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Author Topic: Questions about Black Holes  (Read 1941 times)

Gordon Freeman

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Questions about Black Holes
« on: September 24, 2015, 11:44:22 PM »
1. Does US2 measure the radius of a black hole from the event horizon or from the actual "surface"?

2. Will Hawking Radiation ever be simulated? This could be fun to play around with microscopic black holes.


Plutonium

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Re: Questions about Black Holes
« Reply #1 on: September 25, 2015, 02:31:16 AM »
In GR there is no "actual surface" but a singularity, which is infinitely small. So in US2 it should be the size of the event horizon.
In ST's fuzzball theory the event horizone is the actual surface, as far as I understand.

Arian

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Re: Questions about Black Holes
« Reply #2 on: September 25, 2015, 02:14:56 PM »
That thing about a singularity is a myth that is really hard to kill. A singularity is a mathematical model, that is physically impossible, hence the many people who claim, black holes couldn't exist.
In fact, a black hole is not much different from any massive body, except that it's density is extremely high. So high even that atomic structures break down because gravity overcomes at least two of the four forces and maybe in effect even the third.

For any "normal" massive body the event horizon is the surface but for a black hole the event horizon is the distance at which gravity is strong enough to make the escape velocity bigger than the speed of light.
Nothing can be said about the "surface" of a black hole, because nobody could ever see whether any surface exists at all. The size of the compactified matter would likely depend on the actual materials (elements and particles) that contributed to it's mass so far.
So yes, the event horizon is the size of the black hole and physically the only thing that matters about it because the matter inside is at best proto-material.

As for microscopic black holes: They wouldn't survive hawking radiation for more than fractals of nanoseconds. Once they have more mass than the Moon, they simply wouldn't evaporate because cosmic background radiation would feed them more than they'd lose.