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Slowing time

  1. Apr 26, 2010 #1
    I know this has been asked tons of times on here. But I never seem to understand the answers. So I challenge all you smart people to explain it as simple as possible. How does time slow down for a person who is traveling at a hihg speed and not for someone standing still? The person standing still is still moving around the solor system, that is traveling around the solor system. There is no universal time frame. So if someone is traveling very fast away from me why would he age slower and not me, how could time now who is traveling and who is not. Please make the answer as easy as possible.
     
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  3. Apr 26, 2010 #2

    D H

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    If someone is traveling very fast away from you, that other person will appear to you to be aging slowly. From the perspective of that other person, her watch is working just fine, thank you, but yours is not. From her perspective, it is you who is aging slowly.
     
  4. Apr 26, 2010 #3
    Really? Then why do I always hear about how if someone was in a space ship traveling close to the speed of light would return to earth to find that everyone else has aged more than him?
     
  5. Apr 26, 2010 #4

    bapowell

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    That's the twin paradox. The difference in this set-up is that one twin returns to Earth. In doing so, this twin must at some point slow down and change direction. It is this acceleration that breaks the symmetry. But you are right to be surprised -- that's why it's a seeming paradox! If the two twins never meet up again, they both go on aging normally according to themselves, but each ages slowly according to the other.
     
  6. Apr 26, 2010 #5

    D H

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  7. Apr 26, 2010 #6

    George Jones

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    Actually, it is a paradox. :wink:
    Twins?!
     
  8. Apr 26, 2010 #7
    This is one of the interesting predictions of the theory of relativity. It was verified experimentally, see the "Haefele-Keating" experiment.
     
  9. Apr 27, 2010 #8
    Yes, i have read all of these things. But that is where I get confused. How could one twin age more than the other if there is no universal time frame? If these twins were the only 2 things in the universe how would anyone know who is traveling more than the other. tehy would both be traveling equal to eachother?
     
  10. Apr 27, 2010 #9

    JesseM

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    There is no universal truth about an object's velocity, but there is a universal truth about whether an object is moving inertially or accelerating. If you have two twins that move apart and then reunite, with one twin moving inertially between the two meetings and the other accelerating to turn around, all frames agree that the inertial twin aged more between meetings than the accelerated twin (and they all agree on their precise ages when they reunite), despite the fact that they disagree about each twin's velocity and rate of aging during individual parts of the trip (for an example of the same trip calculated from two different frames, see my post #36 here)
    The twin that accelerates will feel G-forces when she accelerates, the twin that moves inertially will feel weightless the whole time (here we are talking about the twin paradox in special relativity where there is no gravity, though because of the http://www.aei.mpg.de/einsteinOnline/en/spotlights/equivalence_principle/index.html [Broken] general relativity says that the G-forces of gravity can also be understood in terms of acceleration relative to a locally inertial frame)
     
    Last edited by a moderator: May 4, 2017
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