X-Message-Number: 22178
From: 
Date: Thu, 10 Jul 2003 16:13:06 EDT
Subject: Re: Time Travel

There are serious and reputable physicists who think time travel is possible, 
and their ideas for ways to do it are reported from time to time in 

Scientific American and other periodicals. The latest Wired (Aug. 2003), for 
example, 
summarizes four methods.  Granted, Wired is purposely sensational and S.A. is 

not as solid as it used to be, but the scientists and their ideas are serious.
The ideas are wildly impractical for now, usually requiring the manipulation 
of black holes or superstrings, but I think they are generally accepted as 
possible.  Will future genius manage the engineering?  I think it probable -- 

most things we have tried to engineer in the past we have succeeded at -- but of
course we cannot know.

As for the usual paradox of killing your grandfather etc., the latest answer 
I read is that you just can't.  The laws would say that if your ship went 

forward in time through a black hole, and then tried to return and collide with

yourself going in, the hole would just eject you to one side so you didn't hit.
And nothing you could do, nothing that would change that loop, would work -- 
it would be like trying to scratch your right elbow with your right hand -- it 
just can't be done no matter how you twist, for deep reasons regarding the 
geometry of your bones.

Of course, it's easier to observe the past (e.g., to record the state of 

Alexander's brain) than to go back and change it. There is no paradox involved 
in 
that.  Every night we see stars as they were thousands or millions of years 
ago, when the light left.  Not that I have any idea how to see details from 
Alexander's time, but that is just a practical problem, not an innate physical 
impossibility.

BTW, someone mentioned curled dimensions.  I believe the way to understand 

what the theorists are trying to describe is to think of Flatland, a plane where
Mr. Square lives, as a plane figure might reside on a piece of paper.  Square 
thinks he lives in a two dimensional world, but someone might point out to 

him that he does have *some* thickness -- just very little.  The third dimension
in Flatland has been crushed  down to almost nothing.  In the same way, the 
theorists think there is a larger universe with many dimensions --11, 27, who 
knows -- but in our universe these are very "thin" as I would say, or "coiled 
up" as they do.

In any event, such hard-to-explain phenomena as Bell's Paradox (the influence 
of one  entangled particle on its partner, which seems to go far faster than 
light, and by the latest measurements, thousands of times faster at least)  -- 
these phenomena show there is still much to discover about the fundamental 
nature of our universe. Until we understand that better, it is far to early to 
say that something like time travel cannot be done.

Alan Mole

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