Time, Memory and Change: A Philosophical Exploration

[Prometheus]

Time is what a clock measures. It may be frame depedent, but so what? It doesn't mean that the clock is not measuring time.

Doesn't it?

If a clock is in greater motion through space than another, then the time that it measures is slower. Clocks do not measure motion through time, they measure motion through space-time.

 

[Prometheus]

All measuring devices of "Time" (whatever that is) measures movement.

I agree with this statement. However, I do not agree with your examples.

All of your examples of motion are motion through space. You use time as a measure of motion through space. This is a Newtonian usage of time, and does not take into account motion through space-time.

 

[jcsd]

Doesn't it?

If a clock is in greater motion through space than another, then the time that it measures is slower. Clocks do not measure motion through time, they measure motion through space-time.

I'm not sure 'motion through spacetime' could be given a reasonable defintion. Personally if I had to give a defitnion tho' it would be the velocity 4-vector which is not analogus to time and always has a square norm of c^2 (so you could say that we move through spacetime at the same 'speed'). Also remember there is certainly no such thing as a 'greater motion' as all motion is relative as is time dialation.

So time is what a clock measures and what a clock measures is not Lorentz invariant, but that shouldn't be suprising as time isn't Lorentz invariant.

 

[jcsd]

Hmm I suppose you could say that the proper time of a clock between two events local to the clock relates to the 'length' of that clocks worldline between those two events.

 

[Prometheus]

IAlso remember there is certainly no such thing as a 'greater motion' as all motion is relative as is time dialation.

Huh?

There is greater motion through space and there is greater motion through time.

There is no such thing as greater motion through space-time, as there is only one rate of motion through space-time.

How can you say that there is no such thing as greater motion? or, what do you mean?

 

[jcsd]

Huh?

There is greater motion through space and there is greater motion through time.

There is no such thing as greater motion through space-time, as there is only one rate of motion through space-time.

How can you say that there is no such thing as greater motion? or, what do you mean?

What I mean is that 'motion' (i.e. velcotiy) is reative, so it is impossible to order it in such a manner that is frame invariant. i.e. in one frame my speed is greater than yours, but there must also exist another frame where my speed is less than yours. Think of the twin paradox and how both twins observe each others clocks to be slowed.

 

[Prometheus]

What I mean is that 'motion' (i.e. velcotiy) is reative, so it is impossible to order it in such a manner that is frame invariant.

I still do not understand what you mean by motion. Do you mean motion through space or motion through space-time?

If we race, and I run faster than you, am I or am I not in greater motion than you? I do not understand your perspective.

Think of the twin paradox and how both twins observe each others clocks to be slowed.

OK. Think of a clock, and two observers observing the clock. How can they relate themselves to each other on the basis of observing some clock?

 

[jcsd]

I still do not understand what you mean by motion. Do you mean motion through space or motion through space-time?

If an object is in motion it means that it changes it's postion as I said earlier it doesn't mean to much in terms of spacetime, so I mean motion through space (which in can be transformed away by choosing the apporpoiate refernce frames).

If we race, and I run faster than you, am I or am I not in greater motion than you? I do not understand your perspective.

No, because in your rest frame your speedis zero whilst mine is non-zero. This is a key point in relativity, whetehr it be Einsteinian or Galiliean

OK. Think of a clock, and two observers observing the clock. How can they relate themselves to each other on the basis of observing some clock?

Assuming all clocks are equal they could work out their relative velocities.

 

[wespe]

You ask about the error in the measurement of the clock. I ask about the value of it.

As far as clocks are concerned, yours is an excellent example. Let us consider two observers, you and me. You body is in motion through space. Consider that chemical processes are going on within your body, metabolism, etc. My body is in motion through space, in the same way. They are not moving through space at the same rate of time. How is it relevant that we can use some objective third object to measure time? My rate of motion through time is different from your motion through time, as my body interacts with space in a manner different from yours. Using a light clock, or a mechanical clock, or watching the sun rise and set is very useful to create an objective time for us to share. However, how can you consider it completely applicable to either of us, let alone to both of us? Where is the effect of the interaction of space-time? If you are searching for a close approximation, as close as is possible given that you must use a clock, then I accept your example as close, forgiving the fact that you must use a clock.

If you use a clock as an objective way to relate your motion through space-time with mine, then you are ignoring the fact that each object has a unique relationship to space-time.

How can you compare two unique objects in space-time by relating them to a third, irrelevant object in space-time? What is the value of your comparsion. It does have value, I admit. Do you recognize its limitation?

I see your point. However, I think the limitation applies to large objects. For example when I'm walking, my feet experience time a bit differently than my brain. But let's go to smaller scales. Say, we have two electrons stationary wrt each other. Can they not experience the same time, as measured by light clock? I don't know if an electron has smaller particles in it moving (or something). OK, what about a muon? Does its decay time depend on any movement inside itself? (not sure if that make sense, don't know really what I'm talking about)

 

[jcsd]

Yep, I think it's careful you shouldn't get confused the time-depedency of motion with motion actually being time itself.

 

[jcsd]

For example the unitary evolution of the wavefuction in the Schroedinger equation is time-depednet but actually assigning this time-depedncy to motion in the classical sense is something that you can't or will have great problems doing.

 

[Prometheus]

If an object is in motion it means that it changes it's postion as I said earlier it doesn't mean to much in terms of spacetime, so I mean motion through space

Are you saying that an object cannot be in motion through time. It seems that you deny that there is motion through time. How can you say that it doesn't mean much that there is motion through space-time? I think that this is a big point of disagreement between us.

No, because in your rest frame your speedis zero whilst mine is non-zero.

By this standard, no two objects or people can ever have the same frame, and so any measurement is meaningless.

Assuming all clocks are equal they could work out their relative velocities.

An impossible assumtption, in my opinion.



Do you consider that the speed of light is constant? If so, is it constant in space, in time, or in space-time?

 

[Prometheus]

Say, we have two electrons stationary wrt each other.

What is the duration of this stationary relationship? I think that this is not a valid or realistic assumption.

Can they not experience the same time, as measured by light clock?

What does time reflect in this case? They cannot experience the same time. However, as measured by a clock, they can be related, assuming that the value of the creatd relationship is what is important, and what is ignored is not valued.

 

[jcsd]

Are you saying that an object cannot be in motion through time. It seems that you deny that there is motion through time. How can you say that it doesn't mean much that there is motion through space-time? I think that this is a big point of disagreement between us.

what is motion through time tho'? dt/dt? (though the time component of the velcoity 4-vector can be thought of as dt/dT mutplied by c and relatvistic gamma where T is the proper time)

By this standard, no two objects or people can ever have the same frame, and so any measurement is meaningless.

This is relativity, two objects share the same rest frame if they are at rest to each other if they're not they have different rest fra,es; it's simple as that. Spacetime wouldn't be so useful if this wasn't the case.

An impossible assumtption, in my opinion.

Not really, clocks that measure the time perfectly are not disallowed in this model.

Do you consider that the speed of light is constant? If so, is it constant in space, in time, or in space-time?

The speed of light is the same in all inertial frames this is a postulate of relativity.