Re: Galaxy brain problem

Dan Clemmensen (
Tue, 19 Aug 1997 06:51:28 -0400

Hara Ra wrote:
> 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.

[snip of some interesting galactic engineering]

It will take a while to accomplish all this. At the speed of light,
your acquisition probes will take about 50Kyears to reach the limits
of a 50K lightyear sphere surroundng the galaxy. Once there, they can
start sending all the matter back to the collection point. Assuming
transit speeds of .5c, you will expend two thirds of the mass to
accelerate the other third at the start and decelerrate it at the
end of the trip, so after an additional 100K years, you will have
accumulated "only" one third of the galaxy's mass. If you are
willing to wait, you can use longer transit times and end up with
more mass. Of course, you will be able to begin construction with
material accumulated much earlier in the program, as soon
as you reach the galactic center, about 25Kyears from now.