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From: crummer@AEROSPACE.ARPA
Newsgroups: net.physics
Subject: Twins, Inertial Frames, and Gravitation
Message-ID: <283@sri-arpa.ARPA>
Date: Tue, 18-Jun-85 14:00:35 EDT
Article-I.D.: sri-arpa.283
Posted: Tue Jun 18 14:00:35 1985
Date-Received: Sun, 23-Jun-85 08:24:27 EDT
Lines: 39

From:  Charlie Crummer <crummer@AEROSPACE.ARPA>

> Received: by sri-unix.ARPA (4.12/4.16)
>         id AA24360; Fri, 14 Jun 85 19:25:58 pdt
> Message-Id: <8506150225.AA24360@sri-unix.ARPA>
> Date: Tue, 11-Jun-85 22:06:44 PDT
> To: physics@sri-unix
> From: ucbcad!tektronix!teklds!azure!chrisa@UCB-Vax.ARPA (Chris Andersen)
> Subject: Re: speed

> Article-I.D.: <256@azure.UUCP>
> In-Reply-To: Article(s) <359@osiris.UUCP> <56@rtp47.UUCP>,
> 	<11222@brl-tgr.ARPA> <1428@ecsvax.UUCP>

> > 
> > The problem is that NOT all motion is relative.  Inertial reference
> > frames are equally valid, which says something quite different.  The
> > twin at rest is at rest in one inertial reference frame the whole time.
> > The traveling twin has to use her rocket motor to change directions, so
> > that twin is NOT at rest in an inertial frame for the whole time.
> > That's the non-symmetry in the Twin Paradox.
> >
> 	I wonder, can the twin who remains behind *really* be considered
> to be in an inertial reference frame?  After all, he is subject to the gravity
> of the earth.  Doesn't that make his reference frame non-inertial? 

> > -- 
> > D Gary Grady
> > Duke U Comp Center, Durham, NC  27706
> > (919) 684-3695
> > USENET:  {seismo,decvax,ihnp4,akgua,etc.}!mcnc!ecsvax!dgary

>   Chris Andersen
>   USENET:  tekronix!azure!chrisa
The gravitational field of the earth is a red herring in this case.  Just
have the experiment performed in intergalactic space where space-time is
approximately flat.

  --Charlie