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 Wikipedia. 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 articles
Latest comment: 1 month ago46 comments9 people in discussion
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)Reply
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)Reply
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 Wikipedia 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)Reply
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)Reply
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 Wikipedia.
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 Wikipedia: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)Reply
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 Wikipedia), 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)Reply
The French Wikipedia 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)Reply
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)Reply
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)Reply
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)Reply
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)Reply
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)Reply
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)Reply
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)Reply
@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)Reply
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)Reply
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)Reply
During the ISS year-long mission, astronaut Scott Kelly (right) aged 13 milliseconds less than his earthbound twin brother Mark (left).[1][2]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)Reply
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)Reply
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)Reply
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.
No, sorry, I'm not going to check your calculations. Here we can only discuss based on reliable sources along Wikipedia standard. - DVdm (talk) 17:28, 12 October 2024 (UTC)Reply
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 "Wikipedia: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)Reply
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)Reply
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)Reply
Latest comment: 1 month ago5 comments2 people in discussion
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 Wikipedia "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 Wikipedia 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.[1]
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 Wikipedia. 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)Reply
I didn't claim that the mere existence of a Wikipedia article implies Quartz is a reliable source. Rather, I provided a link to that Wikipedia article. Higher on this talk page, I wrote: "I read the Wikipedia: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)Reply
Latest comment: 26 days ago5 comments4 people in discussion
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)Reply
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)Reply
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.
level-5 vital article is rated B-class on Wikipedia's content assessment scale..jpg){kind=small}
. - DVdm (talk) 12:21, 28 September 2024 (UTC)
