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Author Topic: Evidence for large scale length contraction?  (Read 56707 times)

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.
 

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.
 

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?
 

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...
 

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.
 

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.
 

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.
 

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.)
 

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.
 

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.
 

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 »
 

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?
 

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.
 

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:
Quote
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.
 

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 »
 

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'.
 

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 »
 

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.
 

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.
Quote
, flying by very fast" Earth is severely oblate (to say a 1000 mile diameter in the direction of the observer's travel),... this is about how Earth is observed from different frames, not about Earth actually changing shapes as it is seen differently.
 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.
Quote
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.
 

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 »
 

Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #170 on: 26/09/2012 00:36:54 »
lightarrow:
Quote
Even the same word "observer" is misleading. It's not just an "observation", it's a *measurement*. It could be done from an authomatic instrument, in the absence of any living being.

"The observer" is the frame of reference. That is not the issue. The question is, do different frames of reference determine various realities like different shapes of objects, etc.? Does observation determine 'the shape of things' or do they have their own shapes? They do, and observation doesn't change their shapes.... or the distances between objects.
I must sign off again before finishing. (I have a life  :))

    , flying by very fast" Earth is severely oblate (to say a 1000 mile diameter in the direction of the observer's travel),... this is about how Earth is observed from different frames, not about Earth actually changing shapes as it is seen differently.
     Do you understand this difference?

:) It must be the 100th time we tell you in all ways that you haven't undestood that you are *defining* as "actual" what happens in the same frame of reference. What you really mean is this: without changing the frame of reference, to contract an object requires a force.
But here we are not discussing that, we are discussing another thing, that is the change of an object lenght changing the frame of reference.
 

Offline old guy

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

Quote
    Even the same word "observer" is misleading. It's not just an "observation", it's a *measurement*. It could be done from an authomatic instrument, in the absence of any living being.

(The forum linked my last post with a former one... so here it is as intended):

"The observer" is the frame of reference. That is not the issue. The question is, do different frames of reference determine various realities like different shapes of objects, etc.? Does observation determine 'the shape of things' or do they have their own shapes?
The answer is that they do, and that observation doesn't change their shapes.... or the distances between objects.
I must sign off again before finishing. (I have a life  :))
(The rest of what i saw as my post was a mistake.)
 

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.
 

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.
 

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?
 

The Naked Scientists Forum

Re: Evidence for large scale length contraction?
« Reply #174 on: 26/09/2012 18:38:02 »

 

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