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Q & A: time at the edge of a black hole

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Most recent answer: 04/04/2011
Q:
Can you describe what happens to time in and around a black hole, in terms of gravitational time dilation? If a clock runs slower deep within a gravitational field than far from it, does time slow considerably in the immense gravitational field of a black hole? Is there some point at which gravity could cause time to stop or to simply not exist?
- Alex (age 43)
Lexington, KY, US
A:
You've inferred exactly what goes on. As one approaches the event horizon of a black hole, the gravitational redshift (slowing) approaches a factor of infinity. Thus as things start to fall in to form a black hole, the rate at which the last stuff falls in (as viewed from far outside) slows down. It turns out that this slowing is enough to prevent the black hole from ever quite completely forming, as viewed from the outside. However, what forms is so close to a complete black hole as to behave like one for most purposes, with the exception of some issues about abstract information loss.

Mike W.

(published on 04/04/2011)

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