Re: starship-design: FTL idea - Steve

[Steve VanDevender <stevev@efn.org>]

Timothy van der Linden writes:
 > >>OK, I catch your drift. But... knowing that you move this fast with respect
 > >>to the observed phenomenon, you can reconstruct what really(=in a frame at
 > >>rest) happens and remove the apparent causality reversal.
 > >>For those few that happen to see everything at once, they are at a loss,
 > >>they will never be able to reconstruct what happened.
 > >
 > >There's your problem.  There is no "frame at rest".  Relativity has no
 > >preferred frames.  In the FTL case, there is no unique time ordering of
 > >events (what if the "frame at rest" is really a "frame in motion"?  You
 > >can't prefer one over the other!) and hence no way to establish
 > >causality.  In the STL (slower-than-light) case, a unique time ordering
 > >of events exists for all possible observers.
 > 
 > Well, the calculations I did where compared to another (rest)frame. What
 > worries and confuses me is that the event reversal only happens in certain
 > frames and not in all frames.
 > But I'll accept this as one of the oddities of relativisics.

You can't have another "rest" frame.  If you're going to declare a
particular frame to be the "rest" frame, you need to work the problem
consistently with reference to that.

The point, which you now seem to understand better, is that if events
are connected by a spacelike (FTL) worldline, then not all observers
agree on their time ordering, as opposed to the case of events connected
by timelike or lightlike worldlines where all observers do agree on a
time ordering.  I'm not sure what you mean by "the event reversal
happens in all frames".  For any spacelike relation of events there are
always some observers who see one time ordering and some who see the
other time ordering.