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Phoning someone, when Time Dilation is occuring

  1. May 24, 2015 #1
    I was talking to my dad not long ago and he asked me an extremely valid question, so basically, the question is.
    If i'm next to a supermassive black hole, and 1 hour for me is 77 hours on earth, and my dad rings me, bearing in mind you would an extremely good signal, but lets just say i answered, and we spoke for an hour(my time)he would of been speaking for 77 hours back on earth?
    Please can someone give me an answer? (Is this a paradox)
  2. jcsd
  3. May 24, 2015 #2


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    Staff: Mentor

    That is exactly what "and 1 hour for me is 77 hours on earth" means, yes.
  4. May 24, 2015 #3


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    No, that is not a paradox. He would hear you talking very rapidly, you would hear him talking very slowly. (At a ratio of 77 hours to one hour, it would probably be very difficult for either of you to understand the other!)
  5. May 24, 2015 #4


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    Also, I expect what you say will be redshifted by that same factor, he will hear you speaking very very slowly in a truly deep voice - like playing a recording 77x slower than it was recorded.
  6. May 28, 2015 #5
    no his dad will hear him talking very slowly.
  7. May 28, 2015 #6


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    No, HallsOfIvy is correct. This is gravitational time dilation. It is not symmetrical like that.
  8. May 28, 2015 #7


    Staff: Mentor

    But his dad is the one who is distant from the hole, and whose clock is therefore running faster. So dad will see son greatly slowed down, and son will see dad greatly speeded up. There is indeed an asymmetry, but HallsOfIvy had its direction wrong.
  9. May 28, 2015 #8


    Staff: Mentor

    Oops! I was getting who was where mixed up too. My apologies Prashan.
  10. May 31, 2015 #9
    I recall seeing Peter Ustinov sped up on TV as a kid.
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