Time dilation or malfunctioning clock?

[ynot]

I don’t understand why, in some Relativity experiments, a clock slowing down is interpreted as being time per se slowing down (time dilation). We use clocks to measure time, but clocks aren’t time. What has a clock slowing down got to do with time slowing down? All clocks are mechanical and function on some form of predictable and repetitively consistent movement of their components, and they function most accurately in a controlled, stable environment. A clock subjected to external forces, such as inertia or temperature change, is virtually assured to malfunction to some degree. I could take an hourglass skydiving and observe that, during the acceleration of freefall, it slows down and stops. A mechanical clock can be made to slow down and stop by subjecting it to inertial forces that bind its moving parts. This effect can be replicated by holding a magnet close to a mechanical wristwatch. Obviously neither of these examples are proof that time per se has slowed or stopped, just malfunctioned. Why can’t the inertial forces of acceleration and deceleration that are incurred when an atomic clock is taken for a ride in an airplane, cause the clock to malfunction rather than be time dilated?

[Yllanes]

I don’t understand why, in some Relativity experiments, a clock slowing down is interpreted as being time per se slowing down (time dilation). We use clocks to measure time, but clocks aren’t time.


Yes they are. Not that I have time to elaborate, but anything is a clock. The beats of your heart are a clock, the number of times you inhale and exhale, the number of times your cells divide, etc.

A clock is basically anything that gives some kind of increasing measurable output. And time is what clocks measure. It isn't a perfect definition, but think if you can find a better one.

As I said, your pulse is a clock. But it is not a good clock, not a good definition of time. A good clock is one that makes movement look simple. If you plot the position of an object not subjected to any force, it will look like a straight line in seconds, but it would look complicated if you use your heart.

When introducing SR, it is customary to use idealised 'light clocks', which would count the number of times a light ray bounces between two mirrors, for example. Using this very simple device it is easy to show how time dilates. But time dilation means dilation for every process, not just a clock malfunctioning.

The best experiment of time dilation is the behaviour of muons, produced by cosmic rays. Those particles live only a millionth of a second and wouldn't have time to reach the Earth even at their huge speeds. But what feels like a millionth of a second to them is longer for us, due to time dilation, so they do reach the ground. The number of muons arriving relative to the number of muons that were created is also a clock, which tells us how long it has taken them to get here.

[TobiasTheViking]

A good example is particle decay. You can see particles that you create on earth have a halftime as expected, whereas when the same particles are created from interstellar radiation in the atmosphere, and move towards the surface at almost the speed of light, the halftime is quite a bit longer(from our perspective, that is, from the particles perspective it is the same).

For any and all things that takes time, or measure time, or in any way use or apply time, time delation will be a factor.

[Ziggurat]

If it were merely malfunctioning clocks, one would expect different clocks to slow down differently as some should malfunction differently than others. They don't, though. They all (including decaying particles) run the same, regardless of mechanism details, which indicates that it doesn't make sense to consider their slowed-down time as being a malfunction. Add in the fact that you can't remove time dilation without breaking the theory, plus the theory matches every experimental test we can devise, and it looks an awful lot like time dilation is real.

[tracer]

A good example is particle decay. You can see particles that you create on earth have a halftime as expected,
... whereas Janet Jackson has a halftime with a wardrobe malfunction?

[69dodge]

I don’t understand why, in some Relativity experiments, a clock slowing down is interpreted as being time per se slowing down (time dilation). We use clocks to measure time, but clocks aren’t time. What has a clock slowing down got to do with time slowing down? All clocks are mechanical and function on some form of predictable and repetitively consistent movement of their components, and they function most accurately in a controlled, stable environment. A clock subjected to external forces, such as inertia or temperature change, is virtually assured to malfunction to some degree. I could take an hourglass skydiving and observe that, during the acceleration of freefall, it slows down and stops. A mechanical clock can be made to slow down and stop by subjecting it to inertial forces that bind its moving parts. This effect can be replicated by holding a magnet close to a mechanical wristwatch. Obviously neither of these examples are proof that time per se has slowed or stopped, just malfunctioned. Why can’t the inertial forces of acceleration and deceleration that are incurred when an atomic clock is taken for a ride in an airplane, cause the clock to malfunction rather than be time dilated?



Does it matter what we call it? As long as we know what happens, what difference does it make?

A mechanical clock behaves in such-and-such a way, under such-and-such circumstances. An atomic clock behaves in such-and-such a way, under such-and-such circumstances. Etc.

It would be hard to attribute time dilation in relativity to the forces experienced by a clock (or other object) during acceleration, because the amount of time dilation doesn't depend on the duration or strength of the acceleration. If your twin takes a long trip in a spaceship, he might accelerate only for a short time at the beginning of the trip leaving Earth, and for a short time at the middle of the trip turning around, and for a short time at the end of the trip coming to a stop at Earth again. But the difference in ages between you and him, after he returns, depends on the length of the whole trip, during most of which he wasn't accelerating at all.

[~enigma~]

If it were merely malfunctioning clocks, one would expect different clocks to slow down differently as some should malfunction differently than others. They don't, though. They all (including decaying particles) run the same, regardless of mechanism details, which indicates that it doesn't make sense to consider their slowed-down time as being a malfunction. Add in the fact that you can't remove time dilation without breaking the theory, plus the theory matches every experimental test we can devise, and it looks an awful lot like time dilation is real.
Could you see the new ads...Seiko has 85% less time dilation at 90% light speed than other leading brands :D

[ynot]

Thanks for the replies. Unfortunately I don't have time to reply right now but will get to it as soon as I can.

[Orangutan]

Imagine a Clock that measures time by observing a single photon bouncing between two mirrors,

It was at this point I remembered that wikipedia is my friend...

http://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation

:)

[JoeTheJuggler]

You're speaking of clocks used in relativity experiments. It sounds like you're challenging the results of said experiments based on the degree of accuracy and precision of the clocks used.

I would think those values have to be taken into account in analyzing the experimental results. Basically, depending on what exact numbers you've got, that should go into a kind of margin of error. My guess is the clocks used for these experiments are extremely precise and accurate (and impervious to mechanical or magnetic interference), and the errors are quite small.

[ynot]

Thanks again for the replies. Not sure I have a clear understanding of exactly what time is. I tend to think of it as being the comparative pace of relative motions. There is the actual pace and the perceived pace. The perception doesn’t always match the actual. Perception can be time delayed. Whether the actual can be time dilated is what I’m questioning. Or more specifically, the methods used as proof that it can.

Light Clock - Imagine a water clock where a drip of water falls from a height in to a tray exactly every second. In a stable environment the clock functions correctly. In an unstable environment however, a cross-wind blows the drip from its direct path and causes it to take an indirect (and therefore longer) path to the tray. The speed of the falling drip doesn’t change but the time it takes to get to the tray increases because its journey is longer. The clock therefore runs slower. I don’t see that this is essentially any different than the theoretical light clock. In both cases all that seams to be proven is that an indirect route is longer than a direct one.

Twin Paradox - All motion is relative so it can’t be accurately said that either twin is travelling away from and returning to the other, while the other is motionless. All that can be said is that the twins are moving apart and coming back together again. Any effect that motion is having on one twin therefore must also apply to the other in equal measure.

[roger]

Twin Paradox - All motion is relative so it can’t be accurately said that either twin is travelling away from and returning to the other, while the other is motionless. All that can be said is that the twins are moving apart and coming back together again. Any effect that motion is having on one twin therefore must also apply to the other in equal measure. This is false because while motion (velocity) is relative, acceleration is not. We can say definitely which twin experienced acceleration, and thus time dilation.

[temporalillusion]

Light Clock - Imagine a water clock where a drip of water falls from a height in to a tray exactly every second. In a stable environment the clock functions correctly. In an unstable environment however, a cross-wind blows the drip from its direct path and causes it to take an indirect (and therefore longer) path to the tray. The speed of the falling drip doesn’t change but the time it takes to get to the tray increases because its journey is longer. The clock therefore runs slower. I don’t see that this is essentially any different than the theoretical light clock. In both cases all that seams to be proven is that an indirect route is longer than a direct one.

Well first you'd need a cross-wind that would affect the photon..

But what about if you took your clock to the top of a high mountain, and another at sea level. Both are stable, neither are moving. The one on top of the mountain will run faster than the one at sea level. Your longer journey theory doesn't explain that observation.

[Ziggurat]

Light Clock - Imagine a water clock where a drip of water falls from a height in to a tray exactly every second. In a stable environment the clock functions correctly. In an unstable environment however, a cross-wind blows the drip from its direct path and causes it to take an indirect (and therefore longer) path to the tray. The speed of the falling drip doesn’t change but the time it takes to get to the tray increases because its journey is longer. The clock therefore runs slower. I don’t see that this is essentially any different than the theoretical light clock. In both cases all that seams to be proven is that an indirect route is longer than a direct one.

That's true: what you're missing, though, is that in the reference frame of the moving clock, light is NOT taking a longer path, but the speed of light in this moving frame is the same. If every single possible clock you could possibly construct shows time dilation, then it makes absolutely no sense for you to think of it as just a distortion effect and not genuine time dilation. And relativity predicts exactly that. For time dilation to be wrong, relativity would need to be wrong - a slight possibility, but considering the extent of experimental confirmation already existing, don't count on it.

Twin Paradox - All motion is relative so it can’t be accurately said that either twin is travelling away from and returning to the other, while the other is motionless. All that can be said is that the twins are moving apart and coming back together again.

Completely and totally wrong. One twin has a straight world-line (http://en.wikipedia.org/wiki/World_line), the other does not. And the twin with the straight world-line has a straight world-line regardless of which reference frame you pick, while the twin with the curved (or bent) world line has a curved (or bent) world line in all reference frames as well. So the two twins are actually inequivalent in EVERY reference frame, which is why there's no actual paradox involved.

[JoeTheJuggler]

Light Clock - Imagine a water clock where a drip of water falls from a height in to a tray exactly every second. In a stable environment the clock functions correctly. In an unstable environment however, a cross-wind blows the drip from its direct path and causes it to take an indirect (and therefore longer) path to the tray. The speed of the falling drip doesn’t change but the time it takes to get to the tray increases because its journey is longer. The clock therefore runs slower. I don’t see that this is essentially any different than the theoretical light clock. In both cases all that seams to be proven is that an indirect route is longer than a direct one.


So a water clock would have unacceptable accuracy and precision if you were using it for an experiment that involved a cross wind blowing on it.

I think I see what you're getting at, though. In experiments that apparently verify relativistic effects of traveling at very high speed, how do we know that it isn't some "non-relativity" effect of acceleration that causes the differing measures in the clocks? (Is that about right?) In other words, there's no way to test the clocks for the effect of acceleration independent of the effect of relativity.

I'm no physicist, and this is certainly not proof, but I would argue from parsimony: if repeated experiments using different types of clocks consistently agree very closely with the values predicted by the theory (i.e. the mathematical model of relativity), I think it'd be less credible to think that relativity isn't the best explanation--especially in the absence of any non-relativistic explanation for the influence of acceleration on the clocks.

[ynot]

So a water clock would have unacceptable accuracy and precision if you were using it for an experiment that involved a cross wind blowing on it.

I think I see what you're getting at, though. In experiments that apparently verify relativistic effects of traveling at very high speed, how do we know that it isn't some "non-relativity" effect of acceleration that causes the differing measures in the clocks? (Is that about right?) In other words, there's no way to test the clocks for the effect of acceleration independent of the effect of relativity.
Exactly right. Now why couldn't I have simply said that? - Thanks

I'm no physicist, and this is certainly not proof, but I would argue from parsimony: if repeated experiments using different types of clocks consistently agree very closely with the values predicted by the theory (i.e. the mathematical model of relativity), I think it'd be less credible to think that relativity isn't the best explanation--especially in the absence of any non-relativistic explanation for the influence of acceleration on the clocks.
I agree. I guess my questioning is a skeptical form of testing while learning.

[ynot]

This is false because while motion (velocity) is relative, acceleration is not. We can say definitely which twin experienced acceleration, and thus time dilation.
Am I correct in thinking that acceleration is essentially the same as deceleration in effect?

[Rob Lister]

Am I correct in thinking that acceleration is essentially the same as deceleration in effect?

there is no difference between acceleration and deceleration...or better put, there's really no such thing as deceleration. What you call 'deceleration' is just acceleration in the opposite direction.

[Yllanes]

Am I correct in thinking that acceleration is essentially the same as deceleration in effect?

Acceleration is not important for the Twin Paradox. The really important point is that the twin at home is always at rest in the same reference system. You need two reference systems to have the travelling twin at rest during the whole trip. Even if he didn't have to accelerate and could magically jump to his cruise speed the effect would be there.

[Cuddles]

Light Clock - Imagine a water clock where a drip of water falls from a height in to a tray exactly every second. In a stable environment the clock functions correctly. In an unstable environment however, a cross-wind blows the drip from its direct path and causes it to take an indirect (and therefore longer) path to the tray. The speed of the falling drip doesn’t change but the time it takes to get to the tray increases because its journey is longer. The clock therefore runs slower. I don’t see that this is essentially any different than the theoretical light clock. In both cases all that seams to be proven is that an indirect route is longer than a direct one.

Horizontal motion does not affect vertical motion. A drop of water will take the same length of time to fall regardless of whether wind blows it sideways or not.

Twin Paradox - All motion is relative so it can’t be accurately said that either twin is travelling away from and returning to the other, while the other is motionless. All that can be said is that the twins are moving apart and coming back together again. Any effect that motion is having on one twin therefore must also apply to the other in equal measure.

As has been explained by others, special relativity only deals with motion at constant velocity. It is a simple model that does not accurately describe the real world. In general relativity there is no twins paradox.

[Upchurch]

Acceleration is not important for the Twin Paradox. The really important point is that the twin at home is always at rest in the same reference system. You need two reference systems to have the travelling twin at rest during the whole trip. Even if he didn't have to accelerate and could magically jump to his cruise speed the effect would be there.
That magical jump would be acceleration. Infinite acceleration, to be precise. The acceleration is the key to the whole phenomenon.*

One of my undergrad research projects in college was determining the effect of acceleration duration on the age difference between the two twins in the Twin Paradox. I'd have to really dig out my old notes if you want me to prove it to you, but the longer the traveling twin spends accelerating the larger the age difference becomes. Instant jumps show less age difference then gradually speeding up and gradually slowing down.


* eta: In fact, it is only the symmetry of situation that lets us make the calculation using Special Relativity. If it got any more complicated, it would become a General Relativity problem.

[Ziggurat]

As has been explained by others, special relativity only deals with motion at constant velocity.

No. This is wrong. Special relativity can handle acceleration - the math can get ugly, and it's usually taught without getting into acceleration, but there's absolutely nothing about acceleration which precludes its treatment under special relativity. The idea that it cannot handle acceleration comes from a misunderstanding of the equivalence principle. If special relativity were unable to handle acceleration, it would mean that general relativity would not be derivable from the equivalence principle.

It is a simple model that does not accurately describe the real world. In general relativity there is no twins paradox.

There's no twin paradox in special relativity either, because it's not actually a paradox. There is the traveling twin problem, but it can be solved fully (INCLUDING using finite acceleration if you want to wade through the math) using only special relativity. The only thing special relativity cannot accomodate is gravity.

[Cuddles]

Special relativity can handle acceleration

The only thing special relativity cannot accomodate is gravity.

Gravity is an acceleration. There is no way to tell the difference between acceleration due to gravity and any other acceleration. Your post contradicts itself.

[Ziggurat]

eta: In fact, it is only the symmetry of situation that lets us make the calculation using Special Relativity. If it got any more complicated, it would become a General Relativity problem.

As I mentioned to Cuddles, this is wrong. You can easily handle finite acceleration, curved worldlines, unsymmetric journeys, etc. with special relativity. Making the journey symmetric and assuming infinite acceleration at the turnaround makes the calculation easier (it can be done with simple algebra as opposed to using calculus to get a path integral of the metric along the worldline), but special relativity can accomodate finite accelerations and comples paths. The ONLY addition to the problem which would require the use of general relativity is gravity.

[Thabiguy]

Gravity is an acceleration. There is no way to tell the difference between acceleration due to gravity and any other acceleration. Your post contradicts itself.

Ziggurat is correct. Special relativity can deal with acceleration.

General relativity does not explain gravity as acceleration. Quite on the contrary, it assumes that a free-falling observer is at rest not in an accelerating, but in an inertial frame of reference. The consequence is that, unlike in special relativity, inertial frames of reference do not exist globally. - Another way to understand the difference is to realize that an object with mass that is accelerating experiences force, by definition. General relativity however says that gravity is not due to any force but due to space-time curvature.

When gravity is present, special relativity is no longer applicable because inertial reference frames are no longer global in space where gravitational field (or space-time curvature) varies. This means that the outcome of the "twin paradox" will differ in general relativity from special relativity not depending on the acceleration of the travelling twin, but depending on the variations of the gravitational field that the travelling twin goes through.

[Yllanes]

That magical jump would be acceleration. Infinite acceleration, to be precise. The acceleration is the key to the whole phenomenon.*

One of my undergrad research projects in college was determining the effect of acceleration duration on the age difference between the two twins in the Twin Paradox. I'd have to really dig out my old notes if you want me to prove it to you, but the longer the traveling twin spends accelerating the larger the age difference becomes. Instant jumps show less age difference then gradually speeding up and gradually slowing down.


I know that. I was only pointing out that you don't need a finite period of acceleration to have an age difference or to be able to distinguish the two twins. One is all the time in the same reference frame, the other isn't. Of course, changing reference frames is accelerating, so you are right, but the possible side effects of acceleration (ynot's concern) do not enter into the derivation.

Also, Ziggurat is right in saying that you can have accelerations in SR. For example, it is very easy to prove that the relativistic uniformly accelerated motion is

\footnotesize
\begin{align*}
x &=\frac{c^2}{a}\left(\sqrt{1+\frac{a^2t^2}{c^2}}-1\right), &
v &= \frac{a t}{\sqrt{1+\frac{a^2t^2}{c^2}}}
\end{align*}


(for at << c, this formulas are v ~ at, x ~ at2/2). Uniformly accelerated is here a motion such that the acceleration a in the proper reference frame (at each instant of time) is a constant.

[Ziggurat]

Gravity is an acceleration. There is no way to tell the difference between acceleration due to gravity and any other acceleration. Your post contradicts itself.

Wrong. As I stated before, this belief comes from a misunderstanding of the equivalence principle.

If acceleration could not be handled within the context of special relativity, then the statement that gravity is locally equivalent to acceleration would do you absolutely no good, and could not be used as a basis for forming general relativity. It would basically be a statement that two things which existing theory cannot deal with are equivalent - but that wouldn't help you understand either. But that's not the case: the equivalence principle is significant precisely because one side of that equivalence IS understandable within the context of special relativity.

Standing still in a uniform gravitational field is locally equivalent to acceleration, that is true. But the rather relevant point is that gravity is NOT uniform, and that to explain it we need a theory which works on more than just a local level. And the ability to handle acceleration in special relativity cannot be applied to gravity directly without accounting for that non-uniformity and non-locality, and it is accounting for those non-local and non-uniform aspects which lead to general relativity.

Acceleration itself can be handled quite easily in special relativity. Calculating the time taken by the traveling twin with finite acceleration is simply the path integral along his worldline of the Minkowski metric. The math may be ugly, but saying it can't handle such cases is equivalent to saying that Euclidean geometry cannot handle curves.