Talk:Introduction to special relativity

Minkowski diagram

There is an article on Minkowski diagrams that I worked on a little lately, in particular in the section "The speed of light as a limit". I think the material is correct, but I have discovered today that the single (inherited) reference to Rindler in the article apparently does not cover the claims in that section, basically that the speed limit seems to be due to the structure of space, time, and our notions of causality, and appears to have little or nothing in particular to do with EM waves or light, despite its historical origins. I think Taylor and Wheeler's Spacetime Physics must have it and would be a good reference, but I do not have convenient access to a copy. Does anyone have that handy (and know where it is discussed), or know a good a substitute source?

I assume there is no real doubt about the substance of the matter, but if there is I would be pleased to be enlightened about that, of course. Thanks. Wwheaton (talk) 19:06, 19 March 2008 (UTC)

The speed of light as a constant is trivial (cf: null geodesics) but this problem of the speed of light as a limit is problematical. My understanding of Rindler's textbook is that he introduces causality as an auxiliary physical principle and says that if causality applies then the speed of light is a limit (see p54, section 2.10 "the relativistic speed limit"). The statement "These considerations show that the speed of light as a limit is a consequence of the properties of space and time,.." should probably be amended to "These considerations show that the speed of light as a limit is a consequence of the joint assumption of causality and the properties of space and time,.." Robinhw (talk) 16:55, 28 October 2008 (UTC)

Thanks. I agree that causality is essential to the argument about the limit, v < c. Another thing I have noticed, but cannot reference in external reliable sources (I do not have Rindler's text at hand), is the following proposition, which seems somehow related to causality: "Given two arbitrary points (events), say A, and Z, in a connected region of spacetime S, it is possible to construct a (typically but not necessarily finite) sequence of points, say B,C,...,Y, all in S, such that the points in the sequence are all pairwise "simultaneous", where by "simultaneous" I mean that each adjacent pair of events in the chain has a spacelike separation (or, there exists a Lorentz frame in which those two events are simultaneous). That is, any two points in the spacetime can be connected by a chain ("The Chain of Now"?) of other points which are pairwise "simultaneous".

I think this proposition is true, and probably well known (or intuitively obvious) to many physicists, but I am not quite certain it is correct, and if so where it is stated in the literature. I am also very uncertain about what it means in the context of my understanding of causality, and wonder if and where that has been discussed. It is obvious I think that the crux of the matter is that simultaneity is transitive (ie, A simultaneous to B, and B simultaneous to C, implies A simultaneous to C) in Newtonian physics, but not in Relativity. In our folk wisdom we seem to say that the past is gone, the future is "pie in the sky", and the present is "real". But I get a queasy feeling about all this obvious stuff in the light of the forgoing considerations.

Once again, any elucidation from those more familiar with the literature would be appreciated. Wwheaton (talk) 19:08, 28 October 2008 (UTC)

In SR, the concept of simultaneity only makes sense if you choose a frame of reference, and, in any one frame of reference, if A is simultaneous with B and B is simultaneous with C, then A is simultaneous with C. -- Army1987 (t — c) 13:45, 30 October 2008 (UTC)

Yes, I agree. And that is what I mean when I say the events in the chain are pairwise "simultaneous" (with the double quotes), that a Lorentz frame exists for each pair such that that pair is simultaneous in that restricted sense -- which is anyhow the only sense any two events can be simultaneous in SR. So anyhow, do you then agree that my conjectured proposition is correct? Or if not, why not? If so, where is it in the literature (as I think it must be)? Thanks, Wwheaton (talk) 18:51, 30 October 2008 (UTC)

If by "A and B are simultaneous" you mean "there exists at least one reference frame in which A and B are simultaneous" (or, in technical words, "the interval between A and B is space-like", then you're right — the sum of two space-like intervals needn't be space-like. I also think that given any two events A and B there always is some event C such that both intervals AC and CB are space-like, or, at least, this is the first impression I can get by thinking of a 1+1-dimensional Minkowsi diagram. But this is not the standard meaning of "simultaneous"—it usually means "simultaneous in a given frame of reference", so, if the word is used twice in the same sentence, it usually refers to simultaneity in the same frame of reference, unless otherwise specified. -- Army1987 (t — c) 14:17, 31 October 2008 (UTC)

BTW, the causal structure of Minkowski space is given by the (partial) order given by light- and time-like intervals. If the interval AB is light- or time-like, it is either future-directed, zero, or past-directed; meaning, respectively: that A can be the cause of B but not viceversa; that A and B are the same event; that B can be the cause of A but not viceversa. The fact that the interval is space-like simply means the lack of such ordering.

So, saying that any two events can be connected by a chain of space-like intervals is no deeper than saying that, given any two people Alice and Bob, there always exists a third person Charles who is neither an ancestor or a descendant of either Alice or Bob. -- Army1987 (t — c) 18:22, 31 October 2008 (UTC)

Thanks for your comments. By simultaneous of course I mean the only sense simultaneity can have for two events in current physics (at least as I understand it), which is equivalent to their having a spacelike separation. By using scare-quotes on "simultaneous" I hoped to stress the pairwise nature of the term, in view of the non-transitivity discussed above. But my narrow purpose was really to verify that my claim, that such a chain of pair-wise simultaneous events can be constructed to cover all of a connected spacetime, is actually not in dispute, and if possible to find solid sourcing for it in the literature, so that is available for use both in this article and in related ones. This transitivity point may seem vacuous in the strict logical context of special relativity, but when we lay it along side our primitive concepts of "real" (as in local realism and Philosophical realism)) and "cause", I think it is more substantive. Maybe this "Introduction to special relativity" article is not really the best place to inquire, and perhaps I should have taken it to Special relativity. But anyhow, I still solicit further insight or source information from other editors. Thanks Wwheaton (talk) 20:12, 7 November 2008 (UTC)

The point you're making is the Rietdijk-Putnam argument, or something very similar to it. In my own opinion, as long as both the pedestrian and the car driver agree that the declaration of war precedes the launch of the spaceships, there is no paradox at all, but YMMV. -- Army1987 (t — c) 21:05, 7 November 2008 (UTC)

Thanks for the link. I think I understand all that, but I guess I better revisit it. Wwheaton (talk) 06:16, 8 November 2008 (UTC)

What's going on with the quotes?

I was trying to clean up the references. But I found something strange: I have a PDF copy of Einstein's 1916 Relativity: The Special and General Theory, and I cannot find the quoted sentence ("It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence."). I searched for nearly any single word in it. And the translator of my version is the same as the one cited (Robert W. Lawson). My copy lacks Appendix 5 ("Relativity and the Problem of Space") because it is later than the rest of the book and it's still copyrighted. Does the quoted sentence come from there? Also, I have the Italian translation of Six Not-So-Easy Pieces, and I can't find any sentence which could reasonably be a translation of "The idea that the history of the universe should be viewed, physically, as a four-dimensional spacetime, rather than as a three dimensional space evolving with time is indeed fundamental to modern physics." in the chapter about spacetime. Was it taken from Penrose's introduction? If so, that should be made clearer. -- Army1987 ! ! ! 10:30, 4 October 2008 (UTC)

I have both these books.

You were right about both. Einstein's quote is in appendix 5 p152 of the paper copy. Penrose's is in the preface (the book is by Feynman). Robinhw (talk) 14:49, 28 October 2008 (UTC)

Could you fill in the missing fields from the {{cite book}}s in ref.s 7, and 8, then? Thanks in advance. -- Army1987 (t — c) 13:55, 30 October 2008 (UTC)

While you're at it, check whether the emphasis (italics) was present in the original, and, in general, whether the quotes are verbatim. -- Army1987 (t — c) 14:41, 31 October 2008 (UTC)

Speed vs velocity

Take a look at speed and velocity. Shortly, speed only specifies how fast something is, whereas velocity also specifies in which direction it is moving. c is a constant defined as 299 792 458 m/s, which of course specifies no direction, so it is incorrect to refer it as a velocity. What does the Hawking cite actually say, exactly? -- Army1987 – Deeds, not words. 20:23, 9 January 2009 (UTC)

Nevermind, it's supposed to be a direct quotation, and my translation of Einstein's article does say "velocity". (Maybe that's a mistranslation from German?) I'm adding a comment between brackets to clarify that. -- Army1987 – Deeds, not words. 20:26, 9 January 2009 (UTC)

In high school physics classes this distinction is carefully observed, for pedagogical reasons. In the real world of pysics research I believe it is not; context is generally adequate to disambiguate between the vector and scalar notions. It is entirely possible that Einstein would have said velocity in English, even if he'd been a native English speaker.

Note that the "velocity=vector, speed=scalar" thing has no etymological motivation and has no possible counterpart in many languages. In Italian for example you have velocità and that's pretty much it. What else are you going to say? I suppose you could say rapidità for the scalar, but if this convention has been adopted anywhere I have never heard of it. --Trovatore (talk) 20:33, 9 January 2009 (UTC)

The square-brackets insertion from User:Army1987 "actually meaning 'speed' here" now looks like an original research insertion, particularly as the authoritative citation from Hawking has been deleted.--Old Moonraker (talk) 21:02, 9 January 2009 (UTC)

So what? This is the English Wikipedia, that Italian sucks is irrelevant. Are we going to move momentum to quantity of motion because Italian has no word for momentum and has to use such an ugly paraphrase? Are we going to use "scattering" and "diffusion" interchangeably because Italian calls them both diffusione? Matter of fact, we increasingly use English terms when there is risk that the Italian ones can be misunderstood, e.g., nowadays we often say "scattering" even within sentences in Italian. (As for rapidità, I've never heard it either, and if I did hear it I would presume it refers to rapidity; if we want to refer to speed and that is not clear from context, we would say something like modulo della velocità (modulo meaning "magnitude"), or velocità scalare for speed and velocità vettoriale for velocity.)

As for WP:NOR, feel free to remove the brackets if you wish. Maybe adding a hidden comment <!-- This is a direct quotation; do not change "velocity" with "speed" even if the latter term is used for this meaning in modern English. --> could be useful to prevent good faith edits such as 24.23.137.215's and mine.

As for the Hawking cite, I can't understand the point of it: in order to state that Einstein stated something, isn't it enough to cite the article where he stated it? -- Army1987 – Deeds, not words. 21:19, 9 January 2009 (UTC)

This is English Wikipedia, but the claim that velocity always refers to a vector, in English, is false. --Trovatore (talk) 21:24, 9 January 2009 (UTC)

If so, feel free to go to the Velocity article and fix it. Don't forget to add a reliable source that uses velocity to refer to a scalar in modern English, possibly not one from the beginning of last century and not one translated from German. -- Army1987 – Deeds, not words. 21:38, 9 January 2009 (UTC)

We aren't discussing the velocity article. WP articles stand on their own. External consistency, not consistency within WP, is the goal. --Trovatore (talk) 21:42, 9 January 2009 (UTC)

If we aren't, so what? Where does this article claim that velocity cannot refer to a scalar? -- Army1987 – Deeds, not words. 22:06, 9 January 2009 (UTC)

The dispute is the necessity and appropriateness of your interpolation "[actually meaning speed here]". I do not think this is helpful. I would prefer to leave the quote as is and say nothing about the velocity/speed question. --Trovatore (talk) 22:18, 9 January 2009 (UTC)

← OK, OK, I removed it (adding the hidden comment I was referring above). -- Army1987 – Deeds, not words. 22:35, 9 January 2009 (UTC)

That seems fine. --Trovatore (talk) 22:36, 9 January 2009 (UTC)

Article is too technical

The motivation for this article is a superb one. However the execution is too technical. I learned these ideas 40 years ago from a book titled The Universe and Dr. Einstein by Lincoln Barnett. This entry should be pitched at the same level as that book, with aiming a tiny bit higher being forgiven! For my generation, the classic university intro to special relativity was a nice little paperback by Wheeler and Taylor, titled Spacetime Physics.

I had thought that special relativity was now a settled area of physics, but to my considerable surprise, this is not so. Mitchell Feigenbaum has recently shown how to derive special relativity as a careful extension of Galilean relativity, without making any assumptions about the speed of light. See his: "The Theory of Relativity - Galileo's Child," arXiv:0806.1234 .

The citation and referencing system is also eccentric and must be changed. Adding a Further Reading section is an imperative.123.255.28.117 (talk) 17:42, 16 January 2009 (UTC)

For years there have been attempts by many people to simplify this article. The problem is that some people heavily resist all effort to make this a really non-technical explanation. (See the history of this discussion.) Maybe they want to show how smart they are and make it difficult to understand it even though the beauty of this theory is in its simplicity. It can be understood without all the mathematics and the Minkowski crap. The math is just an exact language to describe it and it's already used in the main Special relativity article. Congratulations, gentlemen. This is one of the worst articles on Wikipedia and it's completely useless.

--78.102.85.253 (talk) 22:38, 20 November 2009 (UTC)

I.m.o. this article should not even be here. Everything that must be said in an introduction to the subject should be said in one (1) paragraph in the main article. DVdm (talk) 09:47, 21 November 2009 (UTC)

Unfortunately, not everyone has taken a degree in physics. The biggest problem with science-oriented articles on wikipedia is that the amount of pre-learned information needed to read the article is larger than the amount of information CONTAINED within the article. You should be able to open up one of these "introduction to..." articles and be able to jump right in, regardless of experience or lack thereof. To DVdm: have you read the introduction to the regular special relativity article? Can you imagine approaching that with no previous background in science? This article is here for a reason; a very good reason at that. —Preceding unsigned comment added by 67.204.204.104 (talk) 04:52, 6 January 2010 (UTC)

I never understood why special relativity should be open for lay people and why there should be an article "to jump right in". Approaching an advanced topic in physics with "with no previous background in science"? No, I really cannot imagine that. Physics-, math- and engineering students usually don't get special relativity before their third year, and there is very good reason for that as well. These same students learn about Lagrangian and Hamiltonian mechanics before they learn about relativity. Have a look at these articles, and try to imagine an introduction allowing a person with no previous background to jump in.

Of course in the case of special relativity, there happens to be a demand for jump-in-introductions. So we find many in the literature. Unfortunaly, most are just rubbish and merely present the author's misconceptions and misunderstandings about the subject. The more correct you want the treatment of an advanced subject to be, the less accessible it will be for the lay person. That is why, in my opinion, this article should not be here. It will never serve its purpose. DVdm (talk) 09:32, 6 January 2010 (UTC)

I tried to put in a naive explanation, but ran into edit conflicts with someone that I couldn't overcome because of my Wikipedia inexperience. —Preceding unsigned comment added by Jhm15217 (talk • contribs) 01:36, 21 May 2011 (UTC)

Sorry, but I removed your contribution some 45 minutes after you made it because it was incomplete and finished mid sentence. I see someone else has since reverted it again for the same reason. If you want to add a long contribution it may be worth writing it in something like Microsoft Word and then copying and pasting it in. You can retrieve your original text by clicking on "history" then clicking on "cur" next to your contribution. Then just highlight your text and copy and paste it. Richerman (talk) 12:02, 21 May 2011 (UTC)

There is too much jargon in this article for it to be considered introductory. Where is RobotRollCall when you need her? http://www.reddit.com/user/robotrollcall 93.172.56.90 (talk) 05:50, 26 May 2011 (UTC)

I think a lot of confusion comes from the standard presentation of the subject. Take for example the "Minkowski metric"

$ds^{2}=dx^{2}+dy^{2}+dz^{2}-c^{2}dt^{2}\,$

The truth is that this is just NOT A METRIC in any ordinary sense. Neither is its negative. It is such points, never clearly admitted in books, that lead to misunderstanding. Any clear thinking is glossed over to support the conventional (rather rickety) theory of space-time. — Preceding unsigned comment added by JFB80 (talk • contribs) 18:44, 6 July 2011 (UTC)

I removed the link to the intro article from the main article because right now the main article is far more accessible to the general reader. The intro is too technical and too incoherent. It's more like a garbled intro to advanced physics students, which makes this article pointless. 109.186.38.41 (talk) 07:11, 29 November 2014 (UTC)

A radical reorganization of this could be useful

I think this article is close-to-useless "as an accessible, non-technical introduction to the subject." It mentions concepts such as affine spaces and fibre bundles that even most undergraduate students have no idea of, and say incredibly little of how special relativity came to be. Therefore I'd propose to completely rewrite the article according to the following structure:

• A lead section, summarizing the article;
• An two-paragraph explanation of Galilean relativity, as you would explain it to an average (or below-average) student in their last year of high school;
• A two-or-three paragraph explanation of how Galilean relativity is in contraddiction with electrodynamics, including the Michelson–Morley experiment, and how the experimental data favours the latter;
• Stating how Einstein was able to derive special relativity by keeping the Galilean principle of relativity, but replacing the assumption of absoluteness of time with that of absoluteness of the speed of light; stating that the results of special relativity are extremely close to that of Galilean relativity at speeds much less than that of light;
• Showing in more detail how that implies relativity of simultaneity, time dilation, and length contraction (the classic examples of two flashes at the ends of a moving train, the light pendulum, etc., using as many pictures as practically possible; even if Aunt Tillie can't understand what ct and √c²t² + v²t² exactly mean, she will understand that the latter is longer by looking at the picture.
• Maybe, a mention of four-momentum and mass–energy equivalence? After all, E = mc² is one of the most famous formulas in the world ...
• An informal explanation of Minkowski space (Minkowski diagrams would be very useful here);
• A brief mention of paradoxes of special relativity and their resolution (about two paragraphs per paradox), such as the twin paradox, the ladder paradox, etc.
• A mention of experimental tests of special relativity and some of its consequences to everyday life (gold is yellow, GPS works—but that also requires general relativity, there is a split-second delay in intercontinental telecomunications due to finite speed of light, etc.).
• A one-paragraph mention of general relativity.

What do you think? -- Army1987 – Deeds, not words. 22:50, 27 January 2009 (UTC) Mention that Einstein was lead to the constancy of the speed of light from Maxwell's equations. --Michael C. Price ^talk 23:25, 31 January 2009 (UTC)

I agree it needs reorganising/rewriting but all those references to Galilean Relativity and trains in "popular" introductions to the subject confuse students. Relativity is the discovery that the universe is a four dimensional space-time manifold. See the Wikibook on SR for a really good intro to this subject. 86.4.193.88 (talk) 12:48, 11 February 2009 (UTC)

It has been debated to death why we should be using a geometrical approach instead of the old and unintuitive (speed of light is constant OMG) approach. The battlefield of this talkpage is soaked with blood from mjany such wars. Please don't open the issue again. It was agreed that the geometric approach is more intuitive to introduce SR to the uninitiated, and there's no point in going back to the unwieldy and inelegant Einsteine's postulate approach. 117.194.34.216 (talk) 12:38, 10 March 2009 (UTC)

Rationale for this page

I'm not suggesting an AfD or a merge, but doesn't this page conflict with WP:NOTTEXTBOOK? I presume there was discussion at the main article which led to invoking WP:IAR for this page. A link to the debate and conclusion there at the top of this talk page could help avoid misunderstandings. Regards, Paradoctor (talk) 12:38, 22 November 2009 (UTC)

It is "intended as an accessible, non-technical introduction to the subject", but I agree that right now it fails to be one. --___A. di M. 20:25, 1 December 2009 (UTC)

My problem is not with the current state of the article. It's moot now anyway, I think I misread WP:NOTTEXTBOOK here. Regards, Paradoctor (talk) 21:46, 1 December 2009 (UTC)

This article was supposed to be a non-technical introduction for the main Special Relativity page. But what keeps happening is that physics students come here and add technical details until it is unreadable by non-mathemeticians. Eventually it will just be a dupe of that page. Someone needs to strip out most of the equasions and simplify this immensely. 75.101.11.171 (talk) 17:19, 22 February 2010 (UTC)

I was intrigued by the idea of an article that simplified special relativity so that average people could understand it. But I agree with others here who feel that attempt has failed most miserably. Such a page should be accessible and understandable by people who don't have grasps of advanced mathematics and physics beyond a high-school levels. The non-introduction article about special relativity is the place for all the intricacies. I'm not sure why anyone would argue this point, or why discussion about fixing this very broken article has gone on for so long. Instead of equations, arcane physics lingo, and confusing terminology, I really thing this article needs to be absolutely stripped down to its barest components, done in language students in junior high school can understand. If there's something the scientists in the group feel MUST be added to an article about special relativity, there's another one out there that ISN'T an introduction, and they should edit over there. What do we need to do to move this debate out of the debate room and actually move forward with making this introduction article truly an introduction, with words and terms that average folks can understand? Really, I have a decent understanding of special relativity, and this article confuses me! Indy (talk) 13:55, 5 March 2010 (UTC)

Again, I completely agree. Unfortunately, there are many books out there with the title "Introduction to special relativity", and they are all essentially useless for people who don't have a grasp of mathematics and physics beyond a high-school level. Books with this title are used by university students in physics and maths, and these students do have such a grasp. The consequence of this is simple. No physicist out here will allow an article with this title to be simplified to the extent that it will serve the purpose you have in mind. I think that is the reason why the discussion about fixing this article has gone on for so long, and why it will continue to do so.

It is also the reason why I keep repeating that this article should not be here, as it merely raises false expectations. I.m.o whatever is here, should be moved into the main article. I think that our only chance of ever having a truly lay-intro to the subject, is by using another article title, like, why not, for instance, Special relativity for the layman. That might work, and it might prevent the main authors of this article to be so demanding. DVdm (talk) 14:29, 5 March 2010 (UTC)

Many good points, but I think the article very much belongs. I think articles on Wikipedia should be accessible and understandable by everyone. This is one of those topics that is inherently a long, involved, and difficult one, but unlike others, I think there's a sizable number of average folks who would like to learn the basics.

Merging this article with the main article will accomplish nothing; presumably, everything here is in there anyway. Why eliminate this instead of making it better? That's like saying "Learning to walk on a balance beam is too difficult for these students, so let's make them all walk tightropes instead."

I think you have an excellent point with renaming the article. But will that keep the experts from ruining it? Is the problem that the best stuff has already been incorporated into the big article, so they keep beefing this one up because it's the only place they have to show what they know?

I'm not sure what the answer is, but I do know that having a simple article written in layman's terms without piles of equations would be very valuable to the average person. Right now, an average person visiting the article on special relativity would be completely overwhelmed. And when he finds an easier article, an "introduction" to special relativity, he no doubt will feel relieved -- until he actually sees it.

I think your title idea makes the most sense. Using the word "layman" should make it clear that simplicity is all that is wanted.

And finally, in order to actually WRITE a simple, layman's-terms article about this, we pretty much need at least one sympathetic expert in the field who actually understands what we mean. Any high-school-physics teachers out there? Indy (talk) 18:26, 5 March 2010 (UTC)

.. Just want you to know that I think it looks good, to be all to snotty as some guys seemed to have been here is not necessary, to me those seemed more 'elitist' than those contributing the real work here. A good job as far as I'm concerned. Keep it on. Yoron —Preceding unsigned comment added by 178.30.107.214 (talk) 23:39, 3 October 2010 (UTC)

Invariance of length: the Euclidean picture

The length of a line in a two-dimensional Cartesian coordinate system is given by Pythagoras' theorem:

$h^{2}=x^{2}+y^{2}.\,$

• Note: This is true because the h (projection of the line) is identical to the line

$k^{2}=x^{2}+y^{2}+z^{2}.\,$

File:Rel4.gif

Invariance in a 3D coordinate system: Pythagoras theorem gives $k^{2}=h^{2}+z^{2}$ but $h^{2}=x^{2}+y^{2}$ therefore $k^{2}=x^{2}+y^{2}+z^{2}$. The length of an object is constant whether it is rotated or moved from one place to another in a 3D coordinate system

• Error: The error is that
  

the h of 2D is incorporated into the k of 3D without regard of it variance to the vector.

$h^{2}=x^{2}+y^{2}.\,$ applies for 2D

$k^{2}=h^{2}+z^{2}$ Is true only for one special case when z=0. Plane and vector are identical and the projection of the vector(h)is identical with the lenght of the vector → 2D.
therefore $k^{2}=x^{2}+y^{2}+z^{2}$ This follow through is false unless we deal with 2D. And then the rules of 2D apply.--Martin Lenoar (talk) 22:57, 13 November 2010 (UTC)

Please sign your talk page messages with four tildes (~~~~)? Thanks.

The x-vector and the y-vector define a unique 2D space in which, for some h-vector, h^2=x^2+y^2. This h-vector and the z-vector also define a unique 2D-space in which, for some k-vector, k^2 = h^2 + z^2. Nothing wrong with the article. DVdm (talk) 22:27, 13 November 2010 (UTC)

The answers are coming faster then I expected. I am very new to the editing practices and therefore my editing is not as smooth. So it happens then when I just want to see what it looks like then I might forget to sign. And I was not finished. There is nothing wrong with the article. And nothing wrong with the mathematics. But there is something wrong with the use of mathematics to prove something by simply not considering everything. So please look at it again and then you might see what I mean. --Martin Lenoar (talk) 22:57, 13 November 2010 (UTC)

The math is correct but it doesn't really prove anything, it just illustrates one way of thinking of the length invariance in 3D. As the article says "Note that invariance of length is not ordinarily considered a dynamic principle, not even a theorem. It is simply a statement about the fundamental nature of space itself". So in a sense it's trivial. It makes sense though as the article later looks at the equivalent statement in (special) relativity, which is that the spacetime interval is invariant, in 4D spacetime with Lorentz transformations.--JohnBlackburne^words_deeds 23:09, 13 November 2010 (UTC)

Martin, if, like you say, nothing's wrong with the article, then perhaps this is not really the place to bring this up. See for instance our wp:talk page guidelines: this is the place where we are supposed to discuss the article, not the subject. Anyway, welcome! DVdm (talk) 23:16, 13 November 2010 (UTC)

Thank you, DVdm, for pointing out that this is not the right place to discuss the subject, on the other hand you reply to my observation. So where would I go if I would want to reply to your arguments? Because what you say is basically the main reason why I placed that edit on this page. It would take a long scientific discussion to get to an understanding. Not just between you and me. If you would be interested in how I think then have a look at ACR. A theory of life (space included) which I have worked on for about 10 years now and which made me also look at "special relativity" and other theories of how this universe could be functioning. But I found so many discrepancies, like the one in this article, that I prefer my own version. Thank you for the welcome--Martin Lenoar (talk) 09:56, 14 November 2010 (UTC)

For specific questions or inquiries you can go to the wp:Reference desk/Science, but perhaps that's not what you are looking for. If you like to discuss a theory you have developed yourself, I don't think there's a place to propose or discuss it on the Wikipedia (see our policies on wp:original research), except perhaps on your own talk page, provided of course you find people prepared to discuss it. Outside Wikipedia there are many discussion groups, easy to find with a properly aimed google search. Good luck! DVdm (talk) 10:11, 14 November 2010 (UTC)

Length and time are not fundamentally different, at least there is no evidence for this

In the argument for the space-time interval, the argument is made that length is fundamentally different from time intervals and therefore you need to introduce the factor c. However, this is a bogus argument. Particles follow world lines in space-time. While special relativity implies constraints here, that's not evidence for time being fundamentally different from space. Quite the opposite, I would say. Also, many theoretical physicist use natural units in the literal interpretation of c = 1 being dimensionless.

Physics can be formulated in a completely dimensionless way, so the whole idea that "dimensions" as used for units, constants etc. are fundamental properties of Nature, is unfalsifiable nonsense. Count Iblis (talk) 17:05, 18 September 2011 (UTC)

I don't see the problem: it is a topic that can be described in many different ways, and the way its written seems valid if not especially rigorous. Which parts in particular do you think are wrong?--JohnBlackburne^words_deeds 17:30, 18 September 2011 (UTC)

This article has lost the plot

I read this article about 4 years back and thought well done!

The article back then was a bit mathematical but it got over the main points which were that:

1. Spatial length is not invariant

2. In a 4D coordinate system there is indeed an invariant quantity, the space-time interval

3. Equating the formulae for the space time interval between coordinate systems gives you time dilation, length contraction, relativistic phase using no more than simple algebra.

I can still see remnants of this approach in the current article but it is obvious that many of the contributors dont understand the modern approach to Relativity. — Preceding unsigned comment added by 86.4.30.2 (talk) 12:44, 7 October 2011 (UTC)

Wikimedia already has a first class http://upload.wikimedia.org/wikipedia/commons/7/74/Special_Relativity_V2.11.pdf Wikibooks Special Relativity Introductory Text and this is just a lengthy explanation of the first page or two of any good graduate level Relativity textbook such as http://ned.ipac.caltech.edu/level5/March01/Carroll3/Carroll1.html Sean Carroll's Book.

I would recommend that contributors read http://upload.wikimedia.org/wikipedia/commons/7/74/Special_Relativity_V2.11.pdf Wikibooks Special Relativity Introductory Text before changing this article

this orphaned Section Heading is unsigned and innappropriate imo.  References should
be made in the article itself or against the section in the Talk page concerned. 
LookingGlass (talk) 12:09, 16 November 2012 (UTC)

Not encyclopedic

I have flagged this article as imo it reads like a magazine article instead of an encyclopedia.

The article currently veers between elementary examples (eg passengers on a train) and mathematical proofs. While these two styles are suited to text books, though for widely separated age/competency classes, they are insufficient in style and gradation to satisfy the needs of an encyclopedic article. IMO this is an article that is oriented to a general audience rather than towards a technical one. While the mathematical theorems may be appropriate on wiki (even if to me they seem out of place), in any event I believe that in an encyclopdic entry they should be secondary to the general explanation of the thesis concerned. This would mean that a progression, from everyday examples (passengers on a train) to progressively more complex thought experiments, such as the relativity of simultaneity (the Andromeda paradox), should be followed. These should all be set out in general not mathematical terminology, and with as little recourse to the latter as possible. Extended mathematical proofs could be added as the equivalent of appendices in later sections.

LookingGlass (talk) 21:07, 18 October 2012 (UTC)

Removing the "mathematics" is problematical because modern special relativity is simply the four dimensional form of Pythagoras' Theorem. The article could say "The square on the hypotenuse equals the some of the squares on the other four sides" but would that be clear? The real issue is whether or not people understand Pythagoras Theorem, if they can understand h^2 = x^ + y^2 they can, with a bit of reflection, understand s^2 = x^2 + y^2 + z^2 - (ct)^2. The "passenger train" derivations are definitely not easier than Pythagoras' Theorem and lead people to ponder dynamical explanations for why the speed of light is constant - does the light slow down then speed up?, are the clocks wrong?, does time not exist?. There are no dynamical explanations because Special Relativity is a geometrical theorem, not a dynamical postulate. 86.4.193.171 (talk) 11:18, 16 November 2012 (UTC)

Excellent explanation Anonymous, and good points, but different I think to the one I am trying to point at. The formulae are generally quite a bit more complex than Pythagoras' theory, but more importantly do not relate to any "legend" ie a drawing or description to explain their terms. The issue for me is that the article currently is a demonstration of the quantity of knowledge of the authors more than the quality of the attempt to communicate that knowledge to readers. Take the opening paragraph as an example: unless the reader is already well versed in the subject it is, to all intents and purposes, useless, however if the reader is well-versed they probably have no need of reading the article at all. The article is a reasonable "holding" page for notes on the subject but imo not a good article. The theory is of Einstein but further historical notes shouild surely come under an historical section rather than bloat the introduction. Einstein arrived at the idea via thought experiments, not calculation - so why not proceed from a general outline of those thought experiments and thence to the mathematics, if required. The whole should then be referenced to detailed technical articles elsewhere. I believe that it is unhelpful for any general audience seeking a reference/introduction to the theory, perhaps having come across it several times and now wanting a little more clarity. LookingGlass (talk) 12:06, 16 November 2012 (UTC)

What Aristotle said

The article states that Aristotle thought that all objects tended to cease moving and came to rest if there were no forces acting on them. This is the common view but actually it is not true: he said that they would continue in motion because there was no reason why they should stop (i.e. he originated "Newton's first law of motion"!). I cannot give the exact reference just now -it is in his book on the heavens. When I can I will correct the article. JFB80 (talk) 22:12, 7 January 2013 (UtTC) Later: It is in his work on physics, not the heavens. In book 4 section 8 on motion in a void there is found the quotation Further, no one could say why a thing once set in motion should stop anywhere; for why should it stop here rather than here? So that a thing will either be at rest or must be moved ad infinitum, unless something more powerful get in its way.JFB80 (talk) 08:07, 27 January 2013 (UTC)JFB80 (talk) 18:00, 27 January 2013 (UTC)

Another external link

http://www.pbs.org/wgbh/nova/physics/special-relativity-nutshell.html --Jerome Potts (talk) 19:30, 13 March 2013 (UTC)

Clock delays and rod contractions

I believe this section does a good job of presenting these Lorentz distortion concepts, but I'm at a loss to understand the scenario. Perhaps it is missing an introduction. The quote, "Let us return to the example of John and Bill" seems orphaned from a narrative describing their motion through spacetime. Pardon my formatting, this is my first post to a wiki talk page. --davidtheterp (talk) 13:47, 23 July 2013 (UTC)

I have moved the new section to the bottom. Otherwise the formatting is pretty okay.

Yes, good point. The johnbill section is a partial left-over from part of some section of part of some other article. That's what happens when an article is split into an introduction to itself and a new version of itself. As far as I am concerned, this entire "introduction article" should be decimated, and then inserted as a little section into the article in which it belongs. <mild sarcasm> Good luck with that :-) </mild sarcasm>. - DVdm (talk) 14:06, 23 July 2013 (UTC)

To User DVdm: While I appreciate your position and value your opinion about the possible difficulty in properly editing this article, your answer is not what the user Davidtheterp asked about -- he asked simply about a single problem, namely he asked what had happened to the story of John and Bill -- in the article this story starts from nowhere with the sentence "Let us return to the example of John and Bill...". All that is needed to correct this problem is to add the missing part, which is as follows (here taken from the version of this article of 6/Apr/2012):

"We have already discussed that in classical mechanics coordinate frame changes correspond to Galilean transformations of the coordinates. Is this adequate in the relativistic Minkowski picture?

"Suppose there are two people, Bill and John, on separate planets that are moving away from each other. Bill and John are on separate planets so they both think that they are stationary. John draws a graph of Bill's motion through space and time and this is shown in the illustration below:

"John sees that Bill is moving through space as well as time but Bill thinks he is moving through time alone. Bill would draw the same conclusion about John's motion. In fact, these two views, which would be classically considered a difference in reference frames, are related simply by a coordinate transformation in M. Bill's view of his own world line and John's view of Bill's world line are related to each other simply by a rotation of coordinates. One can be transformed into the other by a rotation of the time axis. Minkowski geometry handles transformations of reference frames in a very natural way."

If no one objects I can insert this missing part of the story into the article (I suppose it was edited out without due revision and attention to the integrity of the article, so it deserves to be reinstated).

Plamen Grozdanov (talk) 02:32, 17 December 2013 (UTC)

Mass-energy equivalence

Not sure how to add another talk subject, so I'll add it to this one: the concept of relativistic mass is quite dated and proves no real use in the understanding of special relativity. (D.J. Griffiths, Introduction to Elementary Particles, Chapter 3, p90) Although anecdotal, my professor reacted almost annoyed when I asked if γm corresponded with relativistic mass. All in all it is confusing and counterintuitive to define mass as such, since the gamma-factor is rather a consequence of the properties of four-space than an intrinsic property of a point-like particle. — Preceding unsigned comment added by PatronBernard (talk • contribs) 12:45, 31 July 2013 (UTC) (this was inserted in the middle of the page so I moved it to the end -DavRosen. p.s. you should be able to click on "New Section" at the top of the page)

In order for mass and energy to be truly equivalent, any type of energy must have a corresponding amount of mass. E=mc^2 relates the rest energy to the rest mass; it also relates the total energy of a system to the total mass of the system, which we can simply call the total mass, but in the case where the total energy includes some due to relativistic motion, this is often called the relativistic mass. Did the professor and the textbook make it clear that, for example, the rest mass of a galaxy as a whole (its mass in the galaxy's center of momentum frame where it's at rest) is greater than the rest mass of all its individual bodies, because part of the galaxy's mass is due to the relativistic motion of some of those bodies! This isn't just theoretical -- this mass of the galaxy is the one that determines the inertia of the galaxy as a whole (the m in F=ma for the galaxy) and its mutual attraction with other galaxies! Also, if we ignore the total mass (and only talk about rest mass) then we make it easy to ignore the fact that light has mass in spite of the fact all of light's mass is due to its (relativistic) motion (since none of it is rest mass), whether you call this relativistic mass or not. See [Energy-mommentum relation] to see how light (zero rest mass) is just a special case of relativistic mass in general. I agree with you and your professor to the extent that we should emphasize that it's the total mass, whether or not its also called "relativistic mass" in a given situation. But in the case of a body moving at relativistic velocities, it's hard to understand why the mass that you would get for the body if you actually measured it at these velocities would be greater than its rest mass, without pointing out in some way that part of this mass is due to the relativistic motion. DavRosen (talk) 14:00, 31 July 2013 (UTC)

Why Does This Article Exist? Pure Original Research

Since there is already an article on Special Relativity, which includes an introduction, why do we also need a separate article on "Introduction to Special Relativity"? This article is almost entirely unsourced. It seems to be just a place where people can come to present their own personal ideas about special relativity. I don't think there's anything in this article that isn't already in the article on special relativity (other than some things that don't belong in Wikipedia at all).

Shouldn't this article be proposed for deletion?Urgent01 (talk) 23:51, 13 November 2013 (UTC)

Yes, see my comments in sections #Article is too technical and #Rationale for this page. - DVdm (talk) 07:31, 14 November 2013 (UTC)

It might be possible to convert this article to something like a survey of published introductory expositions of special relativity, similar to the Wikipedia pages on subjects such as “TV Westerns”, “Mystery Fiction”, and so on. This would keep the article focused on actual sourced material, eliminate the novel narrative, and wouldn't be so redundant to the article on special relativity. The unique content of this article would be its exhaustive survey of this popular genre of books. If an editor’s pet introductory explanation of special relativity has already been published in a reputable source, he can just cite it here. If it hasn’t, then it doesn’t really belong in Wikipedia. It could be broken down by decades, such as 1900-1909, 1910-1919, etc. It might actually be an interesting and useful article (unless this is already covered elsewhere). Probably best to focus on the popular expositions in the secondary literature - which is already a huge number of books.Urgent01 (talk) 04:12, 21 November 2013 (UTC)

Yes, we should get rid of this article. Stigmatella aurantiaca (talk) 05:39, 17 December 2013 (UTC)

it's an essay, which has some virtues and some of its material should be incorporated into the main article. But the essay is completely unencyclopedic. CecilWard (talk) 12:39, 27 December 2013 (UTC)

It's been about 1 1/2 years since I last looked at this article, and it hasn't improved any. It is far too technical for poets and middle schoolers, and it offers nothing that is not covered better in the main article on special relativity. I am tempted to put an Afd tag on it, recommending that what little of value exists in the article be merged into the main article. Alternatively, I am considering a bold rewrite. Either course of action will probably meet with considerable opposition. Can I have a straw poll of opinion? Stigmatella aurantiaca (talk) 23:11, 9 June 2015 (UTC)

Yes, move a few relevant bits (if any) to a little section in Special relativity and then Afd what remains here. - DVdm (talk) 10:32, 10 June 2015 (UTC)

Merge analysis

Paragraph-by-paragraph comparison of Introduction to special relativity with Special relativity.

Section	Paragraph	Comment
Lede	In physics, special relativity is... Einstein postulated that the speed of light... The predictions of special relativity... (list) Relativity of simultaneity... Special relativity predicts a non-linear... As Galilean relativity is now considered...	Nothing is here which is not already in the main Special Relativity article. Would be redundant in a merge.
Reference frames and Galilean relativity: a classical prelude	A reference frame is simply... One oft-used example... Consider the seats... The distances between these objects... An observer standing on the platform... Why can't we select one of these frames...	Unsourced Essay Violates WP:NOTTEXTBOOK However, there are interesting bits and pieces. Possibly there may be some things worth keeping in a merge?
Classical physics and electromagnetism	Through the era between Newton... As electricity and magnetism... Under the classic model... Designing an experiment... These experiments all showed... The development of a suitable...	Unsourced Essay Borderline Violates WP:NOTTEXTBOOK Most is already covered in the main article, and would be redundant in a merge.
Invariance of length: the Euclidean picture	In special relativity, space and time... In everyday experience, it seems... The length of a line... One of the basic theorems... This is invariant under all... Note that invariance of length... Note that rotations are...	Unsourced Essay Violates WP:NOTTEXTBOOK
The Minkowski formulation: introduction of spacetime	After Einstein derived special relativity... The concept of a four-dimensional space A path through the four-dimensional... In the same way as the measurement... But there is a problem; time is... There are two major points... In Minkowski spacetime the spacetime... Now comes the physical part... Since by definition rotations must... With the statement of the Minkowski metric... As has been mentioned before...	Almost completely unsourced Essay Violates WP:NOTTEXTBOOK This is the crucial section: Does this tutorial essay succeed in teaching poets and middle-schoolers the essence of relativity, or does this essay, which tries to be both textbook tutorial and at the same time an encyclopedia article, fail in its mixed purpose? This section liberally drops terms such as "rotations in Minkowski space", "Galilean transformations", "Lorentz transformations", "Maxwell's equations and Dirac's equation" without adequate explanation. I do not see how an uninitiated reader can interpret this section as anything other than mysterious mumbo-jumbo.
Reference frames and Lorentz transformations: relativity revisited	Changes in reference frame... Maxwell's equations are written...	Unsourced Essay Violates WP:NOTTEXTBOOK As with the previous section, this section drops terms such as "Schrödinger equation", "four-vectors" and "manifestly covariant form" without explanation. As a result, these last two sections really explain nothing at all to an uninitiated reader.
Einstein's postulate: the constancy of the speed of light	Einstein's postulate that the speed... Proposition 1... Proposition 2...	In this section, we see a drawback of shared authorship. The lede was mostly written by editors who took a classic "two postulates" approach towards understanding special relativity, while the intervening sections were dominated by editors who preferred an approach starting with Minkowski spacetime. This section, which shows that the 2nd postulate arises naturally from the Minkowski formulation, is confusing because the distinctiveness of these approaches was not made clear enough in the lede. The next-to-last section The postulates of special relativity also presents the two postulates, adding to the confusion for an uninitiated reader.
Clock delays and rod contractions: more on Lorentz transformations	Another consequence of... John observes the length... The spacetime interval... So, if John sees a clock... In special relativity... Similarly it can be shown... These two equations... The above formulas... Alternatively, these equations... A consequence of...	Unsourced, but accurate so far as I can see. Non-controversial material doesn't always have to be sourced. However, violates WP:NOTTEXTBOOK The question is, is this presentation any more understandable over the equivalent material in the main article? I would say, yes, just a bit more so, at the cost of being non-encyclopedic.
Simultaneity and clock desynchronisation	The last consequence... Observers have a set of... The net effect... Great care is needed...	This section is very unsatisfactory. It reads as a set of unjustified assertions. It is not well integrated with the accompanying figure. Overall, inferior to the equivalent section in the main article.
General relativity: a peek forward	Unlike Newton's laws of motion... One says that the Minkowski metric...	What is this doing in an Introduction to Special Relativity?
Mass–energy equivalence	As we increase an object's energy... Any object that has mass... Similarly, the total of amount of energy...	Essentially nothing here that is not already covered in the main article.
Applications	There is a common perception...	A number of inaccuracies. The yellow color of gold ia not an "application". CRTs were designed empirically. GPS requires general relativity to enable coordination of the control and space segments.
The postulates of special relativity	Einstein developed special relativity... Special relativity can be derived...	As I stated previously, this article does not do a good job of explaining that although Einstein's original 1905 derivation began with two postulates, modern pedagogy prefers alternate approaches to teaching this subject. Having this as a last section is rather confusing, since the main body of the article has concerned itself with the Minkowski spacetime approach to understanding special relativity.

I will expand this comparison over next few days to encompass the entire article. Stigmatella aurantiaca (talk) 08:08, 11 June 2015 (UTC)

Things are "sort of OK" until I reach the section on The Minkowski formulation, which liberally drops advanced vocabulary terms such as "rotations in Minkowski space", "Galilean transformations", "Lorentz transformations", "Maxwell's equations and Dirac's equation" without adequate explanation. To an uninitiated reader, this section and the ones after must seem a bunch of mumbo-jumbo. Stigmatella aurantiaca (talk) 02:38, 14 June 2015 (UTC)

I agree with DVdm. From what I can see, this article merely raises false expectations. Stigmatella aurantiaca (talk) 02:46, 14 June 2015 (UTC)

Summary

Overall, the material that I see in this article is either already covered in the main article on Special relativity, or constitutes unsourced textbook-like essay (rather inferior as such things go), completely non-encyclopedic in style. To quote from WP:NOTTEXTBOOK:

Textbooks and annotated texts. Wikipedia is an encyclopedic reference, not a textbook. The purpose of Wikipedia is to present facts, not to teach subject matter. It is not appropriate to create or edit articles that read as textbooks, with leading questions and systematic problem solutions as examples. These belong on our sister projects, such as Wikibooks, Wikisource, and Wikiversity. Some kinds of examples, specifically those intended to inform rather than to instruct, may be appropriate for inclusion in a Wikipedia article.

I do not want to be the person performing the merge. That would be setting myself up as prosecutor, judge, jury, and executioner, which is too much of a role for me to take. If somebody else agrees with my analysis and, in performing the merge, decides that nothing is worth saving, I will back him/her up. Stigmatella aurantiaca (talk) 17:57, 15 June 2015 (UTC)

Excellent job. Any opposition to deletion should have manifested itself by now. I would gladly create an AFD, but I have no idea what they mean in part III of Wikipedia:Articles for deletion#How to nominate a single page for deletion, so unless I understand that, I will not go for parts I and II. - DVdm (talk) 14:22, 17 June 2015 (UTC)

How?

How is any of this even remotely acceptable as a wikipedia entry? No citations, all original thought. Shouldn't this be flagged with about 6 different problems? — Preceding unsigned comment added by 24.19.13.66 (talk) 03:03, 23 June 2013 (UTC)