On Wed, Dec 01, 1999 at 04:33:20PM -0800, Jeff Davis wrote:
> 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 think you're on the right track. From the perspective of thermodynamics the Matrioshka design is highly inefficient since each computing element is polluting everyone else with waste heat. The theory of reversible computation says you're only forced to generate waste heat when you erase information. There is no minimum entropy increase per operation as long as the operation is reversible. This suggests that the computational core should never erase bits but instead ship them out to erasure sites at the outer periphery of the civilization or around black holes.
The MB design assumes that energy collection, computation, and entropy management (i.e. bit erasure) are all done at the same place. It makes more sense to distribute these functions to specialists. The optimal design for the computational part is probably exactly what you suggested: a single supercooled sphere with no moving parts (except maybe at the nano scale).