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Time dialation and ageing

  1. Aug 7, 2008 #1
    i have read about the experiment of people ageing slower when moving at velocity and don't quite understand.

    here's my experiment:

    two people, person A and B, start off in the same referance frame (both are, say 20yrs old). person A flies off in one direction and person B in another. they accelerate to 99% c and stay like that for 5 years. from my understanding they would both see the other person age faster than themselves. now, after 5 years they turn around and come back to the same referance frame however they have seen the other person age faster than themselves. so my question is, who is older, or are they both the same age still. if we add person C who stayed in the initial referance frame and didn't accelerate, would A, B and C all be the same age or would C be older than A and B.

    i suppose i may have missed some subtleties in how A and B observe each other when moving at 0.99c. is it possible that the amount of time it takes the light from A to reach B compansate for the slower ageing B would observe if the light travelled instantly.

  2. jcsd
  3. Aug 7, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Short answer: A and B are the same age. C is older.

    Check out my standard explanation here, or do a search for "twin paradox" to see other people's explanations.
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