Drexler–Smalley debate on molecular nanotechnology

The Drexler–Smalley debate on molecular nanotechnology was a public dispute between K. Eric Drexler, founder of the field of molecular nanotechnology, and Richard Smalley, a recipient of the 1996 Nobel prize in Chemistry for the discovery of the nanomaterial buckminsterfullerene. The dispute was about the feasibility of constructing molecular assemblers, which are molecular machines which could robotically assemble molecular materials and devices by manipulating individual atoms or molecules. The concept of molecular assemblers was central to Drexler's conception of molecular nanotechnology, but Smalley argued that fundamental physical principles would prevent them from ever being possible. The two also traded accusations that the other's conception of nanotechnology was harmful to public perception of the field and threatened continued public support for nanotechnology research.

The debate was carried out from 2001 to 2003 through a series of published articles and open letters. It began with a 2001 article by Smalley in Scientific American, which was followed by a rebuttal published by Drexler and coworkers later that year, and two open letters by Drexler in early 2003. The debate was concluded in late 2003 in a "Point–Counterpoint" feature in Chemical & Engineering News in which both parties participated.

The debate is often cited in the history of nanotechnology due to the fame of its participants and its commentary on both the technical and social aspects of nanotechnology. It has also been widely criticized for its adversarial tone, with Drexler accusing Smalley of publicly misrepresenting his work, and Smalley accusing Drexler of failing to understand basic science, causing commentators to go so far as to characterize the tone of the debate as similar to "a pissing match"^[1] and "reminiscent of [a] Saturday Night Live sketch".^[2]

The participants

K. Eric Drexler

K. Eric Drexler developed and popularized the concept of nanotechnology and founded the field of molecular nanotechnology.

Main article: K. Eric Drexler

K. Eric Drexler was the first person to develop the concepts of nanotechnology and was a key figure in popularizing these concepts. Trained as an engineer, Drexler was inspired by a then-obscure 1959 talk by physicist Richard Feynman called There's Plenty of Room at the Bottom, which posited that it should be physically possible to manipulate individual atoms using top-down engineering methodologies. Drexler was also inspired by recent advances in molecular biology such as recombinant DNA technology. In a 1981 publication in Proceedings of the National Academy of Sciences, considered to be the first journal article on nanotechnology, he argued that biological systems such as the ribosome were already capable of building molecules atom-by-atom, and that artificial machines with this capability could also be constructed. Drexler went on to publish two books on nanotechnology: Engines of Creation in 1986, which was intended for the public, and the technical work Nanosystems in 1992. He also co-founded the Foresight Institute, a public interest group devoted to increasing public awareness and information about molecular nanotechnology.^[3]

Drexler's vision of nanotechnology, now called molecular nanotechnology, is based on the concept of the molecular assembler, a molecular machine which would manufacture molecules and molecular devices atom-by-atom. Drexler drew a distinction between wet nanotechnology based on biological systems, and "second-generation" dry nanotechnology which would be based on mechanosynthesis, positional control of molecules through principles more related to mechanical engineering. Drexler and his followers have focused almost exclusively on the latter form of molecular nanotechnology, but Drexler has stated that both are valid pathways to creating molecular machine systems.^[3]

Richard Smalley

Richard Smalley won the 1996 Nobel Prize in Chemistry along with Harry Kroto and Robert Curl for their 1985 discovery of buckminsterfullerene.

Main article: Richard Smalley

Richard E. Smalley, a chemist at Rice University, is best known as a co-discoverer of the C₆₀ form of carbon known as buckminsterfullerine in 1985, along with Harry Kroto, Robert Curl, James Heath, and Sean O'Brien. Buckminsterfullerene was the first to be discovered of the class of molecules known as fullerenes, which also includes carbon nanotubes. The study and application of fullerenes forms a significant part of the fields of nanomaterials and nanoelectronics, and Smalley, Kroto, and Curl were awarded the 1996 Nobel Prize in Chemistry for their discovery of buckminsterfullerene.^[4]

Smalley had also taken a prominent public policy role in relation to nanotechnology, and was an outspoken advocate for using nanotechnology to develop solutions to the world's energy and health problems, for example raising the possibility of using nanomaterials for efficient energy storage and transmission, and of developing nanomaterial-based drugs for targeted drug delivery. Smalley was also active in commercializing his academic research into carbon nanotubes, having founded Carbon Nanotechnolgies Inc., and serving on the scientific advisory board of two other biotechnology and nanotechnology startups. Smalley died of leukemia in October 2005, after the conclusion of his debate with Drexler.^[5][6]

The debate

Smalley's Scientific American article

Smalley wrote an article, "Of Chemistry, Love, and Nanobots", for the September 2001 issue of the popular science magazine Scientific American, which was a special issue on the topic of nanotechnology.^[7] Smalley opened by comparing a chemical reaction to an intricate dance of atoms:

"When a boy and a girl fall in love, it is often said that the chemistry between them is good. This common use of the word 'chemistry' in human relations comes close to the subtlety of what actually happens in the more mundane coupling of molecules. In a chemical reaction between two 'consenting' molecules, bonds form between some of the atoms in what is usually a complex dance involving motion in multiple dimensions.... And if the chemistry is really, really good, the molecules that do react will all produce the exact product required."

He then referenced the idea of a molecular assembler, a nanorobot capable of manipulating individual atoms to build a desired product. He posed the question of how long it would take such an assembler to produce a meaningful amount of material; for one assembler he estimated that it would take millions of years to produce one mole of material, but if the assembler were allowed to self-replicate, a large ensemble of assemblers could be created in a minute which would then be capable of producing a mole of product in a fraction of a millisecond. Smalley then talks about the implications of this result and the fears that have been arisen about it, namely the fear that the nanorobots could mutate and reproduce indefinitely, causing a grey goo scenario, or, referring to Bill Joy's previous article "Why the future doesn't need us", that the nanorobots could develop swarm intelligence and become alive in some sense.

Smalley then asks how realistic the concept of a self-replicating nanorobot is. He states that, in a chemical reaction, the chemical bonds are all interconnected and that the placement of each atom is sensitive to the position of all the other atoms in the vicinity. He then asserts that a molecular assembler would thus have to control many atoms simultaneously in order to work, and would thus have to have many manipulator arms. This led him to raise two objections to the concept of molecular assembler, which he calls the "fat fingers problem" and the "sticky fingers problem":

"Because the fingers of a manipulator arm must themselves be made out of atoms, they have a certain irreducible size. There just isn't enough room in the nanometer-size reaction region to accommodate all the fingers of all the manipulators necessary to have complete control of the chemistry.... [Also,] the atoms of the manipulator hands will adhere to the atom that is being moved. So it will often be impossible to release this miniscule building block in precisely the right spot. Both these problems are fundamental, and neither can be avoided. Self-replicating, mechanical nanobots are simply not possible in our world."

Smalley closed the article by returning to the analogy of chemistry as a dance of love, remarking that "you don't make a girl and a boy fall in love by pushing them together."

Drexler's response

Top, a schematic of the ribosome, which Drexler advanced as an example of a biological molecular machine due to its ability to precisely construct protein macromolecules from smaller amino acids. An animated version is also available. Bottom, a schematic of a scanning tunneling microscope, which Drexler cited as being able to manipulate individual molecules via positional control.

Drexler responded by publishing a rebuttal later in 2001 through the Institute for Molecular Manufacturing, which was co-authored with others including Robert Freitas, J. Storrs Hall, and Ralph Merkle.^[8] The authors first refute the "fat fingers" argument by attacking Smalley's notion that a chemical reaction must involve five to fifteen atoms. They note that many reactions involve only two reactants, one of which can be immobilized and the other attached to a single "finger". They briefly cite an experimental result using a scanning tunneling microscope (STM) tip and a theoretical result indicating that this may be possible. They also bring up the idea of a ribosome as an example of a natural molecular machine, and note that atomically precise final products do not require precise control of all aspects of the chemical reaction.

The authors next refute the "sticky fingers" argument by noting that, while this is a problem in some reactions, it is fallacious to conclude that all reactions have this problem. They return to the idea that because the ribosome suffers from neither problem, they must not be fundamental problems, saying:

"This ubiquitous biological molecular assembler suffers from neither the “fat finger” nor the “sticky finger” problem. If, as Smalley argues, both problems are “fundamental,” then why would they prevent the development of mechanical assemblers and not biological assemblers? If the class of molecular structures known as proteins can be synthesized using positional techniques, then why would we expect there to be no other classes of molecular structures that can be synthesized using positional techniques?"

They go on to cite more experimental and theoretical results indicating that using STM tips and related technologies could be used as a reactive structure for positional control and for interaction with surface-bound molecules.

The authors then question Smalley's figures for the replication time of nanomachines. Instead of Smalley's figure of 1 GHz for the atomic placement frequency, they point out that Nanosystems suggested a frequency of 1 MHz, and that Smalley's frequency would lead to a power density so large that the diamondoid nanomachines would decompose in milliseconds. The authors accuse Smalley of making a straw man argument, and write "in a serious scientific discussion, a discrepancy of three orders of magnitude between what has been proposed in the literature and what is criticized suggests at best an inadequate grasp of the proposal." The authors close by stating that the best way to find out whether molecular assemblers are feasible is through experimental and theoretical work, and that "there are many worthy molecular systems engineering challenges to overcome, but thus far, there has been no credible argument that these devices are infeasible."

Drexler followed up with two open letters to Smalley in April and July 2003. The April letter^[9] begins, "I have written this open letter to correct your public misrepresentation of my work." Drexler accuses Smalley of continually dismissing his work by publicly describing molecular assemblers as requiring what Drexler calls "Smalley fingers", which he states are unlike the systems he had actually proposed which rely on positional control of molecules rather than atoms, in a manner similar to ribosomes and enzymes. He asserts:

"The impossibility of "Smalley fingers" has raised no concern in the research community because these fingers solve no problems and thus appear in no proposals. Your reliance on this straw-man attack might lead a thoughtful observer to suspect that no one has identified a valid criticism of my work. For this I should, perhaps, thank you."

Drexler states the importance of the debate about nanotechnology by comparing it to discussions of spaceflight before Sputnik or to theoretical work on nuclear chemistry before the Manhattan Project. He disputes Smalley's arguments that the fears related to grey goo scenario will hinder continued funding of nanotechnology research, saying instead that the potential for long-term risks makes research even more important. His conclusion states, "your misdirected arguments have needlessly confused public discussion of genuine long-term security concerns."

The July 2003 letter^[10] references a note from Smalley promising to respond, which had yet gone unfulfilled. Drexler mentions inconsistencies in Smalley's previous public statements on atom-by-atom construction, and ends by stating "I would not ordinarily raise an issue so persistently, but the question of what nanotechnology can ultimately achieve is perhaps the most fundamental issue in the field today—it shapes basic objectives and expectations—and your words have been remarkably effective in changing how this issue is perceived."

Exchange of letters in Chemical & Engineering News

A depiction of a putative technomimetic molecular gear set. Smalley questioned whether devices like these could be constructed using an enzyme-like mechanical process, either in an aqueous solution or with some other chemistry, and whether such devices would be operational at all.

The debate was concluded in a point–counterpoint feature that was the 1 December 2003 cover story of Chemical & Engineering News, the newsmagazine of the American Chemical Society.^[11] The feature first reproduced Drexler's April 2003 open letter to Smalley. Smalley's response began by apologizing for any offense his September 2001 article had caused, and stating that Drexler's book Engines of Creation had triggered his own interest in nanotechnology. He goes on to agree that "Smalley fingers" could not work, and then asserts that the same reasons that preclude atomic control of reactions would also preclude the manipulation of larger building blocks, since each molecule would have multiple atoms which would need to be controlled. He then agrees that something like an enzyme or ribosome would be capable of precise chemistry, but asks how the nanorobot would be able to obtain, control, and repair such an enzyme. He then brings up the incompatibility of many reactions with water-based biological systems, noting that:

"Enzymes and ribosomes can only work in water, and therefore cannot build anything that is chemically unstable in water. Biology is wonderous in the vast diversity of what it can build, but it can't make a crystal of silicon, or steel, or copper, or aluminum, or titanium, or virtually any of the key materials on which modern technology is built."

Smalley then asks Drexler what kind of "nonaqueous enzymelike chemistry" he envisions for his molecular assemblers to operate upon, calling this "a vast area of chemistry that has eluded us for centuries."

Drexler's counterresponse began by returning to Feynman's 1959 talk, stating that "although inspired by biology... Feynman's vision of nanotechnology is fundamentally mechanical, not biological," and characterizing the challenges as being that of systems engineering rather than solely chemistry. He refers Smalley to Nanosystems, with its vision of mechanical control of chemical reactions:

"These nanofactories contain no enzymes, no living cells, no swarms of roaming, replicating nanobots.... In machine-phase chemistry, conveyors and positioners (not solvents and thermal motion) bring reactants together.... Further, positional control naturally avoids most side reactions by preventing unwanted encounters between potential reactants. Transition-state theory indicates that, for suitably chosen reactants, positional control will enable synthetic steps at megahertz frequencies with the reliability of digital switching operations in a computer. The supporting analysis for this conclusion appears in "Nanosystems" and has withstood a decade of scientific scrutiny.

Drexler reiterated that these molecular assemblers will require no impossible fingers, and will have the capability of augmenting solution-phase chemistry to produce macroscopic products with precise arrangements of chemical building blocks by using a bottom-up strategy beginning with solution-phase molecular assemblers to bootstrap the construction of more sophisticated molecular assemblers. He concluded by writing:

"However, because it is a systems engineering goal, molecular manufacturing cannot be achieved by a collection of uncoordinated science projects. Like any major engineering goal, it will require the design and analysis of desired systems, and a coordinated effort to develop parts that work together as an integrated whole.... U.S. progress in molecular manufacturing has been impeded by the dangerous illusion that it is infeasible. I hope you will agree that the actual physical principles of molecular manufacturing are sound and quite unlike the various notions, many widespread in the press, that you have correctly rejected. I invite you to join me and others in the call to augment today's nanoscale research with a systems engineering effort aimed at achieving the grand vision articulated by Richard Feynman."

Smalley begins his concluding letter:

"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 goes on to state his belief that most reactions using mechanosynthesis will simply give the wrong product, and that there must be very few reactions and target molecules which would be compatible with such an approach. He states that any robotic assembler arm will need an enzymelike tool at its end, and asserts that such a tool would require a liquid medium, that all known enzymes use water as that medium, and that this limits the range of products to the "meat and bone of biology." He accuses Drexler of creating "a pretend world where atoms go where you want because your computer program directs them to go there."

Lastly, Smalley recounts a recent exprerience of an outreach visit to middle and high school students, saying that nearly half of them thought that self-replicating nanorobots were possible and that most were worried about the results of them spreading across the world, a response that Smalley calls a deeply troubling bedside story, which he did his best to allay. Smalley concludes his letter:

"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."

Critical response

Tone

The debate has been widely criticized for its adversarial tone. David Berube in Nano-Hype: The Truth Behind the Nanotechnology Buzz characterized it as "two people talking over each other... not conducive to reasonable rebuttal," and quoted nanotechnology blogger and journalist Howard Lovy as saying "the tenor of the debate is about personal pride, reputation, and a place in the pantheon."^[6] Zyvex founder James von Ehr remarked that "Eric [Drexler] didn't do himself any favors by getting into a pissing match with a Nobel-prize winner."^[1] An article in The New York Times called the debate "reminiscent of that old Saturday Night Live sketch... [with] Dan Aykroyd and Jane Curtin tossing insults at each other while ostensibly debating a serious political issue," referring to a version of the long-running Weekend Update segment.^[2]

Technical commentary

The debate has received technical criticism as well. Steven A. Edwards in The Nanotech Pioneers notes that the ambiguity of the specifications and even definition of a molecular assembler makes an evaluation of the argument difficult and minimizes its scientific implications. He remarks that "nowhere in it does Nanosystems contain a blueprint for a molecular assembler.... We are told, for instance, that a manipulator arm would involve 4,000,000 atoms, but we are not told which atoms, or how they would be put together." He concludes that "the debate over mechanosynthesis so far is huge to the participants, but mainly an entertaining academic diversion to most nanotechnologists."^[1]

On the other hand, Ray Kurzweil in The Singularity Is Near declares Drexler as the winner of the debate, ^[12] reiterating the view that Smalley's conception of molecular assemblers is a distorted version of Drexler's ideas, calling Smalley's responses "short on specific citations and current research and long on imprecise metaphors," and asserting that "Smalley is ignoring the past decade of research on alternative means of positioning molecular fragments using precisely guided molecular reactions... [which have] been extensively studied." He quotes further experimental results showing manipulation of molecules using scanning probe microscopes, and on enzyme function in nonaqueous solutions, and points out that modern non-biological technology such as airplanes and computers have capabilities that exceed those of natural biological systems. He also chides Smalley for implying that the limitations of contemporary systems are permanent and can never be overcome, noting that "earlier critics also expressed skepticism that either worldwide communication networks or software viruses that would spread across them were feasible.... [but today] we are obtaining far more gain than harm from this latest example of intertwined promise and peril."^[13]

Commentary on public perception of nanotechnology

The debate's focus on the public perception of nanotechnology has also received commentary. Glenn Reynolds stated that "the business community is afraid that advanced nanotechnology just seems too, well, spooky—and worse, that discussions of potentially spooky implications will lead to public fears that might get into the way of bringing products to market."^[14] Lawrence Lessig criticized the scientific establishment, represented by Smalley, characterizing their strategy as being that "if so-called dangerous nanotech can be relegated to summer sci-fi movies and forgotten after Labor Day, then serious work can continue, supported by billion-dollar funding and uninhibited by the idiocy that buries, for example, stem cell research."^[14][15] Kurzweil writes that Smalley's approach to reassuring the public will backfire because it denies both the benefits and risks of molecular nanotechnology.^[12]

References

1. ^ ^{a b c} Edwards, Steven A. (2006). The Nanotech Pioneers: Where Are They Taking Us?. Weinheim: Wiley-VCH. p. 201. 
2. ^ ^{a b} Chang, Kenneth (9 December 2003). "Yes, They Can! No, They Can't: Charges Fly in Nanobot Debate". The New York Times. http://www.nytimes.com/2003/12/09/science/yes-they-can-no-they-can-t-charges-fly-in-nanobot-debate.html. Retrieved 5 July 2011. 
3. ^ ^{a b} Edwards, pp. 15–21, 27.
4. ^ Edwards, pp. 27, 64.
5. ^ Edwards, pp. 132, 184.
6. ^ ^{a b} Berube, David (2006). Nano-Hype: The Truth Behind the Nanotechnology Buzz. Amherst, NY: Prometheus Books. pp. 69–73. http://www.prometheusbooks.com/index.php?main_page=product_info&products_id=1822/. 
7. ^ Smalley, Richard E. (September 2001). "Of Chemistry, Love and Nanobots". Scientific American 285 (3): 76–7. PMID 11524973. http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=F90C4210-C153-4B2F-83A1-28F2012B637. 
8. ^ Drexler, K. Eric; Forrest, David; Freitas, Robert A.; Hall, J. Storrs; Jacobstein, Neil; McKendree, Tom; Merkle, Ralph; Peterson, Christine (2001). "On Physics, Fundamentals, and Nanorobots: A Rebuttal to Smalley’s Assertion that Self-Replicating Mechanical Nanorobots Are Simply Not Possible". Institute for Molecular Manufacturing. http://www.imm.org/SciAmDebate2/smalley.php. Retrieved 9 May 2010. 
9. ^ Drexler, Eric (April 2003). "An Open Letter on Assemblers". Foresight Institute. http://www.foresight.org/nano/Letter.html. Retrieved 5 July 2011. 
10. ^ Drexler, Eric (2 July 2003). "Toward closure". Foresight Institute. http://www.foresight.org/nano/Letter2.html. Retrieved 5 July 2011. 
11. ^ "Nanotechnology: Drexler and Smalley make the case for and against 'molecular assemblers'". Chemical & Engineering News (American Chemical Society) 81 (48): 37–42. 1 December 2003. http://pubs.acs.org/cen/coverstory/8148/8148counterpoint.html. Retrieved 9 May 2010. 
12. ^ ^{a b} Kurzweil, Ray (2005). The Singularity Is Near: When Humans Transcend Biology. New York: Penguin Books. pp. 236–241. ISBN 0143037889. 
13. ^ http://www.kurzweilai.net/the-drexler-smalley-debate-on-molecular-assembly
14. ^ ^{a b} Berube, p. 58.
15. ^ Lessig, Lawrence (July 2004). "Stamping Out Good Science". http://wired.com/wired/archive/12.07/view.html?pg=5. Retrieved 12 July 2011.