# Consistency of the speed of light

by Moneer81
Tags: consistency, light, speed
 PF Gold P: 717 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.
Emeritus
PF Gold
P: 29,238
 Quote by Aether "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.
PF Gold
P: 717
 Quote by ZapperZ 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.
Emeritus
P: 7,632
 Quote by Aether 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 extremly 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.
PF Gold
P: 717
 Quote by pervect "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 extremly 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?

 Quote by pervect 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."
Emeritus
P: 7,632
 Quote by Aether 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, travelling 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.

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).
 P: 2 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. Lets 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
Emeritus
P: 7,632
 Quote by Didyoueatpaintchips 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?
P: 1,135
 Quote by Aether 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) Mansouri & Sexl 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.
 Sci Advisor P: 1,135 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 Attached Thumbnails
 Sci Advisor PF Gold P: 1,847 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.
PF Gold
P: 717
 Quote by pervect 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.

 Quote by pervect 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?
Emeritus
PF Gold
P: 29,238
 Quote by 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.
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.
PF Gold
P: 717
I have a .pdf of Hans' reformatted version of the Mansouri&Sexl papers (8MB) that I can make available on request.

 Quote by 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.
Great article, thanks!
PF Gold
P: 717
 Quote by Hans de Vries 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.

 Quote by 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?
Emeritus
PF Gold
P: 5,532
 Quote by Aether 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?
P: 1,135
 Quote by 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.
 Quote by Aether 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
PF Gold
P: 717
 Quote by Hans de Vries 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.

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