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From: dgary@ecsvax.UUCP
Newsgroups: net.philosophy
Subject: Re: Gravity anyone?
Message-ID: <3100@ecsvax.UUCP>
Date: Tue, 14-Aug-84 11:02:33 EDT
Article-I.D.: ecsvax.3100
Posted: Tue Aug 14 11:02:33 1984
Date-Received: Fri, 17-Aug-84 01:10:47 EDT
References: decwrl.3290
Lines: 47

<  Quoting ... >
>From: merrill@gigi.DEC (Rick GIGI::Merrill  DECRITE) Mon Aug 13 08:46:28 1984
>Is mass the cause of gravity or does the movement of the gravitons create
>the effect of mass?

The exchange of virtual particles like gravitons for gravity,
Ws and Zs and photons for electroweak, and gluons for strong (color)
force are ways of dealing with the "action at a distance" of the
forces of nature.  Of these particles, only the electroweak ones have
been detected (all but the photon this year, in fact).  Making gluons
would require an accelerator the size of the solar system with something
like a quasar as power source, and Glashow says this seems a little much
to ask from the Reagan administration.  Gravitons are even more theoretical
than the other particles.

To my knowledge, all currently accepted theories of gravitation are
geometrical in nature, with Einstein's General Theory still holding up
well as the front-runner.  To see how a geometric view of force works,
imagine that we are at the Earth's equator and you and I begin walking
north.  We eventually realise that we are drawing closer together,
even though we are carefully walking in a straight line.  By repeating
the trip with different sized loads we can determine that the "force"
between us is proportional to our inertial masses, a mystery indeed
(why should gravitational "charge" equal inertial mass, anyway?).  But
when we discover we are on a curved surface (the Earth) we understand
what gives pretty quickly.  Replace "north" with "forward in time"
and convert the Earth's 2-dimensionasurface to a 4-dimensional one
and you have a good measure of General Relativity.

There's a good deal more, of course, but all that can be summed up as
Einstein did, by saying that "space tells matter how to move, and matter
tells space how to curve."  You might wonder if the other forces of
nature can be dealt with geometrically.  The answer is yes, if you allow
some of the coordinates to be so tightly curved that moving in a given
direction returns you to your starting point in an infinitesimal
distance.  Such geometrical unified field theories (called Kaluza-Klein
theories if my memory and spelling are right) have undergone a recent
resurgance of interest.

Not directly to the point I admit, but maybe that helps.  And yes, this
really does belong in net.sci, but I followed the original poster's
newsgroup choice.

D Gary Grady
Duke University Computation Center, Durham, NC  27706
(919) 684-4146
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