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Gravity time relationship

  1. Nov 13, 2014 #1
    I always wondered when they say as you approach a body having sufficiently high mass time slows down considerably
    but is it possible that if I look at an object and that object were to move close to say a black hole as it nears the event horizon the speed of the escaping light should decrease and hence it should take longer for it to reach us and hence we would assume that time has slowed down whereas time is moving at the same velocity but we are receiving the images much later. So basically what I'm asking is that how can it be possible that a black hole (or any high mass) body having a massive gravitational effect can considerably slow down time.
    In that case when the body emerges fromthe massed structure it should have caught up withthe present time shouldn't it?
     
  2. jcsd
  3. Nov 13, 2014 #2

    ShayanJ

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    Gold Member

    1) What you're describing, is only a constant shift of events in time. We need something that alters the time between the events.
    2) Gravitational time dilation is not an experimentally found phenomenon that people built a theory for. It comes from theory(GR) and is then confirmed experimentally. So its meaningless to try to explain it differently from the beginning. Alternative theories, should be alternatives to the whole GR which after explaining gravity, should predict the same effects that GR does, including gravitational time dilation.
     
  4. Nov 13, 2014 #3

    PeterDonis

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    Staff: Mentor

    Here's a more precise way of stating how this works: suppose you and I start out in a space station far out in empty space, away from all massive bodies. I stay on the space station; you get in your rocket and fly down very close to the horizon of a black hole. You stay down there for a while, then fly back up to the space station and we compare our clocks. We will find that your clock shows far less elapsed time than mine does (how much less depends on how massive the black hole is and how close you get to its horizon).

    Another scenario that illustrates gravitational time dilation is this: suppose I am on a space station, again far out in empty space, and you are in your rocket hovering very close to the horizon of a black hole. We exchange light signals, and each of us times how long it takes the light signals to make a round trip according to our clocks. We will observe the following:

    (1) A given light signal takes much more time to make a round trip according to my clock than it does according to your clock (this is why we say your clock is "running slow" relative to mine).

    (2) I observe your light signals to be redshifted.

    (3) You observe my light signals to be blueshifted.

    No. See the first scenario above.
     
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