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From: ethan@utastro.UUCP (Ethan Vishniac)
Newsgroups: net.physics
Subject: Re: Radius of Universe
Message-ID: <545@utastro.UUCP>
Date: Tue, 18-Sep-84 14:56:38 EDT
Article-I.D.: utastro.545
Posted: Tue Sep 18 14:56:38 1984
Date-Received: Tue, 25-Sep-84 09:41:32 EDT
References: <13494@sri-arpa.UUCP>
Organization: UTexas Astronomy Dept., Austin, Texas
Lines: 15

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This is a well known problem in the unification of gravity and
the rest of physics.  Simply put the problem is that the energy
zero-point is arbitrary in most of physics.  If you add a potential
energy which is constant in space and time it doesn't affect anything.
However, one's naive interpretation of gravity would be that since
all mass-energy couples to gravity that this uniform background is
self-gravitating and produces a gravitational field.  The hope
is that when gravity is unified with the other forces of nature
there will be some obvious way of seeing that the zero-point oscillations
of the various background fields don't couple to the gravitational field.  
There is no generally accepted approach to solving this problem.

                          Ethan Vishniac