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From: ohgs@chatham.demon.co.uk (Oliver Sparrow)
Path: cantaloupe.srv.cs.cmu.edu!nntp.club.cc.cmu.edu!miner.usbm.gov!rsg1.er.usgs.gov!jobone!newsxfer.itd.umich.edu!europa.eng.gtefsd.com!howland.reston.ans.net!pipex!demon!chatham.demon.co.uk!ohgs
Subject: Re: Predicting the Future
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Date: Tue, 6 Sep 1994 08:41:01 +0000
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Time travel is irrelevant to this conference but it's a good morning for 
trout: I'll rise to the bait.

If an event-particle can be characterised by four co-ordinates and four vectors
(ie when or where it is and how fast it is moving in respect of that 
particular dimension) then I suppose that one can arrive at a formalism in 
which the vectors can point in either direction. Time being apparently 
unidirectional and quantised (all points move in the same direction at the same 
rate) most formalisms do not have anything very interesting to say which 
matches what one observes with a casual glance about. It may be, however, that 
a particle can have a negative vector in time and that this would show up as a 
reversal of (some of the) properties of its conventionally-oriented neighbour. 
This issue is, however, whether it is possible to convey information from one 
co-ordinate system to another by this means.

At first glance, you could: change the particle now and a detector in the past 
pops. Change it it back and it clicks. Modulate the signal and telephone 
yourself some good advice about the markets. There is, however, a false analogy 
at play here: time plays a double role, as itself and as an analogy to a 
spacial dimension. Change it and *then* and *after that* and so forth. There is 
no "before" or "after" in a time line: it is all that there is. One cannot 
invoke a meta-time within which changes are evoked. Signalling this way would 
not be possible. 

Suppose, however, that you can flip the orientation of an existing particle 
such that this is mirrored in its state throughout its existence. (This is not 
time travel, more time tattooing). If one knew where a group of particles were 
at a particular time, one could alter them individually at some other time such 
that the pattern that they made could be read as information: a book, tattooed 
on the body of space time, so to speak. If the "flip" were possible, then I 
suspect that this could be done. Might the "flip" be achieved?

Think what this would imply. A particle is a world line in four space: it just 
is. The arrow in one world line might point back, others forward. You cannot,
however, move any part of the world-line except the bit accessible to you at 
this instant (which looks like a particle). Suppose that you could reverse the 
polarity of the arrow on that particle. This would imply the reversal of the 
arrow on the entire world line. There would be consequences to this: notably, 
the path which led the particle to the state which allowed you to change it 
would no longer pertain. It would have interacted with the universe in a 
different way and would no longer be there for you to manipulate.

Ergo: forget it. Rotating black holes and superdense hollow cylinders may offer 
a path for energy to other wheres, other whens without the need to traverse the 
intervening space time. It has been shown, however, that the information 
content of the emergent material would be lost. Capn' Kirk would emerge as a 
diffuse plasma.
 
_________________________________________________

  Oliver Sparrow
  ohgs@chatham.demon.co.uk
