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From: gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>)
Newsgroups: net.physics
Subject: Re: Mach's Principle
Message-ID: <7855@brl-tgr.ARPA>
Date: Wed, 30-Jan-85 12:12:50 EST
Article-I.D.: brl-tgr.7855
Posted: Wed Jan 30 12:12:50 1985
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Mach's principle was that it should be possible to describe the
"forces" on a rotating body in either of two ways, the more
interesting of which is to conside the body at rest and the
forces as due to the rotation of the rest of the universe w.r.t.
the body.  Einstein started out a firm believer in Mach's
principle but rather lost interest in it (perhaps because it
was difficult to show how the effect could be explained in
general-relativistic terms).

There is no "instantaneous action at a distance" involved, though.
Remember that gravitational effects propagate via a field at the
speed of light.  In all such field theories one has to allow that
the field itself can play an active role (e.g. the energy of a
solenoid is in its field, which does not "instantaneously collapse"
when the current is interrupted).