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Q & A: relativity revisited

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Most recent answer: 10/22/2007
Q:
A ball has accelerated to 1/2 the speed of light, it is now running at a slower rate of time. Does this effect end at the boundary of the ballís surface or does a field emerge around the ball in where the rate of time increases with distance from the ball? ... similar to how the rate of time might increase with distance from Earth
- Richard (age 45)
U of Waterloo
A:
The important thing to realize is that time is not essentially any different for the ball than for the bigger ball, the Earth. From the ball's point of view, its clock is perfectly normal and the Earthís clocks are all running slow. None of this involves any fields around either the ball or the Earth, just a set of surprising rules for translating the time and space coordinates of one observer into those of another observer when the two are moving relative to each other. There just isnít any observable quantity one can measure to ascertain which one is íreallyí moving and which one íisnítí.

The change in rates of clocks up or down in a gravitational field is a different effect. Here, instead of each clock thinking that the other is slow, both agree that the 'up' clock is faster than the 'down' clock. That change does occur gradually, as a function of how far up or down the clocks are in the field.


Mike W.

(published on 10/22/2007)

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