Time dilation explaination with mechanical clock instead of light clock

[R Power]

This page http://en.wikipedia.org/wiki/Time_dilation clearly explains time dilation by exampling with the light clock. But how can it be explained if suppose there was a simple mechanical clock instead of light clock. So, now for moving observer there is no light (in light clock) to follow longer path and hence elongate one second but only a second hand that rotates.

 

[Doc Al]

This page http://en.wikipedia.org/wiki/Time_dilation clearly explains time dilation by exampling with the light clock. But how can it be explained if suppose there was a simple mechanical clock instead of light clock. So, now for moving observer there is no light (in light clock) to follow longer path and hence elongate one second but only a second hand that rotates.

The principle of relativity tells us that all clocks must behave similarly and demonstrate identical time dilation. The advantage of the light clock is that it's easy to analyze.

 

[R Power]

The principle of relativity tells us that all clocks must behave similarly and demonstrate identical time dilation. The advantage of the light clock is that it's easy to analyze.

You are right! but can you explain ? It will help me further understand time dilation.

 

[Doc Al]

I don't think there's any simple way of deducing time dilation using mechanical clocks, if that's what you're looking for. (At least I've never seen such a demonstration.)

 

[R Power]

I don't think there's any simple way of deducing time dilation using mechanical clocks, if that's what you're looking for. (At least I've never seen such a demonstration.)

I've tried it! In this case, second hand traces an arc at 6 deg/sec to show one second increment, so when an observer travels with speed of light c beside the clock, the second hand for him will trace the arc + the elongated distance (the locus will be a big arc) appearing due to motion of traveling observer(as in case of light clock light had to travel greater distance) but since velocity of second hand can't be "6deg/sec + c" with respect to traveler i.e it can't exceed speed of light..so it will take more time to trace 6 deg.

 

[Saw]

You are right! but can you explain ? It will help me further understand time dilation.

The standard interpretation of SR stops at this level. Nature conforms to the Principle of Relativity (PoR) and that is it. My personal view is that this is not enough. I think we should put forward hypotheses about the root causes for that, but this is not usually regarded as necessary.

If you want my view, the answer is clear: the mechanical clock also suffers time dilation (as per the same pattern as the light clock) because a clock is a moving thing inside an enclosed space; the clock ticks when the moving thing bounces against the walls or otherwise changes direction. The cause for this "acceleration" is an electromagnetic interaction (light) or any another force that does its job in a manner that is analogous, at least for this purpose, to light.

 

[R Power]

What about my explanation in post #5?

 

[Saw]

What about my explanation in post #5?

I myself did not catch it.

 

[mangaroosh]

I've been wondering about this as well.

If the light clock were to be replaced with say, an infinitely precise pendulum clock, how would the thought experiment be explained then?

Would it be different if the thought experiment were "re-located" to deep space, using the infinitely precise pendulum clock?

 

[questionpost]

I don't get what the problem is. Any clock measures time, so when the fabric of space is distorted, time will flow slower, and thus any clock measurement will be slower since the flow of events is slower proportionally to the gravity. Although I will admit I don't quite understand completely why the shape of a well actually makes time run slower, but we know that it does. That's why if you are in an airplane, your clock will run ever-so-slightly faster than clocks on the ground.

 

[bahamagreen]

The request for an explanation is a good one.

If you take for granted that all possible clocks will be identically time dilated, then using the light clock as your generic clock in all subsequent though experiments is fine.

But all must admit that light is a very special entity with extraordinary properties, and if you are attempting to verify the universality of clock dilation in your own thinking before moving to just take it for granted, it makes sense to wonder what would be the effect on the actions of a mechanical clock - something with size and mass. It makes sense to wonder that different orientations of the oscillating and rotating parts of the clock might change their lengths and radii in one dimension, and therefore effect centers of mass, centers of rotation, and thereby effect linear and angular accelerations, etc.

This is not just "physical processes slowing down"... there are gross mechanical effects to account for, as well as smaller things in chemistry like molecular bonds, orbitals, and even smaller things, etc.

Surely someone has done this analysis and demonstrated that all these effects must balance out so that the mechanical clock may be replaced with the simple light clock without reservation?

 

[harrylin]

I don't get what the problem is. Any clock measures time, so when the fabric of space is distorted, time will flow slower, and thus any clock measurement will be slower since the flow of events is slower proportionally to the gravity. Although I will admit I don't quite understand completely why the shape of a well actually makes time run slower, but we know that it does. That's why if you are in an airplane, your clock will run ever-so-slightly faster than clocks on the ground.

I'm afraid that you confound gravitational time dilation with special relativistic time dilation; for a lucid discussion those are better not mixed up.

 

[harrylin]

The request for an explanation is a good one.

If you take for granted that all possible clocks will be identically time dilated, then using the light clock as your generic clock in all subsequent though experiments is fine.

But all must admit that light is a very special entity with extraordinary properties, and if you are attempting to verify the universality of clock dilation in your own thinking before moving to just take it for granted, it makes sense to wonder what would be the effect on the actions of a mechanical clock - something with size and mass. It makes sense to wonder that different orientations of the oscillating and rotating parts of the clock might change their lengths and radii in one dimension, and therefore effect centers of mass, centers of rotation, and thereby effect linear and angular accelerations, etc.

This is not just "physical processes slowing down"... there are gross mechanical effects to account for, as well as smaller things in chemistry like molecular bonds, orbitals, and even smaller things, etc.

Surely someone has done this analysis and demonstrated that all these effects must balance out so that the mechanical clock may be replaced with the simple light clock without reservation?

The course of progress was originally like that, but failure to either do that or to demonstrate the contrary led to relativity theory. Thus from then on one adjusts physical laws such that they adhere to the relativity principle, and insofar as this is done well, analyses based on those laws should find the same. It's similar to the principle of conservation of energy: it's easy to construct an apparatus that is so complex that it is a big job to demonstrate by means of the laws of Newton etc., that the principle of conservation of energy is not broken.

 

[R Power]

In case of light clock even, when observer travels at some speed, path of photon appears elongated to the moving observer now the velocity of observer should have been added to velocity of light which we know is not possible so the overall velocity of photon for the observer is constant i.e c (which causes dilation) but does this mean that photon has to slow its speed down in order to maintain total speed(photon speed + speed of observer) equal to speed of light?

 

[harrylin]

In case of light clock even, when observer travels at some speed, path of photon appears elongated to the moving observer now the velocity of observer should have been added to velocity of light which we know is not possible so the overall velocity of photon for the observer is constant i.e c (which causes dilation) but does this mean that photon has to slow its speed down in order to maintain total speed(photon speed + speed of observer) equal to speed of light?

The speed of light can not be affected by observation. Consequently it is the observation of the observer that is altered by the observer's speed (together with his choice of clock synchronization), and not the photon which propagates unaffected by the observer.

 

[R Power]

Consequently it is the observation of the observer that is altered by the observer's speed (together with his choice of clock synchronization), and not the photon which propagates unaffected by the observer.

The clock was relatively moving for the observer(for he himself was moving) and the photon in the clock which was traveling at speed c must now be moving with [ c+observer or clock speed] but that is not possible, so it travels with c. That means the photon in moving clock (to the observer) still travels with c for the observer which is only possible when the photon slows its speed down by an amount equal to the speed of clock (or observer) so that to observer it still moves with speed c.

When clock at rest...

speed of photon = c
speed of photon to observer = c

When clock moves...

speed of clock = v
speed of photon = c
speed of photon to observer= c+v
but that is not possible...
so let speed of clock = v
speed of photon = c-v
speed of photon to observer = c-v+v = c.

 

[harrylin]

The clock was relatively moving for the observer(for he himself was moving) and the photon in the clock which was traveling at speed c must now be moving with [ c+observer or clock speed] but that is not possible, so it travels with c.[..]

To elaborate, it depends on the reference system that the observer chooses. Apparently you have him choose a system in which he is moving, which is less common in this kind of discussions; commonly one refers to a system in which the observer is in rest. In a system in which the observer is measured to have velocity v and the light velocity c, their relative velocity (in jargon "closing velocity") is the vector subtraction (c-v) - this is so by mathematical definition. As a matter of fact, that is also how GPS receivers calculate.

 

[lalbatros]

Man-made mechanical clocks might not be well suited for this analysis.
After all, it is almost impossible practically to test time dilation with such clocks.

I see two "mechanical" alternatives:

1) atomic clocks that are based on a (quantum) mechanical system, indeed
2) astronomical bodies

Given that several astronomical observations support special relativity, it is very likely that time dilation could be explained by taking an astronomical system as an example. This would amount to comparing astronomical observations made in differents frame of references.

I was impressed by a paper from Julian Barbour on the nature of time:

http://platonia.com/nature_of_time_essay.pdf

Starting from this point of view would not only offer you some insight about how to answer your question, but it would also invite you to reflect about your question itself.

 

[R Power]

To elaborate, it depends on the reference system that the observer chooses. Apparently you have him choose a system in which he is moving, which is less common in this kind of discussions; commonly one refers to a system in which the observer is in rest. In a system in which the observer is measured to have velocity v and the light velocity c, their relative velocity (in jargon "closing velocity") is the vector subtraction (c-v) - this is so by mathematical definition.

Whether the clock is moving or the observer, its one hand same thing for the observer. I prefer taking observer to be mobile because if clock is moving (say at very high speed) then photon will not move along with clock and at some instance it will miss one of the reflectors. Moreover, the speed will be c+v (although that's not possible) which is why dilation occurs.

 

[harrylin]

Whether the clock is moving or the observer, its one hand same thing for the observer. I prefer taking observer to be mobile because if clock is moving (say at very high speed) then photon will not move along with clock and at some instance it will miss one of the reflectors. Moreover, the speed will be c+v (although that's not possible) which is why dilation occurs.

Sorry, that's simply wrong. Effectively you call "1+1=2" "not possible". Did you learn SR? A detailed presentation can be found in section 3 of:
http://www.fourmilab.ch/etexts/einstein/specrel/www/
Most textbooks have a clearer derivation but lack the clarifications concerning c+/-v.

 

[questionpost]

It seems like the problem is how clocks measure time depending on their speed. If they are going fast, then relative to the speed of time, which is c, time flows slower, so to the clock other things would have time flowing at a faster rate and we wouldn't see the ticking go as fast, and with traveling very close to the speed of light, there's some property of space that only allows speed to increase in a sort of "asymtotic" way as to only come infinitely clsoe to c, so the way you add speeds in v=(u+a) in terms of vectors is only an approximation at low speeds, not high near-light speeds.

 

[harrylin]

It seems like the problem is how clocks measure time depending on their speed. If they are going fast, then relative to the speed of time, which is c, time flows slower, so to the clock other things would have time flowing at a faster rate and we wouldn't see the ticking go as fast, and with traveling very close to the speed of light, there's some property of space that only allows speed to increase in a sort of "asymtotic" way as to only come infinitely clsoe to c, so the way you add speeds in v=(u+a) in terms of vectors is only an approximation at low speeds, not high near-light speeds.

A vector addition isn't a system transformation - but these are often confused. In a single reference system, as Einstein phrased it in the section that I pointed at, "the ray moves relatively to the initial point of [the moving system] k, when measured in the stationary system, with the velocity c-v".
Obviously, the distance variation over time between two moving entities as expressed in a single reference system is the vector subtraction of their velocities. And of course, such basics of vector algebra has nothing to do with time dilation, the topic of this thread.

My main point here is to stress (to the OP) that "relativistic velocity addition" is in reality a transformation equation between two independent systems of measurement.

 

[R Power]

And of course, such basics of vector algebra has nothing to do with time dilation, the topic of this thread.

But in the light clock article, when the observer is moving the light should have traveled at c+speed of observer but according to STR its speed remains constant and hence dilation occurs. Thus basic velocity addition fails at speed of light.

 

[harrylin]

But in the light clock article, when the observer is moving the light should have traveled at c+speed of observer but according to STR its speed remains constant and hence dilation occurs. Thus basic velocity addition fails at speed of light.

That "velocity addition" is a system transformation, as I already mentioned... moreover the "hence" confounds cause and effect (the observer's instruments cannot affect the light ray's speed!). And as you started with "but", it may be helpful if you can tell me why you think that the sentence that I cited from the SR derivation is not basic vector algebra.

 

[salvestrom]

But in the light clock article, when the observer is moving the light should have traveled at c+speed of observer but according to STR its speed remains constant and hence dilation occurs. Thus basic velocity addition fails at speed of light.

I think of it in this order: physical processes are 'hampered' by high velocity, described as time dilation, and so the speed of light is observed to be constant regardless of reference frame. In other words, the speed of light is constant because of time dilation.

As for what time dilation is... I'm on board with your description of the mechanical clock. A pendulum swinging in the direction of motion of its parent clock will, as it is accelerated closer to the speed of light, eventually need to move faster than c in order to keep swinging, before the rest of the clock does.

This is calculated to require infinite energy and is therefore considered impossible. I see no reason not to describe any mechanism in such a fashion - even our ultra-precise atomic clocks. At increasing speed these clocks can no longer decay at the same rate, owing to increasing amounts of energy required to do anything. So too the aging of a human, the rotting of fruit and the material decay of a spaceship transporting either.

 

[questionpost]

Isn't "velocity addition" not even the actual way your suppose to measurement and is nothing more than an approximation at low speeds? Why are people basing understandings off of it?

 

[harrylin]

Isn't "velocity addition" not even the actual way your suppose to measurement and is nothing more than an approximation at low speeds? Why are people basing understandings off of it?

Sorry I can't parse your sentence ... can you parse the sentence of Einstein's 1905 paper that I cited in post #22?
I hope that you understand the fundamental difference between a velocity difference in a single reference system, and the "velocity addition" equation for a transformation of one reference system to another one.

 

[A.T.]

If the mechanical clock would not be dilatated by the same amount as the co-moving light clock, you would run into paradoxes. Imagine the clocks trigger a bomb when they go out-of-synch. All observers must agree on whether the bomb exploded or not. But some observers would observe the clocks in-synch (those at rest to the clocks), some out-of-synch (those moving relative to the clocks).

Another way to think about it: On the atomic level, a mechanical clock also depends on EM-force fields, in which changes propagate at c.

 

[Saw]

Another way to think about it: On the atomic level, a mechanical clock also depends on EM-force fields, in which changes propagate at c.

I agree with that. I said something similar in post #6 above:

the mechanical clock also suffers time dilation (as per the same pattern as the light clock) because a clock is a moving thing inside an enclosed space; the clock ticks when the moving thing bounces against the walls or otherwise changes direction. The cause for this "acceleration" is an electromagnetic interaction (light) or any another force that does its job in a manner that is analogous, at least for this purpose, to light.

Why don't books ever mention this physical explanation? It is true that, if mechanical clocks did not suffer TD as per the same pattern as light clocks, the principle of relativity would suffer. But the principle of relativity is a description of how nature works, it is not the reason why it works that way. In this sense, it can be noted: if we had found out TD first in mechanical clocks, we would then say that light clocks must conform to the same pattern or otherwise the principle of relativity would be broken. Isn't that circular reasoning?

 

[Dale]

the principle of relativity is a description of how nature works, it is not the reason why it works that way.

This is a useless complaint because it applies to all of science. All science, including the principle of relativity, is a description of how nature works, not a reason why. If you are unwilling to accept such explanations then you do not want a scientific explanation.

if we had found out TD first in mechanical clocks, we would then say that light clocks must conform to the same pattern or otherwise the principle of relativity would be broken. Isn't that circular reasoning?

No. Circular reasoning would be something like: mechanical clocks time dilate, so by the principle of relativity light clocks time dilate, so mechanical clocks time dilate.

In general, you can take any logically self-consistent set of statements, and divide them up into a set of axioms and a set of theorems such that the axioms logically imply all of the theorems. The set of axioms is not unique, in other words, you can swap the place of some of the theorems and the axioms such that what was previously a theorem is now an axiom and the previous theorems logically imply the previous axioms. There is nothing circular about either selection of axioms.

 

[harrylin]

[...] Why don't books ever mention this physical explanation? It is true that, if mechanical clocks did not suffer TD as per the same pattern as light clocks, the principle of relativity would suffer. But the principle of relativity is a description of how nature works, it is not the reason why it works that way. In this sense, it can be noted: if we had found out TD first in mechanical clocks, we would then say that light clocks must conform to the same pattern or otherwise the principle of relativity would be broken. [..]

It's not that no books at all ever mention it, for example it's just how Lorentz (post-relativity) and Bell taught physics in their books. However, regretfully it's a minority of books that values such physical, constructive explanations. IMHO, a good book provides both type of explanations.
Compare: http://ndpr.nd.edu/news/25025-physical-relativity-space-time-structure-from-a-dynamical-perspective/

 

[Dale]

In general, it is more valuable to teach a student how to reason from physical principles than to provide a large collection of unrelated phenomenological explanations. That is why most textbooks will use explanations from first principles whenever possible.

 

[harrylin]

This is a useless complaint because it applies to all of science. All science, including the principle of relativity, is a description of how nature works, not a reason why. If you are unwilling to accept such explanations then you do not want a scientific explanation. [..]

Some of the greatest scientists of history were not satisfied with such lack of constructive explanations. Your suggestion that they did "not want a scientific explanation" doesn't make any sense to me; lack of explanation is not a scientific achievement. And his complaint is useful, as they suggested a solution which a few books do apply.

 

[Dale]

Some of the greatest scientists of history were not satisfied with such lack of explanations.

Can you provide an example? I am not aware of this. AFAIK, no "great scientist" has ever developed a scientific theory which was not a description of how nature works rather than a reason why it works that way.

 

[harrylin]

Can you provide an example? I am not aware of this. AFAIK, no "great scientist" has ever developed a scientific theory which was not a description of how nature works rather than a reason why it works that way.

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).

 

[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.