Re: Understanding Nanotech [PLEASE READ] [was Re: New government?]

Robert J. Bradbury (
Thu, 26 Aug 1999 12:53:36 -0700 (PDT)

On Thu, 26 Aug 1999 wrote:

> Robert's essay was very interesting and enlightening. I haven't
> seen this kind of detailed analysis before. But 5 years to build a
> Gates-style mansion? I had no idea it would take so long.

I should have made a couple of assumptions clearer: (a) I wanted everyone to be able to have the result. (b) You want to do it at as low a cost as possible.

(in this case the cost of the land and perhaps the seeds) (c) You must play nicely. I.e. you can't use more carbon,

      produce more heat, etc. than your personal allocation of
      the Earth's heat capacity.  (You probably can, but then you
      should probably have to "buy" or borrow it from someone else,
      you are stealing from the commons.)
      [Though some of this assumption may be flawed -- see below].

> I wonder if this energy cost isn't off by a couple of orders of magnitude.

As I said, it could be. It comes down to the costs of getting pure materials out of the air & soil and putting them into an assembler feedstock.

> but I think he is assuming high-energy feedstocks.

Yep! You would have to buy coal, oil or some other feedstock which violates my principle (b). That drives the costs up significantly (I think Eric says to about $1.00/kg). The consequence of my approach is that if you like it, then you are very *pro* fossil fuel burning, gas guzzlers, etc. Nobody "owns" the CO2 in the atmosphere, they are "giving it away"!

> If you are starting with oxidized carbon, aluminum and silicon
> (like you'd find in the air and in the soil) then you first have
> to expend energy to get these things ready to use.


> Re: Discussion of Nanosystems discrepancies on pgs 397 & 441.

The 1.5x10^6 J/kg is the figure for the chemical steps. The 3.6x10^6 J/kg I believe includes things like computing, arm motion, macro assembly, etc.
> In terms of sapphire, Al2O3, molecular weight about 100, a mole would be
> about 100 grams, so 1 mole would be about .1 kg. We should be able to
> construct a mole for .1 the kg cost, or 1.5 x 10^5 J if we use Drexler's
> lower estimate. Robert has 1.5 x 10^7 which is two orders of magnitude
> higher.

Yep. If you want to buy your high energy feedstock from some price gouging monopoly then you are welcome to do so. I'm being very conservative in my costs to do feedstock conversion. Doing better would require a complex set of chemical reactions to determine how to get the best results. For example, one typical refining technique to get oxygen away from the metals in the ground is to transfer it to carbon. But in a nanotech world that isn't a good way to go. You probably want a system to transfer the O2 from things like CO2 or basalt to something like O2 or Iron(making Fe2O3). Something like split water into H2+O2, release O2, use H2 to reduce CO2 to C + H2O.

I suspect we don't have a system to do this yet, so I want lots of extra energy in the system to deal with having to drive chemical reactions backwards, etc. The energy I use is that required to turn saphire into ionized gasses (which is very high!).

> I want that factor of 100 back! Then I can build my mansion in 20 days
> rather than 5 years.
> > It turns out that you probably don't want to assemble more than
> > 10 kg/hour because if everyone on the planet is doing it you
> > start to interfere with the heat carrying capacity of the planet [3].
> How would you interfere with the heat carrying capacity if you're getting
> all your energy from sunlight? Isn't that virtually all dissipated as
> heat now anyway, minus a tiny fraction captured chemically, in both
> biological and nonbiological processes?

This is a very good point that I hadn't considered. I'm going to have to ask Robert about this limit in Nanomedcine. He is claiming that limit on the maximum quantity for operating nanobots on the Earth. I'm not sure if he has done the calculations of where the energy comes from to do that. [It may be that he assumes we will be beaming down extra energy from power satellites.]

If we are only using natural solar energy, I suspect it depends on the energy states of the inputs and the outputs. If the final energy state of the outputs (e.g. diamond & saphire) is lower than that of the inputs (air & earth) then you are going to be a net producer of energy. The question comes down to how much energy from the gravitational collapse of the solar nebula, the formation of the earth and the past solar energy accumulated on the planet is locked up in chemical bonds in the atmosphere and crustal material. Since converting CO2 into diamond is significantly reducing the motion of the atoms (entropy), I suspect you are going to have to dump that someplace. Whether the bonds in diamond can absorb it all is unclear to me right now (looks like more work to do).

> It would seem that all we
> could hope to do is to capture it more efficiently and bind more of
> it chemically, so that if anything there would be less heat radiated.

You have to get rid of the energy involved in the motion of the gas molecules, but if you return it as O2, then it probably balances out fairly well.

> Or is that the issue? By "interfere with the heat carrying capacity"
> is it meant that we might make the earth too *cold*? (Sucking CO2 out
> of the atmosphere to get carbon for construction purposes might further
> cool things off.) That ought to be easy to fix, by sending up a few
> solar collecting satellites.

You, can probably convince the "environmentalists" to let you take out of the atmosphere the carbon we put into it (to combat global warming). You may have a debate as to whether to put the carbon back into trees or your car/house/yacht/mansion. You probably won't get much argument about removing the carbon in the coal/oil deposits. So probably you can remove the atmospheric carbon while slowly replenishing it from the coal/oil reserves to let some of the trees grow back. If you remove too much CO2 you will definately have a problem with global cooling (unless you want to import some of it from Venus).

> The total solar energy impinging on earth is about 2 x 10^17 Watts, which
> with a population of 10^10 gives everyone over 10^4 kW to play with.
> That would be enough to assemble 10^4 kg/hour, four orders of magnitude
> more, and lets us build our mansion in 4 hours instead of 5 years.
> However this would require an infrastructure to capture solar energy
> over much of the globe and pump it where needed.

Yep, you can clearly do it faster if you build the infrastructure. But the right-of-way and environmental legal battles would probably keep you tied up in court longer than my scheme takes. I was looking for a very low cost, "nice" way for *everyone* to get the food, housing, education, etc. that was asked for in the original post without requiring you do anything but buy an affordable piece of land and convince your friends to share their open-source designs.

Of course there are likely to be some environmental battles if many people at the same time start solar-cell-ize-ing acres that happen to be primary habitats of some species of interest. But given that we have an ~10:1 land-to-person ratio, there is probably a lot of environment left to go around. Since you are moving from plant power harvesting @ 1-2% efficiency to solar cell power harvesting @ 20-30% efficiency, plus some other things like wind or geothermal power, then you probably get to turn a huge amount of land currently devoted to agriculture back into forests. I think the environmentalists would rate this a "buy".