From: Jeff Davis (jdavis@socketscience.com)
Date: Wed Dec 01 1999 - 17:33:20 MST
For Robert Bradbury and others,
I've been following the discussion about ETCs--enjoying it thoroughly--and
just finished reading your (RB's) paper on Matrioshka
brains--delightful--and have a coupla of questions.
First, there's the sometime implication that SIs will gobble up the
universe--I've always wondered where that idea comes from, beyond the
simple fact that given the capability of exponential growth and the
availability of sufficient energy to carry it off, that they COULD. Beyond
prudence, consideration, moderation, restraint, or some similar
value-mediated reason for self-limitation, I wonder about one particular
structural limiter on boundless cosmic consumption.
You (RB) have often mentioned the light speed limit on internode
communication. The larger the MB gets the slower the entire brain thinks.
Wouldn't that suggest a range of acceptable values centered around that
point with the best (as judged by the SI community) trade-off between speed
of thought--which I equate with rate of experience, how much living you
accomplish per fixed unit of time--and complexity of thought-- which I
think of as "depth" of experience (intelligence, sophistication?)
Even granting that different SI communities could have different "best"
trade-off points, wouldn't any such point suggest a stabilization of
consumption of local cosmic resources? (Of course, expansion and increased
consumption would continue to the extent that SI communities "spawned" new
SIs.)
Second, (and here I think I'm probably gonna put my foot in it) isn't there
going to be a type of "computronium" which will operate in a
superconductive regime? Won't that "resistanceless" condition make it
possible to function virtually without generation of entropy/waste heat (I
have heard of a fundamental principle of computing/information theory that
assigns a minimum entropy per op/(state change?), but I have also heard of
some other theory of reversible or quantum computation which suggests a
means to circumvent or drastically reduce this minimum entropic cost;
though such theories are waaay over my head.)
I suspect that you and Eric D. have already factored this into you
thinking--I mean it IS obvious,...isn't it?) With such a superconducting
design I envision a spherically symmetric(for optimal density) array (I
would call it a MB except that it's more like a solid planet than a
rotating, concentric, orbiting array. Hmmm. I guess you could have the
full-star-surrounding collection of these, but the central brain must be
kept superconducting cool.) To whatever degree there was heat generation, I
would see the array as porous and immersed in liquid hydrogen or
helium--the former is more abundant, the latter the natural by-product of
the energy source that runs the system. The coolant would naturally take
advantage of superfluidity to carry away the waste heat frictionlessly. (Is
hydrogen capable of superfluidity?)
As I was conjuring up this coldest of "dark matter" hydrogen(or helium)
super-giant planets, it occurred to me that the ignition of a regular star
occurs when the temperature at the center of gravitationally-compressed
protostar/gas cloud rises by gravitational compression (the accumulation of
the gravitational energy of the infalling hydrogen atoms) to the ignition
point. If one calmly and deliberately "assembled" the coolant in already
incompressible liquid form, then ignition could be forstalled right up to
the point (which would define the limit on the size of the array) where the
pressure alone would overwhelm the internuclear repulsive forces. Hydrogen
and helium would have different ignition pressures. Additionally, if the
architecture of the array was of closed self-supporting spherical shells,
then the pressure of the coolant at each layer could be isolated and
prevented from building up to critical at the center. This might permit a
larger upper bound on the size.
I would not mention this at all, except that all previous discussions of J
and M brains have settled upon heat dissipation as one of the prime
controlling factors in architecture. All the designs I've heard of have
envisioned operation of the brain at blistering heats, mostly in close
proximity to the power source/star. This, with the single exception of your
discussion of MBs in globular clusters, which envisions remote siting, and
which would also be ideal for a superconducting-regime array (which would
require its power absorption and waste heat emission be conducted entirely
at its surface, whether in a GC or elsewhere.)
Perhaps I'm missing something, but isn't the superconducting regime the way
to go?
(Been there, done that, right?)
How would this affect the crucial and fascinating question of the
"visibility" of SI K1, 2, & 3 ETCs?
Best, Jeff Davis
"Everything's hard till you know how to do it."
Ray Charles
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