## A question about time dialation

I understand that clocks move slower as they approach c.

I also understand that clocks move slower on more massive bodies.

My question is are these two phenomena consistant and cumulative?

For example. We have two masses of significantly differeing masses and both have clocks on them. Both of these clocks are accelerated at the same rate and will slow down accordingly.

My question is will the slow down be consistant with both clocks or will the clock on the larger mass slow more slowly until their rates merge just before c?

Thanks

 PhysOrg.com science news on PhysOrg.com >> Hong Kong launches first electric taxis>> Morocco to harness the wind in energy hunt>> Galaxy's Ring of Fire

Blog Entries: 3
Recognitions:
Gold Member
 I understand that clocks move slower as they approach c.
You've missed the main point of relativity - all motion is relative - so the above does not make sense unless you say in which frame ( ie who) is measuring the speed of the clock. If the clock was in someones pocket, they would not notice any change. Only an observer in a frame moving relative to the clock *sees* it running slower. It actually isn't running slower.

 Johnny R, are you asking something like this: Consider a massive non-rotating object M and a test particle T approaching or moving away from each other with relativistic speeds. Do we have to add both the gravitational and kinematical effects to calculate the perceived time dilation at M as observed by T or does the gravitational effect already include the kinematical effect? Is it this you want to know? If so then the answer is that in general relativity the kinematics is built-in already. Consider spacetime, while in special relativity it is possible to think of spacetime as some kind of 4 dimensional fixed ice surface on which particles trace paths without friction, this is not the case in general relativity. In general relativity, spacetime is exactly the complete configuration of all the particles including their masses and energy. Looking at it through time, spacetime continuously reshapes itself. Each particle's relative position, mass and energy contributes to the overall shape of spacetime. So when particles move with respect to each other, the spacetime shape changes. All these configurations of spacetime are actually all the same but just in a different form, a bit like all the different appearances of a Rubic's cube.

## A question about time dialation

 Quote by Mentz114 You've missed the main point of relativity - all motion is relative - so the above does not make sense unless you say in which frame ( ie who) is measuring the speed of the clock. If the clock was in someones pocket, they would not notice any change. Only an observer in a frame moving relative to the clock *sees* it running slower. It actually isn't running slower.
You are right, I am missing a major point here.

A clock on earth ticks faster than a clock in orbit around the earth. A clock on earth ticks faster than a clock on the Sun.

My question is that you have two masses in which one is much larger than the other and I assume that from a third person position the clock on the smaller mass body will tick faster. Now if you accelerate the two bodies at the same rate would the time dialation be consistant for the two bodies or would the clock on the smaller mass body show a more rapid rate of time dialation as they approach c?

Recognitions:
 Quote by Johnny R You are right, I am missing a major point here. A clock on earth ticks faster than a clock in orbit around the earth.
This situation is less ambiguous because the motion is non-inertial (although you could find frames where at certain moments during a satellite's orbit its clock would be ticking faster than a clock on the Earth, even though the average rate of ticking over a complete orbit would be slower), but when two clocks are moving inertially, at constant velocity relative to one another (constant speed and direction), relativity says that in each clock's rest frame, it is the other clock that is ticking slower, and that neither perspective is more correct than the other.

 Quote by JesseM This situation is less ambiguous because the motion is non-inertial (although you could find frames where at certain moments during a satellite's orbit its clock would be ticking faster than a clock on the Earth, even though the average rate of ticking over a complete orbit would be slower), but when two clocks are moving inertially, at constant velocity relative to one another (constant speed and direction), relativity says that in each clock's rest frame, it is the other clock that is ticking slower, and that neither perspective is more correct than the other.
So let's explore a triplets problem.

One triplet in on a space station, one is on a highly massive space ship and the third is on a space ship the same size as the space station. The two ships take off together traveling at the same rate, say 3/4c. Who would be young, younger and youngest when they get back?

Recognitions:
 Quote by Johnny R So let's explore a triplets problem. One triplet in on a space station, one is on a highly massive space ship and the third is on a space ship the same size as the space station. The two ships take off together traveling at the same rate, say 3/4c. Who would be young, younger and youngest when they get back?
Well, I assume by "highly massive" you mean "enough to cause noticeable gravitational time dilation", right? If so this is a problem for general relativity rather than special relativity, but in this case I think the answer would be that the combination of travelling on a non-inertial path and experiencing gravitational time dilation would make the twin on the massive ship youngest, while the twin on the station would be the oldest. In the case of your other question:
 Quote by Johnny R My question is that you have two masses in which one is much larger than the other and I assume that from a third person position the clock on the smaller mass body will tick faster. Now if you accelerate the two bodies at the same rate would the time dialation be consistant for the two bodies or would the clock on the smaller mass body show a more rapid rate of time dialation as they approach c?
I would think that if you take a large-scale view where most of the curvature is confined to the immediate neighborhood of the masses and spacetime is almost flat farther from them (the term for this is an 'asymptotically flat' spacetime), then you could treat this like two clocks that have been artificially slowed down by different amounts (to simulate gravitational time dilation) in SR, which means that one clock will continue to run slower than the other by the same ratio in any frame where they are moving together at relativistic speeds (but although the ratio would be the same in all frames, of course the actual rate of ticking of each clock would be slower in frames where their velocity was closer to c). I don't know enough general relativity to be able to verify that it would actually work this way in the case of real gravitational time dilation as opposed to just simulated time dilation, but I'm pretty sure it would.

 Blog Entries: 3 Recognitions: Gold Member The time dilations of the moving ( wrt space station) triplets is caused by their accelerations and decelerations during their trips. If gravity is indistinguishable from acceleration, then I go with JesseM's ranking - massive ship youngest other ship space station oldest

 Quote by JesseM In the case of your other question: I would think that if you take a large-scale view where most of the curvature is confined to the immediate neighborhood of the masses and spacetime is almost flat farther from them (the term for this is an 'asymptotically flat' spacetime), then you could treat this like two clocks that have been artificially slowed down by different amounts (to simulate gravitational time dilation) in SR, which means that one clock will continue to run slower than the other by the same ratio in any frame where they are moving together at relativistic speeds (but although the ratio would be the same in all frames, of course the actual rate of ticking of each clock would be slower in frames where their velocity was closer to c). I don't know enough general relativity to be able to verify that it would actually work this way in the case of real gravitational time dilation as opposed to just simulated time dilation, but I'm pretty sure it would.

I know that when a clock reaches c (it can't because it would require and infinate amount of energy) it will stop. So the clock with the greater mass would stop before the one with the lesser mass. Does this mean that there is a lower speed limit for more massive objects at some speed less than c? Does a greater mass reach the point where it needs an infinate amount of energy to increase velocity before an object of lesser mass?

Recognitions: