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Observable Universe and Black Holes

  1. Oct 18, 2012 #1
    Hi, my first post here!

    Galaxies outside the observable universe (that we can't see their light) can affect us with their gravity?
    If the answer is no, we can say that gravity information travels at the speed of light.
    So, in a black hole how gravity information from an object inside, escapes the event horizon?
    An object inside a black hole is also outside our observable universe.
    I know that in general relativity mass of a black hole is responsible for the curvature of spacetime, but where this curvature begins in our universe? Does it begin from the Event Horizon limit? Can we say the event horizon itself carries all the gravity information of a black hole?

    I can't figure it out, I have it, all in a mess inside my mind
  2. jcsd
  3. Oct 18, 2012 #2


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    Thats...tough to answer properly. Consider that gravitation is, as far as we know, infinite in reach. Very early in the universe it is believed that the universe was compressed to a very high degree. The matter and energy here was very close together, so it would have easily had time for its gravity to affect our area. However, inflation and expansion have pushed some of that matter and energy outside of our view for the future. BUT, this process hasn't happened instantly, it has taken time, and the gravity, while having weakened, should still be affecting us at least a tiny amount. (REALLY tiny. So tiny that expansion overwhelmingly dominates gravitation between us)

    Similarly, infalling objects do not fall in instantly, they take time. Plus, from our perspective they don't actually ever fall in thanks to time dilation! For practically all intents and purposes their gravity simply adds to the black hole.
    This curvature is not something you can say "starts" or "ends" somewhere. It simply exists. It is an intrinsic part of spacetime. I don't think I can explain it very well.
  4. Oct 18, 2012 #3


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    We are pretty confident objects, like galaxies, that are outside the observable universe are causally disconnected from the observable universe. Or, in other words their light, gravity, etc., have no effect on bodies within the observable universe. We are not causally disconnected from black holes within the observable universe. We still experience the effects of gravity and charges generated by black holes.
  5. Oct 18, 2012 #4


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    Certainly we wouldn't be affected by changes in them since they moved out of our observable universe, but in the past was there ever a certain point where their influence on us through gravity simply disappeared?
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