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Can someone explain this time dilation problem to me?

  1. Oct 24, 2009 #1
    I'm going to use the time traveling twins example to try and explain the crossroads I'm at with special relativity. The one twin is back on earth while the other twin is traveling to a star 10 light years away at .8c. We calculated how long it would take on the earth-star frame of reference, it would take approximately 12.5 years. However, it would ony take 7.5 years in the twin in the spaceship frame of reference due to length contraction. That's all well and good, I understand that. The end of the story is the one twin comes back and 25 years elapsed on Earth and only 15 years elapsed for the twin, the twin came back 10 years younger. I would like to know how come the twin on Earth isnt the twin who had only 15 years elapse. One could say that in the spaceships frame of reference that the Earth was moving away at .8c and not the ship. Someone explained it to me that it's because the ship turned around and wasnt in uniform motion anymore and whatnot but I just don't understand that. Any help will be appreciated.
  2. jcsd
  3. Oct 24, 2009 #2


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    Staff: Mentor

    Try doing a search on "twin paradox" in this forum. Maybe one of the previous threads on this issue will help you. :smile:
  4. Oct 24, 2009 #3
    This problem has been discussed ad nauseam at these boards, as you may well imagine.

    Short answer is that the twin at Earth stays in the same inertial frame at all times, while the twin moving switches frames. If you were to calculate the proper time difference elapsed between the twins, you would get a compatible answer in all three frames. However, twin 2's spaceship is not a proper inertial frame, and that is where your logic goes wrong.
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