From: cpyy@vax5.cit.cornell.edu
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
Subject: Re: Fossil Paradox (was: Structure of Time)
Date: 12 Aug 92 09:19:57 EDT
Distribution: sci,talk
Organization: Cornell University

> It sounds like those questions where one is asked if you could go back and
> kill Adolph Hitler even if it would mean your own death, would you do it?
> This has always sounded logically impossible to me.  If in 1992 I was sent
> back to 1930 (or some such year) to hunt down a man named Hitler and I
> was successful, but I was killed, then none of the atrocities of WWII would
> have happened (in theory).  However, when 1992 rolled around I would never
> be asked to go back and kill Hitler because he would never have committed
> those crimes.  So if I WASN'T sent back, then no one would have killed him
> and he WOULD have committed the crimes.  Aaaugh.....no wonder I majored in
> engineering ...the answers were in the back of the book.

This is the standard father-son paradox as re-present by Carl Sagan.
The junior time-fan imangines himself going back in time and killing
his father.  No father, no son, no time travel... back to the beginning.
Chaos would have that it would only be necessary to remove a single
pea from your mother's dinner, or to remove a grain of sand from one
of her paths as a youngster for events to be radically different.
What would happen if you spit in the primordial pea soup (you know--
the organic scum from whence we all come) ?

This paradox is often used in proofs against backward time travel.

Seemingly, such \ital\free\ital\ time travel mandates what
physicists dub "violation of causality".

Intuitively, it seem to suggest a few items:

1.  You cannot go backward in time.

2.  You can go back in time, but are locked into a set of
    events that have already happened (ie predestination).

3.  You can go back in time, but cannot in anyway communicate
    with the time you left.  It's akin to never being
    able to get out of a black hole after passing the event
    horizon.

________________________________________________________________________

There are a few constructs which astrophysicists have conjured and
conjectured up which seemingly allow for causality to be violated
(which is as bad to physicists as losing virginity is to fundamentalists).

One such scenario involves a solution to GR called a worm hole
which looks kind of like a double-sided black hole.  Keep one side
still, and accelerate the other side to close to c.  Go through it
(if you can, you have to protect your ship with space potatoes (sp?),
mirror-like substances, and other exotic matter) and you'll come
out being able to see and possibly interact with yourself entering into it.
It is unknown whether worm holes exist or whether they can be made to
remain in existence for any reasonable amount of time.  They also
probably start out on a very small scale and would have to be
propped-open by funny-matter.

Another instance involves cosmic strings orbiting each other.

Both of these seem pretty far out to me.  But as far as I can tell,
would I know?

Jon C. Russo
internet : cpyy@vax5.cit.cornell.edu
phone    : 607.277.3295
Newsgroups: sci.physics