Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1a 12/4/83; site rlgvax.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!rlgvax!guy
From: guy@rlgvax.UUCP (Guy Harris)
Newsgroups: net.sf-lovers
Subject: Re: FTL does not create paradoxes - future not past
Message-ID: <1976@rlgvax.UUCP>
Date: Fri, 1-Jun-84 00:09:15 EDT
Article-I.D.: rlgvax.1976
Posted: Fri Jun  1 00:09:15 1984
Date-Received: Sat, 2-Jun-84 11:49:18 EDT
References: <7162@rochester.UUCP>
Organization: CCI Office Systems Group, Reston, VA
Lines: 23

I'm not sure that FTL travel doesn't imply "time travel into the past".
In your example, star systems A and B weren't moving relative to one
another, so their reference frames differed only by choice of the origin
of the space and time coordinate systems.  However, if I remember my
relativity correctly, if one has someone leaving system A at time TA and
arriving at system B at time TB (in, say, system A's reference frame), a
reference frame can be found in which time T'A is the same or earlier than
time T'B.  This reference frame would be moving relative to the frames of
systems A and B.  The space and time separation between the departure from
A and the arrival at B is "spacelike", which means that there exists a
reference frame in which it is purely a spatial separation (i.e., the
trip *is* instantaneous!) and also that the difference in times can be
positive *or* negative (i.e., the guy can be observed arriving at B earlier
than they leave A).  It's geometrically equivalent to the spatial distance
along a particular coordinate between two events with a "timelike" separation
(i.e., connected by something moving slower than light; there exists a
reference frame in which the separation is purely a temporal separation)
being positive in one frame and negative in another - just rotate the
frame of reference.  Ask a physicist about this one; I don't have my
old relativity text at hand so I can't check it out easily.

	Guy Harris
	{seismo,ihnp4,allegra}!rlgvax!guy