Talk:Time dilation/Archive 2010

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Other Forces that Dilate Time?
My question is are there other forces or ways two clocks might experience time dilation? Would any cosmic phenomena, stars or forces have an impact on atomic or caesium clocks similar to the effect of traveling at near the speed of light? 209.40.210.222 (talk) 19:48, 23 February 2009 (UTC)


 * I'm no expert, but I believe the answer is yes. Gravitational fields can slow down the passage of time, for objects inside them. Especially with really intense gravity fields like those around Black Holes (read that article for more on that). --Hibernian (talk) 21:15, 27 February 2009 (UTC)

Hibernian is not quite correct. Gravitational time dilation is related to one's position in a gravitational potential, NOT to the strength of the gravitational field at that point. For example, if you had a galaxy-mass black hole, the time dilation near the event horizon would be huge, but the force of gravity would only be around 1G. Anyway, the stationary time dilation factor in General Relativity is e^(φ/c^2) or, in the weak-field approximation, 1+(φ/c^2). In neither case does the field strength (the derivative of φ) enter.

Time dilation due to other forces/fields has been proposed by several authors including Apsel, van Holten, and myself, but this is not widely known in the physics community. Rather than rehash the entire discussion here, I'll simply give some references:
 * D. Apsel, ”Gravitation and electromagnetism”, General Relativity and Gravitation v.10 #4 297-306 (Mar 1979) DOI: 10.1007/BF00759487
 * D. Apsel, ”Time dilations in bound muon decay”, General Relativity and Gravitation v.13 #6 605-607 (Jun 1981) DOI: 10.1007/BF00757247
 * L.C.B. Ryff, ”The Lifetime of an Elementary Particle in a Field”, General Relativity and Gravitation v.17 #6 515-519 (1985)
 * R.G. Beil, ”Electrodynamics from a Metric”, Int. J. of Theoretical Physics v.26 #2 189-197 (1987)
 * J.W. van Holten, ”Relativistic Time Dilation in an External Field”, NIKHEF-H/91-05 (1991)
 * J.W. van Holten, ”Relativistic Dynamics of Spin in Strong External Fields”, arXiv:hep-th/9303124v1 (24 Mar 1993)
 * H.A. Landman. "Quantum Time Dilation" v.1.3, http://www.riverrock.org/~howard/QuantumTime13.pdf (20 Feb 2010)

It is worth noting that there is disagreement among the above authors over whether potentials, or only fields, can cause a time dilation. If it is only fields, then the theory becomes extremely difficult to test (for example van Holten calculates that one might need a 5 GT magnetic field to see significant dilation of a spin-down muon relative to a spin-up muon, which is 8 or 9 orders of magnitude stronger than the strongest fields used in current MRI machines (about 11 T)). On the other hand, if potentials have an effect, then one should be able get about 1% dilation of a muon per 1 MV of electrostatic potential, and the theory should be testable with existing Van De Graaf generators and muon detectors. I am already planning such an experiment.

Potential having an effect violates the gauge invariance of classical EM with respect to potential and, since the Standard Model of particle physics is also gauge invariant, would imply that the SM is wrong. However, it does not violate CPT invariance, as one might naively think it should; see the discussion in my paper.

Since most of the above theories are based on energy, they predict that other forces such as the weak and strong nuclear forces should also cause time dilation. Testing this prediction may be quite difficult. Howard Landman (talk) 15:08, 26 June 2010 (UTC)


 * Intesting as this could or might be, none of this belongs on the talk page of this article. The talk page is for discussing the shape and format of the article, not to discuss its subject or current research about it. The question posed by 209.40.210.222 should not have been answered here. It should have been referred to the science reference desk. I propose we remove this section from this talk page. DVdm (talk) 15:22, 26 June 2010 (UTC)


 * The usual approach, if I understand correctly, is to use and  to collapse the discussion rather than to remove it outright. --Christopher Thomas (talk) 16:48, 26 June 2010 (UTC)

Rhetoric in Need of Refining
The rhetoric used in this article is not specific enough to give an adequate explanation. For example, in the section "Overview of time dilation", it becomes confusing as to which clock is being referred to at what point in the explanation. With the choice of words being used, it could be either of the two clocks that is being referred to. A possible solution for this would be to refer to them as "Clock A" and "Clock B", or something similar to this.

This appears to be a problem throughout the entire article. —Preceding unsigned comment added by 97.127.196.196 (talk) 08:28, 20 January 2010 (UTC)


 * I just read the 'overview' section.  Like many explanations of technical things, it repays a little care in reading. (Also, technical explanation is hardly rhetoric and will not yield its meaning if read as rhetoric.) Nearly all the references to clocks are already specific about what they refer to.  'Clock A', 'clock B' would in several places be factually misleading and wrong, especially when the situation contains two observers, each with their clock, and the subject is what either of them observes about the other's clock. How about these quotes for example:
 * [1] (for time dilation due to relative motion) "the point of view of each will be that the other's (moving) clock is ticking at a slower rate than the local clock".
 * [2] (for time dilation due to proximity to gravitational mass) "each still makes the local clock to be correct; the observer more distant from the mass (higher in altitude) makes the other clock (closer to the mass, lower in altitude) to be slower than the local correct rate, and the observer situated closer to the mass (lower in altitude) makes the other clock (farther from the mass, higher in altitude) to be faster than the local correct rate".
 * How are these not clear? How could references to clock A and clock B be incorporated in a way that leaves the result both clear and correct? Terry0051 (talk) 12:39, 20 January 2010 (UTC)


 * "Rhetoric" is inappropriate here. I'm working up a draft forked from today's state. The article is good but as usual sags at the highest levels. In particular, the effects of travel near c are the interesting effects and may do a calculator for same in my draft. 72.228.177.92 (talk) 07:06, 14 February 2010 (UTC)

Electromagnetic time dilation
I've reverted the the following change, added by : An electromagnetic time dilation, similar to gravitational time dilation, has been proposed by several different authors but is not widely accepted and must be considered speculative until more definitive experimental test.

This was done per discussion at WT:PHYS (with additional replies directed here, to avoid splitting the discussion). I can't speak for others, but my main concerns are:
 * 1) The material was flagged by the original editor as not being widely accepted. I don't think it belongs in the article under those conditions.
 * 2) The last paper cited was published by the editor who added it. This raises substantial WP:COI concerns, given that it's also non-mainstream material.
 * 3) The arguments made in the last paper - that changes in the DeBroglie frequency of matter-wave oscillation represent time dilation in the relativistic sense - are demonstrably false (consider a muon orbiting a proton and a muon orbiting a helium nucleus; they'll have very different frequencies, but the same muon decay half-life).

I invite other editors to present arguments for reinsertion or confirmation of removal. In particular, if anyone can get copies of the other articles cited and comment on them, that'd be very handy. --Christopher Thomas (talk) 00:33, 4 March 2010 (UTC)

Landman replies
Christopher,

On point 1, I was just trying to be honest. However, I have seen a number of online discussions (a couple are mentioned in the History section of my paper) which were basically clueless about the previous history of this idea. If someone thinks that an electromagnetic time dilation might exist, or has questions about it, what are they going to search for and what page will they find? Probably this one. Even after a year of combing the literature, I only found the van Holten papers a few weeks ago. I think there is some public-service value in collecting and publishing these references, as they are hard to identify any other way. Perhaps we need a separate "Electromagnetic Time Dilation" page?

Point 2: I also had some concerns about including my own paper, given that it is still under development and I am only beginning experimental tests this month. I ended up including it, somewhat reluctantly, for completeness, since it is the only one which has any kind of survey of earlier work. I would be completely OK with removing that reference if other people feel that is more honest or produces a higher-quality page.

On point 3 you are completely wrong. See Apsel (1981) and the references therein. The lifetimes of negative muons ARE extended in low-Z atoms, and more so as Z increases. (At higher Z, capture by the nucleus dominates and it becomes impossible to see what the decay lifetime would have been.) This would be predicted to happen to some degree even just from special-relativistic considerations: the muon has an orbital kinetic energy (as given by the virial theorem) which makes its velocity a big enough fraction of c to get some dilation due to motion. What Apsel argues is that the measured lifetime extension is GREATER than can be explained by SR dilation alone, and that his version of the theory gives an additional dilation which more-or-less exactly fills in the discrepancy. (The large table in my paper is my attempt to crank through the same numbers for my version of the theory. I have not yet determined whether it matches Apsel's calculations or the latest experimental data.  The data is surprisingly hard to locate.)

When you say "in the relativistic sense", you need to be clear that it is in the GENERAL relativistic sense, not the special relativistic sense. All three main versions of the theory give a time dilation due to change in potential which is the same for gravitational and electrostatic potential-energy changes; in my own paper I mostly only consider non-relativistic speeds where Newtonian mechanics is still a decent approximation. The dilation does not require close-to-light speeds any more than gravitational time dilation does.

One reason the theory has been controversial is that it violates the principle of classical EM that only fields matter, potentials do not. Many people are loathe to give this up. However, the Aharonov-Bohm effect also violates that principle, and it has been measured and proved true beyond any reasonable doubt. "Nature is not classical, dammit!" -R.P. Feynman

I have PDF of (or URLs for) all of the papers given. Would you like me to mail them to you? I've said pretty much all I have to say about them, at this point, in the History section of my paper. Some other perspectives might be helpful.

199.254.238.4 (talk) 09:13, 6 March 2010 (UTC)

Planet of the Apes example
This example has always bothered me. If the astronauts were traveling near the speed of light, Earth would observe their clock running slowly and them aging slowly. However, likewise, the astronauts would observe Earth's clocks running slowly, and thus it aging slowly as well. What happens when they "return" to Earth? From their observation, Earth should have aged more slowly, thus be BEHIND where they expected, not AHEAD as is implied in the movie and the example given here. But, the astronauts could not have "returned" to Earth without an acceleration involved because they would have had to "turn around" at some point, messing up the "free-fall" motion aspect. So, what would Charlton Heston have really seen upon his return? Earth as he expected given the time gone, Earth in the future, or Earth in the past? Tescher (talk) 02:25, 1 May 2010 (UTC)


 * Please take this to the Science reference desk. This really, really, really is not the place for such. This is where we discuss the content and the format of the article - not of the subject. Thanks and sorry... and good luck over there. DVdm (talk) 08:25, 1 May 2010 (UTC)

Equations for constant acceleration effects are incorrect
The equations listed in the "Time dilation at constant acceleration" are incorrect, both by simple logic and by the equations listed in source 19. To see that they are false, just take the assumption that t=0, that is, no time has passed. The velocity must reduce to Vo (it does), the position to Xo (it does not, and the equation listed gives no reference to Xo at all), and proper time to 0 (it does not) (if no time has passed in one frame, no time will pass in any others). The source given lists the proper equations on p15 and 16, and involve hyperbolic trigonometric functions (cosh, sinh, tanh). —Preceding unsigned comment added by 128.12.15.207 (talk) 11:43, 31 August 2010 (UTC)


 * Note that the article assumes that t0 = x0 = 0. With the abbreviation for &gamma;0, the source's eq (3) page 5 reduces to our article's eq for x(t), resulting in x0 = x(0) = 0. Likewise, the source's eq (4) reduces to our eq for v(t).  Our equation for &tau;(t) seems to have a problem indeed. It produces &tau;(0) = c/(2g) ln( (c+v0)/(c-v0)), so to make it right, we should probably subtract this, or add c/(2g) ln( (c-v0)/(c+v0)) to make it right. But that is not in the source, so how about we just take the source's more general eqs (40), (41) and (42) from page 14 and copy them here?


 * Position:
 * $$x(t) = \frac{c^2}{g} \left( \frac{ \left( 1+ \frac{g x_0}{c^2} \right)^2 }{ \left( 1+ \frac{g x_0}{c^2} \right) \cosh{ \frac{g(t-t_0)}{c} } - \frac{v_0}{c} \sinh{ \frac{g(t-t_0)}{c} } } - 1 \right) $$
 * Velocity:
 * $$v(t) = -c \frac{ \left( 1+ \frac{g x_0}{c^2} \right)^2 \left( \left( 1+ \frac{g x_0}{c^2} \right) \tanh{ \frac{g(t-t_0)}{c} } - \frac{v_0}{c} \right) }{ \left( \left( 1+ \frac{g x_0}{c^2} \right) - \frac{v_0}{c} \tanh{ \frac{g(t-t_0)}{c} } \right)^2 } $$
 * Proper time:
 * $$\tau(t)=\tau_0+ \frac{c}{g} \frac{ \sqrt{ \left( 1+ \frac{g x_0}{c^2} \right)^2 - \left( \frac{v_0}{c} \right)^2 } \left( 1+ \frac{g x_0}{c^2} \right) \tanh{ \frac{g(t-t_0)}{c} }  }{ \left( 1+ \frac{g x_0}{c^2} \right) - \frac{v_0}{c} \tanh{ \frac{g(t-t_0)}{c} } } $$


 * Perhaps we can then also add a special case where t0 = &tau;0 = x0 = 0. I think that would be okay with WP:CALC:
 * Position:
 * $$x(t) = \frac{c^2}{g} \left( \frac{ 1 }{ \cosh{ \frac{gt}{c} } - \frac{v_0}{c} \sinh{ \frac{gt}{c} } } - 1 \right) $$
 * Velocity:
 * $$v(t) = -c \frac{ \tanh{ \frac{gt}{c} } - \frac{v_0}{c} }{ \left( 1 - \frac{v_0}{c} \tanh{ \frac{gt}{c} } \right)^2 } $$
 * Proper time:
 * $$\tau(t)= \frac{c}{g} \frac{ \sqrt{ 1 - \left( \frac{v_0}{c} \right)^2 } \tanh{ \frac{gt}{c} }  }{ 1 - \frac{v_0}{c} \tanh{ \frac{gt}{c} } } $$
 * DVdm (talk) 13:46, 31 August 2010 (UTC)

Hm. Scratch the above. This is something rather different as can be seen in the introduction of section 3, starting page 10. It seems like the original eqs are ok, except perhaps for the last one. If have some time, I'll check it out later. DVdm (talk) 18:06, 31 August 2010 (UTC)


 * Ok, for the time being, I have brought the proper time eq in line with the source's eqs (6) and (9) on pages 5 and 6. Everything seems to fit now. DVdm (talk) 18:32, 31 August 2010 (UTC)

Rest mass?
(warning, I am not physics trained and wikipedia amateur). I find the following statement rather strange: "Current space flight technology has fundamental theoretical limits based on the practical problem that an increasing amount of energy is required for propulsion as a craft approaches the speed of light."

My previous understanding is that the statement above is only true if the accelerating force is being applied from another body e.g. on a particle in an accelerator. Any body, moving at any speed with respect to some other body can consider itself stationary. If it wants to accelerate it only has to use the energy (carried with it of course) to accelerate it's rest mass. If I received a message from a body approaching me at 0.8C saying that I was getting heavier and needed more energy than before I knew that, I think I would ignore it and still expect my car to behave as normal. I fully accept that making an engine to deliver 1G acceleration for several years is gonna be tricky, but a constant energy output is all that is needed, not an ever increasing energy as "speed" (relative to what?) increases.

Anyway ignore this comment if all the physics gurus are happy with the "increasing amount of energy" as relative speed approaches the speed of light - just sounds unlikely to me. Rayfoulkes (talk) 12:46, 21 November 2010 (UTC)


 * You are correct. That reference appears to be in reference to an observer of the body. For example, if we had a satellite accelerating to relativistic speeds, the benefit from adding energy to its speed decreases with increased speed, so fuels become less efficient in terms of velocity per unit energy. The limits the article mentions is that precipitously more fuel would be required for smaller gains in acceleration relative to us.

139.62.83.228 (talk) 03:50, 3 December 2010 (UTC)