Time dilation explaination with mechanical clock instead of light clock

[Saw]

I agree with DaleSpam's answer to my argument of circular reasoning and withdraw that comment, but still think (thanks harrylin for your comments) that the issue of mechanical clocks and TD calls for a deeper explanation than merely resorting to the PoR.

It is true that to do science (i.e., to solve practical day-to-day problems, which is what this is about, after all) you do not need to answer the ultimate why-questions, but it is also true that you do better science to the extent that you dig more deeply, to the extent that you find better models, which may have higher problem-solving capacity.

For example Newton, Lorentz, and likely Kepler. They did not consider such lack of explanation a scientific feature but instead as an incitement for further scientific investigation. For example, I read somewhere (sorry, don't recall where) that Kepler was himself not happy with his theory because he could not explain the "why"; one had to wait for the answer on Newton who provided a deeper level of insight (just one level deeper, as is usual with that kind of answers).

This is a good example. Kepler's laws were only experimentally based. On those grounds, he said for example (third law) that all planetary motion conforms to the principle T^3/R^2 = constant. But Newton went deeper and understood that gravity is caused by mass and so the mass of the two planets involved in an interaction matters, hence Kepler's rule is only an approximation that exclusively holds when one of the concerned planets has a huge mass compared to which the other's is negligible. Yet... we still have no clue as to why mass generates gravitation force (or the curvature of space-time, if you wish), but Newton's explanation is to be thanked, since it is deeper than Kepler's. BTW, I am not very familiar with GR, but probably space-time curvature is a "deeper" model than Newton's.

Another example: the kinetic theory of heat. We could have contented us with describing that when two bodies get in contact, they conform to the "principle of thermal equilibrium". But knowing that this happens because bodies are composed of particles in motion that collide with each other, is a great insight, which generates many other insights.

Anyhow, leaving the abstract discussion aside... what is the problem with saying that mechanical clocks dilate because the force that causes acceleration (of the moving thing inside the clock) is either light (electromagnetic interaction) or another force that conforms to light's pattern. I know this is not terribly profound, it is quite obvious, but precisely for that, what is wrong with using this answer when somebody asks?

 

[Dale]

the issue of mechanical clocks and TD calls for a deeper explanation than merely resorting to the PoR.

I don't think there is a deeper explantion than the PoR. IMO, the PoR is the deep explanation, and the other ones (e.g. mechanical clocks can in principle be described using QED) are shallower.

Most of modern physics, at the deepest levels, is based on symmetries. The symmetries of nature are the fundamental principles which explain everything else but are not themselves explained by anything. The PoR is one such symmetry.

 

[Saw]

I don't think there is a deeper explantion than the PoR. IMO, the PoR is the deep explanation, and the other ones (e.g. mechanical clocks can in principle be described using QED) are shallower.

Most of modern physics, at the deepest levels, is based on symmetries. The symmetries of nature are the fundamental principles which explain everything else but are not themselves explained by anything. The PoR is one such symmetry.

Again, I read you and "feel" as if you were right, too. This is probably an indication that we have hit on a semantic issue, which -to my taste- does not make it less interesting. It is likely that, if we kept discussing, I ended up agreeing that what you mean by "shallow" is what we mean by "deep". In this line, I can perfectly concede that symmetries are beautiful and they are because they sound and feel like truth: they are usually right and, when they are, they work like binoculars that synthesize in two words (principle, relativity) the widest territory. Am I well in your shoes?

But I think you were too radical in deprecating our own approach as non-scientifical. Again there is nothing wrong in pursuing the idea, let us put it like this (I am getting definitely romantic), that "there is a light clock at the heart of every mechanical clock". Coming back to the example proposed above, "thermal equilibrium" is also an instance of a wider (more abstract) and beautiful principle, which is the tendency to stability of physical systems. That did not prevent scientists, however, to develop the idea that matter particles seek that equilibrium through collisions.

 

[Dale]

For example Newton, Lorentz, and likely Kepler. They did not consider such lack of explanation a scientific feature but instead as an incitement for further scientific investigation.

These seem like counter-examples to your point, they all did what I stated above: they each described how nature works in a few principles, not why those principles worked.

It may be true that they expressed dissatisfaction with that situation, but nevertheless they each did it, and when asked to explain things that could be explained using their "how" principles, they did so.

 

[Dale]

Again there is nothing wrong in pursuing the idea, let us put it like this (I am getting definitely romantic), that "there is a light clock at the heart of every mechanical clock".

I agree with this, and have nothing against pursuing the idea.

What I think is wrong is rejecting out of hand an answer based on a fundamental scientific principle. Particularly, the formulation of the objection that the scientific-principle answer was insuffucient because a "reason why" was needed instead of a "description how". If you are going to classify the PoR as a "description how", then science is fundamentally only capable of "description how" answers.

 

[salvestrom]

These seem like counter-examples to your point, they all did what I stated above: they each described how nature works in a few principles, not why those principles worked.

It may be true that they expressed dissatisfaction with that situation, but nevertheless they each did it, and when asked to explain things that could be explained using their "how" principles, they did so.

Quantum mechanics is a really good example of a theory that allows prediction of an event, yet may not accurately describe the how let alone the why. Interpretation of QM is varied and ongoing. Newton's maths was accurate, while not really describing gravity at all. It seems wrong to say he described how nature worked. All he really had was an equation that arrived at the same answer the universe did. Which is a fantastic achievement, but not to be confused with having any understanding of reality. The same could probably be argued of Realitivity, although it has by far a stronger correlation between the mathematics and the observed reality.

As far as describing mechanical clocks with relativity, I think it's really a case of deciding how time works. Does it actually exist to be slowed and if not, what causes the apparent time dilation.

 

[Saw]

I agree with this, and have nothing against pursuing the idea.

What I think is wrong is rejecting out of hand an answer based on a fundamental scientific principle. Particularly, the formulation of the objection that the scientific-principle answer was insuffucient because a "reason why" was needed instead of a "description how". If you are going to classify the PoR as a "description how", then science is fundamentally only capable of "description how" answers.

Well, yes, you are right. In my original expression, I may have hastily used old mental routines, which in principle I put aside long ago, but sometimes I forget.

In fact, one could even go farther: science does not even describe how "reality" is, it describes how we "interact (through measurement) with reality" and thus solve problems.

In the light of this, pursuing the idea I mentioned is like going into the intricacies of the instrument, the mechanical clock. It is going "more deeply" in the sense of zooming in, making your hands dirty with details, although clearly the PoR is a beautiful shorthand, a master key, a magic word that multi-solves problems with one shot.

 

[Dale]

In the light of this, pursuing the idea I mentioned is like going into the intricacies of the instrument, the mechanical clock. It is going "more deeply" in the sense of zooming in, making your hands dirty with details

I have nothing against that, and looking at the dirty details can often illuminate interesting connections between things that may have previously been assumed to be unrelated.

 

[harrylin]

These seem like counter-examples to your point, they all did what I stated above: they each described how nature works in a few principles, not why those principles worked.

It may be true that they expressed dissatisfaction with that situation, but nevertheless they each did it, and when asked to explain things that could be explained using their "how" principles, they did so.

The (side) issue was your suggestion that not being satisfied with not knowing the deeper "why", would "not want a scientific explanation". I would say that the contrary is true. The scientists that I mentioned either wished for "deeper" explanations (which you perhaps would call shallow explanations) or they postulated deeper explanations (physical models) as working hypothesis on which they founded their theoretical development. Those researches that combined that constructive approach with the application of principles such as symmetry (think also of Maxwell) were really successful.

 

[Dale]

The scientists that I mentioned either wished for "deeper" explanations (which you perhaps would call shallow explanations) or they postulated deeper explanations (physical models) as working hypothesis on which they founded their theoretical development.

Sure, but those deeper explanations they postulated were always descriptions of how nature works, not reasons why it works that way. That is inherent in the scientific method, and that is all I was pointing out.

 

[harrylin]

Sure, but those deeper explanations they postulated were always descriptions of how nature works, not reasons why it works that way. That is inherent in the scientific method, and that is all I was pointing out.

Sorry, here you completely lost me: an explanation is by definition a proposed "reason why"; and those explanations could not be directly verified. However, I agree that it is inherent in the scientific method - as I also tried to point out to you - so we were in a way arguing in agreement?

 

[Saw]

looking at the dirty details can often illuminate interesting connections between things that may have previously been assumed to be unrelated.

That is very true. It is the wisdom of the technician.

so we were in a way arguing in agreement?

So now that we all agree that we were disagreeing while we agreed, could we discuss how to answer the OP based on the details of how a mechanical clock functions?

I myself will try to write something as short as possible.

 

[Dale]

Sorry, here you completely lost me: an explanation is by definition a proposed "reason why"

Not if you classify something like the PoR as a "description how" instead of a "reason why". Under that classification all scientific explanations are fundamentally in the "description how" category.

However, I agree that it is inherent in the scientific method - as I also tried to point out to you - so we were in a way arguing in agreement?

That is the main point, recognizing a limitation inherent in the scientific method, so at least we agree there.

 

[Saw]

I have nothing against that, and looking at the dirty details can often illuminate interesting connections between things that may have previously been assumed to be unrelated.

So if we have permission (hope it is OK with PF rules), I will share my reflections on the subject for your comments.

The (apparent) weakness of the light clock thought experiment is that it bases TD on the fact that "light is different", in that its motion is unaffected by the motion of the source.

The objection some people make is: then TD applies only to light clocks, but not to ball clocks, since the motion of the balls is affected by the motion of the source.

The counter-objection is: balls are like light in their acceleration, which is caused by an EM interaction; any other process responsible for changes (and susceptible of being used for building clocks), like for instance beta decay, follows the same pattern as light, at least in this respect.

The challenge is then showing why this similarity renders the adequate quantitative result, i.e. why light clocks and ball clocks tick exactly alike.

My proposal is the following. If you want a clock that measures absolute time, you need one of these two:

- A moving thing inside the clock with infinitely high velocity.
- A moving thing with infinitely low velocity, that is to say, without acceleration.

Obviously, none of these clocks would "work" since they would not mark changes. But they serve as ideal models against which to compare real clocks:

- Light clocks choose the first reference: they try to accommodate to the fastness ideal.
- Mechanical clocks choose the second, the slowness ideal, from which they only depart to the extent they are accelerated through a "lightlike" process and hence to this extent they conform to light's pattern.

Metaphorically: in the case of mechanical clocks their virtue is slowness, their sin is speed, but their sin comes with an inherent penitence, which is that to the extent they are faster, they are more accelerated and hence more like light.

If you feel like that, we could discuss on the related math. Otherwise, I would not bore you.

 

[Dale]

I wouldn't throw in anything about beta decay, since it is mediated by the weak interaction instead of EM interactions. Also, the beta decay comment seems to not be essential to the rest.

 

[Saw]

I wouldn't throw in anything about beta decay, since it is mediated by the weak interaction instead of EM interactions. Also, the beta decay comment seems to not be essential to the rest.

It is true that, if the approach is "let us talk about the practical details of how the mechanical clock works", there is little to say about, for instance, weak interaction (who knows how a muon decays, for instance). I just wanted to make it clear that here we do not put into question the PoR: ALL periodic processes follow the same pattern, not only EM ones. Once this is clear, we can concentrate on the latter.

 

[Dale]

I just wanted to make it clear that here we do not put into question the PoR: ALL periodic processes follow the same pattern, not only EM ones.

I thought that the whole point was to avoid the PoR discussion. If you are going to make this point then you may as well use the PoR in the usual manner.

 

[harrylin]

I thought that the whole point was to avoid the PoR discussion. If you are going to make this point then you may as well use the PoR in the usual manner.

Saw probably tries to analyse how the PoR is achieved in practice by means of a detailed analysis, just as one may explain how the gas law is achieved by means of the dynamics of gas particles, or how energy is conserved in a mechanical system according to a detailed analysis. Is that correct Saw?

It's really nothing new... perhaps a number of old (very old?) publications could be dug up that do something similar. And of course, that also corresponds to the way Bell taught SR - but I don't know if he discussed mechanical clocks.

 

[Saw]

Saw probably tries to analyse how the PoR is achieved in practice by means of a detailed analysis, just as one may explain how the gas law is achieved by means of the dynamics of gas particles, or how energy is conserved in a mechanical system according to a detailed analysis. Is that correct Saw?

Exactly.

It's really nothing new... perhaps a number of old (very old?) publications could be dug up that do something similar. And of course, that also corresponds to the way Bell taught SR - but I don't know if he discussed mechanical clocks.

Any reference of studies in the same line would be appreciated.

 

[harrylin]

Exactly.

Any reference of studies in the same line would be appreciated.

I found several books and papers that follow the Lorentzian approach as favoured by Bell, as well as several other papers that discuss clocks; but regretfully I didn't see a detailed discussion of mechanical clocks - except for one paper that theorized about mechanical clocks without time dilation.

One book I should check out in the library, but I doubt that it has the example that we are looking for. So, it looks like one of us should write a paper on that topic...

 

[Saw]

So, it looks like one of us should write a paper on that topic...

Hmm. We may not have enough substance for that yet, but we might as well gather it as soon as we dig up a little. As Dalespam said, looking at the details is rewarding in that it may reveal hidden connections. Not in vain the devil dwells amongs them...

I was thinking in this sense about another FAQ that was recently raised again: the question of why the light pulse hits the target (the mid-point of the top mirror) in the light clock experiment. One could also answer the question by resorting to the PoR, which is perfectly legitimate. But one can also enquire about the mechanics of the process. I think we all mentioned those mechanics in that recent thread: basically, photons are produced omnidirectionally inside an apparatus but only those with the right direction, those moving in parallel with the "tube" are let out.

I said then: what if we extrapolate the same question to mechanical clocks? If a ball clock is to work, it needs to hit the mid-point of the upper wall, bounce back and return to its origin. We assume that if we shoot it upwards, it will. But that requires aiming and ultimately this means the same as you do with the photons. You need a tube. If you shoot with your hand or foot (transfer of kinetic energy), you must make the latter traverse, before the collision, a path in the line of the trajectory you want the ball to follow. If you make an explosion (release and transfer of potential energy), you need a barrel where the bullet "learns" the right path, otherwise it would take any random direction.

Well, this, I think, is an argument in favor of the idea that the acceleration of the moving thing inside the clock is the key for explaining why the mechanical clock time-dilates. In the classical view, the ball of the ball clock was accelerated with the right direction, by the sheer will of the shooter, and instantaneously. In the relativistic view, the ball has to learn the right direction inside a tube, just like the photon, and the ball takes time to start, the time that the EM force takes to do its job.