Re: starship-design: FTL and time travel

[Steve VanDevender <stevev@efn.org>]

Kyle R. Mcallister writes:
 > You told me it was caused by increasing the magnetic permeability of the
 > vacuum. There's no need to go off the deep end, I wasn't intending to
 > use this (not until we find a way to use something like it on a larger
 > scale. Wouldn't a simple casimir cavity violate causality if you passed
 > photon through it?

I told you that's what I _supposed_ it was, based on my incomplete
understanding of the effect and my now distant college physics course in
electromagnetism.  You misrepresented my words by saying I really knew
something about it, and I'd prefer that you not.

 > > It isn't that time runs backward in FTL, it's that observers of a
 > > hypothetical FTL trip won't agree on the direction that it proceeded
 > > based on their measurements of the times and locations of each end of
 > > the trip.
 > 
 > Then I don't see why causality violation is such a big deal. A
 > disagreement I can live with.

It is a big deal because this disagreement in event ordering for a
one-way trip also implies that, should you allow FTL, you can build
causality loops that every observer will agree are causality loops,
which is a much more serious problem.  It's something that's not
physically observed or compatible with the existing structure of
physics.  You can't wave your hand and say "oh, it's not really a
problem, I can live with that" except out of sheer ignorance of the
problem.

I think we've run this whole FTL and causality business into the ground,
and it's time to move on.  Face it, Kyle, we aren't going to build an
FTL starship nor am I particularly interested in having to keep
revisiting this issue because you won't accept that limitation.  If you
have to talk about speculative physics with someone, find a group that
is actually interested in dealing with it.