Re: Hawking in Dublin
From: Serenus Zeitblom (serenuszeitblomphd_at_yahoo.com)
Date: 07/28/04
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Date: 28 Jul 2004 04:58:46 -0400
baez@galaxy.ucr.edu (John Baez) wrote in message news:<ce61d0$9fi$1@glue.ucr.edu>...
>
> >For example, can we feed the black hole indefinitely with a
> >realistic process within the assumed universe?
>
> Not if there's a finite amount of matter around, as would
> be the case in an asymptotically Minkowskian universe.
I suppose that you can imagine
feeding it with a finite diet in ever-decreasing meals which
extend for an infinite time; the restaurant at the end
of the Universe. Oh, he said "realistic". Sorry.
As
> for a universe like ours, who knows? Right now it seems to
> hold an infinite amount of stuff
No, it doesn't. Nobody knows whether the Universe is finite,
though a surprising number of experts think they do. Ted
Bunn set us straight on this a few months ago. Bottom line:
we just don't know.
and to be expanding ever faster
> in an roughly deSitter way.
Sure. But see http://arxiv.org/abs/astro-ph/0307185
There's still good reason to doubt that we are going
to be diluted to death. Again, bottom line: we just
don't know.
>
> However, Hawking's calculations, insofar as he sketched them, were
> all done in an asymptotically *anti-deSitter* universe, where the
> cosmological constant is the opposite sign from ours. I forget if
> you can stuff an arbitrary amount of matter in a universe like this,
> but I guess not.
Well, AdS as usually understood has infinitely large spatial sections.
They are just hyperbolic spaces. But as you know, if you allow complicated
topology these can be made to have finite volume; they can even be made
compact. Anyway if we stick to ordinary AdS, in theory we can put in an infinite
amount of matter if we keep it at a low enough density so as not to
disturb the AdS geometry too much. But this last bit is the kicker:
see http://arxiv.org/abs/hep-th/0406134
Seems that AdS might not survive having even a finite amount of
stuff crammed into it! I guess the inhabitants of AdS better hope
that they can push everything into black holes and thereby somehow
prevent a total disaster. So maybe the question we are talking
about is not as irrelevant as it seems....
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