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Re: cosmology and quantum gravity



A lot of the technical details I added were intended merely for the
interested reader and are admittedly superfluous as Jack pointed out below.
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.

To be further superfluous and add one more item of technical detail.

The Ricci tensor, a measure of gravitational effects in a local region of
space, does not diverge at the event horizon of a Schwarzchild black hole.

Joel Rauber




On Fri, 28 Apr 2000, Joel Rauber wrote in part:

Jack wrote in part:
. . .
The static gravitational effects that we can observe are
embedded in the
metric (more strictly, the curvature) outside of the
horizon. In the
usual metric, the gravitational effects get larger and
larger as we
approach the black hole until they blow up at the horizon,
where there is
a coordinate singularity. . . .
--------------------------------------snip-------------------
---------

There exist other coordinate systems to describe a
Schwarzchild black hole
that have no coordinate singularities at the event horizon.
One oft cited
example are the Kruskal-Szekeres coordinates (named after
their creators, I
assume) See the book "Gravitation" by Misner, Thorne and
Wheeler (know to
many students as MTW) around page 831 for a discussion.

Joel

And, conversely, I would not have put it Joel's way, having
specifically referred to "coordinate singularity" and "event horizon".
I would not get into such technical details as Kruskal-Szekeres
coordinates in responding to a simple, naive question about gravity.
My description was accurate; it spoke of gravitational effects
<in the usual metric>. Since the question was, "how do the
gravitational
forces get out" the additional details would seem to be irrelevant to
the question asked.
Regards,
Jack