On Thu, Dec 5, 2013 at 8:11 PM, LizR <lizj...@gmail.com> wrote:

> Ah yes I've heard that the gravity at the event horizon can be as weak as
> you like with a suitably large hole - that you might not even realise you'd
> crossed it


> though surely you'd get some optical effects?

If you were falling back first into a Black Hole things that were behind
you would start to look as if they were ahead of you, and as you got very
close to the event horizon all the light from the entire external universe
would be coming to you from a small disk directly in front of you. When you
actually crossed the event horizon (the point of no return) the diameter of
that disk would shrink to zero and you'd be forever cutoff from the
universe you knew. If the Black Hole were large enough you could still be
alive when you crossed the event horizon, although a few seconds later
tidal forces would rip you apart through spaghettification

> So the Michell star is effectively like a solid version of a black hole's
> event horizon.

It's more than that, at the event horizon of one of Einstein's Black Holes,
even if the gravity was only 1g, you could never escape the Black Hole and
return to Earth no matter how powerful your rocket is; on the surface of
Michell's dark star even if it was a billion g you could escape if your
rocket was powerful enough (assuming a billion g didn't prove harmful to
your health).

  John K Clark

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