From: bcr@cernapo.cern.ch (Bill Riemers)
Subject: Re: Time Travel and Causality Violation
Organization: CERN, European Research Center for High Energy Physics
	<BCR.92Dec12023142@hfl3sn02.cern.ch>
	<1992Dec14.110310.1128@newstand.syr.edu>
Date: Tue, 15 Dec 1992 19:54:39 GMT

>>>>> On Mon, 14 Dec 92 11:03:09 EST, pksuk@mothra.syr.EDU (Peter K. Suk) said:

	Peter> We dealt with this in the previous discussion.  If the entire history of
	Peter> the universe is predetermined, such that no paradoxes occur, the simplest
	Peter> configuration for this universe would be:

	Peter> 	There is no time travel.

	Peter> If the time continuum heals itself by changing history such that no paradoxes
	Peter> occur, the simplest change would be:

	Peter> 	There is no time travel.

Let me point out:

  1) I never suggested that a HEALING process was taking place.  I
     was simply suggesting that impossabilities are impossable before
     the fact.  i.e. Lets say we do a time with an electron such that
     it would be a paradox for us to measure the spin of an electron
     in the spin-up state.  In your model, the scientist could measure
     the electron in the spin-up state, then the universe would heal
     itself (somehow) and he would measure the electron in the spin-down
     state.  In my model, it is simply impossable to measure the
     electron in the spin-up state to begin with.  Thanks to quatum 
     mechanics, this would lead to a testable difference from your
     model.
     
  2) Either a HEALING or a RESTRICTED form of LIMITED PRE-DETERMINATION
     is a valid.  (I just didn't think to include your model.)

I agree with you up to this point, so please continue.

	Peter> So if time travel were possible in a single-timeline universe, then 
	Peter> things would happen to insure that no one invented and successfully
	Peter> operated a time machine.  (And if time machines are at all complicated,
	Peter> one could easily see how this would happen.)

==

I don't agree with this conclusion.  For possability of PRE-DETERMINATION you
state that the simplest configuration would be that there is no time travel.
To this I agree, but let me point out:  

  1) The simplest configuration for the universe would be for it not to 
     exist at all.

  2) Therefore, the universe is far from simple!

Thus, I conclude that time travel is not ruled out from your argument.

==

For the possability of LIMITED PRE-DETERMINATION you argue that if the
continuum "heals" itself by changing history, the simplest change would
be "There is no time travel."

In the case of both HEALING and RESTRICTED LIMITED PRE-DETERMINATION,
my previous argument applies.  However, in the case of my RESTRICTED
LIMITED PRE-DETERMINATION I can make an even stronger argument:

   Since RESTRICTED LIMITED PRE-DETERMINATION only only directly effects
   the last "random" event which can prevent the paradox.  Events
   further seperated in "history of causation" are less effected.  Lastly,
   most paradoxes consist of a complex series of events that occure after
   time travel.  Ergo, the prefered universe (that occupying the most
   phase space) is unlikely to be the one without time travel.

==


Now let me try to generalize my above arguments to include all 
types of universes:

   1) A universe in which time travel is possable but requires
      things to happen to insure time travel does not occure
      occupies less phase space than an identical universe without
      such a requirement.

   2) All systems evolve to occupy the maximum amount of available
      phase space.

Therefore, I conclude that in any universe in which time travel
is possable(i.e. part of phase space), there is no tendancy for
events to prohibit such time travel.  

                                Bill


--
"Yeti!  Saw them in the London Underground twenty years ago.  Ghosts!
A headless woman used to walk through my bedroom at midnight.  Mermaids?
Grandpa was rescued from the Marie Celeste by one.  Vampires?  I always
wondered where my dad went to at night.  Telepathy?  Right now you're
thinking that I'm talking crap.  So what can you tell me that I won't
believe in?" - Andrew Hunt, "CAT'S CRADLE: WITCH MARK"