Evidence for large scale length contraction?

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Offline old guy

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Evidence for large scale length contraction?
« on: 31/08/2012 17:51:10 »
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.
(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?

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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #1 on: 31/08/2012 18:09:37 »
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.

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #2 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.
(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?
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).

1. + 2. = ...

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #3 on: 31/08/2012 20:29:20 »
Thanks folks for the replies and welcome. What I am still confused about however is the difference between the phrases "for a muon" (the atmosphere is contracted) or "for the ship flying by Earth (its diameter is contracted) and the actual depth of earth's atmosphere and its actual diameter(s) (polar a bit shorter than equatorial) as well known and documented by Earth science.

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?

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #4 on: 31/08/2012 22:36:41 »
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.
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #5 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.

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #6 on: 01/09/2012 03:44:43 »
That's a question I'm working with too. Assuming, as I do, that a contraction/time dilation in some terms become a 'symmetry', you want the experimental proofs for it. the only proofs we have so far, that I know, ius those done high energy experiments in where we observe particles 'live' longer that they should, and in those astronomical as observing muons. But it is a very tricky thing to proof , if you think of it. Assume that you are on a very fast rocket measuring a distance. You may swear to that it is 'contracted', but that neigboor measuring you will swear to that it is your 'clock/time' that has slowed down. Time dilations, as gravitational are so much easier to proof experimentally and has been done by NIST at decimeters though. And if you think of it

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.
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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #7 on: 01/09/2012 04:06:53 »
The problem we meet is one of 'rigidity' relative 'plasticity'. Relativity is about 'plasticity' from a global perspective, comparing 'frames of reference', as you measuring some other position in (your local) time using that local ruler of yours. Locally 'rigidity' exist though, and object will behave the same when measured (uniform motion again:) as proved in our 'repeatable experiments'.

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?
« Last Edit: 01/09/2012 04:52:17 by yor_on »
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #8 on: 01/09/2012 18:40:00 »
So far no replies seem to have addressed my title question. I will reply to each point and ask more specifically in each case, in order of replies.
Imatfaal said:
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.

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:

Quote
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.
« Last Edit: 01/09/2012 18:52:17 by old guy »

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #9 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.

Quote
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.

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #10 on: 01/09/2012 21:55:41 »
David Cooper:
"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."

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #11 on: 02/09/2012 04:31:45 »
Heh :)

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.
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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #12 on: 02/09/2012 04:47:24 »
You could choose to interpret it as 'time' doesn't exist, but then you will have to explain how a gravitational 'time dilation' measured on Earth at decimeters can exist, and they do, everywhere. Why the discrepancies if it isn't something that differs? And if something differs there, what is it you would like to call it :) I call it time, or the arrow.

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.
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #13 on: 02/09/2012 18:02:56 »
I really need answers to my reply #6 before proceeding, or at least to my last question:
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:
Quote
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.
« Last Edit: 02/09/2012 18:07:12 by old guy »

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #14 on: 02/09/2012 19:15:58 »
It's geometry, not a force. The same way you can assume a gravitational wave to deform you, without yourself ever noticing. and there are no 'window dressing' implied in it. The muon will reach Earth although according to Newtonian values it should be unable to do so. And there are two frames of reference involved, the Earthly observer and the muons own frame of reference. Earths is a time dilation, the muon's 'clock' is slower than our local, The muon's perspective will be that its clock is as always, and that can only leave a contraction to be considered from its perspective. And as we have gravitational time dilations proofed, without us ever noticing them, you may assume that we have length contractions too.

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?
« Last Edit: 02/09/2012 19:35:09 by yor_on »
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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #15 on: 02/09/2012 20:10:45 »

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.”
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 #).
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".
« Last Edit: 02/09/2012 20:17:41 by lightarrow »

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #16 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.

Quote
...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.

Quote
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).

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #17 on: 03/09/2012 21:12:53 »
David Cooper:
Quote
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.
... with Einstein's theory there is no real contraction at all, but just the appearance of contraction when viewed from other frames.
(Yes, I got your PM.)

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:
Quote
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.


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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #18 on: 03/09/2012 21:37:22 »
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 :) 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
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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #19 on: 03/09/2012 21:56:30 »
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?

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.

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #20 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.

Quote
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.

Quote
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.

Quote
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.

Quote
"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.]

Quote
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.

Quote
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.

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #21 on: 04/09/2012 00:15:31 »
What it says to me is that it depends on what frame of reference you use. And so a contraction becomes a observer dependent fact, not illusion. And that's what Einstein himself say too.

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.
« Last Edit: 04/09/2012 01:06:01 by yor_on »
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Re: Evidence for large scale length contraction?
« Reply #22 on: 04/09/2012 01:20:59 »
As for your comment on all lengths being 'the same' if measured from a 'same frame of reference' I totally agree :) That's what I call a 'principle of locality'. The same principle that allow us to have 'repeatable experiments'. And I think you are perfectly correct in deeming that as the most important cohesive principle for a 'unified SpaceTime', that is if I read you right?
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Re: Evidence for large scale length contraction?
« Reply #23 on: 04/09/2012 19:36:25 »
David Cooper:
Quote
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)
Quote
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.
« Last Edit: 04/09/2012 19:40:08 by old guy »

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #24 on: 04/09/2012 20:06:11 »
David Cooper:
Quote
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.

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.

Quote
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.

Quote
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.

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Re: Evidence for large scale length contraction?
« Reply #25 on: 04/09/2012 20:26:04 »

I agree with your statement:
Quote
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.
"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.

Quote
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?
Certainly. In a frame of reference which is still with respect of our planet, the Earth is spherical (and of course every human being is flattened too); in another, moving, frame, it's not (and of course every human being is flattened too). Where is the problem?

Quote
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.

Quote
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".

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?
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/polebarn.html
There are an infinity of relativity "paradoxes". Of course they are not real paradoxes, after an accurate analysis of the problem's physics.

Quote
... 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.
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..."
« Last Edit: 05/09/2012 13:27:22 by lightarrow »

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #26 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...

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #27 on: 04/09/2012 23:12:28 »
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.
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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #28 on: 05/09/2012 13:29:46 »
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.
At least you agree with me  [:)]

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Re: Evidence for large scale length contraction?
« Reply #29 on: 05/09/2012 15:33:11 »
Yep, I do :)
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.
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #30 on: 05/09/2012 18:29:07 »
OK, as author of this thread, I think it's time to "cut to the chase."
Lightarrow said:
Quote
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:
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?

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.)

Quote
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:
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."

Wiki on Realism (my bold):
Quote
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.)
« Last Edit: 05/09/2012 18:44:45 by old guy »

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #31 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.

Quote
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).

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #32 on: 05/09/2012 20:29:55 »
Yep, it's frame dependent.
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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #33 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?

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #34 on: 06/09/2012 00:08:37 »
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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?
I "ditto" that. Also...
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?

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #35 on: 06/09/2012 00:57:28 »
Here is a point about special relativity that I hope might help clear up some of the confusion and controversy in this debate:

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.
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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #36 on: 06/09/2012 03:50:27 »
 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.




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Offline CPT ArkAngel

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Re: Evidence for large scale length contraction?
« Reply #37 on: 06/09/2012 03:54:51 »
In particles accelerators like the LHC, there is proofs that particles are flattened in the velocity direction.
« Last Edit: 06/09/2012 04:23:36 by CPT ArkAngel »

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #38 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.
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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #39 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?

Quote
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.....

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #40 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:
Quote
...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
Yes! Thank you.
« Last Edit: 06/09/2012 18:14:06 by old guy »

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #41 on: 07/09/2012 06:20:52 »
Flr, we all need somewhere to stand. You can construct the most lovely system and let it flow, but if you do you will get a headache :) So, relativity use 'c', and from that fact we get the time dilation, contractions (and relative motion). Then we have accelerations and 'gravity' as the next step to accept :) But I agree, and it's a cool way of thinking. It's the way I feel about it, as something 'plastic', but 'invariant locally'.

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.
« Last Edit: 07/09/2012 06:40:15 by yor_on »
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Offline hubble_bubble

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Re: Evidence for large scale length contraction?
« Reply #42 on: 07/09/2012 07:29:36 »
When a photograph of a moving vehicle is taken from a stationary position then the image is stretched simply because more photons are received from the moving surface. The car hasn't actually streched. At near light speed this effect would be enormously magnified so what does this say about length contraction?

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Offline hubble_bubble

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Re: Evidence for large scale length contraction?
« Reply #43 on: 07/09/2012 07:33:54 »
Think of it this way. Somewhere in the region of 300000000 m worth of photons will be received by your eyes, from your perspective, in a fraction of a second due to time dilation. This will give the impression of contraction. An enormously magnified 'apparent' contraction in the direction of motion.
« Last Edit: 07/09/2012 07:37:15 by hubble_bubble »

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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #44 on: 07/09/2012 18:23:04 »
OK - Enough.  This is a semi-official note that we either return to accepted ideas or the thread gets closed.

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!
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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #45 on: 07/09/2012 18:24:11 »
Nope :) Or yeah, you're correct, but the contraction exist. It's not what we want, we want a universe that 'makes sense', fitting our normal day impressions. And the idea of rods contracting due to 'frames of reference' is uncomfortable, not fitting with what we see. I can give you links to those using this length contraction, explaining 'forces' etc, but preferably not now, it's friday after all and? :)
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #46 on: 07/09/2012 18:45:51 »
imatfaal,
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.

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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #47 on: 07/09/2012 18:58:26 »
imatfaal,
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.
 

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. 
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #48 on: 07/09/2012 19:13:46 »
imatfaal:
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.

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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #49 on: 07/09/2012 19:30:14 »
I didn't agree with you - but I did address it.  You have decided - on the basis of zero evidence - that earth has an essential, absolute shape that forms part of a natual universal truth; the products of special relativity threaten your preconceptions therefore you reject the proven science and embrace your intuitions.  The idea of absolutes in time and space, of a universal reference frame, of immutability have been shown to be incorrect.  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.  If the question is positing a reality I do not recognize how could I begin to answer it based on my knowledge of my datum existence?
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