Quote:
Originally Posted by tommac
I thought about this on the way into work ... and I realize my wording is not great and in fact I realize that they may not be the same after all. From our vantage point the EH is really the singularity because a more defined singularity can never be created.
Now a sphere ... hmmm ... I cant picture this sphere. the sphere would have 0 volume but is not a point. It needs to have 0 volume because space is fully compacted at the event horizon.
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Listen carefully: space is
not fully compacted at the event horizon. That only happens (if at all) at the singularity, which is beyond the horizon,
inside the black hole. It's not at the event horizon that all the mass in the black hole is supposed to be compacted into infinite density, or that time is supposed to stop. All of that is supposed to happen at the singularity.
The event horizon is merely the spherical boundary of the black hole. It's an imaginary boundary, like meridians on a globe, or the edge of Earth's atmosphere. And it's the point of no return (or rather the surface) for an infalling object. Once you cross it, you're inside the black hole, and you can no longer turn back. You must keep falling; in a Schwarzschild-type black hole you keep going until you hit the singularity along with the rest of the infalling matter.
Quote:
Originally Posted by tommac
However I cant picture a sphere with 0 volume. Please elaborate.
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It's a hollow sphere -- or a spherical surface, more correctly. As such, it has a radius and a surface area, but zero volume. Like the surface of the Moon, or of a lake.
Quote:
Originally Posted by Pittance
"From a distant observer, no star has collapsed into a singularity". This is a bit weird.
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Weird but, I believe, true. In general relativity, the reference frame of a distant observer is no less legitimate than the reference frame of an observer falling into the star that's collapsed into a black hole.