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From: ins_amap@jhunix.UUCP (Mark Aden Poling)
Newsgroups: net.sf-lovers
Subject: Re: Time travel, center of mass
Message-ID: <1106@jhunix.UUCP>
Date: Tue, 5-Nov-85 13:57:07 EST
Article-I.D.: jhunix.1106
Posted: Tue Nov  5 13:57:07 1985
Date-Received: Fri, 8-Nov-85 05:54:31 EST
References: <291@caip.RUTGERS.EDU> <153@duts.UUCP>
Organization: Johns Hopkins Univ. Computing Ctr.
Lines: 43

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

	I may regret this, but I'm going to throw two pennies into
this mess.  If we are to bandy about relativity, then it must be
recognised that any appreciable gravity well affects the "rate" at
which time flows.  Falling into a black hole has the same effect as
nearing the speed of light.  Things age slower with respect to us in
our more normal inertial frame.  Time travel will obviously involve
mucking about with relativity, since changes in the rate of flow,
or even removal from it, will also affect everything else in the
inertial frame.  If we assume that we can "break" relativity in a
localized area, such a break would still have an effect on the frame
around it.
 
	Therefore, I propose that the gravity well of earth
would be sufficient to "capture" the effect produced by time travel.
Basically, a traveler would remain in the same inertial frame, and wind
up in the same general vicinity as he started.  Any changes in the
inertial frame from one time to the next would cause displacement
from his point of departure.  There is also the problem of the non-
negligible effect of the moon on the earth-moon system's center of
mass, which is really what would catch said traveler, but I'll
assume it's solvable.

	Unfortunately, I still haven't come up with a good reason
why any form of time travel shouldn't involve formation of a singularity,
which we all know is a bad thing :-).

Disclaimer: *Please* don't quote any of this to a physicist.  And yes, I
	    *am* using it in a story I'm presently writing.

"Ogden understands.  Ogden understands everything."
						-My girlfriend.

								Mark!