Re: starship-design: FTL Navigation

[Steve VanDevender <stevev@efn.org>]

Kyle R. Mcallister writes:
 > At 10:25 PM 8/22/01 -0700, you wrote:
 > >FTL is physically meaningless for a variety of reasons, and therefore
 > >it's similarly meaningless to talk about "FTL navigation".

 > Now how about some real discussion on this subject?

A slightly less terse answer would be that most of the speculative but
remotely plausible means of travelling faster-than-light (wormholes,
Alcubierre "warp bubbles", etc.) seem to preclude much useful
interaction with the universe while travelling at FTL velocities.  So
FTL navigation isn't done while you're travelling FTL; you pretty much
have to aim where you intend to go and turn on the FTL drive for the
period of time you expect to require.  Or, in the case of wormholes,
navigation is mainly a matter of aiming yourself into the wormhole so
that you come out the other end instead of being destroyed.

There's actually a rather entertaining science fiction novel called "The
Cassini Division" by Ken MacLeod which, among other interesting
speculations, includes an artificially-constructed wormhole.  One end of
the wormhole was anchored in orbit around Jupiter, and the other was
carried on a relativistic spacecraft.  The interesting feature of this
wormhole is that you can travel to any location that the far end of the
wormhole went by, at the time that end of the wormhole went by it; this
was supposedly achieved by entering the wormhole at exactly the right
angle and velocity.  This isn't even physically problematic on the
surface; by travelling into the wormhole you travel into the future
(when entering the Jupiter end) along a nearly light-like worldline.
MacLeod conveniently sidesteps the question of travelling back into the
past in the story, but presumably travel into the wormhole from the far
end would bring you out in the past at time that would not allow
causality violations.