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From: tim@unc.UUCP
Newsgroups: net.religion,net.misc
Subject: Re: Earth Centered Universe
Message-ID: <5579@unc.UUCP>
Date: Mon, 18-Jul-83 15:31:05 EDT
Article-I.D.: unc.5579
Posted: Mon Jul 18 15:31:05 1983
Date-Received: Tue, 19-Jul-83 19:03:17 EDT
References: dciem.249
Lines: 47


            What could a "stationary earth" mean in
        relativistic terms? To have a "stationary earth" means
        that there must be an absolute frame of reference with
        respect to which the earth is stationary.

    All right, so I used slightly misleading terms.  My meaning was
still clear, so let's not pick nits.  What I meant to say was that
there exists a consistent formulation of the laws of physics in which
the earth is considered to be non-rotating.  This is an extension of
relativity that was in the general theory, which applies to
accelerating frames of reference as well.

        Sure the earth is stationary with respect to me (when
        I am pursuing my favourite pastime).  The rest of the
        universe isn't moving faster than the speed of light
        with respect to me, though.

    Very perceptive.  The reason for this is that the special theory
of relativity introduced a new equation for computing relative
velocity.  Consider two rockets hurtling away from an asteroid in
opposite directions.  Each has a speed of three quarters of the speed
of light, as measured by an observer on the asteroid.  However, the
speed of one relative to the other is NOT half again the speed of
light -- it is a (large) fraction of the speed of light.  This is
totally counterintuitive, but that's how it works.  Similarly, no
matter how fast Earth spins, we will never percieve any object as
moving faster than the speed of light relative to our point on the
surface of the planet.

        It is moving faster than the speed of light with
        respect to some mythical Newtonian absolute frame of
        reference connected to me, but who cares?  The objects
        in that universe do not change their motions relative
        to one another or with respect to potential other
        observers just because I happen to take myself as a
        reference observer for now, and the earth is
        stationary in my frame.

    I'm sorry, I'm not clear on what it is you're saying here.

______________________________________
The overworked keyboard of Tim Maroney

duke!unc!tim (USENET)
tim.unc@udel-relay (ARPA)
The University of North Carolina at Chapel Hill