Re: Hard Sci-fi?

On Sun, 20 Apr 2008 13:07:20 -0700, Ben Crowell
<crowell08@[EMAIL PROTECTED]
> wrote:

>Leonard Erickson wrote:
>> On Sat, 19 Apr 2008 09:46:46 -0700, Ben Crowell
>> <crowell08@[EMAIL PROTECTED]
> wrote:
>> 
>>> When it comes to FTL, I think there's also a lot of fuzziness
involved.
>>> FTL is not entirely forbidden by relativity. However, there are
certain
>>> flavors of FTL that smell more clearly bogus to a physicist than
others.
>>> The FTL in Sagan's "Contact" smells relatively non-bogus to me,
whereas
>>> the FTL in Star Wars smells completely bogus. One of my bogosity
>>> criteria is that the structure of relativity dictates that any
mechanism
>>> for FTL should also be a mechanism for time travel. Another is that,
>>> because of the way general relativity is put together, any mechanism
for
>>> FTL should require control over godlike amounts of mass and energy.
>>> "Contact" passes both of these tests, and Star Wars passes neither.
>> 
>> Read the late Dr. Robert Forward's "Timemaster". for FTL that does
>> include time travel and *doesn't* require godlike amounts of mass or
>> energy.
>> 
>> It merely requires the existemce of matter with negative mass. Which
>> is not forbidden by theory. :-)
>> 
>> He even dealt with causality problems.
>Now you've got my curiosity piqued, but probably not enough to get me to
>read the whole novel. What's the dodge that allows it to be done without
>large amounts of mass and energy? Basically any strong curvature of
>spacetime requires that the stress-energy tensor be big.
>
>As far as the negative mass, my impression is that various
>FTL/time-travel/closed-timelike-loop solutions have a tendency
>to require *both* the large amounts of mass and energy (for the
>reasons above, which are well understood) and the negative mass (for
>reasons that are less well understood, especially by me but probably
>by experts to a lesser extent).

Paired negative & positive masses give you a "free" constant boost
drive. 

I forget what they did to use it to create stable wormholes.

You got the time travel by moving one and at near C speeds and
bringing it back.