Tim Little wrote:
> On 2008-03-16, Ben Crowell <crowell07@[EMAIL PROTECTED]
>
wrote:
>> AFAIK, the only way to accelerate flesh at 100g without causing
>> death is to use gravitational fields.
>
> Does this acceleration have to be *comfortable*? ;-)
>
> A really technologically advanced race could just disassemble the body
> for transit (keeping careful track of which bits went where) and
> reassemble it at the other end. So what if it causes a tem****ary loss
> of life? ;-)
Sure, that's actually probably the most believable technology for
running a galactic civilization. E.g., Greg Egan did that in
"Riding the Crocodile." I'm just working on a story idea that
requires physical travel.
> Though if it's only 100g acceleration you want, you wouldn't have to
> go nearly that far. Just build sup****ts for the bones (internally if
> needed), immerse in fluid very similar in density to the body, and
> fill the lungs with some denser medium than air.
>
> It has to be easier than protecting them from the power required to
> accelerate a hundred-trillion-tonne black hole.
"Every Hole is Outlined," by John Barnes, does something like that.
Again it makes sense, but doesn't work for my story.
>> Hmm...10^29 W is 300 suns, and you'd have to collimate it into a beam
>> with a diameter of 0.1 nm. Seems like diffraction would be a problem.
>
> Minor engineering problem! Getting somewhat worse if the base
> generating the laser is a few light-hours away, as it will be in less
> than a day.
Mmm...I would consider diffraction to be a fundamental physical
limitation, not a minor engineering problem. If the laser is
at rest with respect to the galaxy, then it has to operate over
distances of light-years. That means the opening angle of the beam
has to be <~10^-27 radians. Assuming the laser can be 10^6 m in
diameter, then that restricts you to a wavelength of less than
~10^-21 m, corresponding to an energy per photon of 10^15 eV.
I suppose that's conceivable, although I'm not sure if processes
like photon-photon pair production would absorb the beam:
http://adsabs.harvard.edu/abs/1990ApJ...349..415S
In any case, there's another issue that seems more fundamental,
which is that 10^29 W converts via E=mc2 to 10^12 kg/s, which
is enough to double the mass of our black hole in hours. In my
earlier post, I mistakenly only applied this to the case of a beam
of material particles, but it also applies to a beam of photons.
>> For the requirements of my story, I'm thinking that the magnetic-
>> monopole-charged-black hole probably works best. All you need is an
>> absurdly large heat engine to drive an uncrewed rocket ****p, which
>> then accelerates the black hole with magnetic fields, which then
>> tows the passenger module using gravitational fields.
>
> How do you keep the rocket exhaust away from the passenger? It seems
> to be the same problem as radiation from an accretion disk. Even
> 0.0000000000000000001% leakage would be easily enough to fry a human,
> just a hundred metres away or so.
Good point. Well, the exhaust velocity can be a small fraction of
c -- you want it to be a small fraction of c in order to get a decent
thrust-to-power ratio. The exhaust also doesn't have to be hot; I
said "rocket," but actually you probably need something more like
the beam from a particle accelerator. So the exhaust beam isn't
necessarily radiating at all. It just has to be aimed so as to
miss the thing you're towing, and you can have two or more beams
if you like, pointing at slightly different angles, so that the
net force is on-axis. I think a more general problem with any
relativistic reaction drive is that it's probably a heat engine,
so even if the exhaust isn't a danger, the waste heat from the
engine itself is. One way around that is to use energy that's beamed
in.
I don't think you want the distance between the thrust module and the
black hole+passenger module to be as short as 100 m if you can
possibly avoid it. The longer that distance can be, the better.
Maybe the magnet is on the end of a 10 km superconducting cable
trailing behind the thrust module. The distance might be limited
by the tensile strength of the cable, like a space elevator, or
maybe you could use magnetic forces to relieve the tension and make
it even longer.
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