Re: Nanonukes and square cube law

Michael S. Lorrey (
Thu, 28 Jan 1999 10:11:14 -0500 wrote:

> Spike Jones, <>, writes:
> > ok now go back down the scale. we are accustomed to getting power
> > from violent chemical reactions such as octane and air, but a plant can
> > get all the energy it needs from photosynthesis. plants on our scale
> > generally need a lot of leaves, but single celled plants have so little
> > chlorophyll they sometimes dont even look green, and yet they seem
> > wildly active under a microscope. chlorophyll creates sugars, which
> > break down in a much gentler reaction than oxygen combustion.
> Our chemical reactions are violent in part because we don't have the
> technology to extract the energy efficiently, the way plants do. We
> have to burn gasoline or other fuels to produce heat in a rather crude
> way.

On what basis do you say this? From stats I've seen, photosynthesis is only about 1% efficient, or less. If you have other data I'd love to see it.

> > so, if the lesson of nature is not misleading, we dont need nanonukes,
> > or even nanoscale combustion. the square cube law would suggest
> > that nanobots should be able to create all the energy they need using
> > chlorophyll and the fusion reactor nature has already generously
> > provided: the sun. right? spike
> The square-cube law says that smaller units have a larger surface area
> per volume. If sunlight is proportional to surface area, then this does
> give an advantage to smaller entities. But that is only true for those
> entities in favorable positions to get sunlight. If you have a solid
> mass of nanomachines, then the ones in the middle don't get any light.
> So you still have an energy problem.

Not if you have bots that get light decide to specialize in producing 'food' for bots that are in the dark. Also, see my comment below on fuels...

> In fact, if we think of the surface of the nanomachines as being where
> energy is expended, then smaller units will have a bigger energy problem,
> because they have more functional area but a smaller volume to power it
> with.

No, if we are talking about using solar power, then they won't have a power problem. They may have a problem absorbing it all and using it, which could lead to problems dumping excess power, which they could use to build food for bots that are in the dark, but I'm also concerned with the efficiency of a nanoscale solar cell. Thickness is an important factor in cell design.

> So there does seem to be a power question with regard to nanobots. Solar
> is an option for those outside, as long as they are in a thin layer.
> In other environments they will probably need a fuel supply of energetic
> chemicals.

Fortunately there is plenty of organic material everywhere that can be burned by nanobots. There is coal, methane, oil, as well as more volatile chemicals all over the place, just not concentrated enough to be useful for refinement at our macro scales...

Mike Lorrey