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Apr3-08, 01:58 AM
Sci Advisor
P: 8,472
Quote Quote by anonymoussome View Post
When we read that two twins would age differently when one moves with relativistic speeds.
i.e. When one twin travels at speed near to speed of light then the twin on earth would see that time for the travelling twin has slowed down. Thats what we say time Dilation.
Similar is the case with the other twin. He may also say on returning back that time had slowed for the twin on earth. But his claim is refused because he was initially and finally in a non inertial frame. But what about the time when he was moving with constant velocity. At that time he was moving in an inertial frame. Why does it happen then that what he sees is false and the OP is true??
If he continued moving inertially, then what he measures in his frame (which is different from what he see--look at this thread if the distinction isn't clear to you) is just as valid as what is measured in any other frame. But as long as you stick to a single inertial frame for the entire problem you'll conclude the traveling twin ages less in total (the laws of physics work the same in every inertial frame, but they don't work the same way in non-inertial frames). For example, you could take the perspective of the frame where the traveling twin was at rest during the first phase of the journey while the Earth is flying away, and in this frame, he will age more than the Earth prior to the turnaround, but after the turnaround he'll be moving at an even greater speed than the Earth, and so be aging slower. It'll work out that when you add how much he ages in both the outbound stage and the inbound stage, and compare it to how much the Earth ages from start to end, the traveling twin still ages less, by exactly the same amount as if you had used the rest frame of the Earth.