Re: cosmology and quantum gravity

["Glenn A. Carlson" <gcarlson@MAIL.WIN.ORG>]

Perhaps this is all a matter of semantics and style, but --

Mr. Uretsky's post raised the same concerns for me as it apparently
did for Mr. Rauber.  I attribute my reasonable confusion to the
ambiguous terms "usual metric" (the Schwarzchild metric with coord.
singularity or the Kruskal metric without coord. singularity?) and
"gravitational effects" (What effects?  Not all physical effects blow
up at the event horizon).

And, while a diamond-hard reading of Mr. Uretsky's post could find he
did not say the gravitational effects at the event horizon were
*caused by* or a "consequence of* the coordinate singularity at the
event horizon, a reader could reasonably infer this.  If this is not
what was meant, why mention the coordinate singularity at all.

Mr. Bowman (thank you!) certainly describes "gravitational effects"
(i.e., physical effects), but they have nothing to do with the
(nonphysical) coordinate singularity of the Schwarzchild metric except
that they are all "blow up" at the event horizon.

I think it's important to emphasize Mr. Rauber's point (as I read it)
that the "blowing up" of the gravitational effects (as described by
Mr. Bowman) and the Schwarzchild metric are very different things; and
the (non-physical) coordinate singularity does not cause the blowing
up of the (physical) gravitational effects.  I would even go as far to
say the blowing up of the Schwarzchild metric is not a gravitational
(i.e., a physical) effect.

Just my opinion.

Glenn A. Carlson, P.E.
gcarlson@mail.win.org

> Subject: Re: cosmology and quantum gravity
> Date: Fri, 28 Apr 2000 22:13:30 -0400
> From: David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>
[snip]
> Any stationary observer would have an *infinite* weight at the
> event horizon, and would weigh *very much* just a little above the
> horizon.  The event horizon in this case is also a stationary limit
> surface in that it would require an infinite amount of station-keeping/
> supporting force to keep from falling through the horizon when trying to
> hover *at* the horizon.  I *would* call this a gravitational effect that
> 'blows up' at the horizon.
[snip]
> gravitational red shift for light signals from from a stationary
> object just outside the horizon as observed by another stationary
> observer farther out from from the hole tend to diverge to infinity as
> the inner observer approaches the horizon (very gingerly).  Also, the
> gravitational blue shift in the light from the outer observer as observed
> by the inner observer *also* diverges as the inner observer gingerly
> sneaks up (ever so slowly) on the horizon from above. Also the time
> experienced by the inner fixed observer becomes infinitely dilated
> relative to another fixed outer observer as the inner observer sneaks up
> on the horizon infinitely slowly.  I would call these effects as
> 'blowing up' as well.
[snip]
> David Bowman
> David_Bowman@georgetowncollege.edu