Re: starship-design: Re: Paradox

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

Ken Wharton wrote:
>Clarification:  When I presented those three time travel possibilities,
>the difference I meant to specify between B) and C) was that in B) the
>universe you leave continues to exist, while in C) it is destroyed.

So in case B, what happenned to your ship in the old universe?  Does
it just wink out of existence when someone travels FTL?  In that case,
you'd know that lots of people have tried traveling FTL in the past
and instead ended up vanishing into nowhere.  Take that trip?  No
thanks!  Or does a duplicate copy of the ship remain, but with its FTL
drive mysteriously inactive?

(Note that it's insufficient to try and restrict universe splitting
to "time travel" cases and not FTL.  FTL travel _is_ always time
travel in at least some frames of reference, assuming the universe
is flat/convex.)

>In C) I did not mean that the universe would then proceed identically
>the second time around; whoever travels back in time can survive and
>change things around as reality unfolds again.

But this is exactly the same case as in B, except that the old universe
doesn't exist anymore.

>As for the infinite-universe idea, there are some very good philisophical
>reasons why it's very improbable.  After all, people we know behave in
>predicable ways some of the time.  Why would this be if we're in one of
>many universes?  Every past decision made by anyone would be random; there
>would be no pattern to human behavior.  It's a strong argument against
>the many-worlds idea.

No it isn't.  Just because decisions are random doesn't mean there's
no pattern.  Consider the act of randomly rolling a pair of dice.
While the outcome is random, there are certain patterns--the result
is always an integer between 2 and 12 (inclusive), sevens are most
common, etc...

>Finally, I agree with Issac that there is a link between quantum mechanics
>and time travel.  But I currently think that it is not quantum that allows
>reverse-causality, but rather reverse-causality that creates quantum effects.

Huh?  I don't think there's such a link.  Quantum mechanics does allow
a mechanism by which what appears to be reverse-causality is possible,
but OTOH it does so in a way which makes "normal" causality invalid
(the idea that a cause will have one of the possible effects in one
future universe, rather than _all_ of the possible effects in an
infinite continuum of future universes).

We currently think that this infinite continuum of possible futures
eventually collapses into one, but this _is_ just an assumption--there's
simply no way we can test it one way or another.  Even if the other
possible futures exist, we can never "run into" them, so we can neither
prove nor disprove their existence.  Thus, for all practical purposes
the other futures don't exist.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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