Talk:Time dilation/Archive 2020

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How much dilation on the ISS?

The picture caption says 6 months on the ISS, time lags .007 seconds, but the third paragraph of Velocity says it is .005 seconds. I don't know the answer so can't correct one or the other... Pbackstrom (talk) 03:42, 11 January 2020 (UTC)

 Done: the cited source says 0.007. [1]. - DVdm (talk) 10:07, 11 January 2020 (UTC)

The cited source determined 0.007 seconds based on a beta of 3E-5, not a speed of 7,700 m/s. Therefore, the sentence "With current technology severely limiting the velocity of space travel, however, the differences experienced in practice are minuscule: after 6 months on the International Space Station (ISS) (which orbits Earth at a speed of about 7,700 m/s[2]) an astronaut would have aged about 0.007 seconds less than those on Earth" is incorrect, as it is not consistent with the Lorentz factor, nor is it consistent with the cited source. Chriscmanu (talk) 02:14, 6 July 2020 (UTC)C. Manu

@Chriscmanu: thanks for having noticed. Indeed, the original value of .005 seconds was better, as can be seen in both images in section Time dilation#Combined effect of velocity and gravitational time dilation, where the daily (negative) gain for ISS is about -25 microseconds. So in 6 months that results in 0.005 seconds. I have removed the unreliable source with its incorrect numbers and put the correct value in place with a footnote ([2]). - DVdm (talk) 12:10, 6 July 2020 (UTC)

@DVdm: Thanks for making the change. I concur with the change made. Should we also revisit the original comment here? The 1st figure's caption is again inconsistent with the text in the article. Perhaps the caption of the figure should be edited as well. Chriscmanu (talk) 12:43, 6 July 2020 (UTC)C. Manu

 Done: [3]. Thanks again . - DVdm (talk) 12:52, 6 July 2020 (UTC)

FWIW, from Taylor & Wheeler chap 4, page 4-7, equation 13, there applied to GPS, here to ISS:

${\frac {dt_{H}}{dt_{L}}}=1-{\frac {M}{r_{H}}}-{\frac {{v_{H}}^{2}}{2}}+{\frac {M}{r_{L}}}+{\frac {{v_{L}}^{2}}{2}}$ (approx from the Schwarzschild expression)

where

$M=0.742\ 10^{-27}\times 0.597237\ 10^{25}$ (reduced mass per T&W chap 3, page 3-8, eq 10 and Earth),

$r_{L}=6380000$ (radius low per Earth),

$r_{H}=6380000+410000$ (radius high per ISS),

$v_{L}=465/c$ (rotational speed equatorial ground station per Earth),

$v_{H}=7700/c$ (orbital speed satellite per ISS),

$c=3\ 10^{8}$ (light speed),

resulting in

loss per ground second = $1-{\frac {dt_{H}}{dt_{L}}}=2.862\ 10^{-10}$,

and so

daily loss = $\left(1-{\frac {dt_{H}}{dt_{L}}}\right)\times 24\times 3600=24.7\ 10^{-6}$ (the 25 microseconds),

and finally,

half yearly loss = daily loss x 183 = 0.00452.

- DVdm (talk) 13:46, 6 July 2020 (UTC)

About twin paradox

The article explanation about twin paradox is that the earth brother will only experience negligible acceleration, due to rotation and revolution of Earth. In twin paradox page something more intuitive is provided, that the turnover acceleration of the traveling twin makes the difference. I assume that the rotation and revolution of the earth, as explanation, is not only a special case but also it presupposes something useless. It presupposes that the traveling twin direction is perpendicular to the rotation axis or parallel to the plain of revolution. I am a biologist not a physicist, so someone more qualified can explain me.Vardos (talk) 20:47, 16 August 2018 (UTC)

Explanations about this can be on-topic at our wp:Reference desk/Science. Here we discuss the article, not its content. See wp:Talk page guidelines. Good luck. - DVdm (talk) 08:43, 17 August 2018 (UTC)

This criticism appears to be a misapplication of wikipedia rules. The question is directly relevant to the article, and the article is nothing but its content. To argue that users cannot discuss article content would seem to imply that article content can only be changed, and that no discussion about such content can ever take place. This is clearly not the intent of any reasonable set of participation rules. In fact, the Talk page guidelines explicitly say "Comment on content, not on the contributor."

Regarding the initial question, it seems directly relevant to the article, since the explanation currently provided implies, I assume incorrectly, that only differences in acceleration are important in the twin paradox. As the 2013-11-26 version of the article says:

The dilemma posed by the paradox, however, can be explained by the fact that the traveling twin must markedly accelerate in at least three phases of the trip (beginning, direction change, and end), while the other will only experience negligible acceleration, due to rotation and revolution of Earth. During the acceleration phases of the space travel, time dilation is not symmetric.

If only differential acceleration mattered, any acceleration (assuming one could deal with the likely fatality such acceleration would cause to any human twin) to some high % of C, turn-around, and deceleration to again match velocity with the "stationary" twin should be sufficient to induce the same time dilation of a longer term journey. Yet it is my understanding that the length of time the traveling twin actually travels at near C is the primary determining factor in observable time dilation. Assuming that no far weirder effects of relativistic travel than I have read/heard are operating (such that, for example, a 100 year journey at .99999999 C creates the same time dilation as a 1 year journey at .99999999 C), the example given is at the very least incomplete. The earlier observation by Vardos seems directly relevant to the article. LUxlii (talk) 01:58, 27 November 2018 (UTC)

The acceleration explanation is not true, according to FermiLab's Don Lincolm: https://www.youtube.com/watch?v=GgvajuvSpF4 LosD (talk) 09:14, 16 January 2019 (UTC)

if the acceleration is relevant - by changing the frame of reference it would seem that the planet (& the other twin) is equally accelerating away from the spaceship, so not sure this explanation is quite enough yet EdwardLane (talk) 10:21, 8 July 2020 (UTC)

Does time dilation give you extra time?

Does time dilation give you extra time, so that you can get more done? 2A00:23C5:C105:7B00:A8B8:F512:2799:B80D (talk) 18:53, 11 August 2019 (UTC)

Here we can only discuss the article, not its subject—see wp:Talk page guidelines. You can try asking at the wp:Reference desk/Science. - DVdm (talk) 11:45, 12 August 2019 (UTC)

Not convinced this is a good application of those guidelines - seems like the question above effectively is a question of the article - and means that the article needs to be simplified into more natural language. EdwardLane (talk) 10:25, 8 July 2020 (UTC)

If the point of the question is that some specific section of the article needs simplification, it should be stated as such. The way it is, the discussion clearly intends to discuss the topic of the article, and not the article itself. --uKER (talk) 17:03, 8 July 2020 (UTC)

Dilation in parallel movement

I propose including the case of a moving observer traveling parallelly. Since all calculations are elementary arithmetic operations, I would like to invoke WP:CALC. Anyway, readers need more mathematical knowledge to understand the orthogonal case. 84.120.7.178 (talk) 05:05, 31 August 2020 (UTC)

We could only add that other case if there is a reliable source. Otherwise it is wp:original research, and this is way beyond wp:CALC. But the idea of the section is to give a simple inference of time dilation as a consequence of the invariance of light speed, and orthogonal movement w.r.t. to the light signals is the way it is almost always done in the literature. So I don't think we need another way here. - DVdm (talk) 06:35, 31 August 2020 (UTC)

1. You should undo your reversion because the edit is independent of this discussion. It is not original research, but a clarification of the described case. It does not reach any conclusion about the parallel case.

   It is as in Lorentz factor: "The simplest case is a boost in the x-direction."

2. Wikipedia asserts that time dilation is:

   $\Delta t'=\gamma \Delta t$

   This insinuates that it is always true, so WP:NPV is broken.

3. Why do you say this is way beyond WP:CALC? Do you know the result? Do you not understand the calculations? 84.120.7.178 (talk) 14:30, 31 August 2020 (UTC)

1. I undid your edit because it is irrelevant in the context of the section.
2. Without specification of the physical meanings of the variables and the context, that equation is meaningless. This is physics, not mathematics.
3. Yes, I understand the calculations, but what you have in mind, aren't just routine calculations: again this is about a physical situation with a relevant physical context, and a source is needed to establish (1) correctness of the physical reasoning, and, just as importantly, (2) whether the content is wp:noteworthy to be included in Wikipedia to begin with. If no textbook ever mentions it in the context of time dilation inference from light speed invariance, then it has no place in Wikipedia—by design. I don't recall having seen in the literature any inference of time dilation from LS-invariance with a light clock and an observer moving non-perdendicularly w.r.t. the clock. - DVdm (talk) 15:35, 31 August 2020 (UTC)

You say that you understand the calculations. Tell us what is the time dilation in parallel movement and I will be convinced. 84.120.7.178 (talk) 16:15, 31 August 2020 (UTC)

Alas, that is off-topic here on the article talk page per wp:Talk page guidelines; here we cannot discuss the subject, but only the article and proposed changes to it, based on wp:reliable sources.

I know there are many webpages out there where the time dilation of the "horizontal" light clock is shown as some sort of verification, where the reasoning also relies on length contraction of the clock, derived from the Lorentz transformation. But the idea in this section in this article is to infer time dilation from LS invariance (and the Pythagorean theorem) only, in other words, where length contraction is not yet known, let alone the Lorentz transformation. - DVdm (talk) 18:21, 31 August 2020 (UTC)

So you do not understand the calculations after all. Someone should publish the research for the general case first. Thank you for your time . 84.120.7.178 (talk) 22:55, 31 August 2020 (UTC)

Yes, someone should publish the research for the general case first, generating a wp:primary source—that Wikipedia does not really want. As soon as that primary source is discussed and cited in the established literature, there will be wp:secondary sources establishing the noteworthyness of the research—which is what Wikipedia really needs, by design. So patience is what you probably need here. And some luck. - DVdm (talk) 23:07, 31 August 2020 (UTC)

I still believe the section could be improved now. I would add this sentence to the end:

In this reasoning, L is perpendicular to v; thus, it is not affected by length contraction.

Then I would remove length contraction from "See also". 84.120.7.178 (talk) 23:10, 1 September 2020 (UTC)

The reasoning does indeed not depend on length contraction, but neither does it depend on relativity of simultaneity, or on temperature or on atmospheric pressure . But all that is irrelevant in the context of the section. Remember, the section is about inference of a phenomenon (time dilation) from first principles (light speed invariance). Bringing in length contraction here would be wp:original research, and even with a source, it would still be a school book example of wp:synthesis. Unless of course you find a source that —in the context of this particular reasoning— states that LC is not applicable due to the perpendicularity of the clock. None of the four cited sources mention this. The see also entry for length contraction is there because length contraction is another consequence of the postulates. - DVdm (talk) 09:14, 2 September 2020 (UTC)

I disagree with your argument, but do as you wish. You are negligibly benefiting the not-so-smart reader at the expense of not heavily penalizing the smart one. If you had some people reading that section, you would understand my suggestion. Thanks again. 84.120.7.178 (talk) 04:50, 3 September 2020 (UTC)

This explanation of what SYNTH is not may be useful to editors with time travel capabilities. 84.120.7.178 (talk) 08:30, 4 September 2020 (UTC)

Is this source good enough 4U? 84.120.7.178 (talk) 09:35, 5 September 2020 (UTC)

I hadn't seen that before and it looks correct, thanks for sharing. It is not widely cited ([4]) but it is indeed a nice thought experiment to independently infer both length contraction and time dilation from first principles. It is of course a different thought experiment (with a more complicated physical setup) than the usual standard "vertical" clock. Perhaps we can include a little sourced remark at the end of the subsection. Something along the lines of this: "In a thought experiment using a square light clock, both time dilation and length contraction can be independenly infered from fist principles."

References

Afaiac, go ahead... - DVdm (talk) 11:01, 5 September 2020 (UTC)

I would also like to include the part that compares a vertical clock to a horizontal one. I will edit the article later. 84.120.7.178 (talk) 08:40, 6 September 2020 (UTC)

I have added the remark: [5]. For the horizontal clock we need a source. And, of course for a comparison with the vertical clock, we need another source. To make sure we don't anything wp:UNDUE, let's first discuss before we add anything here. - DVdm (talk) 09:13, 6 September 2020 (UTC)

Note, actually, I think that the addition I just made, might be borderline undue—as in hardly covered in the relevant literature—so I undid that ([6]). I think the section is sufficiently complete. Any addition about different types of light clocks would only add needless complication and would surpass the intention of the section. Others, feel free to comment. - DVdm (talk) 09:29, 6 September 2020 (UTC)

You requested a source. I presented you one that supports the comparison explicitly. Are you telling me now that one reliable source is not enough? 84.120.7.178 (talk) 00:29, 7 September 2020 (UTC)

The only things the source says about the vertical clock, are "A thought experiment that includes a square light clock is similar to the traditional vertical light beam and mirror clock, except it is made up of four mirrors placed at a 45^o angle at each corner of a square of length L0, shown in Fig 1." and "The traditional “vertical light clock” and “horizontally moving train” are combined into a single device where the horizontal length of the square light clock is measured independent of time dilation." I.m.o. these are just an introductory statement and a remark, and not really much of a comparison. And again, there are tons of sources for the vertical clock, but just this one (with its few independent cites) for a square clock, and none for the horizontal clock. So I think mentioning it in the context of this section in this article is a bit wp:UNDUE. - DVdm (talk) 10:16, 7 September 2020 (UTC)

Perhaps the article would be best placed in the "Further reading" section. Regardless of how the analysis/comparison turns out, because of the relativity of simultaneity a horizontal light clock in the same frame and spatial location and with the same period as the vertical light clock must exhibit the same time dilation. A comparison might be interesting as a physics exercise, but the result has to be the same in the end, so I agree that a mention in this article would appear as undue weight. --FyzixFighter (talk) 13:39, 7 September 2020 (UTC)

I do not suggest including any physics exercise, but the result you are trying to describe. It is not undue weight. 84.120.7.178 (talk) 02:40, 8 September 2020 (UTC)

• I do not want to talk about square clocks. Please read the source, page 212, paragraph The assertion that T_V = T_H follows from the first principle. 84.120.7.178 (talk) 02:40, 8 September 2020 (UTC)

Yes, T_V = T_H. I don't see how that would be helpful or clarify anything in the context of the section. - DVdm (talk) 08:56, 8 September 2020 (UTC)

I asked you to read the paragraph. I will edit the article in order for you to see the proposal. 84.120.7.178 (talk) 03:45, 9 September 2020 (UTC)

Here is the proposal. 84.120.7.178 (talk) 04:35, 9 September 2020 (UTC)

Ok, unless anyone else objects, I have no problem with that. - DVdm (talk) 09:53, 9 September 2020 (UTC)

It is settled then. Thank you. 84.120.7.178 (talk) 01:05, 11 September 2020 (UTC)

Rescue section "Time dilation in popular culture"

This section would be good for the article to be broad in its coverage, but only if there are secondary sources. List of time travel works of fiction mentions time dilation without references. Planet of the Apes (1968 film), The Ice Pirates, and Andromeda (TV series) do not mention it. Flight of the Navigator, Time Trap (film), and Gunbuster mention it without references. Interstellar (film) has one reference from Jean-Pierre Luminet.

Thus, I would add this small section with the source for Interstellar. I would also move here the sentence about fiction from the lead section. 84.120.7.178 (talk) 08:11, 12 September 2020 (UTC)

This other source if from The New York Times. 84.120.7.178 (talk) 08:34, 12 September 2020 (UTC)

This source is recent. It is from Inverse (website) regarding Time Trap. 84.120.7.178 (talk) 08:50, 12 September 2020 (UTC)

One from North by Northwestern and another one from BBC regarding Interstellar. 84.120.7.178 (talk) 09:10, 12 September 2020 (UTC)

One from Den of Geek that also mentions Planet of the Apes and another from Scientific American and Jon Spaihts about Passengers (2016 film). I think this section is justified. 84.120.7.178 (talk) 09:30, 12 September 2020 (UTC)

For the record, this edit was no Easter egg; look at the source. 84.120.7.178 (talk) 23:40, 28 September 2020 (UTC)

I have looked at the source. Nothing in it warrants a hidden, piped link of the page number, "42", to 42 (number). I have never seen this done for any other reference. Also, this seems contrary to MOS:EGG (hence why I called it an "easter egg"). What is the purpose of linking the page number to 42 (number)? What in the source warrants that hidden, piped link? --FyzixFighter (talk) 00:01, 29 September 2020 (UTC)

"I cannot say what it is"[7] 84.120.7.178 (talk) 00:30, 29 September 2020 (UTC)

Regarding this edit, I would like to point out that I generally use references from sources already present in Wikipedia. 84.120.7.178 (talk) 22:55, 30 September 2020 (UTC)

Not a good idea. It's not because a bad source (a blog) is used somewhere, that it can be used again. Read some thoughts about this in wp:otherstuffexists, so I undid the edit. As a bad wp:primary source, blogs are at best just someone's personal, irrelevant opinion. And the replies shouldn't even be looked at. - DVdm (talk) 23:24, 30 September 2020 (UTC)

I disagree: it is a good idea when combined with other reasons. 84.120.7.178 (talk) 23:40, 30 September 2020 (UTC)

IMO, DVdm is correct. Context matters for sources, especially for blogs and other self-published sources. If Regehr were a known expert on modern science fiction literature, WP:SPS might allow it; or if this were an article on compiler correctness or undefined behavior or on Regehr himself, it might as well. However, I don't see how his blog for this article fits the allowed exceptions of WP:SPS. --FyzixFighter (talk) 01:55, 1 October 2020 (UTC)

... because science fiction writers know more about physics than computer science professors. 84.120.7.178 (talk) 12:05, 1 October 2020 (UTC)

I have finished this section. Expansion should focus on new media, like theater plays or paintings, rather than adding more than three examples per medium. Interstellar and Tau Zero are exceptions because of their coverage; perhaps someone can find similar coverage for other works. 84.120.7.178 (talk) 22:15, 9 October 2020 (UTC)

• Extraordinary claims need a secondary source (t · c) buidhe 04:48, 23 October 2020 (UTC)

Time contraction

Regarding this reversion, what is this arXiv excuse? What is wrong with a source from American Journal of Physics? 84.120.7.178 (talk) 21:00, 11 October 2020 (UTC)

Every once in a while, a bad paper slips through the review process. J. H. Field is a respected experimental physicist who, unfortunately, has turned his hand to theoretical work, publishing in arXiv a series of fringe articles. In arXiv:1405.5174, he says that the Hafele-Keating experiment was incorrectly analyzed and that length contraction is false, thus resolving the Ehrenfest paradox. In arXiv:1307.7962, he claims that length contraction is spurious. In arXiv:1210.2270, he claims that relativity of simultaneity is unphysical. In arXiv:0811.3562, he claims that the conventional analysis of the twin paradox is full of holes. Naturally, he has self-published (arXiv:physics/0612041) an "Einstein was wrong" paper. And so on and so forth. He also has a lot of fringe stuff in arXiv on quantum mechanics. Prokaryotic Caspase Homolog (talk) 22:15, 11 October 2020 (UTC)

... which is one of the many reasons why WP:Reliable sources/Perennial sources says that "arXiv is a self-published source, and is generally unreliable..." - DVdm (talk) 08:09, 12 October 2020 (UTC)

I rephrase the question: On what grounds an article from J. H. Field that is published in American Journal of Physics is deemed as unreliable? 84.120.7.178 (talk) 11:34, 12 October 2020 (UTC)

By reason of the fact that a consensus of Wikipedia editors consider it so. WP:RELIABLE provides guidelines, which are interpreted and enforced by Wikipedia editors in a consensus process. You will find not find it possible to overturn this consensus, so I would advise you to just drop the matter. Prokaryotic Caspase Homolog (talk) 13:41, 12 October 2020 (UTC)

Really? By WP:CCC, I request that you point me to the discussion which establishes that an article from J. H. Field that is published in American Journal of Physics is unreliable. 84.120.7.178 (talk) 14:00, 12 October 2020 (UTC)

This is the discussion. I consider the article, by a known fringe contributor to arXiv, to be unreliable. DVdm also considers it to be unreliable. I suspect that you have some personal stake in seeing the reverted material going into Wikipedia, in which case, WP:CONFLICT may bear on this topic. Prokaryotic Caspase Homolog (talk) 15:07, 12 October 2020 (UTC)

Not much to be found on the topic: Google Books: mostly off-topic, other wp:FRINGE, so definitely wp:UNDUE here. - DVdm (talk) 16:02, 12 October 2020 (UTC)

For the record, I also consider articles by a known fringe contributor (in this case J. H. Field) published at arXiv to be unreliable. Coldcreation (talk) 17:00, 12 October 2020 (UTC)

I ask for the last time here: What does arXiv have anything to do with American Journal of Physics? 84.120.7.178 (talk) 17:15, 12 October 2020 (UTC)

As I stated before, occasional mistakes happen in the review process, and bad papers do get published in reputable journals. That is one reason why Wikipedia also includes recommendations to avoid primary sources whenever possible, but to instead use mainly secondary sources so that primary source material can be put into proper context.

We have so far, without any attempt at "canvassing" on my part, three editors (including me) who agree that material based on J. H. Fields' work should not be in Wikipedia. It will not be allowed in, so give it up. Prokaryotic Caspase Homolog (talk) 18:47, 12 October 2020 (UTC)

So you are implying that this source from Am. J. Phys. is unreliable without any reliable source proving this is the case indeed. I propose a compromise: I will use conditional tense, like "Time contraction would be a similar special relativistic effect", to soften the certainty of the claim. If you disagree and feel we have discussed enough, I will continue to the dispute resolution noticeboard. 84.120.7.178 (talk) 23:35, 12 October 2020 (UTC)

By itself, the unconditional would stack wp:original research on top of an wp:unreliable source, making the edit even worse. - DVdm (talk) 09:00, 13 October 2020 (UTC)

I guess you mean "the conditional would stack". No problem, I will not use conditional. We are not going to reach a compromise. Are we done discussing here? 84.120.7.178 (talk) 14:15, 13 October 2020 (UTC)

Indeed, the conditional, yes. Struck the un. - DVdm (talk) 14:56, 13 October 2020 (UTC)

Note: anon filed Wikipedia:Dispute resolution noticeboard#Time dilation without notifying community. - DVdm (talk) 08:59, 15 October 2020 (UTC)

Note: RFC closed: [8]. - DVdm (talk) 21:46, 21 October 2020 (UTC)

It has now been brought to Wikipedia:Reliable_sources/Noticeboard#J._H._Field_on_American_Journal_of_Physics. Plumbum208 (talk) 09:18, 22 October 2020 (UTC)

The IP editor has been extremely persistent in the discussion on the Reliable Sources Noticeboard. Prokaryotic Caspase Homolog (talk) 03:12, 29 October 2020 (UTC)

• Wikipedia:Fringe theories/Noticeboard#Time contraction --Guy Macon (talk) 19:44, 29 October 2020 (UTC)