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Time and Clock Specifics


Suxamethonium
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Hi,

 

This question (below) has always bugged me. I searched through the existing posts but just managed to confuse myself even more.

 

It is often said that time slows due to gravity (I'm fine with this) but then they use an example "If I put a clock next to a source of gravity, it would run slower than a clock away from that gravitational source". I have a few issues with this that I would like some clarification on please:

 

1) I can slow my watch/clock or whatever, but it has no effect on time (though it works wonders for making me late). Likewise, speeding my clock up does not accelerate me into the future- so I feel there is some disconnection between how we measure time, and time itself as a fabric of our universe.

 

2) (Also, specifically noting reason 1) If time was to noticeably slow down at a particular location would this actually slow my clock? I would have thought that mathematically speaking my clock should actually move ahead of time (i.e. it is now ticking more than once for every real second).

 

Is this just me reading too analytically into a poor example? Or am I missing something fundamental in my reasoning?

 

(I thought relativity was the best place to put this).

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The proper statement is "time slows down", not "clocks slow down". "Time slows down" actually means "all physical processes slow down". This means: Take two similar systems. Place them at locations A and B. Some time later, bring them back to the same location. If "time slows down" at place A, then the system having been there will have undergone less physical (and therefore presumably also chemical, biological, ...) processes. A functional clock (say, driven by counting the amount of decay of some radioactive substance) is merely an experimental measure of this effect. Likewise, any properly working clock that foots on physical processes for the measurement (read: every clock) will show the slowdown (this point is probably the closest one to "miss something fundamental in my reasoning").

 

Two related comments:

- Time is, in this case, a measure for the progress of physical effects.

- For something to "slow down" you need a reference that you define "normal progress". That's what place B is for.

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To add to what timo said, there is a distinction between influences that are environmental in nature, such as temperature and humidity, and those from relativity. The relativistic effects happen to all clocks, regardless of construction, because all processes are affected — you can't build a clock that is unaffected. Environmental effects will vary according to the clock construction or physical process. Great care is taken to minimize the size of the effect by making the coefficient and/or the fluctuation in the offending parameter small.

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The proper statement is "time slows down", not "clocks slow down".

That is incorrect. The two statements are synonymous. Of course when such statements (or similar statments) are made it is understood that one is refering to an ideal clock where ideal clock is defined as a clock whose operation is unaffected by its acceleration. Also, as stated above by swansont, one ideally one also wishes the ideal clock to be unaffected by temperature, humidity, radiation etc. No use having an idea clock if the cold temperatures of interplanetary space causes the clock to malfunction.

Edited by pmb
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So you're saying that if an sufficient amount non-outspoken extra criteria are applied to B, then A and B become equivalent, and that this then makes "the proper statement is A, not B" incorrect?

Edited by timo
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Um, so the net thing I should take out of this is that what we measure as time directly corresponds to "real"-time regardless of the location of calibration? (i.e. a clock matches A time, is moved to B and will match B time). So if that is the case than at B all our bodily processes would be slowed in correlation and we wouldn't observe any change of time given our frame of reference, but we would be slow in A's point of reference?

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So you're saying that if an sufficient amount non-outspoken extra criteria are applied to B, then A and B become equivalent, and that this then makes "the proper statement is A, not B" incorrect?

Sorry, but I have no idea what that says/asks.

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That is incorrect. The two statements are synonymous. Of course when such statements (or similar statments) are made it is understood that one is refering to an ideal clock where ideal clock is defined as a clock whose operation is unaffected by its acceleration. Also, as stated above by swansont, one ideally one also wishes the ideal clock to be unaffected by temperature, humidity, radiation etc. No use having an idea clock if the cold temperatures of interplanetary space causes the clock to malfunction.

 

No, timos's statement is correct. If I move a pendulum clock from a valley to a hill the clock slows down even though time speeds up, because [math]\sqrt{\frac{g}{L}}[/math] is a much bigger effect than [math]\frac{gh}{c^2}[/math]

 

But even with that, I think it is not understood that one is dealing with an ideal clock when discussing the difference between clocks changing and time changing, because these are the details that are in question.

 

"Time changes rate" is a subset of "clock changes rate". They are not equivalent.

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No, timos's statement is correct. If I move a pendulum clock from a valley to a hill the clock slows down even though time speeds up, because [math]\sqrt{\frac{g}{L}}[/math] is a much bigger effect than [math]\frac{gh}{c^2}[/math]

I'm way ahead of you swansont. A pendulum clock is not an ideal clock. That's why your counter example fails.

 

Details: Consider using a pendulum clock as a ship's clock in a rocket ship. The rate at which the clock runs will depend on the rate at which the rocket accelerates. That means that a pendulum clock is not an ideal clock.

 

What I'm saying in this thead is not my own personal opinion/definition but the definition as it is found in the relativity literature. For example: see http://home.comcast....s_textbooks.htm for an illustrative list of relativity texts and each one is consistent with what I've said above.

Edited by pmb
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To add to what timo said, there is a distinction between influences that are environmental in nature, such as temperature and humidity, and those from relativity. The relativistic effects happen to all clocks, regardless of construction, because all processes are affected you can't build a clock that is unaffected. Environmental effects will vary according to the clock construction or physical process. Great care is taken to minimize the size of the effect by making the coefficient and/or the fluctuation in the offending parameter small.

 

Swansont, I've read your post through several times, and need some help. Could you clarify this point, please:

 

You say: "there is a distinction between influences that are environmental in nature, such as temperature, ...and those from relativity."

That seems clear, but then you go on to say: "the relativistic effects happen... because all processes are affected"

 

Well, if all processes are affected - won't process of temperature change be affected too. Temperature just means how fast atoms are moving about. So if relativistic affects make the atoms slow down, won't that make temperature go down also?

 

I'm thinking of a starship, speeding away from Earth at 0.999 light-velocity. Will relativistic effects make the ship seem to be at ultra-low temperature - so if we look at it from outside - we'll see all the water in the ship, turned to ice?

Edited by Dekan
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I'm way ahead of you swansont. A pendulum clock is not an ideal clock. That's why your counter example fails.

 

Details: Consider using a pendulum clock as a ship's clock in a rocket ship. The rate at which the clock runs will depend on the rate at which the rocket accelerates. That means that a pendulum clock is not an ideal clock.

 

What I'm saying in this thead is not my own personal opinion/definition but the definition as it is found in the relativity literature. For example: see http://home.comcast....s_textbooks.htm for an illustrative list of relativity texts and each one is consistent with what I've said above.

 

Aren't tautologies grand?

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Um, so the net thing I should take out of this is that what we measure as time directly corresponds to "real"-time regardless of the location of calibration? (i.e. a clock matches A time, is moved to B and will match B time).

I don't know what you actually want to know. In my opinion, with respect to your original post you should take out that it is the "real time", defined as a measure of progress of physical processes, that changes (with respect to some reference "real time"). The behavior of clocks is just a lemma [a consequence] to this more fundamental and more interesting statement.

 

So if that is the case than at B all our bodily processes would be slowed in correlation and we wouldn't observe any change of time given our frame of reference, but we would be slow in A's point of reference?
Kind of "yes" to the first part. For the second part, note that "frame of reference" is a popular buzzword in the context of relativity, but not really an appropriate concept here. Didactically, physically, and from the point of logic it is much cleaner to take two samples, bring one at place A and the other at place B (such that the transport process can be neglected), and bring them back to after some time to compare them at a common location. One of them, the one deeper into the gravitational potential, has aged less. Simple as that. Super-surprising effect. No buzzwords involved. Edited by timo
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Swansont, I've read your post through several times, and need some help. Could you clarify this point, please:

 

You say: "there is a distinction between influences that are environmental in nature, such as temperature, ...and those from relativity."

That seems clear, but then you go on to say: "the relativistic effects happen... because all processes are affected"

 

Well, if all processes are affected - won't process of temperature change be affected too. Temperature just means how fast atoms are moving about. So if relativistic affects make the atoms slow down, won't that make temperature go down also?

 

I'm thinking of a starship, speeding away from Earth at 0.999 light-velocity. Will relativistic effects make the ship seem to be at ultra-low temperature - so if we look at it from outside - we'll see all the water in the ship, turned to ice?

 

I can have a temperature change that affects a real clock. Wiring changes length, quartz crystals oscillate at different rates (your quartz watch slows down a small amount when you take it off). None of that implies that time has changed. However, clocks have their own temperature coefficients — different clocks respond in different amounts to the same change in temperature. Relativistic effects, on the other hand, have the same effect regardless of the construction of the clock.

 

Observing an object in motion will not cause the water to freeze. Onboard the ship the temperature does not change, since they are at rest in their own frame. An outside observer would, at best, be able to say that their thermometers (like their clocks) aren't appearing to be working properly in the other frame, and there is a disagreement with the readings. Temperature is not a quantity that will be the same across frames (i.e. not an invariant), though I think entropy is. One of the confounding effects of relativity, a I recall, is that the concept of thermal equilibrium gets muddled. It's not as simple of an analysis as time and length effects.

 

If you believe there was a tautology in my post then why don't you simply post an arguement proving it?

 

When you assume that all clocks are ideal, then all conclusions you reach are valid for ideal clocks. In case I wasn't clear before: I am not discussing ideal clocks. Thus, your point is moot.

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When you assume that all clocks are ideal, then all conclusions you reach are valid for ideal clocks. In case I wasn't clear before: I am not discussing ideal clocks. Thus, your point is moot.

 

I was very clear about the fact that I was talking about ideal clocks when I responded to timo. That you weren’t discussing ideal clocks is the real moot point here since my response to timo was in post 4 and not earlier. And I still don’t see where the tautology that you spoke of was. Please point it out for me. Thanks.

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I was very clear about the fact that I was talking about ideal clocks when I responded to timo. That you weren’t discussing ideal clocks is the real moot point here since my response to timo was in post 4 and not earlier. And I still don’t see where the tautology that you spoke of was. Please point it out for me. Thanks.

 

Ideal clocks behave as ideal clocks.

 

 

I think it was clear that timo wasn't limiting the discussion to ideal clocks by the time "all physical processes slow down" came up since ideal clocks exclude most physical processes. And yes, your response came after timo's and my posts. Causality and all that. But since you responded, you might consider that not changing the context of the discussion would be a good thing.

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Ideal clocks behave as ideal clocks.

"You're kidding!? Wow! I never knew that. :D

I think it was clear that timo wasn't limiting the discussion to ideal clocks by the time "all physical processes slow down" came up since ideal clocks exclude most physical processes. And yes, your response came after timo's and my posts. Causality and all that. But since you responded, you might consider that not changing the context of the discussion would be a good thing.

Ideal clocks come up quite often. Physicists quite often use ideal clocks when working out theortetical problems.

Edited by pmb
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Ideal clocks come up quite often. Physicists quite often use ideal clocks when working out theortetical problems.

 

Yes, they do. But that's beside the point. It's not what everyone else is discussing in this thread.

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Yes, they do. But that's beside the point. It's not what everyone else is discussing in this thread.

This is a forum to discuss relativistic effects so when someone comes in talking about the slowing down of clocks then it is, by definition, and ideal clock they are referring to. All questions regarding slowing down come from relativity and not good clocks gone bad,

 

Tell ya what. I'll aswer the questions which address the slowing down of good clocks and you answer the questions about broken/poorly synchronized clocks. In any case my response was correct.

 

 

Okay. Enough of this. At this point Suxamethonium wants to know more about bad cocks or he wants to know about ideal clocks. Anything other that the laer I'm not interested.

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This is a forum to discuss relativistic effects so when someone comes in talking about the slowing down of clocks then it is, by definition, and ideal clock they are referring to. All questions regarding slowing down come from relativity and not good clocks gone bad,

 

No, I think that's obviously false. Real clocks change rate owing to relativistic effects. Real clocks capable of measuring relativistic effects actually exist.

 

Tell ya what. I'll aswer the questions which address the slowing down of good clocks and you answer the questions about broken/poorly synchronized clocks. In any case my response was correct.

 

How about "no".

 

The issue wasn't the technical accuracy of your response, the issue was the relevance of it in this discussion.

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Regarding ideal clocks. Let's say two spaceships each have there own clock which is a light source emitting waves with wavelength X (both clocks use the same wavelength).

Now they move near the speed of light relative to each other and meet up again (let's imagine a 1D universe which is circular, so one ship can travel around the Universe and meet up with the stationary ship without acceleration). If each person measures time by the number of peaks in the light wave of there clock, and the speed of light is always the same, won't they agree on the total elapsed time (they will have to count the same number of peaks)?

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Regarding ideal clocks. Let's say two spaceships each have there own clock which is a light source emitting waves with wavelength X (both clocks use the same wavelength).

Now they move near the speed of light relative to each other and meet up again (let's imagine a 1D universe which is circular, so one ship can travel around the Universe and meet up with the stationary ship without acceleration). If each person measures time by the number of peaks in the light wave of there clock, and the speed of light is always the same, won't they agree on the total elapsed time (they will have to count the same number of peaks)?

 

A circular universe means acceleration.

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Sorry, circular was the wrong terminology. I meant a 'closed' 1D Universe.

 

Still, you have a geometry that implies an acceleration or an equivalent effect (like in GR) in returning to your starting point.

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