starship-design: FTL travel

["Kyle R. Mcallister" <stk@sunherald.infi.net>]

Walker, Chris wrote:
> 
> Bjorn,
> 
> I meant that I agreed that FTL travel was *necessary* for attempting serious
> interstellar exploration, rather than I thought FTL travel was *possible*.
> I'm still learning much about the various theories regarding  this subject,
> so do not feel qualified to comment on whether or not it is possible -
> that's why I was curious as to Kyle's beliefs in FTL flight.

A theory cannot tell you if something is or is not possible. Many of the
scientists who hold power today fail to recongnize this. Experiments can
give you proof, but not theory. I am not saying theory is bad, however.
It is necessary to logically organize experimental results and make
predictions.
> 
> The planet-hopping method may be a more realistic/achievable goal in the
> shorter term (next century), given that without a major breakthrough in
> propulsion technology, FTL flight may not be achieved for some considerable
> time. It seems to me that production of a working reactionless drive is more
> within our immediate reach than breaking the light barrier. 

No one can say. It may happen tomorrow, or it may take hundreds of
years.

> Does anyone know what is (theoretically) meant to happen re. time dilation
> when you travel FTL? (eg. travelling back in time?)

According to special relativity, when an object travels FTL, it can
create what is known as a causality violation. What this is is when some
observer disagrees as to whether the FTL object left point A and went to
point B, or went from point B to point A. In other words, to this
observer, the ship's arrival at its destination occurred before it left
its origin. You can set up a situation with round trip FTL travel that
can allow a ship to return to its origin before it leaves (time travel).
(If you want to learn more about special relativity, read "Spacetime
Physics" by Taylor and Wheeler.)

What really happens? No one knows. If FTL is possible, then it certainly
will not involve time travel...there are many strong arguments against
time travel. But it is wrong, and quite arrogant for some scientists to
preclude FTL because time travel is impossible. Notice, I am not saying
time travel is impossible. It may or may not be. The same with FTL. FTL
and time dilation: First, calculate gamma. Gamma is equal to
1/((1-v^2)^.5) so gamma for an object travelling .6c relative to another
observer is 1.25. This means that the moving object's time goes 1.25
times slower than the stationary object. For an object going 3c, try it
on a scientific calculator. gamma=1/((1-3^2)^.5) gamma= approx
(0,-.35355) An imaginary number. This is where things really get
complicated. So, does this mean that FTL is impossible, or that
relativity can't correctly predict what happens for FTL? That is a very
good question, and if you can figure it out, you will likely be in the
textbooks. It is fun to theorize about FTL, but this really isn't the
place. 

Best regards,
Kyle R. Mcallister

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