Talk:Special relativity/Archive 11

Archived (again)
I have archived the latest discussions. Once again, it is requested that future discussion be on the article and not on the theory. If no one other than Cadwgan objects, I propose that it be our policy that blatantly anti-relativity content will be removed from this page in the future. --EMS | Talk 21:27, 23 May 2006 (UTC)


 * Let's stick to Wikipedia policy - in fact we are obliged to do so! For sure, the discussions must be about the redaction of the article. Harald88 19:12, 24 May 2006 (UTC)

Compare Einstein's version with WIKI's
Even Jimbo Wales could see the difference, and he's not a serious student of special relativity.

CURRENT VERSION OF WIKI SECOND POSTULATE:

"Second postulate - Invariance of c - The speed of light in a vacuum is a universal constant (c) which is independent of the motion of the light source."

compared with

EINSTEIN'S VERSION OF THE SECOND POSTULATE:

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 § 1.

EINSTEIN'S DEFINITION FROM § 1:

We have not defined a common "time" for [two clocks at points] A and B [in space], 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 [point] B to [point] A.

EINSTEIN STATED THAT HE DID NOT POSTULATE RE LIGHT'S ROUND-TRIP SPEED:

In agreement with experience [experiment] we further assume the quantity 2AB/(t'A-tA) = c

to be a universal constant--the velocity of light in empty space.

It is impossible to measure light's one-way speed without two clocks, but Einstein used only one clock (clock A) here, along with the round-trip distance (2AB). We therefore know that he was speaking here of light's round-trip speed.

It is not necessary to use two clocks to measure light's round-trip speed, but Einstein used two clocks in his second postulate, so we know that this postulate pertains solely to light's one-way speed.

Light's round-trip speed and its one-way speed differ fundamentally in that the time of the latter currently depends entirely upon a definition.

In other words, the time in Einstein's second postulate is given by definition, which makes it imperative to mention the word "definition" in any version of the second postulate, just as Einstein did, but as WIKI does not.

It is also imperative to mention the fact that the second postulate pertains only to light's one-way, two-clock speed, and not to light's round-trip speed, but, again, WIKI does not do this, even though Einstein did (by completely separating the two as we saw clearly above). Cadwgan Gedrych 18:53, 26 May 2006 (UTC)


 * People are liable to ignore you when you use such attention-grabbing formatting and use e.g. "WIKI" instead of "Wikipedia". —Keenan Pepper 19:07, 26 May 2006 (UTC)


 * That's according to Cadwgan. The only time interval that I see above is: (t'A-tA) - the two-way speed. Apparently according to Einstein as well as Lorentz, Einstein postulated not about one-way speed but about speed as defined here above which he called "the velocity of light in empty space". BTW, this perfectly describes the MMX.
 * After endless discussions (none of which you seem to recall) we settled to not burden the readers with a discussion of that debate upfront in the article, and to leave that sentence open for interpretation.
 * Regards, Harald88 19:48, 26 May 2006 (UTC)


 * Harald88 - I have always wondered why you ever accepted that wording. Now I see that you do not even understand what it says.  The speed of light in a vacuum cannot be a universal constant unless its one-way speed is c.  There is no need for interpretation in this regard.  The 2AB/(t'A-tA) = c business is not a definition of c.  Instead it represents Einstein pounding it into our heads that the speed of light must be c.  Perhaps it would help if you looked above, and noted that Einstein wrote that
 * In accordance with definition, the two clocks symchronize if tB - tA = t'A - tB.
 * Since Einstein is assuming the use of synchronous clocks in the 2AB/(t'A-tA) = c statement, it follows that AB/(tB - tA) = AB/(t'A - tB) = c.  Given that, I would like end this silliness about "one-way" and "two-way" light speeds here now.
 * Beyond that, let's give this devil (Cadwgan) his due. He is right in that neither this article nor the postulates of special relativity article notes how time and distance are defined.  That is a legitimate issue, and it needs to be dealt with sooner or later. --EMS | Talk 03:31, 27 May 2006 (UTC)


 * I know of no peer reviewed paper claiming that that equation "represents Einstein pounding it into our heads that the speed of light must be c". Instead, the here above specified operational definition of light speed doesn't contain any assumption about simultaneity at all - and probably everyone here understands that.
 * Anyway, I'm glad to see that you agree on writing a section that discusses the OWLS speed and synchronization issue, and happily we've already collected a number of relevant sources. Harald88 08:20, 27 May 2006 (UTC)


 * Harald - Does the work "context" mean anything to you? You and Cadwgan keep holding up 2AB/(t'A-tA) = c in isolation.  It is not presented at the beginning of a section, but instead near the end of a section called "Definition of simultaneity", in which the equivalence of the outward time and return time are explicitly stated.  Have you bothered reading the the 1905 article?  At the beginning of that article Einstein states that
 * light is always propogated through empty space with a definite velocity c.
 * Kindly note the word always. I bolded it because it means just that: always!  Perhaps Rindler's description of the second postulate (from ) may be helpful to you:
 * Light signals in a vacuum are propagated rectilinearly, with the same speed c, at all times, in all directions, and in all inertial frames.
 * Kindly get it through your head that you are dead wrong in this matter. --EMS | Talk 00:03, 30 May 2006 (UTC)


 * EMS you still seem to be unaware that "in all directions" is and was used for two-way speed, typically with the MMX; and that is relevant for editing the article. And I do agree that in the second paragraph Einstein apparently mixed definition with postulate. But although it was a milestone, Einstein's 1905 paper isn't "the Bible" in this matter. And I have to remind you that it doesn't matter what you and I think. Harald88 19:48, 30 May 2006 (UTC)


 * "The same in all directions" means "the same going from A to B as from B to A" and there is nothing someone with an agenda to push the ancient ether theories can do about it. I do agree that it does not matter what you think. DVdm 20:41, 1 June 2006 (UTC)


 * (sigh) It doesn't matter what you claim as I already included the evidence for those who know what MMX measured, while Alfred Centaury already cited the AJP: "having taken from the idea of light waves in the ether the one aspect that [Einstein] needed". That excluded Ritzian emission theory, as we also learned from Pauli (thanks to Pjacobi). Nothing to discuss. Harald88 21:49, 1 June 2006 (UTC)

Dear EMS (don't you just love it when I go formal!),

Pardon me for saying so, but you yourself omitted an extremely critical part of the very context that you alluded to, namely, Einstein's phrase "apparently irreconcilable."

There is simply no way that anything saying c-invariance-per-coordinate-measurements could in any way be even apparently irreconcilable with Einstein's PR-in-this-case (which is "Null results always" or "No absolute motion detection by any means, including optics.")

What could be (and certainly is) apparently irreconcilable with Einstein's PR-in-this-case is simply light's natural motion through space, which, as Einstein said, is always at the definite (not coordinate-measured) velocity (or propagational speed, to be precise) c, which is (as Einstein went on to say) really due to light's source independency.

This is all just another way of putting what Einstein stated a little clearer in his book.

It is simply his statement that due to light's constancy of movement through space at the raw speed c, observers using absolutely synchronous clocks must find w = c ± v when using the clocks to measure light's passing speed w.

But why did Einstein say it was only apparently irreconcilable?

Because he saw a loophole.

Actually, the loophole consisted of two separate smaller loopholes, viz.,

(i) no one could absolutely synchronize clocks, and (ii) clocks can be manually forced to get c one-way, even though such clocks will not be truly or absolutely synchronous.

As any fool can see, if we really cannot synchronize clocks (absolutely), and if we manually set clocks to get c one-way, we can obliterate that (terrible, to Einstein) irreconcilableness. That is, we can obtain our wish-for (baselessly) null result (even though it is not per experiment, but by definition) despite the simple law of the constancy of the velocity of light in empty space.

In other words, we can get our (baselessly) desired one-way "null result" despite the simple fact that light travels in space exactly as if there were an aether (although no aether is needed for light to propagate through space).

Dear Harald88,

You wrote: "The only time interval that I see above is: (t'A-tA) - the two-way speed."

Your remark is only apparently irreconcilable ;-) with the fact that Einstein's second postulate contained its own cute little time interval, as follows:

VELOCITY = LIGHT PATH/TIME INTERVAL

But this (two-clock) "time" is measured by absolutely asynchronous clocks, so it cannot reflect reality. Reality can be reflected by using synchronous clocks, and, in that case, as Einstein himself admitted mathematically explicitly, light's one-way, two-clock speed would be c ± v. Cadwgan Gedrych 17:53, 30 May 2006 (UTC)


 * Dear Cadwgan, first of all, SRT doesn't make any statements about "reality" other than about what will be measured. Also, duration and velocity can be measured with one clock, which is as physical as it can get - as demonstrated in Einstein's first paragraph. That he didn't stress in the next paragraph that any one-way speed measurement is indirectly a two-way speed measurement doesn't affect the theory in practice - and it has been amply discussed in the literature that no "physically true" or "absolute" OWLS measurement can be done. Of course, this article must mention that. I now stop wasting time on this; instead I'll start a sandbox draft. As soon as I have something I'll invite others to contribute to it. Harald88 19:48, 30 May 2006 (UTC)

Hello, Harald88, if it has indeed (as you claimed above) "been amply discussed in the literature that no 'physically true' or 'absolute' OWLS measurement can be done," then how could Einstein postulate about such a measurement? (As the 1905 paper stated, the second postulate allegedly pertains to light's one-way speed per two clocks, but if there is no such experiment, then there can be no postulate about it.) Cadwgan Gedrych 18:21, 31 May 2006 (UTC)


 * Roundtrip speed is c and one way speed after Einstein synchronisation is c. And both this statements are equivalent.
 * Note that I did not write this now - it was Pjacobi's first reply three weeks ago! In a few sentences he said all that was needed. Now please help to collect the abovementioned source materials for my sandbox that is still empty user talk:Harald88/sandbox, and next we can summarize the essentials in a short section. Harald88 19:24, 1 June 2006 (UTC)


 * Harald88 - I am not sure that I 100% agree with the above as written, but I do agree with the one-way speed of light being c for any observer using the Einstein synchronization procedure to determine the time-of-flight of a photon. Maybe the only disagreement we have at this time is one of emphasis.  Still, I advise being careful in your writing. --EMS | Talk 14:11, 2 June 2006 (UTC)

Harald88 claimed above that the "statements are equivalent"; that this is not so is easily seen by the simple facts that even though the round-trip experiment was performed in 1887, no one-way experiment has ever been performed, not even on paper using ideal rulers and clocks. These simple facts tell us that the statements differ fundamentally, in stark contrast with Harald88's claim. Cadwgan Gedrych 18:39, 2 June 2006 (UTC)


 * As I said, that wasn't my phrasing but Pjacobi's reply to you, and I think that it was very good - but somehow it didn't "reach" you(?!) Here's a second chance:
 * 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 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)


 * Also it's not true (or highly misleading) if you claim that no one-way experiment has ever been performed. Please don't turn this into a semantics game but instead comment to the OWLS "test" on my sandbox if you have something useful to say about it. Harald88 10:25, 3 June 2006 (UTC)

Please see my final remarks at my Talk+ discussion. Cadwgan Gedrych 18:29, 6 June 2006 (UTC)

Lorentz transformation
In the 'Physics in spacetime' section in this article, it's claimed (in fact I think I wrote it) that the Lorentz transformation is a tensor. Does it truly transform as a tensor? (I was hoping someone already knows and so it'd save me from doing a tedious bit of algebra).

--Masud 13:54, 5 June 2006 (UTC)


 * Yes, it it a tensor. Just note that $${\Lambda^\mu}_\nu {\Lambda_\mu}^\pi = \delta^\pi_\nu$$.  Then $${\Lambda^\mu}_\nu {\Lambda_\mu}^\pi {\Lambda^\nu}_\sigma =  {\Lambda^\pi}_\sigma $$. --EMS | Talk 15:37, 5 June 2006 (UTC)

question
what are wrong in these 2 situations:

many far away stars are measured to be traveling faster than the speed of light from us

this concept of warp bubbles takes the spaceship inside it faster than light speed by twisting space and so on

both these situation can carry information. wat is wrong? i think it might be something to do with the fact that the objects themselves arent accelerating itself from some experimenter, but rather spacetime is pushing them like a wave. can someone correct me? —The preceding unsigned comment was added by Duel me (talk • contribs) 13:04 UTC, June 8, 2006.


 * Please be advised that these talk pages are for discussion of the related articles. Wikipedia is not a buliten board.  However, since you are a newbie, I will respond briefly.
 * You are asking about general relativity related phenomena. The "warp bubble" business involves the Alcubierre metric, which may not desribe a physically realizable situation.  On the other hand, I can only guess at that you mean by "far stars measured to be traveling faster then light from us".  If I take out the words "measured to be" (as such stars cannot be seen), then I get a reference to the Big Bang and its related expansion of the universe.  --EMS | Talk 15:33, 8 June 2006 (UTC)

Survey of recent edits
Survey of edits by the 11 most recent anon editors: By my count, 4 vandals, 2 anons making dubious edits, and 5 anons making legit edits.
 * 1) Half Hollow Hills Central School District, CVNET, in Huntington Station, NY: repeated silly vandalism by a known vandal
 * 2) legit edit
 * 3) legit edit
 * 4) Budker Institute of Nuclear Physics, Novosibirsk, Siberia: added link to arXiv eprint in Russian by Z.K. Silagadze, apparently identifiable with this anon; I am not sure external link in English wiki to expository paper in Russian is appropriate!
 * 5) Half Hollow Hills Central School District, CVNET, in Huntington Station, NY: repeated silly vandalism
 * 6) ns25.sprise.com anon near Amherst, NH: blanking vandalism by a known vandal
 * 7) legit edit
 * 8) act.netspace.net.au anon in Adelaide: link to a webpage at Australian National University; probably legit
 * 9) legit edit
 * 10) BTnet UK Regional network: added link to magen.co.uk and Image:hx3.png; some kind editor should check whether this is legit
 * 11) serial.ac-act.ondsl.gr anon in Greece: rather nasty vandalism (same IP has been used for some other vandalisms)

It is certainly unfortunate that this article attracts to much vandalism (too bad we can't easily semiprotect it, with apologies to the anons who made legit edits).

Please help us monitor edits by, who uses handles such as Hexenmeister, Androcles in UseNet posts which tend toward personal attacks; see Google.---CH 03:45, 15 June 2006 (UTC)

Lead
I'm going to have a whack at rewriting the lead from scratch. I see the following as being problems with the current version: (1) It would be hard for a nonspecialist to understand. (2) It doesn't explain where the word "relativity" comes from, or mention the fundamental idea that all frames of reference are equally valid. (3) It doesn't explain its relation to classical mechanics (the limit of v<<c).--24.52.254.62 00:52, 18 June 2006 (UTC)


 * My only comment is in regard to your first point. While the intro doesn't really address some of the things a nonspecialist might want addressed, I thought that was the point of the Introduction to Special Relativity article, which is linked to right at the top.  Basically, isn't the audience of this article supposed to be more technically minded, or if not to have gone through and read and understood the intro article?  Just food for thought.  DAG 01:10, 18 June 2006 (UTC)


 * Well, you can tell me if you think what I did is an improvement. I don't think there's any virtue in writing unclearly what could be written clearly, and I don't think there's anything in the lead that needs to be expressed in a very technical or mathematical way. I looked through some of the discussion of the relationship between the two articles, and agree with those who say that they should be merged. Every article in WP is theoretically supposed to be understandable to the general reader. Of course that's just an ideal to be striven for, but special relativity is not a subject that inherently requires a lot of math to develop properly -- a little algebra is all that's really needed.--24.52.254.62 01:35, 18 June 2006 (UTC)


 * I don't like the new lead. It is way too big.  The older lead, being shorter and move concise, was much better.  I you think that this materaial needs to be discussed first, then I would advise creating a "Background" section.  I also advise that you get an account if you are going to be bere a lot.  Finally, you may want to consider a broad rewrite of this article.  At this time, it is a hodge-pogde of various viewpoints operating at various levels of sophistication.  (One thing that I would like to do is to take the "phsyics in spacetime" section and turn it into an article entitled "Tensors in special relativity".) --EMS | Talk 02:59, 18 June 2006 (UTC)


 * I agree 100% that the article needs a broad rewrite, and that it's a hodgepodge of levels of sophistication. I think a rewrite should happen in the context of merging it with the Introduction to special relativity article. It's not normal on wp to have two different articles on the same topic. I disagree that the lead is too long, however. If you take a look at the discussion of nominations for FA, the expectation for any substantial article is generally that it should be about four paragraphs. In fact, if you look at the relativity article's own archived discussion on its nomination for FA, you'll see that one of the criticisms was that the lead was too short (although I don't know if it was even shorter then).--24.52.254.62 03:18, 18 June 2006 (UTC)


 * One thing that I would like to do is to take the "phsyics in spacetime" section and turn it into an article entitled "Tensors in special relativity". I like this idea. There is absolutely no reason to be using matrix notation in this article. WP articles are supposed to be written for the general reader, so if there's a fancy mathematical technique that isn't indispensible for the development of the topic, then it should be omitted. I also think the ict stuff should be taken out. Very few authors use ict, and again, it's just an unnecessary mathematical obstacle to allowing a lay reader to follow the article.--24.52.254.62 03:35, 18 June 2006 (UTC)

"or even information"?
I made some corrections in the intro, but for the moment I didn't remove the claim that according to SRT "even information" can't travel faster than light. I've read that claim before but SRT states nothing about something as abstract as "information", it's probably a fable; instead SRT states that no matter can travel as fast as radiation (light).

Interestingly, a few days ago it was on the news that Gisin in Geneva now claims to have succeeded a teleportation experiment of "instantaneous" information by means of two distant but coupled photons. True or not, and no matter how mindboggling this is, it doesn't really matter for SRT. Harald88 09:25, 18 June 2006 (UTC)


 * I agree that special relativity itself, as the theory is usually bounded, doesn't say anything about information. If the theory of special relativity was a person, and you mentioned to it that it prevented the transport of information at speeds faster than that of light, it would stare at you blankly for about five minutes before asking you what information was.  That's not to say that it doesn't seem to imply this restriction, as if you can't send a letter faster than light, and light will always travel at the speed of light ( at least in a vacuum ), the list of possible ways to send "information" ( used here in the generic, off the cuff sense and not in any strict mathematical sense ) becomes, erm, vanishingly small.  ;)  Of course, there is the possibility of the kind of quantum entanglement things Harald mentioned, as well as claims of instantaneous transport of particles via quantum tunneling ( I only vaguely remember hearing about someone trying to work with that somewhere, though the usefulness of a phenomenon that would require the only route between point A and point B be through an extremely large potential barrier seems dubious to me... ).


 * So, I guess the real question would be does anyone know off hand of any proofs or such about the impact of SR on information transport?  DAG 10:59, 18 June 2006 (UTC)


 * The argument is that transmitting information faster than light would violate causality. See the section on "Causality and prohibition of motion faster than light." This is part of the standard, widely accepted interpretation of SR. For a nice discussion of this, see Taylor and Wheeler, Spacetime Physics, 2nd ed., p. 181: "Can no effect whatever produced at A affect what happens at D? If so, D ...forms a spacelike pair with event A." I'll add a footnote.--24.52.254.62 15:07, 18 June 2006 (UTC)


 * Apparently that statement has now been disproved, without anyone claiming that SRT (and thus GRT) have been disproved with it. Thus Taylor and Wheeler's discussion would possibly make an interesting short section somewhere lower in the article. However, the lead is supposed to be a summary of the main points of the theory, as covered in the body of the article. Harald88 20:47, 18 June 2006 (UTC)


 * The proof is fairly simple: What would carry the information?  Neither light nor matter can propagate faster than c, and so nothing known could do it. --EMS | Talk 17:26, 18 June 2006 (UTC)


 * But violating causality doesn't violate relativity.
 * "Causality, Relativity, [unrestricted] FTL: choose any two."
 * —wwoods 20:25, 18 June 2006 (UTC)


 * Indeed, and Lack of knowledge is not "proof". According to the most popular interpretation of QM, nothing "propagates" between entangled photons but the information transfer is instantaneous. SRT has nothing to say about such things. In any case, such inferrences (not by Lorentz or Einstein, right?) don't belong in the intro. Harald88 20:47, 18 June 2006 (UTC)


 * Yeah, there is some quantum weirdness that might be able to do it. Which means that in some sense, the causality of special relativity is very tightly defined.  That is that there can be a causal connection between if it is possible for a light beam ( or anything slower like your friendly neighborhood mailman : ) ) to connect the two events.  It turns out because of what special relativity has to say about getting things to move very fast is that if it has mass, it takes infinite energy to attain the speed of light, and if it doesn't have mass, it moves at the speed of light, and so within this framework it becomes hard to see how to get a message between two events that aren't causally connected in the SR sense.  Of course, SR in and of itself does nothing to define information mathematically and then apply the rest of the theory to show that it can not violate causality a la SR.  Now, maybe someone later did go through this and show this ( or not show it for all I know ), but that's someone else's theory ( in the same sense that the Dirac equation isn't a part of SR even though it uses it to refine the quantum model of the electron ).  Anyway, that's my way of looking at it.  DAG 21:42, 18 June 2006 (UTC)

Someone rewrote the explanation of why it's called "special," stating it in terms of inertial frames instead of no gravity. The two explanations are equivalent according to the equivalence principle. The general reader knows what gravity is, but doesn't know what an inertial frame is, so it makes more sense to explain it in terms of gravity. I've reverted the edit.--24.52.254.62 15:16, 18 June 2006 (UTC)


 * The two explanations are not equivalent: the correct one explains the meaning of "special relativity". See also below; thus I revert to it. Harald88 20:47, 18 June 2006 (UTC)