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Big Question for the Day, In regards to Black Holes;

  1. Nov 30, 2014 #1
    Supposing a man named Bob falls into a black hole, an instant of Bob's perceived time would be a nearly infinite amount of time to the rest of the universe due to relativity and the effects it has in and near black holes. Okay sure, but we also know (to my knowledge) that black holes "evaporate" over time. Could it be that the instant Bob gets sucked in, (an instant in his perceived time) the black hole dissipates (because it has evaporated over countless years, as perceived by an outside observer) leaving Bob completely unharmed?
    Please clarify this. Thank you!
  2. jcsd
  3. Nov 30, 2014 #2


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    Bob's perception of time is that it flows normally and the black hole makes no changes during the brief time he is alive as an observer.
  4. Dec 1, 2014 #3


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    Well, the complete description of physics including black hole evaporation, is not completely understood, since it involves both gravity and quantum mechanics. However, qualitatively, we can say that there are two possible scenarios, depending on when Bob starts falling toward the black hole:
    1. Either the black hole evaporates before Bob gets to it.
    2. Bob gets to the black hole before it evaporates.
    In case 2, things will look very different from Bob's point of view than from the point of view of a distant observer.

    From Bob's point of view, his fall through the black hole and to his death at the singularity is so short that black hole evaporation is pretty much irrelevant.

    From the point of view of a distant observer, Bob will meet his demise at the same "time" that the black hole evaporates completely. I use "time" in quotes, because this conclusion depends on the coordinate system used by the distant observer--the two events are not literally the same event.
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