Talk:Time dilation/Archive 2015

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Time dilation within other view than scientific view

I think the information Ibensis placed in the Time dilation article (which I reverted, but is now back in) would be better placed in another article (say, on Islam). This article is about a physical phenomenon. Coldcreation (talk) 14:09, 2 January 2015 (UTC)

Thank you for sharing your reason for reverting. So, in my opinion. My information is not breaking any wikipedia rules and policies. As i said before, the information i gave is still relevant with the article and have proper source. While it's not necessary to make a new individual page to talk about time dilation in islamic view, and its more spesific to place here than in Islam article. And since wikipedia is Free encyclopedia not pure scientific journal and the like, my information is rightful to stay in the article. The scientifc info is in the upper part of article, and relevant little trivial information about Time dilation place in the bottom. it will not bothering anyone. i hope your understanding. ibensis (What’s the Story?) 15:44, 2 January 2015 (UTC)

I think it shouldn't be placed anywhere on Wikipedia, as it is a school book example of original research, based on some source—see wp:NOR. I have removed it from the article. - DVdm (talk) 15:47, 2 January 2015 (UTC)

Apparently user Ibensis has restored the content both here and in article Time. Clearly whether this passage in the Quran is really referring to time dilatiion—as described in this article—is a matter of opinion and interpretation of a wp:primary source. As such this is original research. - DVdm (talk) 16:02, 2 January 2015 (UTC)

I agree. The Quran is an outstanding example of a primary source and Ibensis's use of it here and in Time is clearly in breach of policy - see Wikipedia:Verifiability. NebY (talk) 16:26, 2 January 2015 (UTC)

are you really fair with what you talk about. if my information is an original research, then im afraid you must removed most article in wikipedia. after all its just trivia, it said what it said. dont even need to take a research to know it. how about you googling about this to figure its an original research or its just a simple information base on a writting of notable book. please search: the text and number of verses of my paragraph with google search. its easy ibensis (What’s the Story?) 16:31, 2 January 2015 (UTC)

We are fair with what we talk about in so far as we are talking about Wikipedia's policies - please do read about wp:primary sources and wp:original research. Then, unless you can produce reliable wp:secondary sources, please remove, or—if already removed by others—do not restore the addition in both articles. Thanks. - DVdm (talk) 16:36, 2 January 2015 (UTC)

Simple inference of time dilation due to relative velocity

The diagram showing the moving reference frame in this section needs to have the arrows' direction swapped. The moving plate should have the opposite directional velocity than the photon moving at the speed of light. The photon does not receive any lateral velocity input from the plate, it still only moves up and down, the plate is what is moving relative to the photon. Ex: Plate moving -->, photon moving <-- instead of the current which is: Plate moving -->, photon moving --> Xenocide321 (talk) 15:02, 4 February 2015 (UTC)

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The diagram is correct (and backed by 4 sources). This was discussed before—see archives. - DVdm (talk) 15:31, 4 February 2015 (UTC)

i wonder if what just read is accurate or it is my misunderstanding?. "The (time-speeding up) effects of low-gravity would not cancel out these (time-slowing down) effects of velocity unless the ISS orbited much farther from Earth." should this read "unless the ISS orbited much slower" ?Wikimalkindy (talk) 18:59, 15 February 2015 (UTC) i erase my case, my mistake, i was reading the word"farther" as faster !!!Wikimalkindy (talk) 19:02, 15 February 2015 (UTC)

Formula for Schwarzschild metric is not correct

In the subsection Time dilation due to gravity and motion together the formula for the Schwarzschild metric is not quite correct. Further, it is attempted used for a more general situation than its validity (outside a rotation symmetric mass distribution). A similar approximate expression, valid to first order in the gravitational potential, exist. There is a confusion between these two cases. Kåre Olaussen — Preceding unsigned comment added by 89.151.212.160 (talk) 08:27, 4 April 2015 (UTC)

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I don't have access to the first source (Moyer), but looking at the second source (Ashby), starting from the expression of the article,

$dt_{\text{E}}^{2}=\left(1-{\frac {2GM_{\text{i}}}{r_{\text{i}}c^{2}}}\right)dt_{\text{c}}^{2}-\left(1-{\frac {2GM_{\text{i}}}{r_{\text{i}}c^{2}}}\right)^{-1}{\frac {dx^{2}+dy^{2}+dz^{2}}{c^{2}}},\,$

and writing the potential sum as

$\Phi =-{\frac {GM_{\text{i}}}{r_{\text{i}}}},$

we get

$dt_{\text{E}}^{2}=\left(1+{\frac {2\Phi }{c^{2}}}\right)dt_{\text{c}}^{2}-\left(1+{\frac {2\Phi }{c^{2}}}\right)^{-1}{\frac {dx^{2}+dy^{2}+dz^{2}}{c^{2}}},\,$

and thus approximately

$dt_{\text{E}}^{2}\approx \left(1+{\frac {2\Phi }{c^{2}}}\right)dt_{\text{c}}^{2}-\left(1-{\frac {2\Phi }{c^{2}}}\right){\frac {dx^{2}+dy^{2}+dz^{2}}{c^{2}}},\,$

which is the timelike counterpart of Ashby's spacelike form in equation 2, page 3 at Relativity and the Global Positioning System, Ashby:

$ds_{\text{E}}^{2}\approx -\left(1+{\frac {2\Phi }{c^{2}}}\right)(c\ dt_{\text{c}})^{2}+\left(1-{\frac {2\Phi }{c^{2}}}\right)\left(dx^{2}+dy^{2}+dz^{2}\right).\,$

See also equations 10 and 11, page 2-19 of Exploring black holes, Taylor and Wheeler. - DVdm (talk) 09:26, 4 April 2015 (UTC)

So this seems correct and at least consistent with the Ashby source. Can someone check the Moyer source? - DVdm (talk) 09:26, 4 April 2015 (UTC)

The last approximate formula is OK for a distribution of massive static (or slowly moving) sources, as I alluded to. But that does not mean that the expression which was approximated is correct. It isn't, not even for a single point source. Just look up the Wikipedia article on the Schwarzschild geometry: Schwarzschild metric, which looks fine. 2001:700:300:1725:0:0:0:23 (talk) 14:25, 5 April 2015 (UTC)Kåre Olaussen

It still looks correct to me. Can someone with access to the Moyer source please check? - DVdm (talk) 14:39, 5 April 2015 (UTC)

If A implies B, it does not mean that B implies A. The expression is correct (enough) only to first order in $\Phi$. The formula given for the exact Schwarzschild metric is wrong! And it is not the formulas given by Ashby or Moyer (seen http://web.phys.ntnu.no/~kolausen/FY3452/.Moyer.pdf), as indicated by the citation. There only exist an exact formula similar to the Schwarzschild metric for a rotational symmetric matter distribution, not for an arbitrary distribution as presented.2001:700:300:1725:0:0:0:74 (talk) 17:44, 5 April 2015 (UTC) Kåre Olaussen

Ah, you've got that Moyer source, good. So these equations are essentially wp:unsourced, and clearly somebody has been doing some wp:original research here, leading to counter-wiki-policy discussions like this. Good find. In that case either an explicit source should be found to back the exact equations, or we should remove the equations altogether, and take something (perhaps simpler) that can be directly sourced in, for instance, the Taylor and Wheeler book. - DVdm (talk) 18:04, 5 April 2015 (UTC)

For copyright reasons I will have to remove the Moyer file in a little while. I think a section with the Schwarzschild solution with its time dilation formula (which has to be checked) is nice, and should be kept after correction. I can write a draft for that, if you want (and don't find the original text, which was probably right). The general linear approximation of the metric, in the form of the last formula you wrote, is relevant for the GPS system. But I am not sure if one can find a nice analytic expression for the time dilation. That would in any case belong to its own section. There is also an even more general linear approximation for the metric, including contributions from gravitational waves; a recent proposal suggests the use of the accompanying time dilation for detection of gravitational waves. — Preceding unsigned comment added by 2001:700:300:1725:0:0:0:74 (talk) 18:29, 5 April 2015 (UTC)

Well, we're not supposed to make corrections to the formulae here, unless the final results can found in the (established) literature. Wikipedia policy does not allow us to make corrections and recalculations based on equations in the literature—see wp:NOR, wp:SYNTH, and the exception for extrelemy trivial wp:CALC: whatever we would change here would be far beyond basic arithmetic. It is essential that the equations can be directly found in the sources. So to retain the obviously important link to the GPS I propose we take something from this section in Taylor and Wheeler's book, and/or from the Ashby source.. - DVdm (talk) 19:20, 5 April 2015 (UTC)

Technical Aspects of the Clocks

The opening section mentions "This effect arises neither from technical aspects of the clocks nor from the fact that signals need time to propagate, but from the nature of spacetime itself." and I wanted to see the references for such a bold statement. How many different time keeping methods have been used to detect time dilation? Have we detected time dilation using techniques other than atomic clocks? Gavinpalmer1984 (talk) 23:25, 11 November 2015 (UTC)

The statement appears in the lead (—see wp:LEAD—) and is backed by two sources in the body of the article, in the first paragraph of the Overview section. We could add some more, like and , but this is so well known that I guess the two already cited refs should be suffucient. - DVdm (talk) 06:44, 12 November 2015 (UTC)

References