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Re: starship-design: FTL and time travel

Kyle R. Mcallister wrote:

>Actually, the speed of light is not constant in a vacuum, but can be
>sped up...its too in depth to post, but it happens in a casimir cavity.
>Ask Steve, he knows more.

Actually, the speed of light is constant in a vacuum, its just that
what we normally think of as vacuum isn't really completely empty.
The casimir effect is a means by which one can "suck out" from a
normal vacuum, making it a more perfect vacuum.  The speed of
light within this cavity is thus made slightly faster than that
outside, closer to its "true" speed (in a "true" vacuum).  It's
potential to "increase" the speed of light is an imperceptibly
small percentage, however.  It's still less than 300,000km/s.
>> >Unanswered question: If I travel 1600 light years in 2 years earth time,
>> >how far back in time do I travel upon return?

>> It depends upon how much you accelerate away (sublight) from Earth
>> before returning.

>Lets say I navigate around the star system 1600 lightyears away for, say
>5 years, and return to earth in 2 years earthtime. Is there an equation
>for this?

Sorry, you just don't understand.  It depends upon how much you
accelerate away from Earth before returning.  I won't go through
all the calculations, because you won't understand them.  Not
without drawings of space-time diagrams, at least, which really
can't be drawn in ASCII.  Jay Hinson's FAQ on relativity and FTL
does a noble attempt at it (he regularly posts it on rec.arts.sf.
startrek.tech and rec.arts.sf.science less regularly).

>Question: How do we know time runs backwards in FTL? Then again, how do
>we know time runs forward here...

The problems with FTL causing causality problems have nothing at all
to do with time "running backwards" in FTL.  It only has to do with
stuff in STL frames of reference.  A naive calculation of time
dilation with FTL frames of reference would show time running in
an _imaginary_ direction.  Strange?  Yes.  But it's because this
naive use of the formula for time dilation isn't valid for FTL
frames of reference.

Like I said before, you'd have real difficulty getting an atom,
much less an entire clock, to exist in an FTL frame of reference.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi