Date: 11/12/97 at 23:18:05 From: Parminder Kang Subject: Black Holes I have always been somewhat dumbfounded by the conclusions one can draw from the existence of black holes. This problem has been bothering me. Imagine an observer outside a black hole watching someone wearing a clock moving into the black hole. I know that the outside observer will see the clock moving slower and slower as the person approaches the black hole. Of course, after the person passes the event horizon, he will lose contact with the rest of the universe. I know that the person will still be able to see me as he is entering the black hole. My question is, how will the person in the black hole see the observer? Since the person inside the black hole perceives time to be slowing down, he must see my time speed up. Consequently, he will see me age very fast. Does this also imply that he is actually seeing into the future?
Date: 11/13/97 at 11:29:26 From: Doctor Mitteldorf Subject: Re: Black Holes Dear Parminder, He's seeing the future the same way that a person who travels very close to the speed of light and then returns to earth sees the future: by slowing down his internal clock and living a long time. From the point of view of a person falling into a black hole, it takes a short time. But from the point of view of someone outside, it takes an infinitely long time for him to fall in. Yes - he sees the entire future history of the universe on the way in. But another way of saying this is that he won't make it into the black hole during the (infinite) lifetime of this, our universe. In fact, it takes an infinite amount of time for matter to collapse to form a black hole, too. All the astronomical objects that are loosely called "black holes" are really in an irreversible, dynamic process of collapsing, and are asymptotically close to their event horizon, but not through it. Technically, you might reserve the word "black hole" for matter that is inside its event horizon; for that to be the case, the black hole must have existed since the beginning of (our) time. -Doctor Mitteldorf, The Math Forum Check out our web site! http://mathforum.org/dr.math/
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