Re: A partial black hole?

On 2008-03-07, Jonathan L Cunningham <spam@[EMAIL PROTECTED]
> wrote:
> Presumably you are saying that, at that distance, the gravitational
> force is infinite (= arbitrarily high acceleration).

In the sense of "force required to keep you at constant distance", yes
it is.


> Since it increases as you approach the singularity, sounds like you
> are saying that it exceeds infinity as you get closer! :-)

Yes, in a sense it does.  Inside the horizon even an instantaneous
****ft of velocity won't keep you at constant radius.


> I think we agree that the tidal forces are not infinite, but vary as
> the inverse cube?

Something like that - I can't recall the exact formula for tidal force
in the Schwarzschild geometry.  Perhaps I'll derive it when I get home.


> And certainly the gravitational force varies as the inverse square
> at large distances ... and with a very large mass black hole, the
> event horizon *is* at a large distance. But is it large enough?

No it isn't, pretty much by definition.  Large distances are so named
for being far outside the event horizon.


> So what's the formula for the gravity at a distance D from a black
> hole?

If I haven't totally messed up the derivation, it should be
pro****tional to (sqrt(D/(D - R)) / D^2) for a Schwarzschild black hole
with event horizon at R.  (I would not be surprised if I have)


- Tim