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From: @S1-A.ARPA,@MIT-MC.ARPA:cef@cmu-cs-spice.arpa
Newsgroups: net.space
Subject: Re: Re: twin paradox
Message-ID: <2094@mordor.UUCP>
Date: Wed, 5-Jun-85 13:56:20 EDT
Article-I.D.: mordor.2094
Posted: Wed Jun  5 13:56:20 1985
Date-Received: Mon, 10-Jun-85 02:58:33 EDT
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From: Charles.Fineman@CMU-CS-SPICE

> 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. 

What if we assume that the universe is closed? Then it would be possible to 
return to earth without changing your accelration. What happens then?