Re: SETI/ASTRO: MBrains/JBrains & Globular Clusters

From: Anders Sandberg (
Date: Tue Jul 17 2001 - 09:08:59 MDT

On Tue, Jul 17, 2001 at 10:39:16AM -0400, Mike Lorrey wrote:
> wrote:
> >
> > The energy output is inversely proportional to the mass squared,
> > so a Jupiter sized black hole would be outputting 10^31 times less,
> > which would be an unmeasurably tiny amount of power, at a temperature of
> > almost absolute zero. Hawking radiation is insignificant for planetary
> > sized objects.
> Yes, but what about extracting energy from purposely injecting mass into
> the hole, as well as from the gravitational potential of dropping mass
> into it?

You can get a few percent of energy out of it, but the efficiency ratio
isn't that great. I haven't got my copy of _Gravitation_ within reach, but
I think it was a few percent of the black hole mass-energy that could be
extracted using the Penrose process and somewhat less from infalling
sacrificial mass.

I would go for 10^12 kg holes instead, keeping them critical inside a
mini-Dyson but blasting enough mass into them to keep them stable. OK, hard
engineering, but you likely get a better mass-energy conversion efficiency
than a fully grown black hole. The efficiency ought to be very high,
although overheads might be big too.

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y

This archive was generated by hypermail 2b30 : Fri Oct 12 2001 - 14:39:49 MDT