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The power density is large compared to that of macroscale motors: >1e15 W/m^3. For comparison, Earth intercepts ~1e17 watts of solar radiation. (Cooling constraints presumably preclude the steady-state operation of a cubic meter of these devices at this power density.)
Nanosystems p. 339

It is difficult, even for someone who has been working with these ideas and numbers for the past couple of decades, to get one’s head around the utter raw power potential of real nanotechnology. What Drexler is saying in this dry passage is that the amount of nanomotors needed to power a Kardasheff type I civilization, using all the sunlight that hits the Earth, would fit in a 500 square foot apartment (with 8-foot ceiling).

Let’s put it another way: The amount of nanomotors to power a Type II civilization, using all the energy output of the Sun (1e27 W), would fit in a ten-kilometer cube.

Or another way: a 1000-horsepower motor — let’s round up to a megawatt — is one cubic millimeter.

Or to put it one final way: Compared to what can be built, nanotech is likely to be energy-starved for the foreseeable future.

Why should we care? After all, nanotech is likely to allow us to use whatever energy we have more efficiently, improving our situation even in a flatline energy scenario. Yet, we’d be much better off with more, cheaper, energy. Here are a few simple scenarios where just going from 1 to 10 kW per person (1 is the current average in industrialized countries) makes a big difference:

Before the Industrial Revolution, most power humans used was their own muscles. A human eating a 2000-calorie per day diet averages about 100 watts — a factor of 10 below current industrialized levels of energy use of 1 kW. It doesn’t seem unreasonable at all to imagine a nanotech industrial revolution going another factor of ten. As I pointed out in my previous post, we’d be at roughly that level now if we’d just continued on the trajectory of before 1970. And we might just have flying cars, space travel, and the rest.

How is nanotech going to help us get there? In the short run, ground-based solar isn’t too bad; that million square kilometers of area is only 100 square meters per person (at an estimated 10 billion people in 2050). The key is to make it cheap and incorporate it into structures we were going to build anyway, and nanotech can help there. A slightly longer term option is nanograss — a synthetic replacement for lawns that wouldn’t need watering or insecticides, and would act as a solar collector. This should work up to typical suburban population densities.

There are a number of developments coming or possible in nuclear energy that could make a big difference and should be investigated, but aren’t on the topic of nanotech per se. The other significant possibility is new physics, but of course that’s impossible to predict.

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