Consistency of the speed of light

[ZapperZ]

SR and LET are empirically equivalent. It is impossible to prove SR by experiment, and impossible to disprove LET by experiment.

It is not! There are two extra terms in M-S theory regarding the ratio between c(\theta , v)/c. The Lipa et al. results have put severe limits on the value of those two extra terms! To claim no one has gone looking for it is false.

Zz.

 

[pervect]

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 job of making experimental predictions should be the responsibility of the Lorentz Ether theorists.

Unfortunately, they appear to be a very diffuse group, who while they all use the same name, don't actually all believe the same thing.

If, as in one subsection of the LET group claims, there is no difference between LET and relativity, then it is not a different theory than relativity.

If, as in another subsection of the LET group claims, there is a difference between LET and relativity, it is (or should be) up to the LET theorists to pin down what experimental predictions the theory makes, so the theory can be tested.

Part of the problem is that I don't think LET actually has any qualified theorists who write refereed papers that one can point to as "the" LET theory, rather it has only a muddle of individuals who have somehow given the same name to their differing ideas.

 

[Aether]

It is not! There are two extra terms in M-S theory regarding the ratio between c(\theta , v)/c. The Lipa et al. results have put severe limits on the value of those two extra terms! To claim no one has gone looking for it is false.

Zz.

"Summarizing these results we may say that the following statement is in perfect agreement with all experimental evidence: A preferred system of reference, the ether system, exists." - Mansouri & Sexl I

"All experiments can be explained either on the basis of special relativity or by an ether theory incorporating time dilation. This demonstrates again the impossiblity of an "experimentum crucis" deciding between ether theories and the special theory of relativity." - Mansouri & Sexl - II

"First-order tests cannot be used to distinguish between special relativity and ether theories, as has sometimes been stated. No such "experimentum crucis" is possible in principle, since the two classes of theories can be transformed into one another by a change in conventions about clock synchronization..." - Mansouri & Sexl - II

"According to these authors this experiment [similar to the Michelson-Morley experiment] is able to decide between the special theory of relativity and an ether theory incorporating Lorentz contraction and time dilation. As we have shown quite generally in the first and second parts of this paper such a distinction is impossible in principle." - Mansouri & Sexl III

 

[Perspicacious]

The job of making experimental predictions should be the responsibility of the Lorentz Ether theorists.

Unfortunately, they appear to be a very diffuse group, who while they all use the same name, don't actually all believe the same thing.

If, as in one subsection of the LET group claims, there is no difference between LET and relativity, then it is not a different theory than relativity.

If, as in another subsection of the LET group claims, there is a difference between LET and relativity, it is (or should be) up to the LET theorists to pin down what experimental predictions the theory makes, so the theory can be tested.

Part of the problem is that I don't think LET actually has any qualified theorists who write refereed papers that one can point to as "the" LET theory, rather it has only a muddle of individuals who have somehow given the same name to their differing ideas.

Very well said. I agree.

 

[Aether]

I have scanned-in the three Mansouri & Sexl papers. If anyone is interested but doesn't have easy access to a library with the journal, let me know and I'll give you a web address where you can go to download the file (it is about 143MB); right click on the link, and save. It is in MS Word .doc format, and it comes from my working copy so please excuse that it has been heavilly highlighted and is somewhat marked up and wrinkled.

 

[ZapperZ]

"Summarizing these results we may say that the following statement is in perfect agreement with all experimental evidence: A preferred system of reference, the ether system, exists." - Mansouri & Sexl I

"All experiments can be explained either on the basis of special relativity or by an ether theory incorporating time dilation. This demonstrates again the impossiblity of an "experimentum crucis" deciding between ether theories and the special theory of relativity." - Mansouri & Sexl - II

"First-order tests cannot be used to distinguish between special relativity and ether theories, as has sometimes been stated. No such "experimentum crucis" is possible in principle, since the two classes of theories can be transformed into one another by a change in conventions about clock synchronization..." - Mansouri & Sexl - II

"According to these authors this experiment [similar to the Michelson-Morley experiment] is able to decide between the special theory of relativity and an ether theory incorporating Lorentz contraction and time dilation. As we have shown quite generally in the first and second parts of this paper such a distinction is impossible in principle." - Mansouri & Sexl III

Then I suggest you or them write a rebuttal to the Lipa et al. paper in PRL, and a number of other papers that I cited. The Lipa paper has been out since 2003 and NO ONE has challenged either their interpretation or results. It takes nothing to whine about it on here. Put your name and reputation on the line and do it officially if you think there's any credibility in what you believe in.

Zz.

 

[Aether]

Then I suggest you or them write a rebuttal to the Lipa et al. paper in PRL, and a number of other papers that I cited. The Lipa paper has been out since 2003 and NO ONE has challenged either their interpretation or results. It takes nothing to whine about it on here. Put your name and reputation on the line and do it officially if you think there's any credibility in what you believe in.

Zz.

Zz, as I understand this, those two terms could be exactly what is predicted by SR and that still wouldn't select out SR over LET because the two theories transform into each other by a change in conventions about clock synchronization. Please stop referencing what I "believe in", and deal with the fact that SR and LET are empirically equivalent.

Lipa et al. references M-S without complaint, but they also reference two more recent (2001 & 2002) papers from Kostelecky & Mewes (KM) that are supposed to have an even more general transformation than M-S. I'll go to the library today and get the KM papers; if they are as thorough as M-S, then I'll be happy to start using them in their place.

 

[pervect]

Zz, as I understand this, those two terms could be exactly what is predicted by SR and that still wouldn't select out SR over LET because the two theories transform into each other by a change in conventions about clock synchronization. Please stop referencing what I "believe in", and deal with the fact that SR and LET are empirically equivalent.

"LET" is a name for a theory which is unfortunately not very well defined, as far as I can tell. If you've got references that have a definitive defintion of what the theory actually is, please do post. Note that I took a quick look at the link you did post, however it displayed scanned text on my screen running up and down, making it extremely hard to read. (I use 602 Text to read .doc format files, I don't know if that makes any difference or not). So I doubt I'll be reading it unless I find a way to make it run right-left.

While it is possible that one or more of the two papers you cite make an outright error, the more probable state of affairs is that they each have different defintions of exactly what "LET" really means (what the fundamental assumptions of the theory are).

I think more care needs to be taken to make sure that the authors are *really* talking about the same theory.

If we take your defintion of LET as "a theory that is mathematically equivalent to SR", then it really isn't very clear why you find LET interesting at all. If you find it easier to understand the theory in its new formulation, great, but the general tone of your question doesn't seem to be that of an enlightened person who is trying to explain a simpler way of doing something. Rather it seems like you are experiencing doubts about something, but the only thing that I can see to doubt is the details of the formulation of LET.

 

[Aether]

"LET" is a name for a theory which is unfortunately not very well defined, as far as I can tell. If you've got references that have a definitive defintion of what the theory actually is, please do post. Note that I took a quick look at the link you did post, however it displayed scanned text on my screen running up and down, making it extremely hard to read. (I use 602 Text to read .doc format files, I don't know if that makes any difference or not). So I doubt I'll be reading it unless I find a way to make it run right-left.

The images are scanned photos of each page of the paper, so a text editor is not going to work. Is there a better format, like pdf that would be easier for you to view?

While it is possible that one or more of the two papers you cite make an outright error, the more probable state of affairs is that they each have different defintions of exactly what "LET" really means (what the fundamental assumptions of the theory are).

I think more care needs to be taken to make sure that the authors are *really* talking about the same theory.

If we take your defintion of LET as "a theory that is mathematically equivalent to SR", then it really isn't very clear why you find LET interesting at all. If you find it easier to understand the theory in its new formulation, great, but the general tone of your question doesn't seem to be that of an enlightened person who is trying to explain a simpler way of doing something. Rather it seems like you are experiencing doubts about something, but the only thing that I can see to doubt is the details of the formulation of LET.

Until there is a confirmed detection of a locally preferred frame, then LET and SR are empirically equivalent; if there is ever such a detection, then LET takes charge. I would probably not care if that were the end of the story, however SR is not the end of the relativity story, not by a long shot. It is a starting point for everything else; a local approximation to reality. There are big problems on the largest scales with dark matter, dark energy, and on the smallest scales with the unification of QM, EM, and gravity, and more. That's what I'm really interested in, but applying SR can be something like trying to climb a greased flagpole (that's something that we sometimes try to do here in the US), take VSL as an example; SR forbids it by definition. It is flat wrong to claim that experiments constrain the speed of light to be forever constant; so I'm looking for the most efficient ways to argue that, and to model that.

It is not likely that there are other than a few typographical errors in M-S. This is what Kostelecky & Mewes, Phys. Rev. D, 66, 056005-4 (2002) have to say about M-S: "In this simple example, the transformation T^\mu_\nu leaves invariant the rods and clocks, while \Lambda^\mu_\nu leaves invariant the speed of light. Both are equally valid. In the frames related by T^\mu_\nu, observers agree on rod lengths and clock rates but disagree on the velocity of light. Moreover, the velocity of light is no longer isotropic as measured by these rods and clocks. In contrast, observers related by Lorentz transformations agree that light propagates isotropically with speed 1 but may disagree on rod lengths and clock rates. The description is a matter of coordinate choice, and one can move freely from one to the other using T^\mu_\nu, \Lambda^\mu_\nu, and their inverses."

 

[pervect]

The images are scanned photos of each page of the paper, so a text editor is not going to work. Is there a better format, like pdf that would be easier for you to view?

I think pdf would work much better.

Until there is a confirmed detection of a locally preferred frame, then LET and SR are empirically equivalent; if there is ever such a detection, then LET takes charge.

I would probably not care if that were the end of the story, however SR is not the end of the relativity story, not by a long shot. It is a starting point for everything else; a local approximation to reality. There are big problems on the largest scales with dark matter, dark energy, and on the smallest scales with the unification of QM, EM, and gravity, and more. That's what I'm really interested in, but applying SR can be something like trying to climb a greased flagpole (that's something that we sometimes try to do here in the US), take VSL as an example; SR forbids it by definition. It is flat wrong to claim that experiments constrain the speed of light to be forever constant; so I'm looking for the most efficient ways to argue that, and to model that.

Opinions vary - I find that trying to apply non-SR theories is like trying to "climb a greased flagpole". Metaphorically, anyway, I've never actually tried to do that :-)

In my opinion, if LET wants to accomplish something, it has to at least suggest some experiments which might allow one to detect some sort of preferred frame. If it is just another formulation of SR, it's probably not going to catch on, unless it is simpler to teach (but I suspect that the current formalism is much simpler). It may have a small niche for those who can't adjust their personal philosphies to deal with SR.

It is not likely that there are other than a few typographical errors in M-S. This is what Kostelecky & Mewes, Phys. Rev. D, 66, 056005-4 (2002) have to say about M-S: "In this simple example, the transformation T^\mu_\nu leaves invariant the rods and clocks, while \Lambda^\mu_\nu leaves invariant the speed of light. Both are equally valid. In the frames related by T^\mu_\nu, observers agree on rod lengths and clock rates but disagree on the velocity of light. Moreover, the velocity of light is no longer isotropic as measured by these rods and clocks. In contrast, observers related by Lorentz transformations agree that light propagates isotropically with speed 1 but may disagree on rod lengths and clock rates. The description is a matter of coordinate choice, and one can move freely from one to the other using T^\mu_\nu, \Lambda^\mu_\nu, and their inverses."

Well here's my take on isotropy via a physical example, giving some examples about what is involved in making such a coordinate choice.

Let us suppose that we decide that it is perfectly OK to use an arbitrary clock synchronization to determine speeds, and that we decide to synchronize our clocks by noontime, when the sun is directly overhead. (This is a continuous version of the "time zones" used in the US).

Now, let's compare airplanes flying east-west and west-east with our new clock synchronization methods. We find that airplines flying west travel much faster than the same airpanes flying east, even after we correct for the prevailing winds (which are significant, but I want to ignore this issue).

When we measure the speed of light, we find that it actually arrives before it left with this defintion of synchronization going west - making it have a negative speed (ouch). And it (light) is very pokey going east, traveling verrry slowly.

We also find that the physical expression of momentum depends on the direction one is moving.

With our old definiton of speed, in stil air we could say that the airplanes were going 600 mph east, and 600 mph west, and when they collided, they fell straight down to the ground with no net average velocity.

WIth our new definition of speed, the speeds of identical airplanes flying in still air east-west and west-east are *not* the same. Let's make this concrete, and say that the airplines are going something like 200 mph east, and 1000 mph west in our new system of measurement.

But these airplanes still fall straight down to the ground when they collide (well, that's idealized, but their pieces don't have any net average velocity, and if we could build the airplanes strong enough so that they didn't break apart, we would observe them falling straight down).

Now if we look at two identical airplines colliding with the same velocity, using our new system of synchroniation we find that when they have the same mass and speed, they do not have the same momentum, and that airplanes moving "at the same speed" (with our NEW defijntion of speed) in opposite directions don't fall straight down when they collide.

THe point of this exercise is that clock synchronizations don't really make new physics, which is exactly what the authors you quote are saying.

[add] By this I mean that there are no different experimental predictions. Clearly, Newton's laws have a different appearance when we adopt a non-isotropic clock synchronization method. But the behavior of the actual colliding masses (airplanes in this example) is unchanged.
[end add]

Furthermore, working with clocks synchronized in an anisotropic manner yields anisotropic behavior of physical bodies (like airplanes) as well as anisotropic behavior of light. The clock sychronization that makes light act isotropically is the same clock synchronization that makes airplanes and other physical bodies act isotropically (i.e. come to rest when equal masses at equal velocities coming from opposite directions have an inelastic collision).

 

[Didyoueatpaintchips]

With all these posts no one has stated the reason that SR was needed in the first place. Also how could a forum not include posts from people who don't agree with einstein. This is truly intellectual censorship. No wonder we have had to endure 100 years of relativity, this is what all of the colleges also do, so there are no new ideas.

First I'll answer my first question; Why was relativity needed at all? For that we need to go back to the Michaelson Morley experiment. All of great minds at that time, believed that the Earth traveled through space, in a so called aether. This aether carried light waves at the speed of light in space. So if the Earth was moving in relation to this aether, then the observed speed of light on the Earth would be c + v, where c is the constant speed of light in space, and v is the speed of the observer, in this case the Earth as it moves through so called aether. obser-c = c + v. Of course we know that they got a null result. No one could believe it. The greatest minds could not accept this. Let's see what this leads to, if you get a null result, what exactly is null? It is the velocity of the observer. This leads to this equation; v = constant of 0. Which means that no matter the velocity of the observer, relative to light his speed is 0. Since the observer is always a constant 0 velocity, then you need time and space to become variables. Which means you need relativity. Time and space had always been considered constant, and rightly so. I have much more to say but I'm not sure this is the right forum since it appears to be censored.

mike

 

[pervect]

With all these posts no one has stated the reason that SR was needed in the first place.

You'll find lots of posts on that topic if you look, but that wasn't the question. The short answer is "The negative results of the Michelson-Morley experiments".

Also how could a forum not include posts from people who don't agree with einstein. This is truly intellectual censorship. No wonder we have had to endure 100 years of relativity, this is what all of the colleges also do, so there are no new ideas.

Yep, we do have some forum guidelines here, which you've apparently read, though you've decided to disregard them. Please feel free to post your astounding intellectual ideas about why relativity is wrong to an unmoderated forum like, for example, usenet sci.physics.relativity, where "anything goes" and frequently does.

First I'll answer my first question; Why was relativity needed at all? For that we need to go back to the Michaelson Morley experiment.

Oh, I see you already knew. Then why the heck did you try and hijack thre thread to ask the answer to a question that you already knew, and disregard the forum guidelines to boot?

 

[Hans de Vries]

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.

I've been looking at your doc which I turned into a readable version here:
(33 MB) http://chip-architect.com/physics/Mansouri&Sexl_2.doc I'll leave it here for 12 hours.


Aether,

Mansouri and Sexl make a statement that our world can be equally well
described by a transformation other then the Lorentz Transformation.
This is just as true as the statement that our world can be equally well
described by, say, for instance it's Fourier Transform. Although this is
mathematically correct, I is certainly not how we perceive our world.

We perceive non-simultaneity


Regards, Hans.

 

[Hans de Vries]

proof for non simultaneity via computer simulation.

I use images here to proof the non simultaneity of SR rather than math.
I can't make it any simpler.

A remarkable amount of physics can be extracted from the simple rule
that the wave front is always at right angles with the physical velocity,
regardless of the reference frame.

The left half of the image below shows a fast particle chasing a slower
particle with equal mass. The fast particle has a shorter deBroglie
wavelength. The *phase* speed of the faster particle is slower (as given
by c^2/v ) While the *phase* speed of the slower particle is higher.

At the right half we see the same scene from a reference frame moving
upwards. The extra motion has a larger influence on the slower moving
particle. Its relative motion changes downwards more than the faster
particle. As one can see, the combination of Special Relativity and
Quantum Mechanics makes sure that the wavefronts are exactly at right
angles with the physical speed, exactly as one would intuitively expect.

It is only Special Relativity which can rotate wavefronts, and it does so
for both light and matter waves. A Galilean transformation keeps the
wavefronts always directed in the same direction! The mechanism through
which Special Relativity manages this is again via the non-simultaneity
of time.



Regards, Hans

 

[DrGreg]

Readers of this thread might find this article: Breaking Lorentz symmetry of interest. It is from Physics World, the magazine of the Institute of Physics, the professional body for physicists in Britain.

It mentions Mansouri-Sexl and puts their work into a wider context.

 

[Aether]

I think pdf would work much better.)

Can you read Hans' version? If not, I'll post a pdf. I made a .pdf first, but it was very large so I wen't for a .doc; it wasn't any smaller though.

Opinions vary - I find that trying to apply non-SR theories is like trying to "climb a greased flagpole". Metaphorically, anyway, I've never actually tried to do that :-)

In my opinion, if LET wants to accomplish something, it has to at least suggest some experiments which might allow one to detect some sort of preferred frame. If it is just another formulation of SR, it's probably not going to catch on, unless it is simpler to teach (but I suspect that the current formalism is much simpler). It may have a small niche for those who can't adjust their personal philosphies to deal with SR.

Suppose that LET turns out only to be useful as a waypoint (for some) on the philosophical journey to SR. Even so, what is the justification for tolerating false (however well intentioned) claims that the constancy of the speed of light is an empirically determined fact? Why not just state up front that partiality to SR is simply a matter of coordinate choice, and not an empirical necessity?

 

[ZapperZ]

With all these posts no one has stated the reason that SR was needed in the first place. Also how could a forum not include posts from people who don't agree with einstein. This is truly intellectual censorship. No wonder we have had to endure 100 years of relativity, this is what all of the colleges also do, so there are no new ideas.

This is utterly silly. I can show you one, two, three, etc. examples of "new ideas" that came out of "colleges". When was the last time you read PRL? Will this be sufficient to show that your statement here is FALSE?

It is the velocity of the observer. This leads to this equation; v = constant of 0. Which means that no matter the velocity of the observer, relative to light his speed is 0. Since the observer is always a constant 0 velocity, then you need time and space to become variables.

Say what? Relative to light, the observer's speed is ZERO? Do you know what you just said? Relative to me, my computer monitor has a speed of zero. We are both moving at the same speed then. You have just said the observer is moving at the same speed as light!

And this is your argument on why we needed SR? Oy vey! And to think colleges "censor" things like this! How dare they!

Zz.

 

[Aether]

I have a .pdf of Hans' reformatted version of the Mansouri&Sexl papers (8MB) that I can make available on request.

Readers of this thread might find this article: Breaking Lorentz symmetry of interest. It is from Physics World, the magazine of the Institute of Physics, the professional body for physicists in Britain.

It mentions Mansouri-Sexl and puts their work into a wider context.

Great article, thanks!

 

[Aether]

We perceive non-simultaneity

I don't think so, Hans. We actually perceive only dimensionless ratios (http://arxiv.org/abs/hep-th/0208093), and all judgements of simultaneity ultimately depend on one's choice of clock synchronization convention.

A remarkable amount of physics can be extracted from the simple rule that the wave front is always at right angles with the physical velocity, regardless of the reference frame.

Suppose that you are right, doesn't this "simple rule" amount to the choice of Einstein's clock synchronization convention?

 

[quantumdude]

I don't think so, Hans. We actually perceive only dimensionless ratios, and all judgements of simultaneity ultimately depend on one's choice of clock synchronization convention.

How's that? Right now, sitting at my desk, I've just observed someone tying his shoe, followed by someone else clicking a mouse. Why do I need a clock synchronization scheme to say which one comes first? And if some other observer goes zipping by at high speed and observes the events in reverse order, why would he need a clock synchronization scheme to say the opposite?

 

[Hans de Vries]

A remarkable amount of physics can be extracted from the simple rule that the wave front is always at right angles with the physical velocity, regardless of the reference frame.

Suppose that you are right, doesn't this "simple rule" amount to the choice of Einstein's clock synchronization convention?

In fact, The Lorentz transformations them self can be derived directly from
the single statement that "A wavefront is always at right angles with the
direction of the wave in all reference frames."

(This beauty already laid unrecognized in the M&M experiment)

The example I use here (with the Broglie wave functions) works at any speed
let is be at meters per second or centimeters per second.


Regards, Hans

 

[Aether]

In fact, The Lorentz transformations them self can be derived directly from the single statement that "A wavefront is always at right angles with the direction of the wave in all reference frames."

Lorentz transformations amount to an arbitrary choice of Einstein's clock synchronization convention. Lorentz symmetry is equally well represented by transformations in which absolute simultaneity is maintained.

 

[Hans de Vries]

I don't think so, Hans. We actually perceive only dimensionless ratios (http://arxiv.org/abs/hep-th/0208093), and all judgements of simultaneity ultimately depend on one's choice of clock synchronization convention.

Imagine,

Looking at one of the images in my post above sitting right in front of it.
Take a picture from sufficiently far away. The photo will group together all
the space/time points which have equal time in the particular reference frame.
There's no choice here.


Regards, Hans

PS: For two points, say one left and one right of the center, having the same
distance to the viewer. You can take a picture from any distance and you'll
always fetch the same two space/time points togeter. Even though you have
c going at all kinds of angles, with all kinds of different ratios of its x and y
components.

 

[Aether]

Imagine,

Looking at one of the images in my post above sitting right in front of it.
Take a picture from sufficiently far away. The photo will group together all
the space/time points which have equal time in the particular reference frame.
There's no choice here.


Regards, Hans

PS: For two points, say one left and one right of the center, having the same
distance to the viewer. You can take a picture from any distance and you'll
always fetch the same two space/time points togeter. Even though you have
c going at all kinds of angles, with all kinds of different ratios of its x and y
components.

How do you know that these two points have the same distance to the viewer? What are you assuming about the speed of light? Aren't you assuming that its speed is constant and isotropic?

 

[Aether]

How's that? Right now, sitting at my desk, I've just observed someone tying his shoe, followed by someone else clicking a mouse. Why do I need a clock synchronization scheme to say which one comes first? And if some other observer goes zipping by at high speed and observes the events in reverse order, why would he need a clock synchronization scheme to say the opposite?

You interpreted what you observed using a set of assumptions including that the speed of light is very fast, and that it is isotropic; right? That is where you adopted Einstein's clock synchronization convention. If you didn't use these assumptions, exactly which ones did you use? If I postulate that the speed of light is a function of the cosine of the angle that your velocity makes with some other velocity, say the CMB rest frame, then clocks are synchronized absolutely and judgments of simultaneity are generally different. You can transform freely between Einstein clock synchronization and absolute clock synchronization, and in doing so you change the directional speed of light.

A dimensionless ratio can not be freely transformed, and is the only truly invariant outcome for any measurement. For example, say that I measure my desk to be 2 meters wide; where is the dimensionless ratio? 2 meters per 1 meter of my meter stick: the ratio of my desk's width to my meter stick's length is 2/1. In any frame, this ratio sticks.

The speed of light is not a dimensionless ratio, and therefore it is not something that you can ever measure without reference to one artificial convention or another!

"When clocks are synchronized according to the Einstein procedure the equality of the velocity of light in two opposite directions is trivial and cannot be the subject of an experiment." - M-S I p.499

 

[pervect]

OK, I've snagged the files (both sources), and will look them over when I get a chance. The .pdf definitely looks readable, I haven't tried the new .doc yet.

 

[Aether]

It is only Special Relativity which can rotate wavefronts, and it does so for both light and matter waves. A Galilean transformation keeps the
wavefronts always directed in the same direction! The mechanism through which Special Relativity manages this is again via the non-simultaneity of time.

There are two things going on here, Hans. First there is Lorentz symmetry, and that is what is actually measurable in experiments. Galilean transformations fail those tests, and I am not implying otherwise.

The second thing that is going on is that Lorentz symmetry is conserved by at least two types of transforms: Lorentz transforms are one type, and they are characterized by postulating that the speed of light c is isotropic in all inertial frames (e.g., SR). However, there is a second type of transform (e.g., LET) where clocks and rods are isotropic in all inertial frames, but the speed of light is not. These two type of transforms are equally valid, and they have nothing whatsoever to do with any experimental result (so far). Interestingly, BOTH theories (SR & LET) would need to be modified upon the detection of a violation of Lorentz symmetry because they are empirically equivalent.

Violations of Lorentz symmetry are empirically measurable in principle, but the conventional choice as to which terms in the transform are constant and which terms are allowed to vary is not. So which one should we use? SR is convenient as long as you don't have a locally preferred frame to use as a "handle", but LET would be better if we ever find a handle.

It is wrong to claim that the constancy of the speed of light is proven by experiment. Does this go for GR as well? I suspect that it does, but I'm still studying GR myself and can't say for sure at this time.

 

[pervect]

If you look at Einstein's original paper, Einstein *assumed* isotropy, which he did not define in great detail, to arrive at his theory of relativity.

Mansouri and Sexyl, from the papers I skimmed (thanks for posting them) are basically exploring the realm of physics of "what happens if one does not assume isotropy", though they don't discuss it in those exact terms. (I personally think their paper would be improved if they did at least mention the term "isotropy", it's got a lot of history).

A perfectly isotropic space-time can be made to appear non-isotropic by the proper (or improper) choice of clock synchronziation methods. So what Mansouri and Sexyl are basically doing is to *not* automatically choice a coordinate system that conforms to the (apparent) isotropy of space-time, by instead considering arbitrary clock synchronizations.

By not assuming isotropy as a given, (as Einstein did), Mansouri and Sexyl's work helps provide a framework for testing it. (Of course I should add that there is currently no evidence that there is any physical aniosotropy in space-time).

Their (M&S) general approach may also be useful in rotating coordinate systems, where the usual assumption of isotropy has issues. While one can always chose not to use rotating coordiantes, they are convenient enough that sometimes it's worth giving up the conveniences of isotropy for the convenience of using rotating coordinates.

 

[Didyoueatpaintchips]

Zapper,
I believe what i said was correct. To throw out a universe with constant time and space, there had to be a reason. Every one accepted a constant time and space as fact. So it was the the MM experiment which led to SR, which led to variable space and variable time. If you have a constant velocity for the observer, then something else must be a variable, Einstein chose space and time. So the whole reason for coming up with SR is the MM experiment. Without the MM experiment, SR was not needed, and thus would never have been accepted in the scientific community.

And yes, relative to the constant speed of light, the observer's speed was 0.
Remember, everyone expected something other than 0, because they were looking for the so called aether. But the experiment was done in air, so relative to the air, the velocity of the interferometer was 0. Not a good experiment.
mike

 

[JesseM]

And yes, relative to the constant speed of light, the observer's speed was 0.
Remember, everyone expected something other than 0, because they were looking for the so called aether. But the experiment was done in air, so relative to the air, the velocity of the interferometer was 0. Not a good experiment.
mike

What difference does it make what its velocity relative to the air is? Neither relativity nor the aether theory would predict your velocity relative to the air would make any difference in terms of the velocity you measure for light.

And "relative to the constant speed of light, the observer's speed was 0" doesn't make sense. You can only talk about your velocity relative to a thing like a car or a light wave, talking about your speed relative to a speed is meaningless. What is my speed relative to the speed of 70 mph? Maybe the idea you're trying to express is that the experimenters originally believed that only an observer whose velocity relative to the aether was 0 would see light moving exactly at c in all directions, whereas relativity predicts that every observer will see that. But this means that every observer has a speed of c relative to light, not a speed of 0 relative to light.

 

[DrChinese]

With all these posts no one has stated the reason that SR was needed in the first place. Also how could a forum not include posts from people who don't agree with einstein. This is truly intellectual censorship. No wonder we have had to endure 100 years of relativity, this is what all of the colleges also do, so there are no new ideas.

Welcome to PhysicsForums, Mike.

This forum is intended primarily for mainstream discussions of physics topics. It is not intended for presentation of new theoretical ideas, which are normally presented in the context of peer-reviewed journals. Anyone is free to publish their ideas as they like on their own sites; that is what I do with my work (although most of my stuff is in fact mainstream).

And if you think this forum is devoted to Einstein, you haven't followed the discussions here sufficiently. There are skeptics here, but the presentation should be made within the context of legitimate topics. For example, SR and GR are currently generally accepted theories within the physics community. Therefore, a thread about why SR is wrong is not welcome here. On the other hand, EPR is considered to be outmoded (at least as to the incompleteness of QM) due to Bell's Theorem. Therefore, a critique of Einstein's position on this is acceptable.

Please keep in mind that there are many readers here with varying levels of knowledge. This forum is devoted to those interested in learning more about what is going on in physics and science.

...

Regarding your later post: I wonder why you don't feel the M/M experiment is good. Based on your historical description, how do you see that the speed of the air is an issue? Are you saying that the experiment would only be meaningful in a vacuum? Isn't the air itself also moving "faster" relative to the ether in the direction of the Earth's movement?

 

[Hans de Vries]

How do you know that these two points have the same distance to the viewer?

You can do that by using a ruler That's the way we define length.
Under all conditions, even if you might question how we do know that the
ruler is always the same.

What are you assuming about the speed of light? Aren't you assuming that its speed is constant and isotropic?

The example in the postscript shows that you get the same result under
various mixes of c_x and c_y components.



Regards, Hans

 

[Hans de Vries]

Violations of Lorentz symmetry are empirically measurable in principle, but the conventional choice as to which terms in the transform are constant and which terms are allowed to vary is not. So which one should we use? SR is convenient as long as you don't have a locally preferred frame to use as a "handle", but LET would be better if we ever find a handle.

Aether,

All Lorentz transforms are equally well valid. They are just different
representations of the same, single, reality. Just different 3D slices from
the single 4D universe.

What are you looking for? A preferred reference frame? what about Einstein's
beloved Machian reference frame, the center of gravity of all mass in the
universe. Or the modern day cosmologist's co-moving frame. more like the
center of mass of the local universe, so there are different co-moving frames
at different places in the universe.

Are you looking for aether? like your name implies. The vacuum is far from
empty. Look at the vacuums from Quantum Field Theory, All the many
different vacua people discuss in Quantum Gravity research. Just never
call it aether. That's a name which is reserved for a substance with a
classical gas like behavior. It has be shown over and over that that's
not the way how it works with incredible accuracy.

Are you maybe looking for the absolute "NOW" ?
Why should two different space/time events separated billions of light years
from each other be connected instaneously by an invisible link? You may
define a mathematical space in any arbitrary way that does so but does
it matter to physics anymore then a statement that two different events
have the same value for x or y? All what matters to physics is how different
events in space time communicate with each other, and they do so from
neighbor point to neighbor point to neighbor point. Two events at different
sides of the universe are completely disconnected.

Special Relativity holds up an illussion of a "NOW" in each reference frame
but in General Relativity there's no global "NOW" any more in any reference
frame.


Regards, Hans

 

[Aether]

What are you looking for? A preferred reference frame? what about Einstein's beloved Machian reference frame, the center of gravity of all mass in the universe. Or the modern day cosmologist's co-moving frame. more like the center of mass of the local universe, so there are different co-moving frames at different places in the universe.

I'm working on a unification theory that makes predictions that are so precise and consistent that I tend to take them seriously, but a locally preferred frame seems to be implied. So, I raised the Aether flag and went forth to test the waters and found that LET is empirically equivalent to SR. Whether or not my own theory pans out, this empirical equivalence of LET and SR is something that I think people should be aware of.

Are you looking for aether? like your name implies. The vacuum is far from empty. Look at the vacuums from Quantum Field Theory, All the many different vacua people discuss in Quantum Gravity research. Just never call it aether. That's a name which is reserved for a substance with a classical gas like behavior. It has be shown over and over that that's not the way how it works with incredible accuracy.

Aether is used as shorthand for both a rarified gas (which is not how I am using it), and a locally preferred frame (which is how I am using it).

Are you maybe looking for the absolute "NOW" ? Why should two different space/time events separated billions of light years from each other be connected instaneously by an invisible link? You may define a mathematical space in any arbitrary way that does so but does it matter to physics anymore then a statement that two different events have the same value for x or y? All what matters to physics is how different events in space time communicate with each other, and they do so from neighbor point to neighbor point to neighbor point. Two events at different sides of the universe are completely disconnected.

This is getting close to where I'm going, that events on opposite side of the universe are connected instantaneously. Every event has a temporal coordinate on the farthest edge of the universe, so why shouldn't events be connected out there? There is cosmological evidence of such a link (e.g., the "horizon problem").

Special Relativity holds up an illussion of a "NOW" in each reference frame but in General Relativity there's no global "NOW" any more in any reference frame.

And, 98% of the matter-energy in the universe is still missing.

 

[Hans de Vries]

I went forth to test the waters and found that LET is empirically equivalent to SR. Whether or not my own theory pans out, this empirical equivalence of LET and SR is something that I think people should be aware of.

Aether,

Mansouri & Sexl are plainly wrong with the claim that their Lorentz
Ether Theory is empirically equivalent to Special Relativity. There is only
one frame in which it makes some right predictions and that's the frame
in which they did their calculations: The preferred reference frame.
They then erroneously extrapolate that it does work in all the
reference frames.

In the other frames it gives results that are completely different than
those from Special Relativity. The LET is nothing else than a Galilean
transformation with a scaling factor (gamma)

A clear example in where it goes wrong is when you've got two objects,
one moving from left to right and the other from right to left, both with
the same speed. In SR both will have the same Lorentz contraction for
the observer at rest. In their LET however there is no such symmetry.
One object will typically get extended while the other gets contracted.
The only frame where LET and SR give equal results is in their preferred
reference frame.


It's only with the non-simultaneity of SR that two observers both
see each other contracted. With LET one observer will be contracted
and the other will be extended in an asymmetric way.

To see how SR works we can imagine that we instantaneously "freeze"
a bypassing traveler. Walking around him we can now see him "hanging
in the air", indeed being contracted in the direction in he was moving.
The traveler however will complain that his front was stopped first,
before his back was frozen, and argues that this is the reason of his
compressed state.

This now is a symmetric situation. If you'll lend you're "freezing device"
to the traveler then you'll see that you get frozen in the same way:
contracted by non-simultaneity.

With absolute simultaneity this will always lead to a paradox: If A is
contracted in respect with B. Then B is extended relative to A.
It is the non-simultaneity of SR which resolves this paradox.



Regards, Hans


P.S: R.Mansouri and 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

 

[Aether]

Mansouri & Sexl are plainly wrong with the claim that their Lorentz Ether Theory is empirically equivalent to Special Relativity. There is only
one frame in which it makes some right predictions and that's the frame in which they did their calculations: The preferred reference frame.

Are Kostelecky&Mewes wrong too, http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:hep-ph/0205211 , and everyone else over the past 28 years who has cited M-S without mentioning that they are "plainly wrong" about anything other than a few typos? Otherwise, let's assume that M-S are 100% right.

The asymmetrical length contractions that you see are balanced by an anisotropic speed of light. The point is, Hans, that any difference between the predictions of SR and LET are merely the result of coordinate choice rather than Lorentz symmetry. The two theories are empirically equivalent; any difference that you see is in the interpretation of the measurements and not in the measurements themselves.

Some people here already knew this, and some people here have only just realized this. The fact that some people are still struggling with it proves that it isn't a trivial point, and more care needs to be taken with the teaching of relativity: Local Lorentz symmetry is proven by experiment (up to a point, the search for violations of this symmetry are still ongoing), but special relativity per se is not even a valid subject for experiment.

 

[Hans de Vries]

Are Kostelecky&Mewes wrong too, http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:hep-ph/0205211 , and everyone else over the past 28 years who has cited M-S without mentioning that they are "plainly wrong" about anything other than a few typos? Otherwise, let's assume that M-S are 100% right.

This is misleading. The M&S paperer is referred to because of the
parameterization scheme for possible deviations of Special Relativity.
It's only you who uses it to promote your ether theory.

The math of M&S is correct in the preferred frame, not in any other.

Some people here already knew this, and some people here have only just realized this. The fact that some people are still struggling with it proves that it isn't a trivial point, and more care needs to be taken with the teaching of relativity: Local Lorentz symmetry is proven by experiment, but special relativity per se is not even a valid subject for experiment.

Do you at all read my post? do you look at my examples. No you don't

SR is the ABC of physics. Something you have to understand pretty
well before you can start to learn some real physics. The examples I
gave are the simplest it gets in understanding the basic mechanisms in SR
and the simplest way to show that your Ether theory with absolute time
can never work.

Now try to do the math. Try to understand the physics. Don't just rely on
some statement you have found somewhere in a paper. It's now time for you
to prove your ether theory by actually showing how it can account for
these relativistic effects.

1) How can two observers both see the other in a Lorentz contracted state?

2) How can you rotate the deBroglie wavefronts of particles if you go from
one reference frame to another in order to keep them at right angles with
the direction of their speed? How can a single transformation rotate these
wavefront at all kinds of different angles depending on the speed of the
particles?

Let's see if you can do that without non simultaneity.

People here are willing to help others to get ahead. That's why it's called a
Physics Help and Math Help forum. But if there's no response and you just
keep repeating a statement from somewhere then things get pretty useless
after a while. I did the work, the math, the physics, showed you the images
from my simulations.

Now it's up to you.



Regards, Hans.

 

[Aether]

Mansouri & Sexl are plainly wrong with the claim that their Lorentz Ether Theory is empirically equivalent to Special Relativity. There is only one frame in which it makes some right predictions and that's the frame in which they did their calculations: The preferred reference frame. They then erroneously extrapolate that it does work in all the reference frames.

Don't forget to reset your clocks: "where we have chosen to readjust our clocks according to f(x,v)=-vx" -- Eq. 3.5 M&S-I p. 502

This is misleading. The M&S paperer is referred to because of the parameterization scheme for possible deviations of Special Relativity. It's only you who uses it to promote your ether theory.

The math of M&S is correct in the preferred frame, not in any other.

You can't legitimately claim that M&S is plainly wrong, that they erroneously extrapolate, and also that I am misrepresenting their papers to promote my own theory. My own theory has nothing to do with this other than it motivates me personally to care about this particular issue.

Now try to do the math. Try to understand the physics. Don't just rely on some statement you have found somewhere in a paper. It's now time for you to prove your ether theory by actually showing how it can account for these relativistic effects.

M&S and every paper on local Lorentz invariance since then that quotes them is my proof. If they really are "plainly wrong" as you claim, then I'll have to go back to the drawing board. I don't mind working some transformation problems using the M&S papers as a guide to try and show that I am not applying their work improperly. You start by showing the Lorentz transform (Eq. 3.4 from M&S-I p. 501) for any example you choose (M&S restricts their examples to motion along the x-axis, so we will need to agree to do the same), and I will show the corresponding LET transform (Eq. 3.6 from M&S-I p. 502). "This transform is--as far as the prediction of experimental results is concerned--completely equivalent to (3.4)". -- M&S-I p. 502.

Eq. (3.4)
t=(1-v^2/c_0^2)^{1/2}T-vx
x=(X-vT)/(1-v^2/c_0^2)^{1/2}


Eq. (3.6)
t=(1-v^2/c_0^2)^{1/2}T
x=(X-vT)/(1-v^2/c_0^2)^{1/2}

where we have chosen to readjust our clocks according to
Eq. (3.5) f(x,v)=-vx


"We shall investigate here how the results of various experiments, which are usually considered to be tests of special relativity, can be interpreted using [3.6]. The transformation [3.6] is the very relation one would write down if one has to formulate an ether theory in which rods shrink by a factor (1-v^2/c_0^2)^{1/2} and clocks slow by a factor (1-v^2/c_0^2)^{1/2} when moving with respect to the ether. Note that [3.6] implies the existence of absolute simultaneity since \Delta T=0 implies \Delta t=0. We thus arrive at the remarkable result that a theory maintaining absolute simultaneity is equivalent to special relativity." -- M&S-I p. 503

 

[DrGreg]

How do you know that these two points have the same distance to the viewer?

You can do that by using a ruler That's the way we define length.

That's true for an object stationary relative to the observer. For a moving object you must also read a clock, attached to the ruler at the point where the measurement is made.

If you say that two distances are the same, you must mean either they are both constant or else that they were both measured at the same time. So it depends of your definition of simultaneity.

 

[Perspicacious]

The one-way speed of light

Eq. (3.6)
t=(1-v^2)^{1/2}T
x=(X-vT)/(1-v^2)^{1/2}

"We shall investigate here how the results of various experiments, which are usually considered to be tests of special relativity, can be interpreted using [3.6]."

That should clear up a lot of confusion. OK. Let's see you compute the one-way speed of light.

Here's the experiment. In an arbitrary frame of reference in the aether model, start with two synchronized clocks side-by-side and slowly transport one of them to any convenient distance D. Then compute D/(t2-t1). The answer better be c. (t1 is the time on the stationary clock when the light pulse is sent. t2 is the time when the light arrives as measured by the slowly transported clock. Take the limit of ultraslow transport for a perfect answer of c).

 

[Hans de Vries]

You start by showing the Lorentz transform (Eq. 3.4 from M&S-I p. 501) for any example you choose (M&S restricts their examples to motion along the x-axis, so we will need to agree to do the same), and I will show the corresponding LET transform (Eq. 3.6 from M&S-I p. 502). "This transform is--as far as the prediction of experimental results is concerned--completely equivalent to (3.4)". -- M&S-I p. 502.

Eq. (3.4)
t=(1-v^2)^{1/2}T-vx
x=(X-vT)/(1-v^2)^{1/2}


Eq. (3.6)
t=(1-v^2)^{1/2}T
x=(X-vT)/(1-v^2)^{1/2}


where we have chosen to readjust our clocks according to
f(x,v)=-vx

"We thus arrive at the remarkable result that a theory maintaining absolute simultaneity is equivalent to special relativity." -- M&S-I p. 503

Equivalent? Only in the preferred frame.

Note that 3.6 makes both length and speed anisotropic in any other
reference frame besides the preferred frame. Round wheels would be
only really round in the preferred frame.

We at Earth would see al our wheels changing shape in a 24 hours cycle
corresponding with the rotation of the earth.


Regards, Hans

 

[Aether]

That should clear up a lot of confusion. OK. Let's see you compute the one-way speed of light.

Here's the experiment. In an arbitrary frame of reference in the aether model, start with two synchronized clocks side-by-side and slowly transport one of them to any convenient distance D. Then compute D/(t2-t1). The answer better be c. (t1 is the time on the stationary clock when the light pulse is sent. t2 is the time when the light arrives as measured by the slowly transported clock. Take the limit of ultraslow transport for a perfect answer of c).

Lorentz transformation:
t_1=(1-v^2/c_0^2)^{1/2}T_1-vx_1/c_0^2
x_1=(X_1-vT_1)/(1-v^2/c_0^2)^{1/2}

t_2=(1-v^2/c_0^2)^{1/2}T_2-vx_2/c_0^2
x_2=(X_2-vT_2)/(1-v^2/c_0^2)^{1/2}

D/(t_2-t_1)=(x_2-x_1)/(t_2-t_1)=c_0

c(v,\theta)=c_0

M&S-I p.511 Eq. (6.16) gives the following result for first order effects when transport synchronization of clocks is used with the Lorentz transformation: c(\theta)=1-v(1+2\alpha)cos\theta where \alpha =-1/2 corresponds to perfect Lorentz symmetry.

"In discussing the experiments we need the inverse velocity of light to second order in v/c..." M&S-III p. 810 Eq. (2.1) - 1/c(\theta)=1+(\beta+\delta-1/2)v^2sin^2\theta+(\alpha-\beta+1)v^2

LET transformation:
t_1=(1-v^2/c_0^2)^{1/2}T_1
x_1=(X_1-vT_1)/(1-v^2/c_0^2)^{1/2}

t_2=(1-v^2/c_0^2)^{1/2}T_2
x_2=(X_2-vT_2)/(1-v^2/c_0^2)^{1/2}

D/(t_2-t_1)=(x_2-x_1)/(t_2-t_1)=c_0^2/(c_0+v)

c(v,\theta)=c_0^2/(c_0+v \cdot cos(\theta))

Hint: The speed of light c_0 is isotropic in the ether frame: (X_2-X_1)/(T_2-T_1)=c_0.

Assuming perfect Lorentz symmetry and using the LET transformation I get:
c_0/c(v,\theta)=1+(v/c_0) \cdot cos(\theta). This is a dimensionless ratio, and as such it is a measurable (e.g., physical) quantity. However, you must synchronize two clocks to make this measurement; and exactly how you choose to do that determines whether the Lorentz transformation or the LET transformation should be applied.


The speed of light is generally anisotropic in LET (e.g., except for within the ether frame), absolute simultaneity is maintained, and this is empirically equivalent to SR. The trick is that the -vx/c_0^2 term that is used to maintain a constant speed of light in the Lorentz transformation is used instead to maintain absolute simultaneity in the LET transformation. Both ways are equally valid.

 

[Aether]

Equivalent? Only in the preferred frame.

Empirically equivalent, yes; independent of the frame. These transforms operate on abstract coordinates, and not on physical objects.

Note that 3.6 makes both length and speed anisotropic in any other reference frame besides the preferred frame. Round wheels would be only really round in the preferred frame.

We at Earth would see al our wheels changing shape in a 24 hours cycle
corresponding with the rotation of the earth.

Maybe so, but only in the same sense as the arctic circle looks inflated on a Mercator projection. We are talking about mere coordinate systems here, aren't we? My agrument is with taking the attributes of a coordinate system (e.g., constancy of the speed of light) and claiming that it is an emprically proven fact. I do not dispute that for whatever reason one may prefer the Lorentz transform over the LET transform for whatever purpose, but how is this any different than expressing a preference to use spherical polar coordinates over rectangular coordinates in some cases or vice versa? In both cases the two coordinate systems transform into one another quite freely.

 

[Aether]

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.

I have received my copy of Zhang's book "Special Relativity and its Experimental Foundations", (1997). In the preface he says this: "The key point in Einstein's theory is the postulate concerning the constancy of the (one-way) velocity of light, which contradicts the classical (nonrelativistic) addition law of velocities. The postulate is needed only for constructing well-defined inertial frames of reference or, in other words, only for synchronizing clocks (i.e., defining simultaneity). It is not possible to test the one-way velocity of light because another independent method of clock synchronization has not yet been found...Of course one could use the experiments to yield limits on the parameters in Robertson's transformations but not on the directional parameter q in Edwards' and MS' theories."

On the back cover Zhang says this: "...In particular, the discussions indicate that the one-way speed of light is not observable in the present laboratories...In the third part, variant types of experiments performed up to now are analyzed and compared to the predictions of special relativity. The analyses show that the experiments are tests of the two-way velocity, but not of the one-way velocity, of light."

On page 10 he says: "We have known that there is no instantaneous signal in nature and, therefore, the absolute simultaneity cannot be realized in any laboratory...It is well known that one always use a light signal for the clock synchronization in a laboratory. Therefore Einstein's simultaneity can be directly realized in experiments. We want to stress here that only the two-way speed, but not the one-way speed, of light has been already measured in the experimental measurements, and hence the isotropy of the one-way velocity of light is just a postulate...We shall see from Chap. 6 that a more general postulate, a choice of the anisotropy of the one-way velocity of light, together with the principle of relativity, would give the same physical predictions as Einstein's theory of special relativity."

 

[cincirob]

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?

Hi, I'm new to the forum. I didn't read all the responses to your question, but it looks like it wandered away from your original question so I'd like to add a couple of thoughts.

First, if you search the net for "On the Electrodynamics of Moving Bodies" (OEMB for short) you can find Einstein's 1905 paper and read his explanation for the second postulate. Briefly, it can be interpretted this way: When Maxwell's equations (circa 1850) convinced people that light was a wave phenomenon they assumed that the wave must be the motion of some medium. For instance the medium for sound is air. The medium for ocean waves is water, etc.

The name given to the medium for light was aether. A number of experiments were performed over the next half century to observe the properties of aether, the most famous being the Michelson-Morley experiment (you can find Michelson's paper ont he net also). In OEMB Eisntein notes that all the experiments to find the nature or effects of aether failed. He then states his postulate that light propagates in "empty space" at a constant velocity c. Although he doesn't come right out and say it, he is proclaiming that aether doesn't exist (or at least is of no consequence regarding light).

Many people think that this postulate is where he declared that the speed of light is the same for all inertial observers. Actually it is the first postulate that declares this phenomenon. In the first postulate he says that the laws of electrodynamics and optics hold for all inertial observers (inertial means non-accelerating). This means that Maxwell's laws hold. And Maxwell's laws show that the speed of light c is a function of two properites of empty space, the permeability and permitivity of empty space. Since these two properties are constants, then c must be a constant.

In summary then, Einstein made postulates out of what observations of physics seemed to imply; that is, that aether didn't seem to have any measurable effects and that the motion of an observer didn't seem to change the outcome of various physical experiments.

 

[Jimmy Snyder]

Although he doesn't come right out and say it, he is proclaiming that aether doesn't exist (or at least is of no consequence regarding light).

I just popped into nit pick. In fact he does come right out and say it.

The introduction of a "luminiferous ether'' will prove to be superfluous

http://www.fourmilab.ch/etexts/einstein/specrel/www/

 

[cincirob]

Quote:
Originally Posted by cincirob
Although he doesn't come right out and say it, he is proclaiming that aether doesn't exist (or at least is of no consequence regarding light).

I just popped into nit pick. In fact he does come right out and say it.


Quote:
Originally Posted by A. Einstein
The introduction of a "luminiferous ether'' will prove to be superfluous
=======================================

You are correct, he does make the comment above. But my comments were directed specifically to the postulates where you must draw the inferrence.

 

[cincirob]

I have seen some comments in this thread about the Robertson-Mansouri-Sexl framework. I'm not very familiar with the work, but i found this reference to it.

I see that the graphics don't copy so here is the site : http://qom.physik.hu-berlin.de/prl_91_020401_2003.pdf

Modern Michelson-Morley Experiment using Cryogenic Optical Resonators
Holger Mu¨ller,1,2,* Sven Herrmann,1,2 Claus Braxmaier,2 Stephan Schiller,3 and Achim Peters1,†,‡
1Institut fu¨ r Physik, Humboldt-Universita¨t zu Berlin, Hausvogteiplatz 5-7, 10117 Berlin, Germany
2Fachbereich Physik, Universita¨t Konstanz, 78457 Konstanz, Germany
3Institut fu¨ r Experimentalphysik, Heinrich-Heine-Universita¨t Du¨sseldorf, 40225 Du¨sseldorf, Germany
(Received 27 January 2003; published 10 July 2003)
We report on a new test of Lorentz invariance performed by comparing the resonance frequencies of
two orthogonal cryogenic optical resonators subject to Earth’s rotation over
1 yr. For a possible
anisotropy of the speed of light c, we obtain c=c0  2:6  1:7  1015. Within the Robertson-
Mansouri-Sexl (RMS) test theory, this implies an isotropy violation parameter     12
 2:2  1:5  109, about 3 times lower than the best previous result. Within the general extension of the
standard model of particle physics, we extract limits on seven parameters at accuracies down to 1015,
improving the best previous result by about 2 orders of magnitude.

 

[metrictensor]

It may turn out that there is an new theory that explains why the speed of light is the same in all IRF's. This would lead to the same type of question to that theory's foundations. If you understand this you understand the nature of science. It causes one to ask what do I mean by 'why' when I ask a question of science. What am I looking for? What do I expect?

 

[Integral]

In the 1860's Maxwell discovered that he could cast the equations, which bear his name, in the form of a standard wave equation. When he did that, he found a combination of physical constants expressed the velocity of these electromagnetic waves. That constant was \frac 1 { \sqrt{ \mu_0 \epsilon_0}}. It is said that he was surprised to find that expression evaluated to a number which was equal to the then accepted value for the speed of light.
So this was a theoretical prediction that the speed of light was a physical constant. The meaning of this was hotly debated for the rest of the century, it implied that electromagnetism behaved differently from massive bodies. As mentioned Michelson and Morley preformed an experiment in an effort to detect the motion of light through the aether. They failed to detect any medium through which light was propagating.
Einstein's postulate that the speed of light was constant to all observers was a result of the failure, over the previous 50 yrs, of physicist trying to prove that it was not. The constancy was predicted theoretically and verified experimentally. Therefore when A.E. wrote down that postulate, it was accepted by the physics community without debate, because it was common knowledge. Einstein tied together the physics of Newton and Electo Magnetism with a simple and very straight forward derivation.