Re: Galaxy brain problem

Hara Ra (
Mon, 18 Aug 1997 22:39:08 -0700

Assuming that c is the limit speed for data transfer, galaxy brains have
an obvious problem - it takes some 100K years for a message to get to
all parts of a galaxy. The darn things are just too big and too diffuse!

One answer to all this is to make the galaxy more dense.... after all, a
galaxy is mostly space, and I expect computational nanotechnology to
have a density comparable to water.... So I began to think of
mega-ringworlds and beyond dyson spheres.

The area of a black hole's event horizon is proportional to its mass.
The more massive a balck hole, the less dense it is, and the smaller the
gravitational field at the event horizon. Imagine building something
like a dyson sphere whose radius is just slightly larger than the event
horizon of a black hole of the same mass.... The kind of technology
capable of a galaxy brain should be able to move all the matter in the
galaxy essentially at will.

We can eliminate stars as energy production devices, as ALL the matter
in a galaxy is to used for this endeavour. It is much more efficient to
drop a little matter into a black hole, getting 1/2 mc^2 back - rather
than the 0.1% yield for fusion....

Since the super dyson sphere is not tasked to collect stellar radiation,
there is a way to construct one without encountering severe stresses.
Start with an object in orbit. Make the orbit slightly elliptical. Now
imagine a "string of beads" in orbit, like an elliptical necklace. Now
imagine lots and lots of beads, say 1cm beads with 1mm spacing. The
inter bead spacing varies slightly as the beads orbit due to the
ellipticity. Since the ellipse is very nearly circular, this variation
would be in microns. Control of such a system could be via magnetics or
electrostatics between the beads.

Imagine a second beady ellipse, 180 degrees in orientation. To avoid
collisions, make the two orbital planes at a very slight angle to one
another. This pair of intertwined necklaces is now repeated until one
sees a sphere, which becomes two interlaced ellipsoids, very nearly
spherical. We now have a very nearly spherical structure with no
internal stresses. Just add mass until one uses up the galaxy....

The gravity experts will have to answer the next speculation - since the
gravity field within a spherical shell is flat, it may be possible to
have an event horizon for the entire structure slightly below the
orbits, and still maintain a black hole in the very center - provided
gratis by most galaxies anyway....

I don't know the numbers here, I guess that such an object will be a few
tens of light years across - but about 10^4 times faster signaling.....

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