Talk:Special relativity/Archive 8

Self Defense
Dirk Vdm wrote:
 * "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."

Dirk neglected to give the full story.


 * Here is the full story in all its glory:
 * http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/MathProof2.html
 * http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/MathProof.html
 * DVdm 22:10, 10 May 2006 (UTC)


 * Two nearly-the-same snippets is not the full story.
 * See my rebuttal below Cadwgan Gedrych 13:57, 11 May 2006 (UTC)

A single picture shows the entire experiment: (Key: a clock reading -.6 is shown as [-.6].)

Primed Frame           x=1 [0][-.6]---> E2                       E1  [0][+.6]<--- Unprimed Frame         x=1

Note that - as was said above - the unprimed frame's origin clock reads zero as event E1 occurs at t = 0.6 and at x = 1.

All readings and distances are given per the relativistic transformation equations.

Contrary to Dirk, no clock which reads two different times at once.

EMS wrote:
 * "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."

It is not a closing speed. Einstein clearly stated that it was the speed of light relative to the carriage. There is no object involved. But this does not really matter.


 * I will stand corrected on this count. I went to find the c-v reference, and succeeded.  It is in .  As it tuns out, Cadwagan awas right: Einstein was describing the speed of light.  However, he is doing so under the rules of classical mechanics.  It may be instructive to note that the title of this section is "The apparent incompatibility of the law of propagation of light with the principle of relativity".  It should also be noted that at the beginning of the following paragraph Einstein states: "But this [c-v] result conflicts with the principle of relativity ...".   So Cadwgan claiming that Einstein says that the speed of light is c-v is just plain deceitful. --EMS | Talk 03:48, 11 May 2006 (UTC)

What does matter is this:

The Galilean transformation, which was derived using clocks and rulers, just as was the Einsteinian transformation, and yet the former has a variable one-way, two-clock light speed, whereas the latter has an invariant one-way speed.

Neither EMS nor Dirk can tell us how Galileo's clocks physically differ from Einstein's.

Therefore, neither of them can tell us why the clocks get different results.

I challenge them to fill in these blanks:

Galileo's clocks: [??]--1 light-year---[??]

Einstein's clocks: [??]--1 light-year---[??]

(speeds can be supplied to suit your taste)

EMS also wrote:
 * "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."

OK, EMS, you'll have to copy and paste this from my TALK page to here. I do not see it. And if I did say that, I must have been on some very heavy medication because I do not believe for a minute that the 2nd postulate explains a damn thing about anything. Cadwgan Gedrych 20:52, 10 May 2006 (UTC)


 * In his talk page, Cadwgan Gedrych wrote:
 * You claim above that things such as the MMx confirmed the second postulate. ... Yes, any null result is consistent with the second postulate.
 * Let me put it this way: I'd love to know what you were on, and if you would be so kind as to continue taking it.  :-)
 * Beyond that, in writing
 * I do not believe for a minute that the 2nd postulate explains a damn thing about anything
 * you are making it clear that you are here to oppose special relativity instead of helping others to understand it. Given that, you should not be participating here. --EMS | Talk 03:18, 11 May 2006 (UTC)


 * If you like, I can find back mainstream papers that conclude that the 2nd postulate is superfluous for SRT, except for defining the value of c. And in Wikipedia articles are not allowed to have a WP:sympathetic POV; instead they should all be WP:NPOV. Thus, anyone may participate to contribute POV's from existing literature (that last part is of course the weak point for many people here). Harald88 13:05, 11 May 2006 (UTC)
 * Let me get this striaght - The second postulate is superfluous except that what it does is essential. Somehow, I don't think that the point of the article is that the second posulate can be dispensed with, but feel free to cite it if you like.  Let me assure you that Cadwgan either does not know what he is talking about or does not care about the truth of the matter.  His goal is to create confusion and disrupt the article, and you seem to be falling for it.  Please remember that this article is about special relativity, not Brian Jones' objections to it. --EMS | Talk 15:07, 11 May 2006 (UTC)

Smoke and mirrors. Neither Dirk nor EMS could tell us how Galileo's clocks differ from Einstein's. And yet this is essential to any sort of understanding of the difference between classical and Einsteinian flat space-time physics!

I do wish to thank EMS for his clarification re the w = c - v, as far as it went; but it quickly bogged down again.

EMS said: "It should also be noted that at the beginning of the following paragraph Einstein states: But this [c-v] result conflicts with the principle of relativity ....  So Cadwgan claiming that Einstein says that the speed of light is c-v is just plain deceitful."

If I am just plain deceitful, then how did I win my first case against the Wiki article?

If I am just plain deceitful, then how did I win all of my SR arguments in the Newsgroups?

It seems to me that it's EMS who's just plain deceitful because he omitted my prior statement here that it matters not what Einstein claimed about the validty his result w = c - v, but all that matter was the simple fact that Einstein derived this result on paper using two clocks.

I did not say that Einstein said that the speed of light is c. I said that he said that the speed of light would be and could be c given the absolutely synchronous clocks of classical physics.

This is not even hinted at in the Wiki article.

I also said that the only reason we get c today is by definition, and this clearly has nothing to do with physics because it is untestable.

Let EMS tell us why no one has ever used two same-frame clocks to measure the one-way speed of light? This is clearly the definitive one-way light speed experiment, but it has yet to be performed, and the Wiki article fails to mention this extremely important fact, let alone tell us the why's and wherefore's!

EMS wrote: ": In his talk page, Cadwgan Gedrych wrote:


 * You claim above that things such as the MMx confirmed the second postulate. ... Yes, any null result is consistent with the second postulate."

This also seems deceitful. Anyone here should know that merely "being consitent with" does not mean "physically explain by."

Dirk pitifully attempts to cite essentially the same thing on two web pages to make his case look better, but he has no case at all.

Doesn't anyone here think it odd that Dirk has nothing to say about the topic at hand, namely, the second postulate?

Doesn't anyone here think it rather strange that Dirk has not simply pointed out which clock of the 4 reads two different times at once?

Doesn't anyone here think it weird that Dirk simply ignored my simple but critical challenge re Einstein's vs Galileo's clocks?

Doesn't anyone here think it sad that no one except Dirk "sees" an error in the little 4-clock experiment?

Since Dirk continues to insist on posting off-topic, it seems that one way to put a stop to this is by challenging him to bring in at least one other person who agrees with him about the above-mentioned 4-clock case. Cadwgan Gedrych 13:57, 11 May 2006 (UTC)


 * Brian (fake Cadwgan Gedrych), you don't understand the meaning of the variables x and t, so there is no way you could interpret any answer to any question.
 * http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/MathProof2.html
 * http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/MathProof.html
 * I could explain a few things to you, but I will not do it, for the simple reason that you don't even deserve getting an explanation anymore. Belonging in the category of Ken Seto, Androcles and Spaceman, you are much more fun in your clueless state. Face it, you are a Clueless Autistic Imbecile and I like you to stay a Clueless Autistic Imbecile. You are fun :-) DVdm 15:09, 11 May 2006 (UTC)


 * Dirk -
 * Please remember WP:CIVIL. I have debated starting an WP:RfC against Cadwgan, but I will warn you now that if you persist in this flaming, I will start an action against you instead!  I call upon you to apologize to Cadwagan now.  After this, please remember that if you can't say anything nice, then you need not say anything at all.  (It feeds the troll anyway.) --EMS | Talk 15:48, 11 May 2006 (UTC)


 * EMS, yes, I am aware of WP:CIVIL and I fully understand your concern. However, I am also aware of guidelines how to use talk pages where we read:
 * Assume good faith: In other words, try to consider the person on the other end of the discussion is a thinking, rational being who is trying to positively contribute to Wikipedia — unless, and only unless, you have firm, solid, and objective proof to the contrary. Merely disagreeing with you is no such proof.
 * I think that in this case everyone can see, and, after all these years, has seen the firm, solid, and objective proof to the contrary, so as far as I am concerned, an apology to "Cadwgan" is most definitely out of the question. Furthermore, ask yourself whether one should apologize to Cadwgan Gedrych, to Kurt Kingston, to 2ndPostulateDude, to SRdude, to Edward Travis, to Ron Aikas, to Roy Royce, to John Reid, to Martin Miller, or to Brian D. Jones?
 * By the way, looking at your own words ("It feeds the troll anyway"), you might consider an apology yourself - Sorry, couldn't resist ;-)
 * It is clear that a semi-open forum like the WP is essentially defenseless against dishonest and malicious individuals like this. I think the article in question is quite okay, but the discussion pages are as good as taken over by this troll. Anyway, since we indeed should be discussing the article, I will stop discussing this dishonest and silly troll now :-)
 * Keep up the good work, and cheers, DVdm 17:28, 11 May 2006 (UTC)
 * I won't claim that my own words are pure. "deceit", "troll", etc. are certainly fairly strong, but if you cannot express your disapproval at all then WP:CIVIL becomes a millstone around everyone's neck!
 * But look again, for all of the disapproval that Cadwgan has expressed, he has never once resorted to name calling or threats. Therein lies the issue.  I have dealt little if at all before with Cadwgan, but having dealt with others of his ilk I know how the type and I am sure that things have been explained to him many, many times before.  I am not asking you to apologize for saying that he does not deserve an answer.  After all, he does not, and you are entitled to say so, but only in so may words.  Where you went over the line is in calling him "a Clueless Autistic Imbecile".  That and that alone is what you must apologize for.  If you cannot bring yourself to aplogize for that namecalling, then I will happily start the WP:RfC even if the second party supporting it ends up being Cadwgan himself. --EMS | Talk 18:59, 11 May 2006 (UTC)


 * EMS, where you draw the line, and exactly how many "so many words" you deem appropriate, is of course entirely your choice. I appreciate that. So you (and Brian, Cadgwan, Martin, Kurt, Edward, Ron, Roy and John) can start (and support) whatever you feel you must "happily" start. When you do, don't forget to include the rationale for conveniently drawing the line between my "Clueless Autistic Imbecile" and your "Deceptive Troll" (if you forgive me this minor paraphrasing). Personally, I find the combination of the predicates perfectly appropriate and abundantly documented.
 * Anyway, since I like to call Deceptive Trolls by all their names, and since it is clear that this forum is not the place for doing so, I will cut this short. I am forced to, and so I will indeed respect the rules.
 * Good luck with the trolls, and cheers, DVdm 21:52, 11 May 2006 (UTC)

Although I know that he "hated" to do so, I must thank EMS for calling Dirk's hand, so to speak. As we can all see, Dirk is not a fair-play person, and yet he is the only one from the entire Newsgroup world who has come here to jump on my case - baselessly - as we can see from any and all of his above.

I know EMS "hated" to defend me because he wrote: "... with others of his [Cadgwan's] ilk I know how the type and I am sure that things have been explained to him many, many times before."

Although EMS is completely off-topic here, as far as the second postulate goes, I need to state that there are very few others "of my ilk" around. As I said, I am not on any troll or crackpot list, despite my push to reveal the full truths about special relativity. And absolutely nothing about SR "has been explained to [me] many, many times before." I would like to see a retraction and an apology from EMS, who has made serious but completely false allegations here.


 * You are on Dirk's troll and crackpot lists, and most certainly are on my troll list. Then again, beause of my opposition to black holes, I am on a number of crackpot lists myself.  I have nothing to retract, although I will offer you a weak apology for refering to you as "deceitful" and a "troll".  However, while I regret the necessity, I do see those labels an amply justified by your actions in this venue.  (Note however that I draw the line purely personal attacks, which is what Dirk gave you.)
 * You rate a kudo from me for not rising to the bait and responding to Dirk on his own terms. Let's just say that he is not this first mainstream editor to disgrace himself in dealing with a non-mainstream editor, although I see Dirk as being just plain rude and not a "mainstream crackpot" (and I do know of one).
 * As for any specifics on SR and the two-clock experiment: You have already tipped your hand.  You do not accept the second postulate as a description of physical reality.  You therefore do not accept that this article is correct in treating SR as a description of physical reality.  You are screaming that this two-clock experiment is important, but have produced no citations in an respected publication where this is stated.  In the end, it is Cadwagan Gedrych/Brain Jones that is the source of the need for such an experiment, and using your say-so would violate WP:NOR.  --EMS | Talk 15:15, 12 May 2006 (UTC)

For example, why does the article fail to say that no one has ever used two same-frame clocks to measure the one-way speed of light, not even on paper? The second postulate certainly pertains to such a speed, as all books on special relativity certainly say or at least certainly imply. Indeed, it would be very hard to find a person anywhere who does not believe that light's speed from point A to point B is not c experimentally. And the same number of people firmly believe that the second postulate says that light's speed from point A to point B is c experimentally, or would be if the "experiment" were performed today, since it has yet to be performed, much to most folks complete surprise. Even more surprising is the fact that it cannot be performed today. And even more surprising is the fact that were it to be performed tomorrow, the result would not be in favor of the spirit second postulate; i.e., it would not be a null result because the only way to perform the one-way experiment is by using two absolutely synchronous clocks to measure the passing speed of light.

This is all simple and obvious and fully in the realm of current human knowledge, but the article does not even touch on it. Cadwgan Gedrych 13:24, 12 May 2006 (UTC)

RfC filed - and deleted
See Requests for comment/DVdm. Maybe I shouldn't throw stones, but I don't make idle threats. --EMS | Talk 02:13, 12 May 2006 (UTC)

It seems that the Rfc was deleted due to lack of endorsement. DVdm 09:17, 19 May 2006 (UTC)

Winning newgroup arguments
Cadwgan wrote:
 * If I am just plain deceitful, then how did I win all of my SR arguments in the Newsgroups?

For the sake of others: People like Cadwgan feel that they have won the argument when the other side gives up on the discussion. In fact, a win only occurs when the other side explicitly concedes the point. So this is just another piece of deceit on the part of Cadwagan, although it may be unintentional.

It is time to stop feeding this troll. Cadwgan does not accept the second posulate as being even a potential description of physical reality. That is the source of his angst. However, that is not a view that is compatible with an article on special relativity. The focus of this talk page needs to be the article, not Cadwagan. --EMS | Talk 15:38, 11 May 2006 (UTC)


 * "People like Cadwgan" is highly derogatory, EMS. Please cease and desist!


 * And calling me a "troll" sans the least bit of evidence is - to put it mildly - not nice, EMS. You, as does Dirk, seem to have a personal vendetta against me. Why?


 * Although I could give you a current example where the "other side" posted only once, and then was stopped cold, this would still be beside the main point, which is the simple fact that the Wiki second postulate position is inadequate.


 * And even if I had lost every single argument in the Newsgroups (whereas of course, the exact opposite is really the case), this is irrelevant to the current case of the second postulate.


 * Neither EMS nor Dirk has made the slightest dent in anything that I have claimed re the article re its second postulate section.


 * EMS caustically and baselessly wrote:

"It is time to stop feeding this troll. Cadwgan does not accept the second postulate as being even a potential description of physical reality. That is the source of his angst."


 * Does EMS deny that the postulate pertains to the speed of light from point A to point B in an inertial reference frame? Can EMS show us how to make this measurement - if only on paper using perfect clocks? Cadwgan Gedrych 13:47, 12 May 2006 (UTC)

Postulates section revert
Harald88 -

It is your "corrections" that were incorrect. From "On the electrodynamics of moving bodies", Einstein states the second postulate as "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body". Note that there is no reference to any round trip there. --EMS | Talk 02:13, 10 May 2006 (UTC)


 * And some paragraphs abobe Einstein states:
 * ...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
 * So, the the part of the second postulate, which is not a tautology, is a postulate for measured round-trip speeds. Several authors, most notably Reichenbach, have clarified this point.
 * Pjacobi 07:58, 10 May 2006 (UTC)


 * EMS, I agree with the removal of Harry's roundtrip. However, I replaced velocity with speed. The translation of Einstein's article mentions velocity alright, and Einstein uses geschwindigkeit in the original version, but he is clearly talking about the magnitude of the vector. DVdm 10 May 2006, 12:05 CET


 * Good change. You are correct that it is the speed of light that is the same in all frames of reference, but not its direction of travel. --EMS | Talk 14:48, 10 May 2006 (UTC)


 * EMS, not only you were too hasty with reverting my "speed", you were also too hasty with reverting Pjacobi's suggested "roundtrip". See Below. Harald88 21:52, 10 May 2006 (UTC)


 * The word "speed" was the only acceptable part of that edit. As I noted below, there is nothing "roundtrip" about the second postulate itself. --EMS | Talk 17:04, 11 May 2006 (UTC)


 * I must correct myself, generally speaking the constant round trip speed follows from the synchronisation convention plus the first postulate.
 * If one tries to make the three statememts (sync. conv, post 1, post 2), orthogonal, so that each one states only what is not already covered by the previous one, this would remain from the second postulate: Light emitted at point A simultanously by sources with different speeds arrive at point B simultanously.
 * OTOH it is somewhat unclear, whether a orthogonalized set of stattements is preferable to simple and concise form.
 * Pjacobi 11:09, 10 May 2006 (UTC)


 * Actually, Einstein made clear (and this is noticed in a number of articles) that he simply postulated what was already accepted observations - the equivalence for observations of all intertial frames, and the roundtrip speed c (he defined c as roundtrip speed in that article, and pointed out once more in 1907 that the one way speed is only a stipulation, see again the reference that I added).
 * Note also that the endless discussion above was caused by the fact that someone removed that clarification eventhough it had already been discussed earlier
 * Furtheron, it should be understood that what can't be truly verified experimentally (as is the easy to understand majority expert opinion) can't be claimed to be part of a postulate of a scientific theory - it would turn SRT into pseudoscience.
 * In any case, this article should report the consensus about SRT in a logical and easy to understand way. As discussed in the abovementiohn AJP article, "The conclusion is the same as was stated by Einstein in his 1905 relativity paper—synchronization must utilize a convention."
 * Needless to say, a convention isn't a postulate and shouldn't be presented as such - even if Einstein obscured that in his 1905 paper. Imperfections in one paper are not determinant for the theory.
 * Thus I partly revert to an older version; if anyone insists on including mention of the one-way speed in the postulate I suggest that he/she adds the reference to such an paper to the article as well as a remark that some authors include the one-way speed in the postulate, eventhough it can't be verified, strictly speaking. Harald88 21:52, 10 May 2006 (UTC)


 * On second thought, it is probably best to not overstress the postulates; it will be more fruitful to explain in a section furtheron in the article why c is effectively the two-way speed. Harald88 07:04, 11 May 2006 (UTC)


 * PS Pjacobi, you mentioned the "modern" coordinate free formalism that would expose it immediately, that Einstein symchronisation is both a convention and trivial, just a choice of coordinate system which make practical calculations easier. Do you have a good reference that we could sumarize and include in the article? Thanks in advance, Harald88 22:34, 10 May 2006 (UTC)


 * Einstein's synchonization procedure is, in his 1905 paper, explicitly given for one coordinate system only - the stationary system: "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.``".  In other words, he begins by assuming that the speed of light is isotropic in this system and sets his clocks to reflect that assumption.
 * The 2nd postulate, as expressed in his 1905 paper, sets the measured speed of light in the stationary system only to be c: "Any ray of light moves in the ``stationary system of co-ordinates with the determined velocity c".  Now the round trip average speed of light is also c since, by assumption (definition?), the speed of light is isotropic in the stationary system.
 * But, and correct me if I'm wrong here, all of this applies to the stationary system only until the 1st postulate is invoked. That is, Einstein synchronization in all coordinate systems related to the stationary system by uniform translatory motion follows because of the principle of relativity.
 * If, instead of the principle of relativity, we postulated that "what is simultaneous in the stationary system is simultaneous in all coordinate systems related to the stationary system by uniform translatory motion" and in addition, we enforced the observational result that the round trip average speed of light is c in all of these coordinate systems, would we not get the Sellari inertial transformation instead of the Lorentz transformation?
 * If this is true (and I'm not sure that it is), then it would seem to me that all this discussion about synchronization and the 2nd postulate is somewhat off target for the reason that it is the 1st postulate that governs the synchrony choice in the 'non-stationary' coordinate systems. Thoughts? Alfred Centauri 14:05, 10 May 2006 (UTC)
 * I would have to work the details, including looking into the Sellari transformations, but I can tell you that this alternate postulate will give you a different result. Let's just say that the loss of the principle of relativity would have significant consequences, just as its being retained by Einstein in 1905 did.
 * As for your musing about the second postulate discussions, you have hit the nail on the head: You cannot establish absolute universal synchronization because the clocks in the "moving" coordinate system get synchronized in a way which is incompatible with way the clocks of the "stationary" coordinate system were synchronized. --EMS | Talk 14:48, 10 May 2006 (UTC)


 * In Harald88's last edit to the second postulate, he writes: "What also many textbooks overlook is that the isotropy of the one-way speed of light was introduced by definition and not as postulate."  Yes, Einstein introduces the isotropy of the OWSL as a definition but, as I've pointed out above, this definition holds only in what he calls the stationary system of coordinates.  Further, the phrasing of the 2nd postulate in this article does not make it clear that, in Einstein's words, the 2nd postulate refers to the speed of light in the stationary system of coordinates.  In other words, Einstein assumes isotropic OWLS and the independance of c on the motion of the emitting body in a coordinate system.  It is only through the principle of relativity that this state of affairs is extended to all uniformly moving coordinate systems.  At least, this is how I read his 1905 paper.  Alfred Centauri 22:29, 10 May 2006 (UTC)


 * Alfred - You are basically correct in your reading of the 1905 paper. As for Harald88 saying that the isotropy of the one-way speed of light is a definition instead of a postulate: I see it as both!  Here is a larger excerpt from the 1905 article:
 * ... [T]he same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good. We will raise this conjecture (the purport of which will hereafter be called the "Principle of Relativity") to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite [speed] c which is independent of the state of motion of the emitting body.
 * Indeed, Einstein is defining the speed of light as being uniform and isotropic. However, at the same time as Einstein makes this definition, he also assigns it the status of a postulate, since this definition is one of fundamental principle of the theory that he is about to describe.
 * The real key to this business really is the first postulate, the principle of relativity. Even in aether theories the speed of light was expected to be uniform and isotropic with respect to the aether, and so the "stationary frame" for the aether was a preferred frame of reference.  However, in relativity, all frames of reference can potentially act as a "stationary frame".  Similarly, all frames can also have the role of a "moving frame".  Just remember that it is the Lorentz transformation that now describe how events as viewed in one frame of reference will be viewed in a different frame of reference.
 * Beyond that, I ask that all concerned here not let themselves be confused by the inappropriate assertions of those who disapprove of SR to begin with. --EMS | Talk 02:59, 11 May 2006 (UTC)


 * You forgot to cite in conjunction with:
 * light is always propagated in empty space with a definite [speed] c which is independent of the state of motion of the emitting body,
 * how this speed is defined:
 * ''we further assume the quantity
 * ''2AB/(t'A-tA)=c [the two-way speed]
 * to be a universal constant--the velocity of light in empty space Harald88 09:05, 11 May 2006 (UTC)


 * No I did not forget that. The two-way result is a combination of the Einstein synchronization procedure and the second postulate.  It is a derived result, and therefore is not germane.  The second postulate requires the OWLS to be constant.  Given that, of course the TWLS must also be constant! --EMS | Talk 16:56, 11 May 2006 (UTC)

Nothing could be further from the truth. The two-way result was given by experiment, and all Einstein did was to accept this result (incorporating it into SR). See his 1905 paper, noting carefully his words "In agreement with experience [experiment]"; these words were left out of the above quote, thereby completely changing its meaning. Einstein's word "assume" was necessary only because the second two-way experiment had yet to be performed, the one that tied down two-way invariance. (The first experiment tied down only isotropy.) Einstein, therefore, had to assume the former because he was given only the latter in 1905.

How does the second postulate require the OWLS to be constant? Are you talking about an experiment here? Are you talking about an experimental measurement of the OWLS? If so, then please tell us how this alleged experiment can be performed, if only on paper (using ideal rulers and clocks).Cadwgan Gedrych 14:27, 12 May 2006 (UTC)


 * Most fruitful will be to accord a separate section to the definition of c together with issue of OWSL vs. TWSL: there obviously is a need for that. Harald88 07:04, 11 May 2006 (UTC)


 * By accident I've found a fine exposition of the postulates, achieving logical independence from the synchronication convention, without getting them wordier. In fact this formulation of the second postulate is even shorter. It's in Paulis 1921 "Relativitätstheorie" for the "Encyclopädie der mathematischen Wissenschaften", translation available as ISBN 048664152X:
 * The velocity of the light is independent of the motion of the light source
 * Pauli explains both postulates as the antitheses to former theories: The first postulate outrules the aether and the second postulate outrules the emission theories.
 * Pjacobi 17:09, 11 May 2006 (UTC)


 * That's fine as it allows to derive the LT and "sets" the value of c without overlap with the first postulate. No more is needed. Harald88 22:47, 11 May 2006 (UTC)


 * Harald88 - What are you saying here? "without overlap" is an odd way of talking about postulates.  Are you saying the second postulate alone is sufficient (which it is not), and are you finally seeing how the two postulate work together to create SR? --EMS | Talk 15:31, 12 May 2006 (UTC)


 * EMS, I know very well how the two postulates work together, and I say nothing "new". To state that light is always PROPAGATED in empty space with a definite [observer independent] velocity is already implied by the first postulate, since "propagation" implies wave mechanics. The essential difference with the first postulate is in the tail of Einstein's statement: a definite velocity c which is independent of the state of motion of the emitting body'. Harald88 17:15, 12 May 2006 (UTC)
 * PS: I hope thatyou now finally see how the two postulates work together to create SRT. ;-) Harald88 17:16, 12 May 2006 (UTC)
 * ... assuming that one accept's Maxwell's laws. Harald - The first posulate says nothing about Maxwell's laws.  it simply says that the rules of physics should be the same in all frames of reference.  The second postulate then declares that one of those laws is the invariance of the speed of light.  That Maxwell's laws are invariant under the resultant theory is a major derived result, which Einstein describes in the second half of the 1905 article.  I kindly counsel against adding anything to the statement of the postulates, but to leave them as Einstein stated them. --EMS | Talk 17:43, 12 May 2006 (UTC)


 * Sorry to be negative, but you guys will continue to argue with each other about this until the simple truths are known here.

Here is a perfect example:

EMS wrote above: "The second postulate then declares that one of those laws is the invariance of the speed of light."

I like EMS's vigour and obvious abundant interest, but I simply cannot stand by when he makes such a claim.

There are four distinct light speeds. To which one is EMS referring here?

[a] Maxwell's equations have a c. It is not a coordinate c, but was determined from the frame-independent relations between fields. Since it is frame-independent, it of course means that all observers in all frames find this c.

[b] The Michelson-Morley experiment has its own c. This is half of the full round-trip c, and it is the isotropic half. It was found sans any clocks, but rulers were involved, so it is a coordinate c.

[c] The Kennedy-Thorndike experiment experiment has its own c, and it is fully independent of both of the above. (In other words, despite the MMx null result, the KTx could have had a positive result.)

At the time of SR, Einstein considered [a], [b], and [c] closed cases - closed experimentally, just as they must be. He saw nothing about which to postulate concerning these three experimentally-closed cases. This left only the following case for his theoretical pleasure, so to speak:

[d] The very tricky one-way, two-clock case has its very own c, but has yet to have its very own experiment. This is the full coordinate case because it must involve both clocks (two minimum per frame) and rulers. (This case is tricky because it involves all the complexities of clock synchronization. One cannot measure light's one-way speed sans two clocks, and they must be temporally related in some way.)

Let's put EMS's above claim in terms of [d]: "The second postulate then declares that one of those laws is the invariance of the one-way, two-clock speed of light."

(As we have seen, this is actually the only proper version of the postulate, but it is certain that the postulate cannot be devoid of this version; indeed, it is certain that this version is incredibly important to SR since it is the only open case out of all possible cases.)

I now ask EMS to explain how one-way light speed invariance can possibly be (or become) a law of nature.

(It is now not a law of nature because it was given by mere man via a mere definition of clock "synchronization., a definition that admittedly does not absolutely or correctly relate clocks, so even the man-given or artificial result is not a correct one!)

In fact, I will go one step further by asking EMS to explain how there can be any law in the one-way, two-clock light speed case, much less the invariance law of which he spoke.

Here is the rationale behind this question: Any law of nature must be given only by nature, with no part given or controlled by mere man; however, in the case of light's one-way speed per two same-frame clocks, man must step in at the very start and manipulate the clocks by temporally relating them.

The best we can do here is to say that we can have a one-way law only after man has given a clock relationship.

Here is how this works in real life:

One-way case A: If man sets clocks to always obtain the baselessly prechosen value c, then the result will be c for all frames.

One-way case B: If man simply (correctly) synchronizes clocks, then the result will be c±v for all frames.

Oddly enough, even though B has a correct result, it is not a full law of nature because nature did not synchronize the clocks. Only if nature herself sets the clocks can the result be a full law given solely by her.

Also oddly, even though nature herself did both round-trip results, neither of them is correct! That is, these (null) results were due to the use of a slowed clock and/or physically contracted rulers.

If unshrunken rulers and an unslowed clock were used to measure light's round-trip speed, then the result would be variance and anisotropy.

Does the Wiki article say anything about any of this? No. But it is not possible to understand anything about the second postulate unless at least some of the above is given explicitly. And all of it is a part of today's human knowledge; I am not making any of it up.

EMS also wrote above: "I kindly counsel against adding anything to the statement of the postulates, but to leave them as Einstein stated them."

This sounds simple indeed, but in reality, it is extremely problematic. There is no definitive second postulate from Einstein or anyone else. Einstein used various words such as "principle," "definition," "postulate," etc. when speaking of his second postulate. He gave two entirely different versions of his second postulate. Only via very careful analysis can one sift out the truth. Cadwgan Gedrych 19:35, 12 May 2006 (UTC)

Pjacobi, the first postulate did not overrule the aether.

That postulate does not say that observers cannot all get the same result c±v in the case of light's one-way speed.

All the postulate says in that case is that whatever result is found by observers in one frame, observers in all other frames must obtain the same result. The postulate could not care less if the result happens to be c±v or simply c.

Also, the second postulate has no affect on light's source-independency. Einstein simply accepted source-independency as an experimental fact prior to the second postulate.

No definition of synchronization could possibly overrule any theory. The way to overturn theories is via experimentation, and it has been shown experimentally that light is source-independent. Cadwgan Gedrych 14:27, 12 May 2006 (UTC)


 * Cite sources. Don't give your opinion. Discuss the articles. Suggest better formulations for the articles. Don't discuss the subject. --Pjacobi


 * According to Pjacobi's suggestion I propose to follow Pauli's presentation of the second postulate, as it has less risk of being misunderstood. Thus: The speed of light is independent of the motion of the light source. Harald88 17:25, 12 May 2006 (UTC)


 * Let me propose a modification to this:
 * The speed of light is a constant and is independent of the motion of the light source.
 * The bolded addition is highly important, since that is what excludes the aether theories.
 * —Preceding unsigned comment added by Ems57fcva (talk • contribs) Pjacobi 18:39, 12 May 2006 (UTC)
 * Sigh. aether theories are excluded by by postulate 1. If authors like Reichenbach and Pauli quite patiently explain, what are the consequences of each postulate taken for itself, why should we second guess that and merge the postulates. Also the second postulate in its stringent form doesn't need to be restricted to inertial frames of reference. Why should it be amended with a clause only true in inertial frames? --Pjacobi 18:39, 12 May 2006 (UTC)


 * Actually, SRT is neutral about either aether models or other models: as Einstein stressed, SRT is a principle theory (see also the freely downloadable paper about this by Brown on http://www.iop.org/EJ/abstract/0143-0807/26/6/S01.
 * The problem with the speed of light postulate is that only the TWLS is a natural constant independent of convention, as explained in the cited references as well several times on this discussion page. Einstein defined c as the two-way speed of light, in accordance with the M-M experiment which was indeed the main experimental result of that time (perhaps some people don't understand two-way isotropy of light?). The definition of lightspeed needs to be incuded with a statement about lightspeed, as it has been for many months:
 * ''Second postulate (invariance of c)
 * Light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body; here the velocity of light c is defined as the two-way velocity, determined with a single clock. 
 * IOW, the discussion is going in circles - it's gone full circle more than twice already! I agree with Pjacobi that Pauli's formulation avoids these complications. And since the postulates are at the start of the article, the article will benefit from this simpler rendering by Pauli. The trickier issues as here discussed without end are best tackled in a separate section ("The speed of light") furtheron in the article. Let's be kind to the reader and make it both exact and as simple as possible! Harald88 22:02, 12 May 2006 (UTC)


 * Sigh. The first postulate states that the laws are to be the same in all inertial frames. It says nothing about which laws must or must not be found. Therefore, it does not prefer one-way invariance over one-way variance as a law of physics. Therefore, it does not exclude the "absolute" motion detection of any aether theory. Please get your facts straight. Cadwgan Gedrych 19:20, 12 May 2006 (UTC)
 * Cadwgan is correct here, in as far as he goes. Without asserting the constancy of the speed of light, the combination of the principle of relativity and the speed of the light being independent of the movement of the source are compatible with the aether theories.  (In fact, the purpose of the aether thoeries was to explain the astronomically determined independence of the speed of light and the motion of the source in the context of Newtonian physics.)
 * Look at it this way: You have what Pauli is trying to say a bit backwards.  The second posulate alone is enough to exclude the emission theories.  Combining the second posulate with the first postulate, so that the constancy of c must apply in all interial frames of reference, is what then excludes the aether theories.  However, the first posulate alone excludes nothing.
 * As for restricting the first postulate to inerital frames of reference: That is what Einstein did on further reflection.  It turns out that in accelerated frames of reference the speed of light as viewed by the observer is a function of the gravitational potential the light is traveling at.  So in general relativity, Einstein established the "general principle of relativity" in that the laws of physics must be the same in all frames of reference, and replaced the second postulate with local Lorentz invariance which states that locally spacetime must act in accord with the rules of special relativity.  See .   --EMS | Talk 20:17, 12 May 2006 (UTC)
 * I'm thinking about these arguments and looking for more sources. Seems a trip to library is required. E.g. I'd like to read Malament's paper, mentioned in (Hey, my e-mail is enabled, if anybody has it at hands!)  Anyway, I don't consider the article to be that bad, that any urgent action is required. The amount of debate here is totally out of proportion to the amount of tweaking it needs in this point. --Pjacobi 21:38, 12 May 2006 (UTC)
 * I agree that not much tweaking is needed. However, that means that it will be hard to make it better, but easy to make it worse. --EMS | Talk 22:09, 12 May 2006 (UTC)
 * I agree that this article is already quite good - much better, IMO, than when it was proposed as featured article. It will be worthwhile to add a short section on lightspeed if we can agree on what the sources say. Apart of that, it's perhaps time to look it through once more for little glitches, and next re-submit it for featured article status. Harald88 22:19, 12 May 2006 (UTC)