Consistency of the speed of light

[Moneer81]

Hi:

Einstein's second postulate states that the speed of light is constant as viewed from any frame of reference. Most of the books on relativity that I have been reading usually ask the reader to accept that fact because proving it is behind the scope of the book. Can anyone help me understand the actual reason behind the second postulate?

thanks

 

[Aether]

Hi:

Einstein's second postulate states that the speed of light is constant as viewed from any frame of reference. Most of the books on relativity that I have been reading usually ask the reader to accept that fact because proving it is behind the scope of the book. Can anyone help me understand the actual reason behind the second postulate?

thanks

Moneer81, a "postulate" is something that you assume to be true at first for the sake of argument. In this case, the whole special theory of relativity follows from the postulates that the laws of nature are the same in all inertial frames, and that the speed of light is the same in all inertial frames.

So, the acutal reason behind the second postulate is this: special relativity follows from it + the other potulate. That does not mean that you could ever prove that it is true by doing experiments, and as it turns out you can't. On the other hand: nobody has ever proved that it is not true either, but they could.

 

[Moneer81]

hmm...that's interesting. I thought it was experimentally proven that the speed of light is constant from all frames of reference. I could swear that Brian Greene said that too in this book "The Elegant Universe".

 

[Aether]

hmm...that's interesting. I thought it was experimentally proven that the speed of light is constant from all frames of reference. I could swear that Brian Greene said that too in this book "The Elegant Universe".

I can't speak as to exactly what it was that Brian Greene said in his book, but nope, that could never be proven. However, as a postulate, it is simply true by definition within the framework of special relativity. However, don't let me give you the wrong idea: accepting that postulate for the sake of argument is usually a safe bet so long as you keep in mind that it's a postulate and not something that you could ever prove by making measurements.

 

[LURCH]

It has been proven that the speed of light has been the same from all refference frames in which the speed of light has ever been measured. That doesn't meab that it couldn't be different in some instance that we simply haven't measured, or it may even be different in every instance when we are not looking. Maybe we're like a cop sitting at the side of the road with a radar-gun, who concludes at the end of the day that "all drivers everywhere in the universe travell at or below the posted speed limit", not realising that all those drivers are just waiting until he;s not looking so they can floor it! Maybe light travels at all different speeds depending on what mood it's in, and only regulates itself to c when we're watching.

But it seems unlikely to me.

 

[russ_watters]

I thought it was experimentally proven that the speed of light is constant from all frames of reference. I could swear that Brian Greene said that too in this book "The Elegant Universe".

It has been. Aether (as his name would imply) is incorrect. Every attempt to measure the speed of light has always come up with the same answer, to within the margin for error of the experiment. Based on that, it is reasonable to theorize (and for the sake of further theories, postulate) that the speed of light is, in fact, always constant in inertial reference frames.

While Aether is correct that postulates are assumptions for the purpose of the theory, they are based on experimental evidence - and in this case, also the math of Maxwell's equations. It is important to note that theories require postulates. While it is theory that the speed of light is constant, for the sake of logical consistency, it is necessary to assume it to be universallly true for the sake of building other theories on it.

Postulates aren't just some random assumption you pull out of your a- er, um air... They have to be grounded in reality to actually be useful.

 

[Aether]

It has been proven that the speed of light has been the same from all refference frames in which the speed of light has ever been measured.

Special relativity is empirically equivalent to "...an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity..." R. Mansouri & R.U. Sexl, A Test Theory of Special Relativity: I. Simultaneity and Clock Synchronization, General Relativity and Gravitation, Vol. 8, No. 7 (1977), pp. 497-513. In such an empirically equivalent ether theory, the speed of light varies with direction.

This is not just some cherry-picked statement from an article that I pulled out of thin a- er, um air, it is the very crux of a famous paper referenced by most if not all of the experiments published over the past 30 years which measure local Lorentz invariance.

 

[ZapperZ]

Moneer81, a "postulate" is something that you assume to be true at first for the sake of argument. In this case, the whole special theory of relativity follows from the postulates that the laws of nature are the same in all inertial frames, and that the speed of light is the same in all inertial frames.

So, the acutal reason behind the second postulate is this: special relativity follows from it + the other potulate. That does not mean that you could ever prove that it is true by doing experiments, and as it turns out you can't.

This is not correct. A postulate does not mean one cannot verify it with experiment. One can and this is continually done on SR's postulates. A postulate on the other hand cannot be derived from First Principles! If it can, one doesn't need a postulate in the first place!

Zz.

 

[Aether]

This is not correct. A postulate does not mean one cannot verify it with experiment. One can and this is continually done on SR's postulates. A postulate on the other hand cannot be derived from First Principles! If it can, one doesn't need a postulate in the first place!

Zz.

This postulate has so far proven to be consistent with experiment, but so too has "...an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity...". No experiment has ever been able to distinguish between these two points of view, and if one ever does it could only favor the ether view.

 

[quantumdude]

Of course the speed of light postulate can be verified. Just measure the speed of light from any moving source.

In fact this has been done: Alvaeger F.J.M. Farley, J. Kjellman and I Wallin, Physics Letters 12, 260 (1964).

 

[JesseM]

This postulate has so far proven to be consistent with experiment, but so too has "...an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity...". No experiment has ever been able to distinguish between these two points of view, and if one ever does it could only favor the ether view.

Perhaps we could at least agree that it is possible to experimentally test the statement that the speed of light will be measured to be the same by all observers, assuming these observers all use the same type of procedure to make their own measurements (ie if one observer uses rulers and clocks which are at rest relative to himself to make his measurements, then all observers must do so).

 

[Perspicacious]

Can anyone help me understand the actual reason behind the second postulate?

The second postulate is an immediate consequence of Newton's first law of motion and the homogeneity of time.

http://www.everythingimportant.org/relativity/
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000043000005000434000001
http://arxiv.org/PS_cache/physics/pdf/0302/0302045.pdf

 

[JesseM]

The second postulate is an immediate consequence of Newton's first law of motion and the homogeneity of time.

No it isn't--it may be that you can use those assumptions to show that coordinate transformations must have the same general form as the Lorentz transformation equations, except with the constant c having the option of being infinite (and if you plug infinite c into the Lorentz transform you get the Galilei transform), as is suggested on that http://arxiv.org/PS_cache/physics/pdf/0302/0302045.pdf that you linked to. But the c in this equation has no necessary connection to the speed of electromagnetic waves--it is perfectly compatible with Newton's first law and the homogeneity of time that there would be no time dilation so you could synchronize clocks just by setting them to the same time in one location and moving them apart (in which case, assuming there's no Lorentz contraction you'll be using the Galilei transform to convert between different observer's measurements), and yet light would only have a constant speed in one preferred frame, while in other frames it would be measured to go faster in one direction than the other.

 

[Aether]

Perhaps we could at least agree that it is possible to experimentally test the statement that the speed of light will be measured to be the same by all observers, assuming these observers all use the same type of procedure to make their own measurements (ie if one observer uses rulers and clocks which are at rest relative to himself to make his measurements, then all observers must do so).

It is the convention used for the synchronization of clocks which determines the outcome of a one-way speed of light measurement. If you postulate that the speed of light is isotropic, then clocks are synchronized by Einstein's convention, and...voila...all subsequent experiments measure a constant speed of light. That does not constitute experimental proof that the speed of light is constant; it is not possible to ever prove that by experiment. It is possible to disprove it upon the identification of a locally preferred frame, but that hasn't been done yet, and maybe it never will be.

To prove that the speed of light is constant, you would have to prove a negative: e.g., "there is no locally preferred frame".

 

[ZapperZ]

This postulate has so far proven to be consistent with experiment, but so too has "...an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity...". No experiment has ever been able to distinguish between these two points of view, and if one ever does it could only favor the ether view.

You have missed my objection. You said:

"So, the acutal reason behind the second postulate is this: special relativity follows from it + the other potulate. That does not mean that you could ever prove that it is true by doing experiments, and as it turns out you can't."

A postulate does not mean you can't verify it with experiments. Read this again. This has nothing to do with SR.

And I'd like to see you come up with "time dilation" and "length contraction" based on your ether postulate, make just JUST fit together that they happen to cancel any variation to make it agree with the tons of experimental observations, and then publish it. Till then, you'll understand if I don't buy this.

Zz.

 

[Moneer81]

Merriam-Webster's dictionary defines postulate as:

to assume or claim as true, existent, or necessary : depend upon or start from the postulate of b : to assume as a postulate or axiom (as in logic or mathematics)

I guess the whole jargon is getting me a little confused, but what I know is that if we're going to have believe a theory like SR then it better be based on something that makes sense, and for those of us that don't believe in faith, it better be something we can convince ourselves that it is valid.

 

[Aether]

You have missed my objection. You said:

"So, the acutal reason behind the second postulate is this: special relativity follows from it + the other potulate. That does not mean that you could ever prove that it is true by doing experiments, and as it turns out you can't."

A postulate does not mean you can't verify it with experiments. Read this again. This has nothing to do with SR.

I agree that "a postulate does not mean that you can't verify it with experiments", but I don't see where I implied otherwise.

And I'd like to see you come up with "time dilation" and "length contraction" based on your ether postulate, make just JUST fit together that they happen to cancel any variation to make it agree with the tons of experimental observations, and then publish it. Till then, you'll understand if I don't buy this.

Zz.

I haven't suggested that you should buy an ether theory, yet. What I recommend that you should buy today is that the possibility has not been, and never will be, ruled out by experiment.

 

[Moneer81]

Aether (as his name would imply) is incorrect

LOOOOL

Sorry Aether, but that was a real good joke...original

 

[HallsofIvy]

There is a difference between a "postulate" in mathematics and a "postulate" in physics. In fact those blasted physicists should know better than to use the word "postulate" at all. I suspect that those who use it in a physics book are really saying "I don't want to bother to explain how this has be shown".

The fact that the speed of light is constant in all frames goes back to the Michaelson-Morley experiment- it and versions of it are probably one of the most "repeated" experiments in the history of science.

 

[Aether]

The fact that the speed of light is constant in all frames goes back to the Michaelson-Morley experiment- it and versions of it are probably one of the most "repeated" experiments in the history of science.

The round-trip speed of light, such as in MM experiments, is a constant in all frames because the issue of clock synchronization doesn't arise. However, that does not allow one to distinguish between special relativity and "...an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity...".

 

[JesseM]

It is the convention used for the synchronization of clocks which determines the outcome of a one-way speed of light measurement.

That's sort of true, but it's also true that as long as all observers use the same procedure to synchronize their clocks and construct their coordinate system (with no references to external markers--assume each observer is setting up their coordinate system in a windowless box), then if this procedure involves a definition of synchronization such that at least one observer measures light moving at the same speed in all directions, then all observers will measure light to move at the same speed in all directions in their own coordinate systems. Perhaps you could come up with some weird procedure that would result in all observers measuring light to have different speed in different directions, but it would probably be a pretty weird one--can you think of any examples of such a procedure? I suspect the only way to do it would be to use rulers that don't measure lengths the same even when placed side-by-side, or clocks that don't tick at the same rate even when placed side-by-side (and even then, I can't think of a universal procedure that all observers could use to decide how the different rulers and clocks should be oriented--if you have one ruler that's shorter than the other when they're put together, should the shorter ruler go on your left or your right? There's no experiment you can do in a windowless box that'll pick out a preferred axis in space, and you can't just pick randomly or you'll violate the assumption that each observer uses the same procedure to set up his own coordinate system).

 

[ZapperZ]

I haven't suggested that you should buy an ether theory, yet. What I recommend that you should buy today is that the possibility has not been, and never will be, ruled out by experiment.

And you should also never rule out the possibility that you could be entirely wrong (see? I can play that game too).

And you should also never rule out that our knowledge of the semiconductors in our modern electronics are wrong despite of the huge amount of experimental verifications, so at any given time, your life could be in extreme danger, such as when you are in an airplane. You should never rule out that your house could just crash on you because, franky, Newton's laws are based on principles that are never derived, but rather built on a bunch of postulates that were accepted to be valid only based on experiments.

Apply that to EVERYTHING that you know, and you'll see the absurdity of the situation. You ACCEPT a bunch of things that you take for granted to be valid. How come you never raise any question on them, but simply use this mantra on the postulates of SR?

Rather than showing a consistent and comprehensive theory of mechanics on the SAME grounds that SR has done, all you can do here is say "well, it could be wrong, even though I have no experimental evidence for it". Where exactly in the history of physics have things been proven to be wrong simply based on a matter of tastes and preference? Physics isn't a fad nor a fashion show!

Zz.

 

[Hans de Vries]

This postulate has so far proven to be consistent with experiment, but so too has "...an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity...". No experiment has ever been able to distinguish between these two points of view, and if one ever does it could only favor the ether view.

This is not true.


Some very common effects depend entirely on the non simultaneity of Special
Relativity. Take for example the EM wave front of electromagnetic radiation
(say light) which is at right angles with de direction of motion. No matter
from which reference frame you look a it.

see: http://physicsquest.homestead.com/plane-wave.gif

Now if you look from a reference frame which moves at 90 degrees with
the light then you see that the direction of the light changes more the
faster you go.

But the wavefront also rotates. It always stays at right angles to the
direction of motion of the wave.

Now how can you ROTATE the pattern with only Lorentz contraction ??
You can't. This is easy to see because the moving frame's speed is at
90 degrees with the direction of the light, in parallel with the wavefront.

It is the non-simultaneity of SR that performs the trick. In the moving
frame one side of the wavefront has propagated further while the other
side has propagates less, therefor the direction of the wavefront rotates.


Regards, Hans

 

[Aether]

And you should also never rule out the possibility that you could be entirely wrong (see? I can play that game too).

I am not playing a game. I don't rule out the possibility that I could be entirely wrong, but I did quote a strong reference in my initial post and you have ignored that.

And you should also never rule out that our knowledge of the semiconductors in our modern electronics are wrong despite of the huge amount of experimental verifications,

God, I hope so...really. Not altogether wrong, but missing something important.

so at any given time, your life could be in extreme danger, such as when you are in an airplane.

Hmm, I would not rule that out either. For example, see the attached picture of the Mt. Palomar observatory complex...I took this picture a couple of weeks ago from the outside of a glider at 11,000ft!

You should never rule out that your house could just crash on you because, franky, Newton's laws are based on principles that are never derived, but rather built on a bunch of postulates that were accepted to be valid only based on experiments.

Apply that to EVERYTHING that you know, and you'll see the absurdity of the situation. You ACCEPT a bunch of things that you take for granted to be valid. How come you never raise any question on them, but simply use this mantra on the postulates of SR?

Rather than showing a consistent and comprehensive theory of mechanics on the SAME grounds that SR has done, all you can do here is say "well, it could be wrong, even though I have no experimental evidence for it". Where exactly in the history of physics have things been proven to be wrong simply based on a matter of tastes and preference? Physics isn't a fad nor a fashion show!

Zz.

Please see the article that I quoted. It is referenced by most if not all of the published experiments testing local Lorentz invariance over the past 30 years.

 

[Aether]

This is not true.

Some very common effects depend entirely on the non simultaneity of Special Relativity. ...It is the non-simultaneity of SR that performs the trick.

If you will take the time to look up the Mansouri-Sexl reference that I cited earlier, you will find a more general transformation than the Lorentz transformation which accounts for every so-called relativistic effect while maintaining absolute simultaneity.

This article is referenced by most, if not all, of the published experiments testing local Lorentz invariance over the past 30 years!

 

[Perspicacious]

if we're going to have believe a theory like SR then it better be based on something that makes sense, …

it better be something we can convince ourselves that it is valid.

I like basing SR on the first postulate alone. Did you check out my insightful references? Why aren't you convinced of the perfect validity of that approach?

Lorentz transformations from the first postulate
A. R. Lee and T. M. Kalotas
Physics Department, La Trobe University, Bundoora, Victoria, Australia 3083

We present in this paper a derivation of the Lorentz transformation by invoking the principle of relativity alone, without resorting to the a priori assumption of the existence of a universal limiting velocity. Such a velocity is shown to be a necessary consequence of the first postulate, and the fact that it is not infinite is borne out by experiment.

 

[ZapperZ]

I am not playing a game. I don't rule out the possibility that I could be entirely wrong, but I did quote a strong reference in my initial post and you have ignored that.

You quote ONE strong reference? How could there be such a thing since you have claimed that ALL experimental evidence that support the postulate of SR also support YOUR theory. I asked for where has this theory of yours been published, thank you.

God, I hope so...really. Not altogether wrong, but missing something important.

Then the first time you point to me an experiment that support YOUR theory, I'll use the same argument to point out that it could be wrong since that experiment CANNOT prove your idea, per your own logic. But then again, you haven't produced anything on par with SR, have you?

Please see the article that I quoted. It is referenced by most if not all of the published experiments testing local Lorentz invariance over the past 30 years.

Pick out the list that I have down here and show me how any of these prove YOUR point but contradicts SR. If you can't, then you have none.

*************************************
This time there are two separate experimental reports on the test for any possible violation of the Lorentz invariance.

1. P.L. Stanwix et al. PRL v.95, p.040404 (2005).

This is the first results from a "rotating Mickelson-Morley" experiment. It tests for the violations of the Lorentz invariance in the photon sector of the Standard Model Extension and the isotropy of the Robertson-Mansouri-Sexl framework.

This experiment puts an even more stringent upper bound on 7 components of the Standard Model Extension. In other words, still no Lorentz invariance even though the accuracy of the measurement are already way within the realm predicted by some unification theories.

2. P. Antonini et al., PRA v71, p.050101 (2005).

This is essentially a similar experiement as the one listed above in (17) and confirms the result on the upper bound of any possible Lorentze invariance.

3. "Severe Limits on Variations of the Speed of Light with Frequency", B. Schaefer, PRL v.82, p.4964 (1999).
Also see Physics News Update report at http://www.aip.org/enews/physnews/1999/split/pnu432-2.htm .
This is the most accurate measurement to-date that c is independent of frequency/wavelength. If photons have any mass, or if c isn't a constant, this would manifest itself as a variation in speed at different frequencies. So far, none has been detected.

4. http://www.aip.org/enews/physnews/2000/split/pnu484-1.htm .
This is the most recent and accurate determination that the speed of light is independent of the speed of the source.

5. http://www.aip.org/enews/physnews/2002/split/590-1.html .
Again, this is the mostp recise test yet that the speed of light is independent of the direction of propagation.

6. "Tests of Relativity Using a Cryogenic Optical Resonator", C. Braxmaier et al., PRL v.88, p.010401 (2002).
Ether? What ether? This is the most precise determination to-date that the speed of light is independent of the velocity of the lab frame. The experiment used a version of the famous Morley-Michealson interferometer called the Kennedy-Thorndike test. You may read the Physics News Update report at http://www.aip.org/enews/physnews/2002/split/571-1.html .

7. "Tests of Lorentz Invariance using a Microwave Resonator", P. Wolf et al., PRL v.90, p.060403 (2003).

8. "New Limit on Signals of Lorentz Violation in Electrodynamics", J.A. Lipa et al., v.90, p.060403 (2003).
or read here http://physicsweb.org/article/news/7/2/12

In the 14th Feb. issue of Phys. Rev. Lett., there is not one, but TWO new experimental results that put a severe limit on any possible violation of the Lorentz transformation (which is built-in in Special Relativity). These two experiments present the most accurate result so far that c is velocity and earth-orientation independent. You may read the summary of one of this result at the AIP Physics News Update: http://www.aip.org/enews/physnews/2003/split/623-2.html or better yet, read the actual papers in PRL.


9. J. Luo et al., PRL v. 90, p.081801 (2003).
A report on a new measurement for the upper limit of a photon mass. In other words, if photons do have a mass, it can't be any larger than this, which is the current best resolution of our instruments to detect such a thing. This again put severe constraints on anyone claiming that photons do have a mass. http://www.aip.org/enews/physnews/2003/split/625-2.html

10. Muller et al., PRL v.91, p.020401 (2003).
This time, the evidence comes from the most accurate measurement to date of the uniformity of c using a modern version of the infamous Morley-Michealson experiment. Using cryogenic optical resonators, they measured for the possible anisotropy in the speed of light for over a year (as the Earth moves through space in its orbit around the sun and thus, changing its orientiation). The showed with unprecedented accuracy that the upper limit for any possible variation in c would have to be lower than 2.5 x 10^-15, which is 3 times more accurate than previous measurements.

11. M. Fullekrug, PRL v.93, p.043901 (2004).
We have another experimental evidence for the constancy of the speed of light - this time coming from very low frequency radio waves in the frequency range of 5 to 50 Hz. Again, this measurement places the upper limit on the photon rest mass (if any) at less than 4 x 10^-52 kg (yikes!).

12. This continues an earlier collection of experimental observations (listed here) that are consistent with the postulates of Special Relativity. This time the report comes from a workshop paper on the measurement of the isotropy of the speed of light using the cosmic microwave background radiation. This measurement claims the most stringent measurement on any possible anisotropy of c of our observable universe.

http://arxiv.org/abs/astro-ph/0410742

13. This new report provides an even more stringent upper limit on any possible violation of the Lorentz and CPT symmetry. This time it is done on neutrons in a boost frame.

F. Cane et al., Phys. Rev. Lett. v.93, p.230801 (2004).

Such upper limit will cause an even stricter constraints on the various theories of quantum gravity, string, etc., that predict an observable Lorentz violation, especially at the Planck scale.

This time there are two separate experimental reports on the test for any possible violation of the Lorentz invariance.

14. P.L. Stanwix et al. PRL v.95, p.040404 (2005).

This is the first results from a "rotating Mickelson-Morley" experiment. It tests for the violations of the Lorentz invariance in the photon sector of the Standard Model Extension and the isotropy of the Robertson-Mansouri-Sexl framework.

This experiment puts an even more stringent upper bound on 7 components of the Standard Model Extension. In other words, still no Lorentz invariance even though the accuracy of the measurement are already way within the realm predicted by some unification theories.

15. Now comes a report that IMPROVED upon this particular experiment.

http://arxiv.org/abs/physics/0508097

This work is to be published in PRL. However, notice that the same tests was done, this time a more severe restrictions on the upper bound on 8 different parameters was found, with the isotropy violation to being less than 2.1e-10!

 

[Hans de Vries]

which accounts for every so-called relativistic effect while maintaining absolute simultaneity.

We just can't do without non-simultaneity. Just try to envision the example
I gave. It shows it in a pictorial way without a character of math needed.
It doesn't get simpler than this.

1) Envision the Light wave goes from left to right.

2) You start moving downward faster and faster.

3) The effect is that the direction of the light rotates upwards.

Now the wavefront has to rotate over the same angle as well to stay at
right angles with the direction of the light! How do yo do that with only the
Lorentz contraction which just decreases the vertical dimension!
(since you're moving downwards)


Regards, Hans

 

[Hans de Vries]

non simultaneity

You may also want to look at some pictures from a computer simulation
I did on the deBroglie wave fronts of particles moving at an arbitrary speed.
Again, the non simultaneity of SR rotates the wave fronts here to keep
them always at right angles with the motion of the particle. No matter from
which reference frame you look at it.


See section 6 of: de Broglie


Regards, Hans

 

[Aether]

You quote ONE strong reference? How could there be such a thing since you have claimed that ALL experimental evidence that support the postulate of SR also support YOUR theory. I asked for where has this theory of yours been published, thank you.

"Thus the much debated question concerning the empirical equivalence of special relativity and an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity can be answered affirmatively." - R. Mansouri & R.U. Sexl, A Test Theory of Special Relativity: I. Simultaneity and Clock Synchronization, General Relativity and Gravitation, Vol. 8, No. 7 (1977), pp. 497-513.

 

[ZapperZ]

"Thus the much debated question concerning the empirical equivalence of special relativity and an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity can be answered affirmatively." - R. Mansouri & R.U. Sexl, A Test Theory of Special Relativity: I. Simultaneity and Clock Synchronization, General Relativity and Gravitation, Vol. 8, No. 7 (1977), pp. 497-513.

Look at the date of that paper, and look at the date of ALL the citations I have given. Now, use the "physics" from that paper and derive for me how you can show the consistency of those experimental results with that predicted by the paper. Note that in a number of the experiments, there are distinct variations to the test being done that approach the issue from a very different angle. These are not just your run-of-the-mill MM experiments.

I'd settle for that instead of asking for the formulation of a new set of "mechanics" based on such an ether.

Zz.

 

[Aether]

Look at the date of that paper, and look at the date of ALL the citations I have given. Now, use the "physics" from that paper and derive for me how you can show the consistency of those experimental results with that predicted by the paper. Note that in a number of the experiments, there are distinct variations to the test being done that approach the issue from a very different angle. These are not just your run-of-the-mill MM experiments.

I'd settle for that instead of asking for the formulation of a new set of "mechanics" based on such an ether.

Zz.

Which, if any, of your citations do not reference the paper that I cited? Which, if any, of your citations explicitly contradict the paper that I cited? Still, in the past I have collected as many of the papers cited in your journal (and their cited references) as I could get my hands on, and appreciate the list that you keep.

 

[Perspicacious]

"Once correctly and explicitly phrased, the principles of SRT allow for a wide range of `theories' that differ from the standard SRT only for the difference in the chosen synchronization procedures, but are wholly equivalent to SRT in predicting empirical facts."

http://arxiv.org/abs/gr-qc/0409105

 

[russ_watters]

There is a difference between a "postulate" in mathematics and a "postulate" in physics. In fact those blasted physicists should know better than to use the word "postulate" at all. I suspect that those who use it in a physics book are really saying "I don't want to bother to explain how this has be shown".

The fact that the speed of light is constant in all frames goes back to the Michaelson-Morley experiment- it and versions of it are probably one of the most "repeated" experiments in the history of science.

Ehh, I understand your objection, but what else do you call it, though? Logically, you must start with something that is assumed to be absolutely true before you can build on it, otherwise you become burdened with proving every theory related to your new theory, all at the same time. It would make for some awfully long papers... Nothing would ever get done.

To a knowledgeable scientist, this isn't an issue - they already know that the speed of light has been measured half a billion times, so there is no reason to bother explaining it when writing a new theory.

 

[russ_watters]

I am not playing a game. I don't rule out the possibility that I could be entirely wrong, but I did quote a strong reference in my initial post and you have ignored that.

The game you are playing is clinging to the short end of the every-experiment-ever-performed stick. Every experiment ever performed on the subject requires no ether, but you'd prefer to assume that there are some experiments we haven't thought of yet that might show it does exist.

Do you play slots...?

Yeah, I'm an engineer, not a physicist, but the way I see the issue is that as science progresses, the "box" that ether theory can fit into gets smaller and smaller and aether theorists bob and weave and back away further and further into the depths of that box, never wanting to acknowledge that there is an entire universe outside that box that they'd prefer not to live in.

 

[Aether]

The game you are playing is clinging to the short end of the every-experiment-ever-performed stick.

As long as there remains a short end to cling to, then somebody should; but the ether end of the stick isn't really as short as some people say.

Every experiment ever performed on the subject requires no ether, but you'd prefer to assume that there are some experiments we haven't thought of yet that might show it does exist.

Do you play slots...?

98% of the matter-energy in the universe is still missing...isn't a 98% payout considered to be a pretty good deal when it comes to playing slots?

Yeah, I'm an engineer, not a physicist, but the way I see the issue is that as science progresses, the "box" that ether theory can fit into gets smaller and smaller and aether theorists bob and weave and back away further and further into the depths of that box, never wanting to acknowledge that there is an entire universe outside that box that they'd prefer not to live in.

Ether theory is empirically equivalent to SR. It is flat wrong to claim that the constancy of the speed of light has ever been proved by experiment.

What's the difference? Assuming that the speed of light is constant, then x_0=\int{c(t)dt} reduces to x_0=c_0t...but if the speed of light is not constant then these two equations do not give the same result for x_0. Directly measuring x_0 is the future experiment that I have in mind.

 

[ZapperZ]

Which, if any, of your citations do not reference the paper that I cited? Which, if any, of your citations explicitly contradict the paper that I cited? Still, in the past I have collected as many of the papers cited in your journal (and their cited references) as I could get my hands on, and appreciate the list that you keep.

You seem to be ignoring what it is being cited for, and what these experiments are testing. For example, the Lipa paper clearly mentioned that they have come up with very severe limitations of the possible anisotropy of the M-S model. Furthermore, in a comment by Bay and White[1], and responded by Riis et al.[2], there clearly are questionable issues whether M-S model can account for Riis's 2-photon absoroption experiment.

However, in all of the papers that I cited, NOT ONE of them reach the conclusion that the postulate of SR has failed, and that they have found the extra terms of M-S model. NONE! You seem to use the fact that since M-S paper was cited, it has progressed beyond just being called a "test theory". It hasn't!

Zz.

[1] Z. Bay and J.A. White PRL v.62, p.841 (1989).
[2] Riis et al PRL v.62, p.842 (1989).

 

[Aether]

You seem to be ignoring what it is being cited for, and what these experiments are testing. For example, the Lipa paper clearly mentioned that they have come up with very severe limitations of the possible anisotropy of the M-S model. Furthermore, in a comment by Bay and White[1], and responded by Riis et al.[2], there clearly are questionable issues whether M-S model can account for Riis's 2-photon absoroption experiment.

OK, I'll look at that, but that exchange is 16 years old; why hasn't it been pursued since then?

However, in all of the papers that I cited, NOT ONE of them reach the conclusion that the postulate of SR has failed, and that they have found the extra terms of M-S model. NONE! You seem to use the fact that since M-S paper was cited, it has progressed beyond just being called a "test theory". It hasn't!.

Aren't they all looking for spatial anisotropy parameters? Which of these papers were looking for the three temporal parameters of the M-S model? The temporal coordinate x_0 can distinguish between SR and ether theory, but all of these experiments are looking only at x_1, \ x_2, \ and \ x_3 in vacuum.

 

[DrGreg]

The concept of speed depends on your definitions of distance and time. For an object that is static relative to the observer, these definitions are clear and unambiguous -- our pre-relativistic notions suffice. For a moving object, you need to have some mechanism for synchronising two clocks a distance apart; you cannot measure the time taken to travel from A to B unless the clocks at A and B (both static relative to the observer) have been synchronised in some way. And you can't measure the length of an object unless you measure the positions of each end "at the same time", whatever that means.

Therefore you cannot measure the speed of light from A to B unless you have already agreed a convention for synchronising clocks. The method that Special Relativity adopts assumes that the speed of light is constant. So if you measure the speed of light using this convention you are guaranteed to find it is constant. Within SR the speed of light is constant by definition. It's impossible to disprove unless you redefine what you mean by "speed" (or "distance" or "time").

However, you can unambiguously define the average speed of an object that travels from A to B and back to A again, relative to A. The total distance traveled and the total time taken can be measured using a single clock (A's) without any need for a synchronisation procedure. Experimental evidence does indeed confirm that the average speed of light from A to B to A is constant.

Let (t_0, x_0, y_0, z_0) be an inertial frame. Define a new set of coordinates as follows:

t = t_0 / \gamma
x = \gamma (x_0 - v t_0)
y = y_0
z = z_0

(where \gamma is defined in the usual way as 1/\sqrt{1-v^2/c^2}). Do the maths and you will find that in this coordinate system the (one-way) speed of light is not constant but average A-to-B-to-A speed is still c. And in this coordinate system, all clocks agree on what is "simultaneous". In a nutshell, this is Lorentz ether theory and it works. It's just a very ugly theory, compared with SR, because it's not at all symmetric and the equations get much more complicated. The coordinates are not all mutually orthogonal and its has non-diagonal metric tensor

ds^2 = dx^2 / \gamma^2 + 2 v dxdt + dy^2 + dz^2 - c^2 dt^2

I have just demonstrated that it is possible for the one-way speed of light to vary without deviating from the experimental evidence the two-way average speed of light is constant. But I've done by sleight-of-hand by redefining what I mean by "speed" which is the only way it can be done.

 

[Aether]

In a nutshell, this is Lorentz ether theory and it works. It's just a very ugly theory, compared with SR, because it's not at all symmetric and the equations get much more complicated.

An ugly theory compared to SR, in the absence of any evidence for a locally preferred frame, OK. Constancy of the speed of light proven by experiment, NO.

 

[ZapperZ]

OK, I'll look at that, but that exchange is 16 years old; why hasn't it been pursued since then?

Oh puhleeze. You're complaining about a 16-year old exchange while you're citing a paper that's 28 years old? I can play that game too. If the M-S theory is THAT old, why hasn't it been accepted more readily already by now?

Zz.

 

[Aether]

Oh puhleeze. You're complaining about a 16-year old exchange while you're citing a paper that's 28 years old?

You said that

...there clearly are questionable issues whether M-S model can account for Riis's 2-photon absoroption experiment

So, with 16 years gone by since these "questionable issues" arose, is it not legitimate to ask where those threads lead to?

I can play that game too. If the M-S theory is THAT old, why hasn't it been accepted more readily already by now?

Zz.

M-S theory is widely accepted; everyone who is publishing tests of local Lorentz invariance seems to be using it and nobody is knocking it. There are a few typos in it though, and I have seen where those errors have propagated through a few papers.

 

[robphy]

M-S theory is widely accepted; everyone who is publishing tests of local Lorentz invariance seems to be using it and nobody is knocking it. There are a few typos in it though, and I have seen where those errors have propagated through a few papers.

A few words from http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

Test Theories of SR
A test theory of SR is a generalization of the Lorentz transforms of SR using additional parameters. One can then analyze experiments using the test theory (rather than SR itself) and fit the parameters of the test theory to the experimental results. If the fitted parameter values differ significantly from the values corresponding to SR, then the experiment is inconsistent with SR. But more normally, such fits can show how well a given experiment confirms or disagrees with SR, and what the experimental accuracy is for doing so. This gives a general and tractable method of analysis which can be common to multiple experiments.

Different test theories differ in their assumptions about what form the transform equations could reasonably take. There are at present four test theories of SR:

Robertson,Rev. of Mod. Phys. 21, p378 (1949).
Edwards, Am. J. Phys. 31 (1963), p482.
Mansouri and Sexl, Gen. Rel. Grav. 8 (1977), p497, p515, p809.
Zhang, Special Relativity and its Experimental Foundations.​

Zhang discusses their interrelationships and presents a unified test theory encompassing the other three, but with a better and more interpretable parameterization. His discussion implies that there will be no more test theories of SR that are not reducible to one of the first three.

So, I think that it would be more correct to say that "M-S theory is widely accepted merely as a test theory of SR" (that is, a framework for testing SR).

 

[Aether]

So, I think that it would be more correct to say that "M-S theory is widely accepted merely as a test theory of SR" (that is, a framework for testing SR).

Here's Zhang's own summary of his book: "In particular, the simultaneity problem and slow transport of clocks are investigated in detail by means of the test theories of special relativity. In the second part, variant types of experiments performed up to now are analyzed and compared to the predictions of special relativity. This shows that the experiments are a test of the two-way speed of light, but not of the one-way speed of light."

I ordered copy of Zhang, and hope that the promise of "a unified test theory encompassing the other three, but with a better and more interpretable parameterization" is fulfilled.

 

[ZapperZ]

You said thatSo, with 16 years gone by since these "questionable issues" arose, is it not legitimate to ask where those threads lead to?

M-S theory is widely accepted; everyone who is publishing tests of local Lorentz invariance seems to be using it and nobody is knocking it.

But not in the way YOU imagined it. The "extra terms" beyond SR in M-S theory has never cropped up. They have never been measured. And in none of the experimental papers I cited have there been any indication by the authors that these verify the existence of ANY ether, no matter how one "synchronizes" one's clock.

The conclusions in each of the papers are glaringly clear. Why you think this agrees with your ether point of view, I have no idea.

Zz.

 

[Aether]

But not in the way YOU imagined it. The "extra terms" beyond SR in M-S theory has never cropped up. They have never been measured. And in none of the experimental papers I cited have there been any indication by the authors that these verify the existence of ANY ether, no matter how one "synchronizes" one's clock.

All measurements are so far consistent with both SR and Lorentz ether theory (with the possible exception of the example from 1989 that you gave), but you are implying that all measurements select SR over Lorentz ether theory.

The conclusions in each of the papers are glaringly clear. Why you think this agrees with your ether point of view, I have no idea.

The conclusions of each of the papers can't be stretched any farther than to say that SR is empirically equivalent to Lorentz ether theory (LET). What they fail to do is to select LET over SR, but you are claiming that they somehow select SR over LET and that is not true either.

 

[DrGreg]

An ugly theory compared to SR, in the absence of any evidence for a locally preferred frame, OK. Constancy of the speed of light proven by experiment, NO.

Experiments never prove a theory true, they can only ever succeed or fail to disprove a theory.

So there is always the possibility that one day somebody will find circumstances in which the two-way speed of light is not constant. If that day ever comes then SR or GR will have been proven not be a valid model in those circumstances.

Theories are models of reality, not reality itself. They tend to make simplifying assumptions e.g. that friction can be ignored, or that speeds are slow relative to light, or that gravity can be neglected, or that matter is distributed as a continuous density (instead of being particulate). That doesn't invalidate the theory as long as you are aware of its limitations.

Maybe one day we will need to reinvent the ether at quantum level or in some other extreme circumstances. If that ever happens, relativity will still be a valid approximation in the circumstances that aren't extreme.

 

[Perspicacious]

A test theory of SR is a generalization of the Lorentz transforms of SR using additional parameters. …

Different test theories differ in their assumptions about what form the transform equations could reasonably take. There are at present four test theories of SR. http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

Tom Roberts is wrong. Guido Rizzi, Matteo Luca Ruggiero and Alessio Serafini are right. What Mansouri and Sexl have is just the Lorentz transformation with a more general synchronization procedure.

It is possible to reset the clocks of the Mansouri and Sexl synchronization and get back to the Lorentz transformation. It’s silly to call generic resynchronizations of the Lorentz transformation a generalization of SR.

http://arxiv.org/abs/gr-qc/0409105

 

[Aether]

SR and LET are empirically equivalent. It is impossible to prove SR by experiment, and impossible to disprove LET by experiment. So, I suspect that there is some philosophical principle that places the burden of proof on the shoulders of LET. That's fine, but it doesn't license the disciples of Einstein to claim that the constancy of the speed of light has been proven by experiment.

 

[ZapperZ]

All measurements are so far consistent with both SR and Lorentz ether theory (with the possible exception of the example from 1989 that you gave), but you are implying that all measurements select SR over Lorentz ether theory.

The conclusions of each of the papers can't be stretched any farther than to say that SR is empirically equivalent to Lorentz ether theory (LET). What they fail to do is to select LET over SR, but you are claiming that they somehow select SR over LET and that is not true either.

Then you have NOTHING! You are faced with a theory that has tons of verification, have been successful in a lot of applications, including the accurate correction to many band-structure calculations, etc... etc. Given two theories, and one that has been adopted universally and used in REAL application, you chose THE OTHER?

And you see nothing wrong with this?

Zz.