From: utzoo!decvax!cca!JGA@MIT-MC@sri-unix
Newsgroups: net.space
Title: Finite rate of information travel, and orbits.
Article-I.D.: sri-unix.2382
Posted: Sun Aug  1 17:47:01 1982
Received: Mon Aug  2 03:30:08 1982

From: John G. Aspinall 

    Date: 31 Jul 82 16:17:19-EDT (Sat)
    To: space at Mit-Mc
    From: decvax!harpo!npoiv!alice!rhm at Ucb-C70
    Subject: Re: Gravitational Information
    Article-I.D.: alice.824
    Via:  Usenet; 31 Jul 82 15:48-PDT

    References: whuxlb.360

    Are you suggesting that the gravitational force acting on a planet
    acts in the direction that the sun was one light time ago?  If so,
    all of orbit theory has to be revised.

Exactly.  Perhaps you have heard of A. Einstein?

    Or perhaps you suggest that object B suddenly "decides " to move?
    Exactly how can this occur, please?

Seriously, this is exactly the effect that causes the perihelic shift
of the planets, notably Mercury, that Einstein explained in 1915.
There are many ways to "explain" it, but one way to look at it is
to regard the motion of any object as being controlled by the local
space-time metric.  Then the geodesic in a central force field
(the Schwarzschild metric, for you jargon fans), gives the orbit of
a mass that is negligibly small compared to the central mass.

The solution of the geodesic gives you something that looks like
Kepler's Law, but with an extra term that contains 1/c^2 .  This
term disappears in the limit that c approaches infinity, which
is what you'd expect in the classical limit.