Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!cmcl2!lanl!jlg
From: jlg@lanl.ARPA (Jim Giles)
Newsgroups: net.physics,net.origins
Subject: Re: Bogus physics reamplified
Message-ID: <556@lanl.ARPA>
Date: Sun, 16-Mar-86 16:12:52 EST
Article-I.D.: lanl.556
Posted: Sun Mar 16 16:12:52 1986
Date-Received: Fri, 21-Mar-86 06:57:32 EST
References: <368@ihnet.UUCP> <2057@jhunix.UUCP> <2874@sjuvax.UUCP> <446@3comvax.UUCP> <424@lanl.ARPA> <12398@ucbvax.BERKELEY.EDU>
Reply-To: jlg@a.UUCP (Jim Giles)
Distribution: net
Organization: Los Alamos National Laboratory
Lines: 75
Keywords: general relativity, justifying assertions, name-calling
Xref: watmath net.physics:3955 net.origins:2969

In article <12398@ucbvax.BERKELEY.EDU> gsmith@brahms.UUCP (Gene Ward Smith) writes:
>In article <424@lanl.ARPA> jlg@a.UUCP (Jim Giles) writes:
>
>>In article <446@3comvax.UUCP> michaelm@3comvax.UUCP (Michael McNeil) writes:
>>>Returning to Ken's original point, which started off this whole series
>>>of articles, in the above reference Bertrand Russell writes as follows:  
>>>
>>>	But in the modern theory the question between Copernicus and
>>>	his predecessors is merely one of convenience; all motion
>>>	is relative, and there is no difference between the two
>>>	statements:  `the earth rotates once a day' and `the heavens
>>>	revolve about the earth once a day.'  The two mean exactly the
>>>	same thing, just as it means the same thing if I say a certain
>>>	length is six feet or two yards.  Astronomy is easier if we
>>>	take the sun as fixed than if we take the earth, just as
>>>	accounts are easier in decimal coinage.  {Signet, pp. 13-14}
>>
>... Russell is
>correct (almost) in his quote above. You are dead wrong. Try writing a rotating
>coordinate frame in GR (not hard) and you will see.
>
>>For the definition of 'frame' and 'local' I suggest you read the first few
>>chapters of MTW ('Gravitation') again.  I just did - fascinating stuff!
>
>    You need to do more than read it (we both have, apparently). You need
>to understand it. Read it again, using your noggin.

Russell is not even CLOSE to being right.  I suspect he was mislead by
Mach's principle which explains the origin of momentum as being relative
to the distribution of mass throughout space.  The fact that momentum is
relative in no way implies that the choice between Copernicus and Ptolemy
is merely one of convenience.

Consider a pendulum swinging freely at the north pole (disregard
precession effects that are classical).  In classical theory, the plane
through which the pendulum swings will rotate once per day when measured
relative to the Earth, and it will appear fixed relative to the distant
stars (this seems to imply that it is the Earth that is turning).  Now
according to Mach's principle as applied in GR, the pendulum will be
seen to turn relative to the Earth - but not EXACTLY once per day, and
it will seem to rotate SLIGHTLY relative to the fixed stars (this is
even after ALL classical causes of precession have been eliminated).
The emphasized words point out that this is a VERY SMALL (read:
unmeasurable with today's technology) effect for the Earth: for
practical purposes Copernicus was right.

Now, to a small extent, Copernicus was wrong as well: the universe IS
rotating around the Earth (at least around a coordinate system with zero
measured angular momentum) - but VERY slowly.  In either case, a
particle attached to a local reference frame in GR would have NO angular
momentum (and would, therefore, imply that the reference frame was fixed
relative to the distant stars - properly modified by Mach's principle to
include the effect of nearby rotating masses).  Nothing which is fixed
relative to the Earth fits this requirement.

Note: I have always said 'local reference frame', which in GR is ALWAYS
a Lorentz frame.  See box 1.3 in "Gravitation".  End of Note.

The part of "Gravitation" relevant to Mach's principle starts about page
450.

Small flame:
    Some people on the net seem to think that it is the origin of
    knowledge or the accuracy of spelling that constitutes a valid
    argument.  This is NOT true:  I always have to look up 'Lorentz'
    when I put it into text - it just doesn't look right to me.  Perhaps
    the difference with me is that I DO bother to look it up so that my
    contributions to the net are at least spelled right whatever other
    merits they may have.  But, don't tell me something is bogus just
    because the spelling is wrong.  Let the argument stand or fall on
    its own merit. (Maybe it should be spelled 'Larry' :-)
End of small flame.

J. Giles
Los Alamos