# Consistency of the speed of light

by Moneer81
Tags: consistency, light, speed
P: 1,135
 Quote by Aether 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.
PF Gold
P: 717
 Quote by Hans de Vries 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?
PF Gold
P: 717
 Quote by Tom Mattson 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
 Emeritus Sci Advisor P: 7,620 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.
PF Gold
P: 717
 Quote by Hans de Vries 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.
 Emeritus Sci Advisor P: 7,620 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.
 P: 2 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
P: 8,470
 Quote by Didyoueatpaintchips 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.
PF Gold
P: 5,316
 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.
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?
P: 1,135
 Quote by Aether 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.

 Quote by Aether 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 cx and cy components.

Regards, Hans
P: 1,135
 Quote by Aether 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
PF Gold
P: 717
 Quote by Hans de Vries 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.

 Quote by Hans de Vries 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).

 Quote by Hans de Vries 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").

 Quote by Hans de Vries 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.
P: 1,135
 Quote by Aether 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
PF Gold
P: 717
 Quote by Hans de Vries 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/cita...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.
P: 1,135
 Quote by Aether Are Kostelecky&Mewes wrong too, http://www.citebase.org/cgi-bin/cita...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.

 Quote by Aether 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.
PF Gold
P: 717
 Quote by Hans de Vries 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

 Quote by Hans de Vries 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.

 Quote by Hans de Vries 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
PF Gold
P: 1,847
Quote by Hans de Vries
 Quote by Aether 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.
P: 76
 Quote by Aether 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).

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