Re: starship-design: Anti-antimatter

["L. Clayton Parker" <lparker@cacaphony.net>]

Steve,

> On the other hand, if you can get the right evaporation rate and
> maintain it, you also get the advantage that the evaporation products
> will be statistically 1/2 matter and 1/2 antimatter (except for the
> photons).  So if it is possible to keep a quantum black hole just on the
> edge of evaporation at a rate useful for propulsion and power
> generation, you also get near-total matter-to-energy conversion by
> recombining the evaporation products.

I'm not sure that I am remembering this correctly, but I think the problem
was that the evaporation rate of a black hole in a convenient size for a
vehicle was so fast that it made it useless. This argument was originally
advanced as "proof" that miniature black holes could not exist for long and
therefore could not account for the missing matter in the universe.

> My understanding is that evaporation rate is a function of the mass of
> the black hole (and hence the gravity gradient near it), with the rate
> going up asymptotically as the black hole mass approaches zero.  You
> also have the problem that radiation pressure from the evaporating black
> hole will make it difficult to pump more mass into it to prevent runaway
> evaporation, especially as you want more power.  Unfortunately I don't
> know the exact equation that relates evaporation rate to mass to know
> whether it would be feasible to keep a quantum black hole in a stable
> state and get a useful power output.

I think that the above considerations are the reasons for Robert Forward
suggesting spinning the black hole in the first place. A black hole
spinning at relativistic speeds might just be massive enough to exceed the
evaporation limit - and besides, this has got to make for some interesting
physics, a spinning black hole would tend to drag space/time with it
thereby warping the fabric of space/time. The possibilities for a writer of
science fiction are endless here <G>

Lee Parker