Index Key:  PHY051
Author:     Brian Lintz
Subject:    Is time travel possible?
Tex:        Is time travel possible?

Response #:  1 of 2
Author:      Sam Bowen
Text:        I assume that you mean time travel at a different rate than the 
rate that we are all now traveling forward in time.  All of us and all the 
matter around us is currently traveling forward in time at the same rate ( at 
least locally) and there does not seem to be a way in which we can alter that.  
Relativistically time is dilated when we observe it in quickly moving 
reference frames and a twin that has been traveling and returns will be 
slightly younger than the twin that stayed behind in a stationary reference 
system.  This experimental fact indicates that to move into frames where time


is dilated effects all the manifestations of elapsed time for objects or 
beings.  I think that this means the time traveler would be effected by the 
time travel as well.  The mystery in the time travel stories is how the 
travelers have escaped being effected by the change in frames.  There is no 
known way that someone can travel ahead or back in time.  It would appear that 
there are several contradictions that would occur if it were possible.  One of 
these would be the effect on what are called world lines and their restriction 
to be in what is called the forward light cone.

Response #:  2 of 2
Author:      Arthur Smith
Text:        Actually, some physicists a few years back did work out a way in 
which time travel would be possible.  One of the instigators was Kip Thorne, 
and I actually saw him give a talk on this.  It seems that if civilization 
could advance sufficiently far to handle black holes with ease, so we could 
put black holes in a box of some sort, for example, then they found a way in 
which one could start with two black holes close together, and then pull them 
apart, and instantaneous travel would be possible between the two black holes.  
Because of the theory of relativity, instantaneous travel and travel backwards 
(or forwards) in time are essentially equivalent (you actually have to take 
two instantaneous trips to get back to the same point in space at an earlier, 
or later, time).  However, even with this scheme it was impossible to travel 
back to a time before the "time machine" was created.  Which is good, since we 
really do not want people going around killing their grandmothers before their 
mothers were born.  I think I may have read that there was something wrong 
with this scheme.  So, in the end, it could be nobody really knows how to 
travel backwards in time.  It is fun to speculate though!