Talk:Time dilation/Archive 2012

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Is time dilation a consequence of the signal taking longer to get back to an observer?
In the two mirror experiment when the light returns to the bottom mirror it would take some time for this event to propagate back to the observer. Is time dilation a consequence of this delay? Please clarify. — Preceding unsigned comment added by 199.89.103.11 (talk • contribs)


 * Please sign your messages with four tildes ( ~ ). Thanks.
 * This is where we discuss the article, not the subject. You'll probably get an answer at the Reference desk/Science. Good luck. - DVdm (talk) 18:47, 28 February 2012 (UTC)

Time dilation due to relative velocity symmetric between observers
I believe this to be incorrect that "conversely special relativity dictates the opposite". Example: I travel at 90% the speed of light, visit some places, and come back. My trip took a few seconds. But my friend back home says that I've been gone for years. How did time not speed up outside my spaceship? — Preceding unsigned comment added by 41.164.8.107 (talk) 01:18, 24 March 2012 (UTC)

Speed of light
In Overview, speed of light is quoted as 3B km/hr. That should be 1B. — Preceding unsigned comment added by 220.245.109.183 (talk) 06:37, 25 April 2012 (UTC)


 * I expressed the value as 300,000 km/s, which is more standard. - DVdm (talk) 08:24, 25 April 2012 (UTC)

I don't understand this
Now I'm no physicist, but I consider myself a reasonably intelligent person. However, this part doesn't make any sense, and I've been reading around to figure it out with no luck: "When two observers are in relative uniform motion and uninfluenced by any gravitational mass, the point of view of each will be that the other's (moving) clock is ticking at a slower rate than the local clock." Why would it? I think that should be included in the article. --AW (talk) 00:15, 19 November 2011 (UTC)
 * Anybody? --AW (talk) 01:47, 28 November 2011 (UTC)
 * Not really something that should be discussed in article talk space, which is for discussing content and format of the article, not for explaining or clarifying aspects of the subject to readers. You could try having a look at Consequences of special relativity, and if that doesn't help, you'll certainly get a good set of replies at the wp:reference desk/Science. Search the archives first, as this has been asked many times before, I'm sure. Good luck. - DVdm (talk) 08:10, 28 November 2011 (UTC)
 * But I'm saying the article should be clear when you read it. Maybe just a couple extra lines, like "because in the such and such theory, blah blah blah" or whatever, some explanation. The way it reads now it's just not helpful. --AW (talk) 04:48, 29 November 2011 (UTC)
 * It's just "because of the theory of relativity", so to speak, which is mentioned in the first line of the lead of the article. Further down in the article you find a simple inference of time dilation, and a explanation of the symmetry of the phenomenon. - DVdm (talk) 06:27, 29 November 2011 (UTC)


 * The statement is fundamental to relativity - if each observer did not observe precisely the same magnitude of time dilation in the other then it would be possible to determine which of them was moving and which was stationary - and fundamentally there is no such thing as being stationary in the universe. JohnArmagh (talk) 16:18, 29 November 2011 (UTC)
 * Ok. But it still doesn't read very clearly. There's got to be a way to write it so it makes more sense to the average reader. --AW (talk) 00:27, 9 December 2011 (UTC)
 * The problem is perhaps not one of sense, but of common sense. For the average reader this goes just against common sense. That has always been the problem, and it will probably remain. I think that no matter how we say it, to some it will never make sense. We could add a little phrase like, for instance, "... against common sense..." in there, but that might be editorialising. It's a bit like when we look at each other from a distance through a gap between our fingers, we both say that the other one is smaller than ourselves. Why is that? How would we write that in a way so it makes more sense to the "less-than-average" reader? For most readers (including the illusive average one) this makes sense, as it is part of their every day experience, but it still might be against "less-than-common" sense for some. It's just fundamental to the laws of perspective, and in a Wiki article the larger context of articles and references is supposed to provide the explanation. So I don't think that there is anything we can say to convince our average reader that mutual time dilation makes sense, because for them, it just doesn't. - DVdm (talk) 07:44, 9 December 2011 (UTC)


 * I agree with the OP, he isn't questioning the theory, just the exposition and the article could do more to explain this. The reason is of course just the symmetry of the situation so perhaps an animated gif showing the worldlines of two clocks moving apart with "ticks" as dots and lines of simultaneity projecting onto each other with the view changing between the clocks' rest frames would help clarify it.
 * Phrases like "time 'slowing down'" aren't helpful either, what should be conveyed is that the clocks tick at an unchanged rate per unit of proper time and the observed effects are purely geometric in origin. Descriptions saying "clocks tick more slowly" or worse "time slows down" only reinforce the Newtonian view IMHO. I wish I had the time and tools to contribute this content but I won't be free for some weeks at least.
 * George Dishman (talk) 10:18, 7 May 2012 (UTC)
 * Yes, please. --AW (talk) 21:02, 18 May 2012 (UTC)

Science communication
As usual, I'm trying to add verifiable, more concrete examples of the science at work. Sometimes using illustrations. I just wrote in some stuff about what time dilation might look like in concrete examples with astronauts. I am hoping for constructive criticism on this.- Tesseract2 (talk) 15:16, 24 April 2012 (UTC)


 * Good work. I trimmed it down a bit and made some changes. - DVdm (talk) 08:26, 25 April 2012 (UTC)

More bold editing. This was driven by my own being confused about the twin paradox. I continue to welcome any constructive feedback. - Tesseract2 (talk) 01:47, 16 May 2012 (UTC)

images
I think images are not a luxury - as a reader I find them critical. I appreciate that we have moved these images around before. I would like to justify the current layout.

The lead is very short (and this may be for the best, given the complex subject matter). Still, it was lacking any image. I think the current lead image is descriptive, and captures some compelling aspects of time dilation. At the same time, the overview section is now populated with images that relate to particular ideas being discussed there.

Looking forward to discussion. - Tesseract2 (talk) 02:00, 16 May 2012 (UTC)

Shouldn't this be the opposite?
I'm not an expert but I believe I understand this pretty well. The article says, "a climber's time is passing slightly slower at the top of a mountain (a high altitude, far from the earth's centre of gravity) compared to people at sea level." In the previous paragraph it stated that "velocity and gravity each slow down time as they increase." If an increase in gravity slows down time then a decrease in gravity should speed up time. The climber is farther away from earth's gravity well than people at sea level so his gravity is decreased which should speed up time for him. That leads me to believe that the sentence about the climber is erroneous. 24.249.175.130 (talk) 23:26, 22 May 2012 (UTC)
 * Corrected, thanks. --D.H (talk) 16:00, 23 May 2012 (UTC)

Speed of ISS
The article states the speed of ISS as 0.8 km/s. The orbital speed is 7.7 km/s. Is this some other measure? — Preceding unsigned comment added by 83.86.35.62 (talk) 09:17, 28 May 2012 (UTC)


 * Please put recent comments at them bottom, and sign with four tildes. Thanks
 * Good catch. Average oribital speed is 7.7 km/sec—see artilce ISS. I have removed the unsourced 0.8 thing. - DVdm (talk) 10:56, 28 May 2012 (UTC)

Analysis - Simple inference of time dilation due to relative velocity
The final equation in this section ends with the statement that Δt’ = γ Δt where γ is the Lorentz factor. The conventional relationship between Δt and Δt’ is Δt = γΔt’ (1). These equations are mutually inconsistent, except in trivial cases.

Since the final equation was derived, we should examine the foundational statements.

The first three equations in this section, starting with Δt = 2L/c, are all based on the Euclidean metric. Since the Euclidean metric is not invariant under the Lorentz transform, we should use the more conventional Minkowski metric when dealing with moving reference frames.

The Pythagorean Theorem is only valid using the Euclidean metric. (2)

At a minimum, the third equation for the distance D can not be proven using this theorem.

Less obvious, but maybe more interesting, is the fact that the mirrors, A and B, which are assumed to be parallel in the top drawing will likely not be parallel in the bottom drawing. In any case this implicit assumption needs to be proven without recourse to the Euclidean metric.

The reason that I believe it is unlikely that the mirrors are parallel in the bottom drawing is as follows:

If we assume that there is no relative motion between the mirrors in the top drawing, then we might get by assuming that the space is Euclidean. If it is not Euclidean then the equation Δt = 2L/c would be wrong. However, the bottom drawing clearly shows relative motion between the mirrors and we will need to use the Minkowski metric.

Conformal mappings (maps which preserve angles) require the elements of arclength to be proportionate (3). The elements of arclength for the Euclidean and Minkowski are not proportionate (the Minkowski metric depends on time whereas the Euclidean metric does not).

(1)	Robert Resnick (1968). “Introduction to Special Relativity”: New York, NY John Wiley & Sons  page 63.In limiting form,    Lorentz factor. Definition. Retrieved from http://en.wikipedia.org/wiki/Lorentz_factor (2)	Pythagorean Theorem. Non-Euclidean Geometry. Retrieved from http://en.wikipedia.org/wiki/Pythagorean_theorem (3)	Dirk Struik (1961) “Differential Geometry”: (2nd ed.) Reading, Massachusetts Addison-Wesley Publishing Company, Inc. page 170.

P.S.

The same relationship at the end of this section is restated at the beginning of the section entitled “Time dilation due to relative velocity”. It should be changed to the conventional relationship.

Thanks. Emagnus3 (talk) 00:20, 9 August 2012 (UTC)


 * It all depends on how the variables are defined, and how the physical setup is assumed, so of course the equations are mutually exclusive. In sources where Δt’ = γ Δt is used, the mirrors are at rest in the unprimed system. In sources where Δt = γ Δt' is used, the mirrors are at rest in the primed system. Different setup, different equations. Anyway, the section is backed by four solid sources, including the usage of the Pythagorean theorem, which in this case is used in the context of a spatial vector triangle in the Euclidean geometry of a 2-dim strictly spatial schematic drawing. That is in no way related to the Minkowski metric of spacetime, as there are no time-axes in the drawings. Perhaps, if you have problems understanding this, you might try our wp:Reference desk/Science. I'm sure there will be someone prepared to explain in more detail. Cheers - DVdm (talk) 07:00, 9 August 2012 (UTC)

Contradiction with Article "Space travel using constant acceleration"
The current article here says:


 * Indeed, a constant 1 g acceleration would permit humans to travel through the entire known Universe in one human lifetime.[17]

However, the Article Space travel using constant acceleration says:


 * A journey from the sun to the galactic core at 1G constant acceleration takes 340 years

Both articles use the frame of reference of the spaceship.

So, clearly, one of them must be wrong, except if a human lifetime is thousands of years ;-) — Preceding unsigned comment added by 80.187.102.21 (talk) 16:40, 2 December 2012 (UTC)


 * Good find. The text in the article Space travel using constant acceleration is completely wrong and based on a non-reliable source. I removed some of the junk over there, and all references to that source per wp:RS - DVdm (talk) 21:42, 3 December 2012 (UTC)

Inconsistency in "Velocity time dilation tests"
The simplified solution to the time dilation component of frequency shifting (under section: Velocity time dilation tests) does not agree with the textual conclusion of the section or with the simplified equation presented on the Relativistic Doppler Effect page (under the section: Transverse Doppler effect). I believe the simplified equation should read fdetected = frest/γ. The equation from which this was derived also differs in the transverse portion between these two articles and should be corrected. Trevor.karstens (talk) 21:48, 21 December 2012 (UTC)