Talk:Special relativity/Archive 2

A haiku
Light goes the same speed For everyone everywhere Funkiness ensues

Accuracy doubts
Just a few notes for anyone wishing to translate this page for the Pirelli prize. I'm not sure about the section "Status of special relativity", probably best to leave it out. Also I'm not sure of the accuracy of the few setences starting "A common misstatement about relativity". I'll be looking into it, please leave it out for now. -- Tim Starling 01:33, Nov 7, 2004 (UTC)

A few remarks or suggestions

 * 1) in section 1: Newton believed that light was "corpuscular," but later physicists found that a transverse wave model of light was more useful: I propose to drop the word tranverse or this need more explanation. -- I added a link to the transverse wave article to explain it :) Davedx
 * 2) end of section 1: It was Max Planck who suggested the term "relativity" to highlight ... a reference or a least date would be nice.
 * 3) also at the end of section 1, references are made to Lorenz but none to Henri Poincaré.
 * 4) section 3: In addition to events and physical objects, there are a class of inertial observers (which may or may not correspond to an actual physical object): as it is, thsi does bring really any information, event after the next sentence: Each inertial observer has associated to it an inertial frame of reference.
 * 5) Dropped references to inertial observers. Terry 17:38, 14 Feb 2005 (UTC)
 * 6) end of section 3: The second postulate is then an assertion that the four-dimensional spacetime M is a pseudo-Riemannian manifold equipped with a Lorentzian metric g of signature (3,1), which is given by the flat Minkowski metric when measured in each inertial reference frame. the mixture of Lorentzian metric and Minkowski metric is confusing, also suddenly the word flat pop up but nowhere before in the article something is written about curved or flat spaces.
 * 7) Dropped references to Lorentzian metric; also fixed signature to be consistent with rest of text. Terry 17:38, 14 Feb 2005 (UTC)
 * 8) a little beneath: the statement The theory of Galilean relativity is the limiting case of special relativity in the non-relativistic limit c&#8594;&#8734;, while exact is maybe confusing as the term non-relativistic is generally used for v << c. Ok, this mean the same thing, but is confusing for the neophyte I think.
 * 9) reworded slightly. Terry 17:38, 14 Feb 2005 (UTC)
 * 10) section 4: The section is very short and what do General relativity is still insufficiently confirmed by experiment to exclude certain alternative theories of gravitation such as the Brans-Dicke theory. there ? -- No idea. The section is fairly obviously about the status of SPECIAL relativity, not general.. comments on the status of general should be in the GR article. Removed this line Davedx
 * 11) section 5: The twin paradox concerns a twin ...  is it possible to reformulate or explain a little more?
 * 12) section 6: Lack_of_an_absolute_reference_frame is somewhat redundant with previous parts (section 1) and doesn't bring really new information.
 * 13) section 9: The_geometry_of_space-time_in_special_relativity, the signature convention used (+++-) is the reverse than the one used in previous sections (+---), we shouls use the same everywhere (and preferably the +---, as it seems the one the most used).
 * 14) end of section 9: We see that the null geodesics lie along a dual-cone: shouldn't the concept of geodesics first be introduced?

Also, maybe is it posible to use some of the schema on wikibooks (see b:Modern_Physics:Special_Relativity:Contents)?


 * -- Looxix

Posted by 66.147.55.213, who also deleted a large chunk of discussion:
 * The special relativity article currently claims that the second postulate has been experimentally verified. This is absolutely false. As of today, no one has used two clocks in the same frame to measure light's one-way speed, so not only has the 2nd postulate not been experimentally verified, the pertinent experiment has not even been performed.


 * Additionally, the following paper showed that the 2nd postulate's one-way light speed invariance is not a necessity, thereby invalidating the 2nd postulate, which was the very basis of special relativity:


 * Elementary relativity with 'everyday' clock synchronization C Leubner, K Aufinger and P Krumm 1992 Eur. J. Phys. 13 170-177

--Carnildo 21:04, 6 Dec 2004 (UTC)

The second postulate
Hi, I came to be interested in this page after seeing it nominated for Featured Article status. An anonymous user has written in there (presumably the same anon user as 66.147.55.213 above) to say that the second postulate has not been experimentally verified. He makes a second point about the second postulate having been invalidated: I can see this would be arguable. But regarding the first point, that it has been experimentally verified, that must be established, at least to the satisfaction of reputable scientists. Has it been verified? Does anyone have a reference? Slim 22:02, Dec 9, 2004 (UTC)


 * The second postulate is three separate claims:
 * The speed of light is the same to all inertial observers
 * The speed of light is the same in all directions
 * The speed of light does not depend on the velocity of the emitter
 * The second claim was verified by the Michelson-Morley experiments, and the third was verified by the experiments that disproved emitter theory.
 * For the third claim, cites Alvager et al., Physics Letters 12, 260 (1964) as being the definitive study.
 * I don't know of any experiments that that have verified the first claim, but I'm sure they're out there.
 * --Carnildo 22:46, 10 Dec 2004 (UTC)


 * Thanks for your reply. Could someone add references for that part of the article, making clearer what is meant by "experimentally verified" and which experiments have verified it? In fact, I'd say references throughout the article would be very helpful. A lot of work though. But I think if this is to have any chance of Featured Article status, it will need to be done.
 * How common is the view that the second postulate has not, in fact, been experimentally verified? I looked around the Internet tonight and found a lot of angry debate about it, but I don't know enough to be able to judge which objections are valid. Slim 08:17, Dec 11, 2004 (UTC)


 * another interpretation of the second postulate is that
 * the Lorentz transformation has real valued eigenvalues
 * the speed of light is the same as the velocity corresponding to the eigenvectors

217.81.145.70 20:35, 11 Dec 2004 (UTC)


 * We can all agree on claim 3's veracity, but the problem lies with claims 1 and 2, neither of which has been tested in any way experimentally. In fact, there have never been even any on-paper sketches of any such experiments.
 * Contrary to Carnildo, 2 (one-way isotropy) was not verified by the MMx. (Carnildo omitted the key word "one-way" in his claims list above; the MMx does not pertain to light's one-way speed.)
 * But Carnildo was right about 1's (one-way invariance) status - it remains to be tested experimentally, even on paper or in theory (which eliminates any arguments that the necessary technology does not yet exist).
 * Cadwgan_Gedrych Dec 13 2004


 * If you don't want Michelson-Morley as a test of #2, then you can use the laser-ranging experiments for measuring the distance to the moon, the time lag for communicating with the Mars orbiters (or the Voyager spacecraft), or any number of other long-range communications projects. MM is just the most precise measurement of it. --Carnildo 22:07, 13 Dec 2004 (UTC)


 * For testing claim 2, an experiment using the GPS system demonstrated that the speed of light was isotropic to within one part in 109: Peter Wolf and Petit Gerard, "Satellite test of special relativity using the global positioning system," Phys. Rev. A 56 (6), 4405-4409 (1997)


 * Clifford M. Will, "Clock synchronization and isotropy of the one-way speed of light," Physics Review D 45, 403-411 (1992): One-way isotropy, to within one part in 10^8. Also covers the problem of synchronizing clocks.


 * A full citation of Alvager et al. is Alvager et al., "Test of the second postulate of special relativity in the GeV region," Physics Letters 12, 260 (1964).


 * For testing claim 1, there have been any number of tests proposed. For direct measurements, the only problems are practical ones: getting the experimental equipment up to high enough speeds.


 * --Carnildo 20:58, 15 Dec 2004 (UTC)

Picture
While looking for featured picture, I found a page with scan of orginal Einstein notes on the subject. They are from 1918-1919, but the picture has a copyright notice, so I am not sure if we can use it after all. --Piotr Konieczny aka Prokonsul Piotrus 19:12, 10 Dec 2004 (UTC)
 * At least under United States copyright law, the copyright claim is invalid. The creator of that photograph was trying to make an accurate copy of another work.  There is no creative input involved, and so no copyright applies beyond that of the original work. --Carnildo 22:16, 13 Dec 2004 (UTC)

Second postulate
copied from User:Sokane What Exactly Are the Implications?

As everyone knows, Einstein said that special relativity (SR) was based on two postulates, known as the first postulate and the second postulate. Since the former (the principle of relativity) does not give or determine any law of physics (but merely says that once a law has been found in one frame, it shall also be found in all others), we see immediately that the latter (the light postulate) is the only definite or specific basis of SR. This, of course, makes the light postulate extremely important as far as SR goes. Indeed, if this postulate were to be experimentally verified, then SR would no longer be a theory, but would instead be a fact. However, it is currently "on the books" as a theory.

The second postulate (aka the light postulate) did not postulate regarding light's round-trip, one-clock speed (as that case was essentially closed in 1887 by experiment); it postulated only in regards to light's one-way speed between two clocks (which must be in the same frame in order to avoid any clock slowing differences).

Therefore, the only way to experimentally test the second postulate is by placing an unstarted clock at each end of a long table, temporally relating them, and then using them to measure light's one-way speed between them.

Despite the fact that the round-trip case was closed decades ago, the just-mentioned one-way case remains open, and any reasonable person would ask Why?

It cannot be due to a lack of the necessary technology because said experiment has not even been done on paper. (I.e., no one has even shown on paper how to measure light's one-way, two-clock speed without first assuming the result. For example, Einstein assumed the result "invariance," and then set the clocks to match his assumed result.)

Just as the round-trip experiment was done sans man's input, so must the one-way experiment be done. Only then can we find the law of nature in the one-way case.

(Man did not manipulate the clock's natural atomic rhythm in the round-trip case; man did not trim or extend the light-path lengths during the round-trip experiment; similarly, man must not dictate the result in the one-way case by presetting the clocks to obtain man's (and not nature's) prechosen one-way light speed "invariance.")

Only if Nature herself can begin with two unstarted clocks and temporally relate them her way can there be a natural value for this speed.

But Nature cannot synchronize clocks because she has no brain to devise a clock synchronization definition, and she has no means of adjusting clock hands in order to implement any such definition.

Therefore, there can be no natural (or Nature-given) value for the one-way speed of light between two clocks. I.e., there can be no one-way light speed experiment. This is the answer to the above-given reasonable question Why has no one even shown on paper how to test the second postulate?

A postulate that cannot be tested is a postulate that cannot be falsified, and a postulate that cannot be falsified is not a scientific postulate.

And since the light postulate is the sole basis of SR, we see that the latter is not a scientific theory.

The Einsteinian transformation equations are the math of SR. These equations cannot exist sans at least two clocks per frame; thus, the equations depend upon Einstein's baseless definition of clock synchronization or his assumption of one-way light speed invariance; therefore, all of the relativistic results of the transformation equations are circular because they were given at the start. For example, if one assumes one-way invariance at the start, and then one sets one's clocks obtain one-way invariance, then one's clock's will obtain one-way invariance. For another example, since Einstein does not have absolute simultaneity, his observers cannot simultaneously pin down or locate the end points of a passing rod, so an incorrect length measurement is made which turns out to be smaller than that of the rod's "rest length." (Similarly, Einstein's "time dilation" and "mass variance" are also merely point-of-view effects caused by Einstein's lack of absolute simultaneity.)

We see that Einstein's "length contraction," "time dilation," and "mass increase" are trivial and of no more importance to space-time physics than is the apparent mutual shrinkage of each of two departing people.

Thus, the full implications of "There are currently no experimental tests of Einstein's second postulate, not even on paper" are "Not only is the second postulate untestable, but special relativity itself is not a scientific theory."

I seriously doubt that Slim envisioned such dire (for SR) ramifications! Cadwgan_Gedrych Dec 13, 2004

Retrieved from "http://en.wikipedia.org/wiki/User_talk:Sokane"


 * Recent papers express the clock synchronization problem as one of the equivalence of distant clock synchronization in inertial frames by slow clock transport and by Einstein synchrony (i.e. light transport). The one-way transmission speed has been measured, in this sense.  A quick literature search, for example, turns up the following recent papers, and I'm sure there are many others that explicitly or implicitly test the "one-way" speed. &mdash;Steven G. Johnson 04:03, Dec 14, 2004 (UTC)


 * Peter Wolf and Petit Gerard, "Satellite test of special relativity using the global positioning system," Phys. Rev. A 56 (6), 4405-4409 (1997). Abstract: A test of special relativity has been carried out using data of clock comparisons between hydrogen maser clocks on the ground and cesium and rubidium clocks on board 25 global positioning system (GPS) satellites. The clocks were compared via carrier phase measurements of the GPS signal using geodetic receivers at a number of stations of the International GPS Service for Geodynamics (IGS) spread worldwide. In special relativity, synchronization of distant clocks by slow clock transport and by Einstein synchrony (using the transmission of light signals) is equivalent in any inertial frame. A violation of this equivalence can be modeled using the parameter delta c/c, where c is the round-trip speed of light (c=299 792 458 m/s in vacuum) and delta c is the deviation from c of the observed velocity of a light signal traveling one way along a particular spatial direction with the measuring clocks synchronized using slow clock transport. In special relativity delta c/c=0. Experiments can set a limit on the value of delta c/c along a particular spatial direction (henceforth referred to as "direction of delta c"). Within this model our experiment is sensitive to a possible violation of special relativity in any direction of delta c, and on a nonlaboratory scale (baselines >= 20 000 km). The results presented here set an upper limit on the value of delta c/c<5 x 10-9 when considering all spatial directions of delta c and delta c/c<2 x 10-9 for the component in the equatorial plane.
 * (This paper cites 5 other papers that measure the clock synchronization equivalence and one-way speed isotropy either directly or indirectly.)


 * S. A. Lee, S. J. Sternberg, C. Flynn, N. Bjerre, E. Riis, O. Poulsen, and J. L. Hall, "Tests of special relativity," Quantum Electron Laser Sci Conf, 130 (1989). Abstract: Two classes of optical experiments for testing the theory of special relatively are described. One group, typified by the Michelson-Morley experiment, looks for variations in the round-trip speed of light as a function of spatial direction. The second group of experiments measures the relativistic (or second-order) Doppler shift in the transition frequency of fast moving atoms. It is shown how these experiments can benefit from the development of highly stabilized lasers and the advances in superstable high-finesse optical cavities. In addition, it is possible to design novel experiments that are sensitive to possible one-way variations in the speed of light.


 * I think I agree with you, though, in the sense that the definition of clock synchronization, and in particular the equivalence between Einstein's light-pulse scheme and any other "reasonable" scheme (in particular, slow clock transport), is arguably more at the heart of special relativity than the more-popular postulates. (This equivalence is falsifiable, however.)  The Wolf and Gerard paper, above, cites some commentary by Einstein on this subject; maybe I'll get a chance to look it up later this week. &mdash;Steven G. Johnson 05:23, Dec 14, 2004 (UTC)

Steven, you have changed the rules. The clocks must be in the same frame in order to avoid any possible clock slowing difference. (This eliminates slow clock transport). Also, one cannot use light signals because one must then "preassume" a light speed between the clocks. (This eliminates Einstein synchronization.) And the optical Doppler shift has nothing to do with a direct, two-clock measurement of light's one-way speed.


 * Sorry, I won't play your game. Some definition of how to relate times at different points in an inertial frame is required in order to describe motion and mechanics.  Light-pulse synchronization is one possibility, and the limit of slow transport of clocks between points in an inertial frame is another.  If the two were inconsistent (which is measurable/falsifiable), that would be a major problem because it would mean that relativity would be inconsistent with our non-relativistic view of the universe &mdash; in some sense, an implicit postulate of relativity is that the classical picture is correct in the non-relativistic limit.  If the two are consistent then you could object that, in principle, you could come up with a model of physics that changes all clocks by the precise amount needed to match Einstein synchrony even under slow transport (which would not be the same as relativistic time-dilation).  However, I'm not sure if any such model has ever been advanced, and even if it were it might not be falsifiable. &mdash;Steven G. Johnson 15:37, Dec 14, 2004 (UTC)

Ironically, given that he was the "premier champion" (no disrespect intended) of light speed invariance and isotropy, Einstein himself had to explicitly (mathematically, even) admit that, under certain conditions, light's one-way, two-clock speed would vary with frame velocity. Look at the following:

Quoting Einstein: "w is the required velocity of light with respect to the carriage, and we have
 * w = c - v.

The velocity of propagation of a ray of light relative to the carriage thus comes out smaller than c."
 * http://www.bartleby.com/173/7.html

This math result is still obtainable today on paper, just as it was when Einstein wrote about it. All that one needs are absolutely synchronous clocks instead of Einstein's absolutely asynchronous clocks.


 * You're quoting him out of context &mdash; as far as I can tell, that paragraph is describing the pre-relativity picture of a light pulse traveling next to a train. A similar example appears in practically every textbook, as a necessary prelude to describing the modified picture in special relativity. &mdash;Steven G. Johnson 15:37, Dec 14, 2004 (UTC)

Since one cannot prove a negative, Einstein was unable to prove that clocks cannot be absolutely synchronized. He also failed to prove that the principle of relativity (the PR) conflicts with the math result w = c - v. The PR does not call for any specific law of physics; it merely says that whatever law is found in one frame must also be found in all others. This means that the PR did not rule out Einstein's c - v, despite Einstein's insistence otherwise.

We must address the second postulate explicitly, and it explicitly states that the correct experimental result for light's one-way speed between two clocks in the same frame is invariance/isotropy.

My main points are that since no such experiment exists, not even on paper, there can be no postulating in this case, so the so-called second postulate is not really a scientific postulate, which, in turn, means that special relativity is not a scientific theory.

Thus, the implications persist. The second postulate is not testable because it pertains to a nonexistent (or impossible) "experiment." (The one-way light speed between two same-frame clocks cannot be measured sans man's input for the clock synchronization, but this makes the result artificial (i.e., not from nature), so it is not a law of nature.)
 * Cadwgan Gedrych 14:19, 14 Dec 2004 (UTC)

I see no reason to continue debating this. The possiblility that the second postulate is correct is clearly not part of Cadwgan Gedrych's belief system, so all discussion of the matter is merely people making noises at each other. --Carnildo 19:30, 14 Dec 2004 (UTC)


 * "Some definition of how to relate times at different points in an inertial frame is required in order to describe motion and mechanics."


 * Of course, Steven, but any definition of synchronization means that man controls the result in the one-way, two-clock light speed case, and a man-given result is not a law of nature. (BTW, I don't play games in the case of special relativity.)


 * "You're quoting him out of context — as far as I can tell, that paragraph is describing the pre-relativity picture of a light pulse traveling next to a train. A similar example appears in practically every textbook, as a necessary prelude to describing the modified picture in special relativity."


 * There is no "out of context" problem unless you can prove that Einstein's equation w = c - v is invalid, or, equivalently, prove that Einstein's w = c for all (one-way, two-clock invariance/isotropy) is valid. (Ignore any possible intrinsic clock slowing and intrinsic rod shrinkage.)


 * Furthermore, as I said, the "modified picture in special relativity" was not justified by the facts of the case. To repeat, the principle of relativity does not call for Einstein's one-way light speed invariance between two same-frame clocks. (The principle of relativity does not even apply at all until after a law has been found, and, as of today, no one has found any law in the one-way, two-clock light speed case.)


 * Allow me to state the critical problem more specifically: Suppose you are given two unstarted ideal clocks. Suppose you are asked to use them to experimentally measure light's one-way speed. Suppose you are asked to keep them from moving relative to each other in order to avoid any difference due to possible intrinsic clock slowing. How could you conduct the experiment without giving the result at the start by synchronizing the clocks per some man-given definition?


 * (We can all agree that if the clocks are forced via Einstein's definition to obtain invariance, then they will of course obtain invariance, and we should also all agree that if the clocks are absolutely synchronized, then they will not obtain invariance (just as Einstein's w = c - v said), but neither of these results is a law of nature because of man's controlling input at the start.)


 * Haven't studied physics in about 8 years and I'm very rusty on the scientific method, and this is probably a poor attempt to refute your assertions concerning the circularity issue... but isn't that why we perform statistical analysis on our results? E.g. 'significant difference', and so on. It seems that you're trying to say the movement of the clocks after synchronisation distorts the result of the experiment beyond measure. Wouldn't it be true that since the clocks are moved apart slowly, the time-dilation effect is negligible? Also, if you moved the synchronised clocks apart at the same speed, wouldn't the time-dilation effect on each clock be the same, resulting in them being synchronised after moved apart?


 * I apologise in advance if this is a stupid answer. I noted your accusation of intellectual cowardice to another user further down the page though and couldn't resist! Davedx


 * I think that I will go ahead and cut to the chase instead of waiting for you to try to show that Einstein's w = c - v is invalid by simply presenting my little proof that it is valid, as follows:


 * Let two observers meet in passing as a light ray approaches them.


 * (Oa = Observer A and Ob = Observer B)


 * ........Oa
 * ......................................<-light ray
 * ........Ob


 * When the two observers briefly meet, they know that the light ray's tip is equidistant from them because they are at a single point in space, and the ray's tip is also at one point in space. We can qualitatively label this distance "X".


 * After the observers separate, the light ray will reach one of them, as shown below:


 * ...Oa
 * ............<---light ray
 * ...........Ob


 * Since the tip of the light ray cannot be in two places at once, the observers will see it sequentially at absolutely different times. (Here is a down-to-earth example: If I see the real you in both Texas and New York, then this proves that I saw you at absolutely different times because you cannot be in two places at once.)


 * We can - again purely qualitatively - label the ray's absolutely different arrival times "Ta" and "Tb." (All we care about here is the fact that these times are absolutely different.)


 * The observers can now compare one-way light speeds. (Having no rulers or clocks, they must do this qualitatively.) Here are their extremely simple results:


 * Light's speed wrt Oa = X/Ta


 * Light's speed wrt Ob = X/Tb
 * Cadwgan Gedrych 20:26, 14 Dec 2004 (UTC)


 * May I suggest you read up on relativity? Under relativistic physics, Oa and Ob will not agree on the distance "X" if they are moving relative to each other.  Further, they will disagree on how long Ta and Tb are. --Carnildo 21:22, 15 Dec 2004 (UTC)

Oh come on, give me a break, dude; what a fallacy; your assumption of the validity of some silly theory cannot touch my experiment. As I tried to make very clear, I used no clocks, and I certainly did not use the rigged clocks of SR (which are forced by definition to find c always, regardless of the reality which was shown by my experiment). (And I would love to know how any SR observers can measure the distance between two points in space.) (Also, I would love to see your proof that when the origins of two passing frames coincide, that their points (x,0,0) do not, although this is of course irrelevant to my experimental proof of one-way variance.)(The only way such distant points would not coincide would be if the physical Lorentz contraction exists, and no relativist would admit to that!) Cadwgan Gedrych 01:30, 17 Dec 2004 (UTC)

No original research
Excuse me for butting in here. I don't mean to disturb your discussion, but I'm wondering whether Cadwgan's views count as "original research" (i.e. uses unpublished data or analysis, or is a novel narrative, interpretation or new synthesis of published information), because if it is, it's not allowed in Wikipedia, even if it's true. My problem is that I don't know enough about SP to judge whether these views count as "original research" or not. Cadwgan, have your views been published in a peer-reviewed journal? If so, can you provide a reference? Slim 04:15, Dec 15, 2004 (UTC)
 * My understanding of Cadwgan's view is that
 * The second postulate can only be experimentally verified by measuring the one-way speed of light using two synchronized clocks in the same reference frame.
 * These clocks cannot be synchronized in their final locations using light, as the speed of light is what is being measured.
 * These clocks cannot be synchronized in their final locations, as there will be a propogation delay in the synchronization.
 * These clocks cannot be synchronized before being moved into location for the experiment, since any movement will create relativistic effects that will de-synchronize the clocks.
 * Thus, the second postulate cannot be proven.
 * --Carnildo 06:49, 15 Dec 2004 (UTC)


 * My point is that, whether Cadwgan is saying A, B, C or whether he's saying X, Y, Z, if what he's saying has been published in a peer-reviewed journal or book, then it can be used. If it hasn't, it can't be. Those are the Wikipedia rules. See No original research. And references must be provided by the people who have written this article, and by Cadwgan if he wants to add anything. Slim 07:42, Dec 15, 2004 (UTC)

My counterclaim is that the second postulate has not been experimentally verified, i.e., that no one has ever shown that light's one-way speed between two same-frame clocks is invariant or isotropic; and I can easily back up this view of the postulate with a peer-reviewed paper from Einstein himself, as follows:

[quoting Einstein from his 1905 relativity paper] "In agreement with experience we further assume the quantity                       2AB/(t'a-ta) = c to be a universal constant - the velocity of light in empty space." http://www.fourmilab.ch/etexts/einstein/specrel/www/

This brief Einsteinian statement proves that Einstein did not postulate at all regarding light's one-clock, round-trip speed; instead, he merely accepted round-trip invariance and isotropy as experimental ("In agreement with experience") facts, which, we can all agree, they practically were even in 1887. (However, Einstein was forced to use the word "assume" because the 1887 experiment did not actually cover invariance, but covered only isotropy, but of course invariance was a very safe assumption.)

[again quoting Einstein from his 1905 relativity paper] "1. Any ray of light moves in the 'stationary' system of coordinates with the determined velocity c, whether the ray be emitted by a stationary  or by a moving body. Hence                   velocity = light path/time interval where time interval is to be taken in the sense of the definition in §1."

Note Einstein's use of coordinate systems. These systems consist of rulers and clocks; therefore, Einstein was talking about light's one-way speed per two clocks in the same frame. (He did not use slow clock transport.)

Furthermore, as I have already pointed out, Einstein himself declared mathematically that under certain circumstances light's one-way, two-clock speed could be c - v. It has been falsely claimed that this was taken out of context, but here is my simple proof to the contrary:

Despite any and all of the words of Einstein preceding or following his presentation of the simple equation w = c - v, Einstein did in fact derive that equation; all I ask of those who "yell" Out of context! is that they simply show us Einstein's derivation.

Moreover, there is a peer-reviewed 1992 paper which shows that light's one-way, two-same-frame-clock speed need not be invariant or isotropic. Here is the citation:

Elementary relativity with 'everyday' clock synchronization C Leubner, K Aufinger and P Krumm 1992 ''Eur. J. Phys''. 13 170-177

Finally, I wish to know if anyone, anywhere really believes that Einstein's second postulate does not pertain to light's one-way speed between two same-frame clocks. It should be clear to anyone that this is at least a major part of the Wiki claim, and it is my counterclaim that this measurement has yet to be made. (And the very fact that it has not been made, not even on paper, tells anyone who will listen that it cannot be made.) Cadwgan Gedrych 14:16, 15 Dec 2004 (UTC)