[ExI] fermi question alive and well

John Clark johnkclark at gmail.com
Sat Mar 30 13:49:46 UTC 2019

On Fri, Mar 29, 2019 at 10:25 PM Keith Henson <hkeithhenson at gmail.com>


> * > I think the second law prevents a Jupiter Brain from being built.The
> problem is that computation produces waste heat and that has to be radiated
> to keep the "brain" from overheating.  There are conflicting problems with
> large computational nodes, you need to keep the size small to minimize
> speed of light delays and you need to make it large to get rid of the waste
> heat.  (Or you can sink it in the deep ocean.)*

It's true Jupiter Brain engineers would have to be careful with the heat
but it would not represent a insurmountable problem. As far as speed is
concernedthe fastest signals in the human brain move at a couple of hundred
meters a second, many are far slower, light moves at 300 million meters per
second. If you insist that the 2 most distant parts of the Jupiter Brain
communicate no slower than they do in a human brain then parts in the brain
of a AI could be at least one million times more distant. The human brain
is about half a foot in diameter so the AI could have a brain about a
hundred miles in diameter. Another problem is the outside surface where
heat is radiated away only increases with the square of the radius while
the volume increases with the cube, so the density of the heat producing logic
components would have to decrease with 1/r.

So OK, "Jupiter Brain" may be a bit of an exaggeration, perhaps "Asteroid
Brain" would be a more accurate (but less poetic) name, although the mind
such a brain could produce would be more Jupiter size than  Asteroid size
because the components of the AI's brain would be much smaller than the
components of our human brain.

And a hundred miles across is still pretty big for a brain. The volume
increases by the cube of the distance, our brains are about half a foot in
diameter so such a brain would physically be a million trillion times
larger than a human brain. Even if 99.9% of that space were used just to
get rid of waste heat you'd still have a thousand trillion times as much
volume for logic and memory components as humans have room for inside their

Helium would be the ideal substance to fill those cooling pipes. Helium
liquefies at 4.2 K but when it gets below 2.17 K it becomes a super-fluid
called Helium-2 that has zero viscosity (provided the pipe the helium is
flowing through does not have a diameter smaller than 10^-9 meters) so you
can pump a lot of Helium through a pipe very quickly. And Helium-2 is also
by far the best conductor of heat known, it conducts heat so fast (over 20
meters a second) that all the Helium is at the same temperature, there are
no hot spots in it and thus no bubbles to interfere with the free flow of

 John K Clark
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