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From: chrisa@azure.UUCP (Chris Andersen)
Newsgroups: net.physics
Subject: Re: speed
Message-ID: <256@azure.UUCP>
Date: Wed, 12-Jun-85 01:06:44 EDT
Article-I.D.: azure.256
Posted: Wed Jun 12 01:06:44 1985
Date-Received: Fri, 14-Jun-85 01:24:29 EDT
References: <359@osiris.UUCP> <56@rtp47.UUCP>, <11222@brl-tgr.ARPA> <1428@ecsvax.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 20

> 
> 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