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From: lindley@ut-ngp.UUCP (John L. Templer)
Newsgroups: net.misc,net.physics
Subject: Re: perpetual motion
Message-ID: <1535@ut-ngp.UUCP>
Date: Sun, 31-Mar-85 23:52:51 EST
Article-I.D.: ut-ngp.1535
Posted: Sun Mar 31 23:52:51 1985
Date-Received: Wed, 3-Apr-85 02:19:19 EST
References: <608@vortex.UUCP> <368@talcott.UUCP> <> <388@nmtvax.UUCP>
Organization: U.Texas Physics Department; Austin, Texas
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Xref: watmath net.misc:7752 net.physics:2387


From: hennessy@nmtvax.UUCP (Greg Hennessy)
> Greg Kuperberg object to a statement attributed to Einstein about "if
> you can create matter, then you can create momentum."

> I for one don't see anything wrong with the statement. As of now we
> can't create EITHER but rewriting ONE law of physics is worse than
> eating one peanut, to quote Larry Niven.

There's a small problem of terminology here;  depending on what you
define as matter and momentum, we both can and can't make them.

To explain, in special releativity, momentum is a four-vector.  The
firt three components are just the three components of what we normaly
think of as momentum, and the fourth component is proportional to the
total energy.

Now, changing refference frames is equivalent to transforming the
four-vector according to the Lorentz transformations.  So the energy
and momentum can change, but the momentum vector's magnitude doesn't.

As far as "making" momentum or energy, all you can do is trade one off
against the other by using this process.

Looking back at what I just wrote, I see I wasn't too clear.  I can
only say it's been a while since I took phy 353.
-- 

                                           John L. Templer
                                     University of Texas at Austin

       {allegra,gatech,seismo!ut-sally,vortex}!ut-ngp!lindley

      "Freedom's just another word for nothin' left to lose."