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Re: starship-design: FTL

L. Parker wrote:
>Steve wrote:
>> Sure they did.  If you reappear at Tau Ceti in less time than it would
>> take for light to go from Earth to Tau Ceti, then observers won't
>> agree on whether you disappeared from Earth and reappeared at Tau Ceti,
>> or disappeared from Tau Ceti and reappeared at Earth.

>Huh? So what? It doesn't matter if you get there before the light does
>as long as you can't get BACK before you left. Assuming that this mythical 
>drive is ONLY instantaneous or nearly so, you can't get back to the 
>original (rest) frame prior to leaving it.

This is right, and Steve is confused.

But you have to remember that "instantaneous" is a relative notion.
Assuming relativity is valid and there are no special frames of
reference, what you can do is thrust a little bit (sublight)
before making your trip back.

With your new frame of reference, "instantaneous" correlates
different points in space-time.  When you "instantaneously"
travel back, you travel back instantly in your _new_ frame of
reference.  This will let you travel back to meet yourself
before you left.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi