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RE: starship-design: FTL

[Kyle]  I have a question (don't I always?):

If you dissapear from orbit above earth, and later on reappear in orbit
of tau ceti I, is causality violated? If so, why? No one saw you. 

Kyle Mcallister

[L. Parker]  Kyle poses a rather interesting question which I am going to 
expand a little for the sake of clarity:

If you can move from here to there instantaneously, or nearly instantaneously, 
is causality violated? If you go from here to Tau Ceti in 1 second of real 
time, you don't arrive at Tau Ceti 11 years ago you arrive at t+1 sec. There
is no FTL communication that I can see and no causality violation.

Now expanding on this theme and ignoring everything except relativity for the 
moment, there would seem to also be a point or factor if you will beyond c at 
which causality is violated but only if you exceed that factor. That point 
would seem to be 2c - the speed which would put you at your destination at 
exactly t+0. Delta t for this trip would be -1 putting your arrival at any 
destination at exactly the point necessary to produce a causality violation.

Am I being to simplistic here, or does this adequately describe causality? If 
so, then time travel isn't necessarily impossible, just USEFUL time travel.