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Author Topic: Evidence for large scale length contraction?  (Read 56674 times)

Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #75 on: 12/09/2012 06:49:55 »
I think it's fairly simple what the mods want. We can all soar, but that's for 'New theories', (although) it's quite hard not to put in your own interpretations in this Physics, Astronomy & Cosmology forum and we're all failable. This site was once constructed for giving people the chance to have in depth discussions, but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions, and to be perfectly strict also the math behind the reasoning. And the last demand is definitely the hardest. But that is if one want people to take one seriously, and then one probably publish elsewhere :)

« Last Edit: 12/09/2012 06:53:25 by yor_on »
 

Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #76 on: 12/09/2012 20:02:26 »
This reply will be appropriate to the parameters of the forum stated in yor-on's last post:
yor_on:
Quote
...but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions,...
(my bold.)

There seems to be an exception made for large scale length contraction of objects as a theory with no empirical evidence to support it, since, as JP pointed out, no one has yet observed Earth, for instance, from that ubiquitous, thought-experimental near 'c' fly-by frame. But Einstein loved a good thought experiment, and I thought I presented one as a reasonable test of length contraction in reply 17.
Quote
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
Also, from my reply 34:
Quote
The probe in my example is not actually 10 meters long, as (it was) observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)

The above was not directly addressed here the first time around. I hope it will generate relevant replies this time.
 

Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #77 on: 12/09/2012 20:44:31 »
I think it's fairly simple what the mods want. We can all soar, but that's for 'New theories', (although) it's quite hard not to put in your own interpretations in this Physics, Astronomy & Cosmology forum and we're all failable. This site was once constructed for giving people the chance to have in depth discussions, but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions, and to be perfectly strict also the math behind the reasoning. And the last demand is definitely the hardest. But that is if one want people to take one seriously, and then one probably publish elsewhere :)

There was a long argument caused by people using different interpretations of the word "real". Length contraction is absolutely real for Lorentz (though it's impossible to tell whether something's really been contracted as you can't tell if it's moving), while for Einstein it's real as a measured phenomenon. We can argue as much as we like about the degree to which Einstein considered it to be real in any other sense, but none of that makes any difference to his theory. Some people even think that objects are physically changed in shape by being observed by moving observers, and they can think that if they like, but so far as I am aware it is not a requirement of SR that you believe such a thing. It may be that Einstein considered all possible observed shapes of things as being absolutely real at the same time and that the one which maximised all its dimensions not to be superior - I haven't seen enough evidence to know what he believed on that point, but I certainly don't think it's crucially important to SR. Regarding the case where the dimensions of an object are all maximised as the real shape of that object would simply be a slightly different interpretation of a trivial detail of SR and not a new theory.
 

Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #78 on: 12/09/2012 21:01:33 »
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.

Is it Groundhog Day? This has already been answered. It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.

Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger. This allows you to decelerate the ship without a pile-up, and maybe it should be applied inwards from the sides of the cargo bay to avoid the force acting on one end of the ship before the other. You would close the rear door just as the end of the alien ship has entered the cargo bay (which is theoretically possible if the ship is very thin), and then you apply the force to stop the ship. The ship is completely contained in the cargo bay for a moment and is still moving at high speed, but that speed is completely removed in the next instant, thereby preventing it from crashing into the end wall. What will happen next? Well, all the atoms are too close together in the direction in which the ship was moving a moment earlier, so they will push out against each other and the ship will lengthen, either breaking its way through the wall and the door, or the ship will buckle badly in order to lengthen without exceeding the 10m space available to it.

I hope that helps.
« Last Edit: 12/09/2012 21:06:12 by David Cooper »
 

Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #79 on: 12/09/2012 22:03:16 »
David Cooper:"I hope that helps."
No, it only confuses the experiment, as I laid it out, with your own conditions.
The rules of engagement for a thought experiment are set by its author's conditions.
You say:
Quote
It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.

I said that the shuttle pulls alongside of the probe and finds that it is way longer than the 10 meters it was measured to be from earth. Yes, it will "be too large to fit", which was my point illustrating that its "contracted length" is much shorter than its actual length, as observed from its own frame of reference "alongside" it. The bay is a standard shuttle bay, not "open at both ends" for a brief fly-through by the probe. It either will fit in a 10 meter bay or it will not.

Quote
Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger.

This is blatant obfuscation of the thought experiment as I presented it.
The project was to retrieve the probe. The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

... And your 'evangelism' above is not helping the credibility of this thread. I expect it will be closed primarily because of your continuing rants, like about "The Church of Einstein" and such. You are hijacking this thread with your radical opinions.
I am still hoping for an intelligent replies to my experiment as I presented it.
 

Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #80 on: 12/09/2012 23:06:27 »
David Cooper:"I hope that helps."
No, it only confuses the experiment, as I laid it out, with your own conditions.
The rules of engagement for a thought experiment are set by its author's conditions.
You say:
Quote
It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.

I said that the shuttle pulls alongside of the probe and finds that it is way longer than the 10 meters it was measured to be from earth. Yes, it will "be too large to fit", which was my point illustrating that its "contracted length" is much shorter than its actual length, as observed from its own frame of reference "alongside" it. The bay is a standard shuttle bay, not "open at both ends" for a brief fly-through by the probe. It either will fit in a 10 meter bay or it will not.

I answered the question. It's up to you to interpret the results. While they were moving at different speeds, it did fit, and once they aren't, it won't.

Quote
Quote
Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger.

This is blatant obfuscation of the thought experiment as I presented it.
The project was to retrieve the probe. The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

It was a very clear way of looking at how things work and it will allow the shuttle to retrieve the probe.

Quote
... And your 'evangelism' above is not helping the credibility of this thread. I expect it will be closed primarily because of your continuing rants, like about "The Church of Einstein" and such. You are hijacking this thread with your radical opinions.
I am still hoping for an intelligent replies to my experiment as I presented it.

My radical opinions? I'm trying to be neutral about things, not pushing any theory forward as being correct, but making it clear where the failings of different theories lie so that people can make up their own minds, or better still, not make up their minds but continue to be open to all reasonable possibilities. I'm not interested in hijacking your thread - I'm only still posting here because I thought you were looking for help in understanding this, but you clearly aren't. You've had the answers you need from various people, but you simply reject them every time. I'm now being won over by the mods - they read you absolutely right. Goodbye.
 

Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #81 on: 13/09/2012 00:32:30 »
My last contribution to this thread, and an emphatic re-iteration of my previously stated position. My only reservation in the very definite statements I am about to make is that I know little of general relativity and its consequences, but I am well versed in special relativity.

Any object does have intrinsic properties. That is not a matter that hinges on any observational result -- it is a matter of definition. An intrinsic property of any object is one that is measured in or calculated to an observation in the inertial frame of reference that is stationary with respect to that object's centre-of-mass.

This definition automatically gives rise to the fact that an inertial frame of reference that is stationary with respect to the centre-of-mass of an object is a privileged frame in that it allows an observer to directly measure the object's intrinsic properties.

Both of these assertions are a matter of definition -- you cannot deny either of them unless you can establish that there is some ambiguity or indeterminacy in my definitions.

It is only through the operation of these definitions that we are able to make tables of atomic mass, Earth's shape and size, and 100,000 other intrinsic properties that are listed in the CRC Handbook of Chemistry and Physics.

It is only through the operation of these definitions that we are able to make generalizations such as "the (intrinsic) shape of any sufficiently large and plastic planet must be an oblate spheroid of revolution", and similar issues that were quite legitimately worrying old guy around posting #30 of this thread.

There is one other matter that I think needs to be cleared up:
Any idea that mentions "large scale" suggests a theory that treats large scale and sub-microscopic systems differently. If that is what is intended, then we need a smooth boundary condition at the swap-over scale. This is consistently achieved for quantum theory as a "sub-microscopic theory". I do not see how it could be for a Lorentz transformation that is well-established for sub-microscopic objects, but would become "switched off" for macroscopic ones.
 

Offline JP

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Re: Evidence for large scale length contraction?
« Reply #82 on: 13/09/2012 04:26:04 »
Hi Damocles,

I admit this thread has so many different subjects being discussed that I haven't kept up on all of them.  I tend to agree with you that a lot of properties of an object can be, and are in practice, defined in its center-of-mass rest frame.  And we definitely know when something is in our inertial reference frame.  It's center of mass won't be moving with respect to us, which is easy to observe. 

So we can define the properties of a known object by specifying them in its rest frame, but we cannot practically redefine our definitions of measurement of length and time in such a way.  If we did so, our clocks and meter sticks would have to change length to match the speed anything was moving with respect to us. 

What I've also argued against is the idea that length doesn't contract simply because we can define the length of an object in its center of mass reference frame.  Just as the laws of physics say a planet should be (roughly) spherical in it's COM frame, they also say it should be squashed if you're moving with respect to it.  Unless you choose to completely redefine how we make measurements, you're going to measure the planet as squashed and all physical laws formulated in your reference frame are going to treat it as squashed.  Of course, special relativity also allows you to formulate the laws from the planet's COM frame, in which case it's spherical and you are squashed.  Neither is more correct than the other because they both describe physical reality as measured by observers. 

-----------------------------------

The following isn't addressed at you, Damocles, but there's so many viewpoints being expressed in this thread that I feel I should make my point of view clear.

What I've also argued against  is the introduction of extra complexity to special relativity in order to preserve some preconception about the universe.  Science doesn't work that way.  We can always hold an infinite number of preconceptions about the universe and introduce extra hidden variables into a model to preserve them.  Obviously no one's arguing something this far out, but if I were more comfortable with unicorns causing length contraction, I could always introduce unicorns who zip about the universe shrinking our rulers with magical pony power.  As long as the unicorns are undetectable by measurement, and their pony power works identically to Lorentz contraction, I can claim that my results are completely in line with observations.  That doesn't this viewpoint valid science, nor does it make other viewpoints with far less absurd preconceptions valid science.  Science is generally about using the simplest possible model to describe some phenomenon, not choosing the more complex model because it fits your preconceptions.

A far more real point than the unicorns is that many scientists are also deeply religious and believe that a deity or deities play an important role in the universe.  Their personal view probably involves a complex theory that allows the deity to act but remain undetectable.  However, they also generally realize that good science does not involve complicating a theory with undetectable variables that have no influence on measurement, so when they present their work to other scientists, they present the 'mainstream' version of the theory. 

Einstein's special relativity is the mainstream scientific explanation because it is the simplest model which introduces the fewest extraneous variables and preconceptions and explains observations.
 

Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #83 on: 13/09/2012 04:37:00 »
There is no disagreement JP; I was simply wanting to defend the notion and status of intrinsic properties, because without them we lose an enormous amount of clearly correct, convenient, and valid science.

I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.
 

Offline JP

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Re: Evidence for large scale length contraction?
« Reply #84 on: 13/09/2012 04:44:28 »
I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.

Are intrinsic and extrinsic the usual technical terms used here?  It's been a while since I studied special relativity, but I don't recall ever learning terms other than "rest ____" to describe properties measured in the rest frame.
 

Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #85 on: 13/09/2012 04:49:55 »
Quote
Are intrinsic and extrinsic the usual technical terms used here?  It's been a while since I studied special relativity, but I don't recall ever learning terms other than "rest ____" to describe properties measured in the rest frame.

Probably not, but their meanings are fairly clear, they are much loved of philosophers, old guy had already used the terms, and someone in the earlier posts in this thread had objected to the use of "rest ..." properties.
 

Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #86 on: 13/09/2012 11:07:10 »
I was up till two this morning re-reading my Wolfgang Rindler - couldn't sleep.  I don't remember him using the words.  He tends to talk about rest frame, inertial frame, etc.  I must admit that in a discussion regarding Special Relativity I think they are potentially misleading in that they may lead to a misconception that the length contraction is not "real" - ie that it is merely an artifact of vision/observation rather than an actual consequence of frames in relative motion. 
 

Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #87 on: 13/09/2012 13:02:39 »

Any object does have intrinsic properties. That is not a matter that hinges on any observational result -- it is a matter of definition. An intrinsic property of any object is one that is measured in or calculated to an observation in the inertial frame of reference that is stationary with respect to that object's centre-of-mass.

This definition automatically gives rise to the fact that an inertial frame of reference that is stationary with respect to the centre-of-mass of an object is a privileged frame in that it allows an observer to directly measure the object's intrinsic properties.
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be  non identifiable.
« Last Edit: 13/09/2012 13:04:28 by lightarrow »
 

Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #88 on: 13/09/2012 13:23:58 »
I am sorry to have caused more confusion in what was already a confused and confusing discussion. Intrinsic is not a recognized technical term in the SR field.

It is purely and simply a term that I chose to define and use because there were a couple of problems with "rest" properties
(1) An objection to "rest mass" that Lightarrow expressed that I did not quite understand but attempted to accommodate. He suggested "invariant" but I had my problems with that particular term because I would want to restrict that term to quantities like c0 that are genuinely the same to all observers. The rest mass is indeed the same to all observers, but only privileged observers in the rest frame can measure it directly. Others have to deduce its value from the measurements they make of a non-invariant related property.
(2) A rather more trivial, but possibly confusing ambiguity in a rest property of a complex object: The rest property should be taken as the value of a physical quantity in the frame of the centre-of-mass of the complex object, but could be confused with a very different property that would be measured if all of the parts of the complex object were brought to rest relative to one another. This particular problem seemed about to come to the fore when someone -- lightarrow? -- started talking about neutron stars with incoherent internal motions at relativistic relative speeds.

I chose the words "intrinsic" and "extrinsic" because their normal meanings in the English language seemed very apt for the flavour I was trying to give them. The dictionary definition of "intrinsic" is "belonging to a thing by its very nature". The Earth has an "intrinsic" shape because local application of the laws of physics say that the equipotential surfaces in its gravitational field will be shaped as oblate spheroids of revolution, and it is plastic enough as a planet to have its surface adopt an equipotential shape (to a very close approximation). Basically, if the Earth were an observer, the intrinsic shape of the Earth is the one that it would know it had, in spite of whatever others may observe. It is a part of the Earth's nature. The opposite of intrinsic -- extrinsic -- means something that belongs to a thing only by virtue of a relationship with an external force or object. Extrinsic properties are every bit as "real" as intrinsic ones, but they can and do vary according to different relationships with different external objects.

But these terms are not SR technical terms. They are simply English words that I have chosen that in their normal English meanings capture the character that I see operating in properties of objects under SR conditions. The meanings are also congruent with those that several philosophers give them as technical terms.

From lightarrow:
Quote
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be  non identifiable.
Oh, and lightarrow, i have already in an earlier post in this very long thread, pointed out that an argument that a particular object might not possess a particular intrinsic property is not an argument against intrinsic properties per se. If the monochromatic light that it emits at a particular time is a property of a star, then it did have a unique rest frame at the time it emitted it; if we can no longer determine what that frame was that does not deny its existence, and nor does the fact that the star might since have died. And if the light is regarded as a property of the photons, then it cannot be intrinsic, because the photons themselves have no rest frame.
 

Offline flr

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Re: Evidence for large scale length contraction?
« Reply #89 on: 13/09/2012 15:25:26 »
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be  non identifiable.

Interesting point, but I have a quick question.
Let's assume there is a distant source (like our Sun) that emits harmless visible light for an Earth observer.
The observer take a  relativistic ship (0.9999c)  and travel toward the source. His ship screen out all radiation except those wavelengths that for the Earth frame were harmless visible light. Due to Doppler Effect the light that penetrates the ship will be now gamma-ray.
My question is: Will the observer on ship get hurt by gamma rays? Or in his ship those penetrating gamma rays (that on Earth were visible light) have the same impact as the visible light on Earth frame, i.e. they will be harmless?
« Last Edit: 13/09/2012 15:29:44 by flr »
 

Offline JP

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Re: Evidence for large scale length contraction?
« Reply #90 on: 13/09/2012 16:00:33 »
SR definitely has invariant quantities, which may be defined in terms of some formula entirely in terms of local measurements (in any inertial reference frame), and which turn out to be constant, no matter which reference frame is chosen. 

Rest properties seem a bit different, since they require a reference frame to be fixed.  However, it seems at first glance that (aside from light) you could always use local measurements to figure out the required transformation into a rest frame of the measuree and then transform whatever measurements you make to that rest frame.

However, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic.  Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic.  It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).
 

Offline JP

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Re: Evidence for large scale length contraction?
« Reply #91 on: 13/09/2012 16:14:39 »
His ship screen out all radiation except those wavelengths that for the Earth frame were harmless visible light.
 Due to Doppler Effect the light that penetrates the ship will be now gamma-ray.

What type of shielding are you using?  Most shielding will only care about how fast the light wave peaks hit its surface, i.e. the frequency.  Let's say the sun emits only one wavelength of visible light when your ship is at rest with respect to the sun.  The light wave's peaks hit your shielding at a slow enough rate that they pass through the shielding. 

Now you start flying really fast towards the sun.  Because you're flying into the peaks, they'll start hitting your shield faster.  Since your shield only cares about how fast the peaks hit it, it blocks the light and no light gets into your ship. 
« Last Edit: 13/09/2012 16:16:32 by JP »
 

Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #92 on: 13/09/2012 16:25:16 »
SR definitely has invariant quantities, which may be defined in terms of some formula entirely in terms of local measurements (in any inertial reference frame), and which turn out to be constant, no matter which reference frame is chosen. 

Rest properties seem a bit different, since they require a reference frame to be fixed.  However, it seems at first glance that (aside from light) you could always use local measurements to figure out the required transformation into a rest frame of the measuree and then transform whatever measurements you make to that rest frame.

However, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic.  Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic.  It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).

Now I am getting confused - a single photon has no invariant mass, it must be zero. Spin - yep
 

Offline JP

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Re: Evidence for large scale length contraction?
« Reply #93 on: 13/09/2012 16:37:30 »
Zero is still a number!   :)

I meant that having an invariant mass of zero still counts as having an invariant mass in the case of a photon, even though it has no rest frame.  You can calculate it from the length of it's energy-momentum four vector in any reference frame and get zero as a result.
 

Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #94 on: 13/09/2012 16:42:38 »
You had me worried there for a moment JP!
 

Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #95 on: 13/09/2012 18:34:10 »
A really nice discussion.
 

Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #96 on: 13/09/2012 18:52:06 »
While y’all are sorting out the semantics of technically acceptable language for describing length contraction... “rest frame, inertial frame, invariant or not”... and answering unrelated “trick questions,”
I still have received no unequivocal answer to the “will it fit?” question, illustrating the difference between the intrinsic length of the probe measured from at rest with it and the extrinsic , contracted length measured from Earth’s frame.

A very brief recent summary from my post 79, edited (...) for clarity of detail:
Quote
The project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

 As I said, “I am still hoping for intelligent replies to my experiment as I presented it.”

Damocles:
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The dictionary definition of "intrinsic" is "belonging to a thing by its very nature". The Earth has an "intrinsic" shape ...

So does my alien probe: its shape as it was built, obviously “at rest” with it.
Substitute “as it was originally formed by gravity” and you have the intrinsic shape of Earth.

Damocles said:
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It is only through the operation of these definitions that we are able to make generalizations such as "the (intrinsic) shape of any sufficiently large and plastic planet must be an oblate spheroid of revolution", and similar issues that were quite legitimately worrying old guy around posting #30 of this thread.

The core of my “worry” as expressed in post 30:
Me:
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Does this claim that Earth changes shape as it is measured from different frames of reference?
Lightarrow:
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Certainly. In a frame of reference which is still with respect of our planet, the Earth is spherical...; in another, moving, frame, it's not (and of course every human being is flattened too). Where is the problem?
Me:
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The "problem" is that, "in the real world" Earth does not change shape with every different possible measurement of it.

Damocles:
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I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.
(my bold)

Very contradictory! The “contracted length” of the probe or shape of Earth’s diameter is NOT the “actual” length/shape in either case.

Imatfaal:
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...misconception that the length contraction is not "real" - ie that it is merely an artifact of vision/observation rather than an actual consequence of frames in relative motion.

My thought experiment illustrates what is “real” about the length of the probe as compared with the “vision/observation”/measurement of it from Earth’s frame. It “really” will not fit into a 10 meter bay!

 

Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #97 on: 13/09/2012 19:14:56 »
"The project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built."

If you think of it OG. To retrieve that probe it will have to be in its so called 'rest frame'. And in that frame of reference the probe will have its 'rest properties', if you like. Assuming that the cargo bay is built to the dimensions we found the probe to have before joining up with it, becoming 'still' relative it, it will be found not to fit. The whole idea with a length contraction is that frames of reference will differ when compared, not that you will find length contractions being in the same frame of reference, 'at rest' with what you measure. As you are, approximately, on any planet.

 

Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #98 on: 13/09/2012 19:20:59 »
You still don't get it OG? We measure, and from there construct what is 'real'. There is no better way. Doing so we find that from the frame of the muon, if it could measure a distance, that distance must be contracted. You mix 'rest frames' with comparisons between frames, and somehow seem to assume that they are the same, always?

That's wrong.
=

What you can do is to assume that locally (locality) must be the preferred frame, just as the idea of 'invariant mass' have a same property assumed, no matter where it is measured. But the discussion about what is more 'real', comparisons between frames of reference, or comparisons being at rest with what you measure, is meaningless. They are both as real from the frame measuring. Instead of complaining, embrace it :)
« Last Edit: 13/09/2012 19:30:59 by yor_on »
 

Offline JP

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Re: Evidence for large scale length contraction?
« Reply #99 on: 13/09/2012 20:09:47 »
I still have received no unequivocal answer to the “will it fit?” question, illustrating the difference between the intrinsic length of the probe measured from at rest with it and the extrinsic , contracted length measured from Earth’s frame.

A very brief recent summary from my post 79, edited (...) for clarity of detail:
Quote
The project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

 As I said, “I am still hoping for intelligent replies to my experiment as I presented it.”

You've received plenty of replies, Old Guy.  You haven't received any that you happen to like, but that's now this forum operates.  :)

I think it's clear from almost every poster in this forum that the 'rest length' of the probe is longer than the 'rest length' of the cargo bay, while the measured length of the probe as it passes through the cargo bay in motion will be exactly as long as the cargo bay. 

You're engaging in evangelism of your viewpoint by continually restating the same arguments without engaging in discussion.  That is not acceptable on this forum.

If you do want to discuss what 'rest length' means vs. length measured in non-rest frames, there is an interesting discussion going on about that and you're welcome to engage in it, so long as you keep it a discussion.
 

The Naked Scientists Forum

Re: Evidence for large scale length contraction?
« Reply #99 on: 13/09/2012 20:09:47 »

 

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