X-Message-Number: 22160
From: 
Date: Tue, 8 Jul 2003 08:39:54 EDT
Subject: what is time travel?

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Again minimal relevance, but anyway.

To prove that travel into your own past is logically impossible, you don't 
need matricide etc. Here's the basic inconsistency:

If a location (space and time) can be unambiguously denoted, then (say) peek 
into your office at noon on July 8, 2003. There is no one there ("before" the 
time travel). At a later date you time travel to that location; now there is 
someone there ("after" the time travel). So something is flatly and 
unambiguously both true and untrue, a logical impossibility. 

That isn't even the worst, perhaps. The worst is trying to define time 

travel. You can draw all the graphs you want, but trying to make sense of them 
is 
beyond me at present. In the simplest case, you imagine a two-dimensional 

space-time, one dimension of space and one of time, say X  (horizontal) for 
space 
and Y (vertical) for time. You can then draw "trajectories," but what do they 

mean? A dot means that something, such as you, is present at the specified place
and time. One dot above another means you are in the same place at different 
times. Two dots at the same height means you are in different locations at the 
same time. If the dots appear to form a curve that loops around, ...........a 
royal mess.

Then there is the "subjective" vs. "outside" view. If a person could time 

travel in the science fiction sense, we would need at least two different kinds
of time, one from the viewpoint of the traveler, applying to his constituent 
parts, and a different one as seen from outside. Does that mean anything? 

I might also mention the "coiled" dimensions sometimes discussed in string 
theory. What carelessness! You can't coil a dimension, only matter within a 
dimension. Try "coiling" length--it isn't meaningful.

Remeber too that all representations are suspect. All. Ed Fredkin, MIT 

physicist, is a maverick but with scholarly status. He thinks the universe might
BE 
a cellular automaton, with an absolute space and time, quantized. Others think 
it may be possible to model the universe as a cellular automaton, but that 
wouldn't prove that it IS one. 

Math isn't physics, and drawing trajectories doesn't prove anything about 
time travel.

Robert Ettinger


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