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From: jtb@kitc.UUCP (John Burgess)
Newsgroups: net.movies
Subject: Re: Time Travel
Message-ID: <179@kitc.UUCP>
Date: Wed, 28-Aug-85 13:02:18 EDT
Article-I.D.: kitc.179
Posted: Wed Aug 28 13:02:18 1985
Date-Received: Fri, 30-Aug-85 08:58:14 EDT
References: <95@decwrl.UUCP>
Reply-To: jtb@kitc.UUCP (John Burgess)
Distribution: net
Organization: my terminal @ So. Plainfield @ ATT-IS @ USA @ ...
Lines: 54
Keywords: Doctor Who, science fiction
Summary: There are many time travel scenarios

In article <95@decwrl.UUCP> metz@troll.DEC writes:
>
>In order to make any sense of time travel, as in "back to the Future" or
>H. G. Wells' "The Time Machine", it must be realized  that each event which 
>creates a change in the time line itself will cause anoth time line to be
>created and a new series of events to transpire. This could lead to an 
>infinite number of time lines for a series of acts caused by a time
>traveler. If it is assumed that time is a positive flowing river, a move
>back in time would place the traveler in position to retrace a given path.
>Since the future from the point at which he/she intrudes could not be 
>changed or else the traveler himself would be changed, it must be true and
>necessary for a new time line to be formed and the travelers path be in
>a new direction. ...

What is stated above is One possible postulate for the way time travel
might work - or rather, the way it DOES work in some real fictional
universes, for example Doctor Who  (see net.tv.drwho).

Just as in Geometry, where different sets of postulates make
for different (so-called non-Euclidian) geometries,
an author can postulate different time-travel postulates,
and create different (fictional) universes!

Some other postulates, which create different universes,
but which are used by various other science fiction authors, are:

1) Since the past is past, one cannot change it, therefore
any particular time travel event into the past was/is NECESSARY
in order to make the past what it was/is.  This assumes there is
one and only one time line, and thus one can return to the present
with no changes evident.  One can even THINK one has "changed the past",
but in this type universe, all one is doing is forcing an event
that would have happened anyway.

2) "Free" time travel.  Some authors don't get hung up over
stuff like infinite time lines and such, and merely allow time
travel to happe.

3) "Uncertain time" - in this model, the only point in time that
is "true" is the current instant, whatever that may be.  The
past and future fade away (as a function of time) into uncertainty anyway,
so time travel is sort of like moving in a fog.  (This one is the toughest
to explain, much less deal with!)

4) Are there others?  beats me.  This discussion should probably move
to net.sf-lovers, anyway.

There are interesting paradoxes that can happen in ANY of these.
Think about it!
-- 
John Burgess
ATT-IS Labs, So. Plainfield NJ  (HP 1C-221)
{most Action Central sites}!kitc!jtb
(201) 561-7100 x2481  (8-259-2481)