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

From: Mike Lorrey (
Date: Tue Jul 17 2001 - 10:46:31 MDT

Anders Sandberg wrote:
> 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.

Okay, now imagine a Matrioshka Brain that owns a number of these. Is
there any limit to how many one brain could posess? Add them up along
with the surrounding brain, and you've got a significant mass able to do

Another question: Isn't the microlensing estimates of mass dependent
upon how far from us the object doing the lensing is? Shouldn't a
smaller mass that is closer be able to do the same amount of lensing?

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