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From: edwardsg@cc4.crl.aecl.ca
Subject: RE: Roger Penrose's New Book (in HTML) 1.0
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Date: Fri, 4 Nov 1994 16:19:45 GMT
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An 'event' is a point in space and time.

Two events which occur at the same time, but different places are separated
by a space-like interval.

Two events which occur at different times and places are separated by a
space-like interval if ANY observer in the universe sees them happening
at the same time.  (Assume the universe is filled with observers travelling
with all possible velocities.  Special Relatiivity says that is impossible
for observers with a relative motion to keep their clocks synchronized).

Communication across a space-like interval therefore needs the message to
travel at infinite velocity in the point of view of one observer.  In the
point of view of other observers, the message will appear to originate in
the later-time event and be absorbed in the earlier-time event.  All very
upsetting to people who like the principle of causality.

G.E.
