Will nanotechnology culminate with diamondoid nanorobots produced in nanofactories by atomically precise mechanosynthesis, or with “soft” machines that mimic the way biological molecular machines work? The June issue of IEEE Spectrum online contains a special report on “The Singularity”, the concept popularized by Vernor Vinge, Ray Kurzweil and others that near the middle of this century self-improving machine intelligence will first equal—and then rapidly exceed—human intelligence. Various views are represented, but the overall tenor of the report is skeptical. On the contents page, the article “Rupturing the Nanotech Rapture” by Richard A.L. Jones is subtitled “Tiny robots that can fix all our bodily flaws sound lovely, but they violate the laws of physics.” However, Jones’s actual article is subtitled “Biological nanobots could repair and improve the human body, but they’ll be more bio than bot”. Richard A. L. Jones is the author of Soft Machines: Nanotechnology and Life, which I reviewed in Foresight Update 55 (PDF). The argument that Jones makes in this Spectrum article is the same that he made in Soft Machines: that advanced nanotechnology will use “soft” machines that mimic the way biological molecular machines work—not “hard” machines that mimic the way macroscale machines work. From “Rupturing the Nanotech Rapture“:

…In the latest vision of the nanofactory, the reproducing replicators give way to Henry Ford–style mass production, with endlessly repeated elementary operations on countless tiny production lines.

It’s a seductive idea, seemingly validated by the workings of the cells of our own bodies…

If biology can produce a sophisticated nanotechnology based on soft materials like proteins and lipids, singularitarian thinking goes, then how much more powerful our synthetic nanotechnology would be if we could use strong, stiff materials, like diamond. And if biology can produce working motors and assemblers using just the random selections of Darwinian evolution, how much more powerful the devices could be if they were rationally designed using all the insights we’ve learned from macroscopic engineering.

But that reasoning fails to take into account the physical environment in which cell biology takes place, which has nothing in common with the macroscopic world of bridges, engines, and transmissions. In the domain of the cell, water behaves like thick molasses, not the free-flowing liquid that we are familiar with. This is a world dominated by the fluctuations of constant Brownian motion, in which components are ceaselessly bombarded by fast-moving water molecules and flex and stretch randomly. The van der Waals force, which attracts molecules to one another, dominates, causing things in close proximity to stick together. Clingiest of all are protein molecules, whose stickiness underlies a number of undesirable phenomena, such as the rejection of medical implants. What’s to protect a nanobot assailed by particles glomming onto its surface and clogging up its gears?

The bottom line is that we have no idea whether complex and rigid mechanical systems—even ones made from diamond—can survive in the nanoworld.

Put all these complications together and what they suggest, to me, is that the range of environments in which rigid nanomachines could operate, if they operate at all, would be quite limited. If, for example, such devices can function only at low temperatures and in a vacuum, their impact and economic importance would be virtually nil.

…We shouldn’t abandon all of the more radical goals of nanotechnology, because they may instead be achieved ultimately by routes quite different from (and longer than) those foreseen by the proponents of molecular nanotechnology.

Nevertheless, Jones never states that nanotechnology based on rigid diamondoid structures and mechanosynthesis violates the laws of physics. On page 215 of Soft Machines he writes “I do not think that this approach fundamentally contradicts any physical laws, though I think that some of its proponents underestimate the problems that features of the nanoworld, like Brownian motion and strong surface forces, will pose for it.”

Certainly the “soft machines” approach to nanotechnology holds great promise for the near term, while the diamondoid mechanosynthesis approach is only in the very early stages of computer simulation. Those interested in the status of diamond mechanosynthesis might want to check out the excellent “Introduction to Diamond Mechanosynthesis” and the “Nanofactory Collaboration” by Robert A. Freitas Jr. and collaborators, as well as the thoughtful critiques by Philip Moriarty and by Richard Jones.

Can we say yet what form advanced nanotechnology will take 20 or 30 years from now? Will our nanorobots be more bio or more bot? For more on the possible roads to advanced nanotech, check out the “Technology Roadmap for Productive Nanosystems“.