Robert J. Bradbury, <firstname.lastname@example.org>, writes:
> That is what Hal has been complaining about, he wants the difference
> between the NM limit of ~10^4 W (10kg of nanobots) and ~10^7 W.
> Those 3 orders of magnitude let him build that mansion much faster.
> [Of course if he gets the entire power budget, we don't have any plants
> and very few animals left.]
> I would generally agree with Hal, in that I think we can get almost
> an order of magnitude more power without too much trouble.
> More than that and it is going to start creating problems
> until we have a lot of computer power to simulate the potential
The interesting point remains that this limit exists and is relatively low, within about one order of magnitude of 10^5 kW per person. This is based either on renewable energy, if we assume less than perfect efficiency, or in any case on avoiding destroying the natural energy distribution of the earth and allowing most existing plants and animals to remain in existence. I had not seen this limit stated explicitly before and it is very interesting and sobering to realize that even with nanotech we will be constrained in this way.
Things get worse, probably, if we use nonrenewable energy sources, so that our heat is added to the existing solar energy. There's plenty of deuterium in the sea if we can get D-D fusion working, and we may even be able to find new fossil fuel deposits with improved drilling and mining technology. (Robert Freitas presented the picturesque image of diesel-powered nanobots; I pictured a Drexlerian assembler chugging along with puffs of black smoke coming out.)
> But I suspect you can get probably 2-4 orders of magnitude
> better by doing more efficient assembly (i.e. chemical reactions
> that utilize/reuse the free energy effectively), reusing building
> blocks (so once you have invested in building them, you don't rebuild
> them) and going to more efficient nanodesigns. So we are probably
> wasting mental energy on the wrong side of the problem.
Yes, plus these calculations are assuming that you are building stuff all the time (or at least using all that nanomachinery in a highly energy intensive mode). In practice people may build things and then use them for a while before they get tired of them and want something new. During the usage phase probably only a fraction of the materials need to be nanotechnically active. Even a utility fog is mostly only doing stuff in the part that's within a few inches of you; the rest of it (assuming you even need more than that) is just sitting there.