Rupturing The Nanotech Rapture

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 watery nanoscale environment of cell biology seems so hostile to engineering that the fact that biology works at all is almost hard to believe. But biology does work--and very well at that. The lack of rigidity, excessive stickiness, and constant random motion may seem like huge obstacles to be worked around, but biology is aided by its own design principles, which have evolved over billions of years to exploit those characteristics. That brutal combination of strong surface forces and random Brownian motion in fact propels the self-assembly of sophisticated structures, such as the sculpting of intricately folded protein molecules. The cellular environment that at first seems annoying--filled with squishy objects and the chaotic banging around of particles--is essential in the operation of molecular motors, where a change in a protein molecule's shape provides the power stroke to convert chemical energy to mechanical energy.

In the end, rather than ratifying the ”hard” nanomachine paradigm, cellular biology casts doubt on it. But even if that mechanical-engineering approach were to work in the body, there are several issues that, in my view, have been seriously underestimated by its proponents.

First, those building blocks--the cogs and gears made famous in countless simulations supporting the case for the singularity--have some questionable chemical properties. They are essentially molecular clusters with odd and special shapes, but it's far from clear that they represent stable arrangements of atoms that won't rearrange themselves spontaneously. These crystal lattices were designed using molecular modeling software, which works on the principle that if valences are satisfied and bonds aren't too distorted from their normal values, then the structures formed will be chemically stable. But this is a problematic assumption.

A regular crystal lattice is a 3-D arrangement of atoms or molecules with well-defined angles between the bonds that hold them together. To build a crystal lattice in a nonnatural shape--say, with a curved surface rather than with the flat faces characteristic of crystals--the natural distances and angles between atoms need to be distorted, severely straining those bonds. Modeling software might tell you that the bonds will hold. However, life has a way of confounding computer models. For example, if you try to make very small, spherical diamond crystals, a layer or two of carbon atoms at the surface will spontaneously rearrange themselves into a new form--not of diamond, but of graphite.

A second problem has to do with the power of surface forces and the high surface area anticipated for these nanobots. Researchers attempting to shrink existing microelectromechanical systems to the nanoscale have already discovered that the combination of friction and persistent sticking can be devastating. Nanobots are expected to operate at very high power densities, so even rather low values of friction may vaporize or burn up the minuscule machines. At the very least, this friction and sticking will play havoc with the machines' chemical stability.

Then there's the prospect of irreversible damage if reactive substances--such as water or oxygen--get caught up in a nanobot's exposed surfaces, upsetting the careful chemistry of each. To avoid those molecules, nanodevices will have to be fabricated in a fully controlled environment. No one yet knows how a medical nanobot would be protected once it is released into the warm, crowded turbulence of the body, perhaps the most heterogeneous environment imaginable.

Finally, there's the question of how an intricate arrangement of cogs and gears that depends on precision and rigidity to work will respond to thermal noise and Brownian bombardment at room temperature. The turbulence that nanobots will be subjected to will far exceed that inflicted on macroscopically engineered structures, and even the most rigid materials, like diamond, will bend and wobble in response. It would be like making a clock and its gears out of rubber, then watching it tumble around in a clothes dryer and wondering why it doesn't keep time. 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.

In 15 years of intense nanotechnology research, we have not even come close to experiencing the exponentially accelerating technological progress toward the goals set out by singularitarians. Impressive advances are emerging from the labs of real-world nanotechnologists, but these have little to do with the Drexlerian vision, which seems to be accumulating obstacles faster than it can overcome them. Given these facts, I can't take seriously the predictions that life-altering molecular nanotechnology will arrive within 15 or 20 years and hasten the arrival of a technological singularity before 2050.

Rather than try to defy or resist nature, I say we need to work with it. DNA itself can be used as a construction material. We can exploit its astounding properties of self-assembly to make programmed structures to execute new and beneficial functions [see sidebar, ”The Real Nanobot”]. Chemists have already made nanoscale molecular shuttles and motors inspired directly by biology, with exciting applications in drug delivery and tissue engineering.

We will reap major medical advances by radically reengineering existing microorganisms, especially in nanodevices that perform integrated diagnosis and treatment of some disorders. But the timescales to reach the clinic are going to be long, and the goal of cell-by-cell repair is far, far beyond our incomplete grasp of biological complexity.

Much the same can be said about the singularitarian computers that are needed to generate a complete reading of a mental state and brain implants that seamlessly integrate our thought processes with a computer network. True, brain-interface systems have already been built. A state-of-the-art system can read about 128 neurons. So: 128 down, 20 billion or so to go.

Nonetheless, I'm an optimist. I think that in the near future we'll successfully apply nanotechnology to the most pressing social challenges, such as energy and the environment. For example, new polymer- and nanoparticle-based photovoltaics may soon lead to dramatic improvements in the price and production of solar cells.

What, then, of software-controlled matter? Complete control will remain an unattainable goal for generations to come. But some combination of self-assembly and directed assembly could very well lead to precisely built nanostructures that would manipulate the way light, matter, and electrons interact--an application of nanotechnology that's already leading to exciting new discoveries. We've barely scratched the surface of what we'll eventually be able to do with these custom-built nanostructures. It is altogether possible that we will finally harness the unfamiliar quantum effects of the nanoscale to implement true quantum computing and information processing. Here, I suspect, is the true killer application for the idea of software-controlled matter: devices that integrate electronics and optics, fully exploiting their quantum character in truly novel ways--a far cry from the minuscule diamond engines foreseen by the transhumanists.

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. Perhaps we should thank Drexler for alerting us to the general possibilities of nanotechnology, while recognizing that the trajectories of new technologies rarely run smoothly along the paths foreseen by their pioneers.

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