December 01, 2003

Assembler Debate Heats Up

Eric Drexler and Richard Smalley are finally having it out one-on-one over the issue of nano assemblers in the current issue of Chemical and Engineering News. Since the nanotechnology bill has passed both houses of Congress and is awaiting the President's signature, and in light of the fact that there's a certain amount of confusion as to how far the bill is going to take us in the direction of molecular manufacturing, this debate couldn't be more timely.

The difference of opinion between these two nanotechnology luminaries originated in 2001 when Smalley blasted (via misrepresentation) some basic molecular manufacturing concepts in an article in Scientific American. Drexler responded by issuing an open letter to Smalley challenging him to debate these issues. The crux of their original disagreement was whether nano-assemblers as envisioned by Drexler would require the use of tiny pincers to move atoms around. As explained by Smalley, any such mechanical pincers or fingers that could be built would be either too "fat" or too "sticky" ever to work. Drexler countered that these "Smalley Fingers" (as he dubbed them) are a straw man that have nothing to do with the basic concepts of molecular manufacturing that he has developed:

I have a twenty year history of technical publications in this area and consistently describe systems quite unlike the straw man you attack. My proposal is, and always has been, to guide the chemical synthesis of complex structures by mechanically positioning reactive molecules, not by manipulating individual atoms. This proposal has been defended successfully again and again, in journal articles, in my MIT doctoral thesis, and before scientific audiences around the world. It rests on well-established physical principles.

In the new debate, Smalley immediately concedes this point and even takes to calling these things "Smalley Fingers" himself.

In the infinity of all conceivable ideas for self-assemblers, we agree that at least this computer-controlled "Smalley finger" type of assembler tool will never work.

Drexler goes on to explain the kind of assembler environment he has in mind:

These nanofactories contain no enzymes, no living cells, no swarms of roaming, replicating nanobots. Instead, they use computers for digitally precise control, conveyors for parts transport, and positioning devices of assorted sizes to assemble small parts into larger parts, building macroscopic products. The smallest devices position molecular parts to assemble structures through mechanosynthesis--'machine-phase' chemistry.

Direct positional control of reactants is both achievable and revolutionary; talk of additional, impossible control has been a distraction.

Smalley, however, just can't buy in:

I see you have now walked out of the room where I had led you to talk about real chemistry, and you are now back in your mechanical world. I am sorry we have ended up like this. For a moment I thought we were making progress.

You still do not appear to understand the impact of my short piece in Scientific American. Much like you can't make a boy and a girl fall in love with each other simply by pushing them together, you cannot make precise chemistry occur as desired between two molecular objects with simple mechanical motion along a few degrees of freedom in the assembler-fixed frame of reference. Chemistry, like love, is more subtle than that. You need to guide the reactants down a particular reaction coordinate, and this coordinate treads through a many-dimensional hyperspace.

Smalley seems inordinately fond of his "love" analogy for chemistry. It's hard to imagine a scientist taking a more obstructionist position toward his own field. You can't understand this. It's like boy meets girl. It's the birds and the bees. It's magic.

Ralph Merkle counters in Foresight's official press release on the debate:

Ab initio quantum chemistry calculations don't involve love, or mushing, or pretending. For example, a carbon-deposition reaction which a colleague and I studied using standard quantum chemistry methods moves a carbene tool along a barrier-free path to insert a reactive carbon atom into a dimer on a diamond (100) surface. The tool is then twisted 90 degrees, breaking an internal pi bond, and pulled away to break the remaining sigma bond, leaving a single carbon atom bonded to the dimer on the surface." Merkle adds, "Further computational chemistry research into fundamental mechanosynthetic reactions should be an integral component of any national nanotechnology program. Smalley's metaphors merely cloud the issues.

Smalley concludes with this disturbing story:

A few weeks ago I gave a talk on nanotechnology and energy titled "Be a Scientist, Save the World" to about 700 middle and high school students in the Spring Branch ISD, a large public school system here in the Houston area. Leading up to my visit, the students were asked to write an essay on "Why I Am a Nanogeek." Hundreds responded, and I had the privilege of reading the top 30 essays, picking my favorite five. Of the essays I read, nearly half assumed that self-replicating nanobots were possible, and most were deeply worried about what would happen in their future as these nanobots spread around the world. I did what I could to allay their fears, but there is no question that many of these youngsters have been told a bedtime story that is deeply troubling.

You and people around you have scared our children. I don't expect you to stop, but I hope others in the chemical community will join with me in turning on the light, and showing our children that, while our future in the real world will be challenging and there are real risks, there will be no such monster as the self-replicating mechanical nanobot of your dreams.

Presumably, Smalley will be in Alaska next week telling children that they don't need to worry about being eaten by polar bears because there are no polar bears. The question of whether polar bears actually exist is secondary; the main point is that children shouldn't be frightened. It apparently hasn't occurred to Smalley that this "frightening bed-time story" is as gross a distortion of any message ever to come out of Foresight as were his fat and sticky fingers.

But then, that wouldn't occur to him, would it?

Howard Lovy provides an excellent analysis of this debate, which he concludes with cautionary note about why a correct assessment of feasibility can be so important:

What if the scientists who believed atomic power was physically impossible had the ear of the U.S. government during World War II? If you think that's a ridiculous thought, go look up Leo Szilard. He had some crazy idea about creating a nuclear chain reaction so powerful that it could change the balance of power in the world in an instant. He said such harnessing of atomic energy was so dangerous that society should figure out a way to control it. The leading physicists of his day, including Enrico Fermi, said such a thing was not possible. It took a letter from former atom-splitting skeptic Albert Einstein, who by 1939 had come around to the possibilities of uranium, to finally convince President Roosevelt to toss some money Szilard's way for a feasibility study on atomic chain reactions.

The rest, as they say, is history.

Perhaps as the debate continues here at home, we should keep a watchful eye on other powers who are already actively working to build the first assembler—whether we decide it's possible or not.

UPDATE: Ray Kurzweil provides a thorough anlaysis of the debate (inlcuding an excellent background on the field of nanotechnology) and Glenn Reynolds has a good round-up of links.

Posted by Phil at December 1, 2003 07:18 AM | TrackBack

Some of Smalley's comments are jaw droppers. He has said there is no evidence molecular machines and assemblers can exist . . . which is pretty amazing considering we are MADE OF THEM. A particular conceptual design may not work, but clearly molecular assemblers of some form can be made because clearly they do already.

There are real questions about how far we can take nanotech and how fast - many of the "gee whiz" about cell repair machines, utility fog and such are based on the ability to build very complex nanomachines. It isn't clear how hard (or easy) this type of thing will be. It is a bit like a sentient computer, an AI that can pass the Turing test - we didn't know how hard that would be until we tried to build one, and we don't know what it will take to get there. Complex nanotech MAY be that difficult, or it may not. We just don't know yet.

Posted by: VR at December 2, 2003 06:44 PM
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