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From: @S1-A.ARPA,@MIT-MC.ARPA:Ghenis.pasa@Xerox.ARPA
Newsgroups: net.space
Subject: Re: Twin Paradox
Message-ID: <2042@mordor.UUCP>
Date: Mon, 3-Jun-85 12:49:37 EDT
Article-I.D.: mordor.2042
Posted: Mon Jun  3 12:49:37 1985
Date-Received: Thu, 6-Jun-85 10:50:49 EDT
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From: Ghenis.pasa@Xerox.ARPA

>I've heard the twin paradox, and until recently I thought I had it
>straight.  I thought of something recently, though.  When one twin
>takes off, leaving the other here, why does the one in space age
>more slowly?  Why can't you use a reference frame travelling with
>him and say that the earth is travelling at a great velocity?  Am
>I missing something?  (Obviously I am.)

The key to the twin paradox is that the travelling twin goes on a ROUND
TRIP, so his frame of reference is an ACCELERATED FRAME (you cannot
return to Earth without changing direction, and you cannot change
direction without acceleration) whereas the stationary twin has an
INERTIAL FRAME. This is what makes their frames of reference
non-equivalent, thereby they will experience time differently.