Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site mordor.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!ut-sally!mordor!@S1-A.ARPA,@MIT-MC.ARPA:TERRY%LAJ.SAINET.MFENET@LLL-MFE.ARPA
From: @S1-A.ARPA,@MIT-MC.ARPA:TERRY%LAJ.SAINET.MFENET@LLL-MFE.ARPA
Newsgroups: net.space
Subject: Twin paradox
Message-ID: <2071@mordor.UUCP>
Date: Tue, 4-Jun-85 17:01:24 EDT
Article-I.D.: mordor.2071
Posted: Tue Jun  4 17:01:24 1985
Date-Received: Mon, 10-Jun-85 02:57:09 EDT
Sender: daemon@mordor.UUCP
Lines: 27

From: TERRY%LAJ.SAINET.MFENET@LLL-MFE.ARPA



Since the subject of special relativity's twin paradox has come up,
let me add one small note.  Many people believe that the "paradox" part
of the twin paradox is that the two twins are no longer the same age.
This is not the case.  The paradox referred to as the "twin paradox" is
precisely the question posed by the original posting on this subject:
"Since all motion is relative, why should the twins have different
ages?  We can regard either twin as being stationary and the other
twin as moving, therefore we can show that each twin should be younger
than the other."  NOW we have a paradox.

The answer, as has been pointed out, is that the two twins are NOT in
symmetrical situations.  The traveling twin has undergone a fair amount
of acceleration with respect to the Earth that the Earthbound twin has
obviously not.  It is precisely this acceleration that causes the traveling
twin to age more slowly, and thus be younger upon return, than the Earth-
bound twin.  Paradox resolved.

For those of you who are also on the physics mailing list, we are in
a similar situation here as all the postings regarding objects such as
the Moon moving much faster than the speed of light if you are sitting
on a spinning turntable while watching it.  As was concluded by a number
of folks, accelerated (non-inertial) reference frames don't count in
special relativity.