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Apr3-08, 06:12 AM
Sci Advisor
P: 8,470
Quote Quote by MeJennifer View Post
Perhaps I misunderstand you but, if we have:

1. Twin A and B on planet P and point X, a fixed distance away from planet P.
2. A accelerates away from P towards X.
3. A accelerates towards P to stop at X.
4. A records the total elapsed time since 2.
5. A accelerates away from X towards P.
6. A accelerates towards X to stop at P.
7. A records the total elapsed time since 5.

Then all observers must agree on both recorded proper times recorded in step 4 and 7.
Yes, I agree. I was talking about comparing how much A had aged at step 4 with how much B had aged "at the same moment", which of course is frame-dependent since different frames disagree on simultaneity. In some frames B has aged more than A at the moment A stops at position X, while in other frames B has aged less than A at the moment A stops at position X. In a frame where B (the twin on planet P, which we can think of as earth) has aged less at the moment A stops/turns around, then I would interpret that as contradicting your statement that "After accelerating away from the twin on earth his clock is going to accumulate less time compared to his twin on earth until he reverses the direction of acceleration."