Subject: Time Travel 
Distribution: world
Organization: Keristor Systems
Date: Sun, 16 Aug 1992 17:04:12 +0000


In article <4eUp6ru00VIGA36rtv@andrew.cmu.edu> rt16+@andrew.cmu.edu writes:

> We argued about alternate timeline views and such (mostly in reference
> to "Yesterday's Enterprise").  Anyway, the point was made that the
> universe (and atmospheres in particular) is a chaotic system, meaning if
> you change the tiniest little thing, the difference diverges
> exponentially with time (EXTREME sensitivity to initial conditions is a
> hallmark of chaotic behavior).  So Data popping up in San Francisco (not
> to mention all other ST time travel on Earth) back in time would for one
> thing eventually greatly alter weather behavior because of his effect on
> the air around him.  Just depends how long this effect would take to
> start showing up (years, centuries?), but it would happen.

There's another way of looking at this (one which makes for more
interesting stories) and that is similar to the one Asimov used in 'The
End Of Eternity'.  This is that a change MAY have catastrophic effects
(say killing Churchill or Hitler in 1938), but that most changes will
cause localised 'ripples' which will then die away.  Under this system
it would imply that killing your own great^n grandfather would probably
just result in you having a very slightly different hair color, or such,
as (because of convergence) the contribution of that individual is very
small.

As an analogy, my model is like throwing a stone into a pool of water,
and seeing if you can detect any effect 10 minutes later.  OTOH, your
example is like dropping that stone into a super-cooled liquid and
causing it to crystalise.  I suspect that both examples are valid, but
it depends on your model which will happen.

Does it really matter whether Homer wrote the Odessy, or someone else?
How about the person who discovered fire - or atomic fission?  The
latter we would tend to say 'yes', because we are still very close to
the events (we are still within the 'wavefront' of the 'ripples') but in
a million years time would anyone be able to tell?

>      Hmm, maybe that's why weathermen have so much trouble making accurate
> forecasts - all them dang time travelers screwing things up :-)

It's as good an explanation as any <g>.

>    Alternatively, one could take a deterministic view and say that any time
> travel interference is *supposed* to happen in the first place (they mention
> something to this effect in "Assignment: Earth").

This IMO is something of a 'cop-out' but it can still be used to good
effect if the story is well written.

Oh, there's another one as well, as used (if I remember correctly) in
Larry Niven's "The Filight Of THe Horse".  That is that if you travel
back in time, change something, and then go forward again then you will
end up in a parallel universe where the events were different.	So if I
go back from now (1992) to 1938, kill Hitler, and come back forward
again, I will end up in the universe which reflects my change, but the
'original' timeline will be continuing and people there won't notice any
change (their history won't have any record of me).  To people in 'my'
universe, I didn't cause any change because *to them* it 'had to happen
that way'.

Chris

P.S. this is the sort of discussion I like - it reminds me of when I was
at university, sitting around discussing unprovable things into the
night...  One of the main reasons I'm involved with SF fandom.

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*  chris@keris.demon.co.uk	*				      *
*  chriscr@cix.compulink.co.uk	*  FIAWOL (Filking Is A Way Of Life)  *
*  100014.3217@compuserve.com	*				      *
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