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Einstein synchronisation

Please note that there is a small article, especially covering the problem of synchronization of clocks at different places and the related 1-way-LS vs 2-way-LS issue: Einstein synchronisation. It follows the treatment by Hans Reichenbach (obviously heavily condensed -- and not for the note reagrding GPS). A very thorough discussion can be found in his book "The philosophy of space and time", §19 and §20. --Pjacobi 12:37, 1 May 2006 (UTC)

The debate over second postulate

I was skimming through the long debate above over the wording of the second postulate. I feel it arises from a misinterpretation of how Wikipedia works. The wording of the second postulate in the article does not depend on which postulate is "right", but which postulate is sourced. WP:V, WP:NOR and WP:CITE tell us that we must attribute statements of controversial points to reputable sources. You can say "Einstein stated the second postulate thus, but recently researcher X disputed this in a paper published in a peer-reviewd journal(citation here)". You can not say "Einstein stated the second postulate thus, but editors after debating in the talk page of this article have arrived at the conclusion that Einstein was wrong." The debate can only be a purely academic one without any consequences to the article.

On the other hand, if a researcher has claimed a different version of the second postlate in a paper, then the claim should be included as a claim with proper citations irrespective of whether his claim can be said to be valid or not. Wikipedia is not the place to judge the merits of a scientific theory, we must only judge whether we cna provide sources for the theory. I hope the dispute is either resolved or continued with the understanding that its results will not have a bearing on the article. Loom91 06:01, 2 May 2006 (UTC)

Dear "Mr. Loom91," the debate has indeed been long, but it need not have been.

Anyway, since you seem to care a little, let's look back at the existing article's version of the postulate:

[quoting the article:]

"Most current textbooks mistakenly include a major derived result, that the speed of light is independent of the state of motion of the observer measuring it, as part of the second postulate. A careful reading of Einstein's 1905 paper on this subject shows that, in fact, he made no such assumption. The power of Einstein's argument stems from the manner in which he derived startling and seemingly implausible results from two simple assumptions."

Note that it begins by countering most current textbooks. So much for your point about using proper sources! Note further that it says that "A careful reading of Einstein's 1905 paper ...." Whose "careful reading" was this? Was it some Wiki editor's? What does this do to the cited source? Moreover, note that the word "assumptions" was used in relation to the second postulate, whereas Einstein stated that he was not making an assumption about the nature of light, but was merely giving a definition.

[quoting the article:]

"One of the most highly counterintuitive of these results (and, as stated above, commonly included in statements of the second postulate), is that the speed of light in vacuum, commonly denoted c, is the same to all inertial observers. An observer attempting to measure the speed of light's propagation will get the same answer no matter how the observer or the system's components are moving."

This omits the most important part of the second postulate. Einstein's version does not omit it. That important part is the fact that the speed of light between two clocks is given by definition, not measured.

Why would a given-up-front-by-definition "result" be "counterintuitive"?

Why does the Wiki article say "An observer attempting to measure the speed of light" when the speed was given up front by Einstein's definition?

Since Einstein's definition is the only difference between Lorentz's theory and Einstein's, it seems that no article about the second postulate (and special relativity) could rightly omit a direct comparison of Lorentz's and Einstein's clocks. How do they differ? It is impossible to fully understand either special relativity or the second postulate until one knows the physical difference between Einstein's clocks and Galileo's/Newton's/Lorentz's clocks (in the critical case of two same-frame clocks).

It may surprise you to hear that Einstein explicitly admitted that he could not measure time (in the case of two same-frame clocks), whereas Newton's/Galileo's/Lorentz's clocks could measure such time. But I saw no mention of this "perfectly-valid-source" fact in the Wiki article.

Cadwgan Gedrych 14:21, 2 May 2006 (UTC)

Cadwgan, I disagree with much of what you claim to be true above. Consider:

(1) The synchronization of clocks in a frame in which Newtonian mechanics is valid such that the speed of light is measured to be isotropic in this frame does not set the speed of light to c.

(2) The observed one-clock result that the closed path average speed of light is c is simply that, an observed result that suggests a principle.

(3) The postulate that the speed of light is c independent of the speed of the emitter when measured by the clocks in the frame so described in (1), while fixing the speed of light as c in this frame, does not imply that the speed of light is c in any other frame. However, it does imply (2) in this frame.

(4) The additional postulate that the changes of state in physical systems are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion, now fixes the speed of light at c in all coordinate systems that are related to the system defined in (1) by uniform translatory motion which clearly requires that clocks belonging to any of these other frames are synchronized according to (1)

(5) We now know that any synchronization procedure that is consistent with an invariant one-clock closed path average speed of light in any inertial coordinate system necessarily results in transformation equations that belong to a continous set of transformations with the Lorentz transformation at one end of the spectrum (OWLS absolute, simultaneaty relative) and the Selleri transformation at the other end (OWLS relative, simultaneaty absolute).

(6) Although the choice in synchronization procedure cannot affect the underlying physics, the Einstein synchrony choice (by design) leaves the form of Maxwell's equations unchanged in any inertial frame.

(7) There is no objective answer to the question of whether such information as in (5) and (6) rates a prominent position in this SR article but, IMHO, a link to a separate article is appropriate.

(8) Wikipedia doesn't need armchair editors. Make your changes already or go on about your mission elsewhere. Alfred Centauri 21:52, 2 May 2006 (UTC)

TO ALFRED: I am not being an armchair editor.

Your above is utterly useless, as far as I can see; for example, it failed to address these two important questions, which I now must repeat, thereby adding unnecessarily to the length of this discussion:

[1] Why would a given-up-front-by-definition "result" be "counterintuitive"? [2]Why does the Wiki article say "An observer attempting to measure the speed of light" when the speed was given up front by Einstein's definition?

Also, the article fails to tell us the difference between Einstein's and Newton's clocks, which is what the 2nd postulate is all about.

Moreover, you made no mention of this critical omission by the article: Einstein's explicit admission that he could correctly measure any two-clock times, including light's one-way, two-clock speed.

And why the heck are you talking for Loom91, anyway??? Where did he go!!!

And as for me going ahead and changing the article, don't you think that that would be silly with absolutely nothing having been resolved here? Cadwgan Gedrych 15:15, 3 May 2006 (UTC)

Cadwgan said "[1] Why would a given-up-front-by-definition "result" be "counterintuitive"?"

As I explained in my comments above, the result is not given by definition. This is our disagreement. You claim it is given by definition - I claim you are wrong.

Cadwgan said "[2]Why does the Wiki article say "An observer attempting to measure the speed of light" when the speed was given up front by Einstein's definition?"

You are repeating yourself so I will repeat myself. You are claiming it is given by definition and I claim that you are wrong.

Further, I claim that your are wrong when you say "...the difference between Einstein's and Newton's clocks, which is what the 2nd postulate is all about."

If you are waiting for a consensus before editing the article to reflect your claims above, then, IMHO, you might as well be on your way. I will revert any edit to this article that makes the claims you make above for the reason that these claims are POV.

If you wish to speak with Loom91 privately, use his or her talk page. Alfred Centauri 16:15, 3 May 2006 (UTC)

First, I will state my personal views regarding this debate. Then I shall hive my opinion about this article.

As I understand it, the statement that the propagation velocity of electro-magnetic waves is the same to all inertial observers is equivalent to the statement that it is the same irrespective of the motion of the emitting body, because a trivial Lorentz tramsformation of the inertial reference frame switches between the two. A textbook wouldn't be wrong unless it included BOTH these as postulates.

I also don't feel that Einstein DEFINED the velocity of light. He simply assumed the existence of one such velocity c invariant under inertial reference frame changes and then used this assumption to derive the mathematical expresssions for the Lorentz transformations. That this constant velocity is indeed the velocity of light comes from Maxwell's electro-magnetism. I do not understand what you mean by saying Einstein defined lights velocity and it can not be measured. The velocity of light can not be measured in meters or any units derived from meter because meter is defined in terms of c, but that has nothing to do with SR. Einstein does assume c to be a constant, but that doesn't stp an observer from performing experiments to actually verify that assumption. See Speed of light (FA).

Now for the article. I think we are to take On the Electrodynamics of Moving Bodies as the primary source of our information on the postulates of SR. Anything creative must be attributed. No saying second postulate is redundant or textbooks are mistakes without sourcing. I dug up an English translation of the paper and Einstein begins the paper by saying that c is indepent of the motion of the emitting bodies. We can't call the textbooks wrong, simply mention that they do not present the postulate in the form used by Einstein. Weasel words such as "a careful reading shows" have to go. If the second postulate is redundant, then that stement has to be attributed. In any case, what are the prefered versions of either party? Loom91 06:43, 4 May 2006 (UTC)

To Alfred Centauri:

I asked "Why does the Wiki article say 'An observer attempting to measure the speed of light' when the speed was given up front by Einstein's definition?"

You replied "You are claiming it is given by definition and I claim that you are wrong."

It is not my claim, it is Einstein's statement. Here, for your reference,

is that statement:

[From Section 1 of Einstein's 1905 special relativity paper:]

If at the point A of space there is a clock, an observer at A can determine the time values of events in the immediate proximity of A by finding the positions of the hands which are simultaneous with these events. If there is at the point B of space another clock in all respects resembling the one at A, it is possible for an observer at B to determine the time values of events in the immediate neighbourhood of B. But it is not possible without further assumption to compare, in respect of time, an event at A with an event at B. We have so far defined only an "A time" and a "B time." We have not defined a common "time" for A and B, for the latter cannot be defined at all unless we establish by definition that the "time" required by light to travel from A to B equals the "time" it requires to travel from B to A. Let a ray of light start at the "A time" ta from A towards B, let it at the "B time" tb be reflected at B in the direction of A, and arrive again at A at the "A time" t'a.

In accordance with definition the two clocks synchronize if

tb - ta = t'a - tb.

Did you see that not only is light's one-way, two-clock speed controlled by and given by the definition, but so are all other two-clock measurements in SR?

Here is Einstein's subsequent statement of his 2nd postulate, which shows how it is directly affected by the definition:

2. Any ray of light moves in the "stationary" system of co-ordinates 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 Section 1.

Did you notice that the time interval for light's one-way, two-clock speed in special relativity is controlled by the definition in Section 1?

Cadwgan Gedrych 18:27, 4 May 2006 (UTC)

To Loom91:

If light's one-way speed invariance were given by anything in nature, such as Maxwell's equations, then Einstein would never had had to use a definition to make it so.

Here is the relevant part of your cited source:

"One consequence of the laws of electromagnetism (such as Maxwell's equations) is that the speed c of electromagnetic radiation does not depend on the velocity of the object emitting the radiation; thus for instance the light emitted from a rapidly moving light source would travel at the same speed as the light coming from a stationary light source (although the colour, frequency, energy, and momentum of the light will be shifted, which is called the relativistic Doppler effect). If one combines this observation with the principle of relativity, one concludes that all observers will measure the speed of light in vacuum as being the same, regardless of the reference frame of the observer or the velocity of the object emitting the light."

Maxwell's c is not the c of the 2nd postulate because Maxwell did not use two clocks to measure light's speed, and yet the 2nd postulate pertains solely to light's speed between two same-frame clocks. Since this cannot be done sans some definition of clock synchronization, Einstein was forced to provide such a definition, and he did, as I pointed out above to Alfred Centauri.

Yes, as your source says, it is of course true that the principle of relativity implies that all frames will find Maxwell's speed to be c, but, again, this has nothing to do with the 2nd postulate, which, as Einstein said, requires a synchronization definition. Cadwgan Gedrych 18:41, 4 May 2006 (UTC)

Cadwgan: I've already explained why your claims are wrong. Restating your claims with quotes and all is unnecessary because I already understand why we disagree. Your claims are illogical and your conclusions do not follow from the quotes you've given. I've already stated why you wrong point by point based on the very same quotes you have used. This is the basis of our fundamental disagreement and there is no reason for any further discussion between us regarding this. Alfred Centauri 23:32, 4 May 2006 (UTC)

If I might throw another two cents in, after going back and reading On the Electrodynamics of Moving Bodies, I have to say that Einstein both stated that light "is always propogated in empty space with a definite velocity c which is independent of the state of motion of the emitting body", and apparently defined c in terms of the round trip speed. In regards to the first of Einstein's statements, it is this that he calls his second postulate. In regards to the second of his statements, regarding the round-trip speed of light, the last sentence in the sub-section taken up by it ("It is essential to have time defined by means of stationary clocks in the stationary system, and the time now defined being appropriate to the stationary system we call it `the time of the stationary system.'") that he was using the round-trip not to define the speed of light, but to use the already constant speed of light to define time intervals, and not the other way around. Basically, I believe the second postulate simply is the assumption that to all observers, no matter how it is measured, the speed of light is always equal to c, whether measured via Maxwell's equations, using two clocks, or using one clock and a reflected beam. This assumption was then plugged into the round-tip scenario to define time intervals for stationary clocks. At least, that's how I read it. DAG 15:26, 5 May 2006 (UTC)

You read it correctly. In fact, since the "two clock" experiment cannot be done without first synchronizing the clocks using a two-way exchange of signals, a case can be made that this "one-way two-clock" experiment is impossible to do (and ironically Cadwgan notes that impossibility below). However, scientific proof and/or refutation cannot occur on the basis of an experiment that cannot be done. So Cadwgan's concern is moot. --EMS | Talk 19:57, 5 May 2006 (UTC)

Although the round-trip, one-clock light speed case was closed experimentally (for all practical purposes) decades ago, the one-way, two-clock light speed experiment (with both clocks in the same frame, nonrotating, and not moving relative to each other in order to avoid any possible clock slowing differences) has never been performed, not even on paper. Unless and until you know exacly why this is so, you will simply never understand either SR or its postulates. Sorry, but I tells it the way it is! Cadwgan Gedrych 18:18, 5 May 2006 (UTC)

Is there any dispute regarding the article?

I see there is much debate on many fine theoritical points that frankly escape me. But is there any dispute as to what content should be in the article? Loom91 08:24, 5 May 2006 (UTC)

Let me put it to you this way: Cadwgan Gedrych wrote

If light's one-way speed invariance were given by anything in nature, such as Maxwell's equations, then Einstein would never had had to use a definition to make it so.

This demonstrates a total lack of understanding of special relativity and even of how theoretical physics works on the part of Cadwgan. After all, Maxwell's equations do suggest the invariance of the speed of light (c). Given that suggestion, one can construct a theory based on it, and that is what Einstein did. Cadwgan acts like Einstein created something unacceptably artificial, but in reality what Einstein did was to say "let us assume the principle of relativity and the invariance of c as emitted as a rule of physics, and see where it leads". The result is a theory that is highly consistent with observation, such that those observations prove the invariance of c.

For that reason, there is a consensus of editors that Cadwgan's concerns are unfounded and that the article is not in need of his proposed modifications, which is why he is belly-aching here. As for "disputes over what the content of this article should be": This is Wikipedia and there will always be someone who wants some content added or removed for whatever reason. In fact, I recently revised the "Physics in spacetime" section and am also wondering if that material shouldn't be elsewhere as it is higly technical and makes the overall article less accessible. None the less, the immediate issue is Cadwgan's complaints, and there is no question that his viewpoint is not appropriate for this article. --EMS | Talk 15:44, 5 May 2006 (UTC)

Cadwgan Gedrych is a well known crackpot/troll on the newsgroup sci.physics.relativity. His real name is Brian D. Jones. During the last 10 years he has been using the following false names:

• Cadwgan Gedrych
• 2ndPostulateDude
• SRdude
• Edward Travis
• Ron Aikas
• Roy Royce
• John Reid
• Martin Miller

Currently he is trolling the newsgroup under the name

• kk (Kurt Kingston).

To get an idea of his intelligence, see for instance: [1] —Preceding unsigned comment added by DVdm (talk • contribs) 16:23, 5 May 2006

In the first place, there is no proof of any of the above newsgroup-related claims, so there is no place for it here.

In the second place, my personal reputation matters not in any case; all that matters is the condition of the Wiki SR article, especially the second postulate part.

In the third place, I have already won one major case against the article's given condition, which involved removing the claim that the second postulate had been experimentally confirmed.

In the fourth place, as I just wrote in another section here, no one in Wiki or anywhere else can possibly understand the second postulate until and unless they can explain why the one-way, two-clock experiment has never been performed even though the round-trip, one-clock case was closed decades ago, along with the Maxwellian light-speed case.

In the fifth place, I have just proved that EMS is dead wrong about my understanding of SR by my just-given paragraph. (He/she wrote above: "This demonstrates a total lack of understanding of special relativity and even of how theoretical physics works on the part of Cadwgan.")

[To explain, because I know that an explanation is needed: The facts that the two other light speed cases (the round-trip, one-clock case, and the Maxwellian case) are closed whereas the one-way, two-clock experiment cannot be performed even on paper shows clearly that the latter case differs fundamentally from the other two, so only if this important fact is understood can anyone understand special relativity and its postulates.]

In the sixth place, let's please settle this simple second postulate issue so I can move on to another one, the case of the false claim that special relativity predicted the famous equation E = mc^2. Cadwgan Gedrych 18:43, 5 May 2006 (UTC)

I must agree that the above allegations against Cadwgan are not germane to this discussion, and even raise issues under WP:CIVIL. I hope that my point was pretty much made in my previous posting in this thread. However, on what Cadwgan said "in the sixth place", I rest my case. --EMS | Talk 19:39, 5 May 2006 (UTC)

Thanks for the fairness re the allegations issue, EMS. (FWIW, you can rest assured that I am not on any "troll" or "crank" list in the Newsgroups, and you can also take it to the bank that I have not lost a single argument re SR in the Newsgroups. You may also like to know that only one person - Dirk - is involved in the Newsgroup allegations.)

Now, as regards your above statement re my sixth place item, since it consisted of two parts, I am left to wonder to which of them you referred. I hope that it was the E = mc^2 part, because that is the only one that really matters here. Assuming that's the case, I would like you to prove that this equation cannot be derived sans special relativity. Cadwgan Gedrych 18:39, 6 May 2006 (UTC)

Above, EMS wrote

"After all, Maxwell's equations do suggest the invariance of the speed of light (c). Given that suggestion, one can construct a theory based on it, and that is what Einstein did."

It is demonstrably false that Maxwell's equations "suggest" one-way or even two-way (round-trip) light speed invariance or isotropy. The proof lies in the simple fact that even Maxwell himself, along with all other physicists of the day, firmly believed in a positive result for the Michelson-Morley experiment - despite the existence of Maxwell's equations. In other words, these equations have nothing to do with coordinate (ruler/clock) measurements of light's speed. Cadwgan Gedrych 18:57, 6 May 2006 (UTC)

Please stop feeding the ...

From SRdude profile on google groups: cadwgan_gedr...@yahoo.com

From SRdude on sci.physics, Dec 16, 2004:

.................Simple Math Derivation Needed..................

Even after deliberately disregarding all preceding and subsequent words in the book, the fact remains that Einstein at one point definitely derived the very simple equation w = c - v.

Here are his own words: "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---------------------

All I am looking for is one brave soul who will show this derivation.

From Cadwgan Gedrych in this talk page:

[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.

But this result comes into conflict with the principle of relativity...." http://www.bartleby.com/173/7.html

From kk on sci.physics Feb 2, 2006:

Einstein said that the clocks of classical physics would obtain the value w = c - v for light's one-way speed (departing light ray). Einstein's clocks, on the other hand, obtain the value c. Therefore, the two sets of clocks differ.

How do Einstein's clocks differ from those of Newton and Galileo?

You cannot understand the basics of SR without knowing the answer to the above question.

From Cadwgan Gedrych in this talk page:

Since Einstein's definition is the only difference between Lorentz's theory and Einstein's, it seems that no article about the second postulate (and special relativity) could rightly omit a direct comparison of Lorentz's and Einstein's clocks. How do they differ? It is impossible to fully understand either special relativity or the second postulate until one knows the physical difference between Einstein's clocks and Galileo's/Newton's/Lorentz's clocks (in the critical case of two same-frame clocks).

From Cadwgan Gedrych on sci.physics.relativity Mar 31, 2003:

One-way light speed invariance cannot be a law of nature. Thus, one-way light speed invariance cannot be a scientific postulate. And since SR is based solely upon Einstein's "postulate" of one-way invariance, SR is not a scientific theory.

(My emphasis added).

I dunno EMS, I'm of the opinion that Dirk's assertion regarding Mr. Gedrych, in conjuction with the above, are germane to this discussion. I for one cannot assume good faith in the case of Cadwgan Gedrych. I do not believe that Mr. Gedrych is interesting in improving this article but is instead interesting in disproving the subject of this article. Alfred Centauri 20:40, 5 May 2006 (UTC)

(Note: This response was added after this page was archived.)

I don't see that Dirk's comments are needed to reach the conclusion that Cadwgan is trying to disprove the subject. Cadwgan's comments in the talk page (now archived) more than suffice to make that point. --EMS | Talk 03:00, 7 May 2006 (UTC)

In this context, I'll add a link in the references to the article (apparently published in Foundation of Physics) [2]; that saves a long story as it can be freely downloaded by everyone. Harald88 00:20, 6 May 2006 (UTC)

This article was indeed published in the December 2004 issue of 'Foundations of Physics' (Vol. 34, No. 12). Alfred Centauri 02:15, 6 May 2006 (UTC)

Reply to Alfred Centauri:

Why not invite Dirk into this Wiki discussion? If you would look a little closer at his Newsgroup posts, you would see that he has rarely discussed physics, but merely feeds his obsession for fighting anyone who he feels does not see SR as he does, which is merely mathematically, and not physically.

Contrary to Centauri's belief, I am working in perfectly good faith here, just as I did in the Newsgroups. And that is why I have never once lost a single SR argument there, probably much to Dirk's chagrin.

My good faith re the article demands that I properly present my case to Alfred Centauri. To that end, I proffer the following challenge to him/her:

I had written somewhere above:

Why does the Wiki article say "An observer attempting to measure the speed of light" when the speed was given up front by Einstein's definition?

Here is my challenge:

Will Centauri please show how an observer can attempt to measure light's one-way speed between two clocks that are in the same frame?

(Please start from scratch, using two ideal atomic clocks still in their shipping crates, and show all pertinent steps. Thanks!) Cadwgan Gedrych 19:19, 6 May 2006 (UTC)

Archived

I've just archived the entire (>130k) discussion page by a complete page move, is the nicest method for the struggling Wikipedia servers and for users editing over slow line.

Despite some points hotly debated, U'd very much prefer starting with a blank. It is easy to link to older arguments on the archive page. If someone violently disagree, feel free to copy from the archive page to the current page, but try to find smallest subset of old postings you absolutely need here.

Pjacobi 20:05, 6 May 2006 (UTC)

Talk page discipline

Please remember the guidelines how to use talk pages: Don't discuss the subject, discuss the article. And don't take controversies from other places to Wikipedia. --Pjacobi 20:09, 6 May 2006 (UTC)

A serious 2nd postulate discussion (with all rules followed)

Please note carefully that I am not here to bash special relativity per se. (Feel free to fully ignore any words of mine which even seem to do that.)

I am here to point out the problems with the article's treatment of Einstein's second postulate:

Problem 1

Here is a direct quote from the article (re the second postulate):

"An observer attempting to measure the speed of light's propagation will get the same answer no matter how the observer or the system's components are moving."

The following shows the problem with this statement:

"Measure" can refer to using two same-frame clocks.

It is a part of current human knowledge that no such experiment (i.e., the one-way version of the Michelson-Morley experiment) has ever been performed.

It is a part of current human knowledge that no such experiment (i.e., the one-way version of the Michelson-Morley experiment) has ever been performed, not even on paper, using the ideal rulers and clocks of theoretical physics.

The latter proves that it is currently impossible* to experimentally measure light's one-way speed between two relatively-at-rest clocks. (If this cannot be done even on paper using ideal or perfect instruments, then it clearly cannot be done as an actual experiment.)

(*although by no means perpetually impossible - since absolutely synchronous clocks could easily do the job)

Those who think otherwise must prove it by showing on paper how we can use two ideal atomic clocks still in their shipping crates to measure light's one-way speed between them.

Problem 2

Here is another direct quote from the article (re the second postulate):

"One of the most highly counterintuitive of these results (and, as stated above, commonly included in statements of the second postulate), is that the speed of light in vacuum, commonly denoted c, is the same to all inertial observers."

As I noted above, it is currently not possible to experimentally measure light's one-way speed between two same-frame clocks (which is the definitive one-way experiment), so it certainly was not possible in 1905; therefore, Einstein had to give the "result" via a mere definition of clock "synchronization." (He had to because there simply was no other way of obtaining a one-way, two-clock light speed result.)

I placed quotes around the word "result" because Einstein's "result" in this case was not an actual experimental result,. but was merely given up front by a mere definition of clock "synchronization."

The fact that Einstein gave a definition of clock "synchronization" that directly gives the "result" c for light's one-way, two-clock speed before the performance of any actual one-way, two-clock light speed experiment is certainly a part of current human knowledge.

It should now be obvious that, contrary to the Wiki view stated above, there is nothing counterintuitive about the "result" c in the definitive one-way case. In case it is still not obvious, think about it: It cannot be counterintuitive if was given up front via a mere definition. Cadwgan Gedrych 16:55, 7 May 2006 (UTC)

Roundtrip speed is c and one way speed after Einstein synchronisation is c. And both this statements are equivalent. This was known and published in the times of Einstein and Reichenbach and is still valid and re-iterated today. In modern coordinate-free formulation the issue of Einstein synchronisation vs. consistent alternatives doesn't even arise, it's clear that it's only about the choice of coordinates.

Do you suggest that we re-word to the more correct but obscure sounding:

One of the most highly counterintuitive of these results (and, as stated above, commonly included in statements of the second postulate), is that inertal observes can choose their coordinate systems so, that the speed of light in vacuum, commonly denoted c, is the same to all of them.

Pjacobi 18:27, 7 May 2006 (UTC)

I still fail to see how the article is discussed. A serious discussion according to Wikipedia would be to say "in [citation], expert X says that it is impossible to test the second postulate because of problem Y. Therefore we should reword the article to reflect the view expounded by X that "synchronization" is only used to mean "two-way synchronization". I don't buy anyone's statement that "it's obvious" as a reference. --Alvestrand 19:19, 7 May 2006 (UTC)

You can cite Reichenbach all day long on this issue, but I don't think it should be phrased, that it is impossible to test the second postulate. Because the second postulate, taken in the form Roundtrip speed is c or one way speed after Einstein synchronisation is c or For every initial observer there is a choice of foliation (co-ordinate system) which makes the non-coordinate-free formulation of Maxwell Equatations valid is testable and tested to great precision. Also the equivalence of Einstein synchronisation via exchange of light signals and by slow transport of clocks is testable (and tested, but I'm not sure about the precision). --Pjacobi 19:33, 7 May 2006 (UTC)

In fact (and on my initiative) such has been the formulation for a long time, exactly to avoid this kind of useless fuss. See [3]. I suggest to reinsert that precision. Harald88 21:03, 8 May 2006 (UTC)

I think that Cadwgan is at best trolling on us. The speed of light being uniform and isotropic for all observers is quite counter-intuitive given everyday experience and classical mechanics. Once you have accepted Einstein's second postulate, it is a given, but only then. Also, I find this business of needing to do a vary specific test of the second postulate itself to be bogus. There has been plenty of experimental confirmation of SR, including a number which have validated the second postulate (such as the Michelson-Morley experiment). That this has not been done to Cadwgan's satisfaction is irrelevant. I strongly suggest that people stop responding to Cadwgan. --EMS | Talk 13:31, 8 May 2006 (UTC)

Indeed. He has been trolling the Usenet physics groups since at least a decade, using the names Kurt Kingston (kk), Cadwgan Gedrych, 2ndPostulateDude, SRdude, Edward Travis, Ron Aikas, Roy Royce, John Reid, Martin Miller, Brian D. Jones (which we think is his real name), and probably many more. As soon as he is cornered, he picks another name and starts all over. He will soon show up here under a different name. Talking and arguing in technical terms with this kind of troll just does not work and is a waste of time. User:DVdm 16:25, 9 May 2006 (CET).

DVdm - On that last sentence, agreed. For example, Cadwgan wrote below:

... the second postulate says absolutely nothing theoretical about light's one-way speed between two same-frame clocks ... .

If he truly believed that, he would not be calling for a two-clock test! I see this as proof that Cadwgan is just rattling our chains, and the sooner we stop responding the better. --EMS | Talk 15:22, 9 May 2006 (UTC)

I agree that he's probably trolling, or at least is such a die-hard opponent of the second postulate and SR that it's probably useless to debate these issues with him. I say this after having taken a brief look through some of sci.physics.relativity where he has appeared to exhibit such behavior, as well as using other names. Still, I felt it was worth one statement. <shrug> DAG 16:47, 9 May 2006 (UTC)

Pjacobi wrote below:

Don't discuss the subject, discuss the article. ...

That really is the bottom line here. This page is not here for SR itself to be debated. Instead what we should be debating is what the article should contain. Admitedly the two are linked, but what Cadwgan is asking us to do is to report his view that the second postulate is bogus as opposed to a finding of the same which has been published in a reputable source. That is improper under WP:NOR and WP:NPOV, meaning that Cadwgan should be expected to keep his thoughts in sci.physics.relativity. --EMS | Talk 18:17, 9 May 2006 (UTC)

Apparently, EMS has simply made up his mind, so there is probably nothing that anyone can do about that, but maybe others can see what EMS cannot, so I will now directly address EMS' above objections:

Of course the invariance of light's speed would be counterintuitive if found by experiment; EMS misread what I said, so he missed the point entirely, and then held that against me, calling for others to boycott me. What I did say was that a result that is given by man up front by mere definition (and not by any experiment) is not in the least unexpected or in any way counterintuitive. Einstein began by presetting his distant clock to read his prechosen one-way "time" x/c, which, of course, results in the clock "finding" the value c for "light's one-way speed."

EMS wrote:

"Also, I find this business of needing to do a vary specific test of the second postulate itself to be bogus."

EMS finds it "to be bogus" only because (as in the just-given case) EMS simply failed to understand.

Here is precisely what he failed to understand in this case:

Before special relativity, there was Maxwell's equations, but despite being given these equations, every physicist on the face of the Earth firmly predicted a positive (non-null) result for the Michelson-Morley experiment (round-trip light speed variance with Earth's velocity). Thus, if Einstein had postulated re these equations prior to the MMx, then he would clearly have postulated variance, not invariance, along with every other physicist. However, Einstein did not have to postulate pertaining to Maxwell's equations because they (as I just noted) pre-existed special relativity. Therefore, the second postulate does not postulate regarding Maxwell's equations.

Similarly, since the Michelson-Morley null result itself pre-dated special relativity, Einstein did not have to postulate about that result.

Indeed, in his 1905 relativity paper, Einstein specifically stated that he was simply accepting up front the experimentally-given fact of round-trip isotropy, and was also accepting round-trip invariance (because it was so closely related to the former).

Clearly, this left only one case about which Einstein could possibly postulate, and that case was the one-way, two-clock light speed case.

Since all roads lead to the truth, we can arrive at the just-given conclusion by using an entirely different path, as follows:

Let's say that the second postulate calls for 500 different things, one of which is the invariance and isotropy of light's round-trip, one-clock speed, another of which is the constancy of light's speed c (not measured by a frame's rulers and clocks, but determined by using magnetic and electric fields) in space (as per Maxwell's equations), and yet another of which is the invariance/isotropy of light's one-way speed per transported clocks, and so on, until we reach "the invariance/isotropy of light's one-way speed per two same-frame clocks."

Let's now assume that 499 of the cases have been closed experimentally, some of them even prior to the creation of special relativity.

Just as we found above, we are left with only one case to which special relativity currently applies theoretically, so it is only this one case that is currently critical as far as the future of special relativity is concerned, despite EMS' above opinion that -

He finds this business of needing to do a vary specific test of the second postulate itself to be bogus.

In other words, if special relativity does not currently state specifically that light's one-way speed between two same-frame clocks is "blah-blah-blah," then special relativity does not currently make any theoretical statement about light's speed.

The burning question now is What does special relativity state about light's one-way speed between two same-frame clocks?

Does special relativity say that if this speed is experimentally measured, that it will be invariant and isotropic?

If so, then how can this experiment be performed, and why has it not been performed yet, not even on paper using ideal or perfect clocks and rulers?

It should be clear that if an alleged experiment cannot be performed even on paper using perfect instruments, then it cannot be performed in real life, which, of course, is why no one has performed it in real life.

And since no one here has shown how this critical experiment can be performed on paper, much less in real life, no one has shown how to currently test the second postulate re the only case that counts, the one-way, two-clock case.

The burning question now becomes Why can't we currently test the second postulate in the only case that currently counts?

The answer is as follows:

Because the second postulate says absolutely nothing theoretical about light's one-way speed between two same-frame clocks except the following:

[a] Since absolutely synchronous clocks would yield a variable one-way light speed, and since Einstein's main rule is "No absolute motion detection by any means," we must assume that such clocks cannot be found, even though we cannot prove this negative, and

[b] we must further assume that clocks are properly set only if they do not allow us to detect out motion through space, even though such clocks will not be absolutely synchronous, but will be absolutely asynchronous.

Now we can see the second postulate a little more clearly. For example, we can see why the word "currently" - as in "currently test" - was used above; it is because we could test the postulate if we could find a way to absolutely synchronize clocks.

But we can see a lot more.

For example, a blind person can now see the fact that all two-clock measurements in special relativity are incorrect due to the absolute asynchronousness of Einstein's clocks.

This means that SR's transformation equations are incorrect. It also means that the SR composition (or addition) of velocities theorem is incorrect, as well as all of the other two-clock results such as "time dilation" and "length contraction."

Most of all, it means that the SR "result" of one-way light speed "invariance/isotropy" is incorrect, so Einstein's prime rule is also incorrect, which, as was noted above, was "No absolute motion detection can possibly happen by any means." This is flatly contradicted the simple fact that we could easily detect absolute motion (or motion through space) by using a pair of absolutely synchronous clocks to measure light's one-way speed.

But we can also see that Einstein did not disprove the Galilean transformation because Einstein did not (and could not) prove that absolutely synchronous clocks cannot exist.

And we can further see that one-way light speed invariance has not only not been shown experimentally, but cannot be shown experimentally because it cannot happen unless it has been given up front artificially (i.e., by man via definition).

In conclusion (for now): As long as we cannot absolutely synchronize clocks, we are forced to live with incorrectly related clocks (such as Einstein's), so we are forced to obtain incorrect results, which of course are not valid physics results. However, Einstein's results are the best we can get since he mainly ignores only the actual (and different) light travel times in different frames, and light's speed is very great. But if we could get our hands on a pair of truly synchronous clocks, then we could instantly forget all about special relativity, and go about the much better business of making correct two-clock measurements. For example, as mentioned above, we could easily determine our speed through space by correctly measuring light's passing speed. (None of the above lies outside current human knowledge.) Cadwgan Gedrych 19:05, 8 May 2006 (UTC)

Who said it was impossible to absolutely synchronize clocks? SR rules out such synchronization in frames moving with respect to each other, but Einstein went to lengths to show how two clocks in the same frame can be synchronized, and define what it meant for them to be synchronized. This is done as follows. Starting with two good clocks (atomic clocks, ideal clocks, what have you), in their crates if you'd like, one is chosen to act as a clock for the starting point, and set, and this clock will be called A. The other, to be called B, is moved to the desired location of the second clock, at a known distance away from the first clock. This distance can be determined by laying out rulers, keeping careful track of the motion of the clock to ascertain how far it has travelled, or any other method. Then a signal is sent from clock A to clock B, containing the time at clock A. Obviously, as this signal takes time to reach clock B, depending upon the method used to send it. One could use the second postulate and use a light signal to send the information, but it is equally acceptable to have someone walk it over or any other method where the speed can be well known (for instance via Doppler shift to keep track). However sent, the velocity and known distance are used to correct the time from clock A to account for passed time. I should stress that time dialation or length contraction do not enter into the issue as both the speed and distance are obtained from the stationary frame of the clocks. Clock B is set to the correct time thus calculated. This setting can be checked between the two clocks, but we'll assume that the clock setters don't screw it up the first time or that the process is suitably automated.

Then it would be necessary to check that the two clocks are indeed synchronized, so clock A sends a signal to clock B, let's say containing the time it was sent, then clock B sends a signal back to clock A, and clock A sends one last signal to clock B. Assume that there is zero turnaround time, or that turnaround time is suitably accounted for. Call the times at which the signals were sent $t_{A,0}$, $t_{B,0}$, $t_{A,1}$, and $t_{B,1}$. Then, according to Einstein's synchronization procedure, the clocks are synchronized if $t_{B,0}-t_{A,0}=t_{A,1}-t_{B,0}=t_{B,1}-t_{A,1}$. This is how one synchronizes two clocks in the same frame.

So, then verifying the second postulate becomes simple. Exchanging light signals between the two synchronized clocks will do the job. Sending a signal from clock A to clock B with the time it was sent from clock A contained therein (or sent along later). Then the speed of light can be determined from knowing the distance between the clocks, determined during the synchronization process, and the time it took for the signal to propogate. Similarly, the round trip speed of light can be confirmed from Einstein's synchronization condition. That is, $c={\frac {2x_{AB}}{t_{A,1}-t_{A,0}}}={\frac {2x_{AB}}{t_{B,1}-t_{B,0}}}$. Moreover, the condition that $t_{B,0}-t_{A,0}=t_{A,1}-t_{B,0}=t_{B,1}-t_{A,1}$ is a proof for the isotropy of light speed. From these confirmations, the second postulate, that "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body", can be confirmed, and used to show that the speed of light is always just the speed of light.

As to Maxwell, it is correct that his equations were known earlier than either Michelson-Morley or Einstein, and that knowledge of Maxwell's equations did not and does not automatically imply the second postulate. Indeed, the fact that the speed of light (or more correctly the speed of EM-waves, which is what light is) did not depend upon any facet of any observer or frame was interpreted as evidence for the aether. The aether would be the frame in which the speed of light was as in Maxwell's equations. However, as history shows, the aether hypothesis ran into a great deal of trouble. What Einstein did, particularly in his first postulate, was propose that Maxwell's equations, like Newton's laws, were the same for all observers in inertial frames. So, in every inertial frame, the result of the equations that EM-waves and light would travel at the speed of light should need to hold true. Otherwise, the first postulate could not be correct, as it would be possible to tell two inertial frames moving with respect to each other from each other by testing Maxwell's equations, testing the strength of the electric and magnetic interactions, and even measuring the speed of light.

As to testing these predictions, and the second postulate, it should be pointed out that SR is in fact not strictly true. It was superseded by General Relativity which complicates the picture. We live in the middle of a gravitational field which is not uniform. So there is a limit to the size of our "laboratory" for making a test. Now, I'm far to lazy to look it up or do any calculations, but it may very well be that the "laboratory" length required to fully test the second postulate is too large to accomodate the assumption of an inertial frame. So, if the second postulate has not been adequately tested, it may be due to these restrictions, and to restrictions in our ability to conduct such experiments.

I hope this has satisfied most people. DAG 20:37, 8 May 2006 (UTC)

DAG, your theory that it is "possible to absolutely synchronize clocks" is non-standard and disproved in a number of articles such as by Ives. See also the linked journal article by Rizzi. Harald88 21:09, 8 May 2006 (UTC)

Firstly, I should note that all this synchronization I propose takes place within one inertial frame. It does not attempt to "absolutely synchronize" between two frames moving with respect to each other. Once the two clocks are placed, the only things which move are signals.

Secondly, I do not see anything in the Rizzi article (presuming you were referring to http://arxiv.org/pdf/gr-qc/0409105) that says my proposed scheme is wrong. Indeed, it appears that what the paper goes on to show is that the "absolute" synchronization therein described is nothing but the special case of synchronization in one inertial frame, which is what I was attempting, and which is entirely valid.

Thirdly, all I have done is show how a system of synchronized clocks might be set up in one inertial reference frame. I have worked to define the time element of the position four-vector inside this frame. I have not said that time might be synchronized between two clocks in different inertial frames, nor that such a scheme implies absolute simultaneity between inertial frames. All I have said is that conceivably, at each point in space, a system of synchronized, relatively-stationary clocks can be set up. This is the whole point of Einstein synchronization, as the following statement from "...Electrodynamics..." shows:

"By means of stationary clocks set up in the stationary system and synchronizing in accordance with § 1, the observer ascertains at what points of the stationary system the two ends of the rod to be measured are located at a definite time. The distance between these two points, measured by the measuring-rod already employed, which in this case is at rest, is also a length which may be designated 'the length of the rod.'" (§ 1 is the section describing Einstein synchronization).

Fourthly, as to Ives, I have not read any of his papers, so a link/reference would be nice, though I would also note that he appears to have been significantly opposed to SR, even though at least one of his experiments is generally taken as confirmation of SR. Again, there's not much I can say about this without seeing what he actually said.

I hope this reassures you that my proposal is entirely standard and was just a careful and canservative statement on how to build a network of clocks to define time in a single inertial reference frame. DAG 21:50, 8 May 2006 (UTC)

See for example the summary conclusion on p.45: we do not think that the one-way speed of light is a meaningless concept because it is not measurable; we simply think that the lack of observability allows a multiplicity of conventional assumptions, encapsulated in some synchronization gauge, which are consistent with any possible experimental evidence. And Ives was opposed to the popular interpretation (he roughly agreed with Langevin and not with Einstein), and he published a lot of high quality peer reviewed papers on the subject - but I now notice that Cadwgan provided links to more of such references, thus it's no use to look up unlinked ones, nor needed for us to explain it. Harald88 21:15, 9 May 2006 (UTC)

Don't discuss the subject, discuss the article. Please refrain from doing original research, however tempting it is --Pjacobi 17:10, 9 May 2006 (UTC)

To DAG:

link.aip.org/link/?AJPIAS/53/53/1

"A proof that absolute synchronization is impossible is sketched."

wwwphy.princeton.edu/~steinh/ph115/Chapter11D.pdf

"Absolute synchronization is impossible."

DAG, "ol' boy," you went through your synch process a little too quickly. Let's slow it down a tad, as follows:

Re your claims that clock slowing and ruler contraction are not involved: You did not prove that the clocks are not physically slowed. Experiment shows that clocks moving at different speeds have different intrinsic atomic rates. Also, you failed to prove that your standard ruler was not physically contracted. (The only way to show the MMx null result on paper is by using a physical length contraction, so this proof is clearly essential. Indeed, it would be essential even sans the MMx case because a "real physicist" must prove all steps.)

You (DAG) wrote:

"However sent, the velocity and known distance are used to correct the time from clock A to account for passed time."

What "velocity" are you talking about? How was it measured? You already have the two possible error sources of intrinsic clock slowing and intrinsic ruler contraction which you did not take into account. How could you have possibly measured any velocity correctly at this point in the game?

I took it for granted that everyone knew that the lack of absolute simultaneity in SR was the same as the lack of absolute synchronization. If Einstein could not determine whether two lightening bolts stuck absolutely simultaneous or not, then he certainly could not absolutely synchronize two clocks, even in a single frame.

Indeed, here is what Einstein himself said regarding a single frame measuring the speed of a light ray. Einstein was so specific that he even specified a departing light ray:

[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.

The point here is not what Einstein thought about this result, but that he derived it on paper, using two clocks in a single frame.

As I said, the only way anyone can understand the second postulate is by discovering for themselves the physical distinction between two same-frame Galilean clocks (which Einstein used to get his w = c - v) and two same-frame Einsteinian clocks, which yield w = c in any frame in any direction. (Note that Einstein would have obtained w = c + v if he had specified an approaching light ray.)

DAG, tell us the difference between Galileo's and Einstein's clocks.

DAG wrote:

"Now, I'm far to lazy to look it up or do any calculations, but it may very well be that the "laboratory" length required to fully test the second postulate is too large to accomodate the assumption of an inertial frame."

Here you overlooked my prior statement that no one has ever shown even on paper (using ideal rulers and clocks) how to test the second postulate's (sole) theoretical prediction that light's one-way speed between two same-frame clocks is c invariantly and isotropically.

You also ignored my comments re Maxwell's equations.

You wrote:

"... it would be possible to tell two inertial frames moving with respect to each other from each other by testing Maxwell's equations, testing the strength of the electric and magnetic interactions ...."

As I noted, even Maxwell himself fully expected a positive result for the MMx. He could not have expected this given your above.

Here is why he did not expect it:

The interactions of magnetic and electric fields have always been frame independent, just the same as the interactions of a comb and a head of hair, or a back scratcher and a person's back. No one should have ever expected to detect their motion through space by using Maxwell's equations or the results of any magnetic/electric interactions, and no one did except a few such as DAG. ;-)

Returning briefly to your synchronization process, let's assume that the ruler-measured distance between the two given clocks was 1 light-year. Let's then emit a light signal at the origin clock, which starts on zero, letting the signal travel to the distant clock. We will assume (as did Einstein) a one-way travel time of 1 year. Giving both you and Einstein the benefit of the doubt in this instance, I will agree that the clocks will be absolutely synchronized if the distant clock reads 1 year when it is struck by the light signal.

However, if we simply add another frame or two, we can see instantly that no other frame's clocks can possibly be absolutely synchronized.

The basis of this fact is the simple fact that we can use the same light source for all other frames due to light's source-independence.

Picture a second frame whose x axis is parallel to that of the first frame, with their origin clocks coincident when the light signal is emitted there.

Although both origin clocks are absolutely synchronous because they both read zero at absolutely the same time, we can't say the same about the two distant clocks.

Indeed, we can say for certain that they get "hit" by the light signal at absolutely different times because nothing - including a light signal - can be in two places at once. (Besides, all observers in all frames see one clock get "hit" when the other clock is not there, which proves that they were "hit" at absolutely different times.)

We have already given the "hit" time for the first frame's distant clock, namely, T1 = x/c.

We now can see that the "hit" time for the second frame's distant clock cannot be T1 = x/c, but instead must be T2 = T1 + T?, where T? is the unknown time for the light signal to travel between the two spatially-separated distant clocks.

Unless light's speed is infinite, T? must be >0.

But DAG's overly-quick analysis did not even mention other frames.

As I said, it is time to get serious here, and getting serious means using in-depth analyses.

I have just proved that Einstein's clocks cannot be absolutely synchronous except in one frame (among all frames whose x axes are parallel).

As I mentioned, it is not possible to obtain correct results by using absolutely asynchronous clocks.

Some may see this as "SR bashing," but I see is as just calling a spade a spade, and I have the proof to back it up, unlike DAG.

Someone who starts a proof with "Let the unprimed frame's origin clock read zero when event E1 occurs at t = 0.6 and at x = 1" should stay away from physics as far as possible. Go troll sci.physics.relativity where we are free to treat you the way you deserve. DVdm 9 May 2006, 23:20 CET

http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/MathProof.html

Anyone interested in fair play can see the section "Self Defense" Cadwgan Gedrych 20:26, 10 May 2006 (UTC)

How does this proved conclusion relate to the article? It tells us in no uncertain terms that it is currently not possible to correctly measure any one-way, two-clock speed, including light's one-way, two-clock speed, which is the only speed to which the second postulate can pertain to theoretically, as I have noted.

In contrast, the article implies that a correct measurement is possible, and that the correct result would be c.

Contrast this with Einstein's own claim that the result would be c - v given the absolutely synchronous clocks of classical physics.

Finally, let me repeat the fact that no one has ever even shown on paper (using perfect clocks) how we can currently experimentally measure light's one-way, two-clock speed, so the article is simply wrong to imply that such a measurement can be made today. Cadwgan Gedrych 19:36, 9 May 2006 (UTC)

Without commenting on off-subject matters, where does the article make such a suggestion? Often it's just a matter of phrasing. For the record, here follows Pjacobi's comment on my Talk page about this subject, when commenting on http://arxiv.org/pdf/gr-qc/0409105: Harald88 21:32, 9 May 2006 (UTC)

What's soreley missing, is making contact with the "modern" coordinate free formalism. IMHO this would expose it immediately, that Einstein symchronisation is both a convention and trivial, just a choice of coordinate system which make practical calculations easier. Pjacobi 19:13, 8 May 2006 (UTC)

Harald88 - The article does imply that the two-clock measurement is possible and that the result would be c. The second postulate just plain does that. What is bogus is the assertion of Cadwgan that "Einstein's own claim that the result would be c - v". That is the closing rate of light in a frame of reference with respect to an object moving in the same direction as the light at a speed of v. Cadwgan is being very cleaver and lawyerly, using any statement that he can get his hands on as a basis for refuting SR. For example, in his own talk page he acknowledges in one paragraph that the second postulate explains the Michelson-Morely experiment null result, and a little later asks me to describe how SR explains that same result as if it does not. He is not imterested in learning. He is not interested in getting answers. Instead he is interested in making people waste their time with him. Please leave him alone. --EMS | Talk 01:59, 10 May 2006 (UTC)

EMS, I already made claer earlier that I'm not interested in abusing this Talk page for discussions about SRT. Let's just report on what the literature says about it. Harald88 22:32, 10 May 2006 (UTC)

I finally got off my lazy ass and looked for some documentation on one-way speed of light measurements, and apparently here (http://prola.aps.org/abstract/PRD/v42/i2/p731_1) and here (http://prola.aps.org/abstract/PRA/v56/i6/p4405_1) are articles about experiments designed to test it (admittedly I don't have access to actually read them, so if anyone here does and can shed some light on the exact procedure, that would be nice).

As to criticism of my procedure, I'd like to point out that I really shouldn't have called it "absolute synchronization". I think that led to a lot of confusion as to what I meant and what I was trying to illustrate, which was that it is possible to synchronize two clocks at rest with respect to each other, and do so without invoking the postulates of relativity. Basically, that you could create a coordinate system with a man with a watch on every corner. But only in one frame. Two or more frames, all bets are off, and what I said gets broken real easily.

Finally, Harald88, do you have links to any of Ives papers on the subject? I performed a skim-the-surface Google (my only option at the moment), and didn't get any good leads (though some nice general bio info and such). Do you (or anyone else) have any of that available? DAG 05:23, 11 May 2006 (UTC)

For the conventionality of synchronization (indeed, this convention predates relativity), see Relativity of simultaneity. I don't have links ot Ives' papers and I only have hard copies of them; if oyu like, I can scan one of them and send you by email.

However, I now looked at the abovementioned AJP paper by Erlichson 1985, "The conventionality of synchronization"; IMO it summarizes everything rather neatly, it discusses so-called OWLS measurements as well as your slow clock transport proposal. I can send you the PDF if you don't have access. Harald88 10:34, 11 May 2006 (UTC)

Note: Looking more carefully at the way that article covers slow clock transport I'd say it's a bit too "light", eventhough it cites a remark by Ives.

Apparently the essential point is missed: Relativity of simultaneity and relativity of light speed isotropy boil down to the same thing, and the LT are valid for the case that we define "our" system to be "in rest" (if one could establish "absolute" synchronization in one measurement system, then that would imply that we could detect one system in which the synchronization is right, making all others wrong).

OK I'll look up which article by Ives explains best how slow clock transport works and why it doesn't yield what is commonly meant with "absolute synchronization". It may come in handy for the article. Harald88 12:53, 11 May 2006 (UTC)

I now found some that explain it, but that sound rather "anti" what he perceived to be SRT, as well as one or two are very volumunous. However, one of the later articles is a kind of summary and more moderate, it's "Extrapolation of the Michelson-Morley experiment" in the JOSA vol.40, no.4, april 1950 pp.185-191. In particular, he demonstrates the relativity of simultaneity between two stationary clocks with slow clock transport.

I can scan it and send it to those in this discussion who are interested but don't have access to the JOSA. Harald88 22:42, 11 May 2006 (UTC)

Anyone interested in fair play can see the section "Self Defense" Cadwgan Gedrych 20:26, 10 May 2006 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Special relativity/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Some work needed on material relating to equations. Tompw 12:50, 5 October 2006 (UTC) The discussion needs a picture or other basic conceptual explanation of each part before getting into the less comprehensible vector calculus. 24.98.65.137 (talk) 10:02, 27 October 2008 (UTC)

Last edited at 10:02, 27 October 2008 (UTC). Substituted at 22:04, 3 May 2016 (UTC)