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From: shiva@duts.UUCP
Newsgroups: net.sf-lovers
Subject: Re: Time travel, center of mass
Message-ID: <153@duts.UUCP>
Date: Fri, 1-Nov-85 16:52:35 EST
Article-I.D.: duts.153
Posted: Fri Nov  1 16:52:35 1985
Date-Received: Mon, 4-Nov-85 02:21:23 EST
References: <291@caip.RUTGERS.EDU>
Organization: Amdahl Corp, Sunnyvale CA
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> From: Alan Wexelblat 
> ....                                Is it the case that the center of
> mass of the universe doesn't move?  Is is (theoretically) possible to
> calculate our position/velocity w.r.t. this non-moving point?

On the contrary, the center of mass of the universe must move, since
all the masses in it are constantly moving. Mass is constantly being
redistributed hence the center of mass has to move *with respect
to any other mass*. It does not make sense to talk about the center
of mass moving with respect to anything else, because there is no absolute
frame of reference (thanks to Dr. Einstein).

As to calculating our velocity with respect to the center of mass
at any one instant, well, wouldn't you have to know the position of
every other mass in the universe at that instant? You can't do
this because of the speed of light (even assuming you could accumulate
all that information in some computer) which will only tell you
where any particular mass was sometime in the past.

Now, having said all this, this is sf-lovers after all, so anything is
possible......

Disclaimer: I am not a Theoretical Physicist,
            although I play one on TV.....

"Anything is possible. Unfortunately, most of it is so damn improbable."
                                          -- me

-- 

                                          Shiva, Amdahl