Talk:Twin paradox

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Incorrect, naive application?[edit]

I edited this to indicate that the application of time dilation referred to cannot be unequivocally ruled as 'incorrect naive', purely on the strength of two citations. The edit I made did not, as has been suggested, introduce incorrect information - on the contrary, it eliminated an expression which was not legitimate, for the reason just given. It's not acceptable for the article to be as dogmatic as it was. My edit simply indicated that the assessment of this application as 'incorrect naive' is a matter of the opinion of the authors of the cited references, or of the author of this article, on the strength of the content of those references. Please restore my edit. Ed Addis (talk) 14:33, 22 September 2016 (UTC)

Ha, sorry for having hit the wrong button - I should have hit the wp:NPOV in stead of the error-button. My mistake.
The content is properly sourced with two relevant sources, and I'm sure that we can find more sources. So there is nothing dogmatic about it. Your change ("... held by some to be incorrect and naive ...") used wp:weasel words, and more or less induced your personal opinion —doubts perhaps— about this. If sufficient relevant authors say that something is naive, then Wikipedia can (and should) say that it is naive. - DVdm (talk) 14:58, 22 September 2016 (UTC)
Nevertheless, the reality is that there are many, myself included, who do not agree with this interpretation. It's therefore not acceptable to just label it as 'incorrect'. It would be OK to say that there is a strong (or even a majority) body of opinion that favours a different interpretation, but you can't escape the accusation of dogmatic I'm afraid. I'd be happy to accept a different wording from the one I used, but it must allow for the existence of differing opinions on the key point of whether the paradox as simply stated here is valid. Or is this going to be another case of the WP police overriding valid objections?Ed Addis (talk) 17:06, 22 September 2016 (UTC)
Wikipedia reports on and reflects the scientific consensus. The overwhelming academic scientific consensus is that incorrect, naive application of the principles is right at the heart of the paradox. Pretending (by using wp:WEASEL words) that this is just a matter of different interpretations would be de-facto wrong, and, creating a false balance, would give undue weight to fringe theories. Please have a careful look at wp:UNDUE, wp:FALSEBALANCE and wp:PROFRINGE. - DVdm (talk) 17:32, 22 September 2016 (UTC)
It is always wrong to describe variant viewpoints as incorrect, when any differences of opinion exist. It is just academic imperialism, and sadly there's far too much of it on this platform. Unfortunately, it undermines the credibility of Wikipedia, and is contrary to its spirit. If you refuse to soften this dogmatic statement, I will take the matter to a higher authority.Ed Addis (talk) 19:20, 22 September 2016 (UTC)
Please indent talk page message as outlined in wp:THREAD and wp:INDENT. Thanks.
You will find that indeed Wikipedia is designed this way. Have you taken a look at the spirit of Wikipedia as it is described in wp:UNDUE, wp:FALSEBALANCE and wp:PROFRINGE? - DVdm (talk) 20:13, 22 September 2016 (UTC)
FWIW, I have added 3 more sources. There's a lot more, but that should be sufficient.- DVdm (talk) 22:11, 22 September 2016 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── @ DVdm. It doesn't matter if there are sources from experts who believe it is naive to believe there is a paradox and whether you've cited it to those experts. The simple fact is this article is full of 6000 words and lots of explanatory formulas, all of which also showed that the experts, including Einstein, wrestled with the paradox and labored to explain it in different ways. For an an encyclopedia directed to a general interest readership to say it is “naive” to believe there is any paradox is insulting, non-encyclopedic, and incorrect given the intended readership.

I deleted it yesterday and you put it back (∆ edit here) with the edit summary of This properly sourced qualifier was extensively discussed on talk page and there was no consensus to remove it.

Well, “well debated” it wasn't; it was just you and one other editor. Now I'm wading in and I feel precisely as user:Ed Addis does: your insulting declaration has no place. There is now a consensus to remove it so…

I’ve deleted it again. Please stop cybersquatting and reverting editors on this issue. It looks like you're more anxious to show off how insightful you are on the subject. We're not here to demonstrate that as wikipedians, we are terribly smart-smart by being insulting to our readership. Greg L (talk) 17:05, 30 March 2017 (UTC)

There was no consensus to make the change to delete it, so per our policy wp:NOCONSENSUS, we can keep it:
  • In discussions of proposals to add, modify or remove material in articles, a lack of consensus commonly results in retaining the version of the article as it was prior to the proposal or bold edit. However, for contentious matters related to living people, a lack of consensus often results in the removal of the contentious matter, regardless of whether the proposal was to add, modify or remove it.
Read the remainder of this talk page. I have restored the properly sourced qualifier, as the text was there since a long time, and there was no consensus to remove it, so please don't try to turn this around as you did in this edit summary. You can always apply for other types of dispute resolution. DVdm (talk) 17:32, 30 March 2017 (UTC)
Well, I see that of the last 500 edits, 42 of them are nothing more than you pressing the “undo” button on other editors. I have better things to do in my life than mess around on Wikipedia with intransigent editors who think they own an article and quickly invite others to delve into “other types of dispute resolution.” Perhaps you thrive on all that drama. I don't. Greg L (talk) 19:48, 30 March 2017 (UTC)

Article needs reorganization[edit]

In principle, a wiki article needs to be able to address the needs of everybody from a middle school student needing a brief introduction to a subject, to a college student who wouldn't dare presume to think that Wikipedia could be a source (horrors!), but still needs a jumping-off platform to guide him/her to interesting directions of research.

Unfortunately, this article displays a considerable amount of bloat from the well-meaning efforts of dozens of contributors over the nearly 15 years of its existence. Even the lede (which ideally should serve as a "gentle introduction" to a topic) presents considerable difficulties to an uninitiated reader.

By way of illustration, compare the current lede with the earliest version of this article, which is about the same length as the current lede. Which is more understandable?

The main body of the article is a mixed bag of essay-style writing and encyclopedic contributions requiring varying degrees of mathematical sophistication. Equal weight is provided to deservedly obscure interpretations of little general interest, such as the "Explanation in terms of Mach's principle". The result is an article that a typical reader has no hope of wading through.

Years ago, I faced similar chaos in the Quadratic equation article. I made a bold reorganization by introducing an "Advanced topics" section so that the first 2/3 of the article would only cover material that the a typical student would be interested in, while shuttling off to the end the advanced stuff (which I am sure represented labors of love on the part of the editors who spent many hours of effort writing about these specialized subjects).

Would such a bold reorganization be applicable here? Who would want to perform it? Stigmatella aurantiaca (talk) 00:27, 23 September 2016 (UTC)

I think that the article is in reasonably good shape, and I'm afraid that revamping it might open a Pandora's box. I would not be in favour of what you have in mind.- DVdm (talk) 08:23, 23 September 2016 (UTC)

Request for comment on neutrality of statement about paradoxical symmetrical ageing[edit]

The following discussion is an archived record of a request for comment. Please do not modify it. No further edits should be made to this discussion. A summary of the debate may be found at the bottom of the discussion.

Text was already adjusted mid-discussion ("incorrect and naive" in particular) to address concerns and to better reflect references. Feel free to start a follow-up discussion if further concerns. - jc37 04:06, 22 November 2016 (UTC)

I believe that the statement in the first paragraph of this article '... according to an incorrect naive application of time dilation and the principle of relativity ...' does not exhibit the neutrality expected from WP articles. Accordingly, I edited it to make it neutral. This edit has been reverted by the moderator. May I please have opinion, not on the correctness or otherwise of the application referred to, but on the appropriateness of such a biased statement in a WP article.Ed Addis (talk) 10:10, 25 September 2016 (UTC)Ed Addis, 25/09/2016

The content is properly and amply sourced and neutrally, adequately reflects the scientific consensus about the matter. Comments in section Talk:Twin paradox#Incorrect, naive application?. - DVdm (talk) 11:29, 25 September 2016 (UTC)
  • Naïve wording is improper - the problem is mostly that it lacks fidelity to the sources so fails WP:V. It is also not following WP:LEAD, is off WP:TOPIC, and could be better written WP:WBA.
  1. It fails WP:V as this is simply not the wording they use or even hint at so seems adding WP:EDITORIAL that is out of order. Looking at the cites I do not even 'incorrect' as common. By simple Google, I see a 650K count of 'twin paradox', with only 126K (one-fifth) even containing 'incorrect', and only 11K (one-sixtieth) containing 'naïve' -- and looking closer, those hits seem almost totally copies from this Wikipedia entry.
  2. It is not following WP:LEAD direction to provide summary of the article and its most important parts, since the topic and article do not involve Naivety. A label relating to moral idealism just doesn't fit to this, and the article below the lead goes into many things but not the alternative views. The lead shouldn't really have or need cites if it's summarizing the article, so having 5 cites on one line smells funny, like WP:CITEKILL.
  3. It is somewhat off WP:TOPIC as the article is about thought experiment and the lesson in inertial frames, rather than about the alternative confusions. They might deserve a small mention in the body during clarification of points (which sms not that clear in the article) but seems just not the main topic of the article. There are many confusions and wrong answers possible and if there's a reason this particular one is key, that is not presented in the article.
  4. The writing is a bit tangled. The 'incorrect naive' is a weird compound and just not necessary so drop it for ease of reading. The whole line could be simplified in length and comma clauses from the 40 words, 4 commas
"This result appears puzzling because each twin sees the other twin as moving, and so, according to an incorrect naive[1][2][3][4][5] application of time dilation and the principle of relativity, each should paradoxically find the other to have aged more slowly." seems more cleanly said as
"This result is an apparent paradox in time dilation and relativity because each twin sees the other as moving, so each might expect the other to have aged more slowly."
The rest of the paragraph could use some work too, since it calls it a paradox then says it is not, which might be better handled by putting the 'not-a-paradox' line at the top rather than the bottom, and saying it 'this is in apparent paradox but not an actual conflict in logic'? That's all I can think of right now, ope it helps hMarkbassett (talk) 00:45, 27 September 2016 (UTC)
An overwhelming scientific consensus agrees that an incorrect and naive interpretation of the postulates directly leads to the twin paradox, so that is exactly what Wikipedia should report. Removing mentions of essential incorrectness and naivity would entirely destroy what the article is about. - DVdm (talk) 07:44, 27 September 2016 (UTC)
DVdm - the overwhelming scientific discussions have nothing to do with naive. Do not use the word, are not discussing the concept, and neither is the article. The 'incorrect naive' is incorrect. Even saying 'incorrect' is a bit off topic of the paradox itself, it's an opinion remark and talking about one possible sidetrack, when the normal practice is busy with stating and explaining the answer -- the topic that the article focus is on.
Otherwise, note what one sees from search on this topic. Trying Bing for variation, first hit is Wikipedia, then about says it as two paradoxes, one paradox that the traveler age has two answers (e.g. born 90 years ago yet is 25 years in physical age,) and the more important paradox of the differing the twins views of each other contradicting (the point of symmetry that the travelling twin ages slower). That's the "twin paradox" where the article focus is and it could/should be working to do a better job. Needing to be better explained (or the point of 'twin paradox' being TO better explain) was also at the third Bing hit (Scientific American - with better description of the clocks involved). I also see that the twin paradox is in recent times still getting variations and different resolution methods, mentions for simultaneity, and puzzled folks.
Regardless, you've got my RFC input and explanation that it's from 'naive' is not part of the cites and 'incorrect' is an unnecessary small sidetrack. If you need me to explain my input further, post below and otherwise cheers. Markbassett (talk) 16:11, 27 September 2016 (UTC)
You say "it's from 'naive' is not part of the cites and 'incorrect' is an unnecessary small sidetrack". You can follow the 5 cited, rather solid, sources. The first two support "naive", so naive is indeed part of the cites: "The so called twin paradox is the seemingly contradictory situation arising from a naive application of the time dilation phenomenon...", "If we naively apply the time-dilation formula...". All of them thoroughly and essentially support "incorrect", which is indeed necessary: "The "paradox" arises from an incorrect application of the principle of relativity...", "Hence Speedo cannot apply simple time dilation to Goslo's motion because doing so would be an incorrect application of special relativity.", "An (incorrect) application of relativistic time dilation yields the paradoxical conclusion that each twin would the other to be older." Many more sources can be found, at least for "incorrect". Surely we're not going to suggest that the validity of special relativity is just a matter of opinion (wp:PROFRINGE, wp:FALSEBALANCE), and that, when applying its postulates, we get unsolvable paradoxes, i.o.w. contradictions that invalidate the theory. It is just a fact that a paradox arises when the postulates and results of relativity are incorrectly applied, and that the paradox is solved by correctly applying them. That part is absolutely essential. Calling it naive might look like a matter of opinion, but we can and do back it with reliable sources (Ohanian is an authorithy, with textbooks used all over the world), so I don't see any reason why we shouldn't do that. I would agree if we pull both words apart though, first the most important "incorrect", then the less important —but clearly still worth mentioning— "naive":
In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. This result appears puzzling because each twin sees the other twin as moving, and so, according to an incorrect[1][2][3] and naive[4][5] application of time dilation and the principle of relativity, each should paradoxically find the other to have aged more slowly.


  1. ^ Crowell, Benjamin (2000). The Modern Revolution in Physics (illustrated ed.). Light and Matter. p. 23. ISBN 978-0-9704670-6-5.  Extract of page 23
  2. ^ Serway, Raymond A.; Moses, Clement J.; Moyer, Curt A. (2004). Modern Physics (3rd ed.). Cengage Learning. p. 21. ISBN 978-1-111-79437-8.  Extract of page 21
  3. ^ Bell, John L. (2016). Oppositions and Paradoxes: Philosophical Perplexities in Science and Mathematics. Broadview Press. p. 87. ISBN 978-1-77048-603-4.  Extract of page 87
  4. ^ D'Auria, Riccardo; Trigiante, Mario (2011). From Special Relativity to Feynman Diagrams: A Course of Theoretical Particle Physics for Beginners (illustrated ed.). Springer Science & Business Media. p. 541. ISBN 978-88-470-1504-3.  Extract of page 541
  5. ^ Ohanian, Hans C.; Ruffini, Remo (2013). Gravitation and Spacetime (3rd ed.). Cambridge University Press. p. 176. ISBN 978-1-139-61954-7.  Extract of page 176
This way the opening sentence perfectly reflects the documented standing scientific consensus, which is what Wikipedia is supposed to do. Pulling apart the words also avoids the current slightly possible wp:SYNTHy combination of the phrase "incorrect naive application". - DVdm (talk) 20:06, 27 September 2016 (UTC)
  • Comment Storm in teacup, threatens to create wall-of-text altercation about items that should be easily resolvable. This is not my line, but the matter should be settled by
1) (In view of the disagreement, careful and punctilious, but not ridiculously long lists of) citations of authoritative sources that satisfy all parties (there are enough SR and even GR sources to satisfy all reasonable parties, goodness knows)
2) In resolving disagreements about acceptable sources, Einstein or Feynman trump Scientific American, which in turn trumps Fox News
3) Aiming for clear expression of concepts relevant to the topic, using wording derived as directly as reasonable from cited sources.
4) Where evaluative language (such as "naive") is used, then if there is disagreement, it must come from agreed sources, not from editor interpretations.
5) Aiming for a coherent and lucid logical structure for the article
All those points (and more, but more should be unnecessary) have been implied in the foregoing, because they are long-standing and standard. The question is how to resolve disagreements about the best competing texts. If such a disagreement does not settle itself pretty soon, then the original text should be the default choice.
Sorry to spout platitudes, but really, that is what storms in teacups evoke. JonRichfield (talk) 07:10, 4 October 2016 (UTC)
  • Naïve is proper and apt. First of all, per DVdm above, the word 'naïve' is fully supported by reliable sources. The objection to the word may simply reflect a misunderstanding of its usage in technical fields. Using the word 'naïve' here is not making a judgment about the people that hold such ideas, it's simply descriptive of 'the first way you might think of approaching this', as opposed to a proper solution with a full understanding of the problem.
Even if the word didn't appear in the relevant literature (as it does), I would consider it a perfectly neutral and apt term in that context, especially as Wikipedia allows paraphrasing from reliable sources, so your argument about editorializing falls flat for me.
Changing what I see as a perfectly reasonable term simply because it rubs you the wrong way gets a bit closer to censorship than I'd feel comfortable with. Arathald (talk) 03:45, 13 October 2016 (UTC)
  • Delete the word "naive". I don't read the sources stating the words "naive incorrect application", the 3 words seem to be assembled from multiple sources. I think the 3 words together are technically alright, but stating "naive incorrect" is redundant and doesn't add any value or clarity to the next, and seems to disparage people new to the subject.CuriousMind01 (talk) 11:14, 13 October 2016 (UTC)
Good point. I have reworded as proposed above: [1], keeping both naive and incorrect. This way the words are separately mentioned and sourced. - DVdm (talk) 11:35, 13 October 2016 (UTC)
  • Bad lead. I think it's ok to discuss the naive and incorrect application, but why can't we discuss the actual matter properly first? Its very confusing and not helpful to open with an incorrect explanation. Consider if magnet opened up with a discussion of how magnets don't work via sympathetic connections- I'd hope most of us would reorder things. Lots of things known as "paradox" are not true paradoxes. For what it's worth, I always heard the term "twin paradox" referring to the correct thought experiment of two twins attaining different ages via high speed travel and return of one. It's not truly a paradox, but it seems as though it might be, much like e.g. Banach-Tarski paradox. SemanticMantis (talk) 13:58, 18 October 2016 (UTC)
Ha, but there are two ways to understand the term "paradox": really contradictory, or just seemingly contradictory. Anyway, as the relevant literature clearly states, an incorrect and naive application of the prinicples directly leads to a situation/statement/delusion that is universally called the "Twin paradox". This is just the essence of the matter, and thus it ends up reflected in the lead of the article, as it probably should per WP:LEADSENTENCE. If, as you perhaps might suggest, the lead should reflect a correct and informed application of the prinicples, then the article should be renamed to something along the lines of differential aging in relativity. That term exists in the literature, but it is not nearly as common, and I don't think we're going to rename the article. People obviously tend to focus on the error. - DVdm (talk) 14:58, 18 October 2016 (UTC)
But the paradox does have a role in SR. The lead does not discuss mistakes people make in writing about it. It just states what it is: a persistent mistake—see the sources. That is the whole point. - DVdm (talk) 18:49, 18 October 2016 (UTC)
  • The wording "incorrect naive" is technically correct, but excessive, over the top, unjustified by the context. "Mistaken" would be better. And the five refences attached to those two words are unnecessary. I haven't look into the history of this article - has it been plagued (like Monty Hall problem) by editors arguing for a mistaken understanding of the paradox? Maproom (talk) 07:56, 20 October 2016 (UTC) Remarks struck in view of following response. Maproom (talk) 09:16, 20 October 2016 (UTC)
The wording "incorrect naive" has already been replaced with "incorrect and naive", with separate sources, 3 for "incorrect" and 2 for "naive". Both exact words do appear in the sources, so there should be no reason to, for example, replace the sourced "incorrect" with "mistaken". That could be interpreted as wp:SYNTHy. Yes, indeed the sources were introduced specifically to avoid a Monty Hall like plague. So far it seems to have helped. Every now and then someone comes to the talk page to discuss, but usually referring to the sources quickly settles things down.

As evidenced by this anon article edit, followed by this, this and this talk page user edit (—clearly the anon is the user—), this RFC was opened by someone who thinks that special relativity is simply mistaken: they removed "incorrect", weaseled out "naive", and deleted the sources, because "the reality is that there are many, myself included, who do not agree with this interpretation" and "It is always wrong to describe variant viewpoints as incorrect, when any differences of opinion exist. It is just academic imperialism." - DVdm (talk) 09:09, 20 October 2016 (UTC)

Thank you for the explanation. I have struck what I wrote above. Maproom (talk) 09:16, 20 October 2016 (UTC)

The above discussion is preserved as an archive of the debate. Please do not modify it. No further edits should be made to this discussion.

How to simplify our vision of the twin paradox.[edit]

Time dilation is since Einstein reported in a rather complicated manner.

We look at the transported clock "A" with the "point de vue" from our fixed clock "B". And of course we find that "A" runs slow.

But we forget that "all the laws of physics are the same in every inertial frame of reference". That means ː if we transport , at constant speed a sister clock "A" of "B" , that sister clock runs exactly at the same rate than "B".

And if we measure , with "A" , a certain amount of time between the initial position of "A" and its final position , we will find the correct answers (that is with the Lorentz transformations) , with never having thought that "A" runs slow. That means we dissipated any confusion between the physical clocks and time they measure ǃ

Of course we must also explain what happens in the acceleration - deceleration phases , but it is now well-known that the contribution of these phases are negligible. And also that modern clocks are almost insensible to accelerations ǃ

That interpretation is not only easier to explain , but it simplifies the experimental analysis. We understand how there is in space-time a sort of trading between space and time.

--Chessfan (talk) 14:01, 30 January 2017 (UTC)

Please note that per our wp:talk page guidelines, article talk pages are for discussions about additions, changes and removals of content of the article. We are not supposed to discuss the subject here. For questions about the subject, please visit our wp:Reference desk/Science. - DVdm (talk) 14:10, 30 January 2017 (UTC)
Perhaps it is worth a addition ? After all these facts are well known. I leave it to You. Cordially. --Chessfan (talk) 15:00, 30 January 2017 (UTC)

Improvements to the Relativistic Doppler Shift section?[edit]

The following sentence in the relativistic doppler shift section of the article confuses me:

  • "At arrival, the image in the ship screen shows the staying twin as he was 1 year after launch, because radio emitted from Earth 1 year after launch gets to the other star 4 years afterwards and meets the ship there."

If the ship has already come to a stand-still and so his space-dilation already tells him he is 4 light-years away from his source, then the sentence is believable.

However, while the ship is still travelling at 0.8c, it will view its distance traveled as only 2.4 light-years (per the earlier sections of the article).

Accordingly, I would expect the passenger on the ship to only be able to see the radio emitted from Earth 0.6 years after launch. (Since the ship's time is 3 years, and light takes 2.4 years to get to him from earth, at his current velocity and length-contraction.)

If the ship crash-lands into a planet and so instantly decelerates from 0.8c to 0 relative velocity, does 0.4 years of radio data from earth instantly arrive at the ship???

I think the article could probably be improved to explain why it uses earth-time and earth-space to calculate the radio arriving at the ship instead of ship-time and ship-space. (And why the discrepancy?)

Tprel (talk) 01:20, 19 February 2017 (UTC)

The distance travelled is not relevant here. It is just about the images as seen by the traveller, which trivially takes place at the traveller's location. These images are the same immediately before arrival, immediately after arrival, and then again immediately after the start of the return trip. There is no discrepancy in the "remote time images", as visually seen by the traveller. There only is a discrepancy in the so-called calculated current time on Earth, but that is not relevant here. This part is about what it looks like for the traveller. - DVdm (talk) 10:59, 19 February 2017 (UTC)

Article lead : Inaccurate summary of the references.[edit]

There has been much discussion of the use of "incorrect" and "naive" in the lead but it seems to me that a more significant problem has been missed. The current sentence is "This result appears puzzling because each twin sees the other twin as moving, and so, according to an incorrect[1][2][3] and naive[4][5] application of time dilation and the principle of relativity, each should paradoxically find the other to have aged more slowly.". I have emboldened the relevant phrase. My understanding is that it is not the rate of ageing that is paradoxical but the total amount by which each has aged. there are five references cited, the relevant extracts are:

[1] "When the travelling twin gets home, she has aged only a few years, while her sister is now old and gray."

[2] "To Speedo, the most significant change is that his brother Goslo has aged more than he and is now 60 years of age. Speedo, on the other hand, has only aged by 34.6 years. ... This leads to the paradox: Which twin will have developed the signs of excess ageing."

[3] "An (incorrect) application of relativistic time dilation yields the paradoxical conclusion that each twin would find the other to be older."

[4] "It follows that the twin B must be younger than the twin A when they meet again. ... it should be also possible to argue that A is younger than B."

[5] "Thus Terra has aged more than Stella. If we naively apply the time dilation formula in the reference frame of Stella, we would reach the opposite conclusion."

In each case, the paradox is not that one or the other "ages more slowly", it is that the total ageing is greater for the twin who moves inertially throughout. To correct this, I suggest the end of the sentence is rewritten as "... each should paradoxically find the other to have aged by a lesser amount."

George Dishman (talk) 19:32, 6 March 2017 (UTC)

Hi George, I don't agree. Time dilation means that A measures (with his t-clock) the time (dt) between two events on B's remote t'-clock as longer (dt = gamma dt', since dx'=0, as you can check with the Lorentz transformation). A says something like "what your clock calls a second, I call 4 seconds". So indeed A measures the aging of the remote clock as "more slowly than his own". If A remains inertial between B's departure and return events, then when they meet again and compare their elapsed times, indeed B's clock has aged more slowly (or just less), and B is indeed younger than A. That is the correct, informed application of time dilation. The converse is not true, simply because B bas not been inertial between the two events. The mistake of assuming that B remains inertial is the incorrect, naive application. Indeed A finds B to have aged more slowly, but B does not find A to have aged more slowly. - DVdm (talk) 20:05, 6 March 2017 (UTC)
Ha... I see what you mean: perhaps we should just remove source [3] because they have the typo: that should be: "... paradoxical conclusion that each twin would find the other to be younger." Good find! - DVdm (talk) 20:27, 6 March 2017 (UTC)
Hi DVdm, your disagreement is exactly why I put the view here rather than editing the text so thanks for replying.
You gave for instance "A says something like "what your clock calls a second, I call 4 seconds" but it'll be easier to use v=0.8c and gamma=1/0.6. Suppose each has a clock that ticks once per second. B departs and travels for 100 seconds at a constant 0.8c as measured by A before turning round and returning in another 100 seconds again at constant speed. Time dilation says that B's clock will measure 60s elapsed time during each leg of their trip giving a total of 120s compared to 200s measured by A. So far, so good. However, B can also apply time dilation to each leg. B says "my outward leg took 60s hence in that time A's clock should have ticked 36 times". Similarly for the return leg, B measures 60s and no acceleration so during that time A's clock should have advanced by another 36s. Thus when B returns, by applying time dilation to both legs, he expects A's clock to have advanced by a total of 72s. This application of the time dilation formula is entirely legitimate and correct for each leg which is why "ages more slowly" is not the nature of the paradox. The cause of the paradox is that using only time dilation means that B predicts that A's clock will have advanced less than his own overall when they are compared at the same location on B's return, but even when resolved, it is still true that each ticks "more slowly" than the other on both legs.
What is "naive" about this is to assume that only time dilation is relevant. When B turned round (assumed to be impulsive so take negligible time), he switched from the inertial frame in which he was at rest on the outward leg to that in which he is at rest on the return leg. That switch of inertial frame needs to be included via the "relativity of simultaneity". If we number the ticks for each clock starting at 0 when B departs, tick 60 on B's clock is simultaneous with tick 100 on A's clock as judged by A but with tick 36 on A's clock as judged by B. Similarly, in the return trip inertial frame, tick 60 on clock B is simultaneous with tick 164 on clock A as judged by B and tick 120 on B is simultaneous with tick 200 on A. Again, A has ticked "more slowly". The resolution of the paradox of course is that the "relativity of simultaneity" effect takes the A clock from 36 to 164 on the change of B's frame. This is illustrated in the diagram in the article and accompanying text. Adding that 128s to the 72s computed using time dilation alone resolves the paradox. The bulk of the article is perfectly correct, it is only the single sentence in the summary that, IMHO, is misleading and not representative of the sources.
You said at the end "but B does not find A to have aged more slowly" but that is incorrect, B does find that A aged more slowly both on the outward leg and on the return leg, there is no finite period when A wasn't ageing more slowly according to B, but on completion of the trip, B finds that A has aged by a greater amount overall, that is the paradox, hence "has aged more slowly" is not the same as "has aged less".
If you consider removing references due to a typo ("older" instead of "younger" which I should admit I hadn't spotted, I even had one like that in my initial submission), I would suggest removing reference [3] which IMHO is more seriously wrong, it states that "This asymmetry, which involves accelerated motion, cannot receive a complete analysis within special relativity since special relativity applies only to uniform motion. It requires the tools of general relativity which is introduced below.". Obviously including relativity of simultaneity in SR is sufficient to resolve the paradox without resorting to GR. It is also incorrect to say that SR only applies to uniform motion, see Rindler Coordinates for example. Reference [5] also uses GR by the way.
George Dishman (talk) 13:29, 8 March 2017 (UTC)
Ok, I have removed source [3] and replaced the somewhat awkward phrase "has aged more slowly" with "has aged less": [2]. That's clearly better. Thanks for having spotted this. - DVdm (talk) 16:33, 8 March 2017 (UTC)
Excellent, thank you. George Dishman (talk) 18:23, 8 March 2017 (UTC)
Parodying "Molière" in the "femmes savantes" , your discussion reminds me of two sligthly pedantic poets having an argument over two versions : "how beautiful is that blue bouquet ... " or "how blue is that beautiful bouquet ..." ! Once you have admitted that simultaneity is relative , that fact plays no further role. A and B have the same clocks , playing the same rhythm , unchanged on the inward trip and the outward trip. Indeed we can say that the switch between the simultaneity planes at the turnaround point has mostly a negligible numerical impact , and no theoretical importance for the resolutions of the "paradox". Cordially ; I apologise if necessary ...Chessfan (talk) 19:54, 10 March 2017 (UTC)
Perhaps I should explain the context, I've been trying discuss the thought experiment with someone who is a newcomer to SR, he understands the basics but has been arguing that the paradox can be eliminated by taking length contraction into account. However, his "solution" only resolved the difference in clock rates which he insisted was the paradox, it couldn't consider what would happen if the twins were reunited. The error on this page made it impossible to explain that the "Twins Paradox" requires one to turn round and return to the other. Changes the rate of ageing to the total amount resolves the problem. George Dishman (talk) 16:26, 17 March 2017 (UTC)

REQUEST FOR COMMENT: Should “naive” statement be deleted?[edit]


The current version of the article (as of this time) states as follows in the first paragraph (with the citations links inactivated):

This result appears puzzling because each twin sees the other twin as moving, and so, according to an incorrect[1][2] and naive[3][4] application of time dilation and the principle of relativity, each should paradoxically find the other to have aged less.

As the host of this RFC, I propose that the “naive” be deleted as insulting and un-encyclopedic.

Let the community discuss this for a while (as long as editors are weighing in) to see if we can arrive at a consensus.

RFC Protocol:

  • Wikipedians who weigh in should feel free to update their support/oppose (*vote*) statements as they see fit so long as no one has commented on it in the Rebuttal and discussion; merely update your autosignature with a fresh quadruple-tilde (~~~~) when finished.
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  • In the Rebuttal and discussion, to begin a thread when responding to another editor, use an “@” reference, e.g. @User:So-n-so: You wrote “blah blah blah” but I have a different take.
  • In the Rebuttal and discussion section, please abide by normal customs where you make no substantive edits to your posts after someone has responded; strike statements if you feel it appropriate.
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  • The duration of this RFC will remain flexible. The general objective will be to achieve a balance amongst three factors. One factor is to run this RFC long enough to give an opportunity to the widest segment of the community—uninvolved wikipedians and I.P. editors included—to weigh in. A second factor is whether—after providing opportunity for ample participation—a consensus one way or another has become apparent. And a third factor is whether there is a protracted period of participation having dropped off due to lack of interest.
  • The procedure for calling this RFC will also be kept flexible. If the consensus is clear based upon a grin test, it's a simple call. If a consensus is anything short of crystal clear, we'll call in an uninvolved admin to bear judgement.

In advance, thanks to everyone for participating. Greg L (talk) 22:35, 30 March 2017 (UTC)

Support deleting “naive”[edit]

[Just single-paragraph posts here, numbered with "#"; discussion and replies below, not here]

  1. Support deletion This isn't a huge deal. The issue is simple: Whether it is any way encyclopedic to state in the lede of an article that people are “naive” if they think the paradox exists. This wording has clearly been a source of controversy and much debate has occurred on this talk page on the subject; it is time to put this one to bed. As RFC proposer, it doesn't matter if certain cited experts believe it is naive to think a paradox exists; they are obviously referring to any other “expert” in the field to make the point that if one has a full understanding of relativity, one would perceive no paradox. Alas, Wikipedia is a general-interest encyclopedia directed to a non-expert readership. The simple fact is this article has 6000 words and lots of explanatory formulas, all of which also showed that the experts—including Einstein—discussed the apparent paradox at length and labored to explain it using various thought experiments and different points of view. For us to say it is “naive” for anyone to think there is paradox and come to Wikipedia to learn about it is insulting to our readership and is non-encyclopedic. Greg L (talk) 15:55, 31 March 2017 (UTC)

Oppose deleting “naive”[edit]

[Just single-paragraph posts here, numbered with "#"; discussion and replies to other editors in the below section, not here]

  1. Oppose deletion. See all over the place on this talk page—including the previous RFC. There is nothing insulting about this well sourced qualifier. It holds no judgment about people and just accurately describes a mistaken (aka incorrect, as sourced) and uninformed (aka naive, as sourced) application of a theory. The qualifier is encyclopedic per the provided sources. The 6000 words of the article also solidly support both these qualifiers, so they are well-placed in the lead. - DVdm (talk) 20:57, 30 March 2017 (UTC)
  2. Oppose deletion. See sources and previous RFC. --D.H (talk) 15:57, 31 March 2017 (UTC)
  3. Oppose deletion It is a paradox, as it is easy to believe that they should age the same. Most people don't find special relativity easy to understand, but the twin paradox requires general relativity. Gah4 (talk) 19:06, 31 March 2017 (UTC)
  4. Oppose deletion. It does not say that anyone is naive. It does not say that it is naive to think that the paradox exists. It is not insulting. This RFC does not make any sense. Roger (talk) 06:31, 1 April 2017 (UTC)

Section for rebuttal and discussion of other editors’ above position statements[edit]

[Unrestricted area for back & forth discussion]

The term non-relativistic is commonly used to describe physics that is correct in Newton's sense, but not in either special or general relativity. I don't know that there is a term for physics that is incorrect with special relativity, but correct with general relativity. The paradox comes when applying special relativity to a case that needs general relativity. Gah4 (talk) 19:08, 31 March 2017 (UTC)

Gah4: Are you clear what the issue is here? You wrote “The paradox comes when applying…” My issue is over how the article currently says you are naive for believing that. This RFC is whether it is appropriate to say that it is “naive” to suspect a paradox exists. That's rather rather insulting language for an encyclopedia directed to a general-interest readership trying to grasp the nuances of the Twin paradox. Greg L (talk) 19:14, 31 March 2017 (UTC)
Note that the article does not say that "you are naive for believing that", or that "it is naive to suspect a paradox exists". It says that an incorrect and naive application of some principles leads to a paradox. You make the same allusion on this other forum. Please don't misrepresent what the article says. And please have a look at WP:FORUMSHOP. - DVdm (talk) 19:27, 31 March 2017 (UTC)

Yes, but I didn't make it so obvious. Since general relativity isn't especially easy, it shouldn't be an insult to not understand it. Or, for the specific case, to not understand when it is needed and how to apply it. Telling someone that they don't completely understand general relativity should not be considered an insult. Gah4 (talk) 20:39, 31 March 2017 (UTC) There is a story, which I don't have a reference for, that the designers of GPS didn't know if the general relativity correction was needed. They included it with a switch to turn it on or off. Soon after it started working, it was found that it was needed. I suspect that they were all pretty smart. Gah4 (talk) 20:39, 31 March 2017 (UTC)

Oh… relax, DVdm. Too much drama—perhaps driven by some WP:OWN. There is a atomic-thin distinction between saying someone is naive and saying the perception that there is any paradox at all is founded upon a naive understanding of science. The text reads This result appears puzzling because each twin sees the other twin as moving, and so, according to an incorrect[1][2] and naive[3][4] application of time dilation and the principle of relativity, each should paradoxically find the other to have aged less. Greg L (talk) 20:19, 31 March 2017 (UTC)
The first time you alluded to intransigence and wp:OWNership was here. I chose to ignore that. Now this is the second time. Please stop resorting to personal comments. Thank you. - DVdm (talk) 21:10, 31 March 2017 (UTC)

Error in the article?[edit]

the History section says, In his famous paper on special relativity in 1905, Albert Einstein deduced that when two clocks were brought together and synchronized, and then one was moved away and brought back, the clock which had undergone the traveling would be found to be lagging behind the clock which had stayed put.[A 4]

I in fact do not see that in Einstein's 1905 paper ?

It should be taken out of Wikipedia. — Preceding unsigned comment added by (talk) 14:02, 17 April 2017 (UTC)


Can you provide source link to this paper. Then use the find and replace tool to search for the text. Once you have determined whether the information is valid, make an edit to this page, and include your source in your edit summary. If the page is semi-protected create an account. Good Luck, CopernicusAD (u) (t) :) 14:08, 17 April 2017 (UTC)

It's near the end of paragraph 4 of
From this there ensues the following peculiar consequence. If at the points A and B of K there are stationary clocks which, viewed in the stationary system, are synchronous; and if the clock at A is moved with the velocity v along the line AB to B, then on its arrival at B the two clocks no longer synchronize, but the clock moved from A to B lags behind the other which has remained at B by (up to magnitudes of fourth and higher order), t being the time occupied in the journey from A to B.
- DVdm (talk) 14:56, 17 April 2017 (UTC)
That is not the twin paradox, that is only one way, with no return trip mentioned. It should be removed from Wikipedia, Einstein did NOT address the twin paradox in 1905. (talk) 15:20, 17 April 2017 (UTC)
Indeed, it is not the twin paradox. It is about time dilation, which plays an essential role in the twin paradox, just like the sentence form the article does, that you have quoted in your message above. The referenced journal supports it, so it should not be removed from the article, as it introduces the concept of time dilation in its historical context.
Oh, by the way, I now see that I had copy/pasted the wrong sentence. That should be:
It is at once apparent that this result still holds good if the clock moves from A to B in any polygonal line, and also when the points A and B coincide. If we assume that the result proved for a polygonal line is also valid for a continuously curved line, we arrive at this result: If one of two synchronous clocks at A is moved in a closed curve with constant velocity until it returns to A, the journey lasting seconds, then by the clock which has remained at rest the travelled clock on its arrival at A will be second slow.
Sorry for the confusion. My bad. - DVdm (talk) 16:06, 17 April 2017 (UTC)
@DVdm: So are you saying the content should be removed from en Wikipedia? If so I will correctly source and remove the content. If it belongs let me know, or either way let me know too. From what I take away, that content should be removed. Good LuckCopernicusAD (u) (t) :) And PS, ping or leave me a talkback 17:53, 17 April 2017 (UTC)
Oh! Stupid me! Duh, keep content, case closed. — Preceding unsigned comment added by CopernicusAD (talkcontribs) 17:54, 17 April 2017 (UTC)

This is a false statement and must be removed from Wikipedia: In his famous paper on special relativity in 1905, Albert Einstein deduced that when two clocks were brought together... Einstein never said that. (talk) 02:28, 18 April 2017 (UTC)

As you can see, the content is properly sourced and formally attributed in the article. - DVdm (talk) 07:19, 18 April 2017 (UTC)
The statement is FALSE. Einstein never talked about bringing the clocks together in 1905. It must be removed from Wikipedia. Einstein never said that in 1905. He said it years later, in 1911. So it must be removed from Wikipedia about 1905. He did NOT address the paradox in 1905. So remove it. (talk) 14:24, 18 April 2017 (UTC)
Indeed, as I said before, he did not address the paradox. He addressed time dilation, which is what is addressed here in the article too. I have put the relevant sentence in boldface. If that is not clear, perhaps the passage in the original language of the 1905 paper ( is helpful:
Man sieht sofort, daB dies Resultat auch dann noch gilt, wenn die Uhr in einer beliebigen polygonalen Linie sich von A nach B bewegt, und zwar auch dann, wenn die Punkte A und B zusammenfallen. Nimmt man an, daB das für eine polygonale Linie bewiesene Resultat auch fur eine stetig gekrümmte Kurve gelte, so erhalt man den Satz: Befinden sich in A zwei synchron gehende Uhren und bewegt man die eine derselben auf einer geschlossenen Kurve mit konstanter Geschwindigkeit, bis sie wieder nach A zurückkommt, was Sek. dauern möge, so geht die letztere Uhr bei ihrer Ankunft in A gegenüber der unbewegt gebliebenen um Sek. nach.
I see no difference between this and the sentence in the article:
In his famous paper on special relativity in 1905, Albert Einstein deduced that when two clocks were brought together and synchronized, and then one was moved away and brought back, the clock which had undergone the traveling would be found to be lagging behind the clock which had stayed put.
Hope this helps. - DVdm (talk) 15:42, 18 April 2017 (UTC)
You are dead wrong. Time dilation is one thing, explaining the twin paradox is quite another. Nowhere in 1905 did he talk about bringing the clocks back together. This Wikipedia article is about the twin paradox, not time dilation. It must be removed about bringing the clocks back together, he NEVER said that in 1905 as Wikipedia incorrectly asserts. Remove it. (talk) 16:44, 18 April 2017 (UTC)
I'm sure that most people will agree that the phrase "It is at once apparent that this result still holds good if the clock moves from A to B in any polygonal line, and also when the points A and B coincide" is precisely about keeping one clock at A, while taking another clock away from A and then bringing it back to A.
And yes, this article is about the twin paradox, which is based on an incorrect application of time dilation, which is introduced in the history section. No problem there. - DVdm (talk) 17:32, 18 April 2017 (UTC)
OK I agree, Einstein did have the twin paradox in his 1905 paper, not much, but it is there. (talk) 19:18, 18 April 2017 (UTC)
All right everybody, were all done here. No more debating, I give to @DVdm:. Are we clear. Bye CopernicusAD (u) (t) :) 01:12, 19 April 2017 (UTC)

Special Relativity alone can explain the paradox[edit]

General relativity is not necessary to explain the twin paradox; special relativity alone can explain the phenomenon.[1] [2] — Preceding unsigned comment added by (talk) 14:10, 30 May 2017 (UTC)


Please sign all your talk page messages with four tildes (~~~~) — See Help:Using talk pages. Thanks.
Yes, but I made a little tweak, replacing that pop-sci blog with a proper textbook source: [3]. - DVdm (talk) 16:02, 30 May 2017 (UTC)