Relevant/irrelevant clocks for experimental tests of relativity

[Dale]

I'm asking for are the clocks actually and successfully used in experiments of interest for relativity,

That is fine to ask here, but I will just point out that the answers you are complaining about were not answers to that question. You had asked a different question and the examples you are complaining about now were perfectly good responses to that question then. Even if they are not good responses to this new question.

In principle you could use all of the clocks you complained about in successful relativity experiments, despite the fact that it has not actually been done to date. In other words, actual and successful are separate criteria.

I meant clocks as manmade devices, not some abstractions. (Such a clock, in my opinion, must have at least the following parts: one for generating events, one for counting the events and one for displaying the results.)

There are many clocks that have actually been used for relativity experiments that do not have these parts.

In relativity experiments interferometers are used as clocks that measure a difference in light travel time between two paths. They produce events, don’t count them (usually the difference is less than one event), but do display the result.

A.A. Michelson and E.W. Morley, "On the Relative Motion of the Earth and the Luminiferous Ether", Am. J. Sci. (3rd series) 34 333–345 (1887).
R.J. Kennedy and E.M. Thorndike, "Experimental Establishment of the Relativity of Time", Phys. Rev. 42 400–418 (1932).

And dozens of less famous other experiments.

Lasers, masers, and optical resonators could qualify as clocks having your three parts, with the laser producing events, the Fabry Perot etalon sort of “counting”, and then the interference sort of “displaying”. As long as you aren’t too picky about counting and displaying. Although I think it is a stretch. E.g., see:

A. Brillet and J.L. Hall, "Improved Laser Test of the Isotropy of Space", Phys. Rev. Lett. 42 549–552 (1979)

Mossbauer absorbers really don’t fit your definition. The clocks are nuclear transitions. The “events” are random and the detectors don’t determine the number of events but rather only if the nuclear clocks frequencies match or not.

Isaak et al., Phys. Bull. 21 (1970), pg 255.
Turner and Hill, Phys. Rev. 134 (1964), B252.
Hay et al., Phys. Rev. Lett. 4 (1960), pg 165.
Kuendig, Phys. Rev. 129 no. 6 (1963), pg 2371.
Sherwin, "Some Recent Experimental Tests of the 'Clock Paradox'", Phys. Rev. 129 no. 1 (1960), pg 17.

Muons are also often used as clocks. They are unstable fundamental particles, so they do not have any parts at all. Furthermore, they decay by the weak interaction, so they are not based on EM and the weak interaction bosons are quite massive.

Bailey et al., "Measurements of relativistic time dilation for positive and negative muons in a circular orbit," Nature 268 (July 28, 1977) pg 301.
Bailey et al., Nuclear Physics B 150 pg 1–79 (1979).
Rossi and Hoag, Physical Review 57, pg 461 (1940).
Rossi and Hall, Physical Review 59, pg 223 (1941).
Rasetti, Physical Review 60, pg 198 (1941).
Redei, Phys. Rev. 162 no. 5 (1967), pg 1299.

 

[russ_watters]

My interest is to find if we have any relevant clock for experimental tests of relativity in which the electromagnetic force (and its force carrier, the photon) is not involved in any way in the clock functioning or at least in generating the events measured by the clock.

Is this the basis for an argument that maybe other types of clocks would not show the same results?

 

[PeterDonis]

The clocks are nuclear transitions.

And since the OP asked about fundamental forces, the fundamental force governing these transitions is the strong interaction, not the eletromagnetic interaction. The strong interaction force carriers, gluons, are massless, at least in the theory, but we can't observe them directly so we have no way of actually measuring their mass.

 

[Nugatory]

a twin paradox experiment of the kind described in books

I'm only interested in real experiments, actually performed, like the H-K, not thought experiments.

But the Hafele-Keating is a twin paradox experiment - the experimenters didn’t have access to spaceships capable of traveling at substantial fractions of the speed of light for many months, so they used commercial airliners instead.

 

[Dale]

And since the OP asked about fundamental forces, the fundamental force governing these transitions is the strong interaction, not the eletromagnetic interaction. The strong interaction force carriers, gluons, are massless, at least in the theory, but we can't observe them directly so we have no way of actually measuring their mass.

Most of the experiments I listed use an isotope of iron. The nuclear transition they use for these experiments produces a gamma, and it is mediated by the EM interaction. So it is still an EM interaction even though it is a nuclear transition.

I believe that some pion decays might be pure strong interaction. A lot of other decays involve the strong force together with some other interaction. So I am not sure how to characterize them.

 

[PeterDonis]

The nuclear transition they use for these experiments produces a gamma, and it is mediated by the EM interaction.

The energy of the gamma is determined by the energy levels in the nucleus, though, and that is determined mostly by the strong interaction (though there is an EM component because of the Coulomb repulsion between the protons). Whether that qualifies as using something besides the EM interaction, according to the OP's idiosyncratic criteria, is a question only the OP can answer.

 

[PeterDonis]

I believe that some pion decays might be pure strong interaction.

AFAIK all pion decay modes involve at least one lepton, and therefore involve the weak interaction as well as the strong interaction.

 

[Nugatory]

@DanMP, I am finding myself wanting to ask the same question that @russ_watters asked above:

Is this the basis for an argument that maybe other types of clocks would not show the same results?

If that is in fact the line of thought you are considering, you should say so now - we will get to the point much faster.

 

[Dale]

AFAIK all pion decay modes involve at least one lepton, and therefore involve the weak interaction as well as the strong interaction.

So then I am not sure if there is any pure strong force decay. It may not be since it is so high energy. But this is definitely not my area of expertise.

Whether that qualifies as using something besides the EM interaction, according to the OP's idiosyncratic criteria, is a question only the OP can answer.

I think most people who have made this argument to me would not. But as you say it is up to DanMP. In any case, muon decay is purely weak interaction, and it is quite well studied in this context.

 

[Vanadium 50]

I'm afraid that pion decays are all weak, or in the case of the neutral pion, electromagnetic.

There are other particles that decay strongly, e.g. the rho or the K*. These decays are too fast for practical clocks (an earth-sized conglomeration would decay in under a picosecond) they are fine for a theoretical clock.

I fear that such an example, however, would be declared not to "count" for his purposes. The only thing in the universe that moves faster than light would be the goalposts in this thread.

 

[Dale]

There are other particles that decay strongly, e.g. the rho or the K*.

Are either of those purely strong? Or is it something that decays through multiple interactions?

 

[Vanadium 50]

There are probably no decays that are purely strong. But is 99% strong decays good enough? 99.99%? Some other number?

As an aside, if the strong decay dominates, the next largest component is usually the interference term between strong and EM. Does that count?

 

[pervect]

TL;DR Summary: What clocks can be considered relevant for experimental tests of relativity?

[Mentors' note: Both this summary and the thread title have been edited to clarify that the question is about the physical clocks used in actual experiments - see post #28]

Recently, in this forum, highly respected members referred to clocks like pendulum and hourglass as if they are relevant for relativity. Are they really? Besides the lack of accuracy, they depend on acceleration/gravity, so they would not work at all in inertial frames and they could not indicate properly gravitational time dilation neither. So why even bother mentioning them when asked about clocks in discussions about relativity?

[Mentors’ note: this post has been edited to remove some off-topic provocation]

They're relevant in principle. As for experiment, they're not the best. However, I don't see any focus on actual experimental results from the original poster. It would certainly be something that we could discuss on the forum if the OP expressed an interest in the outcome of actual experiments. So far, though, I see no signs of such interest. The various muon experiments come to mind.

I also feel that the behavior of light is one of the easiest gateways to learn special relativity, requiring less background than other alternate approaches which do exist and have also been discussed on the forums. It's a bit dissappointing that the OP hasn't acknowledged the existence of such alternate approaches to SR or asked question about them.

Both Newtonian physics and special relativity are internally consistent theories, so one cannot decide between them by pure logic without reference to experiment. Pure logic can only demonstrate internal inconsistencies, it cannot distinguish between what actually works (because it's consistent with experiment), and what doesn't work because, it's not consistent with experiment.

Frankly, my impression is that the OP is more interested in arguing than learning. While I suppose there could be some merit to arguing, among those interested in doing it, it's not one of my personal interests. That's especially true when I see the arguments going nowhere. Arguing can serve a purpose with good faith on both sides, which involves paying attention to the weaknesses in the arguments to learn from them, and acknowledging said weak points. Without this basic intellectual honesty, I personally find it pointless and annoying.

 

[phinds]

Frankly, my impression is that the OP is more interested in arguing than learning.

 

[Mister T]

Recently, in this forum, highly respected members referred to clocks like pendulum and hourglass as if they are relevant for relativity.

Relativity is not a theory to be used only when conditions like high speeds prevail. It deals with all measurements of time, regardless of how fast the measurement-making devices are moving relative to each other. So in this sense at least pendulum clocks and hourglasses are relevant for relativity.

(Everything in newtonian physics is relevant for relativity.)

 

[vanhees71]

My interest is to find if we have any relevant clock for experimental tests of relativity in which the electromagnetic force (and its force carrier, the photon) is not involved in any way in the clock functioning or at least in generating the events measured by the clock. Gluons were suggested in the other discussion. Do we have a clock using gluons? After a short search I find that maybe the forthcoming nuclear clock would possibly use gluons.

How do you want to use gluons for anything? Gluons are not asymptotic free states due to confinement and thus cannot be handled as, e.g., photons.

Regarding the muons, what is the speed of the force carrier involved in their decay? It is lower/different than c?

Thank you all for your interest and replies.

Muons decay due to the weak interaction, $\mu^- \rightarrow \mu_{\nu}+\mathrm{e}^- + \bar{\nu}_{\mathrm{e}}$, i.e., their lifetime is governed by the weak interaction.

The universality of the "speed of light" as a "limiting speed" of relativistic spacetime descriptions is an assumption, which can be tested. With highest accuracy the relativistic spacetime model has been confirmed in all experiments/astronomical observations so far.

 

[vanhees71]

And since the OP asked about fundamental forces, the fundamental force governing these transitions is the strong interaction, not the eletromagnetic interaction. The strong interaction force carriers, gluons, are massless, at least in the theory, but we can't observe them directly so we have no way of actually measuring their mass.

The envisaged Th clock is based on an electromagnetic transition ($\gamma$ decay). The reason, why all accurate clocks are using quantum optics is just, because you can handle these systems related to the electromagnetic interaction (atoms, molecules, astomic nuclei, solid-state quantum dots, Josephson junctions, ...) with the highest accuracy.

As you say yourself there are no free gluons or something like gluon coherent states you could use to build any type of clock.

 

[Nugatory]

This thread has reached the point of diminishing returns and is closed.

As with all thread closures we can reopen it if there is something more to say (PM any mentor) but further discussion of whether relativistic effects have never been been observed outside of electromagnetic interactions is not needed.