# Re: starship-design: FTL idea

Kyle R. Mcallister wrote:

>Can you please explain why the backwards in time travel occurs? If the
>Causality violation has to do with the light arrival from the object, I
>have a solution you might want to consider. Time travel in FTL might not
>occur- see my earlier mention of Stephen Hawking's time protection
>theory. Causality violations do not accur if you do not travel LOCALLY
>FTL, which is not what I'm suggesting doing.

Untrue.  You simply don't understand the physics well enough.  The
way to get FTL without time travel in general relativity is to
assume (or make) spacetime hyperbolic.  That means an average
negative energy density in the universe, so it's not surprising that
Alcubierre's drive requires more energy in exotic matter than there
is in the entire universe.

>If you construct the
>spacetime metric correctly, proper time will be EXACTLY THE SAME as
>apparent time.

That's besides the point.  Alcubierre's metric is carefully conceived
of to prevent time dilation and time travel, but as he says in his
paper:

}As a final comment, I will just mention the fact that even though the
}spacetime described by the metric~(\ref{final_metric}) is globally
}hyperbolic, and hence contains no closed causal curves, it is probably
}not very difficult to construct a spacetime that does contain such
}curves using a similar idea to the one presented here.

In other words, although this metric doesn't result in time travel,
a similar one (using exotic matter as well) would.

>This is real stuff, and I know it. I'm not just making this up.

Unfortunately, you don't understand the concepts of special relativity,
much less general relativity, to understand what this "real stuff" is.
--
_____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
__|_)o(_|__
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi