Evidence for large scale length contraction?

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #150 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.

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Offline wolfekeeper

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Re: Evidence for large scale length contraction?
« Reply #151 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?
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 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 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.

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #152 on: 24/09/2012 21:25:27 »
David Cooper:
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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?

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #153 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   

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...

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #154 on: 24/09/2012 21:39:16 »
David Cooper:
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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?

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.

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #155 on: 24/09/2012 22:35:00 »
:) 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:)

This one might do though? 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.
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #156 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 contraction
Please *define* "real" and "apparent" in this context.

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Offline wolfekeeper

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Re: Evidence for large scale length contraction?
« Reply #157 on: 25/09/2012 12:23:41 »
David Cooper:
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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?
Yes, that's partially true, all the effects are due to distortions when something accelerates.

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.)

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #158 on: 25/09/2012 19:07:47 »
wolfekeeper:
"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.

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #159 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.

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Offline wolfekeeper

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Re: Evidence for large scale length contraction?
« Reply #160 on: 25/09/2012 21:04:29 »
wolfekeeper:
"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.
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).

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.
« Last Edit: 25/09/2012 21:16:15 by wolfekeeper »

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #161 on: 25/09/2012 21:18:11 »
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.
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. 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?

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #162 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?  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 contraction
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.

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #163 on: 25/09/2012 21:25:00 »
David Cooper:
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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?
Yes, that's partially true, all the effects are due to distortions when something accelerates.

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.

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... 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.

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #164 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.
« Last Edit: 25/09/2012 21:34:44 by David Cooper »

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Offline wolfekeeper

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Re: Evidence for large scale length contraction?
« Reply #165 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'.

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Offline wolfekeeper

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Re: Evidence for large scale length contraction?
« Reply #166 on: 25/09/2012 21:49:00 »
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.
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.
« Last Edit: 25/09/2012 21:50:51 by wolfekeeper »

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #167 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.

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #168 on: 25/09/2012 22:57:28 »
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.
When SR speaks of "for observer A, at rest with Earth"... Earth is spherical (almost), while "for observer B
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.
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, 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.
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.
In physics, to change the shape of a physical object, a force must be applied.
No, you're wrong. Not in this case.

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #169 on: 25/09/2012 23:08:24 »
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.
Here you make other two "hazy" statements  [:)]
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...
« Last Edit: 25/09/2012 23:13:14 by lightarrow »

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #170 on: 26/09/2012 00:36:54 »
lightarrow:
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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.

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #171 on: 26/09/2012 00:44:42 »
lightarrow:

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    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.)

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #172 on: 26/09/2012 13:38:49 »
The question is, do different frames of reference determine various realities
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.
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like different shapes of objects, etc.? Does observation
Please, 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.

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #173 on: 26/09/2012 18:09:12 »
lightarrow,
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.

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Offline wolfekeeper

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Re: Evidence for large scale length contraction?
« Reply #174 on: 26/09/2012 18:38:02 »
No, the universe physically changes around you.

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?

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #175 on: 26/09/2012 18:47:50 »
 Me:
 “The question is, do different frames of reference determine various realities”

Lightarrow:
Quote
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.

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Re: Evidence for large scale length contraction?
« Reply #176 on: 26/09/2012 19:14:57 »
wolfekeeper:
"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!

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #177 on: 26/09/2012 19:24:06 »
Me:
 “The question is, do different frames of reference determine various realities”
Me: of course they do. Because for me "reality" means "what I measure".
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.

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lightarrow

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #178 on: 27/09/2012 17:46:29 »
Me:
 “The question is, do different frames of reference determine various realities”
Me: of course they do. Because for me "reality" means "what I measure".
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.

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lightarrow
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.
Thanks for the conversation.
Edit, Ps:
David Cooper, in post 162:
Quote
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.
« Last Edit: 27/09/2012 18:12:38 by old guy »

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #179 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.

Quote
Quote
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.

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.
« Last Edit: 27/09/2012 20:38:28 by David Cooper »

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #180 on: 27/09/2012 20:59:59 »
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 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!

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #181 on: 27/09/2012 21:05:37 »
It's easy to see if it is a true measurement, we only need a relativistic speed. And if those measurements you make tell you a distance, according to your clock and ruler, then it will be real for you. To argue otherwise becomes a statement that no measurements can be true. And this isn't just valid for accelerations, we use that statement (accelerations) for defining a clear point of departure from a uniform motion, but the contraction aka relativistic speed will be measurable in your subsequent uniform motion too, and for that you can use the relativistic effects you will see as blue shift, geometric distortions etc. It would be simpler if a acceleration was what expressed those two, but it's not. they will exist in a uniform motion too, and that's why you in your local frame of reference (the rocket) use blue shifts, distant stars, and/or possibly the CBR (Cosmic Background Radiation)
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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #182 on: 27/09/2012 21:17:57 »
There's another logic implausibility in this discussion. The idea that as my ruler according to some other frame 'shrinks' by my (relativistic) speed, then this also explains the shrinking of distances according to me as i measure a distance locally.  Think about it and then tell me how my shrunken ruler would make it possible for me to measure a shortened distance locally, meaning from my frame of reference measured in/from my speeding rocket. Or you can use the muon and assume as it must have shrunk according to relativity then what it measure as the distance to the ground by all means must give it a farther value, if one can express it that way. A contraction and a time dilation is a symmetry.
=

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.
==

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:)
« Last Edit: 27/09/2012 22:12:49 by yor_on »
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Offline namaan

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Re: Evidence for large scale length contraction?
« Reply #183 on: 28/09/2012 03:11:09 »
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?

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.
« Last Edit: 28/09/2012 03:20:23 by namaan »
Take it with a grain or two of salt...

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Re: Evidence for large scale length contraction?
« Reply #184 on: 28/09/2012 09:39:03 »
Well, yes. From a point of science it should be what is measurable by experiments that defines your theories. But it becomes a quagmire when we wander out in those areas defined by weak measurements, as they all to often build on our old definitions of causality chains. Science builds on the concept of measurements, experiments, and logic as I think. Some things, as logic, are 'archetypes' meaning that those are what we stand on, go out from, and trust in. If we didn't we would have a universe in where unicorns wander freely, so to speak:) depending on ones expectations and further explanations. But accepting the results from theory and experiments can be very hard.
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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #185 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.

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Offline namaan

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Re: Evidence for large scale length contraction?
« Reply #186 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.
Take it with a grain or two of salt...

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #187 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.

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #188 on: 28/09/2012 17:50:25 »
namaan:
Quote
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.

Quote
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.

Quote
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.)

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #189 on: 28/09/2012 18:51:08 »
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.

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Offline namaan

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Re: Evidence for large scale length contraction?
« Reply #190 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.
Take it with a grain or two of salt...

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #191 on: 28/09/2012 19:21:49 »
Yep, I meant the general "you."

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Re: Evidence for large scale length contraction?
« Reply #192 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. 

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #193 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.

Quote
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.

Quote
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.

Quote
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".
« Last Edit: 28/09/2012 20:39:12 by David Cooper »

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #194 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?

Quote
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?
Quote
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.

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #195 on: 28/09/2012 23:49:19 »
It's your thread OG :)
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.
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #196 on: 29/09/2012 18:53:55 »
yor-on,
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.  :(

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #197 on: 30/09/2012 12:19:03 »
In Einsteins definition there is no aether which I read as there is no preferred frame of reference. If there was one we would have absolute motion relative that one, and then you also can link such a frame to your observations of other 'frames of reference', meaning that we suddenly would have a definition of lights speed as not being a 'constant' globally, although still being so locally. In the absence of such a frame discussing space, relating this to Einstein, you have to incorporate time, then becoming SpaceTime. It's a whole concept SpaceTime, but, considering length contractions and time dilations you have two views. One is the one from locality and measurements, as in experimental evidence by yourself first handedly. There your ruler and clock never varies locally making your experiments and observations what you can measure. And that's reality, if we by that mean measurability.

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.
=

correcting spellings etc. Keep missing those small ones :)
« Last Edit: 30/09/2012 12:38:33 by yor_on »
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Offline namaan

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Re: Evidence for large scale length contraction?
« Reply #198 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.
« Last Edit: 01/10/2012 03:03:28 by namaan »
Take it with a grain or two of salt...

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #199 on: 01/10/2012 23:51:30 »
namaan:
Quote
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:
Quote
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:
 
Quote
  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:
Quote
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.