian model has it, while special relativity doesn't. :)
The Lorentzian model has a fabric of space which can't be detected, and Einstein's model has a fabric of space called spacetime which can't be detected either. The fabric of space in the Lorentzian model is automatically the preffered frame, so there's no extra undetectable thing tied up in it.
Except that the preferred frame is undetectable...
Post by: yor_on on 15/09/2012 00:17:13
Post by: JP on 15/09/2012 00:20:50
Now, a lot of confusion comes into things if you try to explain things in terms of clocks ticking at different rates on the planet and in the rocket, because if all frames are genuinely equal there can be no difference between the fundamental rates at which clocks tick and you can't have some ticking faster than others.Clocks don't tick at the same rate for all observers. That's time dilation.
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This can be got round by allowing the rocket to take a shortcut into the future by travelling at a high speed and thereby at a different angle through time, so while its clock is ticking at the same rate, it's also on a different course through spacetime which allows it to get back to the planet far in the future while the planet is still only half way there - the two can still meet up because the future of the planet is already there for the rocket to interact with.You can chart the path through space-time of the planet vs. the rocket and show that the rocket's proper time (time measured by the clock on the rocket in the rocket's frame) is less than the earth's proper time. If that's what you're saying, I agree. Talking about "the future of the planet is already there" is somewhat confusing, but I think we agree on what the clocks see.
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The whole business of clocks ticking is actually Newtonian time, so you must actually get rid of it altogether and just have an eternal block universe where the future is linked to the past by many pathways of different time-dimension lengths.Actually, I am partial to the block universe (and the even more bizarre many-worlds interpretation of QM), but this is introducing philosophy into the mix... I certainly wouldn't go telling people that the many-worlds interpretation has to be true just because I philosophically prefer it!
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By eliminating Newtonian time altogether, the rocket doesn't actually move though - it simply is, and all of its atoms are stretched through the model like spaghetti such that they exist in all times. This is what SR does to the nature of the universe.OK. Each object can have a world line through space-time of all the points in space and time it has occupied. I guess a line is like spaghetti. So what?
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There is nothing in SR to account for how such a universe can be generated, so it just exists eternally without the future ever having been generated from the past and without causes having any opportunity to generate effects.We discussed this in your other thread and you insisted you weren't talking about generating a universe. Now you are again. Talking about generating a universe.
As I told you there, arguing that "there is nothing in SR to account for how such a universe can be generated" is pointless unless you're arguing against a theory that deals with the generation of the universe. Special relativity doesn't. It works within the universe to make predictions. All you've offered is a theory with an additional, undetectable element that does the same job and tries to explain how the universe is generated. But then again, so does believing exactly in special relativity and then adding "God made the universe." That's simply not a scientific way of doing things.
Your point about causes being unable to generate effects is completely wrong as well. Causes obviously generate effects in SR. If you can connect a cause to an effect by a valid world line, it can generate that effect.
Post by: old guy on 15/09/2012 18:32:49
Now we're at the heart of the matter. You're discussing metaphysics behind special relativity. That's a perfectly valid and interesting area, but it's not a matter for this science forum. If we were a philosophy forum, I'd say go at it!It is difficult to see how a thought experimental practical test of the physics of length contraction is metaphysical, not "science." Granted, Einstein's version of idealism (only observations are "real") in contrast with realism (things exist and have properties independent of observation) is a philosophical issue... but one I am sure is of central relevance to this topic. Denying that objects have intrinsic properties is not an argument against realism.
We had some interesting discussions here, but unless you'd like to discuss science, I'll have to ask you again to keep it to "new theories."
Thanks!
Anyway, I have complied with your demand that I move it to my length contraction thread in New Theories.
Please reply to my last post there.
Also, since imatfaal will not be allowed to reply to my last challenge to him in this thread, I have moved that exchange as well and hope that he will reply there.
See you there, I hope.
Edit, Ps: It is weird that David Cooper is allowed to continue to hijack this thread with his pet theory/opinions about different versions of SR, but I am once again gagged here.
Post by: David Cooper on 15/09/2012 21:53:52
The thought experiment provided by Damocles may eliminate this problem...? If the star and telescope are moving instead of the disc, then they will be flattened a little in their direction of travel and the disc will then be larger than the telescope aperture. The flattening of the star doesn't matter as it's acting as a point source effectively at infinite distance, but how can it be that light will enter the telescope throughout? The light that appears to be coming from the star is actually coming from where the star was earlier, so the light reaching the telescope (just before and after the disc gets in the way) is passing the disc at an angle and making it act as if it's narrower than it is... except that the disc could be replaced with a ball, so that isn't going to help. I'll have to think about this for a bit longer, but I'm stuck for now.
Edit: we do know though that the disc/ball will still appear as if it is contracted even if it's stationary and the telescope and star are moving instead. It must be something to do with the different length of time it takes for the light to reach opposite sides of the telescope and to work their way through to the focal plane - I'm beginning to visualise it. Yes: the light from the trailing edge of the telescope aperture takes a lot longer to reach the focal plane, so it's still travelling through the telescope while the eclipse of the disc/ball has begun, whereas the light which gets into the opposite side of the telescope when the eclipse ends has a shorter trip to make to get to the focal plane and will arrive there before the last of the light from the trailing edge gets there.
Post by: David Cooper on 15/09/2012 23:09:07
Now, a lot of confusion comes into things if you try to explain things in terms of clocks ticking at different rates on the planet and in the rocket, because if all frames are genuinely equal there can be no difference between the fundamental rates at which clocks tick and you can't have some ticking faster than others.Clocks don't tick at the same rate for all observers. That's time dilation.
In the thought experiment, it can be observed that the rocket's clock has recorded less time than the planet during the trip, so you might claim that the rocket's clock has been ticking slower than the planet's clock throughout the trip, but if all frames are equally valid it cannot be the case that any frame can make its clock run slow as compared to another frame unless there is a preferred frame being used as a standard to control their relative rates. Without a preferred frame, the rocket cannot know whether to slow down or speed up its clock when it leaves the planet and sets off on its rapid journey, so it cannot be doing either. If the planet is stationary, the rocket would slow its clock when it moves away from it, whereas if the planet is moving fast, the rocket may be slowing down by leaving the planet in which case its clock would have to speed up. These things would work exactly like that in a Lorentzian universe, but cannot do so in SR unless they are to tick both more slowly and more quickly at the same time.
In SR, if a rocket makes a trip timed at a billionth of a second for its clock, you are not allowed to say that its journey actually took a billion years and that its clock was running slow. The rocket really did make its trip in a billionth of a second, and it did so by taking a shortcut into the future. The planet took a billion years to complete its journey from the same starting point in spacetime to the same end point, but the rocket didn't have to wait for a billion years of time to run through before it could land again.
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QuoteBy eliminating Newtonian time altogether, the rocket doesn't actually move though - it simply is, and all of its atoms are stretched through the model like spaghetti such that they exist in all times. This is what SR does to the nature of the universe.OK. Each object can have a world line through space-time of all the points in space and time it has occupied. I guess a line is like spaghetti. So what?
The point is that if you have no Newtonian time in the model you can have things which you call past and future, but you have lost any real kind of before and after - the future is already in place for you to take shortcuts into without having to run slow so that paths which need to pack a lot more action into them can keep pace.
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QuoteThere is nothing in SR to account for how such a universe can be generated, so it just exists eternally without the future ever having been generated from the past and without causes having any opportunity to generate effects.We discussed this in your other thread and you insisted you weren't talking about generating a universe. Now you are again.
You're misremembering - the issue was always about how in SR you can generate the future out of the past without Newtonian time.
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As I told you there, arguing that "there is nothing in SR to account for how such a universe can be generated" is pointless unless you're arguing against a theory that deals with the generation of the universe. Special relativity doesn't. It works within the universe to make predictions.
If you did say that there (I've just read the thread again and still didn't notice), then I appologise for not picking up on that. Thank you for stating it clearly here. I take it from this then that it is a matter of philosophy to think about how an eternal block universe can be generated without adding Newtonian time to it and therefore it doesn't matter whether a block universe can't be generated or not as it is not important to the laws of physics in terms of making predictions.
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All you've offered is a theory with an additional, undetectable element that does the same job and tries to explain how the universe is generated. But then again, so does believing exactly in special relativity and then adding "God made the universe." That's simply not a scientific way of doing things.
I'm simply looking at two theories and trying to see why one of them is "wrong" and the other "right" when the one that's "wrong" has as its fault that its preferred frame (which is its fabric of space) can't be detected while the one that is "right" has a fabric of spacetime that can't be detected either and when only one of the two theories is able to allow a universe to be generated (meaning that the future is generated out of the past through cause and effect). Now it is clear that this is unimportant to physics as it is mere philosophy, and physics doesn't do philosophy. That's fine then, so long as you aren't putting things across as facts when they are philosophically unsound - to do so on the basis of simplicity is actually bringing bad philosophy into play (inadvertently).
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Your point about causes being unable to generate effects is completely wrong as well. Causes obviously generate effects in SR. If you can connect a cause to an effect by a valid world line, it can generate that effect.
Without a Newtonian time being introduced, that is simply wrong. Effects are clearly not being generated by their apparent causes in SR because it is possible to take shortcuts into the future to access the effects at the end of long chains of causation without waiting for those chains to run through - the result of a calculation taking a billion years can be accessed in a billionth of a second by taking a shortcut into the future, but that's only possible with a block universe where the future is ready-built. If you attempt to repeat the thought experiment in a block universe in which the future is not ready-built such that causes actually generate their effects, you have then changed the situation into a construction phase running under a Newtonian time in which the rocket's clock must run in slow motion for a billion years to allow the result of the billion-year-long chain of causation to generate a result which the rocket is to interact with on its arrival home, and that would be running under the rules of a Lorentzian universe.
For SR to be correct, you would need to demonstrate that a block universe can be generated in some way without going through a Lorentzian phase first. Can you do that? You don't have to, I suppose - you can always just write the problem off as philosophy and pretend it doesn't matter.
Post by: JP on 16/09/2012 05:29:50
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I take it from this then that it is a matter of philosophy to think about how an eternal block universe can be generated without adding Newtonian time to it and therefore it doesn't matter whether a block universe can't be generated or not as it is not important to the laws of physics in terms of making predictions.Yes. That is exactly correct.
Everything you're arguing hinges on you assuming that "the eternal block universe" exists, and the block universe is a philosophical interpretation of the model.
I think there are only two scientific points left to discuss that could possibly justify the Lorentzian model as scientifically preferable (in terms of being the simplest predictor and explanation of observations):
1) Does the Lorentzian model offer any predictions of measurements that differ from SR?
2) We already know that the Lorentzian model assumes the existance of the Lorentzian aether (an undetectable, preferred reference frame), while SR doesn't. So that's one complicating factor for the Lorentzian model. While only using the measurable predictions of both theories, does SR have an additional, unmeasurable feature that the Lorentzian model lacks?
Of course, it may be philosophically preferable. But that's not a matter for discussion here, so let's take that to New Theories. :)
Post by: David Cooper on 16/09/2012 21:31:32
1) Does the Lorentzian model offer any predictions of measurements that differ from SR?
No, so that just leaves (2).
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2) We already know that the Lorentzian model assumes the existance of the Lorentzian aether (an undetectable, preferred reference frame), while SR doesn't. So that's one complicating factor for the Lorentzian model. While only using the measurable predictions of both theories, does SR have an additional, unmeasurable feature that the Lorentzian model lacks?
The Lorentzian model assumes the existence of an undetectable three-dimensional fabric of space plus Newtonian time while Einstein assumes the existence of an undetectable four-dimensional fabric of space in which time turns into a special space dimension. Neither brings anything else in, so they are equally simple in terms of their requirements. To say that Lorentz then needs to bring in an undetectable preferred frame is not correct - it automatically comes along with having a three-dimensional fabric of space with Newtonian time and is not an addition because the fabric of space is the preferred frame. It would be equally incorrect for me to claim that SR has to bring extra things in when they automatically come along with having a four-dimensional fabric of space in which the time dimension behaves oddly. Neither theory can claim with any justification to be simpler than the other - the differences between them are down to a single thing, and that is the nature of time chosen for each model.
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Of course, it may be philosophically preferable. But that's not a matter for discussion here, so let's take that to New Theories. :)
That would be fair, provided that everyone is careful not to make statements here about one theory being right and another wrong when such claims cannot be justified on logical grounds. It appears that in physics there is a much lower standard of logic being applied in determining which theories are accepted and which are rejected than there would need to be to justify more global assertions about their validity, but science fails to make that clear on the tin - people tend to look up to it as an authority and to take a considerable amount on trust. In this case we have a theory which is treated as correct in science but which can be shown to have serious problems logically, but logic is being branded as philosophy and ignored on that basis. At the same time, we have a rival theory which is being rejected through incorrect reasoning relating to claims that the other theory is simpler.
Anyway, thanks for taking on the discussion so far as you have - it has been very helpful in clarifying to me why SR holds sway at the moment. Everything is falling neatly into place.
Post by: old guy on 23/09/2012 19:54:44
Post by: David Cooper on 23/09/2012 21:07:09
Post by: wolfekeeper on 24/09/2012 16:43:51
Post by: old guy on 24/09/2012 19:29:43
We all agree that the speed of light does not change with the speed of its source or the speed of observers relative to the source. Nor can light can be "pushed" faster like a bullet from a speeding gun. Also there is no "aether" from which to figure an absolute velocity, so velocity is always a matter of "relative to what?" in all cases. So far so good.
Now, by what force are physical objects and distances contracted, as objects in-and-of themselves, independent of how they may be observed differently from different frames?
If Earth is said to have various diameters when variously observed, what force makes the real physical Earth change shape? Ducking the question does not answer it.
wolfekeeper,
The apparent movement of the stars has nothing at all to do with the claims of length contraction. Read some basic astronomy.
Post by: yor_on on 24/09/2012 20:43:32
And this site is also a pleasure to read, shows that relativity is explainable if you try, not just reserved for those whose brains have outgrown their skulls..
Why does relativistic length contraction (Lorentz contraction) happen? (http://www.askamathematician.com/2011/01/q-why-does-relativistic-length-contraction-lorentz-contraction-happen/)
Why does Lorentz contraction only act in the direction of motion? (http://www.askamathematician.com/2011/01/q-why-does-lorentz-contraction-only-act-in-the-direction-of-motion/)
Post by: David Cooper on 24/09/2012 21:05:16
Now, by what force are physical objects and distances contracted, as objects in-and-of themselves, independent of how they may be observed differently from different frames?
In SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds. Stating things in any more absolute terms than that seems to lead into disagreements. In a Lorentzian universe the shortening is absolutely real, but again no force is applied to bring it about - it would actually require you to apply a stretching force to maintain the original length as you accelerate things because the atoms will naturally sit closer together in the direction of travel as things move faster.
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If Earth is said to have various diameters when variously observed, what force makes the real physical Earth change shape? Ducking the question does not answer it.
The question has never been ducked - the answer has always been that no theory requires any force to be applied to cause the contraction.
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The apparent movement of the stars has nothing at all to do with the claims of length contraction. Read some basic astronomy.
Unless you can pin down a preferred frame (and you can't), then you simply don't know which the real distances are. All you're doing is picking a frame that fits in with your expectations of a preferred frame and asserting that it is the preferred frame so that you can call the distances measured in it absolute. [You may not be directly calling it the preferred frame, but as soon as you assert that the distances measured in some frame are absolute, the preferred frame automatically gets tied to that frame in which you declare your measurements to be absolute.] The distances almost certainly aren't absolute because the preferred frame (if there is one) has not been identified - the one you're treating as a preferred frame may actually be moving at close to the speed of light because all the stars you're using as evidence to pin down the preferred frame may also be moving at close to the speed of light, all in the same direction. It is of course more likely that the frame you've chosen is close to the preferred frame (if there is one), so your error may be fairly small, but there is still a real chance that your error is huge - you're basing everything on an assumption which may be very wrong.
Post by: wolfekeeper on 24/09/2012 21:06:20
Now, by what force are physical objects and distances contracted, as objects in-and-of themselves, independent of how they may be observed differently from different frames?The earth is held together by electromagnetic forces (in conjunction with QM); specifically the electrons are held in the electric potential well of the protons.
If Earth is said to have various diameters when variously observed, what force makes the real physical Earth change shape? Ducking the question does not answer it.
If you solve Maxwell's equations for the moving protons, when the earth is moving, that potential well changes shape; it flattens in the direction of motion and this causes the Lorentz contraction.
Post by: old guy on 24/09/2012 21:25:27
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In SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds.
Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?
How about one question and one answer at a time for a 'change' for the sake of clarity?
Post by: David Cooper on 24/09/2012 21:31:00
David, your examples of light contraction are 'on the spot' as far as I'm concerned. If I remember right Lorentz 'invented' length contraction just to explain the MM experiment. And when it comes to light clocks I have a very sweet link doing the math in a understandable way, using geometry. All Moving Clocks Are Slowed by Motion (http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_basics/index.html#Moving1)
And this site is also a pleasure to read, shows that relativity is explainable if you try, not just reserved for those whose brains have outgrown their skulls.
Sadly the animations don't all appear to work, but I can see what they were meant to do. I wrote a program a few years ago to do the same kind of thing, but then Microsoft dropped Direct Animation and it no longer worked in any browser. I'll maybe have a go at translating it into pure JavaScript...
Post by: David Cooper on 24/09/2012 21:39:16
David Cooper:QuoteIn SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds.
Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?
How about one question and one answer at a time for a 'change' for the sake of clarity?
Within SR (and I'll restrict this reply to that since that's what I was talking about in the box at the top), I don't think there's any real contraction of the object at all - all you're getting is apparent contraction based on observing from other frames which result in some of the length being hidden, though the length is effectively shorter in those other frames for all practical purposes, just so long as the speeds of observer and observed don't change.
Post by: yor_on on 24/09/2012 22:35:00
There are so many thing explainable by introducing length contractions as real from the frame measuring it, from the muon's 'point of view/reality' to how 'forces' behave (had a really good one on that, but as usual I can't seem to find it when I need it:)
This one might do though? What is a magnetic field? (http://www.askamathematician.com/2010/11/q-what-is-a-magnetic-field/) although when speaking of both time dilations and lorentzFitzGerald contractions the text assume that one understand that the descriptions are frame/observer dependent.
But the bottom line (?) is that using lenth contractions and time dilations you get a new view on a lot of phenomena, although it do take some time to melt.
Post by: lightarrow on 25/09/2012 11:52:03
Within SR (and I'll restrict this reply to that since that's what I was talking about in the box at the top), I don't think there's any real contraction of the object at all - all you're getting is apparent contractionPlease *define* "real" and "apparent" in this context.
Post by: wolfekeeper on 25/09/2012 12:23:41
David Cooper:Yes, that's partially true, all the effects are due to distortions when something accelerates.QuoteIn SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds.
Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?
There's a slight difference, between something that accelerates (and hence undergoes a force that gives it a Lorentz contraction) and when the measuring system accelerates (and hence its distortions change the way it views everything else).
But because the Lorentz contractions and time dilations form a symmetric group, it usually doesn't matter much which body accelerates, virtually everything is exactly the same, you can show that contractions and time dilations only depend on relative speed (although it can make a difference when you calculate the proper time; for example in the twin paradox, the one that accelerates is the one that ends up ageing, not the one that just sits there.)
Post by: old guy on 25/09/2012 19:07:47
"Yes, that's partially true, all the effects are due to distortions when something accelerates."
Length contraction advocates insist that it does not involve any force applied to 'contracted' objects or distances between objects. So acceleration is not a factor.
That leaves the "validity" of contracted objects and distances as depending on differences in observed images, not changes in the objects/distances themselves, which would require force, to squeeze Earth flatter, shorten a metallic object or move cosmic bodies closer together in space.
Post by: lightarrow on 25/09/2012 19:32:58
Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?Please, can you write down the physics law which states this?
Hint: there isn't any.
If an object contract *while staying in the same frame of reference* you do need a force for it, but it's not this the case.
If you still think there have to be a force, state the physics law.
Post by: wolfekeeper on 25/09/2012 21:04:29
wolfekeeper:No, there's two things. If *I* as an observer have accelerated, all my rulers distort and my clocks do too, but I don't notice that, directly, because I'm distorted in the same way, but when I measure the positions of things using my distorted clocks and rulers, I get changes in the length of the objects I measure (either longer or shorter, depending on their relative speeds before and after the acceleration).
"Yes, that's partially true, all the effects are due to distortions when something accelerates."
Length contraction advocates insist that it does not involve any force applied to 'contracted' objects or distances between objects. So acceleration is not a factor.
Conversely, if an object accelerates relative to me, then that acceleration causes changes in the distortions of that object alone.
They're two different things.
There are forces that cause this (actually the acceleration directly causes it), but they always act within the object that accelerates. (Note that there is a real physical difference between an accelerating object and a non accelerating object; a mass on a spring can tell you which is which for example).
The net upshot is that, either way, relative to any observer, moving objects get Lorentz contracted, time dilated, and there's a lack of simultaneity between different ends of an accelerated object. That's the principle of relativity.
Post by: old guy on 25/09/2012 21:18:11
When SR speaks of "for observer A, at rest with Earth"... Earth is spherical (almost), while "for observer B, flying by very fast" Earth is severely oblate (to say a 1000 mile diameter in the direction of the observer's travel),... this is about how Earth is observed from different frames, not about Earth actually changing shapes as it is seen differently. Do you understand this difference? This is my point.Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?Please, can you write down the physics law which states this?
Hint: there isn't any.
If an object contract *while staying in the same frame of reference* you do need a force for it, but it's not this the case.
If you still think there have to be a force, state the physics law.
In physics, to change the shape of a physical object, a force must be applied. Do you understand? Observation does not change the shape of physical objects. See what I mean? To crush a stone, the molecular bonds within the compounds must be broken, which requires physical force. Same for Earth as a whole. It can not be flattened without application of a huge force, which would then destroy it anyway, not just compress its diameter to the 1000 miles (in the direction of an observer's pass-by) suggested for the extreme of an Earth with a length contracted diameter.
For the distances between objects (like from Earth to Alpha Centauri) the law of inertia applies. Objects at rest will stay at rest until a force is applied to move them. So Earth will not move closer to AC just because "for a craft traveling at near 'c'", as its clock slows down, the claim is that the distance traveled becomes shorter. Does this make sense to you?
Post by: David Cooper on 25/09/2012 21:20:06
:) Nope ::))
There are so many thing explainable by introducing length contractions as real from the frame measuring it, from the muon's 'point of view/reality' to how 'forces' behave (had a really good one on that, but as usual I can't seem to find it when I need it:)
Things in other frames can treat length-contracted objects as if they are really contracted, but that doesn't mean they really are length contracted. In SR it is perfectly possible to declare that the real shape of an object is the one it has in its own frame and that any other views of it which make it look and behave as if its contracted are illusions. If you look at your reflection in a distorted mirror, the reflected image is an illusion too, but you could still shoot people dead with a laser gun by aiming at their reflections in it, so in practical terms the distorted shapes could be considered to be real. In a Lorentzian universe it is also practical to treat things that appear to be moving as if they are length contracted even if they are completely stationary and it is you who is doing all the moving - in this case you're certainly dealing with an illusion of contracted length, but the measurements and everything practical involving any kind of interaction with the apparently-contracted object make that contraction seem absolutely real, even though it isn't really contracted.
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This one might do though? What is a magnetic field? (http://www.askamathematician.com/2010/11/q-what-is-a-magnetic-field/) although when speaking of both time dilations and lorentzFitzGerald contractions the text assume that one understand that the descriptions are frame/observer dependent.
Nice link.
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But the bottom line (?) is that using lenth contractions and time dilations you get a new view on a lot of phenomena, although it do take some time to melt.
It's still really just a philosophical argument about what counts as real or apparent though. It's as good as real in practical terms, but I don't think that qualifies as real in absolute terms.
Within SR (and I'll restrict this reply to that since that's what I was talking about in the box at the top), I don't think there's any real contraction of the object at all - all you're getting is apparent contractionPlease *define* "real" and "apparent" in this context.
I'm using "real" to mean the shape that things might actually be (if external factors aren't adding undetectable distortions, such as would occur if the universe was rolled up in another dimension). I'm using "apparent" to mean the shape that things appear to be when observed from other frames where you don't get a proper picture of them. It's perfectly possible though within SR to have a different take on things and declare all possible views of things shapes as being equally real such that there is an infinite range of shapes for each object and you simply see different ones from different frames. What doesn't work is the idea that things physically change their shape to accomodate with how they're being observed, but I'm not sure if anyone actually holds that position in the way that I mean it.
Post by: David Cooper on 25/09/2012 21:25:00
David Cooper:Yes, that's partially true, all the effects are due to distortions when something accelerates.QuoteIn SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds.
Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?
Be careful not to give Old Guy anything he might misinterpret easily which might help fix him in a wrong position. The acceleration force does not directly cause the contraction and may indirectly remove contraction instead.
Quote
... in the twin paradox, the one that accelerates is the one that ends up ageing, not the one that just sits there.)
I expect you mean ageing less.
Post by: David Cooper on 25/09/2012 21:32:53
There are forces that cause this (actually the acceleration directly causes it), but they always act within the object that accelerates. (Note that there is a real physical difference between an accelerating object and a non accelerating object; a mass on a spring can tell you which is which for example).
I'm beginning to think you may not understand the mechanism fully. If you accelerate an object to 0.866c it will be length contracted to half its original length. Now turn it sideways without slowing it down and the length contraction will be removed from the object's length and transferred to its width (which is now aligned with the direction of travel). The acceleration force does not compress the object to a shorter length other than temporarily - any compression will be removed when the acceleration force stops. You can see more easily why this is the case if you imagine pulling the object up to high speed by towing it behind a rocket - the acceleration will now stretch it a little, but the object will still length-contract as it travels faster, and when the acceleration force is removed, the tiny bit of stretching will be removed.
Post by: wolfekeeper on 25/09/2012 21:42:26
In physics, to change the shape of a physical object, a force must be applied. Do you understand?Yes, but that turns out not to be the case. If I accelerate, your shape is changed, and you experience no forces; it's not an illiusion, it's a real, physical change.
And it actually makes a difference in the everyday world. That's how magnets work. If you go past a magnet, you actually find that the charges have redistriibuted themselves due to your motion, and the magnet is now *electrically* charged, and it's due to lack of simultaneity; it's due to these distortions.
And it's that charge which we feel in the non moving frame as 'magnetic attraction' because both magnets have charges in constant motion, and they create an electical attraction between themselves, in the moving frame, which we feel in the stationary one and call it a 'magnetic field'.
Post by: wolfekeeper on 25/09/2012 21:49:00
Yes, that stretch is just sound waves; I'm not talking about the sound waves. Whether you push or pull makes virtually no difference, either way the forces cause the atoms accelerate/to change between reference frames, it's not a Hooke law effect in any way. Either way you do it, there's an inevitable distortion to the object as it accelerates.There are forces that cause this (actually the acceleration directly causes it), but they always act within the object that accelerates. (Note that there is a real physical difference between an accelerating object and a non accelerating object; a mass on a spring can tell you which is which for example).
I'm beginning to think you may not understand the mechanism fully. If you accelerate an object to 0.866c it will be length contracted to half its original length. Now turn it sideways without slowing it down and the length contraction will be removed from the object's length and transferred to its width (which is now aligned with the direction of travel). The acceleration force does not compress the object to a shorter length other than temporarily - any compression will be removed when the acceleration force stops. You can see more easily why this is the case if you imagine pulling the object up to high speed by towing it behind a rocket - the acceleration will now stretch it a little, but the object will still length-contract as it travels faster, and when the acceleration force is removed, the tiny bit of stretching will be removed.
Post by: David Cooper on 25/09/2012 22:02:09
In physics, to change the shape of a physical object, a force must be applied. Do you understand? Observation does not change the shape of physical objects. See what I mean? To crush a stone, the molecular bonds within the compounds must be broken, which requires physical force. Same for Earth as a whole. It can not be flattened without application of a huge force, which would then destroy it anyway, not just compress its diameter to the 1000 miles (in the direction of an observer's pass-by) suggested for the extreme of an Earth with a length contracted diameter.
You could theoretically accelerate an object by holding a planet near it such that it would be accelerated by the gravity without feeling any force on it at all. By accelerating the planet along ahead of it you could accelerate the object to very high speeds without it feeling the acceleration forces felt by the planet. Then you can remove the planet and take a look at the object - it has been length contracted.
How does the length contraction happen? As always, it's necessary to divide the answer into at least two different answers, one for SR and the other for a Lorentzian universe, and particularly when so many ideas that should only apply to a Lorentzian universe are commonly used to illustrate SR (which is the main source of confusion when discussing relativity).
In SR I don't think there is any real length contraction (just as there isn't any real slowing of clocks) - I only see apparent length contraction, but it can be treated in practical terms as if it is absolutely real. Some of the length is hidden in the time dimension, but there is no actual contraction being imposed on anything.
In a Lorentzian universe, there is genuine length contraction (and real slowing of clocks). The mechanism for the contraction is the continued application of existing forces within the object. In a fast moving rocket which contains a room with a lamp in the middle of it, the front and rear walls receive the same amount of illumination as the side walls for two reasons: the light is concentrated forwards by the movement of the lamp, and the front and rear walls are moved nearer to the lamp by length contraction of the rocket and all its contents. Forces are also concentrated forwards more strongly as things move faster, and if you imagine that two atoms sit apart at distances where the forces they receive from each other are at a particular strength, that will be affected exactly as brightness is - the strengths and brightnesses required occur closer in the direction of travel to the point from which they were emitted as the object moves faster, so two atoms will sit twice as close together in their direction of travel at 0.866c than they do when they are not moving. This applies to every pair of atoms in the rocket, and to every nucleus and electron, and to every component to every other component. The contraction is completely automatic.
Post by: lightarrow on 25/09/2012 22:57:28
Even the same word "observer" is misleading. It's not just an "observation", it's a *measurement*. It could be done from an authomatic instrument, in the absence of any living being.Please, can you write down the physics law which states this?When SR speaks of "for observer A, at rest with Earth"... Earth is spherical (almost), while "for observer B
Hint: there isn't any.
If an object contract *while staying in the same frame of reference* you do need a force for it, but it's not this the case.
If you still think there have to be a force, state the physics law.
Quote
, flying by very fast" Earth is severely oblate (to say a 1000 mile diameter in the direction of the observer's travel),... this is about how Earth is observed from different frames, not about Earth actually changing shapes as it is seen differently.[:)] It must be the 100th time we tell you in all ways that you haven't undestood that you are *defining* as "actual" what happens in the same frame of reference. What you really mean is this: without changing the frame of reference, to contract an object requires a force.
Do you understand this difference?
But here we are not discussing that, we are discussing another thing, that is the change of an object lenght changing the frame of reference.
You don't want to see it as an "actual" change of lenght? Ok, but this is a definition that you haven't already made. It's not "a fact", as you believe, it's A DEFINITION.
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This is my point.No, you're wrong. Not in this case.
In physics, to change the shape of a physical object, a force must be applied.
Post by: lightarrow on 25/09/2012 23:08:24
Here you make other two "hazy" statements [:)]Please *define* "real" and "apparent" in this context.I'm using "real" to mean the shape that things might actually be (if external factors aren't adding undetectable distortions, such as would occur if the universe was rolled up in another dimension). I'm using "apparent" to mean the shape that things appear to be when observed from other frames where you don't get a proper picture of them. It's perfectly possible though within SR to have a different take on things and declare all possible views of things shapes as being equally real such that there is an infinite range of shapes for each object and you simply see different ones from different frames. What doesn't work is the idea that things physically change their shape to accomodate with how they're being observed, but I'm not sure if anyone actually holds that position in the way that I mean it.
1. "observed". It's not a mere "observation", it's a *measurement*.
2. "physically". You are making another definition: it's "physical" anything which refers to a "proper" frame. Maybe you are right, but it's a definition that physics hasn't given yet...
If you have a gas in a box, you have to put yourself in the frame of reference of every molecule to know the properties of the gas? It would be quite uneasy [;)]
Of course Lorentz lenght contraction has a *different* meaning from the contraction of a spring because of opposing forces at its ends, but this doesn't mean that it's not real.
Otherwise you should say that a magnetic field isn't real, since it's caused by Lorentz lenght contraction of electric charge inside a cable with a current...
Post by: old guy on 26/09/2012 00:36:54
Quote
Even the same word "observer" is misleading. It's not just an "observation", it's a *measurement*. It could be done from an authomatic instrument, in the absence of any living being.
"The observer" is the frame of reference. That is not the issue. The question is, do different frames of reference determine various realities like different shapes of objects, etc.? Does observation determine 'the shape of things' or do they have their own shapes? They do, and observation doesn't change their shapes.... or the distances between objects.
I must sign off again before finishing. (I have a life :))
, flying by very fast" Earth is severely oblate (to say a 1000 mile diameter in the direction of the observer's travel),... this is about how Earth is observed from different frames, not about Earth actually changing shapes as it is seen differently.
Do you understand this difference?
:) It must be the 100th time we tell you in all ways that you haven't undestood that you are *defining* as "actual" what happens in the same frame of reference. What you really mean is this: without changing the frame of reference, to contract an object requires a force.
But here we are not discussing that, we are discussing another thing, that is the change of an object lenght changing the frame of reference.
Post by: old guy on 26/09/2012 00:44:42
Quote
Even the same word "observer" is misleading. It's not just an "observation", it's a *measurement*. It could be done from an authomatic instrument, in the absence of any living being.
(The forum linked my last post with a former one... so here it is as intended):
"The observer" is the frame of reference. That is not the issue. The question is, do different frames of reference determine various realities like different shapes of objects, etc.? Does observation determine 'the shape of things' or do they have their own shapes?
The answer is that they do, and that observation doesn't change their shapes.... or the distances between objects.
I must sign off again before finishing. (I have a life :))
(The rest of what i saw as my post was a mistake.)
Post by: lightarrow on 26/09/2012 13:38:49
The question is, do different frames of reference determine various realitiesIf you have a problem with this, remember that what is a fast travelling bullet against you and so a great danger, is a still bullet if you move at the same speed of it, and so a harmless one... Speed, momentum, energy, wavelenght and frequency, are examples of frame-dependent quantities. "realities" do change, changing the frame.
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like different shapes of objects, etc.? Does observationPlease, don't say "observation", or it can mislead you.
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determine 'the shape of things' or do they have their own shapes?Define "their own". Does it mean: "in their proper frame"? Yes, they have their own shape. Do you understand it's a definition? In physics you can't do anything without definitions.
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The answer is that they do,...but you are not aware that it's a your idea that has never become a definition. I have no problem in being in agreement with this definition, but I can't accept that you pretend to give it as granted.
Post by: old guy on 26/09/2012 18:09:12
I will first back up to unfinished business and then address your last post.
In post 75 I spelled out what I meant by the difference between how something might appear vs how it is, as an object with intrinsic properties independent of observation/measurement ( Ed:I use the two terms interchangeably.)
Please answer.
When SR speaks of "for observer A, at rest with Earth"... Earth is spherical (almost), while "for observer B, flying by very fast" Earth is severely oblate (to say a 1000 mile diameter in the direction of the observer's travel),... this is about how Earth is observed from different frames, not about Earth actually changing shapes as it is seen differently. Do you understand this difference? This is my point.
In physics, to change the shape of a physical object, a force must be applied. Do you understand? Observation does not change the shape of physical objects.
(Edit: Neither does measurement.... nor do changes in frame of reference. Appearances change, not the object.)
Also, did you understand my answers to your “what laws of physics” question?
wolfekeeper:
“If I accelerate, your shape is changed, and you experience no forces; it's not an illiusion, it's a real, physical change.”
The way I appear to you might change. A physical force would be required to *actually* change my shape... and it would either kill me or hurt a lot! This is a physical body, not just an image in your visual cortex.
Post by: wolfekeeper on 26/09/2012 18:38:02
This isn't as strange as you seem to think.
If you accelerate along a road, the road and all the houses are now moving past you. What force caused them to start moving like that? Did they feel that force?
Post by: old guy on 26/09/2012 18:47:50
“The question is, do different frames of reference determine various realities”
Lightarrow:
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If you have a problem with this, remember that what is a fast travelling bullet against you and so a great danger, is a still bullet if you move at the same speed of it, and so a harmless one... Speed, momentum, energy, wavelenght and frequency, are examples of frame-dependent quantities. "realities" do change, changing the frame.
I have no problem with the reality of relative motion. Motion (velocity) must always be specified as "relative to what? The issue is physical changes vs apparent changes.
Regarding my “...do they (objects) have their own shapes?”
You:
Quote
Define "their own". Does it mean: "in their proper frame"? Yes, they have their own shape. Do you understand it's definition? In physics you can't do anything without definitions
Wiki says of Realism that ...”reality exists independently of observers.” I will include independent of the frame of reference from which it is either observed or formally measured. Physical objects exist and have intrinsic properties independent of how (from which frame of reference) they are measured.
Me:
"The answer is that they do,..."
You:
Quote
...but you are not aware that it's a your idea that has never become a definition. I have no problem in being in agreement with this definition, but I can't
accept that you pretend to give it as granted.
The length contraction part of SR takes for granted that what you see/measure is how it is, and as measurement vary, the objects measured vary. And "because Einstein said so"* does not automatically make it true (* that the word "real" is "meaningless.")
This is not true.
Realism insists that things like Planet Earth were formed by the laws of physics, in this case to be about spherical, its true and natural form. That is "Earth’s own" intrinsic physical shape, and it does not change with varieties of ways (frames of reference) from which it can be measured.
Post by: old guy on 26/09/2012 19:14:57
"If you accelerate along a road, the road and all the houses are now moving past you. What force caused them to start moving like that? Did they feel that force?"
You really don't have a clue to my central point here. Nothing is moving the houses past me. They appear to be moving past me as I move past them. See my relative motion comments above.
I agree that they are moving relative to me as vice-versa. But they are fastened to foundations, quite stationary with the ground they are built on, while I am on wheels moving on the road past that ground.
Why is this conversation degenerating into statements of the obvious? No, no force is moving the houses. The power of my engine is moving my car. Sheesh!
Post by: lightarrow on 26/09/2012 19:24:06
Me:Me: of course they do. Because for me "reality" means "what I measure".
“The question is, do different frames of reference determine various realities”
What follows is just your definition of "intrinsic property of a body", on which I can even agree, but it's nothing else than that.
Since I have enough of this discussion, I will not reply to your next post.
Regards.
--
lightarrow
Post by: old guy on 27/09/2012 17:46:29
Suit yourself on quitting the conversation. Physical science (physics, astronomy, earth science) is not about "reality for me" compared to "reality for you." That is the realm of psychology. The job of science is to determine what objective reality is in each case, not subjective differences in observational points of view. Earth and its distance from the Sun, etc. has an objective reality as it is, not depending in differences in how it can be observed and measured from different frames.Me:Me: of course they do. Because for me "reality" means "what I measure".
“The question is, do different frames of reference determine various realities”
What follows is just your definition of "intrinsic property of a body", on which I can even agree, but it's nothing else than that.
Since I have enough of this discussion, I will not reply to your next post.
Regards.
--
lightarrow
Thanks for the conversation.
Edit, Ps:
David Cooper, in post 162:
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What doesn't work is the idea that things physically change their shape to accomodate with how they're being observed, but I'm not sure if anyone actually holds that position in the way that I mean it.
Who here holds that position? I can quote a few. That issue remains the essence of this thread's challenge.
Post by: David Cooper on 27/09/2012 20:36:45
The job of science is to determine what objective reality is in each case, not subjective differences in observational points of view. Earth and its distance from the Sun, etc. has an objective reality as it is, not depending in differences in how it can be observed and measured from different frames.
The trouble is that science cannot determine what objective reality is because we simply can't tell if anything's moving or not. I can see exactly why you aren't satisfied with the idea that if you start walking down the street you aren't suddenly making the houses move past while you are stationary, but that isn't actually in anyone's theory. With Lorentz there is an absolute answer which can't be known, and with Einstein all answers are correct, but not in such a way that you can jump frames and assert that things which weren't moving a moment before are suddenly moving without any force being applied to them - if you jump frame, you're switching to a frame in which the houses were already moving. As for the distance between the Earth and Sun, you don't have enough information to determine what the objective reality is on that either: again Lorentz allows there to be an objective reality which we can't access, and Einstein allows you to have your cake and eat it, but he'll only let you have and eat one cake at a time - shifting frame forces you to reassess everything you'd considered to be the case a moment before from the previous frame.
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QuoteWhat doesn't work is the idea that things physically change their shape to accomodate with how they're being observed, but I'm not sure if anyone actually holds that position in the way that I mean it.
Who here holds that position? I can quote a few. That issue remains the essence of this thread's challenge.
No - it's a diversion. Some people here appear to hold that view, but it isn't mainstream SR. The best point you've made in all this is the one about the atmosphere being made thin (not in terms of the amount of stuff in it, but the distance it spans) by a muon moving through it, but in SR it isn't the case that it suddenly becomes thin for the fast-moving muon. What happens is that the muon finds a shorter path through it which is only available to things in frames which are moving at very high speed. All such paths are available for all suitable frames all the time.
Post by: old guy on 27/09/2012 20:59:59
“What doesn't work is the idea that things physically change their shape to accomodate with how they're being observed,... “ (my bold)
Me:
That issue remains the essence of this thread's challenge.
David:
“No - it's a diversion.”
Lets get one thing straight here. I started the thread. I have focused throughout on the issue as again stated above. You are the one creating a continuing “diversion” based on your personal opinions about the varieties of “length contraction” according to different theories as you interpret them. You constantly contradict yourself, as I have specifically pointed out several times, with no response from you.
No moderators here care about your continuing attempts to hijack this thread for your own purposes.
You have no right or reason to tell me that the issue I have raised as the core of this thread is a diversion. It is only a “diversion” from your agenda. Start your own thread to promote your own agenda!
Post by: yor_on on 27/09/2012 21:05:37
Post by: yor_on on 27/09/2012 21:17:57
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What I mean by the muon example is that those constitute simple proofs of LorentzFitzGerald contractions existence. you can't though discuss 'contractions' from that viewpoint as they are 'pointparticles', having no measurable 'size'. but you can use your logic to see why it must be a symmetry, not a reciprocal Newtonian effect belonging to one absolute same for all light speed. Absolute time was Newton, relative time is Einstein.
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You could, if you like, argue that as a muon falls in to Earth it also 'accelerate' expressed in a blue shift. But if you do that you also have to accept Einsteins definition of our Earth, uniformly moving through space, as constantly 'accelerating at one gravity', as I think. There is another symmetry we see, as the muon speed will not change according to our Earth ground measurements, if we now could follow it from space to ground:)
Post by: namaan on 28/09/2012 03:11:09
So as per the mainstream view of SR, if you measure a contracted length at a particular frame of reference, then that is by definition reality in that frame of reference. Reality, then, is defined in SR for a particular frame of reference (I feel like I'm duplicating lightarrow's comments here). On the other hand, you're essentially arguing for an absolute reality outside of frames of references. But rather than questioning the validity of the details of the mainstream view, you would be better served, I think, if you questioned instead the validity of the idea that reality is to be defined exclusively by the measurable. If I'm understanding the discussion, then this is the more fundamental question that needs to be answered.
And I think it has been made quite clear in this forum that the mainstream view is that reality is by definition what can be measured and nothing else. So if that is the basic position that one takes, there is really no sense to argue about derivative questions such as whether or not a contraction in the measured length of an object moving at a near-c velocity reflects, in reality, actual contraction of that object.
[Edit: My physics-senses are tingling. Hmm, I think I mean to say "contraction in the measured length of an object moving *relative to* yourself moving at near-c velocity"?]
To someone who defines reality as the measurable, then the measured change in length is, by definition, real.
Post by: yor_on on 28/09/2012 09:39:03
Post by: JP on 28/09/2012 14:30:28
And I think it has been made quite clear in this forum that the mainstream view is that reality is by definition what can be measured and nothing else.
I don't think that's true of the forum. I think it is probably more accurate to say that realities are what can be measured PLUS some set of immeasurable assumptions. Since you can add infinitely many assumptions, an infinite set of realities are possible. And since they differ only in immeasurable quantities, science (which tests theories based on measurement) can't discriminate which are valid and which aren't. That's when science passes the buck to metaphysics or religion. Since we're a science forum, not a metaphysics or religion forum, that's why we tend to avoid discussions of ultimate definitions of reality.
Post by: namaan on 28/09/2012 17:10:26
I don't think that's true of the forum. I think it is probably more accurate to say that realities are what can be measured PLUS some set of immeasurable assumptions.
Right, I just remembered the basic assumption of SR is that the physics laws that apply here apply everywhere. Does this assumption fall into the immeasurable? Or I guess the laws we work out here are measurably true as far as we can see.
Post by: JP on 28/09/2012 17:44:51
I don't think that's true of the forum. I think it is probably more accurate to say that realities are what can be measured PLUS some set of immeasurable assumptions.
Right, I just remembered the basic assumption of SR is that the physics laws that apply here apply everywhere. Does this assumption fall into the immeasurable? Or I guess the laws we work out here are measurably true as far as we can see.
Well, we can measure it insofar as if it weren't true, we'd probably notice. Of course, we can only measure a small part of the universe, and we can only perform experiments on a very small part, so testing it conclusively is tough. There are some subtle hints that some fundamental constants, and therefore the laws of physics, might change, but I don't think it's been widely double-checked and accepted. What is immeasurable is why the laws of physics apply everywhere. We'd have to come up with another theory beyond SR that renders this testable.
More of what I was going after is that "reality" is not the same as "scientific theory." Scientific theories generally use the simplest explanation for observations. Their main goal is to make useful predictions, so carrying around lots of extra immeasurable quantities is just extra work. When we talk about "mainstream science" it's in this sense.
"Reality," is a philosophical/religious concept. You care less about predictions and want to know some ultimate truth, even if you might not be able to test that truth with measurement. If you believe in science, then your idea of reality has to match with the predictions of science, but it can include all sorts of immeasurable aspects on top of those predictions. This is why, for example, a Christian scientist, a Hindu scientist and an atheist scientist can all agree completely on scientific theories, but disagree about the ultimate nature of reality beyond science.
In the above example, saying "the laws of physics are the same everywhere," makes no real assumptions about why the laws are the same, so that's essentially what SR does as a scientific model.
Saying "the laws of physics are the same everywhere because God made them that way," introduces something immeasurable to explain why the laws are the same. So does saying, "the laws of physics are the same everywhere because of the weak anthropic principle." These are perfectly valid views of reality, but they're not scientific theories.
Post by: old guy on 28/09/2012 17:50:25
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I can't comment on SR in any detail, but would it be correct to say that the major source of disagreement here is that you, Old Guy, acknowledge a reality outside of the measurable, whereas the mainstream view is to bind reality exclusively to the measurable?...
On the other hand, you're essentially arguing for an absolute reality outside of frames of references.
No, no “reality outside the measurable” and no “absolute reality." Rather that the “reality” of lengths and shapes of objects and distances between them is best measured from at rest with them, in the same frame with the object of measurement rather than from frames flying by at relativistic speeds, which will, for instance, (probably, theoretically) distort the naturally formed (by the law of gravity) nearly spherical shape of Earth into a more flattened image with a contracted diameter, not its true shape.
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But rather than questioning the validity of the details of the mainstream view, you would be better served, I think, if you questioned instead the validity of the idea that reality is to be defined exclusively by the measurable. If I'm understanding the discussion, then this is the more fundamental question that needs to be answered.
I have already on several occasions questioned that idea. It is called realism, well defined by Wiki, which have quoted several times. Essentially it says that reality does not depend on (is independent of) observation or measurement. That leaves science with the challenge in all cases to find the best way to measure things to determine their intrinsic properties, as they were formed by the laws of physics rather than just as seen from extreme frames of reference.
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To someone who defines reality as the measurable, then the measured change in length is, by definition, real.
Yes, but only by defining real as synonymous with each *variable* measure (*even of the same object.) That is why I introduced the probe retrieval thought experiment. I must assume you have read it and don’t need a replay. The probe does not, in reality, change from the 10 meters *it is measured* from Earth (as it approaches at .866 c) to 20 meters, *as measured from at rest with it* (after “coming alongside”, matching velocities to at rest with it.)
Post by: old guy on 28/09/2012 18:51:08
"Reality," is a philosophical/religious concept."
The claim by the father of relativity that "real" is a "meaningless" concept (that its *all about measurement*)... is itself a philosophical concept. Einstein's version of idealism is an acceptable philosophy in SR, but realism is not an acceptable philosophy. Earth's shape will vary with how it is measured from different frames. Period.
...Just to put philosophy of science in perspective here again. SR's idealism (that there is no reality but what is measured) is an *assumed philosophy.*
"Philosophy" simply examines that assumption explicitly.
Post by: namaan on 28/09/2012 19:10:00
You care less about predictions and want to know some ultimate truth, even if you might not be able to test that truth with measurement.
I appreciate the overall clarification, as well as the logic behind it, but perhaps you meant the general "you" above. If not then I can see why you would think that, but it isn't quite right; I believe in a reality that is fully ascertainable by science (well, there is a subtlety but this isn't the place for it). As I pointed out once before, if in fact a God-reality is true, then my cheer-leading for the existence of God will ultimately make no difference in the thermodynamics of the equation, merely in the kinetics of it. Provided that this version of reality is measurably correct, science will do its thing and come face-to-face with that reality on its own.
Post by: JP on 28/09/2012 19:21:49
Post by: JP on 28/09/2012 19:30:29
JP:
"Reality," is a philosophical/religious concept."
The claim by the father of relativity that "real" is a "meaningless" concept (that its *all about measurement*)... is itself a philosophical concept. Einstein's version of idealism is an acceptable philosophy in SR, but realism is not an acceptable philosophy. Earth's shape will vary with how it is measured from different frames. Period.
...Just to put philosophy of science in perspective here again. SR's idealism (that there is no reality but what is measured) is an *assumed philosophy.*
"Philosophy" simply examines that assumption explicitly.
If Einstein came into the thread and started posting the way you are, we'd move his posts to New Theories as well. :)
Old Guy, you've been asked politely several times to keep you philosophizing to New Theories because your posts have moved from discussion to evangelism, i.e. you keep repeating the same arguments again and again to back up your preferred philosophical interpretation, rather than engaging in discussion of science.
This is your final warning before I move the whole thread to New Theories.
Post by: David Cooper on 28/09/2012 20:37:37
David Cooper:
“What doesn't work is the idea that things physically change their shape to accomodate with how they're being observed,... “ (my bold)
Me:
That issue remains the essence of this thread's challenge.
David:
“No - it's a diversion.”
Lets get one thing straight here. I started the thread. I have focused throughout on the issue as again stated above.
You're arguing against some people who are overstating the case when they say that moving past something at speed changes the thing they're observing. It's really no different from an argument about whether rotating a cube in front of a camera can at some angles turn it physically from a square into a hexagon. Clearly it doesn't physically change at all - you merely get a different view of it. What you do though is this - you find people to argue with about this kind of thing, and then you not only tell them that they're wrong, but you then tell them that because they're wrong, your magical model of reality must be correct; a model in which space is literally nothing and yet it magically enforces systematic location on all its contents and in which the Michelson Morley experiment produces faulty results.
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You are the one creating a continuing “diversion” based on your personal opinions about the varieties of “length contraction” according to different theories as you interpret them. You constantly contradict yourself, as I have specifically pointed out several times, with no response from you.
I have responded to all your accusations of me contradicting myself, and in every case I had not contradicted myself at all - you are simply incapable of understanding that it's possible to analyse the same thing from within different theories and that the different theories contradict each other in places.
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No moderators here care about your continuing attempts to hijack this thread for your own purposes.
My purposes here are to try to help you get past the mental blockages which are blinding you to the errors in your belief system. Everyone here has been doing their best to try to help you understand where you're making mistakes, but you simply don't take anything on board.
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You have no right or reason to tell me that the issue I have raised as the core of this thread is a diversion. It is only a “diversion” from your agenda. Start your own thread to promote your own agenda!
So, you've fixated on attacking something which is not a requirement of SR and that is what this thread is about. Well, not according to the title. What this thread is actually about is a denial of length contraction and an appeal for everyone to take up your belief in a so-called "realism" which doesn't recognise the results of actual experiments which disprove this "realism".
Post by: old guy on 28/09/2012 21:12:16
JP:
"Reality," is a philosophical/religious concept."
The claim by the father of relativity that "real" is a "meaningless" concept (that its *all about measurement*)... is itself a philosophical concept. Einstein's version of idealism is an acceptable philosophy in SR, but realism is not an acceptable philosophy. Earth's shape will vary with how it is measured from different frames. Period.
...Just to put philosophy of science in perspective here again. SR's idealism (that there is no reality but what is measured) is an *assumed philosophy.*
"Philosophy" simply examines that assumption explicitly.
If Einstein came into the thread and started posting the way you are, we'd move his posts to New Theories as well. :)
What if he just started a thread with, "There is no reality but what we measure," as the length contraction part of SR turns out to be based upon? Would this forum allow debate on that assertion?
What if he said, "If a frame of reference flying by Earth at near 'c' measured Earth to have a 1000 mile diameter, then that would be the shape of Earth, which varies with how it might be measured, having no "real" shape independent of measures of it ?"
Would the forum allow debate on that?
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Old Guy, you've been asked politely several times to keep you philosophizing to New Theories because your posts have moved from discussion to evangelism, i.e. you keep repeating the same arguments again and again to back up your preferred philosophical interpretation, rather than engaging in discussion of science.
Labeling realism as evangelism is totally wrong, the bias of a built-in, assumed idealism about all measurements being valid descriptions of the object they measure.
Is implicit (assumed) philosophy ("Things change shape with how they are observed") OK because it's "mainstream," while realism (that things have intrinsic shape in and of themselves) is not OK because it disagrees with the assumptions of length contraction?
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This is your final warning before I move the whole thread to New Theories.I have no choice but to comply. The serious science of debating length contraction would then be effectively swept out of sight (again), under the rug... an obvious form of censorship, which has no place in honest scientific debate.
And please do not let David Cooper's posts be the deciding factor for this (my) thread. Thanks.
Post by: yor_on on 28/09/2012 23:49:19
And it became quite a interesting one. If you want to discuss your view more fully though it would be good to open a new topic asking, maybe, 'is reality a lie' or 'what is reality'? And to get the best answers, letting people take out the turns fully new theories are a cool place to do it on.
Post by: old guy on 29/09/2012 18:53:55
My length contraction thread in New Theories continues to address the "Reality" factor as applied to length contraction. (See my last two replies to D.C. there.) No need for a new thread. I will avoid speaking about that factor (and all philosophy of science) in this thread, or the whole record of conversations here will be 'banished to the outer darkness' never again to see 'the light of day' in this section. :(
Post by: yor_on on 30/09/2012 12:19:03
The other is taking a conceptual global perspective to it, incooperating all those differing local definitions (relative yours) into one 'undivided SpaceTime.' That's a abstract reality, defined and unified through Lorentz transformations, etc.
What space should be seen as I'm not sure, in Einsteins definitions you have relative (uniform) motion, accelerations, mass/gravity, 'energy' and the constant 'c' as the key factors explaining time dilations and length contractions. It would be pleasant to assume that as 'space' classically is 'empty', as in consisting of 'nothing', you could ignore the way it contracts with motion, but it still contain gravity, 'time' and three spatial dimensions, just as everything else. And a contraction will act on matter as well as space although one could then argue that it is the 'space' inside matter that brings with it the contraction.
But then we have the fact that nothing inside its own (local) frame of reference ever contracts, only when comparing can it exist a contraction, and then you will define that relative your own clock and ruler. A repeatable experiment builds on the axiom/assumption of us being in 'equivalent frames of reference' doing them and there Einstein offers us two, uniform constant accelerations, aka 'gravity', versus uniform motions, aka Earths and all other non accelerating celestial objects motion relative each other.
We've been doing most of our experiments on Earth and defined our logic from that, although I will assume that if having equivalent accelerations we also will find this assumption to be true. That doing a experiment in a equivalent environment will lead to a same outcome, never mind if accelerating or uniformly moving. But notice that I'm speaking of equivalent outcomes only, not stating that uniform motions should give you a same outcome as when accelerating. But it's a principle to me, in a way reminding me of a symmetry too.
And both Einstein and Lorentz were perfectly clear on that what you measure locally in your frame of reference will be as true as it can be, in this relativistic world.
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correcting spellings etc. Keep missing those small ones :)
Post by: namaan on 01/10/2012 00:10:29
No, no “reality outside the measurable” and no “absolute reality." Rather that the “reality” of lengths and shapes of objects and distances between them is best measured from at rest with them, in the same frame with the object of measurement rather than from frames flying by at relativistic speeds, which will, for instance, (probably, theoretically) distort the naturally formed (by the law of gravity) nearly spherical shape of Earth into a more flattened image with a contracted diameter, not its true shape.I get what you're saying I think. The laws of physics describe the formation of planets such that the planets have a roughly spherical shape, and since this shape arose from the laws we all agree to be correct, then the shape of the planet is, in reality, roughly a sphere. And said spherical shape is apparent only from a reference frame at rest with said planet, so the real description of an object should be described at rest with that object.
I get all that and as others have pointed out, they might even agree with such a view, but the basic problem is that this question is really just asking "what is reality?" The mainstream view, at least as JP points out, and barring unavoidable assumptions, is that reality is what can be measured. But you are essentially asserting that there is a preferred reference frame in which reality is given definition; the reference frame at rest with whatever object we would like to study the real description of.
I think JP's point is that this adds an unnecessary additional assumption to the SR model, since if SR included a definition of reality, it would then have to explain where this definition comes from. I will grant you that it is an intuitive and straightforward idea, but the buck will never-the-less get passed to you as you'll have to present your argument for why reality should be defined only at rest with an object.
That leaves science with the challenge in all cases to find the best way to measure things to determine their intrinsic properties, as they were formed by the laws of physics rather than just as seen from extreme frames of reference.
Unfortunately for you Sir, science is not taking that job ;) As has been variously mentioned on these forums, it is not the job of science to define reality; they have passed that responsibility to meta-physics and religion. Which I find unfortunate as well. Please do correct me again if I am overstepping on my presumptions here.
Yes, but only by defining real as synonymous with each *variable* measure (*even of the same object.) That is why I introduced the probe retrieval thought experiment. I must assume you have read it and don’t need a replay. The probe does not, in reality, change from the 10 meters *it is measured* from Earth (as it approaches at .866 c) to 20 meters, *as measured from at rest with it* (after “coming alongside”, matching velocities to at rest with it.)
Again, I agree with you on principle, but as it has been said repeatedly, this is a matter of definitions. How you have defined reality, and how it has been defined by most of those who you are having this discussion with is quite different.
Post by: old guy on 01/10/2012 23:51:30
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I get what you're saying I think. The laws of physics describe the formation of planets such that the planets have a roughly spherical shape, and since this shape arose from the laws we all agree to be correct, then the shape of the planet is, in reality, roughly a sphere. And said spherical shape is apparent only from a reference frame at rest with said planet, so the real description of an object should be described at rest with that object.
Yes!!
namaan:
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I get all that and as others have pointed out, they might even agree with such a view, but the basic problem is that this question is really just asking "what is reality?" The mainstream view, at least as JP points out, and barring unavoidable assumptions, is that reality is what can be measured. But you are essentially asserting that there is a preferred reference frame in which reality is given definition; the reference frame at rest with whatever object we would like to study the real description of.
If we all agree that the laws of physics (gravity here) form planets as near spherical, by what stretch of imagination is that not reality? We could, if we went fast enough, probably measure Earth to be quite flattened in its diameter in the direction of travel. Does that reasonably change the reality of Earth's shape? I think not. I agree with your last statement.
I think that the dictum that there are no preferred frames of reference is wrong for the reasons cited above... the agreement on the laws of physics which make planets nearly spherical, not flattened, as the obvious case in point.
Me:
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That leaves science with the challenge in all cases to find the best way to measure things to determine their intrinsic properties, as they were formed by the laws of physics rather than just as seen from extreme frames of reference.You:
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Unfortunately for you Sir, science is not taking that job ;) As has been variously mentioned on these forums, it is not the job of science to define reality; they have passed that responsibility to meta-physics and religion. Which I find unfortunate as well. Please do correct me again if I am overstepping on my presumptions here.Science has been given the job of determining the correct shape (diameters) of Earth, which it has accepted and done so very precisely. It is misleading to call that "defining reality" as if it were a metaphysical task.
The metaphysics is in the theory by which Earth changes shape. It doesn't.
Post by: JP on 02/10/2012 00:22:14
Post by: lightarrow on 02/10/2012 18:17:10
If we all agree that the laws of physics (gravity here) form planets as near spherical, by what stretch of imagination is that not reality?1. Laws of physics say that a planet forms as spherical in their proper frame.
2. Laws of physics say that a planet forms as a deformed sphere in a moving frame.
Did you get it now?
Post by: old guy on 02/10/2012 20:00:19
Do you understand that the phrases "in their proper frame" and "in a moving frame" define the shapes of planets by how they are observed, denying that they have shapes independent of how variously they are observed?If we all agree that the laws of physics (gravity here) form planets as near spherical, by what stretch of imagination is that not reality?1. Laws of physics say that a planet forms as spherical in their proper frame.
2. Laws of physics say that a planet forms as a deformed sphere in a moving frame.
Did you get it now?
Do you think that planets change shapes as they are observed differently? What then causes them to change shape with no application of force, or is it the magical power of different observations that alters massive physical objects?
Everyone but extremist SR theorists like yourself understands that planets and stars are in fact nearly spherical, and that their original formation as such does not depend on from what frame of reference they are observed.
Do you understand that "for this observer" vs "for that observer" makes reality observer dependent, as if Earth's shape depended on who is looking at it from what frame?
Do you get that this is idealism? Do you know what that means? Do you think that a falling tree makes no sound unless there is an "observer" present to hear it?
Do you have any idea how absurd that denial of reality is, or is the difference between idealism and realism beyond your comprehension?
Do as yet undiscovered galaxies simply not exist until they are observed?
How far would you like to carry this obvious absurdity. Is an elephant's shape a rope, because a blind man is feeling its tail. How about claiming that a tree trunk shape is equally valid, as "observed" by the blind man holding a leg? "No, an elephant is like a fire hose," says the one holding the trunk. Or does the whole elephant have a shape of its own independent of observation from limited perspective?
Yes, it does, and so does the Earth. Try to get over your idealism-based misconception about that. Science knows Earth's shape, and SR did not reinvent it.
Post by: lightarrow on 03/10/2012 11:24:26
You insist on using the term "observed" but it's incorrect.Do you understand that the phrases "in their proper frame" and "in a moving frame" define the shapes of planets by how they are observed,If we all agree that the laws of physics (gravity here) form planets as near spherical, by what stretch of imagination is that not reality?1. Laws of physics say that a planet forms as spherical in their proper frame.
2. Laws of physics say that a planet forms as a deformed sphere in a moving frame.
Did you get it now?
The right term is "measured".
At high speeds what you would "observe" is different from what you would measure.
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Science knows Earth's shape.Indeed: science *knows* that Earth's shape is not spherical in a moving frame.
Science doesn't work according to what *you think*, but according to what *everyone measures*.
And this is the last answer of me.
Post by: old guy on 03/10/2012 18:46:34
I don't blame you for quitting, since there are no good answers to the questions/challenges i posed in my last post to you.
You say:
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You insist on using the term "observed" but it's incorrect.Your last statement is a false dichotomy.
The right term is "measured".
At high speeds what you would "observe" is different from what you would measure.
Most SR advocates use the terms 'observed' and 'measured' interchangeably, as "measured" is just the formal quantification of what is observed; and we all know that a 'frame of reference' can be abstract, not literally requiring a personal observer, as I have said here before.
Quite a lame criticism.
You say:
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Indeed: science *knows* that Earth's shape is not spherical in a moving frame.
Science doesn't work according to what *you think*, but according to what *everyone measures*.
See... Earth is a "real" solid physical planet. It doesn't change shape to accommodate all possible differences in how it might be observed/measured. So observing/measuring it "in a moving frame" does not make it flatten out into a very oblate spheroid, even though it my appear so distorted from a high speed frame. That is the source of your continuing confusion, and that of all SR theorists in this forum who agree with you. You fail to distinguish appearance (the image of the object) from the object itself. The elephant is not, in fact, shaped like a rope.
Post by: yor_on on 03/10/2012 19:47:03
Just exchange each 'point' in our universe with a 'observer' but keep 'gravity', to see why I state it this way.
Or you can take a stand in where you define the 'truth' of 'reality' as belonging solely to the 'local description', meaning where you are in space and time, as you observe/measure. From a relativistic point of view that is what I see you try for here, but to do so you now will need to define how all those different 'local definitions' can exist, and all be true for those observing? Because you still have this universe consisting of 'observers', although you now made each one a 'creator' of their own unique universe, as all observations still must differ if compared, if you see my drift there?
What is good with such a reasoning is that it gives us a 'preferred frame of reference' which actually is how it is treated practically as I think, considering the validity and importance we give 'repeatable experiments'. Aways done locally, then tested/compared in equivalent (relativistically seen) frames of reference (measured in uniform motion mostly). '
But it still need to answer how this can be possible? If so?
And that is one tricky subject OG.
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When it comes to 'simultaneity', in a indivisible universe you must need it, or else assume that 'time and its arrow' must be a illusion. But then you by necessity have to do the same with a LorentzFitzGerald contraction, as I see it, as they are a symmetry. And if you allow contractions to 'exist' then you've failed anyway, no matter what you think of 'time'. But we have 'frames of reference gravitationally, on Earth, with time dilations :) so it exist as we can measure it.
In a 'local' definition of reality a time dilation becomes slightly simpler as I think of it as they all become unique descriptions, describing unique universes, slightly shifted out of place/focus from your neighbors. Then there is only one time keeping, and that is the one decided by your wristwatch. And the same will hold true for contractions, meaning that you can treat your local clock and ruler as approximately 'invariant'. But then the next question becomes, if it is so, what is the scale of a 'frame of reference', is it enough with being 'at rest' with what you measure? And there i think one have to answer, no. 'At rest' can only be seen as a approximation as we have gravity as the metric of space. Superimposing light/radiation though can be seen as being 'at rest'. Though we have 'point particles', the Pauli exclusion principle stops them from superimposing, normally treated at least. Anyway, the one thing joining them (when comparing between different frames of reference) is something we only can measure as having a 'beginning', as in a recoil, and a 'end', as in a annihilation, but doesn't exist in between?
Radiation.
Post by: old guy on 03/10/2012 22:01:06
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There is one frame from what you say is (approximately) true OG. The local one where you are 'at rest' with what you measure. But then it becomes a philosophical question which frame is 'more true' than another, if you want a indivisible universe? Because then all frames of reference must be as 'true', as they all need to be in-cooperated in this universe.
The universe is filled with bodies which were formed by various laws. Gravity is the one which makes stars and planets form as nearly spherical. There is no philosophy involved in that. It is the physics of how cosmic dust and debris is formed into planets and stars.
Enter length contraction theory: "For a frame of reference" flying by at near 'c', such objects may appear very oblate, nothing close to spherical.
That does not change the law of physics (gravity) that made them spherical in the first place.
If you are a scientist of the future charged with measuring and describing planets and stars in far away solar systems, flying there at near 'c', what will be your report?... that they are all extremely flattened, or that they are pretty much like our local system?
I would suggest that you slow down and then "park" in the orbit of all objects to be measured to get the most accurate measure. But if that is inconvenient and an inefficient use of rocket power, you could always apply the Lorentz formula to account for your velocity as a factor distorting the images of the bodies your are zipping past. But in no case will you be telling "mission control" that all those bodies are somehow strangely "pancaked" in shape.
Is that clear enough?
(Out of time... More later as "it permits.")
Post by: old guy on 04/10/2012 00:14:13
yor-on:
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Because you still have this universe consisting of 'observers', although you now made each one a 'creator' of their own unique universe, as all observations still must differ if compared, if you see my drift there?
SR theory made each "observer" a "creator" of each frame-specific version of each resulting, as measured, unique universe.
My argument is exactly the opposite.... that the universe and all its objects are "as they were formed by the laws of physics," totally independent of differences in observation. Why is this concept so hard to communicate clearly?
Post by: yor_on on 04/10/2012 13:39:02
Post by: old guy on 04/10/2012 18:37:44
It's not hard to communicate OG. It's just that you have to refute relativity, both versions I presented, to make that statement true. And if you can't do that then is will be a dreamers position, what should have been, but what isn't.So.... Nothing specifically in reply to my last two posts?
I'll walk you through the last point where you had my position exactly opposite.
(The reason I commented on the lack of communication.)
You:
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Because you still have this universe consisting of 'observers', although you now made each one a 'creator' of their own unique universe, as all observations still must differ if compared, if you see my drift there?Me:
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SR theory made each "observer" a "creator" of each frame-specific version of each resulting, as measured, unique universe.
My argument is exactly the opposite.... that the universe and all its objects are "as they were formed by the laws of physics," totally independent of differences in observation.
SR, not I, makes each observer "a creator of their own unique universe." "For observer A" Earth is nearly spherical, while "for observer B" Earth is nearly flattened. Is there a "real Earth" with an intrinsic shape of its own, as originally formed by gravity, or does each different observer (frame of reference) create his/its own unique version of Earth?
Do you understand "my drift" now? Are you willing to answer honestly?
Do you disagree with this, from 206:...
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The universe is filled with bodies which were formed by various laws. Gravity is the one which makes stars and planets form as nearly spherical. There is no philosophy involved in that. It is the physics of how cosmic dust and debris (ed: and gasses) (are) formed into planets and stars....If so, how, specifically?
Enter length contraction theory: "For a frame of reference" flying by at near 'c', such objects may appear very oblate, nothing close to spherical.
That does not change the law of physics (gravity) that made them spherical in the first place.
Ps; as I said to lightarrow above:
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Earth is a "real" solid physical planet. It doesn't change shape to accommodate all possible differences in how it might be observed/measured. So observing/measuring it "in a moving frame" does not make it flatten out into a very oblate spheroid, even though it my appear so distorted from a high speed frame. That is the source of your continuing confusion, and that of all SR theorists in this forum who agree with you. You fail to distinguish appearance (the image of the object) from the object itself. The elephant is not, in fact, shaped like a rope.... nor Earth like a pancake.
Post by: old guy on 04/10/2012 21:42:11
"So to invalidate it (edit: length contraction) one will have to redefine 'c' as a variable instead of a constant.
So are we then left with an impossible choice: To redefine 'c' as a variable or to redefine Earth's diameter as a variable?
How could the latter vary, given that Earth is in fact a solid, immutable (but for trivially) object?
This challenge has consistently been ignored and then the whole thread was moved to where the question will not be noticed.
Maybe the answer is in the difference between the image of an object, obviously conveyed by light, and the solid ("immutable") object itself. (The image could be distorted while the object stays the same.)
We can probably agree that the Earth's diameter does not physically change to 1000 miles under any circumstance... which makes it a serious question of "what changes?"
If this question is allowed in the Physics section, I will start a thread there on the question of what is variable in this case. If the question is still forbidden, this is not science. Please advise.
I am asking you, JP, to allow me to move this question back to the physics section for serious debate by physicists.
Suggested title:
"Does invariant 'c' require a variable Earth diameter?"
Post by: JP on 04/10/2012 22:40:49
If you use it to evangelize (push the same arguments you've been making and are making in this post that the earth must "really" be invariant), then given the number of warnings you've gotten, you may face a temporary or permanent ban.
Post by: yor_on on 04/10/2012 22:43:53
"No OG, this is philosophy, maybe 'philosophy of relativity' but nowhere near science. If you could suggest a experiment in where it could be proved that a length contraction doesn't exist, as defined relative some other frame of reference, then is would close in on science though.
Can you do that?"
Post by: old guy on 05/10/2012 18:36:11
Yes, you can start a new thread.This sounds like, if I started a new thread on the very specific question, "Does invariant 'c' require a variable Earth diameter?", it would automatically be locked and I would be banned. ... but, "Yes, you can." Thanks.
If you use it to evangelize (push the same arguments you've been making and are making in this post that the earth must "really" be invariant), then given the number of warnings you've gotten, you may face a temporary or permanent ban.
I would (still) settle for a straight answer right here in this thread to these questions, as above:
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So are we then left with an impossible choice: To redefine 'c' as a variable or to redefine Earth's diameter as a variable?This challenge has consistently been ignored. "For this frame" vs "for that frame" does not answer it. It only addresses how it might me observed and measured variously... which is not the question.
How could the latter vary, given that Earth is in fact a solid, immutable (but for trivially) object?
Science must not cop out and claim that what we know about Earth (its precise shape) varies with how we look at it. Physics tells us that a change in shape would require application of force, and length contraction theory does not claim to apply any forces.
If only these challenges were directly addressed, no new thread would be needed.
Same for my “suggested title” for a new thread in the Physics section.
So, JP, does Earth’s diameter as a solid object vary with how it is measured or not? If you insist that it would BE contracted if measured from a very high speed frame, how can physics account for such a shrinkage in a solid, rigid planet? This remains a very sincere and reasonable question requiring an explanation from physics besides “It would appear flattened from the extreme frame.” (No doubt it would.)
Also, my "probe," measured to be 10 meters long from Earth as it approached at .866 c,(edit) would not fit into a 10 meter shuttle bay sent to retrieve it. Its "contacted length" was 10 meters, but its actual length (what better adjective, I do not know) was 20 meters.
Why is this NOT a conclusive example proving my point? Traveling at .866 c (edit) did not change its length but only its apparent length. How is this wrong?
Ps; yor_on:
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If you could suggest a experiment in where it could be proved that a length contraction doesn't exist, as defined relative some other frame of reference, then is would close in on science though.
Can you do that?
My above thought experiment did just that. Since we can not travel at relativistic speeds... upon which "length contraction" depends,... such experimental "proof" (evidence, anyway) must depend on thought experiments, as do most "examples" of large scale length contraction from its advocates. Both "sides" are allowed such thought experiments. There is no way a 20 meter probe will fit in a 10 meter bay. What more proof could you ask for?
Post by: old guy on 06/10/2012 19:02:21
If so, how does physics explain the latter... or would it simply appear to vary from and extreme frame?
Post by: wolfekeeper on 07/10/2012 00:12:29
There is no way a 20 meter probe will fit in a 10 meter bay. What more proof could you ask for?Yes it will... and no it won't!
(Surprisingly, both are true!):
http://en.wikipedia.org/wiki/Ladder_paradox
Post by: butchmurray on 07/10/2012 03:36:56
The reason is that there better not be a relativistic difference in velocity – which would cause appreciable length contraction - as the probe enters the bay.
So with the relative velocities of the bay and probe near zero, there is no length contraction to consider.
Post by: old guy on 08/10/2012 21:59:07
You can not have it both ways. That is why I set it up as I did.There is no way a 20 meter probe will fit in a 10 meter bay. What more proof could you ask for?Yes it will... and no it won't!
(Surprisingly, both are true!):
http://en.wikipedia.org/wiki/Ladder_paradox
The probe *appeared to be* 10 meters long from Earth. Since it was approaching Earth at .866c, it was *measured to be* 10 meters, "length contracted" by 1/2 at that velocity. Of course, to retrieve any object in space, the shuttle must match velocities with the object... come alongside. Then the *actual length* of the probe was found to be 20 meters. So it simply will not fit. I have repeated this at least a dozen times. Do you get it yet?
Butchmurray:
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If the probe fits in the bay when they are both at relative rest, the probe will always fit in the bay.See above. It was measured to be 10 meters at a velocity relative to Earth which made it appear contracted to 10 meters. The "proof" that it would not fit is found when the shuttle enters the same frame as the probe. "Ooopse!" It is actually 20 meters long!
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The reason is that there better not be a relativistic difference in velocity – which would cause appreciable length contraction - as the probe enters the bay.It is as given for any retrieval project that the object and the retrieval craft must be traveling at the same velocity. I've repeated that at least a dozen times.
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So with the relative velocities of the bay and probe near zero, there is no length contraction to consider.
Right, but the question was, will it fit in our 10 meter bay? We better know the answer before we send out our shuttle to capture it. (No.)
The same holds true for Earth's diameter as measured from a fast fly-by.
Here is a quick review of that argument from two recent posts:
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So are we then left with an impossible choice: To redefine 'c' as a variable or to redefine Earth's diameter as a variable?Or in 214; here it is in a nutshell, but none of the length contraction experts here dare address the challenge:
How could the latter vary, given that Earth is in fact a solid, immutable (but for trivially) object?
This challenge has consistently been ignored. "For this frame" vs "for that frame" does not answer it. It only addresses how it might me observed and measured variously... which is not the question.
Science must not cop out and claim that what we know about Earth (its precise shape) varies with how we look at it. Physics tells us that a change in shape would require application of force, and length contraction theory does not claim to apply any forces.
Also:
If you insist that it would BE contracted if measured from a very high speed frame, how can physics account for such a shrinkage in a solid, rigid planet? This remains a very sincere and reasonable question requiring an explanation from physics besides “It would appear flattened from the extreme frame.” (No doubt it would.)
[quote]Does invariant 'c' require a variable Earth diameter?
If so, how does physics explain the latter... or would it simply appear to vary from an extreme frame? [/quote]
Post by: butchmurray on 09/10/2012 05:53:18
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So with the relative velocities of the bay and probe near zero, there is no length contraction to consider.
Right, but the question was, will it fit in our 10 meter bay? We better know the answer before we send out our shuttle to capture it. (No.)
Absolutely!
Exercise due diligence. You know its relative velocity. You know its measurements judged from your frame. Crunch the numbers. You will know if it will fit or not. NO PROBLEM.
Post by: old guy on 09/10/2012 18:27:30
"Absolutely!", what? The example clearly shows the difference between the probe's "contracted length" as measured from Earth and its *actual length* as measured from traveling right beside it, as required to retrieve it. Its velocity relative to Earth is .866 c. That makes it *appear to be* 10 meters long. My point, over and over, is that its *apparent, "contracted" length* is only half of its *actual length*, and the proof of this difference is that it is twice as long as our cargo bay.QuoteQuote
So with the relative velocities of the bay and probe near zero, there is no length contraction to consider.
Right, but the question was, will it fit in our 10 meter bay? We better know the answer before we send out our shuttle to capture it. (No.)
Absolutely!
Exercise due diligence. You know its relative velocity. You know its measurements judged from your frame. Crunch the numbers. You will know if it will fit or not. NO PROBLEM.
It was not "really, actually" 10 meters after all but 20. No way! The proof that its "contracted length" is half of its "actual length."
The length contraction "experts" here refuse to acknowledge that "length contraction" is only an "appearance" due to observing it approaching at high speed, whereas is "actual length" remains twice as long.
OK?
What is your answer to the question no one here will touch (for good reason... to avoid making an absolutely absurd claim):
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Does invariant 'c' require a variable Earth diameter?My answer: Yes, it would only appear contracted from the extreme frame. Earth does not change diameters, "actually."
(Edit: The claim is that " because 'c' is invariant, length is not invariant.")
If so, (ed: if Earth's diameter changes) how does physics explain the latter... or would it simply appear to vary from an extreme frame?
Post by: butchmurray on 11/10/2012 13:43:14
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You can not have it both ways. That is why I set it up as I did.
The probe *appeared to be* 10 meters long from Earth. Since it was approaching Earth at .866c, it was *measured to be* 10 meters, "length contracted" by 1/2 at that velocity. Of course, to retrieve any object in space, the shuttle must match velocities with the object... come alongside. Then the *actual length* of the probe was found to be 20 meters. So it simply will not fit. I have repeated this at least a dozen times. Do you get it yet?
I think I understand now.
The shuttle bay can accommodate a 10m probe.
The relative velocity of the probe is .866c.
At relative velocity .866c, the probe is 10m judged from relative rest.
If you know the relative velocity is .866c and you know the length is 10m judged from relative rest, then you know the “at rest” or “proper” length is 20m. You also know the probe will not fit in the 10m cargo bay of the shuttle because when the shuttle’s relative velocity is also .866c the cargo bay will only accommodate a 5m probe judged from relative rest.
In other words your measurements for BOTH the probe and the shuttle bay must be either “rest” length OR contracted length because they will be in the same frame (the same relative velocity or difference in velocity close to zero) as the probe is recovered.
Post by: old guy on 11/10/2012 18:24:34
Finally... someone 'gets it!' Thank you for paying attention to the example *as I presented it.*
If length contraction advocates did not insist that "proper" length and "contracted" length were equally valid (all frames being equal) the whole example would be very simple.
We recognize the difference between "contracted length" as mere appearance due to observing something traveling at high velocity relative to the observer and the *actual length* of something as it was either naturally formed (Earth's diameter does not change) or, in this case, built... its "proper length" as measured in its own frame.
So we see a probe approaching Earth at .866c, plug in the formula, and know immediately that it is *actually* 20 meters long. We will not send out a 10 meter cargo bay to retrieve it, because it is not *really* 10 meters long.
It is really very simple when the dogma of "all frames are equal" is removed.
Just one clarification... you said:
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You also know the probe will not fit in the 10m cargo bay of the shuttle because when the shuttle’s relative velocity is also .866c the cargo bay will only accommodate a 5m probe judged from relative rest.
As seen from Earth, the shuttle, now traveling with the probe, will *appear to have* a bay 5 meters long, "contracted" to half its actual length, as the probe also appears. The shuttle bay did not shrink. It was 10 meters on Earth and remains 10 meters as it approaches with the probe. Just because it now "looks" 5 meters long from Earth did not make it shrink to half its length.
This is an extremely persistent misconception among those advocating length contraction.
Post by: butchmurray on 11/10/2012 20:18:01
The way I reconciled it was, “It ‘is’ when judged from relative rest”.
Here is something else to ponder:
Suppose inside of the probe there is a constant light projected from one end to the other end of the probe in the direction of motion. What is the difference in that light when judged from the shuttle, which is moving at the same relative velocity as the probe (.866c) and when judged from relative rest?
Post by: old guy on 11/10/2012 21:46:48
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I truly understand your misgivings about “is” and “appears to be”.
I think it would bring much needed clarity to the SR conversation if everyone understood the difference and did not insist that Is = Appears to Be.
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The way I reconciled it was, “It ‘is’ when judged from relative rest”.
I agree. Scientists must "put it under a microscope" or at least be at rest (same frame) with 'it' to study and measure 'it' accurately.
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Here is something else to ponder:
Suppose inside of the probe there is a constant light projected from one end to the other end of the probe in the direction of motion. What is the difference in that light when judged from the shuttle, which is moving at the same relative velocity as the probe (.866c) and when judged from relative rest?
Yes, I've pondered that a lot over the years.
Seems as if it makes no difference whether the light source or the observer(s) or whatever frames of reference are moving or how fast. They all observe light to travel at the constant speed 'c.' I can't argue with that. The experiments are very conclusive.
My concern is that what is "observed" is an image reflected or projected from an object or light source, not the object itself. So there could be an appearance of contraction due to the medium of light itself as carrier of the image. I don't pretend to know the specifics of how that all that might work. I just know that the image is not the object, and light carries the image.
Btw, thanks for understanding my "probe" example.
Post by: old guy on 13/10/2012 18:46:54
I also know that a possible image of a flattened Earth (say with a 1000 mile diameter in the direction of an observer's very high speed travel) would/could only be an appearence, an image of a flattened Earth. We all know that Earth's diameter is not, has never been and will never be 1000 miles.
I can not get the "SR experts" here to address this challenge. Since you, butchmurray, win the prize for understanding my probe illustration of "actual vs apparent" length, maybe you would give the shrunken Earth diameter challenge a shot too.
Ps; btw, we are now even on number of posts at 112. Here is your chance to move ahead!
Post by: butchmurray on 15/10/2012 16:17:12
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I can not get the "SR experts" here to address this challenge.
Please restate exactly what the “challenge” is.
Thanks,
Butch
Post by: old guy on 15/10/2012 18:53:45
As in my last post... The "challenge" now bolded:QuoteI can not get the "SR experts" here to address this challenge.
Please restate exactly what the “challenge” is.
Thanks,
Butch
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Regarding this from yesterday: "I just know that the image is not the object"...SR experts have the image and the object as the same, claiming that how it appears is how it is. You seemed to know what I meant earlier. The challenge for SR is to recognize and distinguish the difference. The "all frames are equal" dictum grants equal validity to a shrunken Earth diameter, as I said here:
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I also know that a possible image of a flattened Earth (say with a 1000 mile diameter in the direction of an observer's very high speed travel) would/could only be an appearence, an image of a flattened Earth. We all know that Earth's diameter is not, has never been and will never be 1000 miles.
My challenge to the SR experts is to admit/clarify that Earth's diameter does not change even if it appeared to becontracted to 1000 miles, as above.
Same with the probe example, which you seemed to understand. The shuttle's 10 meter bay would appear to be (from Earth) contracted to 5 meters long as it approaced earth with (same frame as) the probe. But it did not magically shrink after it left Earth to retrieve the probe. Same for the probe, appearing to be 10 meters long from earth, but actually being 20 meters long, as it is, in "reality," in its own frame.
I hope this clarifies the challenge.
Again, I hope you will give "the shrunken Earth diameter challenge a shot too."
Thanks.
Post by: old guy on 16/10/2012 01:23:01
The thing is that the theory of length contraction depends on the concept of 4-D "spacetime", which in turn depends on non-Euclidean geometry and cosmology.
So first, to "get to the bottom of it" we must ask what space is and what time is and what the coalescence of the two into one is supposed to be.
The point of departure for non-Euclidean geometry is the denial of Euclid's fifth postulate, i.e., the assertion that parallel lines do indeed intersect. Who here agrees with that? Please explain. Also, how is that the shortest distance between two points is no longer a straight line?
I know that it all depends on the concept of curved space. There are at least three choices of what shapes space is curved into, but nobody bothers to explain how 3-D volume (space) became a malleable medium, an entity rather than the void in which all things exist and move.
So we have a curved surface (of what?... empty volume?) on which the shortest line between two points *on that surface* is a curved line. But the shortest distance is still straight through, not "on the surface." And parallel lines finally intersect "in infinity" by the magic of math. Never mind that if they intersect, they are no longer parallel.
So... back to length contraction. It is said that "... as you approach the speed of light, you're increasingly looking at the four-dimensional fabric of space and time "edge-on", causing space and time to mix." (Citation available but not handy.)
So two non-entiies "mix" and that makes objects contract. Its too bad that ontology is not allowed in the physics section, being as it is mere philosophy, but it would certainly help to sort out all of the above and maybe even help to clarify how Earth's diameter gets relativistically contracted... and how thaqt might differ from the planet actually getting squished.
Open for deiscussion... if anyone cares. This is an honest inquiry, folks. Is that not the essence of science?
Post by: butchmurray on 16/10/2012 04:46:06
There are 4 ships. All of these measurements occur at roughly the same time on earth.
For 2 bodies with one in motion in relationship to the other, either one can be considered to be at relative rest compared to the other. For these examples the ships will be considered to be at relative rest.
One is on earth so the velocity of that ship relative to earth is zero.
The velocity of one ship in flight is .436c relative to earth.
The velocity of another ship in flight is .866c relative to earth.
The velocity of yet another ship in flight is .977c relative to earth.
The relative velocity of earth for the ship on earth is zero. The diameter of the earth in the direction of impending motion IS 100% of its “proper” or “at rest” judged from the ship at relative rest.
For the ship in flight at .436c relative to earth, the diameter of the earth in the direction of motion IS 90% of its “proper” or “at rest” diameter judged from that ship at relative rest.
For the ship in flight at .866c relative to earth, the diameter of the earth in the direction of motion IS 50% of its “proper” or “at rest” diameter judged from that ship at relative rest.
For the ship in flight at .977c relative to earth, the diameter of the earth in the direction of motion IS 20% of its “proper” or “at rest” diameter judged from that ship at relative rest.
It is obvious that the diameter of the earth cannot have all these values at the same time. The fact of the matter is that those diameters ARE the diameters JUDGED FROM REST for those various relative velocities. It is not that the earth appears to have those diameters, those are the ACTUAL diameters JUDGED from those rest frames.
The rest frame can be reversed, with the earth at relative rest, for all of the examples. In that case it is the length of the ships in the direction of motion that is contracted by the corresponding amount and not the diameter of the earth.
Thank you for the vote of confidence.
Butch
I generally like to “sleep on” whatever I post but I didn’t want to keep you waiting unnecessarily.
Post by: old guy on 16/10/2012 19:27:47
A thousand different ships fly by Earth in 1000 different directions at 1000 different relativistic velocities. They all measure the diameter differently in all different directions.
You are correct to say,
"It is obvious that the diameter of the earth cannot have all these values at the same time. " But then you say, "The fact of the matter is that those diameters ARE the diameters JUDGED FROM REST for those various relative velocities. It is not that the earth appears to have those diameters, those are the ACTUAL diameters JUDGED from those rest frames.
Forget for a moment about the "as judged from" relativistic psuedo-reality depending on how observer A sees it vs how observer B sees it vs how all the other 998 observers see it.
EARTH DOES NOT CHANGE DIAMETERS. It is a relatively solid planet. Do you understand that? Do you agree?
You seemed to agree earlier that there is a difference between "IS" and "APPEARS TO BE." Must I now revoke my "vote of confidence?"
The "ACTUAL" diameter of Earth is nearly 8000 miles... a little shorter through the poles than through the equator. Earth science KNOWS this very precisely from measurements taken at rest with Earth... which is the "preferred frame" for accurate measurements of anything, as we discussed earlier.
Do you also think that the aforementioned cargo bay magically shrinks from its 10 meters at launch from Earth to the 5 meters it APPEARS TO BE as it approaches Earth at .866 c in the frame with the probe (as required to capture it?)
I would certainly appreciate a straightforward answer. Thanks.
Ps: Any comments, anyone, on my post 227 above... say on "intersecting" parallel lines or on how a curved line is now imagined to be be the shortest distance between two points... or how 3-D volume became a malleable medium... other than in imatinative minds?
Post by: butchmurray on 16/10/2012 21:07:08
If you are on any of those ships, the “judged from” diameter is what you will see.
Post by: old guy on 16/10/2012 22:05:09
Look at it this way:I see that you are still missing the whole point of this thread.
If you are on any of those ships, the “judged from” diameter is what you will see.
The point is that EARTH DOES NOT CHANGE SHAPE.
So, even if a fast flying observer SAW an Earth with, say a 1000 mile diameter, that would not make its ACTUAL diameter 1000 miles. It remains always nearly 8000 miles, and its shape remains nearly spherical, not extremely flattened.
Will you acknowledge this fact?
You said, "It is not that the earth appears to have those diameters, those are the ACTUAL diameters JUDGED from those rest frames." "Judged from" different frames does not make the actual diameter change. Do you see that?
Do you not, after all, know the difference between "IS" and "APPEARS TO BE?"... the difference between "ACTUAL" length and a contracted APPEARENCE due to high speed... the difference between an IMAGE of an object conveyed by light and the OBJECT ITSELF?
Did the cargo bay "ACTUALLY" shrink from its 10 meters as constructed and as launched to 5 meters AS OBSERVED approaching with the probe at .866 c?
Please explain.
Ps, I said:
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Forget for a moment about the "as judged from" relativistic psuedo-reality depending on how observer A sees it vs how observer B sees it vs how all the other 998 observers see it.Do you think that different observations create different shaped objects, that observation dictates reality... that objects have no intrinsic reality of their own?
EARTH DOES NOT CHANGE DIAMETERS. It is a relatively solid planet. Do you understand that? Do you agree?
Post by: butchmurray on 16/10/2012 23:34:52
A rocket takes off.
It finally disappears.
Does it really disappear? If you are on the ground, yes, of course it does.
Does it really disappear? If you are in the rocket, no, of course it doesn't.
It’s largely semantics. Don’t give yourself a headache!
May I have my “vote of confidence” back, PLEASE?
I have already told everyone!
Thanks,
Butch
Post by: old guy on 17/10/2012 00:05:09
You refuse to engage in conversation with me after several attempts on my part. The whole point of this thread is that different observations/measurements do not create different lengths or shapes of the objects/distances observed, as length contraction claims.
Last question of my last post as a case in point:
"Do you think that different observations create different shaped objects, that observation dictates reality... that objects have no intrinsic reality of their own?"
Of course when someting disappears from the sight of one observer it doesn't cease to exist.
How about answering even one of my length contraction challenges?
Does the cargo bay change from 10 meters to 5 meters after it enters the frame at rest with the probe? (Does it "actually" shrink to half its length-as-built-and-launched?)
Does Earth change shape/diameter when it is observed to contract from relativistic frames.
Do "things" have intrinsic shapes/lengths of their own, as formed by gravity (like Earth) or as built (like the probe and shuttle?)... or does observation make things change shape/length.
JP stuck this thread here to avoid scrutiny of these challenges, I must presume. Now you are doing the same dance of avoidance.
Please answer the above questions, and I will restore my vote of confidence in you, as if you really cared!
I do care. The issue is not semantics. It is the very core of "length contraction."
If a solid planet does get squished or a rigid craft get shrunken, what laws of physics, what forces cause the physical changes?
Seriously.
Post by: JP on 17/10/2012 02:14:53
JP stuck this thread here to avoid scrutiny of these challenges, I must presume. Now you are doing the same dance of avoidance.
Actually, I've explained several times why I moved this thread here. If you'd like to us it keep making accusations about us censoring you, I'd be happy to lock the thread, though. :)
Please keep it a discussion, not a complaint thread.
Post by: bizerl on 18/10/2012 05:59:11
Why should space be any different? It is just as intangible as time when you consider what length actually is. You've asked me to make definitions of abstract concepts in another thread, and I put it to you to define "length".
If time can slow down for someone on a spaceship travelling at .866c, yet remain constant for the "stationary" observer on Earth, I think that's incredible and goes against the logic that has been ingrained in our human psyche that time is constant. Yet if it is true, it follows that anything that we once held to be "solid", may in fact be as fluid as time.
I've always thought that the diameter of the Earth remains at 8000kms, it's just that 8000kms becomes 1000kms long when you are travelling at speed.
But that's just more semantics I'm afraid. [:P]
Post by: bizerl on 18/10/2012 06:17:56
Therefore, the Earth gets squashed for the traveller - including the atmosphere etc, but the humans on the Earth also get squashed so they don't notice.
They move at double the speed as well...
I think...
Post by: butchmurray on 18/10/2012 15:14:55
The 4-year-old girl said, “I can’t wait to go into the sky so we can be small.”
A passenger jet is at the terminal.
An identical jet is 30,000 ft. above.
Which one is larger?
Are the jets the same size? Yes.
When you are at the terminal is the jet at the terminal larger? Yes.
When you are in the jet at 30,000 ft. is the jet you are in larger? Yes.
Post by: old guy on 18/10/2012 19:38:06
"Philosophical realism is the belief that reality exists independently of observers."
Is anyone here besides me a realist? Does anyone else here 'real-ize' that the "real" Earth stays the same shape (has the same diameter(s) independently of how it is observed?
Does anyone else 'real-ize' that a shuttle cargo bay built 10 meters long wouls stay that length even if it were possible to observe it approaching Earth at .866 c, then appearing to be 5 meters long... alongside a 20 meter alien probe which appears to be 10 meters long from Earth? (Practical test of length contraction: The probe, appearing 10 meters long from Earth will not fit into a 10 meter bay sent to capture it.)
Does anyone here 'real-ize' that the distance between stars as they are formed and distributed in space (by the laws of phyics, including gravity) would not get shorter (stars would not move closer together) if it were possible for intersteller observers to travel near 'c' between them?
(Note: I did not say "would not appear shorter" but "would not get shorter".)
Again, would stars actually move closer to each other if so obseved by high speed travelers? What amazing power that would grant to mere observation!!
Does anyone here get my point, the whole point of this thread?
Post by: old guy on 18/10/2012 19:57:34
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Old guy, You don't seem to question the impact of time dilation and the well known idea that time passes differently for observers based on how close to c they are travelling.
I've said this quite a few times already, so it would indeed be helpful if you had read the thread.
Empirically we observe that clocks "tick" more slowly at higher velocities (and "deeper in a gravity well.") Time is the concept of the duration of physical processes, that which elapses as things move. That does not make it an entity which "slows down."
A clock on a future high speed spacecraft traveling to Alpha Centauri (4.37 light years away) will show much less elapsed time than those on Earth. But Earth will have orbited the Sun many more than 4+ times during the journey. More than four years will have passed, as a year remains a standardized Earth orbit of the Sun. The craft has mass, so it can not travel at 'c', therefore it will take more than 4.37 years for the craft to reach AC. Relativity has not changed that fact. Saying that "for the spacecraft less that four years have passed" does not alter fact that more than four years would have passed by the standard reckoning of what "a year" means. It wouldn't make Earth move closer to AC either.
Post by: bizerl on 19/10/2012 06:00:54
It got me thinking about a lot of things. Firstly, if a ship is coming directly towards Earth, how can we measure it's length? - but that's a side issue.
If two ships were coming towards Earth in tandem at .866c, both lengths would appear contracted from Earth. If a tether was placed between them, the tether would also appear contracted. If the tether was then taken away, the distance between the ships would still be the contracted distance.
This makes me think that the length contraction has nothing to do with the physical properties of what is travelling, but of space itself. The only way I can see it working is if, like time, space is actually distorting in the direction of travel.
Because it is space distorting and not any physical matter, whatever exists in that space also distorts.
If someone was travelling at .866c towards Earth, they would see a flattened disc facing them. Now the Earth rotates, but the rotation would follow only the surface of the Earth, the "disc" would never actually be edge on to anyone observing it.
I think that to address some recurring questions you've had, old guy, an intrinsic measure of the properties of the Earth is possible, only if stated as a function of relative speed. For instance you can say that the instrinsic diameter of the Earth is 8000km0c which is equal to 4000km0.866c etc.
I don't see why it can't be "real" for space and therefore length to distort when one is travelling at speed, and therefore "real" that the Earth is 8000 x 4000km if you're travelling towards it at .866c.
In regards to
Quote
EARTH DOES NOT CHANGE DIAMETERS. It is a relatively solid planet.
What is solid? "Solid" is made of sub-atomic particles. Lots of them in the case of the Earth. They exist in "space". Three dimensions of it (that we know of so far...[:D]) and time. If "length" is defined as the shortest amount of space that separates two points (I don't know if it IS defined as that, but I don't know how else to define it) then if space is contracted relativisticly, it is "real" that "length" should "contract" too.
Post by: old guy on 21/10/2012 21:08:15
So... no comment on realism, top of post 248 or "time" in post 249 or what space is, if anything besides 3-D volume, the void in which things and forces exist and move,i.e., NOT a malleable medium.
You simply assume that reality changes as it is differently observed, including that Earth changes shape as seen from a fast fly-by and that Earth moves closer to Alpha Centauri, as reckoned by a ship with a slowed down clock.
Neat trick, moving stars and panets closer to each other and changing their shapes/diameters simply by the magical power of observation/measurement.
So objects have no intrinsic properties of their own, huh? It all depends on how you look at them? No "reality" per se. Each observer creates his own unique reality.
Does the falling tree make no sound if it is not heard? Idealists say sound doesn't exist unless it is heard. What do you say?
At this point, you are not responding to what I am posting... not a conversation.
Post by: bizerl on 21/10/2012 22:20:43
bizerl,
So... no comment on realism, top of post 248 or "time" in post 249 or what space is, if anything besides 3-D volume, the void in which things and forces exist and move,i.e., NOT a malleable medium.
Sorry OG, I must be seeing a different thread to you. As far as I can see, this reply is only 242, so not sure what aspects of these you'd like a reply to.
You simply assume that reality changes as it is differently observed, including that Earth changes shape as seen from a fast fly-by and that Earth moves closer to Alpha Centauri, as reckoned by a ship with a slowed down clock.
Yes, I'm afraid I do, as I pointed out in a previous post. I don't have the luxury of understanding all the nitty gritty details of relativity but I do believe that it has been extensively tested and has not yet been adequately disproven. Length contraction is an integral part of this theory and since the theory seems so well fitted to all our (I say "our", I mean scientists) observations, it stands to logical reason that length contraction is true too.
I find it interesting that you "assume" that length contraction doesn't exist on large scales and I'm yet to hear a convincing argument in your favour, other than "the Earth is solid". You've stated previously that
Quote
The "ACTUAL" diameter of Earth is nearly 8000 miles... a little shorter through the poles than through the equator. Earth science KNOWS this very precisely from measurements taken at rest with Earth... which is the "preferred frame" for accurate measurements of anything, as we discussed earlier.
Earth science also KNOWS that this value changes depending on how fast you are travelling, relative to the Earth.
Neat trick, moving stars and panets closer to each other and changing their shapes/diameters simply by the magical power of observation/measurement.
The world is an incredible place. A great many things that are common knowledge would have been ridiculed as "magic" in more ignorant times.
So objects have no intrinsic properties of their own, huh? It all depends on how you look at them? No "reality" per se. Each observer creates his own unique reality.
Does the falling tree make no sound if it is not heard? Idealists say sound doesn't exist unless it is heard. What do you say?
Yes, everything has intrinsic properties of their own. The properties are governed by strict laws of physics. A 10m (at rest) cargo bay will always be 5m long when travelling at .866c. That is an intrinsic property.
Your definition (or rather, wiki's definition) of realism - "Philosophical realism is the belief that reality exists independently of observers." is not one I follow. It is a philosophical viewpoint that does not have any grounding in science. It conveniently contains "reality" in it's definition which leaves everything open to interpretation.
Unfortunately (for some), science has shown that in fact, what we experience as "reality", changes depending on how it is observed.
At this point, you are not responding to what I am posting... not a conversation.
I am stating my viewpoint. I apologise if you feel I am not trying to address your queries.
Post by: bizerl on 22/10/2012 05:40:38
Quote from: http://en.wikipedia.org/wiki/Scientific_realism
Scientific realism is, at the most general level, the view that the world described by science (perhaps ideal science) is the real world.
Post by: old guy on 22/10/2012 22:32:37
" So... no comment on realism, top of post 248 or "time" in post 249 or what space is, if anything besides 3-D volume, the void in which things and forces exist and move,i.e., NOT a malleable medium."
You:
"Sorry OG, I must be seeing a different thread to you. As far as I can see, this reply is only 242, so not sure what aspects of these you'd like a reply to."
Sorry. I meant post 238, quoting Wiki:
"Philosophical realism is the belief that reality exists independently of observers."
If you don't think there is a "real world/cosmos" with real things in it with intrinsic properties of their own and distances between things determined by how they were distributed in space when they were formed... independent how they are observed....
And that Earth's diameter varies between 1000 and nearly 8000 miles...
And that Earth/Sun moves a lot closer to Alpha Centauri if a fast ship so observes...
And that, likewise Earth moves much closer to the Sun (ditto above)... without getting incinerated...
Then you live in a length contraction fantasy world where variations in observation cause variations in physical objects and distances between them.... where each observer creates his own unique "reality."
The job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
The above is subjective idealism, not objective science.
There were quite a few questions/challenges left unanswered, (time and space assumptions, sound with no one to hear it... but if you believe that an Earth with a 1000 mile diameter is an accurate description of it we have nothing left to say. A squished Earth is fiction, not science. Observation does not alter physical things or distances between them.
Post by: old guy on 24/10/2012 20:55:53
Maybe you haven't had time to reply... or maybe it's that we have nothing left to say, as in,
... "but if you believe that an Earth with a 1000 mile diameter is an accurate description of it we have nothing left to say. A squished Earth is fiction, not science. Observation does not alter physical things or distances between them."
Do you really believe that Earth's diameter changes drastically with how it is observed?... no "real world" at all?
Post by: old guy on 25/10/2012 19:02:36
So I ask the forum (whomever might be still be reading this thread), do you agree with the following, a recent summary statement I made here:
Quote
The job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
This will be my last attempt to communicate in this thread if no one cares about the above enough to answer.
Thanks.
Post by: bizerl on 26/10/2012 01:17:31
OK, so bizerl and the team of length contraction "experts" here insist that an Earth with a 1000 mile diameter is just as valid a description as the well validated nearly 8000 mile diameter. Please correct me if I am wrong.
I can't speak for length contraction "experts" as I am not one of them, but yes. I believe that both measurements are equally valid depending on the observers velocity relative to the Earth. I believe this because it is an integral part of a theory that is continually tested and proven, and furthermore, has been continually contested and has thus far failed to be disproven. I am willing to change my belief if the observed and/or experimental evidence says otherwise.
Quote
So I ask the forum (whomever might be still be reading this thread), do you agree with the following, a recent summary statement I made here:QuoteThe job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
This will be my last attempt to communicate in this thread if no one cares about the above enough to answer.
Thanks.
I don't agree with this statement. In my view, the job of science is to understand how the world works through observation and experimentation, and to come up with theories and models that reflect those observations, regardless of how counter-intuitive their implications may seem.
The fact is that all the observational and experimental evidence that has been gathered so far, indirectly supports the fact that if a 20m spaceship flies through a 10m bay at 0.866c, it will (very briefly) fit exactly inside that bay.
Also, all the observational and experimental evidence that has been gathered so far, has failed to disprove that this is the case.
I wish you well on your journey to obtain observational and/or experimental evidence which dis-proves length contraction. It will surely be a guaranteed ticket to Stockholm.
Post by: old guy on 26/10/2012 21:10:53
Thank you for your reply. I asked if an Earth with a 1000 mile diameter was equally valid with the Earth science measure of nearly 8000 miles. You said, "yes." Please explain by what law of physics the nearly spherical Earth gets squished to nearly flattened, or in lieu of that, how the physical "world" changes by virtue of different observations, or is it just the observations which change?
Do you know of any empirical observations confirming large scale length contraction? I know that, so far, no one has ever observed Earth's diameter to shrink, yet you insist that it does or would "for" a relativistic fly-by frame. Do you see any difference between "Earth as it is" and "Earth as seen from" such a fly-by? Would it change into 1000 diferent shapes if observed from 1000 different frames, do you think?
I said:
Quote
The job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
You replied:
Quote
I don't agree with this statement. In my view, the job of science is to understand how the world works through observation and experimentation, and to come up with theories and models that reflect those observations, regardless of how counter-intuitive their implications may seem.
Do you disagree that it is the job of science is to study and accurately describe things as they are?
Do you think that it is the legitimate task of science to re-create "the world" (whatever is being measured) as subjective versions of an infinite number of "realities" depending on who is measuring whatever from all varieties of different frames of reference?
You said:
Quote
The fact is that all the observational and experimental evidence that has been gathered so far, indirectly supports the fact that if a 20m spaceship flies through a 10m bay at 0.866c, it will (very briefly) fit exactly inside that bay.You, like almost everyone here misunderstood and/or misrepresented my "alien probe retrieval project." There was no ship (the probe) "flying through" the 10 meter bay of the shuttle. In order to retrieve the probe, the shuttle would by necessity need to match the probe's velocity (come to rest with the probe's frame.) The probe was measured from earth to be 10 meters as it approaced earth at .866c. However, as the shuttle pulled alongside the probe, it was then measured to be 20 meters long, so it would not fit in the 10 meter bay, which did not change after launch.
This was offered as a thought experiment (that's all we have to work with regarding lenght contraction on this scale) demonstrating that the "length contracted probe" as seen from earth was not *actually* contracted to 10 meters. Nor would the shuttle bay have *actually* contracted to 5 meters, as it would be measured from earth when traveling with the probe.
I hope you will reply to all of the above before quitting the thread.
Post by: old guy on 29/10/2012 19:16:21
So I ask the forum (whomever might be still be reading this thread), do you agree with the following, a recent summary statement I made here:
Quote
The job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.... as length contraction theory does.
Post by: David Cooper on 29/10/2012 20:58:28
So I ask the forum (whomever might be still be reading this thread), do you agree with the following, a recent summary statement I made here:QuoteThe job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.... as length contraction theory does.
Length contraction theory does not require that. There are two main theories which include length contraction and neither of them requires reality to change in the way you describe. LET (Lorentzian universe) provides for fixed absolute truths in terms of the shapes of things, but provides no means to calculate what those absolute truths are because the preferred frame cannot be identified. SR is a very different approach, but it too can accommodate people who want absolute truths about the shapes of things, so you can easily regard the frame in which an object as stationary as being the one which shows its true shape. Many of the adherents to SR appear to believe that veiwing things from different frames of reference does change their shape though, and however surprising that may be to us, it isn't a requirement of SR that you believe what they do.
I'd be interested to know where you are with this now and whether you feel you've gained anything from it. Have you accommodated length-contraction into your own theory of how things really are, and if so, have you managed to find a way to do so other than LET and SR? So far, you've shown us a model of reality in which you can send light faster than the speed of light simply by switching frames, and that's a broken model. There's no point in going on pushing it unless you can find a way to fix that flaw.
Post by: old guy on 30/10/2012 19:54:46
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SR is a very different approach, but it too can accommodate people who want absolute truths about the shapes of things, so you can easily regard the frame in which an object as stationary as being the one which shows its true shape. Many of the adherents to SR appear to believe that veiwing things from different frames of reference does change their shape though, and however surprising that may be to us, it isn't a requirement of SR that you believe what they do.
I do not not use the phrase or subscribe to the concept of "absolute truths about the shapes of things." I am a realist, and as such reality does not shift with how things are observed/measured. Physical objects have intrinsic properties (like Earth's well known and precisely measured diameter) and the distance between objects, like between Earth and Sun does not contract, as it might be observed to do from the extreme frames discussed. These bodies were formed by gravity, a natural law of physics, and distributed in space by the same natural law. Nothing about that has anything to do with your quoted phrase above.
"Many of the adherents to SR appear to believe that veiwing things from different frames of reference does change their shape though..."
It is to them (and they are many... and they run the show here) that I address my argument.
Regarding your assertions:
Quote
So far, you've shown us a model of reality in which you can send light faster than the speed of light simply by switching frames, and that's a broken model. There's no point in going on pushing it unless you can find a way to fix that flaw.I have answered this false assertion many times. Realism is not concerned with switching frames of reference, as is the main criterion for "reality" or "the shape of things" or "the distance between things" in SR. See above, yet again, on the natural, intrinsic shape of things and their natual distribution in space, i.e., the naturally occuring distances between them... which does not change with how they are observed, as length contraction insists based on relativity's version of idealism.
The speed of light is constant. Light carries the images of things observed. These images vary as seen from different frames of reference. This does not mean that the physical objects themselves vary. That is where length contraction theory is confused. My intent for this thread has always been and continues to be to correct this confusion of images observed with those objects emitting or reflecting those observed images.
The MM experiment you have been discussing in another thread for instance has two arms of equal length, as the apparatus was built. An observer at rest with the apparatus sees them as they are, equal in length. Another observer, not at rest with it, sees one arm contracted in the direction of relative motion. No argument... He would see one arm as shorter. But that is just the image distorted by his velocity relative to the object. A rigid object would require a force to squeeze or compact it into a shorter length than it was built. Lenght contraction theorists totlally ignore this fact, as they do not claim that any force is involved. But they also deny that physical objects have the intrinsic property of length, as manufactured or naturally formed, as above.
Here it is again in a nutshell... anyone...:
Quote
The job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
Post by: David Cooper on 31/10/2012 21:16:23
"Many of the adherents to SR appear to believe that veiwing things from different frames of reference does change their shape though..."
It is to them (and they are many... and they run the show here) that I address my argument.
That difference in opinion has been well established now and it doesn't look as if it will change - there's little to be gained by continuing to try to push them to change their mind. It also has no impact on what they use SR for.
Quote
Regarding your assertions:QuoteSo far, you've shown us a model of reality in which you can send light faster than the speed of light simply by switching frames, and that's a broken model. There's no point in going on pushing it unless you can find a way to fix that flaw.I have answered this false assertion many times.
It isn't false, unless you've incorporated length-contraction into your model, in which case I'd like to know how you've done that without it turning into either SR or LET. If you have turned it into SR and your only point of difference is with those people who think that observing things from different frames physically changes their shape, then I can't see why the discussion didn't end long ago.
Quote
Realism is not concerned with switching frames of reference, as is the main criterion for "reality" or "the shape of things" or "the distance between things" in SR. See above, yet again, on the natural, intrinsic shape of things and their natual distribution in space, i.e., the naturally occuring distances between them... which does not change with how they are observed, as length contraction insists based on relativity's version of idealism.
The trouble with that is that we have two big theories which both conflict with that. One theory (SR) has as part of its dogma the idea that all frames are equal, and that means that whatever distances are measured in any frame are as true as the distances measured in any other. If that dogma was removed (which could be done without destroying the important core of SR), then the solution becomes the same as the one in LET where there is a correct, hidden truth about any distance, but you can't tell what it is. Your intrinsic distances don't take into account the contractions that may actually be applied to them, unless you take the trouble to declare clearly that they are subject to contractions which can't be determined.
Quote
The speed of light is constant. Light carries the images of things observed. These images vary as seen from different frames of reference. This does not mean that the physical objects themselves vary. That is where length contraction theory is confused. My intent for this thread has always been and continues to be to correct this confusion of images observed with those objects emitting or reflecting those observed images.
With SR, the unnecessary dogma that Einstein tied up in it requires multiple conflicting ideas to be true at the same time. A version of SR with that dogma removed can eliminate the problem. LET likewise contains no confusion. If you don't fit into any of those camps, I'd be interested to know where it is that your position diverges from the one you're closest to. I get the impression that you actually fit into a mainstream camp and don't realise it yet - all you need to do is recognise the vital role of length contraction.
Quote
The MM experiment you have been discussing in another thread for instance has two arms of equal length, as the apparatus was built. An observer at rest with the apparatus sees them as they are, equal in length. Another observer, not at rest with it, sees one arm contracted in the direction of relative motion. No argument... He would see one arm as shorter. But that is just the image distorted by his velocity relative to the object.
That is not the case, as demonstrated by the thought experiment involving a train and a platform where a beam of light is split and sent both along the platform and through the train. Either the train or the platform must be length-contracted for you to get correct results out of the experiment.
Quote
A rigid object would require a force to squeeze or compact it into a shorter length than it was built. Lenght contraction theorists totlally ignore this fact, as they do not claim that any force is involved. But they also deny that physical objects have the intrinsic property of length, as manufactured or naturally formed, as above.
In LET, no force is required beyond the ones which are already acting to generate and maintain separations between particles. In SR, no force is required either, so you're really just attacking some people in the SR camp again over their belief that observing things from different angles physically changes those things.
Quote
Here it is again in a nutshell... anyone...:QuoteThe job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
And here is the same attack on those people again in another guise. I agree with you that things aren't physically changed in shape by looking at them from different angles, and everyone's noted your objection to the belief that they do. I can't see any reason to keep repeating this objection as the point's been made dozens of times now and they simply aren't going to budge. What is much more important now is for you to find a position for yourself where the model you're pushing holds together properly, but that's either going to need length-contraction incorporated into it or some fiendishly clever alternative which no one's thought of yet.
Post by: old guy on 01/11/2012 20:16:44
Quote
The trouble with that is that we have two big theories which both conflict with that. One theory (SR) has as part of its dogma the idea that all frames are equal, and that means that whatever distances are measured in any frame are as true as the distances measured in any other.
"The trouble with that is"... That we have a "scientific theory", length contraction, claiming that, either science doesn't know (for instance) the true diameter of Earth, or that it varies from about 1000 miles, as measured from the old near 'c' fly-by, to nearly 8000 miles, as measured at rest with Earth.
Earth does not change diameters. Therefore the theory that its diameter contracts is false.
Any rigid physical object requires a force to compact it into a shorter length (or diameter.) No force is applied in any case of length contraction. Therefore any observed contraction is due to the image being distorted by observation from extreme velocities. Different observations do not make physical objects change shapes or lengths. Claiming that that do is false.
Quote
If that dogma was removed (which could be done without destroying the important core of SR), then the solution becomes the same as the one in LET where there is a correct, hidden truth about any distance, but you can't tell what it is. Your intrinsic distances don't take into account the contractions that may actually be applied to them, unless you take the trouble to declare clearly that they are subject to contractions which can't be determined.
The truth about Earth's diameter (and the distance between Earth and Sun) is not "hidden." They are well and precisely known by legitimate Earth science and astronomy, yet denied by length contraction theory. The theory that objects and distances have no intrinsic properties but instead depend on the frame of reference from which they are observed and measured is false.
Realism says that the world exists and has intrinsic properties independent of how it is observed. (Best observed from at rest with the object.) Idealism says that there is no reality independent of observation, so that as observations vary, the objects/distances observed vary. Length contraction is based on idealism. It is wrong.
Quote
What is much more important now is for you to find a position for yourself where the model you're pushing holds together properly, but that's either going to need length-contraction incorporated into it or some fiendishly clever alternative which no one's thought of yet.
My above replies state yet again "my position." So does the summary statement I've repeated several time now... which you still don't seem to understand:
Quote
The job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
... as length contraction theory does.
You still don't get it, and I am again done with this "conversation" with you.
Post by: David Cooper on 01/11/2012 21:51:39
David Cooper:QuoteThe trouble with that is that we have two big theories which both conflict with that. One theory (SR) has as part of its dogma the idea that all frames are equal, and that means that whatever distances are measured in any frame are as true as the distances measured in any other.
"The trouble with that is"... That we have a "scientific theory", length contraction, claiming that, either science doesn't know (for instance) the true diameter of Earth, or that it varies from about 1000 miles, as measured from the old near 'c' fly-by, to nearly 8000 miles, as measured at rest with Earth.
Earth does not change diameters. Therefore the theory that its diameter contracts is false.
There is not a scientific theory of length contraction: there are different theories which involve length contraction as a component of how they work. In LET the diameter of the Earth in its direction of travel cannot be known unless you can tell which direction it's going in and how fast (which can't be known by any method currently available). In SR, you can argue that the diameter is always the one you measure it as being when measuring from the same frame as the Earth, and then you can see any other measurements made from other frames which conflict with your measurement as being less true, merely being related to how you can interact with the Earth from those other frames. That looks like a mainstream position which is may be compatible with your position. The fact that most of the people in the SR camp here don't share that position within the SR camp is no reason for you to exclude yourself from the SR camp when it appears to be able to accommodate you without difficulty.
Quote
Any rigid physical object requires a force to compact it into a shorter length (or diameter.) No force is applied in any case of length contraction. Therefore any observed contraction is due to the image being distorted by observation from extreme velocities. Different observations do not make physical objects change shapes or lengths. Claiming that that do is false.
I agree with you on that in relation to SR (though it doesn't entirely fit with LET where forces are applied, but they are the forces that are already being applied anyway, simply adjusting the distances between atoms as the body changes its speed through the aether/fabric-of-space/vacuum).
Quote
QuoteIf that dogma was removed (which could be done without destroying the important core of SR), then the solution becomes the same as the one in LET where there is a correct, hidden truth about any distance, but you can't tell what it is. Your intrinsic distances don't take into account the contractions that may actually be applied to them, unless you take the trouble to declare clearly that they are subject to contractions which can't be determined.
The truth about Earth's diameter (and the distance between Earth and Sun) is not "hidden." They are well and precisely known by legitimate Earth science and astronomy, yet denied by length contraction theory. The theory that objects and distances have no intrinsic properties but instead depend on the frame of reference from which they are observed and measured is false.
In LET, the truth about these dimensions and distances is hidden - it can't be known without knowing how fast things are moving through space, and movement through space affects those dimensions and distances. In a modified SR (with the dogma about all frames being equal removed), the situation is similar, but more complicated due to the complex role of the time dimension, but I think it's still possible to decide that the measured distances as measured within the frame in which the things you're measuring aren't moving are the truest measurements.
Quote
Realism says that the world exists and has intrinsic properties independent of how it is observed. (Best observed from at rest with the object.) Idealism says that there is no reality independent of observation, so that as observations vary, the objects/distances observed vary. Length contraction is based on idealism. It is wrong.
In LET, length contraction is very much part of realism. In SR it can be too, but clearly there are many people about who think that observation is reality and who aren't alarmed by contradicting accounts of their "reality".
Quote
QuoteWhat is much more important now is for you to find a position for yourself where the model you're pushing holds together properly, but that's either going to need length-contraction incorporated into it or some fiendishly clever alternative which no one's thought of yet.
My above replies state yet again "my position." So does the summary statement I've repeated several time now... which you still don't seem to understand:QuoteThe job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
... as length contraction theory does.
Your position on length contraction is the key part that needs resolution. If you are actually in the SR camp but in a place within that camp where you do actually recognise the need for length contraction but regard its effects as being illusions, then there's little left to resolve. I'm just not sure that you've worked out how to handle the train experiment properly, because the train needs to be length contracted relative to the platform for light to travel all the way along through it and still be able to get out at the right point sent out sideways to the platform.
Quote
You still don't get it, and I am again done with this "conversation" with you.
I get all of it, but I'm not convinced that you do. Have you found anyone else who has the patience to continue discussing this with you? Have you met anyone else who has tried so hard to help get to the points of misunderstanding with this? I can see exactly where you're making mistakes, but you still can't. You aren't going to find those points so long as you keep refusing to look at them. You say you're done with this "conversation" with me, but that really means you're not interested in testing your own understanding of this to see if it stands up to scrutiny. It doesn't yet. You've got a lot of it right, and there's a lot that we agree on, but your apparent rejection of length contraction suggests that you've still got some work to do. Length contraction cannot be written off as an illusion or something that can be accounted for by the mysterious behaviour of light.
Think about the train experiment. Better still, describe it here to prove that you've understood it properly. I'll remind you of the essentials: a light beam is sent along the platform, but another beam is sent into the back of a passing train which is passing at 0,866c, then reflected right up the middle of the train to the front where it's reflected out onto the platform where it hits a detector on the platform. The light which travels along over the platform must reach the detector first, and the light coming back out of the train must hit the detector which is located at a very specific point such that the light will miss it if it doesn't leave the train at the right location.
If you can do that without the train (or the platform) being length contracted, then you have good cause to go on attacking the idea of "length contraction theory". If you can't, then you'll have shown that you aren't willing to back up your assertions.
Post by: old guy on 02/11/2012 20:17:31
I need help (again) to shake this guy and his personal agenda "off my case."
I am a realist. That means that I know (real-ize) that "the physical world" (broadly speaking) does not "contract" as it may appear to contract from various extreme frames. My favorite examples are Earth's diameter and the distance to the sun. Earth's diameter does not in fact vary from 1000 to nearly 8000 miles. If length contraction ("theory", in the broadest sense) claims that it does, it is wrong. Earth and Sun do not move closer together (ignoring trivial variation in its position in elliptical orbit.) Aside from the absence force required to bring them closer together (or to "flatten" Earth), Earth would be incinerated in much closer proximity, and it would be destroyed by any crushing force posited to actually, physically "contract" its diameter.
These are sincere objections which deserve more than pat answers from the math of "time dilation" and its reciprocal, "length contraction"... *assuming* "spacetime" as a malleable entity with no ontological discussion of *what* either component *is*, let alone their *assumed* coalescense into unity.
I do not debate the empirical obervation that clocks slow down as their velocity is increased. This is a far cry away from the *assumptions* which reify time, making it an entity which "dilates." The same can be said for space. It has not been empirically observed to *be* a malleable medium. There is no evidence that space is anything but 3-D volume.
So, when SR theory insists that the distance between stars would contract "for" a high speed craft with a slowed down clock, realism is a reminder that these are real massive bodies distributed "as is" in space, and that moving massive bodies closer together would require "massive" forces... a fact ignored by length contraction "theory."
Please stop ignoring these facts and provide an explanation besides, "It's all in the math" or "The constant speed of light requires physical bodies to change shapes/ lengths, because they look different from different frames." (paraphrazed.)
It doesn't require a professional philosopher to see the fallacy in the above claims. (Realism trumps idealism every time.)
Post by: David Cooper on 02/11/2012 21:22:46
So I ask the forum (whomever might be still be reading this thread), do you agree with the following, a recent summary statement I made here:QuoteThe job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.... as length contraction theory does.
Here it is again in a nutshell... anyone...:QuoteThe job of science is to study and accurately describe things as they are, not to re-create them as subjective versions of an infinite number of "realities" depending on who is looking at what from whatever different frame of reference.
If you don't mean anyone, don't make it such an open invitation. You're acting as if no one's answered your questions, but they've all been answered repeatedly. Time and time again you simply write off all their replies as if they were worthless and return to where you started, implying that no one has even addressed the issue. This is deeply insulting to everyone here who has tried their best to engage with you.
As expected, you've ignored my invitation for you to show off your understanding of the whole business of length contraction by discussing the train thought experiment, choosing instead to repeat a whole bunch of assertions which are just the same old attack on "length contraction theory" and the beliefs of many people within the SR camp who are comfortable with contradictions. Everyone has got that last point: some people are happy with contradictions in theories while others aren't: we established that this is the case long ago.
And no: you are not a realist. Realism requires you to take length contraction on board in order to account for the results of actual experiments which show your "realism" to be wrong, but you refuse to do that. This is the key point where your position is wrong, so why don't you give it a shot and try to demonstrate that you are actually qualified to push your assertions by picking apart the train experiment to show that it doesn't need to be contracted to half its normal length when moving at 0.866c. If you can't rattle off a sufficiently detailed analysis of that in twenty minutes or so, you shouldn't be firing off all your guns here.
Do you need more help with it? Shall I do 90% of the work for you to make it easier? Let's make it a toy train so that it's only a metre long. We've got a mirror sitting on the top of the train at the back and another at the front, one metre apart if the train's at rest. "Now, hold on a minute!" I hear you say: "There's going to be an alignment problem with the mirrors when they're moving, so they won't reflect the light in the right directions." That's a really good point you make (which only an expert like yourself would spot), so let's instead try to keep the beam on a straight path throughout to eliminate the problem. We can put the source of our light beam over the track slightly higher than the train and send out a pulse of light exactly as the back of the train passes underneath. Further up the track we can have a detector, and what we want to do is get the light to hit that detector at the same moment as the front of the train passes underneath.
How far away from the source is the front of the train when the light is emitted? Is it one metre, or half a metre?. How far from the source is the back of the train when the light hits the sensor? Is it one metre, or half a metre? How far away from the source is the detector going to be placed? I'm not even going to give you a choice for this one - you're going to have to prove that you can actually do the necessary maths.
So, the challenge is set right there for you. Stop messing everyone around and provide us with some hard answers to demonstrate that you are actually sufficiently qualified to make your assertions and to ignore everything everyone else says. You're calling on the mods to get rid of me. I'm calling on you to show them that they shouldn't get rid of you.
Post by: JP on 03/11/2012 16:07:36
Mods,
I need help (again) to shake this guy and his personal agenda "off my case."
The moderators aren't going to get involved here, since this is a legitimate discussion and well within site rules. There is no ownership of threads on this forum: you may have started this thread to discuss your ideas, but other users have equal rights to post comments so long as it's civil, scientifically-based and a discussion.
Post by: old guy on 05/11/2012 19:06:40
Quote
And no: you are not a realist. Realism requires you to take length contraction on board in order to account for the results of actual experiments which show your "realism" to be wrong, but you refuse to do that.Yet again... Wiki:
"Realism... the belief that reality exists independent of observers."
"Observers" include frames of reference as used in the context of lenght contraction.
In other words, realism denies that different observations of the same object or distance (from different frames of reference) reflect real differences in those objects and distances.
(Force is required to actually change the shape or length of a physical object, and length contraction posits no such applied force.)
This is quite obvious in the case of Earth's diameter and distance to the sun, neither of which actually contract, even if they could be observed to contract from extreme relativistic frames.
The same principle holds for other supposedly "contracted" objects like my "probe"* or arms of the MM apparatus, or your train.
* It was measured from Earth to be 10 meters, approaching at .866c, but at as the shuttle pulls alongside to capture it, it is seen as it is... 20 meters long, twice as long as the shuttle bay. You never did get that one, an expose of... a reality check on... the length contraction fallacy.
The operative phrase in length contraction is always some version of "for observer A vs for observer B... the length is measured to be different."
Realism insists that the objects themselves do not change even if observed/measured to change. Observers seeing an object differently does not mean that the same object actually changes.
The latter is no different than classical idealism, which rejects "reality" as independent of observation. So, "for blind man A", an elephant is shaped like a tree trunk, while "for blind man B" it is shaped like a rope... etc. We all know that an elephant exists as a whole animal of its own intrinsic shape which neither of the above describes accurately. Yet we have length contraction "theory" insisting that an Earth with a 1000 mile diameter is equally accurate ("no preferred frame") with the "real animal" which is nearly spherical with a nearly 8000 mile diameter.
The same principle holds for "length contracted trains" and the MM apparatus arms.
No, David, different observations do not crreate different lengths for the same object.
Post by: David Cooper on 05/11/2012 20:06:11
David Cooper:QuoteAnd no: you are not a realist. Realism requires you to take length contraction on board in order to account for the results of actual experiments which show your "realism" to be wrong, but you refuse to do that.Yet again... Wiki:
"Realism... the belief that reality exists independent of observers."
That poses no problem for me, but it does for you because experiments show that length contraction is part of reality.
Quote
"Observers" include frames of reference as used in the context of lenght contraction.
In other words, realism denies that different observations of the same object or distance (from different frames of reference) reflect real differences in those objects and distances.
Realism is fully compatible with LET, and also with some interpretations of SR. It is not compatible though with a model which excludes length contraction altogether.
Quote
(Force is required to actually change the shape or length of a physical object, and length contraction posits no such applied force.)
Repeating that over and over again doesn't make it true. The first bit is true, but in some interpretations of SR the shape isn't really changed, while in LET is isn't changed by observation but by movement through space, and the only forces required for the contraction are in action all the time (whether the thing's moving or not).
Quote
This is quite obvious in the case of Earth's diameter and distance to the sun, neither of which actually contract, even if they could be observed to contract from extreme relativistic frames.
In LET it could be contracted without you knowing it, so there's nothing obvious about it.
Quote
The same principle holds for other supposedly "contracted" objects like my "probe"* or arms of the MM apparatus, or your train.
When you think the train's moving at 0.866c it could actually be stationary for all you know, so you have no idea how long it really is.
Quote
* It was measured from Earth to be 10 meters, approaching at .866c, but at as the shuttle pulls alongside to capture it, it is seen as it is... 20 meters long, twice as long as the shuttle bay. You never did get that one, an expose of... a reality check on... the length contraction fallacy.
If the shuttle is moving with the probe, it is length contracted to 5 metres while the probe remains contracted to 10m. You appear to be the only person here who doesn't "get" your own thought experiment.
Quote
The operative phrase in length contraction is always some version of "for observer A vs for observer B... the length is measured to be different."
Realism insists that the objects themselves do not change even if observed/measured to change. Observers seeing an object differently does not mean that the same object actually changes.
I have always agreed with you on that.
Quote
Yet we have length contraction "theory" insisting that an Earth with a 1000 mile diameter is equally accurate ("no preferred frame") with the "real animal" which is nearly spherical with a nearly 8000 mile diameter.
No, we have one interpretation of SR insisting on that and you are right to attack it. Another interpretation of SR is close to your position, regarding the true shape of an object as the one you see when you are moving/stationary with it. In LET (which you presumably include in "length contraction theory") there is no measurement you can point to and claim to be the true one unless you have access to knowledge which is currently not available by any known method.
Quote
The same principle holds for "length contracted trains" and the MM apparatus arms.
Are you claiming they don't contract then? Surely you can answer this simple question without doing any maths.
Quote
No, David, different observations do not create different lengths for the same object.
How can you think you're disagreeing with me on that? The "No" at the start of that should be a "yes".
Post by: old guy on 06/11/2012 19:40:34
I did not take your test because different observations do not make things change in length. Given that, your "test" is irrelevant. You said that you agree, as follows:
Me:
Quote
The operative phrase in length contraction is always some version of "for observer A vs for observer B... the length is measured to be different."You:
Realism insists that the objects themselves do not change even if observed/measured to change. Observers seeing an object differently does not mean that the same object actually changes.
Quote
I have always agreed with you on that.You contradict yourself.
"Realism... the belief that reality exists independent of observers." (Wiki)
You:
Quote
That poses no problem for me, but it does for you because experiments show that length contraction is part of reality.
There are no experiments showing length contraction outside of particle accelerators. There, subatomic particles are flattened ("pancaked") by overwhelming application of force accelerating them. It doesn't work with Planet Earth, distance to the Sun, or rigid objects on the scale of the examples discussed in this thread. The "contraction", for instance of one arm of the MM apparatus, depends on differences in observation (frame of reference). See again what you agreed to above.
Me:
Quote
* It (the probe) was measured from Earth to be 10 meters, approaching at .866c, but at as the shuttle pulls alongside to capture it, it is seen as it is... 20 meters long, twice as long as the shuttle bay. You never did get that one, an expose of... a reality check on... the length contraction fallacy.You:
Quote
If the shuttle is moving with the probe, it is length contracted to 5 metres while the probe remains contracted to 10m. You appear to be the only person here who doesn't "get" your own thought experiment.
The shuttle bay was built on Earth to be 10 meters long. It stays 10 meters long, even when it is traveling beside the probe, the bay now appearing 5 meters long from Earth. The probe was built 20 meters long, which is why it appears from Earth contracted to 10 meters because of its velocity relative to Earth. The shuttle when at rest with the probe sees it as it is, 20 meters. It is twice as long as the bay. Neither the probe nor the bay changed lengths.
Only appearences changed, (called length contraction) due to changes in relative velocity. You still don't get it.
Me:
"(Force is required to actually change the shape or length of a physical object, and length contraction posits no such applied force.)"
You:
"Repeating that over and over again doesn't make it true. The first bit is true,..."
You agree that "force is required to actually change the shape or length of a physical object" ("the first bit"), yet you say that repeating it doesn't make it true, implying that it is false. More self contradiction. It is true, and of course repeating it doesn't make it more true. Different observations do not make the same object change lengths. Believing that reality changes with observation is idealism, not realism. "For observer A", Earth, the probe appears to be 10 meters. "For observer B" (shuttle at rest with probe) the probe is as it is, 20 meters. It didn't actually ("really") change lengths during the shuttle's mission to capture it.
Do you get it yet?
Me:
Quote
Yet we have length contraction "theory" insisting that an Earth with a 1000 mile diameter is equally accurate ("no preferred frame") with the "real animal" which is nearly spherical with a nearly 8000 mile diameter.You:
Quote
No, we have one interpretation of SR insisting on that and you are right to attack it.
The mods and those who run the show here insist on it, and the purpose of this thread is to argue against their "mainstream" position on length contraction. That is why it was moved to, essentially, the 'theories not to be taken seriously' section.
I am not interested in debating the alternative theory you call LET.
Start your own thread and make your argument there.
Post by: David Cooper on 06/11/2012 22:15:03
David,
I did not take your test because different observations do not make things change in length. Given that, your "test" is irrelevant.
You didn't answer the two simple questions and the other question which required a little bit of maths because you know that it would destroy your position whether you got it right or wrong. That's why you'll never answer it, but you'll find an infinite supply of flimsy excuses instead, starting with this:-
Quote
You said that you agree, as follows:
Me:QuoteThe operative phrase in length contraction is always some version of "for observer A vs for observer B... the length is measured to be different."You:
Realism insists that the objects themselves do not change even if observed/measured to change. Observers seeing an object differently does not mean that the same object actually changes.QuoteI have always agreed with you on that.You contradict yourself.
I agree with the bit about observers seeing an object differently not changing the object. I assumed that was what you were talking about throughout the whole bit there, but if you're actually intending part of it to mean that the change in an object caused by its change of speed doesn't change the object, then I don't agree with that part.
Quote
There are no experiments showing length contraction outside of particle accelerators.
You've missed out the Michelson Morley experiment - the one which disproves your "realism".
Quote
There, subatomic particles are flattened ("pancaked") by overwhelming application of force accelerating them.
The pancaking has nothing whatsoever to do with acceleration forces on them - that is a complete misunderstanding of the physics on your part.
Quote
It doesn't work with Planet Earth, distance to the Sun, or rigid objects on the scale of the examples discussed in this thread. The "contraction", for instance of one arm of the MM apparatus, depends on differences in observation (frame of reference). See again what you agreed to above.
You misunderstood what I was agreeing to: I was only agreeing to the part about the same thing being observed by different observers as having different dimensions not making any change to that object - their contradictory measurements cannot both be correct when it comes to the actual shape of the object.
Quote
The shuttle bay was built on Earth to be 10 meters long. It stays 10 meters long, even when it is traveling beside the probe, the bay now appearing 5 meters long from Earth. The probe was built 20 meters long, which is why it appears from Earth contracted to 10 meters because of its velocity relative to Earth. The shuttle when at rest with the probe sees it as it is, 20 meters. It is twice as long as the bay. Neither the probe nor the bay changed lengths.
Only appearences changed, (called length contraction) due to changes in relative velocity. You still don't get it.
If you're trying to measure length contraction using a ruler which has been length contracted by its movement, you're on a fool's errand.
Quote
Me:
"(Force is required to actually change the shape or length of a physical object, and length contraction posits no such applied force.)"
You:
"Repeating that over and over again doesn't make it true. The first bit is true,..."
You agree that "force is required to actually change the shape or length of a physical object" ("the first bit"), yet you say that repeating it doesn't make it true, implying that it is false. More self contradiction.
Again no contradiction. If you want to change the actual length, forces will be involved in that, but there is no extra compression force added to the mix for this - the forces which contract an object are the same ones which set the distances between its atoms all the time whether it's stationary, moving, accelerating or decelerating. The full quote should be:-
Quote
The first bit is true, but in some interpretations of SR the shape isn't really changed, while in LET is isn't changed by observation but by movement through space, and the only forces required for the contraction are in action all the time (whether the thing's moving or not).
That's fully clear and fully correct.
Quote
It is true, and of course repeating it doesn't make it more true.
You're attacking a straw man - SR doesn't need the contraction to be real, and LET uses existing forces within the object to contract it simply by maintaining the balance of forces between atoms.
Quote
Different observations do not make the same object change lengths. Believing that reality changes with observation is idealism, not realism.
Agreed.
Quote
"For observer A", Earth, the probe appears to be 10 meters. "For observer B" (shuttle at rest with probe) the probe is as it is, 20 meters. It didn't actually ("really") change lengths during the shuttle's mission to capture it.
Do you get it yet?
You're the only one who hasn't got it. In LET it really did change length. In SR, it changed it's alignment in spacetime and hid some of its length in the time dimension.
Quote
I am not interested in debating the alternative theory you call LET.
Start your own thread and make your argument there.
Every time you attack "length contraction theory", you're attacking LET. If you restrict yourself to attacking the camp within SR which you have an issue with, I won't have to keep setting the record straight, though you'll also have to stop laying claim to realism, because LET is realism.
Post by: old guy on 07/11/2012 20:11:18
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I did not take your test because different observations do not make things change in length. Given that, your "test" is irrelevant.D.C.:
Quote
You didn't answer the two simple questions and the other question which required a little bit of maths because you know that it would destroy your position whether you got it right or wrong.
You still claim to know me and my motivations better than I know myself and my reason, as above. If you agree that that different observations do not create different realities (lengths of objects, etc.), then seeing the same object differently does not make it change. Your train does not get shorter with differing observations of it. The details are then moot.
You:
..."
Quote
but if you're actually intending part of it to mean that the change in an object caused by its change of speed doesn't change the object, then I don't agree with that part.
SR theory does not maintain that change of speed physically compacts an object, as a bullet compacts to shorter when fired. It is always, "For observer A," moving relative to an object, it IS shorter than "for observer B," at rest with the object. SR theory (which is the focus of my argument!) does not claim that application of force compacts the object to make it shorter. And, further, physical objects are not shrunken to shorter by the 'power of observation', which is not a force that can change physical objects.
You:
Quote
You've missed out the Michelson Morley experiment - the one which disproves your "realism".
No. It still depends on the usual "for observer A" vs "for observer B" definition of changing "reality." Again, the reality of physical objects (the length of the apparatus arms here) is not altered by differences in observation. That is idealism, not realism. (See the Wiki definition above... again.)
Regarding subatomic "pancaking" as length contraction:
You:
Quote
The pancaking has nothing whatsoever to do with acceleration forces on them - that is a complete misunderstanding of the physics on your part.You are wrong. The machines are built to apply immense force to accellerate minute particles. In the process, they are observed to be flattened in the direction they are traveling. Denying that doesn't help your argument. No force is likewise applied to Earth, yet mainstream SR (my focus here!) claims that "for an observer" traveling past at near 'c', it is pancaked in diameter in the direction of the observer's travel. It doesn't work. It has a load of false assumptions which do not transfer from the empirical observation of contraction of particles with applied force in an accelerator.
You:
Quote
...their contradictory measurements cannot both be correct when it comes to the actual shape of the object.
The MM apparatus was built with arms of equal length. Seeing one arm as shorter under no circumstance makes the actual physical arm shorter.
Yet again, regarding my "alien probe retrieval project," you say:
Quote
If you're trying to measure length contraction using a ruler which has been length contracted by its movement, you're on a fool's errand.
You are stuck in the belief that physical objects change length when they move relative to an observer... the essence of SR's length contraction. The shuttle bay was built and remained 10 meters long, even when it joined the probe's frame and *appeared contracted* to 5 meters. The probe was built and remained 20 meters long, even as it approached Earth at .866c and *appeared* 10 meters long. As said above, the shuttle's launch and change of velocity relative to Earth did not make it shorter, "in the real world" even though it appeared to shrink as it joined the probes frame.
You:
Quote
The first bit is true, but in some interpretations of SR the shape isn't really changed, while in LET is isn't changed by observation but by movement through space, and the only forces required for the contraction are in action all the time (whether the thing's moving or not).You:
"That's fully clear and fully correct."
I repeat, my argument here is with mainstream SR's version of length contraction as advocated by the authorities of this forum, in which there is no force applied to objects to compact/contract them. There is no force applied to Earth to flatten it, but the fly-by guy "sees" it as flattened, and there is no preferred frame, so a flattened Earth is equally valid, they say. I am not interested in what you say about LET. Movement doesn't make objects contract. Only the image of objects gets distorted. They still don't understand the difference.
You:
Quote
...LET uses existing forces within the object to contract it simply by maintaining the balance of forces between atoms.
Nonsense! "Maintaining the balance of forces between atoms" will maintain the object's shape and length. To change an object's shape/length, a force bust be applied to change the space between whaterver units, molecules or atoms, of which the object is composed.
You:
"...because LET is realism."
Nonsense, as exposed above. You really don't understand realism. Objects remain as they were formed or built until a force is applied to crush or compact them to a shorter length or to way out of spherical shape, in Earth's case.
In the real world, observation is not a force which changes physical things. That is my argument, and I've said all I have to say about your argument... yet again... hopefully.
Again, carry on with your LET argument in a thread of your own.
Post by: David Cooper on 08/11/2012 21:05:23
You still claim to know me and my motivations better than I know myself and my reason, as above. If you agree that that different observations do not create different realities (lengths of objects, etc.), then seeing the same object differently does not make it change. Your train does not get shorter with differing observations of it. The details are then moot.
I'm still trying to get you to explain your exact position - it isn't yet clear what you believe based on your attacks on length contraction. I've tried to make it easy for you by pointing to two theories and two interpretations of one of them in the hope that you'll either pin yourself to one of them or put forward a clear fourth alternative which doesn't go against the results of experiments. It still looks as if you could fit into one of the camps within SR, and yet you repeatedly appear to reject that. If you answered the train questions it would maybe help to clear that up. It is perfectly possible to say that the metre-long train when moving at 0.866c fits into a space 50cm long while still remaining one metre long in its own frame where its true length is to be found.
Quote
SR theory does not maintain that change of speed physically compacts an object, as a bullet compacts to shorter when fired.
I'm not clear as to your meaning there in relation to the bullet being made shorter. I can see three different ways in which the bullet length contracts: if it's soft enough, it could be slightly crushed by the force applied to it (that crushing remaining as the bullet slows down); it will have compression waves sent through it (but would rapidly bounce back from those to recover its full length shortly after leaving the gun); and it may be length contracted for relativistic reasons. I suspect the bullet is strong enough not to be crushed, so it's probably only affected by two of these kinds of contraction.
Quote
It is always, "For observer A," moving relative to an object, it IS shorter than "for observer B," at rest with the object. SR theory (which is the focus of my argument!) does not claim that application of force compacts the object to make it shorter. And, further, physical objects are not shrunken to shorter by the 'power of observation', which is not a force that can change physical objects.
That is fine - it is clearly a problem for one camp within SR if they imagine that things are physically changed by being viewed from different frames.
Quote
QuoteYou've missed out the Michelson Morley experiment - the one which disproves your "realism".
No. It still depends on the usual "for observer A" vs "for observer B" definition of changing "reality." Again, the reality of physical objects (the length of the apparatus arms here) is not altered by differences in observation. That is idealism, not realism. (See the Wiki definition above... again.)
You seem to be positioning yourself in one of the main SR camps there. If that's the case, then you simply need to accept length contraction as a phenomenon relating to the effective lengths of things in different frames. If that is your position, I don't know why you haven't made it clear that that was your position from the start.
Quote
You are wrong. The machines are built to apply immense force to accellerate minute particles. In the process, they are observed to be flattened in the direction they are traveling. Denying that doesn't help your argument.
They are accelerated up to speed gradually and any compression from that acceleration is thrown off almost as soon as it is added. Even if they were accelerated in an instant, the resulting compression would be thrown off again a moment later. Length contraction is a totally different thing from compression, and you're mixing up the two.
Quote
No force is likewise applied to Earth, yet mainstream SR (my focus here!) claims that "for an observer" traveling past at near 'c', it is pancaked in diameter in the direction of the observer's travel. It doesn't work. It has a load of false assumptions which do not transfer from the empirical observation of contraction of particles with applied force in an accelerator.
If you accept the length contraction of particles in an accelerator, you have to accept it in relation to the Earth too because it is not a different phenomenon. To avoid contradiction, you really ought to be denying that particles are length contracted in an accelerator because they are not compressed into a pancake shape by acceleration forces.
Quote
The MM apparatus was built with arms of equal length. Seeing one arm as shorter under no circumstance makes the actual physical arm shorter.
You've made another assertion which goes against LET. If you don't intend your assertion to apply universally but are restricting it to SR, then for one camp within SR that is fine: the arm is effectively shorter in other frames, but not actually shorter.
Quote
Yet again, regarding my "alien probe retrieval project," you say:QuoteIf you're trying to measure length contraction using a ruler which has been length contracted by its movement, you're on a fool's errand.
You are stuck in the belief that physical objects change length when they move relative to an observer... the essence of SR's length contraction. The shuttle bay was built and remained 10 meters long, even when it joined the probe's frame and *appeared contracted* to 5 meters. The probe was built and remained 20 meters long, even as it approached Earth at .866c and *appeared* 10 meters long. As said above, the shuttle's launch and change of velocity relative to Earth did not make it shorter, "in the real world" even though it appeared to shrink as it joined the probes frame.
Your experiment is an attempt to prove that length contraction isn't real, but it tries to do that by accelerating a ruler up to the same speed as the thing it's going to measure, at which point any length contraction which has been applied to the thing being measured will also have been applied to the thing doing the measuring, rendering the experiment pointless.
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I repeat, my argument here is with mainstream SR's version of length contraction as advocated by the authorities of this forum, in which there is no force applied to objects to compact/contract them. There is no force applied to Earth to flatten it, but the fly-by guy "sees" it as flattened, and there is no preferred frame, so a flattened Earth is equally valid, they say. I am not interested in what you say about LET. Movement doesn't make objects contract. Only the image of objects gets distorted. They still don't understand the difference.
If you are actually in a camp within SR and not writing off length contraction altogether, then I prefer your position to theirs. They don't actually agree that a force needs to be applied to length contract anything, so I'm guessing they see it more in the way of multiple realities all being true at the same time, and that's a kind of thinking encouraged by some interpretations of quantum mechanics. That is why their position isn't as mad as it may initially seem - it's just a different approach.
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You:Quote...LET uses existing forces within the object to contract it simply by maintaining the balance of forces between atoms.
Nonsense! "Maintaining the balance of forces between atoms" will maintain the object's shape and length. To change an object's shape/length, a force must be applied to change the space between whaterver units, molecules or atoms, of which the object is composed.
Existing forces acting all the time between atoms will do the job automatically. Think about this illustration of how it works. Imagine two people who decide to maintain their distance from each other by shouting across a field, each one shouting back to the other as soon as they've heard the other one shout to them. They continually adjust their positions to try to keep the round trip of the sound to a fixed interval of time. On a windy day, they will automatically end up closer together than on a still day because of the extra distance the sound has to travel through the air, and the exact distance between them will vary in direct response to the speed of the wind. If the wind is moving at 86.6% the speed of sound, they would need to stand twice as close together as they do on a still day if their clocks were also affected by the wind speed, but because their clocks are actually governed by the speed of light they will instead end up standing four times as close together as on a still day. (Ignore the impossibility of standing up in such a strong wind.)
That is how it works in LET: the forces between atoms are actively maintaining the distances between them all the time, and normally that means the distances are constant, but if you move the body of which they are part at high speed through the vacuum, this slows down the communications of these forces between the atoms and results automatically in them settling closer together in their direction of travel. That is why no additional force need be applied, other than to accelerate the body to higher speed. The clue to the fact that no lasting compression has been added is the fact that if you then spin the body the length contraction remains in the direction of travel at all times. That happens to spinning particles in an accelerator too - the pancaking is always in the direction of travel, whereas a crushed bullet if it started to tumble would have that compression rotate along with the bullet. You also need to understand that the acceleration of particles in an accelerator is done as much by pulling them as by pushing, so if you're imagining them being squashed by pushing forces you're getting a warped view of things. Even if all the force was applied by pulling the particles up to speed though, they would still length contract and not be pulled out into long strings.
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"...because LET is realism."
Nonsense, as exposed above. You really don't understand realism. Objects remain as they were formed or built until a force is applied to crush or compact them to a shorter length or to way out of spherical shape, in Earth's case.
LET and SR are both developments of realism: they have taken length contraction onboard in different ways, and in different ways within SR too. Anything which hasn't taken length contraction into account is not realism.
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In the real world, observation is not a force which changes physical things. That is my argument, and I've said all I have to say about your argument... yet again... hopefully.
Fine, but I'm still trying to find out why/whether you think you aren't in an SR camp.
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Again, carry on with your LET argument in a thread of your own.
I only bring LET into it when it is necessary. Your lack of interest in it doesn't give you the right to ban it being mentioned when you make absolute pronouncements which conflict with it.
Post by: lean bean on 09/11/2012 13:24:16
It seems this question of shuttle and probe is an artificial situation or question which would not occur naturally.
Does anyone know of a natural process or natural interaction between particles /fields whereby the particle ‘first’ observes something and then decides to interact with it?
I use the word natural and not intelligent as in… ‘man’ observes a probe and then decides to go and interact with it with a shuttle. An intelligence without knowledge of SR would lean the hard and slow way about chasing after fast moving probes and then matching their speed.
(Superposition, probabilities, SR,GR and quantum theory our models of something we agree to call nature).
Post by: old guy on 09/11/2012 21:11:04
Here again is the essence of my argument against length contraction:
"In the real world,(neither) observation (nor measurement from different frames) is a force which changes physical things."
It is ironic that denying that Earth changes shapes/diameters, as observed from different frames, is now considered a "new theory" not to be taken seriously, because it denies that Earth's diameter contracts, as SR insists.
This basic embrace of a "real physical Planet Earth" with intrinsic properties (size and shape) independent of how it is observed (not changing with changes in how it is observed) is still my answer to D.C."s query:
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Fine, but I'm still trying to find out why/whether you think you aren't in an SR camp.
But I've said this dozens of times... yet you ask the above. SR says that reality depends on how it is observed, that there is no "real, unchanging Earth." They say that "for" a frame of reference flying by at near 'c', Earth is flattened, i.e., contracted in diameter. Re-read the thread if you have forgotten all the insistence by length contraction advocates that earth does change shape with changes in frame from which it might be measured.
The reason I use this as my signature example is because it is so obviously a denial of reality by SR. But the same principle applies to rulers, trains, the MM apparatus arms, my shuttle and probe... and the distance to the sun... which if severely "contracted" would result in Earth's incineration (as a "flattened" Earth would also be destroyed.)
lean bean,
If Earth ever develops near 'c' space travel, and if an "alien probe" were discovered approaching Earth at .866c, the true test of "length contraction" would be to determine the real, actual length of the probe in order to send a ship with long enough bay capacity to capture it. It would *appear to be* 10 meters long from earth, if the equations are correct (which I don't doubt.) However, sending out a shuttle with a 10 meter bay would be folly... a very stupid wast of resources... and perhaps fatal to life on Earth if the probe's mission were to kill all life on Earth. So the question, "How long is the probe, really" becomes one of vital importance.
Turns out it is not "really" 10 meters, as it appears. It is really 20 meters. A shuttle bay 20 meters long, not 10, will be required.
Post by: lean bean on 10/11/2012 18:55:48
lean bean,
If Earth ever develops near 'c' space travel, and if an "alien probe" were discovered approaching Earth at .866c, the true test of "length contraction" would be to determine the real, actual length of the probe in order to send a ship with long enough bay capacity to capture it. It would *appear to be* 10 meters long from earth, if the equations are correct (which I don't doubt.) However, sending out a shuttle with a 10 meter bay would be folly... a very stupid wast of resources... and perhaps fatal to life on Earth if the probe's mission were to kill all life on Earth. So the question, "How long is the probe, really" becomes one of vital importance.
Turns out it is not "really" 10 meters, as it appears. It is really 20 meters. A shuttle bay 20 meters long, not 10, will be required.
Is that all your worried about …an evil alien probe.
Don’t worry old wrinkly, we on earth already know of SR and will know that what we observe travelling at high speeds is length contracted and so will allow for it when we send out a shuttle to retrieve the probe. As I said in my post…“An intelligence without knowledge of SR” will be the ones having your probe retrieval problem. Watch the skies…it may rain.
Post by: David Cooper on 10/11/2012 23:09:38
Here again is the essence of my argument against length contraction:
"In the real world,(neither) observation (nor measurement from different frames) is a force which changes physical things."
That is not an argument against length contraction: it's a argument for (or against, depending on whether the brackets are there or not) the idea that observation changes things physically.
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It is ironic that denying that Earth changes shapes/diameters, as observed from different frames, is now considered a "new theory" not to be taken seriously, because it denies that Earth's diameter contracts, as SR insists.
Don't attribute it to SR as a whole - you are only attacking one camp within SR.
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This basic embrace of a "real physical Planet Earth" with intrinsic properties (size and shape) independent of how it is observed (not changing with changes in how it is observed) is still my answer to D.C."s query:QuoteFine, but I'm still trying to find out why/whether you think you aren't in an SR camp.
But I've said this dozens of times... yet you ask the above. SR says that reality depends on how it is observed, that there is no "real, unchanging Earth." They say that "for" a frame of reference flying by at near 'c', Earth is flattened, i.e., contracted in diameter. Re-read the thread if you have forgotten all the insistence by length contraction advocates that earth does change shape with changes in frame from which it might be measured.
Again you're attacking SR as a whole rather than just the specific camp within SR which holds that view. There are other ways of looking at things within SR where there is no physical change made to the thing being observed, and you may find that you belong there. So long as you keep attacking SR instead of finding out whether you fit within an SR camp, you're putting yourself in a position which either requires you to be wrong, to be in the LET camp (which you aren't interested in and don't understand), or to have an alternative theory which you aren't prepared to set out clearly enough to demonstrate that it isn't wrong. You've been doing this for eleven pages now in this thread and still haven't made your position clear. What makes you think you aren't in a mainstream SR camp which doesn't insist on things being physically changed by being observed from different frames?
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The reason I use this as my signature example is because it is so obviously a denial of reality by SR. But the same principle applies to rulers, trains, the MM apparatus arms, my shuttle and probe... and the distance to the sun... which if severely "contracted" would result in Earth's incineration (as a "flattened" Earth would also be destroyed.)
meters long, not 10, will be required.
All the camps in SR (and LET) require you to build a >20m long container to hold a 20m long object when they are moving/stationary together. Length contraction only comes into it when calculating interactions between things that are moving relative to each other, so your signature example isn't addressing that issue.
Post by: bizerl on 11/11/2012 22:03:56
Couple of points though...
If length contraction is indeed just an illusion created by an observer approaching the speed of light relative to another object, what is the reason for this optical illusion? How does it occur? Why should objects appear shorter if they are travelling really fast?
Also, in relation to this:
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OK, so bizerl and the team of length contraction "experts" here insist that an Earth with a 1000 mile diameter is just as valid a description as the well validated nearly 8000 mile diameter. Please correct me if I am wrong.
and this:
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The fact is that all the observational and experimental evidence that has been gathered so far, indirectly supports the fact that if a 20m spaceship flies through a 10m bay at 0.866c, it will (very briefly) fit exactly inside that bay.You, like almost everyone here misunderstood and/or misrepresented my "alien probe retrieval project." There was no ship (the probe) "flying through" the 10 meter bay of the shuttle. In order to retrieve the probe, the shuttle would by necessity need to match the probe's velocity (come to rest with the probe's frame.) The probe was measured from earth to be 10 meters as it approaced earth at .866c. However, as the shuttle pulled alongside the probe, it was then measured to be 20 meters long, so it would not fit in the 10 meter bay, which did not change after launch.
This was offered as a thought experiment (that's all we have to work with regarding lenght contraction on this scale) demonstrating that the "length contracted probe" as seen from earth was not *actually* contracted to 10 meters. Nor would the shuttle bay have *actually* contracted to 5 meters, as it would be measured from earth when traveling with the probe.
The point is, if you accept that when travelling at 0.866c, the ship will indeed fit very briefly inside the bay, then saying "the ship is 10m when travelling at 0.866c relative to the observer" is as equally valid description of it as saying "the ship is 20m at rest with the observer".
Post by: old guy on 12/11/2012 19:06:31
I'm not worried, skinny kid. The whole point was that the probe is not 10 meters long as it appears from earth, so the transformation formula must first be applied to get its true, actual, real length before going out to capture it.lean bean,
If Earth ever develops near 'c' space travel, and if an "alien probe" were discovered approaching Earth at .866c, the true test of "length contraction" would be to determine the real, actual length of the probe in order to send a ship with long enough bay capacity to capture it. It would *appear to be* 10 meters long from earth, if the equations are correct (which I don't doubt.) However, sending out a shuttle with a 10 meter bay would be folly... a very stupid wast of resources... and perhaps fatal to life on Earth if the probe's mission were to kill all life on Earth. So the question, "How long is the probe, really" becomes one of vital importance.
Turns out it is not "really" 10 meters, as it appears. It is really 20 meters. A shuttle bay 20 meters long, not 10, will be required.
Is that all your worried about …an evil alien probe.
Don’t worry old wrinkly, we on earth already know of SR and will know that what we observe travelling at high speeds is length contracted and so will allow for it when we send out a shuttle to retrieve the probe. As I said in my post…“An intelligence without knowledge of SR” will be the ones having your probe retrieval problem. Watch the skies…it may rain.
This exposes the "for this frame (Earth) vs for that frame (at rest with the probe)" version of reality as a fallacy. The probe is and stays 20 meters, even as it *appears* contracted. The shuttle bay is and stays 10 meters. the probe will not fit into the bay, even for a theoretical instant.
Post by: old guy on 12/11/2012 19:47:22
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Here again is the essence of my argument against length contraction:D.C.:
"In the real world,(neither) observation (nor measurement from different frames) is a force which changes physical things."
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That is not an argument against length contraction: it's a argument for (or against, depending on whether the brackets are there or not) the idea that observation changes things physically.
Throughout this thread I have agrued against the length contraction insistence that physical objects actually change shapes/lengths with differences in frames of reference from which they are observed. SR claims that "length is not invarient," i.e., denies that Earth (etc.) has an intrinsic property of diameter length, i.e., insisting that it IS flattened, as above, not just "appears flattened," based on the dictums, "length is not invarient" and "there is no preferred frame of reference." I've made this case many times and it is you who do not yet get it.
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Don't attribute it to SR as a whole - you are only attacking one camp within SR.As above. I am not interested in your LET "camp" because it insists that physical objects actually do change shapes/lengths as their velocities change.
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...you're putting yourself in a position which either requires you to be wrong, to be in the LET camp (which you aren't interested in and don't understand), or to have an alternative theory...
See above re your misconception, which I bolded.
"My theory" is none of the above, mainstream SR or LET as you have presented it with objects physically changing with changes in velocity... and it is not "my theory." It is realism, which you do not understand, though I've explained it many times. The "elephant" has its own intrinsic shape as a real animal/object, independent of how it is observed. If you accellerate the elephant to .866c, it will not shrink to half its tail-to-trunk length. An "elephant compactor" would be required for that, and that would definitely kill the elepant.
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All the camps in SR (and LET) require you to build a >20m long container to hold a 20m long object when they are moving/stationary together. Length contraction only comes into it when calculating interactions between things that are moving relative to each other, so your signature example isn't addressing that issue.
My example addresses the SR claim that the probe is contracted to 10 meters as measured from Earth. It is not, and it doesn't grow twice as long after the shuttle enters its frame.
Post by: old guy on 12/11/2012 20:10:13
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If length contraction is indeed just an illusion created by an observer approaching the speed of light relative to another object, what is the reason for this optical illusion? How does it occur? Why should objects appear shorter if they are travelling really fast?
I am not an optics expert, but I do know that the image observed is not the object itself, and that all images are carried by light, so when one approaces light speed, one could expect some distortion. I also know that physical objects can not be compacted into shorter lengths without application of appropriate amounts of force, which would then crush the object. Assuming objects are not made of rubber, they could not then 'bounce back" to original length as frame of reference changes back.
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The point is, if you accept that when travelling at 0.866c, the ship will indeed fit very briefly inside the bay, then saying "the ship is 10m when travelling at 0.866c relative to the observer" is as equally valid description of it as saying "the ship is 20m at rest with the observer".No, I do not "... accept that when travelling at 0.866c, the ship will indeed fit very briefly inside the bay..."
The bay is 10 meters long. The probe is 20 meters long. As repeated many times, the probe will not fit into the bay even for an instant. Its length does not actually," really" change even though it is observed to change due to changes in relative velocity as observed from different frames.
Post by: David Cooper on 12/11/2012 23:55:37
Throughout this thread I have agrued against the length contraction insistence that physical objects actually change shapes/lengths with differences in frames of reference from which they are observed. SR claims that "length is not invarient," i.e., denies that Earth (etc.) has an intrinsic property of diameter length, i.e., insisting that it IS flattened, as above, not just "appears flattened," based on the dictums, "length is not invarient" and "there is no preferred frame of reference." I've made this case many times and it is you who do not yet get it.
That is just the view of one camp within SR. It is perfectly possible to have a view within SR that the shape of an object does not actually change and that the true shape is seen when stationary or moving with the object. It doesn't matter how many of the people within SR don't agree with that, it is still a viewpoint from within SR.
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QuoteDon't attribute it to SR as a whole - you are only attacking one camp within SR.As above. I am not interested in your LET "camp" because it insists that physical objects actually do change shapes/lengths as their velocities change.
Now that's a strange reply! LET is not a camp within SR. Maybe you were writing in a hurry again and didn't have time to check and edit.
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Quote...you're putting yourself in a position which either requires you to be wrong, to be in the LET camp (which you aren't interested in and don't understand), or to have an alternative theory...
See above re your misconception, which I bolded.
You clearly don't understand it because you never get the point that things are length contracted in LET without adding any crushing force.
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"My theory" is none of the above, mainstream SR or LET as you have presented it with objects physically changing with changes in velocity... and it is not "my theory." It is realism, which you do not understand, though I've explained it many times. The "elephant" has its own intrinsic shape as a real animal/object, independent of how it is observed. If you accellerate the elephant to .866c, it will not shrink to half its tail-to-trunk length. An "elephant compactor" would be required for that, and that would definitely kill the elepant.
And there we see again that you don't understand LET. Let me just walk you through a little of the history. Up to about a century ago, your theory was the only game in town. The Michelson Morley experiment then disproved it. Lorentz managed to recover the situation by working out how objects automatically become length-contracted in the direction of travel, so he created an improved version of Realism which corrected an incorrect assumption of the earlier kind of Realism. Einstein then came up with another kind of Realism which turned time into a dimension and so far as I know it is only LET and SR that can handle the Michelson Morley experiment - the older version or Realism clashed with it. Now, if there is another theory which can account for the results of MM, I'd like to see it. So far as I can tell, you're just pushing the old, broken version of Realism. If you don't like the idea of Spacetime, the only place you'll find where you've still got a leg to stand on is going to be LET. The advantage that SR has over LET is that GR can be built upon it to provide a startlingly accurate way of calculating the effects of gravity, but that doesn't mean that it's right - I suspect it's just tapping into something which could be accounted for in some other way, but that's another discussion. What matters is that there are two theories which can handle MM, and both of them are well worth getting your head around. If there's a viable third option, I want to get my head round it too because it may be the piece that unlocks the puzzle. I don't believe that you've got a viable third theory though: it looks exactly like the old, broken Realism to me, and the mistakes you keep making confirm that.
That paragraph was important - don't skip it.
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QuoteAll the camps in SR (and LET) require you to build a >20m long container to hold a 20m long object when they are moving/stationary together. Length contraction only comes into it when calculating interactions between things that are moving relative to each other, so your signature example isn't addressing that issue.
My example addresses the SR claim that the probe is contracted to 10 meters as measured from Earth. It is not, and it doesn't grow twice as long after the shuttle enters its frame.
Ironically, you'd only have a vestage of a case if you were in a Realism camp within SR, using the nature of Spacetime to avoid the length contraction being real. You don't like Spacetime though, which leaves you with a straight choice between the old and new Realisms of OGVT and LET (V standing for vacuum). Without Spacetime complicating the issue, we can now state categorically that when the platform is stationary within the vacuum and the train is moving past at 0.866c, the train is length contracted to half its rest length, and this can be demonstrated by sending light along it as set out a few posts back (in the thought experiment which you're too scared to explore). If you don't like that, then you can jump into an SR camp and use Spacetime to escape from the clutches of LET. I don't care which way you jump, but I would like to see you make the leap of understanding necessary to recognise that you're standing in a position which is not viable. OGVT should make the train travel twice as far as it does in reality before the light from the back has reached the front. That is where OGVT falls.
Post by: lean bean on 13/11/2012 19:09:30
This exposes the "for this frame (Earth) vs for that frame (at rest with the probe)" version of reality as a fallacy.
No it doesn’t. if two things interact and one is travelling at a relativistic speed relative to the other, then you must treat the situation of time dilation and length contraction as real… how else does the muon reach earth’s surface without decaying, are you saying this is some kind of optical illusion, who is the observer in this case? The detection is only made when the muon reaches the detector at earth’s surface or below surface.
skinny
Post by: old guy on 13/11/2012 21:29:57
Me:This exposes the "for this frame (Earth) vs for that frame (at rest with the probe)" version of reality as a fallacy.
No it doesn’t. if two things interact and one is travelling at a relativistic speed relative to the other, then you must treat the situation of time dilation and length contraction as real… how else does the muon reach earth’s surface without decaying, are you saying this is some kind of optical illusion, who is the observer in this case? The detection is only made when the muon reaches the detector at earth’s surface or below surface.
skinny
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The whole point was that the probe is not 10 meters long as it appears from earth, so the transformation formula must first be applied to get its true, actual, real length before going out to capture it.
This exposes the "for this frame (Earth) vs for that frame (at rest with the probe)" version of reality as a fallacy. The probe is and stays 20 meters, even as it *appears* contracted. The shuttle bay is and stays 10 meters. the probe will not fit into the bay, even for a theoretical instant.
"No, it doesn't"? In the real world both a shuttle bay and an alien ship are made of rigid metal and would require a crushing force to compact them to half their length-as-built. If you don't agree, then you must believe that observation from different frames, seeing them as half their actual length (in the case of .866c relative velocity) is an actual force which compacts them. If not, they stay the length they were built. The latter is realism. The former is the length contraction version of idealism, in which physical objects change with how they are observed. You believe that and I don't.
"Time dilation" is a misnomer (time is not an entity) for the observed fact that physical processes (like the ticking of clocks) slow down when they travel at higher velocities. Muons enter Earth's atmosphere at very high speed, so thier rate of decay is slowed down accordingly. Therefore they "live longer" and travel further than would be expected at a
Same for the distance to the sun. Never mind that Earth would be incinerated if it were actually a small fraction of the established average of 93 million miles or so from the Sun. SR assumes that math creates new distances between such bodies based on the slower clocks of theoretical high speed space travelers. Total nonsense.
Same applies to the "altered realities" of what D.C. calls LET. He says that the space between atoms in Earth varies with changes in velocity (of Earth relative to near 'c' travelers), thus giving it a 1000 mile diameter in the extreme case. More total nonsense.
Late edit regarding D.C.'s last post: It is trivial and irrelevant whether "LET" is a "camp" within SR. Earth's diameter does not actually change as its image is viewed from various frames of reference. That is the point which D.C. is trying to obfuscate here with his pet project, promoting "LET." Why he doesn't promote it in his own thread, I do not know.
Post by: David Cooper on 14/11/2012 21:30:08
Same for the distance to the sun. Never mind that Earth would be incinerated if it were actually a small fraction of the established average of 93 million miles or so from the Sun.
You're displaying your lack of understanding again there: if it's squished, it's because it's moving, and if it's moving, the light and heat will be concentrated forwards in the direction of travel, the result being the approximately same amount of heat and light reaching the Earth at all times (assuming the orbit is approximately circular from the solar system's own frame of reference).
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Same applies to the "altered realities" of what D.C. calls LET. He says that the space between atoms in Earth varies with changes in velocity (of Earth relative to near 'c' travelers), thus giving it a 1000 mile diameter in the extreme case. More total nonsense.
The Michelson Morley experiment disagrees with you. Things are length contracted in their direction of travel. It's important though that you should understand that things are only length contracted where the separation of their components is strongly locked together by forces. If you had two objects a mile apart and accelerated them both to 0.866c with one following behind the other, they would remain a mile apart without the distance between them being length contracted to half a mile. A train a mile long, on the other hand, would be length contracted to half a mile long. The contraction is the direct result of the interaction of forces or communications between the components which are slowed down by the added communication distances. In the first case we have two objects which are not locked together and which therefore maintain their separation at one mile - they are not making any adjustments on the basis of communications with each other. It's this case where there is no length contraction which led to the old assumption that things maintain their length at any speed, but when they are locked together through forces (as is the case with the MM apparatus and with the solar system), they have to contract in their direction of travel.
Edit: Actually, the solar system isn't locked that way, but if it formed while moving at high speed the orbits of the planets would automatically end up being length contracted in the direction of travel because of the way they form out of a dust ring which in the frame of reference of the solar system is circular.
In SR you must have the same situation with length contraction only applying to things that are locked together by forces, so if you imagine a train one lightyear long and stretching from one star to another, if it was suddenly accelerated to 0.866c it would not suddenly become half the length with the front or back end halfway between the two stars or with one end quarter of the way from one star to the other and the other end three quarters of the way. No, what would happen is that the train would break up into pieces spread across the whole distance between the two stars and with gaps here and there, the length of the gaps adding up to half a lightyear.
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Late edit regarding D.C.'s last post: It is trivial and irrelevant whether "LET" is a "camp" within SR.
Hardly: LET = OGVT with added recognition of length contraction. SR is 4D Spacetime.
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Earth's diameter does not actually change as its image is viewed from various frames of reference.
Correct.
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That is the point which D.C. is trying to obfuscate here with his pet project, promoting "LET."
Cor-wrong. I'm simply waiting with interest to see how long it takes you to realise that OGVT and LET are the same theory, but with the latter recognising the necessity of length contraction while the former ignores the experiment which shows that length contraction actually happens in the real universe.
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Why he doesn't promote it in his own thread, I do not know.
I'm much more interested in studying how people think than in promoting anything.
Post by: lean bean on 14/11/2012 22:05:46
quote from above link.
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Muon-Frame Observer
The muon sees distance as length contracted.
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Note that the muon and ground frames do not agree on the distance and time, but they agree on the final result. One observer sees time dilation, the other sees length contraction, but neither sees both
Old guy quote
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"Time dilation" is a misnomer (time is not an entity) for the observed fact that physical processes (like the ticking of clocks) slow down when they travel at higher velocities.
That’s as seen from or compared to the earth frame. In the muon’s own frame it’s clock is running normal.
To use the above link's figures… Distance in earth frame for muon to travel is 10 Km.
If from the earth frame the muon’s clock is running slow, then earth will reckon the muon will experience only 6.8 microseconds to reach the surface.
That’s 6.8microseconds multiplied by 0.98c (293706Kms)= 1.997Km (nearly 2Km)
Whereas earth will ‘see’ the muon reach the surface in 34microseconds.
That’s 34microseconds multiplied by 0.98c (293706Kms)= 9.986Km (nearly 10Km)
In other words…the muon 'sees' 2Km where the earth sees the distance is 10 Km.
No force required.
Your constant referring to a force is a reflection of your misunderstanding of time dilation and length contraction.
Post by: JP on 14/11/2012 23:14:32
No force required.
Your constant referring to a force is a reflection of your misunderstanding of time dilation and length contraction.
You can also demonstrate that forces can, in fact, be thought of as reshaping things at high speeds. The force holding the probe (in the famous probe example) together are electromagnetic and communicated at light speed. Since electromagnetism travels a the speed of light, and the speed of light is constant as the observer moves, these bonds change length and that changes the length of the probe as it moves. You can interpret this different ways, but it's pretty obvious that it can certainly be interpreted as the electromagnetic force leading to a reshaping of the probe as you fly by it at high speeds.
Post by: lean bean on 15/11/2012 15:47:20
And have noted that you obviously still need two frames.
Post by: old guy on 15/11/2012 20:12:24
Regarding, "You can also demonstrate that forces can, in fact, be thought of as reshaping things at high speeds"... "can be thought of..." is not the same as forces actually physically contracting the probe's length.No force required.
Your constant referring to a force is a reflection of your misunderstanding of time dilation and length contraction.
You can also demonstrate that forces can, in fact, be thought of as reshaping things at high speeds. The force holding the probe (in the famous probe example) together are electromagnetic and communicated at light speed. Since electromagnetism travels a the speed of light, and the speed of light is constant as the observer moves, these bonds change length and that changes the length of the probe as it moves. You can interpret this different ways, but it's pretty obvious that it can certainly be interpreted as the electromagnetic force leading to a reshaping of the probe as you fly by it at high speeds.
If we had near 'c' travel, then the actual fact would be that seeing the probe from Earth (approaching at .866c) as 10 meters would not physically change it to BE 10 meters long. Once the shuttle pullls alongside the probe to capture it, it is seen as it actually IS, 20 meters long, so it will not fit in the 10 meter shuttle bay. No "smoke and mirrors" about a length contracted probe will make it fit.
Also, if length contraction actually made the probe, seen approaching at .866c, half its length in its own frame, then the same principle must apply to other objects, like my "signature example" of Earth. Flying by Earth at .866c would make its diameter contract to about 4000 miles. Can anyone actually believe that? I have no problem with its diameter *appearing* contracted to 4000 miles, but that would be a distorted image of Earth, not a physical planet with a diameter shrunken by half by the power of observation from the fly-by frame.
Earth "can be thought of" as having a shrunken diameter, but "in the real world" it stays just under 8000 miles, regardless of who is flying by howerver fast in whatever direction observing it.
Please address this directly.
Post by: old guy on 19/11/2012 18:45:39
I'm still waiting for an answer to my last post. Does the same principle hold for the force holding the probe together and changing the length of the probe as it moves, as you say, and the force holding Earth together and changing the length of its diameter as an observer flys by at high speed?No force required.
Your constant referring to a force is a reflection of your misunderstanding of time dilation and length contraction.
You can also demonstrate that forces can, in fact, be thought of as reshaping things at high speeds. The force holding the probe (in the famous probe example) together are electromagnetic and communicated at light speed. Since electromagnetism travels a the speed of light, and the speed of light is constant as the observer moves, these bonds change length and that changes the length of the probe as it moves. You can interpret this different ways, but it's pretty obvious that it can certainly be interpreted as the electromagnetic force leading to a reshaping of the probe as you fly by it at high speeds.
How about length contraction of the AU as an observer flys by Earth and Sun at near 'c?'
What are the forces holding together in this case, which then shrink because the observer's clock has slowed way down contracting the distance between Earth and Sun as the reciprocal of "time dilation?"
There is no consistency whatsoever between your explanation of length contraction in the above example and in these two cases.
Ignoring it does nothing to explain it.
Post by: zordim on 20/11/2012 11:35:55
http://www.thenakedscientists.com/forum/index.php?topic=46034.0
There are the commonsense answers to the questions raised in your thread.
Post by: old guy on 21/11/2012 19:35:37
I was hoping for a reply from JP to my last post before getting into what you mean by:
"There are the commonsense answers to the questions raised in your thread."
However, since there is really no answer to how Earth's diameter or the distance between Earth and Sun can "contract" as per "length contraction," he is stonewalling against the challenge.
So in plain English (not a long technical blog) what is your common sense answer to my length contraction challenge?
Post by: zordim on 21/11/2012 23:40:56
The length of an object which moves will shrink: the higher kinetic energy it has, the more it will shrink. The other objects, observed from that moving object will not shrink just because they are observed/measured from that moving object. These other observed objects will only appear to be shorter, to the observer which is on the object which moves.
That is what Einstein himself would tell you. His equations are very good approximation of the physical reality.
On the lowest, elementary level, there are things which have to be taken as axioms, as “that’s the way it is”. „The great desideratum for any science is its reduction to the smallest number of dominating principles.“
In my theory, I present such small set of principles, for the complete, unified physics.
Taking into account that it is just one-web-page long, and that it, nevertheless, unifies the physics, in the new, completely non-abstract and purely scientific way, and completely comprehensible way, classifies it as the very short answer to both “why” and “how” questions, ranging from elementary particles and up to accelerated universe expansion. Of course, including the "why the lengths shrink".
I just hope that many people will read it here, and that I will have an opportunity to discuss it.
Regards,
Zordim
Post by: zordim on 22/11/2012 09:26:45
If elementary inertial-mass-particles are the two-photons-whirls (and for that I provide quite reasonable arguments in FEMME and I also derived equations which are in accordance with experiments, and with reality in general), and since the photons must conform to the relation
, then the bodies should shrink whenever their energy is higher then their energy at rest.
Post by: old guy on 22/11/2012 19:09:19
"The length of an object which moves will shrink: the higher kinetic energy it has, the more it will shrink."
Does this agree with JP's explanation of the mechanism of shrinkage (of "my probe") in post 277?** If so, how does that account for contraction of Earth's diameter to 4000 miles in the direction of travel of an observer flying by at .866c?... or contraction of the distance to the Sun "as observed by" a similar fly-by past the solar system?
** As the probe was approaching Earth at .866c. it was measured to be 10 meters long. How long must the shuttle bay be to capture and retrieve it? If it had actually contracted to 10 meters, the 10 meter bay would suffice. But as the shuttle comes alongside the probe, it is seen as it is, 20 meters long. It had not, after all shrunk to 10 meters, as it appeared from Earth.
How does your, "The length of an object which moves will shrink...*" explain that? You said in your next post: "...then the bodies should shrink whenever their energy is higher then their energy at rest." Same question/challenge.
Another angle: If the probe's velocity relative to Earth had made it shrink, would it then gradually grow longer in the shuttle bay as the shuttle slows down and lands on Earth... like gradually grow back to 20 meters and bust out of the 10 meter bay.
Something is quite wrong with this scenario, don't you think?
Of course, the 10 meter bay would have appeared to shrink to 5 meters as seen from Earth as it came to rest with the probe... so even then it would appear to be half the length of the "apparently contracted" probe. What a bunch of nonsense!
Post by: David Cooper on 22/11/2012 21:14:29
We know that these length contractions happen because of the Michelson Morley experiment.
From the frame of reference of the probe while it is moving at 0.866c, the Earth appears to have been squished to 4000 miles wide. If the Earth is actually moving and the probe is stationary, the Earth really has been squished and the probe is not lengh compressed. The complication only comes into it with SR where all frames of reference are claimed to be equally valid, but switching which frame you analyse things from does not require anyone to think that it physically changes the diameter or length of anything, even if many people in the SR camp think they change - it simply changes the way things appear to be. The non-Euclidian 4D Spacetime stuff is hard to picture, but I've been told by an expert elsewhere that it's Lorentz invarient - I take this to mean that when you accelerate things within it they do not change shape at all and that it is only when we try to convert things from there into the 3D way that we ordinarily see the universe that all these length contractions are introduced. I may be misunderstanding that though.
Post by: old guy on 22/11/2012 22:41:32
Everything is moving. I agree with the part of relativity that says velocity has no meaning without specifying "relative to what?"
I also have no doubt that the faster an observer moves relative to an object, the more contracted that object will appear to the observer, and vice-versa (both frames of reference are "observers" in this context.)
So the probe will appear 10 meters long approaching Earth at .866c if it is actually 20 meters long... and the Earth will appear to have a diameter of 4000 miles from the probe's frame. (Mixing length units for consistency with past arguments here.) The key words are "appear" vs "actually." Earth's diameter does not actually shrink to accomodate how the probe sees it, nor does the probe's length actually shrink to accomodate how Earth sees it in this .866c relative velocity scenario, which works both ways.
The bay IS 10 meters long. The probe IS 20 meters long. All "appearences" aside, the probe will not fit in the bay, and it will not "actually" change lengths. All "appearences" aside, Earth's diameter IS and stays nearly 8000 miles regardless of how it might "appear" to a fast moving traveler. And the probe IS and stays 20 meters long regardless of how it appears from Earth.
Do both of you (zordim and D.C.) understand this? How about you, JP.
Post by: zordim on 23/11/2012 21:33:14
But, I have objections concerning "the velocity has no meaning without specifying "relative to what"".
On one side, we should recall the Newton's bucket, that is, the rotation.
On the other side, we have a photon. A photon's energy is both kinetic and intrinsic, at the same time. In other words, the kinetic and intrinsic energy of a photon is one and the same thing. And, the photon's energy is not relative to anything. It is
.Let us assume we have two photons, which have equal energies, which fly through the
-
-space, along two very near parallel opposite directions. Let us assume that, when they get nearest to each other, they form a two-photons-whirl. That whirl would be in an absolute-rest-position. It's velocity will be 0. A real 0. It would have intrinsic energy of 
. If it is a stable whirl, then it can be moved, that is, it can gain the kinetic energy.
; 
This simple derivation is physically justified in the most essential way possible, and it is also experimentally confirmed: if positron and electron have higher kinetic energy before their „annihilation“, then the photons which are the result of the positron-electron „annihilation“ have higher energies, too. Hence, an infinitesimal increase of their kinetic energy
, manifests itself as during "annihilation" - all in accordance with the energy conservation principle.The velocity of an elementary inertial-mass-particle, that is, of a two-photons-whirl (i.e. electron) which moves through
--spacetime, cannot reach the velocity 
. Because, the is the maximal possible velocity which the --spacetime allows, and, therefore, the intensity of the vector-sum of: - the circular velocity of the photon in the photon’s whirl,
- and the velocity of the whole whirl
can not exceed the velocity
. In the hypothetical case that the whirl as a whole reaches the velocity
, then it would turn into two paralelly and linearly moving photons. These photons will have higher energy then the photons which originally formed the two-photons-whirl.Hence, theoretically, the maximal possible increase of energy (mass) of the inertial-mass-particle is
, that is, about 65% increase of energy (mass) at rest. (I find it odd, that I could not find nothing newer about this, than "The Kaufmann experiments", from the beginning of the last century. I would expect that each particle-acceleration lab should have these data on their internet site, i.e. as a proof of the quality of their lab. I mean, this is, today, the easiest way to test the SR)And, if the time slows down in the system which moves linearly, with high velocity, then the equation for that time dilation is to be calculated from the following equation:
At least, that would be the change of the EM-oscillation period of the single photons which formed the whirl. It will be different than it was before they formed the whirl, because of the energy conservation principle.
Their length would have to shrink, too:
So, to clarify my point:
"Everything is moving". Energy and movement are practically the synonyms. Saying that "velocity has no meaning without spefying "relative to what"", means "existence has no meaning without specifying "relative to what". The photons exist. The electrons exist. The atoms, molecules, the universe exist. Relative to both everything and to nothing.
And the two-photons-whirl concept explains why is the statement "everything is moving" true. The lowest, the most essential level/manifestation of existence, is the photon. And the photon moves. "Moving" is its inherent property. That is how it exist. There are no photons which do not move. That is the existence axiom.
Post by: David Cooper on 23/11/2012 22:56:20
The bay IS 10 meters long. The probe IS 20 meters long. All "appearences" aside, the probe will not fit in the bay, and it will not "actually" change lengths. All "appearences" aside, Earth's diameter IS and stays nearly 8000 miles regardless of how it might "appear" to a fast moving traveler. And the probe IS and stays 20 meters long regardless of how it appears from Earth.
Do both of you (zordim and D.C.) understand this? How about you, JP.
What you're saying can be true with the Spacetime of SR, but if you reject Spacetime you're going to have to have actual, real, genuine, absolute length contraction of moving things. Without it, your theory conflicts with Michelson Morley.
Post by: old guy on 25/11/2012 19:26:56
Quote
What you're saying can be true with the Spacetime of SR, but if you reject Spacetime you're going to have to have actual, real, genuine, absolute length contraction of moving things. Without it, your theory conflicts with Michelson Morley.... and from 11/14:
Quote
The Michelson Morley experiment disagrees with you. Things are length contracted in their direction of travel.
I think you are still missing my point entirely. Here it is again:
Quote
The key words are "appear" vs "actually." Earth's diameter does not actually shrink to accomodate how the probe sees it, nor does the probe's length actually shrink to accomodate how Earth sees it in this .866c relative velocity scenario, which works both ways.
If the principle of length contraction were true, the probe would actually shrink to 10 meters when measured from Earth, approaching at .866c. But it only appeared to be 10 meters. The same holds in reverse for Earth as seen from the probe. To be consistent about length contraction, Earth would actually shrink in diameter to 4000 miles. That is blatant nonsense.
The same holds for the MM experiment, which you keep repeating as proof of length contraction. The arm in the direction of travel appears to shrink as distinct from actually shrinks as in the examples above... and in the example of the distance to the Sun, which might appear to shrink as seen from a fast fly-by frame.
You insist on "length contraction of moving things." Do you get that everything is moving, so velocity must specify "relative to what?"
So Earth is moving at .866c relative to the probe as well as vice-versa. Do you or do you not think that its diameter actually contracts to 4000 miles in that case? A direct answer would be refreshing. I can not get one one from JP, and zordim seems to be living in a universe of his own creation.
We have been over this many times. I hope it is "over" unless you answer the above directly as requested.
Post by: David Cooper on 25/11/2012 20:27:49
The key words are "appear" vs "actually." Earth's diameter does not actually shrink to accomodate how the probe sees it, nor does the probe's length actually shrink to accomodate how Earth sees it in this .866c relative velocity scenario, which works both ways.
If the principle of length contraction were true, the probe would actually shrink to 10 meters when measured from Earth, approaching at .866c. But it only appeared to be 10 meters. The same holds in reverse for Earth as seen from the probe. To be consistent about length contraction, Earth would actually shrink in diameter to 4000 miles. That is blatant nonsense.
You have to avoid mixing up different theories. In SR you can have a lot of what you're after with all the length contraction being apparent rather than actual. If you're prepared to adopt the Spacetime structure of reality, that's where you belong. If you don't like Spacetime though, you're left with OGVT and LET which are identical apart from the latter having objects length contract in their direction of travel such that the Michelson Morley experiment can be accounted for. In LET there are three possible realities. (1) The probe shrinks to half its length and the planet is not squished because the probe is moving and the planet is not. (2) The probe may be stationary and the planet moving, in which case the planet is squished and the probe is not length contracted. (3) Both the probe and planet are moving and both are affected by length contraction. The third of these possibilities is most likely to be the correct answer. Unlike with SR, in LET it is not the case that all of these possible descriptions are true, but there is no way to tell which of the three is correct from studying any lengths or speeds of things relative to each other.
Quote
The same holds for the MM experiment, which you keep repeating as proof of length contraction. The arm in the direction of travel appears to shrink as distinct from actually shrinks as in the examples above... and in the example of the distance to the Sun, which might appear to shrink as seen from a fast fly-by frame.
You are certainly entitled to make that claim if you place yourself in an SR camp.
Quote
You insist on "length contraction of moving things." Do you get that everything is moving, so velocity must specify "relative to what?"
Again you are entitled to make that claim if you are in an SR camp. It simply doesn't apply to LET, and it isn't clear that it applies to OGVT either because that seems to have a 3D space instead of 4D Spacetime.
Quote
So Earth is moving at .866c relative to the probe as well as vice-versa. Do you or do you not think that its diameter actually contracts to 4000 miles in that case? A direct answer would be refreshing. I can not get one one from JP, and zordim seems to be living in a universe of his own creation.
SR gives the appearance of contraction without requiring there to be any actual contraction. LET does not require the Earth to be contracted unless the Earth is moving through space. Because the Earth goes round the sun and the sun goes round in the galaxy, the Earth must be moving most of the time and will therefore be length contracted a little, but it isn't impossible that the galaxy (and all the others we can see) are moving at 0.866c and so all the stars and planets we can see could actually be squished to half their maximum width in the direction of travel - that would be highly unlikely, but it's impossible to tell that this is not the case. It would be fairly safe, however, to assume that they are not moving at all fast and are therefore not contracted to any great extent and that as a consequence any objects which are moving at very high speeds relative to us are going to be significantly length contracted (e.g. your alien probe), but that cannot be guaranteed to be true.
You want a definitive answer, but none is available: there is always going to be an "if". If Spacetime is the correct model, then length contraction can be apparent and everything is stationary and everything is moving, et cetera. If Spacetime is not correct, then LET (or varients of) would be the only game in town, in which case we absolutely do have actual length contraction but can't tell what is contracted and what isn't because we can't determine whether any specific thing is moving or not.
Quote
We have been over this many times.
Indeed we have, and it was all answered right at the start. The answers haven't changed along the way, and they won't change unless we can get some new knowledge about the nature of reality either through scientific discovery or logical reasoning (though the latter doesn't seem to get a lot of respect from the scientific side who pick and choose bits of reasoning to fit in with what they already believe).
Post by: old guy on 25/11/2012 22:53:44
Quote
SR theorists claim that from a frame of reference flying by Earth at near light speed ('c') Earth's diameter as measured in the direction of the fly-by would be contracted, making Earth a very oblate spheroid rather than the near sphere established by Earth science. Further, they claim that the effect is not just a distortion (appearance only) but that Earth is in fact flattened (like the subatomic particles) "for that frame of reference" and that "there is no preferred frame of reference," so that measurement (flattened shape of earth) is "equally valid."
What say you SR experts here?
imatfaal
Reply #1 on: 31/08/2012 17:09:37
Quote
From the rest frame of the ship it is completely valid. From the lab on earth we can predict with accuracy what the ship would observe and it matches what the ship's crew do observe.
D.C.,
I am not interested in your take on other theories as I've said several times before. I am challengeing the length contraction part of SR theory, as my OP clearly stated. I am also not interested in using "spacetime" as a way to explain that length contraction is image distortion or explained by difference in appearence, though that is my argument, sans "spacetime."
Imatfaal, a mod representing this forum as an expert on length contraction, answered my challenge... "so that measurement (flattened shape of earth) is "equally valid""... saying, "it is completely valid."
You continue to try to hijack this thread to promote your agenda about other competitive theories. Again, not interested.
I continue to be interested in getting an honest reply... from those here who speak for SR's version of length contraction... to the challenge of the length contracted Earth and distance to the sun. My probe & shuttle was a smaller scale example of the same principle they promote regarding those examples.
Post by: David Cooper on 26/11/2012 20:04:03
D.C.,
I am not interested in your take on other theories as I've said several times before. I am challengeing the length contraction part of SR theory, as my OP clearly stated. I am also not interested in using "spacetime" as a way to explain that length contraction is image distortion or explained by difference in appearence, though that is my argument, sans "spacetime."
If you reject Spacetime, you clearly must be interested in other theories, but other theories such as OGVT do not offer you any way out of length contraction other than by being incompatible with Michelson Morley.
Quote
Imatfaal, a mod representing this forum as an expert on length contraction, answered my challenge... "so that measurement (flattened shape of earth) is "equally valid""... saying, "it is completely valid."
Like you, I don't think that's the best position to be in - there are other camps within SR which do not suffer from that problem. If you were in such an SR camp, you would have a good position to argue from, but if you reject Spacetime you are rejecting SR and putting yourself into a position that's worse than that of the people you're attacking.
Quote
You continue to try to hijack this thread to promote your agenda about other competitive theories. Again, not interested.
It is impossible to give proper answers without covering all bases. If you don't want proper answers, don't ask for them.
Quote
I continue to be interested in getting an honest reply... from those here who speak for SR's version of length contraction... to the challenge of the length contracted Earth and distance to the sun. My probe & shuttle was a smaller scale example of the same principle they promote regarding those examples.
You've already had answers from them - they believe in something which appears to you and to me to be highly suspect. That is what you have discovered by asking your questions. What is the point in continuing to ask them about this when you already know where they stand? Maybe your aim is to convert them, but I don't think they're going to shift, and particularly when they're being told they're wrong by someone whose own model can't handle Michelson Morley, because whatever may be wrong with their model, it certainly can. Also, if they ever do feel the need to shift position on this, they don't need to change their model at all but can simply shift from one philosophical camp within SR into another without it making any difference to the maths.
Post by: old guy on 27/11/2012 19:24:17
"If you reject Spacetime, you clearly must be interested in other theories,..."
Don't tell me what I'm interested in! See bolded "not interested" comments in last post.
I am interested in debunking large scale (not subatomic) length contraction, and the reification of "spacetime" into a supposed entity which is curved by mass. If it were just a coordinate system/model (fine with me) GR theory would not insist that it is *something* which mass curves or that it is *something* which guides masses in their curved paths.
The same argument against an actually contracted Earth diameter and contracted distances between cosmic bodies holds for a contracted arm of a physical structure like the MM experimental apparatus (or a theoretical "alien probe.") Since you think otherwise, show me the difference, i.e., how the arm actually contracts but Earth's diameter (etc.) does not, as they all depend on the same theory and principle, i.e., that physical objects and actual distances change with how they are observed.
Post by: David Cooper on 27/11/2012 21:38:54
D.C.:
"If you reject Spacetime, you clearly must be interested in other theories,..."
Don't tell me what I'm interested in! See bolded "not interested" comments in last post.
Well, if you aren't actually interested in OGVT, stop telling us it's right.
Quote
I am interested in debunking large scale (not subatomic) length contraction, ...
Which means that Either you want to junk OGVT in favour of something like LET, or you adopt something like SR.
Quote
... and the reification of "spacetime" into a supposed entity which is curved by mass. If it were just a coordinate system/model (fine with me) GR theory would not insist that it is *something* which mass curves or that it is *something* which guides masses in their curved paths.
GR is the best reason for taking SR seriously, so I don't know why you'd want to ditch that.
Quote
The same argument against an actually contracted Earth diameter and contracted distances between cosmic bodies holds for a contracted arm of a physical structure like the MM experimental apparatus (or a theoretical "alien probe.")
And the train thought experiment too. Are you saying now that you are in an SR camp but that you reject GR?
Quote
Since you think otherwise, show me the difference, i.e., how the arm actually contracts but Earth's diameter (etc.) does not, as they all depend on the same theory and principle, i.e., that physical objects and actual distances change with how they are observed.
I assume you want this answered from an SR perspective, in which case I will place myself into a camp there which says that length contraction is apparent and not actual. That is the camp within SR which makes the most sense to me, and it's the one I think you'd be most comfortable in too (as I said long ago). I suppose you don't need to accept GR if you don't want to, so if that's your position then I congratulate you on working out that that is your position. If this is the case, some real progress has been made - next time you start this argument off at a science forum you can do so in more compact style, as follows:-
Quote
Hi,
I'm a believer in SR but not GR. I believe that length contractions are apparent and not actual - they merely show up as length contractions when you convert a 4D object into 3D space. I have a beef to pick with people who believe in SR but who think that objects change their actual shape as you view them from different frames of reference.
O.G.
Then someone can reply thus:-
Quote
Hi O.G.,
Nice to hear your point of view. Food for thought.
End of thread?
Post by: zordim on 28/11/2012 12:10:38
and are the essential properties of the space. Just like the lengths are the properties of the space. That is all. But it turned out to be the hardest thing to realize.Length, time,
and , is everything we need to start with, concerning space. To accept them as axioms, for which Maxwell already discovered the fundamental relation:The change of a photon position in time is equal to the reciprocal value of the
and are something that was discovered, measured, long time ago. They are electromagnetic properties. Of the space.Photon also has electromagnetic properties.
Electromagnetic is that what attaches energy and space, what enables the propagation of a photon, what enables photon's existence in the way it exists - as a linearly propagating EM-energy-oscillation, which has the wavelength (spatial property), and the period of oscillation (time property). The time in which a photon makes one full EM-oscillation is
.Any photon will propagate with the velocity
, regardless of its energy.A photon's energy is
.The equation
is the law that each photon has to obey.In the above text are given all that is necessary to derive all of the most important equations in physics, using simple infinitesimal calculus, because all of the essential properties of space and of a photon can and do change continually.
A photons mass, non-inertial mass, is
, that is, it is the measure of coupling, the convolution of photons elementary energy and epsilon-mu-space.http://www.thenakedscientists.com/forum/index.php?topic=46034.0
Best regards,
Zordim
Post by: old guy on 28/11/2012 21:59:12
" Well, if you aren't actually interested in OGVT, stop telling us it's right."
"OGVT" is your acronym. My "search" in this forum failed to find your first reference, spelling it out. Google just gave "OutGoing Verification Trunk." (?)
Me:
" I am interested in debunking large scale (not subatomic) length contraction," ...
You:
"Which means that Either you want to junk OGVT in favour of something like LET, or you adopt something like SR."
Huh? It means that the constant speed of light as per SR, which is well documented, does not automatically require that physical objects actually contract in length.
As said in my other (locked) length contraction thread, the "warning" on convex mirrors is applicable to the concept of length contraction. "Warning: Objects may appear closer than they are!" The LC version would be: "Warning: Objects approaching at very high velocity may appear shorter than they are!"
(So the "probe retrieval team" would have applied the Lorentz formula to "transform" the 10 meter long "appearance" of the probe... approaching at .866c... to its actual 20 meter length before foolishly sending out a shuttle with a 10 meter bay to retrieve it.)
As I understand your usage of "LET" the Lorentz "camp" says that physical objects do physically contract. I say that would require force to crush the object or compact the distance between the atoms of such objects.
SR claims that all frames are equally valid and that length is not invariant. Realism, my take, disagrees. Physical objects have inherent, intrinsic properties, including length, which do not change with the various frames from which they are observed. This repeats what I have said many times, because you still show no sign of understanding my argument.
You:
"GR is the best reason for taking SR seriously, so I don't know why you'd want to ditch that."
I accept that the math/model of GR improves upon Newtonian prediction of the effects of gravity. I deny that this requires insistence that "mass curves spacetime" (curves what?) and that the resulting "curved spacetime" guides masses in their curved paths. (Again, repeated many times... all lost on you.)
Me:
" Since you think otherwise, show me the difference, i.e., how the arm actually contracts but Earth's diameter (etc.) does not, as they all depend on the same theory and principle, i.e., that physical objects and actual distances change with how they are observed."
You:
"I assume you want this answered from an SR perspective, in which case I will place myself into a camp there which says that length contraction is apparent and not actual."
I wanted you to answer directly, truthfully, as you understand the answer.
If length contraction is "apparent and not actual" (as I see it), then the "contracted" arm of the MM apparatus is "apparent, not actual." Yet you constantly cite it as proof of actual length contraction.
Btw and finally, I find your mock post of my position, signed "O.G." very offensive, as follows:
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Hi,I have explained many times which parts of both SR and GR I reject, and which parts I accept. No such thing as a "4D object." All space and objects in it (not just lines and planes) are 3D (length, width & height) and as 3D objects move through space, "time elapses."
I'm a believer in SR but not GR. I believe that length contractions are apparent and not actual - they merely show up as length contractions when you convert a 4D object into 3D space. I have a beef to pick with people who believe in SR but who think that objects change their actual shape as you view them from different frames of reference.
O.G.
Post by: David Cooper on 28/11/2012 23:53:28
D.C.:
" Well, if you aren't actually interested in OGVT, stop telling us it's right."
"OGVT" is your acronym. My "search" in this forum failed to find your first reference, spelling it out. Google just gave "OutGoing Verification Trunk." (?)
OGVT = Old Guy's Vacuum Theory. I thought you'd understood that the first time.
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Me:
" I am interested in debunking large scale (not subatomic) length contraction," ...
You:
"Which means that Either you want to junk OGVT in favour of something like LET, or you adopt something like SR."
Huh? It means that the constant speed of light as per SR, which is well documented, does not automatically require that physical objects actually contract in length.
You may be interested in debunking it, but you won't be able to, so your interest should then drive you into taking up a position which actually fits the known facts. The train thought experiment, if you worked your way through it, would show up the necessity of actual length contraction in OGVT/LET type theories with a 3D space and it would force you into a Spacetime model if you want to retain the idea that length contraction is merely apparent (with as a side effect the necessity to do all sorts of strange things to time which I suspect you won't approve of).
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As said in my other (locked) length contraction thread, the "warning" on convex mirrors is applicable to the concept of length contraction. "Warning: Objects may appear closer than they are!" The LC version would be: "Warning: Objects approaching at very high velocity may appear shorter than they are!"
Okay, but so far as I can see that's going to force you into an SR camp.
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As I understand your usage of "LET" the Lorentz "camp" says that physical objects do physically contract. I say that would require force to crush the object or compact the distance between the atoms of such objects.
You've had this explained to you many times - the forces that are already applying between atoms (and other particles) have increased communication distances to cover if the object of which they are a part is moving, and that automatically causes them to settle closer together as the object moves more quickly through space. I've illustrated this in several different ways, but you don't appear to have understood any of them so there isn't a lot more that can be done there.
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SR claims that all frames are equally valid and that length is not invariant. Realism, my take, disagrees. Physical objects have inherent, intrinsic properties, including length, which do not change with the various frames from which they are observed. This repeats what I have said many times, because you still show no sign of understanding my argument.
In SR, lengths of things vary as you switch between 3D frames of reference. They do not change at all, however, within 4D Spacetime. SR is 4D Spacetime and it doesn't matter what people say about how things appear within 3D frames of reference, it's a 4D theory which offers you a lot of what you're after. My own opinion is that the people in the camp within SR who think things are physically changed in shape by observing them from different frames of reference are wrong because they don't actually understand SR.
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You:
"GR is the best reason for taking SR seriously, so I don't know why you'd want to ditch that."
I accept that the math/model of GR improves upon Newtonian prediction of the effects of gravity. I deny that this requires insistence that "mass curves spacetime" (curves what?) and that the resulting "curved spacetime" guides masses in their curved paths. (Again, repeated many times... all lost on you.)
I can assure you that everything that's being lost here is being lost in the other direction, but I can predict with considerable confidence now that you'll never realise that.
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I wanted you to answer directly, truthfully, as you understand the answer.
If length contraction is "apparent and not actual" (as I see it), then the "contracted" arm of the MM apparatus is "apparent, not actual." Yet you constantly cite it as proof of actual length contraction.
Don't get the theories mixed up. MM requires actual length contraction in an OGVT/LET type of theory. The alternative is that it requires you to use a 4D Spacetime model. If you have always accepted 4D Spacetime, then OGVT is the wrong name for what I thought was your theory of realism - I thought at that time that you rejected Spacetime, but now you're maybe happy to have it so long as you deny that it has any fabric to it.
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Btw and finally, I find your mock post of my position, signed "O.G." very offensive, as follows:QuoteHi,I have explained many times which parts of both SR and GR I reject, and which parts I accept. No such thing as a "4D object." All space and objects in it (not just lines and planes) are 3D (length, width & height) and as 3D objects move through space, "time elapses."
I'm a believer in SR but not GR. I believe that length contractions are apparent and not actual - they merely show up as length contractions when you convert a 4D object into 3D space. I have a beef to pick with people who believe in SR but who think that objects change their actual shape as you view them from different frames of reference.
O.G.
My intention was not to mock you in any way - I'm trying to help you state your position clearly so that it's possible for people to work out what you're on about. After 12 pages of this, it's still vague in a number of absolutely critical places. It's really quite simple to state your position, but you are clearly not willing to do so because it will trap you in a position that can be directly shown to be wrong, so you play games instead where you keep it all vague enough that you can slide around whenever you're pressed. It's like trying to pick a really awkward piece of soap out of the bath.
Post by: old guy on 29/11/2012 04:18:28
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I wanted you to answer directly, truthfully, as you understand the answer.D.C.:
If length contraction is "apparent and not actual" (as I see it), then the "contracted" arm of the MM apparatus is "apparent, not actual." Yet you constantly cite it as proof of actual length contraction.
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Don't get the theories mixed up. MM requires actual length contraction in an OGVT/LET type of theory. The alternative is that it requires you to use a 4D Spacetime model. If you have always accepted 4D Spacetime, then OGVT is the wrong name for what I thought was your theory of realism - I thought at that time that you rejected Spacetime, but now you're maybe happy to have it so long as you deny that it has any fabric to it.
I am not the one confusing theories here.
This is impossible mis-communication (or intentional distortion by D.C.)
" MM requires actual length contraction in an OGVT/LET type of theory."
D.C. clarified that he invented "OGVT" as "old guy vacuum theory." That space is empty volume is the "vacuum" part. Stuff exists and moves in space. That takes "time." Time is not a fourth dimension. It just passes... Earth goes around the Sun... cesium atoms have a very precise and regular oscillation in atomic clocks.
"... If you have always accepted 4D Spacetime, then OGVT is the wrong name for what I thought was your theory of realism -"
I have never accepted 4D spacetime. Quite the opposite, as is evident above and in all my posts. How can I communicate with someone who presents my argument as the opposite of what I am saying? (Rhetorical. I can't.)
me:
"Btw and finally, I find your mock post of my position, signed "O.G." very offensive, as follows:"
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Hi,me:
I'm a believer in SR but not GR. I believe that length contractions are apparent and not actual - they merely show up as length contractions when you convert a 4D object into 3D space. I have a beef to pick with people who believe in SR but who think that objects change their actual shape as you view them from different frames of reference.
O.G.
" I have explained many times which parts of both SR and GR I reject, and which parts I accept. No such thing as a "4D object." All space and objects in it (not
You:
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My intention was not to mock you in any way - I'm trying to help you state your position clearly so that it's possible for people to work out what you're on about.How condescending and arrogant! I have stated my position clearly and thoughtfully, expressed as "my position" in my own words.
I am "on about" the difference between apparent and actual contraction of physical objects. Not only do I not need your "help" for that, your "help" is just your own agenda ignoring, getting it wrong, and totally distorting what I am actually saying.
I showed how off your mock quote was, but you didn't even acknowledge how i corrected your misrepresentation of my position.
I can't get any help here for this kind of abuse, so I ask you again personally to quit this barrage of misinformation about my position... and express yourself in your own threads.
Post by: David Cooper on 29/11/2012 21:53:52
I am not the one confusing theories here.
Actually, you are. You keep attacking things I've said about one theory as if I'm talking about a different one. You don't seem to be able to compartmentalise them properly, and that's why your confusion never ends.
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This is impossible mis-communication (or intentional distortion by D.C.)
I haven't distorted a thing - you imagine distortions wherever your ability to understand things hits a rock.
" MM requires actual length contraction in an OGVT/LET type of theory."
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D.C. clarified that he invented "OGVT" as "old guy vacuum theory." That space is empty volume is the "vacuum" part. Stuff exists and moves in space. That takes "time." Time is not a fourth dimension. It just passes... Earth goes around the Sun... cesium atoms have a very precise and regular oscillation in atomic clocks.
Indeed I did, and that's exactly what I though your theory was at the time, but then you keep wobbling into SR territory without seeming to be aware of what you're doing, so all I've been trying to do is pin you down as to what your position actually is. You now appear to be accepting that OGVT is indeed your position, in which case your claims of realism don't fit it because it conflicts with MM.
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I have never accepted 4D spacetime. Quite the opposite, as is evident above and in all my posts. How can I communicate with someone who presents my argument as the opposite of what I am saying? (Rhetorical. I can't.)
If you don't do 4D Spacetime, then that pulls out a few rugs from under your feet - you have to have actual length contraction to account for MM.
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"Btw and finally, I find your mock post of my position, signed "O.G." very offensive, as follows:"
So you said in your previous post, and as I said in my previous post it was in no way intended to mock anyone. I'm simply trying to get you to pin your position down properly. Recently you've been talking as if you've adoped 4D Spacetime into your model - you made it clear that you have no interest in any theories other than SR, so that automatically excludes what I correctly understood to be OGVT. It sounded as if you'd shifted ground and didn't want to say so. Now you've made it clear that this is not the case, so your position puts you in a place where you cannot account for MM.
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QuoteMy intention was not to mock you in any way - I'm trying to help you state your position clearly so that it's possible for people to work out what you're on about.How condescending and arrogant! I have stated my position clearly and thoughtfully, expressed as "my position" in my own words.
You may think that, but you have the advantage of knowing what you think. What I see is someone squirming around and avoiding to answer questions which will expose his position as wrong, such as the crucial ones relating to the train thought experiment.
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I am "on about" the difference between apparent and actual contraction of physical objects. Not only do I not need your "help" for that, your "help" is just your own agenda ignoring, getting it wrong, and totally distorting what I am actually saying.
You don't have apparent contraction in your model unless it has Spacetime in it, which you've now stated categorically that it still doesn't. That being the case, I can now state categorically that your model conflicts with MM because it fails to allow for actual length contraction. The train thought experiment would show you that if you bothered to work your way through it.
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I showed how off your mock quote was, but you didn't even acknowledge how i corrected your misrepresentation of my position.
You're misrepresenting it as being mocking when it was nothing of the kind. That's very off indeed.
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I can't get any help here for this kind of abuse, so I ask you again personally to quit this barrage of misinformation about my position... and express yourself in your own threads.
I'm not giving you any abuse - I'm just asking you questions to try to pin down what it is you believe in so that I can show you exactly where you're wrong. Your problem is that you don't like being backed into a corner, and that's exactly where you now find yourself. Your theory is indeed OGVT, and that's just the old "realism" with a mistake in it which held sway until MM shattered it.
Post by: bizerl on 29/11/2012 23:08:57
DC, I too am having difficulty figuring out exactly how OG thinks the world works. It seems to me (and OG, this is purely my opinion based on what you have posted in my thread, I make no attempt to put words into your mouth or read your mind. This is just clarifying the impression I have on exactly what your views are), that OG is happy with the basic idea of relativity, apart from the existence of spacetime and length contraction. I thought these were integral parts of relativity.
It also seems to me (and DC, same disclaimer as above for you) that DC has been trying to find a way to fit OG's opinions on realism into an existing mainstream and thoroughly tested theory. If OG is rejecting these attempts, he really needs to come up with a new theory which (and I may be mistaken) I cannot really find in his posts.
There is a Simpsons quote (http://www.lardlad.com/assets/quotes/season12/CABF13.shtml) that comes to mind when reading this thread...
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Agnes: And you, start over. I want everything in one bag.
Pimple Faced Kid: Yes, ma'am!
Agnes: But I don't want the bag to be heavy.
Pimple Faced Kid: I don't think that's possible!
Agnes: What are you, the possible police? Just do it!
Post by: lean bean on 01/12/2012 13:57:30
"Time dilation" is a misnomer (time is not an entity) for the observed fact that physical processes (like the ticking of clocks) slow down when they travel at higher velocities. Muons enter Earth's atmosphere at very high speed, so thier rate of decay is slowed down accordingly. Therefore they "live longer" and travel further than would be expected at aslower(edit: higher) rate of decay.
Just checking old guy, with all this talk of putting you in a camp ( Hi-de-Hi), I was wondering why you talk of time dilation,above quote,do you 'agree' with SR on that point(time dilation) but not on length contraction?
Late add-on.
In order for you to show that there's no length contraction, can you give us a thought experiment where two frames are interacting Whilst one is moving at a relativistic speed to the other?
Your shuttle and probe idea has both shuttle/probe stationary in the same frame and not interacting whilst one is moving at a relativistic speed.
With all your 'research' I thought you would have notice this point by now.
Hi-de-Ho