Re: Computronium Limits [was ASTRO: Dark Matter problem gets worse!]

From: Charlie Stross (
Date: Tue Feb 01 2000 - 03:57:18 MST

On Mon, Jan 31, 2000 at 05:30:11AM -0800, Robert J. Bradbury wrote:
> I'm not sure if I asked or if anyone ever responded to, but the
> question of what a photon does when it strikes a neutron star
> remains an interesting question to me.... As does the problem
> of the "lifetime" of neutron stars. While the neutrons in the
> center may be constrained from decaying, I doubt the same is true
> for neutrons on the surface. That would suggest that neutron
> stars should evaporate.
I thought most models of neutron stars assumed that they weren't solid
neutronium all the way to the surface, but had a crust of degenerate
matter of some thickness, and then a messy mantle with increasingly
fewer protons and electrons the deeper you go. (I may be wrong, though.)

> > The point here is that an MB that extends all the way down _into_ the
> > surface of a black dwarf has access to vastly more structured matter
> > for computation purposes -- 10 to 1000 Jovian masses doesn't seem
> > unreasonable -- and also doesn't suffer from the same sort of lightspeed
> > propagation lag as an MB with dimensions measured in AU's.
> You *always* have the lightspeed limit, but I agree that removing the
> star at the center of an MBrain and replacing it with computronium
> produces the highest density computing capacity. The problem then
> becomes how do you pump energy in and heat out?

With a dynamo and some sort of momentum-transfer effect to the outer
layers? (Remember, rotating neutron stars tend to have teensy-weensy
magnetic fields -- that's why we can spot them tens of thousands of
light-years away ;-)

> Anders does discuss the computational rates of nuclear matter
> in his Neutronium brain and points out the problems of increasing
> the matter density too much.
> For reference purposes a Matrioska Brain of my design probably falls
> between Anders' Dyson brain "Uranos" and Neutronium Brain "Chronos"
> with an emphasis on power efficiency and heat removal (vis-a-vis
> some of the optimizations Anders makes).
Any chance you could point me at some URLs for these? (Or paper refs?)

> Finally, its worth noting that Xenology says the decay time of a muon
> is 2.2 microseconds (at non-c speeds presumably) and you can do a lot
> of computation in 2.2 mu-sec. The problem is to develop a system that
> regenerates the mu-matter as fast as it decays.

What made me think of muons was an article in New Scientist about the
use of muons as catalysts for "cool" fusion -- not the Fleischman-Pons
thing, but a phenomenon that's been observed but which is unfortunately
endothermic. (Basically, if you replace the electrons in deuterium
atoms with muons you shrink the orbital to much that it's possible for
quantum tunnelling between nuclei to occur, lowering the energy barrier
to fusion; the problem is that each muon can at best catalyse only a
few dozen to hundreds of fusion events, there's a poisoning effect due
to helium nuclei mopping up free muons, and muons are expensive to produce.
But if we've got a muon production source on our neutron star, and can
dump a bit of hydrogen onto it ...

-- Charlie

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