On Thu, 13 Jun 1996, Julian Fong wrote:
 

   Contemporary science holds that Time Travel is impossible. 
This is a good view for contemporary science to take, as it helps 
insure that a functional time device will never be invented.

	What about wormholes?

What about them?

   The biggest argument against time travel is that it spawns 
paradox like a tenement spawns roaches. A humble example:

   You go back in time and shoot your own grandfather, before the 
old bugger met your grandma. This means that you will never have 
been born, which means that you can't go back and plug grandpa. 
BUT, this means that grandpa lives, and you ARE born, and you can 
go back and shoot him, which means...

   See the problem?

	The biggest causality violation introduced by time travel is not
having effect precede cause, but rather having effects that have no cause.
If you can accept that the latter is possible, then it's also possible for
you never to have been born; you just appeared out of thin air, shot
someone, and continued your existence from that point.  It could also be
that you can kill your grandfather and return to the time you started from,
only to find that all trace of your existence has vanished.  This can be
interpreted to mean that you've been shunted into a universe different from
the one you were born in.

That's yet another paradox. That kind of senario is full of 'em. :)

----------------------------------------------------------
PART ONE - BITE ME, ASIMOV

	What's Asimov got to do with this?  (BTW, have you read Larry
Niven's essay "The Theory and Practice of Time Travel"?)

Asimov has nothing to do with it, it's just a cute title. :)
And no, I haven't. It any good?

   One of the biggest pitfalls that sci-fi time travel has is the 
We-must-not-divert-the-time-stream line. Some people even 
make it impossible for history to be dramatically altered.

	This is referred to as backward determinism.  In discussions of
backward determinism "history" is usually used as a synonym for "the past",
but it doesn't have anything to do with recorded history.  Here's an example
of backward determinism at work: say you invent a time machine, and just as
you're about to take it for a test flight, a duplicate of you appears in an
identical time machine, having come from one minute in the future.  If time
is backward-deterministic, then even if you change your mind about using the
time machine, no matter how much you try to resist, you *will* get into that
time machine one minute later, and disappear.

*Nod* Yet another reason why "time travel", as we commonly think of it, is
unfeasible. The "History" example was just that - In one book, written by
a respected author, the universe made it impossible to kill anyone who
was, "important to history". There are several other novels like it,
wherein the author assumes that just because humanity feels someone is
important, so does natural law. :P
 

In other word, the E-W-G model assumes that there are a infinite 

number of universes based on every state vector that has ever 
been. Travel to a specific one of these, one that resembled a past 
frame of your universe, would be to you like time travel.

   It wouldn't change anything in your old universe, of course.

	A strict application of the many-worlds interpretation makes time
travel pointless.  Looking at the Grandfather Paradox again:

 * There are an infinite number of universes in which you go back
   in time and kill your grandfather.
 * There are an infinite number of universes in which you go back
   in time and fail to kill your grandfather.
 * There are an infinite number of universes in which you don't go
   back in time at all.
 * There are an infinite number of universes in which your grandfather
   died of natural causes and you were never born.

...and so on.  If every possible alternate universe exists, then there's no
point in going back to the past and preventing something from happening,
because there are universes out there in which that event failed to happen
without your interference.

*nod* Yup. Exactly right.

	To return the discussion to "Smoke and Mirrors," one could have gone
up to Kasumi and said, "Hey, don't worry, your family is alive and well in
an infinite number of universes, but this universe just happens not to be
one of them," but I doubt she would have found that very reassuring.

	The point is, I don't think it's a good idea to explain time travel
using the Everett interpretation, because if the Everett interpretation were
correct, you wouldn't *need* time time travel.

This was posted as a serious (well, mostly serious) essay on actualities
of physics and the way it's treated in fiction. Like the bottom of the
post reads,
"So which of the two was used in Smoke and Mirrors?
   Neither. The Nanban Mirror, being magic, doesn't have to be logical, or
obey quantum physics.
   So there. :)"
    Or, to put it another way, "It works. Leave it at that." 

	And personally, I think having the time-traveling Kasumi get killed
by the bomb blast was taking the easy way out.  Since the time-traveling
Kasumi is desperate to get her family back, and we know she's capable of
murder, why couldn't she have killed her double and taken her place?  It
would look like Kasumi had aged a month or so spontaneously, but no one
would ever notice.

Kasumi is, at the time of the bombing, slightly insane. Can you blame her?
The driving need to protect her family is enough to have her kill.
   BUT, while Kasumi isn't in her right mind, she's still Kasumi. Killing
a thug out to destroy all you hold dear in life is one thing; killing a
innocent person, especially when the innocent person is yourself, is quite
another, and is something Kasumi would never do.
   It's a creepy idea though. She wouldn't be able to keep it up for very
long...the S&Mirr Kasumi went through hell, and is a very different person
at the end of the story 
   As to me taking the easy way out....I have said from the beginning, it
ain't a sadfic. Kasumi dies in a rather brutal, ugly way (it gets even
worse in the rewrite) and goes through emotional pain that makes the
physical stuff look like peanuts by comparison. 
   Smoke and Mirrors is a redemption-through-sacrifice story. The message
is that love will prevail, even over death.
   Nice to have that happen in fiction, anyway.

	Of course, there are an infinite number of universes in which this
was precisely what happened.

I have a sequel planned in which things turn out....a little differently.
   Not for awhile, though. :)

- Mike of No Particular Title or Handle
===/\=====+==================================================================
  /  \    l   Mike Loader - Lincolnite, Amberite, Illuminatus, Discordian,
 / () \   l      Journalist, Author, Traveler, Historian, Java Fiend.
/      \  l        Trier - LA - LV - Kiev - Reno - Hong Kong. Fnord.
--------  l                    mloader@scs.unr.edu
==========+==================================================================

-- 
"I will chide no breather in the world but myself,                 _____
 against whom I know most faults." - As You Like It         |_____|_____
                                     Act 3, Scene 2    _____|     |
            Julian Fong: fong_jh@sunset.bph.jhu.edu