Re: ASTRO: Dark Matter problem gets worse!

From: Charlie Stross (
Date: Mon Jan 31 2000 - 02:53:21 MST

On Sat, Jan 29, 2000 at 02:07:00AM -0800, Robert J. Bradbury wrote:
> "The halos extend 1.5 *million* light-years from each
> galaxy's center and contain *at least* as much mass as
> 5 trillion suns."
> More detail at:
> Lots and lots and lots of MBrains out there or a really
> really strange universe with magic matter in it.

Funny you should mention that ...

I'm currently participating (in a desultory sort of way) in a thread
on rec.arts.sf.written, about Moore's law and ways round it.

Here's a relevent extract from the thread, with some thoughts about
Matrioshka brains -- and the next step up from them -- towards the

[ First, the kick-off -- how to make smaller atoms ]
>On Wed, 26 Jan 2000 13:49:27 +0000, Nigel Arnot
><> wrote:
>>Therefore, the scaling law is reaching its limits. Extrapolating the current
>>rate of progress, we hit the wall circa 2015. Economic factors may get
>>in the way before then, but even if they don't you can't engineer smaller
>>atoms -- ever!
>Yes you can.
>Start by replacing silicon doped with impurities with carbon doped with
>impurities. Smaller atoms!
>If that isn't enough, you need to replace the electrons in your carbon
>atoms' outer orbitals with muons. Buggered if I know how you'd stabilize
>them for long enough, but their relatively high mass (several hundred times
>that of an electron) would shrink the orbitals right down so that the
>density of your muonized-carbon crystals would rival that of degenerate
>matter -- but it would be structurally and electronically similar to
>Note that this entails waving only one magic wand -- long-lived muons --
>and gets you most of the way to the sort of switching speeds that people
>usually go glassy-eyed and mutter about when discussing strange matter
>interactions inside heavily re-engineered neutron stars. Femtotechnology,
[ Then a suggestion about stabilizing muons ... ]

>From: (Paul D. Shocklee)
>Newsgroups: rec.arts.sf.written
>Subject: Re: What, exactly, is a Vingean singularity?
>You can stabilize muons by Fermi blocking. (This is how neutrons in
>neutron stars are stabilized.) All this requires is that the muons be
>confined inside a degenerate Fermi gas of electrons, with a Fermi level
>higher than the kinetic energy of an electron produced in muon decay.
>Since muons have a mass of 106 MeV, you need a Fermi level about that high.
>So you need a k_F around 0.5 fm^-1.
>That would require an electron density of about 4 X 10^36 electrons/cm^3.
>To get an idea of this order of magnitude, that gas would have a
>mass density of about 4 X 10^9 g/cm^3 in electrons *alone*, not to mention
>all of the nuclei you'd need to squish together to neutralize the charge.
>So, short of a neutron star (or stable strange matter), you're never going
>to stabilize muons in a lab.

[ and a comment about the physical properties of muon matter ]

>From: (Joseph Hertzlinger)
>Newsgroups: rec.arts.sf.written
>Subject: Re: What, exactly, is a Vingean singularity?
>Date: 30 Jan 2000 02:41:09 GMT
>Muons are about 200 times heavier than electrons. I think tensile
>strength will scale as the fourth power of that ratio, density as
>the third power, and melting point linearly.
>The strength/weight ratio and the free-hanging length will scale linearly.
>IIRC, diamond has a free-hanging length of about 1000 miles, so muon
>matter will have a free-hanging length of about 200,000 miles.

Which leads me to daydream aloud on the Extropians list:

Muon matter could be a very useful high-density substrate for computation
if it could be stabilized. It's nearly as dense as degenerate matter, so
it should in principle be possible to achieve outrageously high switching
speeds. Lightspeed signal propagation delays should be a lot less significant,
too, everything being so much closer together. (As far as circuit design
goes, it's a bit like the consequences of raising the speed of light.)

Now, the conditions Paul Shocklee observerd are required for Fermi
blocking are outrageous by normal environmental standards, but they _do_
sound achievable for the surface layers of a neutron star. I don't have
adequate references to hand, but would a red dwarf or black dwarf also
suffice? If so, that environment might be accessible to assembler-built
tools controlled by an MB. Instead of needing to employ starlifting to
get extra material for use in an MB, the MB could directly colonise the
stellar remnant. The issue of how then to generate large amounts of muon
matter stabilized by Fermi blocking is ... interesting, but I'm happy
to leave the details to a Matrioshka Brain ;-)

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. So it can think _faster_ than a normal
MB, and probably has more resources at its disposal -- in return for being
stuck at the bottom of a very deep gravity well.

Is this feasible in principle, or am I missing something?

-- Charlie

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