Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
(920 intermediate revisions by more than 100 users not shown)
Line 1:
Line 1:
{{talkheader}}
{{Talk header}}
{{controversial}}
{{physics|class=B|importance=Mid|relativity=yes}}
{{Not a forum}}
{{WikiProject banner shell|class=B|vital=yes|1=
•Because of their length, the previous discussions on this page have been archived. If further archiving is needed, see ].http://wikimania2007.wikimedia.org/Registration
Some people get lost in the twin paradox presented here (with accelerations and all), so maybe a simpler, symmetrical paradox is in order. So, here is that "gedanken" experiment:
Let's have two identical rockets, carrying two identical high precision (in
today's technology that would be atomic) clocks, with digital displays. The
displays show the number of ticks (cycles) that each clock recorded (this
could be for instance number of nanoseconds - a simple integer) since last reset. The
rockets and clocks include a mechanism that fires the thrusters on detection
of blue light and resets the clocks on detection of red light.
These two rockets are placed in space, away from any gravitational fields, so
that they are pointed to one another, on a straight line. The rockets are far
away from each other and we shall call the left one A and the right one B.
Midway between rockets A and B we place a source of light we shall call S,
capable of emitting blue or red light, each simultaneously to left and right,
toward rockets A and B.
Rockets A and B, together with S form a single inertial frame of reference S
for now (in other words, they are all stationary to one another).
Now we send blue light simultaneously from our source S toward rockets A and
B. This starts the thrusters and the rockets burn their fuel, therefore being
accelerated toward one another, on a collision course. The rockets burn all
their fuel and each reaches constant velocity v in relation to our stationary
frame of reference S, but in opposite direction. The speed at which the
rockets are travelling is "normal" speed (i.e. not nearly close to the speed
of light, but something a normal rocket could do).
After the burn is completed, we send red light simultaneously from our source
S in the direction of rockets, therefore resetting the counters of our clocks.
Now we have a system of three inertial reference frames, A - for rocket A, B -
for rocket B and S - for our source of light S, in linear motion in relation to
one another. And we have our clocks on rockets A and B synchronised, as observed from S.
Just before the collision occurs (i.e. when rockets A and B are in immediate
vicinity of light source S) and if the trip of rockets is sufficiently long, we shall have
the following situation in relation to clocks, as observed from different
frames of reference, due to time dilation as per special theory of relativity:
* clock A displays N as observed from reference frame A
* clock A displays M (different from N) as observed from reference frame B
* clock A displays L (different from N and M) as observed from reference frame S
And due to symmetry of motion and identical construction of clocks:
* clock B displays N as observed from reference frame B
* clock B displays M (different from N) as observed from reference frame A
* clock B displays L (different from N and M) as observed from reference frame S
In comparison, such a system would show N on both clocks as observed from any
frame of reference using only Newton's mechanics.
--] (]) 20:19, 3 January 2008 (UTC)
: Since this is entirely ] we can't of course put it in an article, and it doesn't really belong on this talk page either. You might try Usenet. As a matter of fact it just so happens that someone (or ''you''?) just asked exactly the same question on Usenet in .
: Anyway, I'll give you two hints here. (1) You write: ''"... in linear motion in relation to one another. And we have our clocks on rockets A and B synchronised."'' When they are in relative motion, they are not synchronized. They both see the other one's clock "run slower". (2) You created a symmetric situation, so you get symmetric results. Good luck on Usenet :-) - ] (]) 21:44, 3 January 2008 (UTC)
::Point taken about original research. I thought someone must have done this before (it seemed unlikely that this would be original). And it wasn't me on Usenet - so obviously not all that original ;-)
::In terms of "synchronised" - they are synced in the sense that they are both running equally different as observed from S. About symmetric - yeah, that was my point. I think it would be useful to show that observers in different reference frames would read the same clock differently in immediate vicinity of each other according to SR.
::--] (]) 21:58, 3 January 2008 (UTC)
::: The idea of symmetry is of course not new, but I had never seen this kind of setup with the central light.
::: Little note on ''"... synchronised in the sense that..."''. Sure, but that's another kind of synchronization. From the three clocks in the setup, no pair of clocks is synchronized in any way. You ''could'' perhaps say that the clocks A and B are ''sort of equally desynchronized'' according to S, but as soon as you forget S, A and B are just two systems in relative motion - nothing special about them. In fact, one can construct a "central S" for every pair of systems in relative motion. That can't possibly make the pair physically special.
::: Do try the Usenet thread - it ''might'' become interesting :-)
::: Cheers, ] (]) 22:25, 3 January 2008 (UTC)
::::There are only two clocks in the setup - A and B. If two equidistant stationary clocks can be synced by passing a beam of light simultaneously from the midway to them to "reset" them, so can the same two equidistant clocks in uniform opposing motion be synced as observed from S, unless the beam of light somehow travels to the left at different speed than to the right :-) Sure, from A, B is observed to be different (due to relative motion) and vice versa, but for an observer in S, they will be in sync (i.e. explicitly, both clocks display L when rockets meet, as observed from S). I never thought nor do I think that S would make A and B special. S is just another inertial frame of reference and an observer, just like you said.
::::--] (]) 23:07, 3 January 2008 (UTC)
::::: Well, you ''really do'' have a third clock in there. The minute you mention "reference frame S", you have it. No reference frame without a clock :-)
::::: Do try Usenet for this - it's better suited for this kind of thing. This page is for discussions about the format and content of the article, not the subject. Cheers, ] (]) 08:59, 4 January 2008 (UTC)
::::::No worries. --] (]) 09:41, 4 January 2008 (UTC)
:Actually, all observers in the above example would see one and the same value on both clocks. That is to say, my example does not reach correct conclusions. --] (]) 23:19, 14 February 2008 (UTC)
The problem is: whenever somebody tries to make a setup, which clearifies, what one is talking about, this "problem" is solved with the axe ]. The twin paradox has to be a mystery. There are so many ways to misunderstand what is argued. Simple example: what is a clock. It could be so simple: Two identical laboratories are connected by a loaded spring. This mechanism is released and according to conservation of momentum both labs gain the same speed, relative to each other. Now the have the following instruments: a source of light, that is a resonator, amplifying a certain spectral line of a certain gas of atoms and a prisma or better, grating. This light is directed to a semi reflecting mirror, twisted 45°, so 50% of the light is directed to the grating, 50% is send in direction of the second "twin" lab. So, the grating deflects two different beams: one from the local source and one from the distant source. It should be possible, by elementary calculation to determine the ratio of the detected deflection angles. And it should be possible to have a shutter which modulates the outgoing beam with this determined ratio on and of. And again it should be possible to compare the on/off ratio of the received and send signals. I have to point out: this is no OR, it is just a try to find a common language of what is a clock, how to measure a frequency..., how to measure distance and time in an environment, where nothing is absolute, except "c". ] (]) 06:32, 9 May 2008 (UTC)
: The common language as regards editing the article is in the literature. Check (=read) the references, and you'll find definitions of "clock", "distance", "time" and lots of other terms. If you go and invent your own definitions, chances are ''extremely'' high that you will either get it wrong and somebody has it done before, or you get it right and somebody has it done before. If you're really lucky, you might get it wrong in a spectacular new way. If you want to learn about relativity, you might consider enrolling in . ;) ] (]) 00:52, 1 May 2009 (UTC)
==Accelerated rocket calculation==
IMO the "Accelerated rocket calculation" doesn't add anything valuable to the article, and certainly doesn't add enough to justify its length.--] (]) 15:36, 17 March 2008 (UTC)
:Seconded. ] (]) 09:14, 7 May 2008 (UTC)
== Making the article easier to understand ==
The twin paradox is much easier to understand if one imagines a long line of stationary, evenly spaced, and synchronized clocks extending from the stationary twin to the point where the other twin turns around. Imagine that as these clocks pass the moving twins window a strobe flashes so he can read off the elapsed time. Even though the non-moving twins clock seems to the moving twin to be ticking at half the rate of his own, the elapsed time, as told by the clock immediately outside his window, is passing at twice the rate of his own. More importantly, just before he stops, in order to turn around, the line of clocks are, from his perspective, out of synch but the moment he stops the line of clocks will be perfectly synchronized again which means that the nonmoving twins clock now reads the same as the clock he is next to. That means that his calculation of what the nonmoving twins clock said jumps suddenly while he decelerates (which leads to general relativity).
Of course, this doesnt add anything to the article that wasnt there before but it does make it easier to understand. ] (]) 08:17, 20 May 2008 (UTC)
:There are language and reference problems in your essay. Also sounds like ] because most of the time dilation issues in the article are discussion points on old/accepted papers and books on relativity, and you quote none. ] (]) 02:55, 21 May 2008 (UTC)
::First, its a suggestion not as essay. Second, it can be rewritten by anyone to any form they like. Third, since it doest change anything or add anything to the article that wasn't there before and moreover since every statement made is trivial I dont see why a citation would be necessary. I am simply suggesting it as a way of illustrating what is being talked about. ] (]) 03:57, 21 May 2008 (UTC)
::Where do you draw the line between stating the obvious and publishing original research? If one can do nothing but repeat what has already been published and one cant even make a trivial observation then I have to question the usefulness of WP. People can read the published articles themselves. They look to wikipedia to illustrate and explain these complex ideas in simple terms. At least, I do. ] (]) 08:45, 24 May 2008 (UTC)
== Terracentric universe, redux??? ==
I'm a bit confused.
Surely the homebody is subject to several sources of rotational accelaration: the Earth's axial rotation, the Earth's orbit around the sun and the sun's orbit around the galactic core, as well as whatever gravitation forces are affecting the Milky Way's celestial transit.
There's one bit that may address this, but I've no way of knowing whether it actually does or not:
''The standard textbook approach treats the twin paradox as a straightforward application of special relativity. Here the Earth and the ship are not in a symmetrical relationship: the ship has a "turnaround" in which it undergoes '''non-inertial''' motion, while the Earth has no such turnaround.'' (my emphasis)
So does this "non-inertial" bit mean that relativity doesn't apply to gravitational acceleration? Or is it that the acceleration experienced by the Earth is negligible in relativistic terms (the speed of the Earth's rotation being a sixth of a millionth of c, and orbit a ten thousandth)?
I think we should be told!
] (]) 14:16, 4 July 2008 (UTC)
: The twin paradox is a ], and as such assumes a simplified set-up. In this context "Earth" is meant to represent an inertial observer, one that doesn't undergo accelerations. To avoid confusing readers like Prof Wrong, the article should use something else, like another spaceship, or at least point out that the of effect of accelerations on Earth-based observers is negligible compared to what the traveler suffers. ] (]) 00:24, 1 May 2009 (UTC)
== Capitalisation ==
A quick check in a couple of well known text books ('Introducing Einstein's Relativity' by Ray d'Inverno and 'Special Relativity and its Experimental Foundations' by Yuan Zhong Zhang) confirmed that 'special relativity is not normally capitalised. ] (]) 10:09, 31 December 2008 (UTC)
:Indeed, Downwards' was on the mark, Eeekster's was off. ] (]) 12:18, 31 December 2008 (UTC)
== Article needs massive rewrite ==
The twin's paradox is poorly stated here. The issue of acceleration is a red herring. The real paradox is this: If Twin T travels in an inertial frame near the speed of light, he doesn't age according to Twin S in the stationary frame. This is an experimental fact: Therefore, Twin T outlives Twin S, according to Twin S.
All inertial frames are equivalent. Therefore, according to Twin T, it is Twin S that is moving near the speed of light. Therefore, according to Twin T, Twin S dies first.
The paradox is that we have two apparently contradictory histories: in one history Twin T outlives Twin S, and in the other history things are reversed. Paradox occurs because we believe that only one of these two histories can be true.
I'd guess that the resolution of this paradox is not in any acceleration, because we need not speculate upon a return trip to establish matters. The resolution may be that simultaneity of events is not universally agreed upon. So various observers in various frames all will have varying views of which twin died first.
What say you? ] (]) 22:09, 1 January 2009 (UTC)
: Muon lifetime is not directly related to the twin paradox. The essence of the TP is that both twins are together at one event, get separated, and then reunite in another event, arranged in such a way that, between those two events, one twin remains in one inertial frame, whereas the other twin does not. The latter either undergoes accelerations, or jumps from one inertial frame to another. Failing to understand this difference is the origin of the paradox. You seem to confuse the TP with so-called mutual time dilation. Check in the Usenet Physics FAQ. ] (]) 22:25, 1 January 2009 (UTC)
::I was just about to say much the same. ] (]) 22:28, 1 January 2009 (UTC)
Maybe you can help me out here. I feel that the usual explanation of the twin paradox provided in the article based upon acceleration really is an easy cop-out that amounts to saying: "Hey, there is no paradox because you broke the rules; you have to stay in an inertial frame." It's true that the rules were broken, but "no fair" is neither a very interesting nor a very persuasive explanation. However, to me there is a more interesting paradox, which does not break the rules. You refer to it as the mutual time dilation paradox, but there seems to be no discussion of same on Misplaced Pages. Is that so?
This paradox is that, with no tricks about acceleration, only different inertial frames, Twin T says that he aged more than Twin S, but Twin T says the opposite.
As an example, suppose Twin S and Twin T move toward each other at speed c/(2 + ε) according to observer O. They both die on his doorstep at the same time. All observers agree on simultaneity of events occurring at the same location. Observer O says that Twin S and Twin T aged the same amount.
Now let O move toward Twin T at constant speed. Then Twin T appears to move rapidly toward rendezvous with a slow clock, while Twin S moves slowly toward rendezvous with a fast clock. We arrange that O arrives at rendezvous exactly as Twins S & T meet and expire. For things to work out, we require that Twin S travel a short distance and Twin T a long distance so both have the same number of clicks on their clocks upon meeting. In other words the rendezvous according to O occurs just enough nearer Twin S's house, and just enough farther from Twin T's house. I suppose this what relativity predicts?
I find this version more interesting because it draws upon relativity of simultaneity, and not a cop-out. ] (]) 23:10, 1 January 2009 (UTC)
:I do not quite follow your example, but it is not what is generally known as the twins paradox, see the history section of the article. ] (]) 23:53, 1 January 2009 (UTC)
:There are plenty of paradoxes in SR based on the relativity of simultaneity, for example the ]. ] (]) 23:57, 1 January 2009 (UTC)
: 'Brews ohare', you're talking about ] or the ], more than the twin paradox, which is a way of using those to show the counterintuitive nature of relativity. You're right that acceleration isn't required for time dilation; you can even do a variation of the twin paradox without acceleration, by having three ships resetting their clocks as they coast past each other.
: I think saying someone is {{'}}''in'' an inertial frame' is problematic. A frame of reference is a set of coordinates overlaid on spacetime — all events of interest can be located in any frame. It's just that some frames are convenient to use, because some events occur at the same time or in the same place.
: You might be interested in the diagram in http://en.wikipedia.org/Talk:Twin_paradox/Archive_12#Stationary_in_relation_to_which_frame.3F showing the events of the twin paradox in the three rest frames, side by side.
:] (]) 23:10, 2 January 2009 (UTC)
I had not looked at the archives; thanks. ] (]) 06:11, 3 January 2009 (UTC)
== Rotational motion ==
Most particle accelerators use rings, and particles move in circles. Circular motion is non-inertial. Thus, it would seem that muon lifetime experiments based upon collider experiments are outside special relativity. See & . Is it just fortuitous that lifetime dilation in circles is the same as in straight paths? Do you know of some discussion of same?
Hello! I added an AI generated image to the article, because this is a subject where no image was present. Explaining the complex idea of the twin paradox requires a helping image, as this is a ], not something that has ''actually'' happened ever.
If the twins were placed on contrary rotating concentric carousels, they could compare lifetimes periodically when they happened to ::meet. If we sit in a stationary frame, and the carousels rotate in opposite directions at the same rate, the twins age the same way, and have the same age each time they meet. Suppose for example, the two twins die simultaneously on their third meeting. Then any observer must agree that this event occurred on the third meeting, because everybody agrees on simultaneity of events occurring at the same location.
Using AI generated images for illustration purposes is not forbidden, (]) and, in this case, there's no free alternative nor artist illustrations for this topic. At ] we can read that "The purpose of an image is to increase readers' understanding of the article's subject matter, usually by directly depicting people, things, activities, and concepts described in the article.", which is exactly what this image is doing. ] (]) 06:21, 24 September 2024 (UTC)
If, on the other hand, we rotate with angular rate Ω, one twin ages faster than the other, according to us. That means one will die earlier, and just how much earlier depends on how fast ''we'' rotate, and not upon the twins at all!! Nonetheless, on their third meeting, both must be observed by us to die, regardless of our Ω.
:About the image generated by artificial intelligence, here is my humble argument in favor/defense of the AI (in this case) and the permanence of the image.
Perhaps the circumference of one carousel shrinks and the other enlarges so the twins always meet at the same number of clicks on their differently paced clocks?? That would require the radii of the carousels to shrink or enlarge, even though the radii are everywhere perpendicular to the rotational velocity, and would lead to increased radial separation of the perimeters of the carousels as ''our'' Ω increases.
:Personally, I am in favor of keeping the image in question. helped me to understand the method adopted by the AI when generating this image. I interpreted (with the help of the aforementioned comment) the apparently exaggerated difference between the ages shown in the image as an educational message. As if the AI were showing the result if, hypothetically, the traveling twin had (without realizing it) exceeded/surpassed the speed of light and continued the trip normally (as if not, obeying the duration times predicted before the start of the trip). Although such an interpretation is beyond the basic proposal of the experiment, it is from my interpretative point of view that the image is extremely valuable as a learning mechanism. The choice of females to represent the twins in the paradox also impressed me a lot. ] (]) 23:44, 25 September 2024 (UTC)
::Agreed. I have reverted that removal because of its extremely clueless rationale:
::{{tqb|Misleading image shows vast age difference. 80 years in deep space or in orbit reduces aging by less than one second over an Earth-bound person by way of gravitational effect; and 80 years in the International Space Station reduces aging by less than two seconds by way of kinematical effect.}}
::Apparently ] missed both the fact that this article is about a thought experiment (rather than a specific calculation about the ISS or something) and that such large age differences have been used by physicists to illustrate the issue since at least ] in 1911, as mentioned in this article ({{tq|Upon return, the traveler will find that he has aged two years, while 200 years have passed on Earth}}). If Donbenladd thinks that all these physicists have been "misleading" the world for over a century and wants to educate the world on this personal theory, they should find a different venue than Misplaced Pages to publicize it (]).
::Regards, ] (]) 22:37, 26 September 2024 (UTC)
::Thanks @] for your comment. The prompt used helped with the age difference, because if you just write "some days older" you won't get any result. The prompt was ''The twin paradox. A twin comes from space travel and finds the other twin to be older. Two twins, one old, the other one dressed as an astronaut, young.''. ] (]) 17:35, 27 September 2024 (UTC)
:I am opposed to the image's inclusion. I don't think it adds much to the article and find it fairly garish – most of the image is superfluous AI hallucination (the spacesuit, the blue magic waves, spacecraft in the background). I think the article stands just fine without an image. If this article ''must'' be illustrated with an image, why not a side-by-side of Mark and Scott Kelly? <span title="Signature of Dan Leonard">— <span style="text-shadow: 2px 2px 8px lightskyblue, -2px -2px 8px forestgreen;font-weight:bold;">]</span> • ] • ]</span> 00:16, 27 September 2024 (UTC)
:: I too am opposed to the image's inclusion. I think it is ridiculous, and opens the door to more ridiculous images.] (]) 04:52, 27 September 2024 (UTC)
:::As for {{tq|garish}} and {{tq|ridiculous}}: Tastes obviously differ, but we are not hosting an art competition here where judges get to enforce their personal aesthetic preferences. Rather, what's important here is if the illustration is likely to help readers understand and remember important points about the article's subject. Lots of texts about relativity use artistic illustrations for that purpose (see e.g. the grotesquely shaped astronaut figures in NASA book.)
:::As for {{tq|opens the door}}, that seems to be a ] ] fallacy. (I mean, for sure not every article benefits from an AI-generated - or human-drawn - illustration. But these decisions need to be made on a case by case basis.)
:::Regards, ] (]) 06:17, 27 September 2024 (UTC)
::{{tq|why not a side-by-side of Mark and Scott Kelly?}} - is that a serious question? Basically for the same reason that Langevin and many other physicists who have discussed this thought experiment since him did ''not'' choose a realistic travel duration and speed: Because the effect would be indetectable to the human eye (three milliseconds age difference for the Kelly twins according to one estimate).
::As for {{tq|AI hallucination}}, that term does not quite make sense here (it's not a photo after all), and not presented as such. Maybe you mean that the illustration would be a bit clearer without that extra detail, which, OK, is a reasonable discussion to have - although I can also see an argument that e.g. the spacecraft help to illustrate the notion of long-distance space travel that is central to the thought experiment. But that's not an argument for assuming that the reader would be better off without any such illustration at all.
::Regards, ] (]) 06:09, 27 September 2024 (UTC)
::Ok! As visual content, I appreciated the art as a whole. But after spending last night talking to my imaginary friends, we came to the conclusion that it is best for me to change my mind and be in favor of not including the image. In favor/defense of those who oppose the inclusion of the image, I believe that the appropriate argumentative basis would be:
::* Possible incompatibility with the usage licenses adopted on Misplaced Pages.
::** Since it is an image generated by artificial intelligence, if it cannot be proven that the terms of use of the AI that generated the image allow it to be republished under the license adopted by us (and that the image was, in fact, generated by such AI), we should not include it in the article (nor keep it on Commons).
::I believe that as a non-governmental, non-profit organization with academic purposes, we are even tolerated by the rest of society, but we cannot (at this time) enjoy this immunity in a way that is contrary to what we have already established as standard rules and ethics.
::Note: It's like explaining to an ex-girlfriend that the problem isn't her. Also saves bandwidth and storage space.
::I thank all the colleagues involved in this discussion (helped me reorganize my reasoning), but especially ], who understood and supported my apparently insane passion for AI-generated works and their "imperceptible flaws".
::If I remember correctly, {{Blockquote|"Intelligence is the ability to adapt to change."|Stephen Hawking}} ] (]) 13:39, 27 September 2024 (UTC)
:::{{tq| if it cannot be proven that the terms of use of the AI that generated the image allow it to be republished under the license adopted by us}} - such speculative legal concerns have long been sorted out, see ] or its Commons ] (and its application to AI-generated media: ]). Similar for {{tq|and that the image was, in fact, generated by such AI}} - we don't require such proof for other kinds of image uploads. But in any case we happen to have such proof in this particular case, as the uploader helpfully linked the Bing Image Creator source page in the file description.
:::Regards, ] (]) 16:22, 27 September 2024 (UTC)
::::Indeed, uploading images created by AI is accepted, and now the Wikimedia Commons uploading wizard even has a check for AI generated images, where the generator used should be specified. However, I made some changes to the image myself, like deleting the US flag the original astronaut image had). ] (]) 17:39, 27 September 2024 (UTC)
::::My only concern was related to the legal aspect of the situation (I'm quite "lazy" when it comes to checking every detail). Since I've seen that my colleagues are experienced (most of them have more than 10 years of experience with Misplaced Pages), I have no intention of opposing whatever is decided.
::::The artistic appeal of the image is wonderful, but I believe that our traditional/conservative colleagues are defending the minimum necessary style (with only the necessary diagrams and calculations). Exactly how classes focused on exact sciences used to be.
::::Note: Impressive (about Bing Image Creator)... Before I gave up and went for Linux, Microsoft didn't allow it that way, so "easily". Thank goodness times are changing, for the better. I think we can go back to agreeing with the famous "Better together”. ] (]) 19:03, 27 September 2024 (UTC)
:::::]
:::::The French Misplaced Pages article '']'' uses diagrams with clocks to illustrate the paradox. These are drawn in a very simple style and could be structured more clearly, but are perhaps more educationally useful than a single drawing of the moment when a young astronaut meets their older twin. ] (]) 11:14, 28 September 2024 (UTC)
::::::I find the clocks very confusing in this illustration; in Theklan's AI image(s) it is much clearer that the space traveling twin is the one who aged less. I agree in principle that using more than one image in the illustration (or even an animation?) could be worth exploring. Regards, ] (]) 12:10, 28 September 2024 (UTC)
::::::I agree with this. The standard illustration of this paradox is a ''diagram'', not two people side-by-side. Even if the image lacked the sci-fi nonsense it would still be a poor illustration of the idea in the article. We can see this example in how others illustrate the paradox:
::::::* {{cite web |title=The twin paradox: Is the symmetry of time dilation paradoxical? |language=en |website=Einsteinlight |publisher=University of New South Wales |url=https://www.phys.unsw.edu.au/einsteinlight/jw/module4_twin_paradox.htm }}
::::::* {{cite book |author1-last=Urone |author1-first=Paul Peter |author2-first=Roger |author2-last=Hinrichs |author3-first=Kim |author3-last=Dirks |author4-first=Manjula |author4-last=Sharma |title=College Physics |language=en |date=2012 |publisher=Rice University |url=https://openstax.org/books/college-physics/pages/28-2-simultaneity-and-time-dilation#import-auto-id983596 |at=Figure 28.8 |isbn=978-1-938168-00-0 |oclc=895896190 }}
::::::* {{cite web |title=Twin paradox part II |language=en |date=2016-04-13 |website=Einstein Relatively Easy |url=https://einsteinrelativelyeasy.com/index.php/special-relativity/47-twin-paradox-part-ii }}
::::::I think if we must illustrate this article, we should follow the visual tradition of past reliable sources in this regard and use a similar diagram. As far as I can tell the three I just cited are non-free so until someone makes such a diagram the article should remain illustrated just by the more abstract spacetime diagrams currently in use. <span title="Signature of Dan Leonard">— <span style="text-shadow: 2px 2px 8px lightskyblue, -2px -2px 8px forestgreen;font-weight:bold;">]</span> • ] • ]</span> 18:42, 28 September 2024 (UTC)
:I don't oppose the use of an AI illustration in general, but I don't like that this one has (a) a portal between the twins and (b) an overabundance of spaceships in the background. ] (] / ]) 12:16, 27 September 2024 (UTC)
::This is a reasonable criticism. (I mean, regarding (b), as mentioned above, I think having ''some'' spacecraft in the background can be useful for conveying the long-distance space travel part of the thought experiment, but that could be done with fewer of them.) {{ping|Theklan}} could you try to work on this e.g. by generating more variations and possibly modifying the prompt? (Or by modifying this particular image directly - I don't know if the current version of Bing Image Creator has that functionality.) Regards, ] (]) 16:22, 27 September 2024 (UTC)
:::I can delete the spacecraft from the image using an image editor. However, I don't know if this will change the mind of others here. ] (]) 17:40, 27 September 2024 (UTC)
::::]
::::Here there is a copy of the same image without spaceships in the background. If someone needs to add something in the back (like an equation) it can be done, for sure. ] (]) 17:45, 27 September 2024 (UTC)
:::::Great, what about (a) (removing the "portal"-like disk/circles between the twins)? Regards, ] (]) 18:01, 27 September 2024 (UTC)
::::::@] that may be more difficult, as there's a light effect for them. I can try, buy it will take more time. ] (]) 18:46, 27 September 2024 (UTC)
:::::::]
:::::::Thanks, looking forward to the next version. In the meantime I have updated the article already with the one that resolves (b).
:::::::For reference (so that the above comments don't become intelligible), here is the original version again.
:::::::Regards, ] (]) 01:41, 28 September 2024 (UTC)
::::::::The sci-fi elements seem extremely distracting and misleading here, I've removed the image while this is still being worked on.
::::::::The focus of the thought experiment is that a person can take an otherwise unremarkable rocket trip and return home to find that their twin has aged. There would be no arcing electricity or glowing portal at this meeting, and no sense of danger in the two siblings touching hands.
::::::::If we think a simple concept like {{tq|the traveler returns home to find his twin brother much aged compared to himself}} needs an illustration, perhaps work from the ground up describing that to your AI, rather than asking it to draw a "paradox" as part of the prompt and trying to manually clean up its wild sci-fi ideas of what the general concept of "a paradox" would look like if it appeared in front of somebody. ] (]) 10:58, 28 September 2024 (UTC)
{{clr}}
===Arbitrary break===
* Due to a few days of absence, I have not read the above discussion, but I ''fully agree'' with the latest '''removal''' of the image. The image is nicely made, but it adds nothing to the article. On the contrary, it might give the impression that the travelling twin is somewhere in space when their ages are compared, whereas the essence of the paradox, is that the twins are physically reunited when the comparison is made. I.o.w. that ''barrier'' between the twins should not be there. Furthermore, when they are reunited, the travelling twin does not need her space helmet and suit anymore {{smiley}}. - ] (]) 12:21, 28 September 2024 (UTC)
*:As for my removal of the image: The image was at the top of the article -- not adjacent to the History section with the thought experiments where its caption can at least be considered a short-hand reference to thought experiments. As it was, the caption was misleading: "The twin in space is younger than the twin that was on Earth" gives the impression that one twin simply being in space during the twins' lifetime can generate such a vast difference in aging. Such a difference in aging between two twins during the lifetime of the Earth-bound twin can occur only if there is sufficient distance and speed involved. Simply "being in space" cannot generate more than a second of time difference between the twins (unless the "in space" twin is also in orbit, in which case it's still less than three seconds). Not a good idea to give an impression of vast age difference with such prominence at the top of the article. In fact, the caption had an absurd structure: "The twin in space" implies the twin "is" in space, while the other twin "was" on Earth -- and they're not even reunited yet. ] (]) 12:58, 28 September 2024 (UTC)
*::@] This is a ''thought'' experiment, not a real calculation about aging for a given ISS mission. i suggest to see the classical Carl Sagan's ''Cosmos'' for s very similar ageing metaphor, making the point that the paradox wants to make: {{youtube|lPoGVP-wZv8}} ] (]) 17:55, 28 September 2024 (UTC)
*::The thought experiment is usually discussed with respect to the traveling twin moving at approximately {{Mvar|c}}, and has nothing to do with current space travel. It's a standard example of relativistic time dilation for the classroom. <span title="Signature of Dan Leonard">— <span style="text-shadow: 2px 2px 8px lightskyblue, -2px -2px 8px forestgreen;font-weight:bold;">]</span> • ] • ]</span> 18:24, 28 September 2024 (UTC)
*::: FWIW, I agree with this, as usually the twin paradox is about a ''visibly older'' returning twin traveller. But I think that this particular part of the discussion is not really relevant to the question wether the image is warranted in this article. - ] (]) 18:59, 28 September 2024 (UTC)
*{{xtn|], astronaut ] (right) aged 13 milliseconds less than his earthbound twin brother ] (left).<ref name="Anthony 2017">{{cite interview |last=Kelly |first=Scott |subject-link=Scott Kelly (astronaut) |interviewer=] |date=2017-10-29 |title='I came back from space younger than my twin' |language=en |newspaper=The Guardian |quote=I was already six minutes younger than Mark but, as Einstein predicted, I've come back six minutes and 13 milliseconds younger after a year in space. |url=https://www.theguardian.com/science/2017/oct/29/scott-kelly-astronaut-interview-space-younger-twin-endurance |access-date=2024-09-28 |url-status=live |archive-url=https://web.archive.org/web/20171102003113/https://www.theguardian.com/science/2017/oct/29/scott-kelly-astronaut-interview-space-younger-twin-endurance |archive-date=2017-11-02}}</ref><ref name="Luokkala 2019">{{cite book |author1-last=Luokkala |author1-first=Barry B. |author1-link=Barry Luokkala |date=2019 |title=Exploring Science Through Science Fiction |edition=2nd |series=Science and Fiction |language=en |publisher=Springer |publication-place=Cham, Switzerland |doi=10.1007/978-3-030-29393-2 |isbn=978-3-030-29393-2 |oclc=1126541494 |ol=20717998W |page=32 |quote=A year-long experiment conducted aboard the International Space Station (ISS) provides us with a real-life application of the twin paradox. From March 27, 2015, through March 1, 2016, U.S., astronaut Scott Kelly spent nearly a year aboard the International Space Station, while his identical twin brother, Mark Kelly, remained on Earth.}}</ref>]]}}In lieu or in addition to a diagram (which would be optimal), I'd like to propose the following addition to the article. I don't know if it's acceptable at the top of the article (as it's slightly misleading as the visual differences between the brothers are not due to age) but I also am not sure which section of the article would be best for it. <span title="Signature of Dan Leonard">— <span style="text-shadow: 2px 2px 8px lightskyblue, -2px -2px 8px forestgreen;font-weight:bold;">]</span> • ] • ]</span> 19:06, 28 September 2024 (UTC)
{{xtn|{{Reflist-talk}}}}
:: IMO that's more of a (funny) little joke than a useful addition {{smiley}} - ] (]) 19:16, 28 September 2024 (UTC)
:::I'd be inclined to agree; however, when I was looking for a citation I noticed that lots of reliable sources mentioned the 13 ms difference in age when reporting on Kelly's return to Earth. I think it shows that many RSs – including NASA themselves – consider this real-world example a good starting point for laymen to understand the effects of time dilation and the twin paradox. <span title="Signature of Dan Leonard">— <span style="text-shadow: 2px 2px 8px lightskyblue, -2px -2px 8px forestgreen;font-weight:bold;">]</span> • ] • ]</span> 19:19, 28 September 2024 (UTC)
:::: Yes, I'm inclined to change my mind. If there are indeed more relevant sources, the image with the caption and at least two citing sources might be a really good idea after all. It also has a pretty strong ''educational'' advantage: showing the scale of a real world example of the subject. - ] (]) 20:02, 28 September 2024 (UTC)
:::: Actually, I'm beginning to think that this is an excellent suggestion, so as far as I'm concerned, go ahead. - ] (]) 20:04, 28 September 2024 (UTC)
::::: Good job, . It would also be a good idea to put it in another article at the start of ]. - ] (]) 09:10, 29 September 2024 (UTC)
::::::Is the following correct?
::::::Assuming a net lesser aging for Scott over the 340-day period of precisely 0.013 seconds, then it seems that the positive and negative accelerations of launch and re-entry generated 0.0229 seconds of lesser aging for Scott in addition to his lesser aging of 0.0105 seconds due to the kinematical effect of orbital inertial motion (17,900 mph).
::::::I'm basing that on the increased aging for Scott of 0.0204 seconds due to 340 days of weightlessness as per the "Outside a non-rotating sphere" section of the Gravitational time dilation article. (The calculation in that section does not take into account the apparently trivial effect of the rotation of the earth for the twin on the surface of the earth. It also incorporates a "clock at infinite distance" from the earth; but that would be identical to the effect of orbital weightlessness.)
::::::Lesser aging:
::::::10.5 milliseconds kinematical
::::::22.9 milliseconds for positive and negative acceleration
::::::Greater aging:
::::::20.4 milliseconds for weightlessness
::::::Net:
::::::13.0 milliseconds lesser aging
::::::I wouldn't expect the short durations of just a few g's during launch and re-entry to compare so closely to 340 days of zero g vs one g.
::::::It might be nice to get a handle on the specifics of the combined effects in the event that someone might be wondering. ] (]) 14:44, 29 September 2024 (UTC)
:::::::Can't discuss this here per ]. - ] (]) 18:25, 29 September 2024 (UTC)
::::::::Thanks, and I was amazed by the correction to my long-standing misconception. ] (]) 14:08, 1 October 2024 (UTC)
::::::::: {{rto|Donbenladd}} I undid , as that new source () and your talk page comments are of a ] than the existing sources. Please do not make similar changes without getting some kind of ] on ''this'' talk page first, and make sure to bring along more reliable sources to back the discussion — see ]. - ] (]) 16:58, 12 October 2024 (UTC)
::::::::::Just as you were undoing my revision, I did update my talk page with the following:
::::::::::"Why did Scott state 13 milliseconds in his interview per the previously referenced source? Apparently, he was referring to the combination of his combined GR/SR clock-decrease (using roughly 8 milliseconds) and his biological aging increase of roughly 5 milliseconds (that 5-millisecond value we see here and there on the Net)."
::::::::::This would mean that the 13 milliseconds in the caption is including the biological aspect, which of course is outside of the GR/SR time-dilation.
::::::::::I hope you'll check my calculations which confirm the value for GR/SR combined effect as stated in the source I provided.
::::::::::Thanks for directing me to discuss it on this page. ] (]) 17:12, 12 October 2024 (UTC)
:::::::::::I'm beyond absent-minded: 8 - 5 = 3. I had Scott perhaps adding 5 to 8. I have no idea how he arrived at 13 milliseconds. ] (]) 17:23, 12 October 2024 (UTC)
:::::::::::: No, sorry, I'm not going to check your calculations. Here we can only discuss ''based on reliable sources'' along Misplaced Pages standard. - ] (]) 17:28, 12 October 2024 (UTC)
:::::::::::::Thanks. I'll search for a rock-solid source by and by. ] (]) 17:36, 12 October 2024 (UTC)
::::::::::::::Considering that no two sources are equally reliable, shouldn't one use, as a reliable source, the one that contains the correct number as easily verified by consensus-calculation among wikipedia editors of an article -- especially when there is such a large disparity between the two sources regarding the number?
::::::::::::::I read the "Misplaced Pages:Reliable sources" article for which you provided a link. Quartz does not seem to fail any reliability test that I could find in that article.
::::::::::::::See the Misplaced Pages article: https://en.wikipedia.org/Quartz_(publication)
::::::::::::::Quartz is a large international publication founded in 2012 by members of Bloomberg, The Economist, The New York Times and The Wall Street Journal.
::::::::::::::The source is very reliable. It seems the only thing missing is a consensus here on which of the two reliable sources provide the correct number. The calculation can be done in just a couple minutes.
::::::::::::::I will give this a rest for now. ] (]) 18:15, 12 October 2024 (UTC)
:::::::::::::::My opinion is that the twin paradox is unresolved and that there is no definite right answer that has consensus. I would say that something that has the consensus of Bloomberg, The Economist, The New York Times, and The Wall Street Journal is necessarily unreliable on the present topic. The problem is conceptual, not to be resolved by simple calculations.] (]) 00:20, 13 October 2024 (UTC)
::::::::::::::::The theoretical combined effects of GR and SR on time-keeping have been extensively experimentally tested. The predictions of time-dilation are in agreement with experimental results, and were made using the same simple equations that are applied to the ISS mission, as seen in the graph which is part of the section linked to above.
::::::::::::::::In fact, the graph indicates 25 microseconds per day (8.5 milliseconds per 340 days) combined SR/GR time-difference for ISS, in keeping with those simple equations. ] (]) 00:58, 13 October 2024 (UTC)
:::::::::::::::::Thank you for your response. I can see that you feel that it is all sorted. I would say that different processes can be affected differently by acceleration. In particular, I don't see why biological aging will be affected by acceleration in the same way that atomic clocks are.] (]) 01:58, 13 October 2024 (UTC)
== The caption for the Scott & Mark Kelly image ==
So a more likely explanation seems to be that our notion of the angular rate of the carousels changes with our Ω in a way that reconciles the clocks of the twins? The faster clock must travel less far than the slower clock before rendezvous, so rendezvous occurs at the same number of clicks on each clock? ] (]) 01:23, 2 January 2009 (UTC)
The Scott & Mark Kelly image replaced the AI image.
:Well, exploration of the literature shows that this subject is complicated by gravitational time dilation. I haven't found a thorough discussion, though I added some "Further Reading" to the article. ] (]) 04:40, 2 January 2009 (UTC)
One of the sources (ref 1) in the current caption gives a value of 13 milliseconds simply by way of quoting Scott Kelly, who gave no indication of whether that was a GR/SR effect, a biological effect of orbital weightlessness, or some combination of the two. The other source (ref 2) has a non-functioning specific link (OL 20717998W: Bing: "can't reach this page"), so I could find nothing there to corroborate ref 1.
::I removed the totally ridiculous vanity-press book you added, but I question the "further reading" section entirely. There are already (way too many) external sources in the ] article. This section adds nothing to the article and just invites people to add or spam their personal favorites, or use internet searches to book-mine potentially crappy sources they have never read or do not understand. ] (]) 06:45, 2 January 2009 (UTC)
Nor can I find any source on the Net that specifies 13 milliseconds without simply repeating Scott's words as quoted in the article referenced (ref 1 in the caption).
:Brews, referring to your "''...particles move in circles. Circular motion is non-inertial. Thus, it would seem that muon lifetime experiments based upon collider experiments are outside special relativity.''". Please note that circular motion and even non-inertial motion is '''completely and 100% within''' the realm of special relativity. The only thing that is outside SR, is gravitation. ] (]) 16:58, 2 January 2009 (UTC)
If, as seems apparent, Scott was referring to the combination of his combined GR/SR lesser aging (using 8 milliseconds) and a biological age increase of 5 milliseconds due to orbital weightlessness (that 5-millisecond value we see here and there on the Net, but which actually refers to six months in orbit aboard ISS and is incorrectly used by Mark Kelly in an interview), and then accidentally added instead of subtracting, he would obtain 13 milliseconds. Easy mistakes to make. But of course, the Twin Paradox article should not include any aging difference relating to the effect of orbital weightlessness in any case.
::DVdm: It appears that to the stationary observer the rotating clock is slowed by SR but for a rotating observer the clock is slowed by the gravitational time dilation due to centrifugal force. So the effect on clocks seems to be outside SR for the rotating observer (e.g. the muon). Do you agree? See ] (]) 20:50, 2 January 2009 (UTC)
A graph accompanying the Misplaced Pages "Time Dilation" article indicates about 25 microseconds per day (8.5 milliseconds per 340 days) combined SR/GR time-difference for ISS, in keeping with the simple equations for GR and SR time-dilation. And note the smooth lines connecting ISS to all the satellites.
:::Brews, I had not (nor have now) read your above comments beyond your first paragraph that I quoted and commented upon. Whatever you had in mind, I had to cut it short early. That's also the reason why I had reverted (without paying sufficient attention,) your section on the rotational version. ] (]) 21:32, 2 January 2009 (UTC)
::::Bear in mind that, if we are going to delve onto this subject, we need to make the distinction between an object that is held in circular motion by gravity (for example the moon) which is in inertial motion, and one that is held in circular motion by other forces (for example a particle in a collider) which is not in inertial motion. I would suggest most of this discussion is outside the scope of this article.] (]) 11:18, 4 January 2009 (UTC)
Quartz, a reliable source by Misplaced Pages standards, states the correct value for the GR/SR combined time difference, which is 8.6 milliseconds. See my talk page.
:::::<s>Yes, by all means. That's why I still think we don't need that little section. I vote for removal. ] (]) 11:21, 4 January 2009 (UTC)</s>
Quartz is described in a Misplaced Pages article: https://en.wikipedia.org/Quartz_(publication)
:::::I have made a correction. I suspected something was wrong, so I checked the reference. See in book on page 227. Since R > 3 mu, we have Delta(Tau_B)/Delta(Tau_A) > 1, so Alice is '''younger''' than Bob. She must be, as can be easily seen from an inertial frame attached to the center of the planet. Alice orbits and Bob does not, so her proper time integral is smaller than his. Afaiac, the section can stay now. I have added the page and a direct scholar search link to the reference. ] (]) 13:07, 4 January 2009 (UTC)
The Quartz article to be referenced:
:Martin: ''an object that is held in circular motion by gravity (for example the moon) which is in inertial motion, and one that is held in circular motion by other forces (for example a particle in a collider) which is not in inertial motion.'' I believe this statement to be an error from the viewpoint of SR, which shares with Newtonian mechanics the view that any accelerated frame, whether the acceleration originates in gravity or a Lorentz force, is a non-inertial motion. ] (]) 16:00, 4 January 2009 (UTC)
::Yes but if we are concerned with gravity we need to use GR as SR cannot deal with gravitation. ] (]) 16:48, 4 January 2009 (UTC)
Without objection, I will change the caption to read:
:::Indeed, but in this particular case we don't really need gravity. After all, Alice's orbital speed can be expressed as a function of the R and mu (which are used in the expression of the proper times ratio). So in this particular case we can ignore gravity, and use her speed w.r.t the inertial frame attached to the center of the planet to calculate her proper time integral. Same conclusion. ] (]) 17:04, 4 January 2009 (UTC)
During the ISS year-long mission, astronaut Scott Kelly (right) aged 8.6 milliseconds less than his Earthbound twin brother Mark (left) due to relativistic effects.
== "Rotational version" irrelevant ==
Howdoesthis section appearirrelevant?It is atwin paradox like that outlined in the intro, withthe difference that the pathsarecircular. In fact, the author of the cited reference draws the parallel several times in the book. ] (]) 20:53, 2January2009 (UTC)
And when the Wayback Machine is online again, I'll add the archived page to the reference. ] (]) 08:11, 13 October 2024 (UTC)
:Oops, sorry, you are right, I wasconfused.Ithoughtyouhad gravitational time dilation in mind,wheretheconceptof"mutualtimedilation"isnot present, andthereforecannotbethecauseofwronglyclaimingsymmetry and thusgeneratingtheparadox.Islightlychangedthetexttomakeitsilently implie that the twinsremain at the samedistancefrom the centerofthegravitatingbody,foriftheydon't, the resultcandependonwhetherBobtravelstowardsorawayfromthecenter and back. ] (]) 21:23, 2January2009 (UTC)
: I don't think that a simple article in ] by some non-notable author is a reliable source, even if Quartz has an article in Misplaced Pages. Many publishers and websites have an article, but are not considered reliable sources. See, for instance the entries on the ] and all the ones marked as unreliable in ]. I think that the combination of a Springer text-book and the Kelly primary source is stronger. - ] (]) 11:48, 13 October 2024 (UTC)
::I didn't claim that the mere existence of a Misplaced Pages article implies Quartz is a reliable source. Rather, I provided a link to that Misplaced Pages article. Higher on this talk page, I wrote: "I read the ] article for which you provided a link. Quartz does not seem to fail any reliability test that I could find in that article." Show me how it fails a reliability test.
::I don't think the combination of the Guardian article and a dead Springer link (show me a quote from the Springer reference) is a stronger source than the Quartz article.
::We have Mark Kelly quoted in a saying that he was another 5 milliseconds older than Scott as a consequence of the ISS mission. The only context in that article is "Einstein's Time Dilation".
::We have Scott Kelly quoted in as saying that he aged 13 milliseconds less than Mark as a consequence of the ISS mission. And Scott's exact words in that article are: "as Einstein predicted, I’ve come back six minutes and 13 milliseconds younger." (He had begun the mission six minutes younger than his twin brother.)
::I don't think Scott or Mark Kelly are reliable sources.
::See the ] accompanying the Misplaced Pages Time Dilation ] as a reality check. ] (]) 13:16, 14 October 2024 (UTC)
:::(Incidentally, the 5-millisecond value Mark Kelly provided seems to be an accidental reference to a European Space Agency release that is referring to a six-month ISS mission (Butch Wilmore and Suni Williams) and to only the SR effect. See the that references the European Space Agency statement. Elsewhere on the Net, a 5-millisecond value is referred to as an effect of simply being weightless for six months, which would be a ridiculous number.) ] (]) 14:53, 14 October 2024 (UTC)
:::: Ok, no problem. - ] (]) 05:33, 20 October 2024 (UTC)
== Contradiction: Acceleration ==
The start of the introduction correctly states that acceleration breaks the symmetry in the Twin Paradox, but the end of the introduction falsely claims that it can be "resolved" without taking into account acceleration somehow. I think this misunderstanding can be traced back to a Fermi Lab Youtube video, in which they simply beg the question of which twin ought to be thought of to be in two seperate inertial frames. The answer is of course acceleration, which the rest of this article correctly points out. ] (]) 13:30, 15 October 2024 (UTC)
== History ==
: Everything can be perfectly explained and "resolved" with or without acceleration, as is shown in ample reliable sources througout the article. - ] (]) 05:32, 20 October 2024 (UTC)
Based on the description of the well known historian A.I. Miller (ref. 1), I rewrote the intro and the history section to include the contributions of ]. Already in 1913 he alluded to the fact, that one twin uses two frames for his journey, while the other remains in one, and this accounts for the different aging. Laue also was the first to illustrate those connections by using Minkowskian spacetime. German (p. 58): ''Von allen Weltlinien, welche zwei gegebene Weltpunkte 1 und 2 verbinden, hat die gerade Verbindung die längste Eigenzeit''. (My translation: ''From all world lines, which connect two given world points 1 and 2, the straight connection has the maximal proper time.") --] (]) 15:42, 4 January 2009 (UTC)
:That is interesting history. The attribution to Lord Halsbury in several papers and texts goes back to a reference supposedly in ''Discovery'' in 1955, which appears in fact to be non-existent, as does Lord Halsbury himself as a contributor to relativity. ] (]) 16:03, 4 January 2009 (UTC)
::Discovery was a British science magazine . They carried part of the ], consisting of letters from Fisher, Mccrea, Dingle, Halsbury and a couple of others, and an article by Bondi. Also commenting on the debate is a rather amusing paper by Goodhart on biological time featuring cold-blooded physicists and astronautical frogs. If somebody wants my scans, drop a line on my talk page. ] (]) 22:29, 30 April 2009 (UTC)
::Correct me if I am mistaken, but I think that the just foregoing remark relies on the clock hypothesis?] (]) 08:09, 20 October 2024 (UTC)
== Separate page for discussion of Twin scenario itself ==
::: <small>Off topic here, but yes, on the ] or simply on the definition of the ], upon which the entire modern formulation of special relativity can be built.</small> - ] (]) 12:36, 20 October 2024 (UTC)
::I only found this error at one place in the article and there is no citation, but rather an argument about two travelers passing each other replacing the outgoing twin. That argument is from a Fermilab Youtube video, which I think is the source of this confusion. Why can one twin be replaced with two travelers rather than the other? The answer is that one is accelerated by the space ship. Indeed that's the only thing breaking the symmetry. All other accounts invariably assume absolute location or absolute motion.
::The rest of the article correctly points this out, it's really just that one sentence. ] (]) 16:39, 28 October 2024 (UTC)
== Elapsed time sections ==
I have set up a ]. Please post your reply there, as this is really the place for discussions on how to improve the article. ] (]) 10:04, 17 January 2009 (UTC)
The sections at the end calculating elapsed time for a rocket with finite acceleration cover two different examples. The first section "as a result of differences in twin' spacetime path" sends the rocket on a short journey, and has the elapsed times T=12, tau=9.33 for the two twins. The section "how to calculate it from the ship" sends the rocket on a longer journey, and has the result T=17.3 and tau = 12.
: Quote from the boilerplate on top of this page: "This is not a forum for general discussion about the article's subject.", and "This" means ''all'' of Misplaced Pages. Please self-delete the page, or at least move it to your user space. The latter would be against Misplaced Pages policy, too, but my interest is limited to keeping the talk page on topic. ] (]) 00:08, 1 May 2009 (UTC)
I was brought to this article by an anti-relativist convinced that this is a contradiction - "the spacetime path method gives T=12, tau=9.33, the spaceship method gives T=17.3, tau = 12". The different methods give different answers.
::On what basis do you claim that 'this' refers to all of Misplaced Pages. I set up a separate page to keep the discussion of the twins paradox itself off the article talk page, something I am sure that you will agree with. If my page were removed there would be little either of us could do to prevent off-topic discussions from taking place on the talk page. There is also the matter of exactly where a subject becomes off-topic. What about someone who wants to change the article because they believe that it is incorrect? Where do they state their case? ] (]) 16:52, 1 May 2009 (UTC)
I think it would be clearer to consider the *same* journey in both cases - I would be willing to redo the calculation and redraw the figures.
== ] ==
Alternatively, it should be made very clear that the two elapsed time calculations apply to different journeys (for reasons...) so should not give the same answer. ] (]) 11:02, 6 December 2024 (UTC)
Is it valid to say that, in the "Specific example" given in the article, the travelling twin effectively moved at 1.73c? I understand the length contraction but for ''practical purposes'' the aim of his trip was to travel 8.9 light years (from the home reference frame) and he accomplished it in 5.14 years (from his own reference frame). ] (]) 11:34, 14 April 2009 (UTC)
:I don't think that it is necessary to recalculate/redraw. Indeed, this is a different voyage than the one shown before, as both schemes take the same assumed total ''point-of-view time'': T=12 (stay-at-home), resp τ=12 (ship), so the results of the calculation of the ''other-one's times'' must be different: τ=9.33 (ship), resp T=17.3 (stay at home).
:Speed is defined as distance divided by time. Normally one does not divide distance as measured by one person by time as measured by another. ] (]) 16:26, 14 April 2009 (UTC)
:Having identical point-of view times is probably better than having different ones, otherwise the choice of phase times of a fraction of 2 units would seem arbitrary. But it is indeed a good idea to explicitly specify this in the caption of the latter image. I have done that: . - ] (]) 13:51, 6 December 2024 (UTC)
Latest revision as of 12:02, 10 December 2024
This is the talk page for discussing improvements to the Twin paradox article. This is not a forum for general discussion of the article's subject.
The subject of this article is controversial and content may be in dispute. When updating the article, be bold, but not reckless. Feel free to try to improve the article, but don't take it personally if your changes are reversed; instead, come here to the talk page to discuss them. Content must be written from a neutral point of view. Include citations when adding content and consider tagging or removing unsourced information.
This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Misplaced Pages. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics
This page has archives. Sections older than 90 days may be automatically archived by Lowercase sigmabot III when more than 10 sections are present.
AI generated image
Hello! I added an AI generated image to the article, because this is a subject where no image was present. Explaining the complex idea of the twin paradox requires a helping image, as this is a thought experiment, not something that has actually happened ever.
Using AI generated images for illustration purposes is not forbidden, (WP:AIIMAGE) and, in this case, there's no free alternative nor artist illustrations for this topic. At WP:IMGCONTENT we can read that "The purpose of an image is to increase readers' understanding of the article's subject matter, usually by directly depicting people, things, activities, and concepts described in the article.", which is exactly what this image is doing. Theklan (talk) 06:21, 24 September 2024 (UTC)
About the image generated by artificial intelligence, here is my humble argument in favor/defense of the AI (in this case) and the permanence of the image.
Personally, I am in favor of keeping the image in question. The comment on the second removal helped me to understand the method adopted by the AI when generating this image. I interpreted (with the help of the aforementioned comment) the apparently exaggerated difference between the ages shown in the image as an educational message. As if the AI were showing the result if, hypothetically, the traveling twin had (without realizing it) exceeded/surpassed the speed of light and continued the trip normally (as if not, obeying the duration times predicted before the start of the trip). Although such an interpretation is beyond the basic proposal of the experiment, it is from my interpretative point of view that the image is extremely valuable as a learning mechanism. The choice of females to represent the twins in the paradox also impressed me a lot. GKNishimoto (talk) 23:44, 25 September 2024 (UTC)
Agreed. I have reverted that removal because of its extremely clueless rationale:
Misleading image shows vast age difference. 80 years in deep space or in orbit reduces aging by less than one second over an Earth-bound person by way of gravitational effect; and 80 years in the International Space Station reduces aging by less than two seconds by way of kinematical effect.
Apparently User:Donbenladd missed both the fact that this article is about a thought experiment (rather than a specific calculation about the ISS or something) and that such large age differences have been used by physicists to illustrate the issue since at least Langevin in 1911, as mentioned in this article (Upon return, the traveler will find that he has aged two years, while 200 years have passed on Earth). If Donbenladd thinks that all these physicists have been "misleading" the world for over a century and wants to educate the world on this personal theory, they should find a different venue than Misplaced Pages to publicize it (WP:NOR).
Thanks @GKNishimoto for your comment. The prompt used helped with the age difference, because if you just write "some days older" you won't get any result. The prompt was The twin paradox. A twin comes from space travel and finds the other twin to be older. Two twins, one old, the other one dressed as an astronaut, young.. Theklan (talk) 17:35, 27 September 2024 (UTC)
I am opposed to the image's inclusion. I don't think it adds much to the article and find it fairly garish – most of the image is superfluous AI hallucination (the spacesuit, the blue magic waves, spacecraft in the background). I think the article stands just fine without an image. If this article must be illustrated with an image, why not a side-by-side of Mark and Scott Kelly? — Dan Leonard • talk • contribs00:16, 27 September 2024 (UTC)
As for garish and ridiculous: Tastes obviously differ, but we are not hosting an art competition here where judges get to enforce their personal aesthetic preferences. Rather, what's important here is if the illustration is likely to help readers understand and remember important points about the article's subject. Lots of texts about relativity use artistic illustrations for that purpose (see e.g. the grotesquely shaped astronaut figures in this NASA book.)
As for opens the door, that seems to be a WP:OTHERCONTENTslippery slope fallacy. (I mean, for sure not every article benefits from an AI-generated - or human-drawn - illustration. But these decisions need to be made on a case by case basis.)
why not a side-by-side of Mark and Scott Kelly? - is that a serious question? Basically for the same reason that Langevin and many other physicists who have discussed this thought experiment since him did not choose a realistic travel duration and speed: Because the effect would be indetectable to the human eye (three milliseconds age difference for the Kelly twins according to one estimate).
As for AI hallucination, that term does not quite make sense here (it's not a photo after all), and not presented as such. Maybe you mean that the illustration would be a bit clearer without that extra detail, which, OK, is a reasonable discussion to have - although I can also see an argument that e.g. the spacecraft help to illustrate the notion of long-distance space travel that is central to the thought experiment. But that's not an argument for assuming that the reader would be better off without any such illustration at all.
Ok! As visual content, I appreciated the art as a whole. But after spending last night talking to my imaginary friends, we came to the conclusion that it is best for me to change my mind and be in favor of not including the image. In favor/defense of those who oppose the inclusion of the image, I believe that the appropriate argumentative basis would be:
Possible incompatibility with the usage licenses adopted on Misplaced Pages.
Since it is an image generated by artificial intelligence, if it cannot be proven that the terms of use of the AI that generated the image allow it to be republished under the license adopted by us (and that the image was, in fact, generated by such AI), we should not include it in the article (nor keep it on Commons).
I believe that as a non-governmental, non-profit organization with academic purposes, we are even tolerated by the rest of society, but we cannot (at this time) enjoy this immunity in a way that is contrary to what we have already established as standard rules and ethics.
Note: It's like explaining to an ex-girlfriend that the problem isn't her. Also saves bandwidth and storage space.
I thank all the colleagues involved in this discussion (helped me reorganize my reasoning), but especially HaeB, who understood and supported my apparently insane passion for AI-generated works and their "imperceptible flaws".
if it cannot be proven that the terms of use of the AI that generated the image allow it to be republished under the license adopted by us - such speculative legal concerns have long been sorted out, see Misplaced Pages:Restricted materials or its Commons c:Commons:Non-copyright restrictions (and its application to AI-generated media: c:Commons:AI-generated_media#Terms_of_use_of_AI_providers). Similar for and that the image was, in fact, generated by such AI - we don't require such proof for other kinds of image uploads. But in any case we happen to have such proof in this particular case, as the uploader helpfully linked the Bing Image Creator source page in the file description.
Indeed, uploading images created by AI is accepted, and now the Wikimedia Commons uploading wizard even has a check for AI generated images, where the generator used should be specified. However, I made some changes to the image myself, like deleting the US flag the original astronaut image had). Theklan (talk) 17:39, 27 September 2024 (UTC)
My only concern was related to the legal aspect of the situation (I'm quite "lazy" when it comes to checking every detail). Since I've seen that my colleagues are experienced (most of them have more than 10 years of experience with Misplaced Pages), I have no intention of opposing whatever is decided.
The artistic appeal of the image is wonderful, but I believe that our traditional/conservative colleagues are defending the minimum necessary style (with only the necessary diagrams and calculations). Exactly how classes focused on exact sciences used to be.
Note: Impressive (about Bing Image Creator)... Before I gave up and went for Linux, Microsoft didn't allow it that way, so "easily". Thank goodness times are changing, for the better. I think we can go back to agreeing with the famous "Better together”. GKNishimoto (talk) 19:03, 27 September 2024 (UTC)
The French Misplaced Pages article Paradoxe des jumeaux uses diagrams with clocks to illustrate the paradox. These are drawn in a very simple style and could be structured more clearly, but are perhaps more educationally useful than a single drawing of the moment when a young astronaut meets their older twin. Belbury (talk) 11:14, 28 September 2024 (UTC)
I find the clocks very confusing in this illustration; in Theklan's AI image(s) it is much clearer that the space traveling twin is the one who aged less. I agree in principle that using more than one image in the illustration (or even an animation?) could be worth exploring. Regards, HaeB (talk) 12:10, 28 September 2024 (UTC)
I agree with this. The standard illustration of this paradox is a diagram, not two people side-by-side. Even if the image lacked the sci-fi nonsense it would still be a poor illustration of the idea in the article. We can see this example in how others illustrate the paradox:
I think if we must illustrate this article, we should follow the visual tradition of past reliable sources in this regard and use a similar diagram. As far as I can tell the three I just cited are non-free so until someone makes such a diagram the article should remain illustrated just by the more abstract spacetime diagrams currently in use. — Dan Leonard • talk • contribs18:42, 28 September 2024 (UTC)
I don't oppose the use of an AI illustration in general, but I don't like that this one has (a) a portal between the twins and (b) an overabundance of spaceships in the background. Firefangledfeathers (talk / contribs) 12:16, 27 September 2024 (UTC)
This is a reasonable criticism. (I mean, regarding (b), as mentioned above, I think having some spacecraft in the background can be useful for conveying the long-distance space travel part of the thought experiment, but that could be done with fewer of them.) @Theklan: could you try to work on this e.g. by generating more variations and possibly modifying the prompt? (Or by modifying this particular image directly - I don't know if the current version of Bing Image Creator has that functionality.) Regards, HaeB (talk) 16:22, 27 September 2024 (UTC)
I can delete the spacecraft from the image using an image editor. However, I don't know if this will change the mind of others here. Theklan (talk) 17:40, 27 September 2024 (UTC)
The same image without spaceships in the background.
Here there is a copy of the same image without spaceships in the background. If someone needs to add something in the back (like an equation) it can be done, for sure. Theklan (talk) 17:45, 27 September 2024 (UTC)
The sci-fi elements seem extremely distracting and misleading here, I've removed the image while this is still being worked on.
The focus of the thought experiment is that a person can take an otherwise unremarkable rocket trip and return home to find that their twin has aged. There would be no arcing electricity or glowing portal at this meeting, and no sense of danger in the two siblings touching hands.
If we think a simple concept like the traveler returns home to find his twin brother much aged compared to himself needs an illustration, perhaps work from the ground up describing that to your AI, rather than asking it to draw a "paradox" as part of the prompt and trying to manually clean up its wild sci-fi ideas of what the general concept of "a paradox" would look like if it appeared in front of somebody. Belbury (talk) 10:58, 28 September 2024 (UTC)
Arbitrary break
Due to a few days of absence, I have not read the above discussion, but I fully agree with the latest removal of the image. The image is nicely made, but it adds nothing to the article. On the contrary, it might give the impression that the travelling twin is somewhere in space when their ages are compared, whereas the essence of the paradox, is that the twins are physically reunited when the comparison is made. I.o.w. that barrier between the twins should not be there. Furthermore, when they are reunited, the travelling twin does not need her space helmet and suit anymore . - DVdm (talk) 12:21, 28 September 2024 (UTC)
As for my removal of the image: The image was at the top of the article -- not adjacent to the History section with the thought experiments where its caption can at least be considered a short-hand reference to thought experiments. As it was, the caption was misleading: "The twin in space is younger than the twin that was on Earth" gives the impression that one twin simply being in space during the twins' lifetime can generate such a vast difference in aging. Such a difference in aging between two twins during the lifetime of the Earth-bound twin can occur only if there is sufficient distance and speed involved. Simply "being in space" cannot generate more than a second of time difference between the twins (unless the "in space" twin is also in orbit, in which case it's still less than three seconds). Not a good idea to give an impression of vast age difference with such prominence at the top of the article. In fact, the caption had an absurd structure: "The twin in space" implies the twin "is" in space, while the other twin "was" on Earth -- and they're not even reunited yet. Donbenladd (talk) 12:58, 28 September 2024 (UTC)
@Donbenladd This is a thought experiment, not a real calculation about aging for a given ISS mission. i suggest to see the classical Carl Sagan's Cosmos for s very similar ageing metaphor, making the point that the paradox wants to make: Video on YouTubeTheklan (talk) 17:55, 28 September 2024 (UTC)
The thought experiment is usually discussed with respect to the traveling twin moving at approximately c, and has nothing to do with current space travel. It's a standard example of relativistic time dilation for the classroom. — Dan Leonard • talk • contribs18:24, 28 September 2024 (UTC)
FWIW, I agree with this, as usually the twin paradox is about a visibly older returning twin traveller. But I think that this particular part of the discussion is not really relevant to the question wether the image is warranted in this article. - DVdm (talk) 18:59, 28 September 2024 (UTC)
During the ISS year-long mission, astronaut Scott Kelly (right) aged 13 milliseconds less than his earthbound twin brother Mark (left).In lieu or in addition to a diagram (which would be optimal), I'd like to propose the following addition to the article. I don't know if it's acceptable at the top of the article (as it's slightly misleading as the visual differences between the brothers are not due to age) but I also am not sure which section of the article would be best for it. — Dan Leonard • talk • contribs19:06, 28 September 2024 (UTC)
References
Kelly, Scott (2017-10-29). "'I came back from space younger than my twin'". The Guardian (Interview). Interviewed by Andrew Anthony. Archived from the original on 2017-11-02. Retrieved 2024-09-28. I was already six minutes younger than Mark but, as Einstein predicted, I've come back six minutes and 13 milliseconds younger after a year in space.
Luokkala, Barry B. (2019). Exploring Science Through Science Fiction. Science and Fiction (2nd ed.). Cham, Switzerland: Springer. p. 32. doi:10.1007/978-3-030-29393-2. ISBN978-3-030-29393-2. OCLC1126541494. OL20717998W. A year-long experiment conducted aboard the International Space Station (ISS) provides us with a real-life application of the twin paradox. From March 27, 2015, through March 1, 2016, U.S., astronaut Scott Kelly spent nearly a year aboard the International Space Station, while his identical twin brother, Mark Kelly, remained on Earth.
I'd be inclined to agree; however, when I was looking for a citation I noticed that lots of reliable sources mentioned the 13 ms difference in age when reporting on Kelly's return to Earth. I think it shows that many RSs – including NASA themselves – consider this real-world example a good starting point for laymen to understand the effects of time dilation and the twin paradox. — Dan Leonard • talk • contribs19:19, 28 September 2024 (UTC)
Yes, I'm inclined to change my mind. If there are indeed more relevant sources, the image with the caption and at least two citing sources might be a really good idea after all. It also has a pretty strong educational advantage: showing the scale of a real world example of the subject. - DVdm (talk) 20:02, 28 September 2024 (UTC)
Actually, I'm beginning to think that this is an excellent suggestion, so as far as I'm concerned, go ahead. - DVdm (talk) 20:04, 28 September 2024 (UTC)
Assuming a net lesser aging for Scott over the 340-day period of precisely 0.013 seconds, then it seems that the positive and negative accelerations of launch and re-entry generated 0.0229 seconds of lesser aging for Scott in addition to his lesser aging of 0.0105 seconds due to the kinematical effect of orbital inertial motion (17,900 mph).
I'm basing that on the increased aging for Scott of 0.0204 seconds due to 340 days of weightlessness as per the "Outside a non-rotating sphere" section of the Gravitational time dilation article. (The calculation in that section does not take into account the apparently trivial effect of the rotation of the earth for the twin on the surface of the earth. It also incorporates a "clock at infinite distance" from the earth; but that would be identical to the effect of orbital weightlessness.)
Lesser aging:
10.5 milliseconds kinematical
22.9 milliseconds for positive and negative acceleration
Greater aging:
20.4 milliseconds for weightlessness
Net:
13.0 milliseconds lesser aging
I wouldn't expect the short durations of just a few g's during launch and re-entry to compare so closely to 340 days of zero g vs one g.
Just as you were undoing my revision, I did update my talk page with the following:
"Why did Scott state 13 milliseconds in his interview per the previously referenced source? Apparently, he was referring to the combination of his combined GR/SR clock-decrease (using roughly 8 milliseconds) and his biological aging increase of roughly 5 milliseconds (that 5-millisecond value we see here and there on the Net)."
This would mean that the 13 milliseconds in the caption is including the biological aspect, which of course is outside of the GR/SR time-dilation.
I hope you'll check my calculations which confirm the value for GR/SR combined effect as stated in the source I provided.
I'm beyond absent-minded: 8 - 5 = 3. I had Scott perhaps adding 5 to 8. I have no idea how he arrived at 13 milliseconds. Donbenladd (talk) 17:23, 12 October 2024 (UTC)
No, sorry, I'm not going to check your calculations. Here we can only discuss based on reliable sources along Misplaced Pages standard. - DVdm (talk) 17:28, 12 October 2024 (UTC)
Considering that no two sources are equally reliable, shouldn't one use, as a reliable source, the one that contains the correct number as easily verified by consensus-calculation among wikipedia editors of an article -- especially when there is such a large disparity between the two sources regarding the number?
I read the "Misplaced Pages:Reliable sources" article for which you provided a link. Quartz does not seem to fail any reliability test that I could find in that article.
Quartz is a large international publication founded in 2012 by members of Bloomberg, The Economist, The New York Times and The Wall Street Journal.
The source is very reliable. It seems the only thing missing is a consensus here on which of the two reliable sources provide the correct number. The calculation can be done in just a couple minutes.
My opinion is that the twin paradox is unresolved and that there is no definite right answer that has consensus. I would say that something that has the consensus of Bloomberg, The Economist, The New York Times, and The Wall Street Journal is necessarily unreliable on the present topic. The problem is conceptual, not to be resolved by simple calculations.Chjoaygame (talk) 00:20, 13 October 2024 (UTC)
The theoretical combined effects of GR and SR on time-keeping have been extensively experimentally tested. The predictions of time-dilation are in agreement with experimental results, and were made using the same simple equations that are applied to the ISS mission, as seen in the graph which is part of the section linked to above.
In fact, the graph indicates 25 microseconds per day (8.5 milliseconds per 340 days) combined SR/GR time-difference for ISS, in keeping with those simple equations. Donbenladd (talk) 00:58, 13 October 2024 (UTC)
Thank you for your response. I can see that you feel that it is all sorted. I would say that different processes can be affected differently by acceleration. In particular, I don't see why biological aging will be affected by acceleration in the same way that atomic clocks are.Chjoaygame (talk) 01:58, 13 October 2024 (UTC)
The caption for the Scott & Mark Kelly image
The Scott & Mark Kelly image replaced the AI image.
One of the sources (ref 1) in the current caption gives a value of 13 milliseconds simply by way of quoting Scott Kelly, who gave no indication of whether that was a GR/SR effect, a biological effect of orbital weightlessness, or some combination of the two. The other source (ref 2) has a non-functioning specific link (OL 20717998W: Bing: "can't reach this page"), so I could find nothing there to corroborate ref 1.
Nor can I find any source on the Net that specifies 13 milliseconds without simply repeating Scott's words as quoted in the article referenced (ref 1 in the caption).
If, as seems apparent, Scott was referring to the combination of his combined GR/SR lesser aging (using 8 milliseconds) and a biological age increase of 5 milliseconds due to orbital weightlessness (that 5-millisecond value we see here and there on the Net, but which actually refers to six months in orbit aboard ISS and is incorrectly used by Mark Kelly in an interview), and then accidentally added instead of subtracting, he would obtain 13 milliseconds. Easy mistakes to make. But of course, the Twin Paradox article should not include any aging difference relating to the effect of orbital weightlessness in any case.
A graph accompanying the Misplaced Pages "Time Dilation" article indicates about 25 microseconds per day (8.5 milliseconds per 340 days) combined SR/GR time-difference for ISS, in keeping with the simple equations for GR and SR time-dilation. And note the smooth lines connecting ISS to all the satellites.
Quartz, a reliable source by Misplaced Pages standards, states the correct value for the GR/SR combined time difference, which is 8.6 milliseconds. See my talk page.
Without objection, I will change the caption to read:
During the ISS year-long mission, astronaut Scott Kelly (right) aged 8.6 milliseconds less than his Earthbound twin brother Mark (left) due to relativistic effects.
I don't think that a simple article in Quartz (publication) by some non-notable author is a reliable source, even if Quartz has an article in Misplaced Pages. Many publishers and websites have an article, but are not considered reliable sources. See, for instance the entries on the WP:SPSLIST and all the ones marked as unreliable in wp:perennial sources. I think that the combination of a Springer text-book and the Kelly primary source is stronger. - DVdm (talk) 11:48, 13 October 2024 (UTC)
I didn't claim that the mere existence of a Misplaced Pages article implies Quartz is a reliable source. Rather, I provided a link to that Misplaced Pages article. Higher on this talk page, I wrote: "I read the Misplaced Pages:Reliable sources article for which you provided a link. Quartz does not seem to fail any reliability test that I could find in that article." Show me how it fails a reliability test.
I don't think the combination of the Guardian article and a dead Springer link (show me a quote from the Springer reference) is a stronger source than the Quartz article.
We have Mark Kelly quoted in a space.com article saying that he was another 5 milliseconds older than Scott as a consequence of the ISS mission. The only context in that article is "Einstein's Time Dilation".
We have Scott Kelly quoted in the Guardian article as saying that he aged 13 milliseconds less than Mark as a consequence of the ISS mission. And Scott's exact words in that article are: "as Einstein predicted, I’ve come back six minutes and 13 milliseconds younger." (He had begun the mission six minutes younger than his twin brother.)
I don't think Scott or Mark Kelly are reliable sources.
(Incidentally, the 5-millisecond value Mark Kelly provided seems to be an accidental reference to a European Space Agency release that is referring to a six-month ISS mission (Butch Wilmore and Suni Williams) and to only the SR effect. See the New York Post article that references the European Space Agency statement. Elsewhere on the Net, a 5-millisecond value is referred to as an effect of simply being weightless for six months, which would be a ridiculous number.) Donbenladd (talk) 14:53, 14 October 2024 (UTC)
The start of the introduction correctly states that acceleration breaks the symmetry in the Twin Paradox, but the end of the introduction falsely claims that it can be "resolved" without taking into account acceleration somehow. I think this misunderstanding can be traced back to a Fermi Lab Youtube video, in which they simply beg the question of which twin ought to be thought of to be in two seperate inertial frames. The answer is of course acceleration, which the rest of this article correctly points out. 2A02:810D:1600:3BF8:7371:A91E:AA0E:C7DF (talk) 13:30, 15 October 2024 (UTC)
Everything can be perfectly explained and "resolved" with or without acceleration, as is shown in ample reliable sources througout the article. - DVdm (talk) 05:32, 20 October 2024 (UTC)
I only found this error at one place in the article and there is no citation, but rather an argument about two travelers passing each other replacing the outgoing twin. That argument is from a Fermilab Youtube video, which I think is the source of this confusion. Why can one twin be replaced with two travelers rather than the other? The answer is that one is accelerated by the space ship. Indeed that's the only thing breaking the symmetry. All other accounts invariably assume absolute location or absolute motion.
The sections at the end calculating elapsed time for a rocket with finite acceleration cover two different examples. The first section "as a result of differences in twin' spacetime path" sends the rocket on a short journey, and has the elapsed times T=12, tau=9.33 for the two twins. The section "how to calculate it from the ship" sends the rocket on a longer journey, and has the result T=17.3 and tau = 12.
I was brought to this article by an anti-relativist convinced that this is a contradiction - "the spacetime path method gives T=12, tau=9.33, the spaceship method gives T=17.3, tau = 12". The different methods give different answers.
I think it would be clearer to consider the *same* journey in both cases - I would be willing to redo the calculation and redraw the figures.
Alternatively, it should be made very clear that the two elapsed time calculations apply to different journeys (for reasons...) so should not give the same answer. PCrayfish (talk) 11:02, 6 December 2024 (UTC)
I don't think that it is necessary to recalculate/redraw. Indeed, this is a different voyage than the one shown before, as both schemes take the same assumed total point-of-view time: T=12 (stay-at-home), resp τ=12 (ship), so the results of the calculation of the other-one's times must be different: τ=9.33 (ship), resp T=17.3 (stay at home).
Having identical point-of view times is probably better than having different ones, otherwise the choice of phase times of a fraction of 2 units would seem arbitrary. But it is indeed a good idea to explicitly specify this in the caption of the latter image. I have done that: . - DVdm (talk) 13:51, 6 December 2024 (UTC)
level-5 vital article is rated B-class on Misplaced Pages's content assessment scale..jpg){kind=small}
. - DVdm (talk) 12:21, 28 September 2024 (UTC)
