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Re: cosmology and quantum gravity



David wrote:


I'm not sure it would be wise for me to butt into this dispute between
Joel and Jack, but I'm not very wise.


But I doubt I can recall a time when David didn't have something
interesting, pertinent, and educational to say!!!

Regarding where Joel wrote:
...
However, I must reiterate, there are no physical effects
that blow up at the
event horizon of a Schwarzchild black hole, at least in the
usual physics
sense of the words "blow up", which I interpret as loose language for
diverging to infinity. That does not mean interesting
things don't happen
at the event horizon, as several well known interesting
things do occur at
the event horizon.


I have no quarrel with what David wrote: (not repeated here for the most
part.)

Naturally I do not disagree with what Glenn A. Carlson wrote later in the
discussion, either.


I think I would have to side with Jack on this one. Although it is
certainly true that all the components of the various
curvature tensors
remain well behaved at the event horizon

This is all I meant to say. And to furthermore make sure that a common
misconception be pointed out; namely that a free-falling observer that
passes through the event horizon would notice "horribly strange things", by
that I mean infinite tidal forces. David certainly mentioned many of the
interesting things that can be discussed wrt the event horizon. Some of
which have quantities that diverge.

And very importantly, David added later in his post.

Actually, for a black hole the Ricci tensor doesn't measure *anything*
because a black hole is a vacuum solution of Einstein's
equations and the
Ricci tensor for a vacuum vanishes identically. In a region
that is not a
vacuum the Ricci tensor measures a local encoding of the
stress-energy of
the matter and radiation present into the curvature of spacetime. I
suspect that what Joel means is that the *Weyl* tensor for
the black hole
measures gravitational effects since even in a vacuum the Weyl tensor
measures the tidal distortions of spacetime (which certainly *are*
present around the hole).


Absolutely, I meant to refer to Weyl tensor; thanks for the correction!

Joel Rauber