Foresight Debate with Scientific American

Foresight Institute vs Scientific American
Debate on nanotechnology: Round 1 from Merkle

Overview of the Debate

Round 1 | Round 2 | Round 3 | Round 4 | Epilogue

Round 1 -- Part 1 | Letters | Part 2

A response to Scientific American's news story Trends in Nanotechnology

by Ralph C. Merkle, Xerox PARC, Palo Alto, CA.

Scientific American staff writer Gary Stix wrote Trends in nanotechnology: waiting for breakthroughs (Scientific American, April 1996, pages 94-99). The text of this news story appears below, with detailed commentary and corrections.

Brief overview

Scientific American has evidently concluded that developments in molecular nanotechnology have become too big to ignore. In consequence, they published a six page story on "nanotechnology."

The story conflates two very different definitions of "nanotechnology." The consequences of this lead to various erroneous claims and a great deal of confusion.

Several lines of evidence and a great deal of published work support the feasibility of molecular nanotechnology. Three mentioned in the story are the statements of Feynman, Nanosystems, and a significant and growing body of computational studies. The Scientific American story attempted to neutralize all three using a variety of attacks that carefully avoided the technical issues. The absence of any effective technical criticism in the story is quite telling.

Scientific American, by denigrating molecular modeling and computational work, is implicitly advocating a purely experimental approach to the development of molecular nanotechnology. In sharp contrast, we advocate a mixed approach which includes the aggressive use of molecular modeling as an integral component of a long range strategy to develop molecular nanotechnology.

The story devoted over a column to the only published argument against molecular nanotechnology that they found worth citing, a book review (not a peer-reviewed journal article) by David Jones (a chemist and Nature columnist). Jones' criticisms were refuted last year shortly after they appeared, a refutation that Scientific American conveniently omitted. The story then devoted two sentences to the misleading claim that the only response was to read Nanosystems. As Jones' criticisms were based on gross ignorance of the field -- an ignorance that was made clear in our response -- it is difficult to understand Scientific American's uncritical embrace of his views.

There are repeated ad hominem attacks against Eric Drexler (a major researcher in the field). Many researchers think that nanotechnology is feasible and should be developed; ad hominem attacks against one researcher say more about the agenda of Scientific American than about the technical issues.

Many of the readers of the Scientific American story will never be made aware of the errors and omissions it contains. If it had been published on the web, and if backlinks and filtering were implemented (various groups are working on this), then anyone who read the original story would also have rapid and easy access to the critiques of that story. The reader is left to imagine the consequences if debates and discussions of public and other issues took place in a medium where inaccurate and misleading information was rapidly squelched.

What you can do

In the meantime (before we have backlinks) if after reading this page you think the Scientific American story was unduly biased we encourage you to pass along the URL of this page, , to friends, relevant newsgroups, etc. and encourage discussions about it. Some relevant questions that could be discussed are at the end of this page.

To stay informed about developments in nanotechnology join the Foresight Institute (email: and get the Foresight Update.

Our offer

To encourage an open dialogue, we publicly offer to Scientific American the opportunity to rebut our statements. We will include a link to a page provided by Scientific American. If that should be inconvenient for them we will offer to host their rebuttal at the Foresight web site.

The link to Scientific American's rebuttal is:

Scientific American earlier requested that the Foresight Institute remove the web page you are now reading from the Foresight server.

For an overview of the debate, see

The response in brief

This section gives the highlights of the more detailed critique which follows.

The definition of "nanotechnology"

The first and perhaps most serious error in the article is to adopt a definition of "nanotechnology" that is grossly inappropriate. The article says:

"Nanotechnology is the manufacture of materials and structures with dimensions that measure up to 100 nanometers (billionths of a meter)."

While this definition would be quite reasonable in an article on high resolution lithography, its use in an article which is centered on molecular manufacturing as discussed both in Nanosystems and at the Fourth Foresight Conference on Molecular Nanotechnology is not only inappropriate but extremely misleading.

An appropriate definition for this article would be: a manufacturing technology able to inexpensively fabricate, with molecular precision, most structures consistent with physical law.

A consequence of the appropriate definition is that nanotechnology is today theoretical. We do not yet have the defined ability, and it is unlikely that we will develop it in the near term (i.e., the next 5 to 10 years).

As the distinction between nanoscale technologies (i.e., technologies in which some critical dimension is less than a micron) and nanotechnology was made repeatedly at the Fourth Foresight Conference on Molecular Nanotechnology, and as the author of the story attended this conference, it is hard to avoid the conclusion that either (a) the writer failed to understand a very basic point or (b) he deliberately selected an inappropriate definition.

The selection of an inappropriate definition leads, as might be expected, to a series of inappropriate and erroneous conclusions. Among these was the confusion of today's lithographic technology with nanotechnology. As today's lithographic technology is both unable to achieve the objectives of nanotechnology and is generally viewed as unlikely ever to achieve these objectives, its inclusion creates a great deal of confusion. Arguing that molecular manufacturing is likely to be uneconomical or infeasible because evolutionary developments in today's lithographic technology will be unable to deliver the capabilities that molecular manufacturing promises is to create a most glorious muddle. (As an aside, there is also a turf-war over the term "nanotechnology." That is, "nanotechnology" is a term which has an aura of excitement and great promise. Much of this aura was created by Drexler's adoption of the term and its association with molecular manufacturing. As a consequence, many researchers wish to adopt a definition of "nanotechnology" which includes their own work. An unfortunate consequence of this is that the unqualified term "nanotechnology" has come to mean very little. In the present critique, "nanotechnology" is defined as a synonym for "molecular manufacturing." In contexts where it might be unclear which usage is appropriate, the term "molecular nanotechnology" or "molecular manufacturing" can be used. In any event, it is essential to establish an appropriate definition if a discussion of "nanotechnology" is to make any sense. The usage in the story is variable.)


One of the arguments in favor of nanotechnology is that Richard Feynman, in a remarkable talk given in 1959, said that "The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are too big."

Even more strongly, he said "The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed---a development which I think cannot be avoided."

Feynman's classic talk is now available on the web and is well worth reading.

Scientific American faces a significant challenge in dealing with Feynman's talk, as taken at face value it supports the feasibility of nanotechnology. The response was to misinterpret a different paper by Feynman as being applicable to research in nanotechnology.

In "Cargo Cult Science" Feynman said: "But even today I meet lots of people who sooner or later get me into a conversation about UFO's, or astrology, or some form of mysticism, expanded consciousness, new types of awareness, ESP, and so forth. And I've concluded that it's not a scientific world."

Pretending that Feynman's essay opposing ESP and mysticism applies to theoretical and computational work in nanotechnology completely avoids the awkward need to comment directly on what Feynman said in his talk, while at the same time creating a spurious notion that Feynman did not support the development of nanotechnology. Nothing could be further from the truth.

Evidently, Carl Feynman (the son of Richard Feynman) agrees. In a post to sci.nanotech he said: "I was dismayed to read in your April 1996 issue ("Waiting for Breakthroughs") an extended quotation from Richard Feynman's essay "Cargo Cult Science" used as a critique of nanotechnology. I am sure he would have found such misuse of his idea quite unreasonable. I should know, because I talked with him at length about the prospects of nanotechnology."


Scientific American faces a difficult problem with Nanosystems. Nanosystems: Molecular Machinery, Manufacturing and Computation, is an extension and enlargement of Drexler's MIT Ph.D. thesis. Published by Wiley in 1992, it provides a dense and technical analysis of the issues involved in nanotechnology. Drexler negotiated with Wiley to get a purchase price low enough that students could afford it. Over 10,000 copies are now in print. No technical errors of significance have been found, despite several years of exposure to the entire scientific and technical community, including both critics and supporters.

As the reader might appreciate, if there were any serious technical objections to Nanosystems, Scientific American would have been more than happy to point them out. The absence of any technical criticisms of Nanosystems is glaring.

Computational modeling results

Computational chemists generally seem able to absorb the idea of nanotechnology quite easily. One reason for this is that they have the training and the tools to evaluate proposals for molecular machines. Give them a PDB file and tell them that it describes a molecular structure that's supposed to do something useful, and they'll happily model it. Sometimes they come back and tell you that it works and it's a great design. Sometimes they torture it in horrible ways and it behaves in some strange and unexpected manner.... at which point, it's back to the drawing board.

To select a specific example, there has been significant modeling work done on mechanosynthetic reactions that should be useful in the controlled synthesis of diamondoid structures. In particular, the ability to selectively remove a hydrogen from a hydrogenated diamond surface appears to be a fundamental reaction in the controlled synthesis of diamond and related structures.

The analysis of the hydrogen abstraction tool has involved many people, including: Donald W. Brenner, Richard J. Colton, K. Eric Drexler, William A Goddard, III, J. A. Harrison, Jason K. Perry, Ralph C. Merkle, Charles B. Musgrave, O. A. Shenderova, Susan B. Sinnott, and Carter T. White. The institutions involved include the Materials and Process Simulation Center at Caltech; the Department of Materials Science and Engineering, North Carolina State University; the Institute for Molecular Manufacturing; the Department of Chemicals and Materials Engineering, University of Kentucky; the Chemistry Department, United States Naval Academy; the Naval Research Laboratories, Surface Chemistry Branch; and the Xerox Palo Alto Research Center.

The response to this work by the story is straightforward: it is labeled "cargo cult science." No technical argument is advanced to explain why the results of computational modeling and computational chemistry should be ignored.

David Jones' book review

The story presents the book review by David Jones as the only published argument against the feasibility of nanotechnology. Jones cited no references, and even a casual reading of his criticisms clearly shows that he is almost completely ignorant of the field which he claims to be criticizing.

The story quotes Jones as saying: "Single atoms of more structurally useful elements [more useful than Helium at 4 kelvins] at or near room temperature, are amazingly mobile and reactive. They will combine instantly with ambient air, water, each other, the fluid supporting the assemblers, or the assemblers themselves." Earlier in the paragraph Jones said "...the nanotechnologists do not seem to realize the chemical obstacles in their path."

It is evident from reading Jones' criticism that he is literally unaware of the computational and molecular modeling work that has been done. In particular, the molecular dynamics simulation of the hydrogen abstraction tool provided a vivid and very clear illustration of why such reactive species as radicals, carbenes and the like would not react with "ambient air, water, each other, the fluid supporting the assemblers, or the assemblers themselves." The reactions take place in vacuum -- there is no ambient fluid with which to react -- and the reactive species are positionally controlled -- they cannot react with the assembler because they are positioned away from the structural components of the assembler. In a similar way, a hot soldering iron does not react with the skin of the operator provided it is positioned so that it does not come into contact with the skin.

While Jones' excuse is ignorance, the writer of the news story has no such excuse. He attended the conference where the video of the hydrogen abstraction tool was presented; and sat through more than one lecture discussing mechanosynthesis -- the reactions that would be involved, the molecular tools that would be used, and the environment in which those tools would operate. Again, either the writer (a) is grossly ignorant of the basics or (b) deliberately chose to omit inconvenient facts.

Detailed response

The following is a point by point response to the story. We have added some relevant links to Scientific American's text -- these are our additions. The original article, not being on the web, had no links.

As this detailed response is rather long the reader might wish to scan through it for points of particular interest (or perhaps skip directly to the conclusion). If there are any criticisms in the story that the reader was particularly interested in, it would be worthwhile to find the particular statement and read the critique of that statement presented here. It is difficult to convey with a few short quotes the rather pervasive bias which emerges when the article is viewed as a whole.

"'That's the messiah,' confides Edward M. Reifman, D.D.S. The Encino, Calif., dentist has paid hundreds of dollars to attend a conference to hear about robotic machines with working parts as small as protein molecules. Reifman nods toward K. Eric Drexler, the avatar of nanotechnology."

In response, Reifman said "...I was quite upset to be quoted entirely out of context regarding Eric Drexler being 'the messiah'. That comment was mentioned in jest when I talked briefly with the writer..."

The introduction is obviously designed to distract attention from the basic technical issues. It establishes that the story is not about nanotechnology so much as it is about Drexler.

Don't get me wrong. I like Drexler, and think he's done some remarkable work. But that's not the point. Either nanotechnology is feasible within the presently understood framework of physical law, or it is not. This question exists entirely independent of Drexler. If nanotechnology is feasible, we've got a lot more to be concerned about than the conference registration fee or whether Reifman called Drexler the messiah. If it's not, we still don't care about these things. Scientific American is attempting to distract us from the core issues.

"Drexler has just finished explaining to a strange mix of scientists, entrepreneurs and his own acolytes that nanotech may arrive in one to three decades. The world, in his view, has not fully grasped the implications of molecular machines that will radically transform the way material goods are produced."

The use of biased words such as "strange" or "acolytes" is pervasive. It's an easy way to put a negative spin on a story in the absence of anything technically substantive. Some biased usages are noted in the following text, but their sheer number makes it awkward to comment on all of them.

This story is itself evidence that at least some parts of the world have "... not fully grasped the implications..." of nanotechnology. This is certainly true for Scientific American.

"Nanotechnology is the manufacture of materials and structures with dimensions that measure up to 100 nanometers (billionths of a meter)."

This is a more subtle bit of misdirection. There are now a myriad different definitions of the word "nanotechnology." While this definition would be quite unobjectionable in a story on (say) ultra high resolution lithographic methods, in the present story -- which is focused almost exclusively on molecular manufacturing -- its use is inappropriate and leads to confusion. For purposes both of the story and of this review, an appropriate definition of "nanotechnology" is: a manufacturing technology able to inexpensively fabricate most structures consistent with natural law, and to do so with molecular precision. This is radically different from "structures with dimensions that measure up to 100 nanometers."

As the writer of the story attended the Fourth Foresight Conference on Molecular Nanotechnology, where the basic distinction between structures on the scale of nanometers and structures that are molecular in their precision was repeatedly emphasized, it is difficult to understand how he decided to include such a misleading definition. Either he was unaware of the appropriate definition or he chose to use a definition at odds with the established usage in the field upon which he was reporting.

By way of analogy, suppose a story on "chemistry" defined a "molecule" as "an aggregate of atoms with dimensions less than 100 nanometers." The confusion wrought by this initial blunder would be remarkably difficult to repair.

It is important to remember that there are three major objectives to nanotechnology: (1) Low cost. The ability to very expensively make a few very small very precise structures will not, per se, have a major impact. (2) Molecular precision. While certain limits are imposed by such factors as thermal noise and radiation damage, error rates that are remarkably low by current standards should be feasible. Appropriately designed structures with tens of billions of atoms should be stable (in the sense that no single atom in the structure would be out of place, except for the limited excursions that thermal noise creates) for many decades. (3) Able to make most structures consistent with physical law. While there will no doubt be some structures that simply can't be synthesized, current manufacturing methods are able to make only a remarkably small subset of what's feasible.

Today's computational modeling in nanotechnology typically focuses on the class of stiff diamondoid structures -- structures made primarily of hydrogen and first row and second row elements in the upper right hand region of the periodic table. While this is a significant reduction in scope from structures involving the entire periodic table, it makes the problems involved in the design and analysis both of the structures and of the synthetic pathways for making the structures more tractable; in addition, the diamondoid structures appear to include many structures of potentially major economic interest. This includes (among others): molecular semiconductor electronic devices, very high strength very light materials, many molecular machines and, of course, many types of assemblers.

This review uses the term "nanotechnology" as a synonym for molecular manufacturing. The usage by Scientific American is variable. In other contexts, where the appropriate definition might not be obvious, the more specific terms "molecular nanotechnology" or "molecular manufacturing" can be used.

"Its definition applies to a range of disciplines, from conventional synthetic chemistry to techniques that manipulate individual atoms with tiny probe elements. In the vision promulgated by Drexler, current nano-scale fabrication methods could eventually evolve into techniques for making molecular robots or shrunken versions of 19th century mills."

Properly speaking, none of the items mentioned is nanotechnology. The synthetic methods used in chemistry today can economically make many structures, but certainly cannot make (for example) molecular computers or low-cost shatterproof diamond sculpted with molecular precision. Scanning probe methods are even more limited in the range of structures they can currently make. However, further developments in both chemistry and proximal probe methods could be important or crucial in the development of nanotechnology. Some of the research in these areas can reasonably be described as "leading to nanotechnology."

"Current nano-scale fabrication methods" is a phrase that typically refers to today's high resolution lithographic manufacturing methods. There is fairly wide agreement that these methods are neither able to make structures of molecular precision, nor are they likely to do so in the future. Something new is needed. Drexler, among others, has repeatedly emphasized this point.

We should remember: nanotechnology is today a theoretical field. We want it but we haven't got it.

"In the course of a few hours, manufacturing systems based on Drexler's nanotechnology could produce anything from a rocket ship to minute disease-fighting submarines that roam the bloodstream. And, like biological cells, the robots that populate a nanofactory could even make copies of themselves. Finished goods in this new era could be had for little more than the cost of their design and of a raw material - such as air, beet sugar or an inexpensive hydrocarbon feedstock.

While manufacturing costs will be low, other factors will likely increase the purchase price of "finished goods." As an example: the manufacturing cost of software is low, but the purchase price varies over a wide range.

The Drexlerian future posits fundamental social changes: nanotechnology could alleviate world hunger, clean the environment, cure cancer, guarantee biblical life spans or concoct superweapons of untold horror."

Eric Drexler testified at the senate hearings on "New Technologies for a Sustainable World" held by Al Gore shortly before Gore became a candidate for Vice President. The transcript of the statements by both Drexler and Gore is available on the web, as is Drexler's prepared statement.

"Scientific visionaries have turned their attention from outer to inner space, as the allure has faded from dreams of colonizing another planet and traveling to other galaxies. Computer mavens and molecular biologists have replaced rocket scientists as the heroes that will help transcend the limits imposed by economics and mortality. 'Whether or not Drexler's utopian ideas are correct, they come at a time when a variety of fields have reached stasis,' says Seth Lloyd, a professor and specialist in quantum computation at the Massachusetts Institute of Technology. 'You don't come across many fields that have as bold a project as the space program was.'"

The National Space Society might object to the claim that the allure of space development and settlement has faded. Note also that we are going to "transcend the limits imposed by economics and mortality." This is a hyperbolic exaggeration by the writer. The ability to manufacture products at a lower cost does not "transcend the limits imposed by economics"; nor do improvements in medical technology -- even the rather remarkable improvements that nanotechnology is likely to make feasible -- render us immortal. Today we live in a world of greater material abundance than in centuries past, and we live longer and healthier lives. In the future this trend is likely to continue and nanotechnology is likely to play a major role.

A RAND study, The Potential of Nanotechnology for Molecular Manufacturing, concludes that further research is warranted.

"Submicroscopic machines that can save or destroy the world appeal to anyone from a retired navy admiral to a technophile dentist to eager students - all of whom attended the nanotechnology conference. Reifman, the dentist, is a disciple who carries the message of nanotechnology to patients waiting nervously in his dental chair. He tells them of robots as small as a microbe that will painlessly refurbish a tooth or build a new one from scratch. 'You'll be able to be a chocoholic without guilt,' he predicts."

Referring to Admiral David Jeremiah, USN (Ret.), former Vice Chairman of the Joint Chiefs of Staff for Generals Powell and Shalikashvili as "...a retired navy admiral..." is somewhat like referring to Colin Powell as "... a retired general." Jeremiah was more than an attendee: his presentation on Nanotechnology and Global Security was extremely impressive.

Scientific American conveniently omitted researchers from the above list. The interested reader is invited to peruse the conference web page and examine the list of attendees. The affiliations of the attendees are shown, so it's easy to get a feel for which institutions are involved.

For the record, the sponsors or co-sponsors of the Foresight series of conferences on molecular nanotechnology have included (in no particular order): Apple Computer; Beckman Instruments; Biosym Molecular Simulation; The Materials & Process Simulation Center, Caltech; The Laboratory for Molecular Robotics, USC; The Institute for Molecular Manufacturing; JEOL; Loral Systems Manufacturing Co.; Molecular Manufacturing Enterprises, Incorporated; Digital Instruments; Fenwick & West; Niehaus Ryan Haller; Stanford Univeristy Dept. of Materials Science & Engineering; Molecular Graphics Society (USA); Global Business Network; Weil, Gotshal & Manges; Autodesk; Mitsubishi Research Institute; Nomura Research Institute; Xerox Palo Alto Research Center; The Univeristy of Tokyo, RCast (Research Center for Advanced Science & Technology); and the Micromachine Society of Japan.

"Drexler has purveyed his nanovisions for almost two decades. In recent years, however, his intricately constructed pictures of the next century and beyond have begun to be overtaken by real investigations into nanotechnology. What inspires actual researchers at the nanoscale is infinitely more mundane than molecular robots - but also more pragmatic. Nanotechnology, in this guise, may not contain the ready promise of virtually limitless global abundance and human mastery of the material world. But it may move beyond mere speculation to produce more powerful computers, to design new drugs or simply to take more precise measurements."

Drexler's first published paper on nanotechnology, which appeared in the Proceedings of the National Academy of Sciences USA in 1981, is now available on the web.

Here we see the erroneous definition of "nanotechnology" coming into action. Making more precise measurements, making better drugs, making more powerful computers by improving current lithographic methods: these are all laudable accomplishments. But are they nanotechnology? Do they give us the ability to inexpensively manufacture diamondoid structures? No. Are they "real nanotechnology?" Not really.

Terminological confusion has led to misclassification of existing and near term research and development. We do not have nanotechnology today, and are unlikely to achieve it in the near future. It is not going to fall out of the sky into our lap, it will not be developed by a serendipitous experimental accident. It's going to take quite a bit of hard work, and it's going to take planning on a time horizon that's long by present standards.

The heartwarming story of the young scientist who accidentally leaves the Bunsen burner on in his laboratory when he goes to lunch, and comes back to find that he's accidentally made a new, unique, and remarkably valuable material is well known. The story of the same young scientist coming back to find he has accidentally made a Saturn V booster is -- well, let us say that it would be an unusual occurrence. Some things require planning, organization, and the cooperative efforts of many people working towards a common objective.

By this time we hope the reader is adept at noting and ignoring the continuous use of biased words and slanted adjectives: "purveyed," "real investigations," "move beyond mere speculation," "actual researchers," etc. etc. etc. As might be appreciated, a complete analysis of the biased terminology in the story would be extremely tedious. Again, sheer volume forces us to ignore most of the lesser examples of evident bias.

"Researchers can now manipulate atoms or molecules with microscopic probe elements, marshal the 20 basic amino acids to form new proteins not found in nature, or help organic molecules spontaneously assemble themselves into ordered patterns on a metal surface. This work certainly presents the prospect of providing new tools for the engineering community. Ironically, it also demonstrates the difficulties of using individual atoms or molecules as building blocks, given the presence of a host of physical forces that may displace them. In fact, some of Drexler's sharpest critics are engineers and scientists who spend their time toiling in the nanorealm."

The "host of physical forces" is too vague to comment on -- later in this review we'll see some more specific "problems." We'll also defer comments on the unspecified "critics" until some specific examples are presented.

"Drexler's fanciful scenarios, nonetheless, have come to represent nanotechnology for many aesthetes of science and technology. The phenomenon is not uncommon in the sociology of science. The public image of a certain field or concept, shaped by futurists, journalists, and science-fiction scribes, contrasts with the reality of the often plodding and erratic path that investigators follow in the trenches of day-to-day laboratory research and experimentation."

Yet another example of biased terminology. Drexler's scenarios are "fanciful." The terms "infeasible" and "contrary to physical law" have well defined meanings. As the question of interest is the feasibility of nanotechnology, the more hard edged statements that the proposals are feasible or infeasible should be used. This would, of course, force a more rigorous (and useful) discussion of the issues. "Fanciful" is a term which means nothing, other than the writer can't find any substantive grounds for criticism.

Next, we find we're "aesthetes." Having slipped in the wrong definition of nanotechnology, Scientific American is now explaining to us that we're not working toward nanotechnology. Then they tell us that journalists create the public image of a field and often get it wrong -- much to the discomfiture of the practitioners -- I heartily concur!


Drexler, the 40-year-old guru of the nanoists, speaks with an exaggerated professorial tone that is faintly reminiscent of the pedantic 1960s cartoon character Mr. Peabody. Over a buffet lunch in early November at the biennial conference sponsored by his Foresight Institute - an organization he set up in Palo Alto, Calif., to help pave the way for nanotechnology - Drexler pours milk into his ice tea. He explains that the milk binds the tannins that may lead to throat cancer."

"Mr. Peabody"????

(A picture of Mr. Peabody "and his boy, Sherman" is available on the web).

The story has now abandoned all pretense of discussing technology. We're back to Drexler. Drexler this, Drexler that, Drexler the other. How he speaks, how he takes his tea. Insinuations about his character. Scientific American has adopted People magazine as a role model.

"During the meal, he complains about the shortsightedness of the scientific and technological research establishment in the U.S., which has largely ignored his brand of nanotechnology. Drexler is familiar with dreams that don't come true. In the 1970s he volunteered to work with space colonization advocate Gerard K. O'Neill to plan various scenarios for extraterrestrial living; he even wrote a paper on mining asteroids in his freshman year at M.I.T. Drexler and other nanoists view their technology as a means to rejuvenate a moribund space program that has no immediate plans to create retirement communities on Mars. Nanotechnology would allow the manufacture of strong, light materials that would go into space transport vehicles."

Scientific American has just published a story based largely on ad hominem attacks on Drexler, using systematically biased language, which constantly denigrates a technological objective that is widely thought to be feasible. This would appear to provide some evidence in support of Drexler's statement. We'll have more to say on planning horizons later.

The non-statement "Drexler is familiar with dreams that don't come true" is another example of the pervasive bias in the story.

Regarding the rejuvenation of a moribund space program: The National Space Society has a position paper on molecular manufacturing, and the Numerical Aerodynamic Simulation program at NASA Ames is pursuing an initiative to develop a world class capability in computational molecular nanotechnology.

It's also amusing to note the following quote from Willy Ley: "The idea of a rocket-accelerated airplane bomb must have been "in the air" in those days, for it had occurred to me too. In early fall 1940 Schaefer and I set out to test the idea on a few examples on paper. The result was an article entitled "How about Penetration Bombs?" which made the rounds of various technical and semitechnical magazines without evoking the response we wanted. The editor of The Scientific American wrote curtly that it was "too far-fetched to be considered."" from Rockets, Missiles, and Space Travel, Revised Edition, by Willy Ley, New York Viking Press, 1957, page 172, footnote 3.

"The basic ideas behind small, self-replicating machines did not originate with Drexler. The renowned mathematician John Von Neumann, a father of the field of artificial life, ruminated about a machine that could make copies of itself. And in a much cited 1959 speech, Nobelist Richard P. Feynman talked about the ability to build things by placing each atom in a desired place. The self-assured Feynman used to toy playfully with the notion of making things small, musing on the theme with the humor of a Brooklyn-accented, Borscht Belt comic. Feynman even proposed a competition between high schools: "The Los Angeles high school could send a pin to the Venice high school on which it says [on the pinhead], 'How's this?' They get the pin back, and in the dot of the 'i' it says, 'Not so hot.'" Drexler, unlike the puckish Feynman, approaches his passion with a dour earnestness. The message: Nanotechnology is coming, we must prepare now."

It's quite entertaining to watch the mental gymnastics of those who think nanotechnology is infeasible but who simultaneously respect Feynman, who said: "The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are too big."

A similar observation holds for von Neumann. Somehow it is necessary to believe that the self-replicating systems proposed for nanotechnology are impossible, while at the same time believing both that von Neumann's proposals are entirely reasonable and that living systems are exempt from the ban on self-replication that applies to molecular manufacturing systems (perhaps living systems have "vital force").

A brief introduction to some of the concepts of self-replication relevant to nanotechnology -- along with links to further information -- is available on the web.

If Feynman is right that we can arrange atoms and von Neumann is right that we can design self-replicating machines then the basic requirements for nanotechnology are satisfied: we should be able to make self-replicating machines that can arrange atoms. The rest of the discussion should not be about whether this capability is feasible, but rather about the best method of achieving it. Drexler's dourness or lack thereof is irrelevant.

"Drexler, though, can rightly claim credit for bringing wide exposure to an enticing idea. In his 1986 work Engines of Creation, Drexler, like Jules Verne and H.G. Wells, succeeded in depicting a world altered forever by the advent of a new technology. In Engines, Drexler introduced the concept of an "assembler," a robotic device with dimensions of a tenth of a micron (a millionth of a meter) or less, that can pick up and position a reactive molecule so that it interacts with another molecule, as though it were a Lego block snapping into place. He has also described mills equipped with belts and rollers to process molecules. A battery of nanocomputers - perhaps collections of molecular rods that change position to represent distinct logic states - could broadcast instructions to trillions of assemblers at once. The computers could also instruct assemblers to self-replicate. In his book, Drexler set down a detailed description of how society would be transformed by nanotechnology. Engines presents a picture of a Manichaean balance of utopian/dystopian scenarios."

Damning with faint praise. Also note that "...Drexler set down a detailed description...." The implication here is that "a detailed" prediction of the future is impossible, Drexler made a detailed prediction, therefore Drexler is attempting to do the impossible. Both Engines and Unbounding the Future present several plausible scenarios. Note that considering multiple plausible scenarios about what might happen in the future is very different from giving a single detailed description about what will happen. Scenario planning is an established method of guiding decision making in the face of an uncertain future, and Drexler quite explicitly adopted this methodology. Given that nanotechnology is feasible -- a technical question that Scientific American seems intent on avoiding -- then scenario planning is a useful tool for gaining some insight into the range of issues that might arise and some of the possible options.

"The Good and the Goo"

Combining nanocomputers with molecular machines would allow almost anything that can be designed to be made from a variety of inexpensive raw materials, perhaps even dirt, sunlight and air. Assemblers could string together atoms and molecules so that most goods could be made from diamond or another hard material, giving the most ordinary objects a remarkable combination of strength and lightness."

An unbiased paragraph describing some things that nanotechnology should make feasible.

"The cost per kilogram of goods produced by nanomanufacturing would equal the price of potatoes. The resulting nanoworld, in which everyone is wealthy because of the drastic reduction in the cost of goods, would flummox economists, those scientists of scarcity. A jumbo airliner could be purchased for the current price of an automobile. A homeowner would pour acetone into a household manufacturing system, similar in appearance to a microwave oven. An hour later, out would come a computer, a television set or a compact-disc player. A home food-growing machine could rapidly culture cells from a cow to create a steak, a godsend to the animal-rights movement."

The potential payoff from the development of nanotechnology is indeed quite large.

"Minuscule submarinelike robots made by assemblers would extend life or reverse aging by killing microbes, by undoing tissue damage from heart disease or by reversing DNA mutations that cause cancer; the nanomachines would help revive bodies preserved in cryogenic storage by repairing frostbite damage to the brain and other organs. (Drexler, in fact, plans to sign up to have his body frozen after death.) Engines of Creation even speculates about nanotechnology providing the basis for telepathy or for radically changing one's body."

There is experimental work today involving the interpretation of electroencephalograms to control equipment. There is also work aimed at alleviating certain handicaps by connecting an electronic control system to the nerves controlling a muscle if the person's own nervous system is unable to stimulate those nerves; and work aimed at directly stimulating the auditory nerves of a deaf person. Future extensions of this type of research can be envisioned. Engines, in a section explicitly aimed at disentangling what is likely to be feasible from what is not, discusses the feasibility of directly connecting transducers to nerves, making possible what might be viewed as a limited type of "telepathy." (In some sense, ordinary speech is a type of "telepathy," as it permits the thoughts in one mind to be transferred to another mind).

For further information about cryonics, see

"On the dark side, assemblers would streamline the production of superweapons, allowing rapid fabrication of a tank or a surface-to-air missile. And then there is the "gray goo" problem - the possibility that nanodevices might be designed to replicate uncontrollably, like malignant tumor cells, and reduce everything to dust within days."

"Military applications of molecular manufacturing have even greater potential than nuclear weapons to radically change the balance of power." --- Admiral David E. Jeremiah, USN (Ret), former Vice Chairman of the Joint Chiefs of Staff.

"Ruminations in Engines of Creation about gray goo and extended life spans provoked guffaws from many scientists. In 1992 Drexler responded to the criticism with Nanosystems, which attempts to give his tiny machines a grounding in the underlying essentials of physics, chemistry and biology. Nanosystems heavy technical emphasis was a plea from Drexler for respectability. The subtext: I am not a flake. But the book remains largely an object of curiosity to the scientific community. It has been hard for many scientists, engineers and technicians to take seriously a section at the end that shows components of assemblers similar to large-scale mechanical devices. For example, a six-legged platform imitates the ones used to tilt flight simulators into different attitudes of yaw, pitch and roll. Its size: only 100 nanometers across, no bigger than a virus. "This is not science - it's show business," says Julius Rebek, a leading researcher in the chemistry of self-assembly at M.I.T."

We're now back to Drexler this, Drexler that, and biased adjectives. Drexler makes a "plea," has "ruminations," etc. etc. etc. The basic technical issues are once again pushed aside to focus on the irrelevant.

Scientific American faces a difficult problem with Nanosystems. Nanosystems: Molecular Machinery, Manufacturing and Computation is an extension and enlargement of Drexler's MIT Ph.D. thesis. Published by Wiley in 1992, it provides a dense and technical analysis of the issues involved in nanotechnology. Drexler negotiated with Wiley to get a purchase price low enough that students could afford it. Over 10,000 copies are now in print. No technical errors of significance have been found, despite several years of exposure to the entire scientific and technical community, including both critics and supporters.

As the reader might appreciate, if there were any serious technical objections to Nanosystems Scientific American would have been more than happy to point them out. Instead, we are treated to a series of non-statements about Nanosystems: it "attempts", it is a "curiosity," it is "hard" to take "seriously." Readers are invited to look at a copy and see for themselves.

The non-statement "This is not science - it's show business" raises an issue that is usually overlooked: people often ask if a particular piece of experimental work "brings us closer to nanotechnology." The answer is: it depends on what you think nanotechnology is going to look like. If, as the Rebek quote suggests, he thinks that nanotechnology will not use positional control then logically he should conclude that current experimental research that demonstrates the basic capabilities of positional control is not moving us closer to nanotechnology. He would presumably argue that the recent work at IBM Zurich which demonstrated an ability to position individual molecules at room temperature -- while perhaps being very nice science -- is in fact irrelevant to the goal of developing nanotechnology. This, of course, contradicts the claim made earlier in the story that experimental research with scanning probe systems is "real." Evidently, the "reality" of a particular line of research depends on what you think nanotechnology is going to look like.

The denigration of positional control (which sometimes appears in the self-assembly research community) is unjustified. We note that positional control is used extensively at the macroscopic scale. Indeed, Homo sapiens is viewed as the tool using species -- without the ability to hold tools and apply them in a positionally controlled fashion to workpieces ranging from flint knives to computer keyboards we would no doubt still be shivering in a cave. Recent experimental work has indeed demonstrated that positional control can be applied at the molecular level, and theoretical work has long supported exactly the same conclusion. Recent theoretical work on the use of a positionally controlled ethynyl radical to selectively abstract chosen hydrogen atoms from the diamond (111) surface provides the most recent and specific support for the idea that positionally controlled molecular tools can provide a mechanism for synthesizing specific complex diamondoid structures.

"Despite his alienation from mainstream science and engineering, Drexler continues to amass devotees, particularly among computer scientists enticed by the prospect of making tangible anything they can specify with a set of three-dimensional coordinates. "Nanotechnology will reduce any manufacturing problem, from constructing a vaccine that cures the common cold to fabricating a starship from the elements contained in sea water, to what is essentially a software problem," writes physicist and science-fiction author John G. Cramer."

There is growing interest in nanotechnology from the mainstream, though the significance of "alienation" from the mainstream is debatable. When I submitted the first paper describing a public key system in 1975, it was rejected by the referee with the note that "I am sorry to have to inform you that the paper is not in the main stream of cryptography thinking...." That was, of course, the point of the paper. Public key cryptography introduced a new paradigm -- a point that the referee was too dull to grasp.

Computer scientists do indeed seem to grasp nanotechnology quite easily. Bright folk.

"Silicon Valley, that mecca for aficionados of things small, hosts a disproportionate number of nanoists. Apple Computer has helped sponsor the Foresight Institute's conferences - the most recent one last November drew more than 300 people, double the attendance of the 1993 gathering. A researcher at the Xerox Palo Alto Research Center, Ralph C. Merkle, who made a name for himself in computer cryptography, spends his time creating models of molecular machine components. (Merkle has already signed up to have his head frozen.)"

Silicon Valley does indeed have a relatively high proportion of highly trained, technically competent people who are used to making their own judgements about new technologies.

Again, further information on cryonics is available on the web.

"In 1991 John Walker, the reclusive founder of Autodesk, a California software company, donated $175,000 to help start the Institute for Molecular Manufacturing, a research organization. Most of the institute's grant money has gone to pay Drexler to work on projects such as computer simulations of molecular gears, bearings and other parts."

Drexler has not sought grants from government sources but has instead sought to fund research and education through nonprofit public foundations. He has done a remarkable amount on a shoestring budget -- I encourage donations to the Institute for Molecular Manufacturing and the Foresight Institute.

"The Drexler following includes speculative thinkers such as artificial-intelligence pioneer Marvin L. Minsky. Nanotechnology also seems to inspire government laboratories seeking to remake their image. Oak Ridge National Laboratory has let one of its modeling groups devote extensive effort to simulations of molecular bearings and shafts. Administrator Daniel S. Goldin of the National Aeronautics and Space Administration sees nanotechnology as a means of building smaller and lighter space vehicles. And the NASA Ames Research Center has scheduled a workshop for this spring to examine how its supercomputers might be used to provide models of nanodevices. Perhaps the most noteworthy trend - or the most disturbing one, to critics of the nanoist vision - is the appeal that the technology holds for students."

Students are indeed taking a strong interest in nanotechnology:

"A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." Max Planck

"The human mind gets creased into a way of seeing things. Those who have envisaged nature according to a certain point of view during much of their career, rise only with difficulty to new ideas. ... Meanwhile, I observe with great satisfaction that the young people are beginning to study the science without prejudice." Antoine Lavosier.

"Study groups in nanotechnology have established themselves at universities such as M.I.T. and the California Institute of Technology. "It's captured the imagination of bright, young scientists and engineers," says William A. Goddard III, a professor of chemistry and applied physics at Caltech. Goddard, an admirer of both Drexler and Merkle, occasionally works with them on simulations of molecular machine parts."

Computational chemists generally seem able to absorb the idea of nanotechnology quite easily. One reason for this is that they have the training and the tools to evaluate proposals for molecular machines. Give them a PDB file and tell them that it describes a molecular structure that's supposed to do something useful, and they'll happily model it. Sometimes they come back and tell you that it works and it's a great design. Sometimes they torture it in horrible ways and it behaves in some strange and unexpected manner.... at which point, it's back to the drawing board.

The story attempts to portray "actual scientists" as a group that is disjoint from "acolytes," "devotees," and "disciples." Unfortunately, Professor Goddard, head of the Materials and Process Simulation Center at Caltech, is rather obviously neither a disciple nor an acolyte. A great many others supportive of nanotechnology are quite capable of analyzing the technical issues and drawing their own conclusions -- and have.

The analysis of the hydrogen abstraction tool has involved many people, including: Donald W. Brenner, Richard J. Colton, K. Eric Drexler, William A Goddard, III, J. A. Harrison, Jason K. Perry, Ralph C. Merkle, Charles B. Musgrave, O. A. Shenderova, Susan B. Sinnott, and Carter T. White. The institutions involved include the Materials and Process Simulation Center at Caltech; the Department of Materials Science and Engineering, North Carolina State University; the Institute for Molecular Manufacturing; the Department of Chemicals and Materials Engineering, University of Kentucky; the Chemistry Department, United States Naval Academy; the Naval Research Laboratories, Surface Chemistry Branch; and the Xerox Palo Alto Research Center. None of these people are "acolytes" "devotees" or "disciples." Again, the reader is invited to peruse the list of conference attendees and decide whether it's possible to neatly classify people as either "disciples" or "actual scientists." (Or, as the old joke says, "What am I, chopped liver?")

"Drexler and his nanoist disciples view molecular nanotechnology as a grand challenge of science and technology. And they comb the pages of journals such as Science and Nature for evidence of research advances that might lay the groundwork toward the ultimate self-replicating assembler. At the Foresight conference last fall, Merkle showed a schematic chart illustrating how the current work being done at a scale below 100 nanometers by chemists and materials scientists might one day lead to nanomachines. Lines on the left of the chart represented experimental approaches, such as probes that can manipulate atoms, tubes of graphite about a nanometer in diameter, and novel types of proteins. On the right side resided lines that corresponded to computer simulations of molecular machine parts for assemblers. In the center appeared a noticeable gap."

Back to Drexler, biased adjectives, hints and innuendoes.

As for the "schematic chart:" I have been using charts similar to the one at the left for several years to illustrate the advantages of pursuing a mixed strategy for developing nanotechnology. The basic idea is simple: neither a purely experimental nor a purely theoretical/computational approach will be most effective. The strengths of the two approaches are complementary, and their combined use will move us towards the goal more quickly than either alone. Scientific American is advocating a purely experimental approach (which they term "real nanotechnology") while denigrating the value of computational and theoretical work.

It is interesting to note that recent work at IBM Zurich used computational models to design a molecule that could be precisely positioned on a surface, at room temperature and in ultra high vacuum. They then verified that the molecule that the "computational experiments" favored also worked experimentally. As we seek to build more and more complex molecular machines, the use of extensive modeling will become increasingly important. The design of an assembler will require extensive analysis on a computer if it is to be developed in a reasonable time frame.

The work at IBM Zurich also illustrates quite nicely that computational experiments can be used to model near-term as well as intermediate-term and long-term objectives. The particular chart I used at the conference had some dotted lines crossing the gap -- computational models of the intermediate systems that we'll have to design and build if we are to move from our present technology base to nanotechnology.

"Real Nanotechnology"

Most researchers whose work moves beyond computer simulations and into the laboratory do not view the challenges of nanotechnology as leading toward the goal of nanoists such as Merkle. A number of them, some of whom even capitalize on the "nano" label in promoting their work, pursue a series of more modest objectives. Differences of opinion about Drexlerian nanoism do not prevent the two camps from occasionally rubbing elbows."

The computational modeling of molecular machine proposals creates a problem for Scientific American: it supports the conclusion that nanotechnology is feasible. Therefore, it's necessary to discredit computational models without actually addressing their substance.

Keep in mind that not all simulated molecular machine proposals work. Far from it. Failures are in fact numerous but are usually not published (a fact I can attest to from personal experience). What's interesting is that, with effort, it's possible to develop molecular machine designs that survive computer simulation.

As for pursuing "modest" objectives: it's not unusual when selecting a goal to estimate an expected return: multiply the payoff if it works times the estimated probability that it will work. Goals with a modest payoff require a high probability of success before pursuing them can be justified. Goals with a high payoff should be pursued even if the probability of success is modest. Nanotechnology will have an extremely high payoff and the evidence to date (contrary to anything Scientific American might imply) suggests a very high probability of payoff. The only disadvantage is that there is still significant uncertainty about how long it might take and what resources might be needed.

"Harvard University chemistry professor George M. Whitesides presented a review of his work at the Foresight conference. Whitesides investigates how simple natural objects self-assemble by minimizing thermodynamic instabilities at a surface, such as those between air and water [see "Self-Assembling Materials," by George M. Whitesides; SCIENTIFIC AMERICAN, September 1995]. At the meeting, Whitesides described how he and his colleagues have used self-assembling hydrocarbon molecules, called alkanethiols, to form ordered rows on a gold surface. They have demonstrated how his fabrication method might be used in a process to pattern far thinner circuit lines on a computer chip that can be achieved through conventional lithographic methods. Eventually, self-assembly of small silicon cubes that contain devices that alter information might lead to news methods for manufacturing computer processors."

A good talk. Whitesides' expertise in self-assembly was evident. Self-assembly is a powerful method of synthesizing a very useful range of structures. The reader should keep in mind that self-assembly is not, by itself, nanotechnology. A simple way of seeing the difference is to note that a diamondoid structure cannot be self-assembled, and that a self-replicating manufacturing system is based on more than just the principles of self-assembly (this is true even for a cell).

While self-assembly is not nanotechnology, it should be possible to self-assemble systems that are sufficiently powerful that they could in turn build more powerful systems.

"Whitesides does not see the goal of his work as edging toward the assembler. He distinguishes between his investigations into self-assembling monolayers and the still distant goal of achieving self-assembly by following a coded set of instructions. Biological cells use this latter approach to make copies of themselves, and so would nanoassemblers. 'What makes [Drexler's vision] exciting is self-replication, and at the moment, it is pretty much science fiction,' Whitesides says. 'Even after a fair amount of thought, there's no way that one could see of connecting this idea to what we know how to do now or can even project in the foreseeable future.'"

Another non-statement: self-replication is "science fiction." This statement is made more intriguing by the fact that the planet is covered by self-replicating systems.

Again, an introductory page about self replicating systems is available on the web.

"The complexity of making objects with individual molecular building blocks may eliminate any of the dramatic cost savings envisioned by the nanoists, except in a few clearly delineated technological areas. Fabricating computer chips has already become a form of engineering the small, with the tiniest circuit elements measuring less than a micron. The cost of a new semiconductor plant now reaches into the billions of dollars, in part because of the technical challenges posed by the need to craft ever smaller features onto the surface of a chip. Chipmakers can still justify the added expense because packing circuits more densely lead to higher computational performance and ultimately lower costs. For most other goods, nanotechnologies may receive tough competition from Mother Nature. 'Drexler's grand vision is a nice one, but sometimes some of the specifics are not entirely correct,' comments Jane A. Alexander, who established the nanoelectronics program at the Advanced Research Projects Agency. 'I once heard him say we'd make tables out of nanotechnology. Wood is awfully cheap, and trees do it very nicely.'"

Present manufacturing methods involve a very big and increasingly expensive thing (a semiconductor fabrication facility) to make a very small and not too expensive thing (a computer chip -- note that silicon computer chips on a per pound basis are quite expensive: hundreds of thousands or millions of dollars per pound). In sharp contrast, we have examples of very small things (cells) that make other very small things (other cells) and do so inexpensively (perhaps a dollar a pound). Nanotechnology proposes to use self-replication to achieve low cost, and certainly does not propose to use something resembling current semiconductor fabrication methods.

The question posed is therefore quite crisp: if self-replicating systems able to manufacture a wide range of interesting and valuable products are feasible, then low cost manufacture of the products that such systems can make follows as a consequence. If no such system can be designed and built, then this proposal for achieving low cost is infeasible. Present evidence that self-replicating systems are feasible includes the existing biosphere, the theoretical studies of von Neumann, the NASA Ames study Advanced Automation for Space Missions, the work of Drexler in Nanosystems, articles by Ralph C. Merkle, and other articles too numerous to mention (see the references in the NASA study and elsewhere).

To quote the open letter to Scientific American by R. Freitas: "As co-editor of the historic 1980 NASA study of self-replicating machine systems (Advanced Automation for Space Missions, NASA CP-2255, 1982), I was astonished to see this concept decried as "science fiction" in the pages of Scientific American, a magazine which has been publishing articles praising the idea for nearly half a century (e.g. John G. Kemeny, "Man Viewed as a Machine," (Apr 1955):58-67; Edward F. Moore, "Artificial Living Plants," (Oct 1956):118-126; L.S. Penrose, "Self-Reproducing Machines," (Jun 1959):105-114). NASA's robots-assembling-robots replication demonstration, first proposed in 1980, now occurs daily in Japanese factories. Self-reproducing software such as worms and viruses prowl the Internet, preying on unprotected PCs, networks and mainframes. Machine replication has been extensively studied. It is eminently feasible."

The argument against the feasibility of such systems is that they are "science fiction."

As for the implied assertion that tables will continue to be made from wood: the table on which I am typing this is made from metal and plastic (already a change from centuries past) and is quite heavy -- I'd have a hard time moving it if I wanted to rearrange my furniture. I'd like to have a table that was light enough so that I could easily move it -- a diamondoid table would be quite nice. New technologies often replace old, even for humble applications.

"Keeping every atom in its place may also prove exceedingly onerous at the atomic level. David E. H. Jones, a researcher in the department of chemistry at the University of Newcastle upon Tyne, who may be best known as the author of the irreverent "Daedalus" column in Nature, has provided a pointed critique of the idea that individual atoms and molecules could serve as construction elements in the ultimate erector set. Jones made his case a year ago in a review of a popular book about Drexler by science writer Ed Regis, called Nano. Regis's account generally treats the chief nanoist's ideas favorably."

Shortly after Jones made his case, we responded and rebutted his arguments point by point on the web. As Jones was grossly ignorant of the field, this was a relatively straightforward exercise. The existence of this rebuttal was conveniently omitted in Scientific American's story.

"Jones describes the contortions often required to achieve atomic control of matter. In 1989 two IBM researchers penned their employer's acronym by manipulating 35 xenon atoms with a scanning tunneling microscope - a device that dragged the atoms across a nickel surface. The atoms moved because of chemical bonding interactions that occurred when the microscope's tungsten tip came to within a tenth of a nanometer or so of each atom. Jones notes the difficulties involved: The IBM logo was created in an extremely high vacuum at the supercooled temperature of liquid helium using inert xenon atoms. Outside this rarefied environment, the world becomes much less stable. 'Single atoms of more structurally useful elements at or near room temperature are amazingly mobile and reactive,' Jones writes, 'They will combine instantly with ambient air, water, each other, the fluid supporting the assemblers, or the assemblers themselves.'"

This issue was specifically addressed in the rebuttal. Briefly (a) he has confused the concept of "atomically precise" with the method of manufacture, (b) proposals that call for the use of highly reactive compounds also call for an inert environment, such as vacuum or a noble gas, and (c) some specific reactions that involve single atoms, such as the hydrogen abstraction tool discussed earlier, have been modeled both with ab initio quantum chemistry and molecular dynamics. It is obvious from reading Jones' comments that he was literally unaware of this body of work.

While Jones' excuse is ignorance, the writer of this story has no such excuse. A video of the molecular dynamics simulation of the hydrogen abstraction tool successfully abstracting a specific hydrogen atom from the diamond (111) surface at 300 K (approximately room temperature) showed in clear and graphic detail the influence of thermal noise, the specifics of the chemical reactions involved, the nature of the environment in which the reaction should take place (vacuum), and other details. The video was shown at the conference that the writer attended, and in a telephone conversation he told me he had seen it. Other presentations at the conference discussed specific reactions for the mechanosynthesis of diamondoid structures, including detailed descriptions of both the reactions and the environment in which they should take place. As these talks did not include an easily understood video, we might forgive the writer for having failed to understand their significance.

"Jones believes that the nanoists fail to take into account critical questions about the thermodynamics and information flow in a system of assemblers. 'How do the assemblers get their information about which atom is where, in order to recognize and seize it? How do they know where they themselves are, so as to navigate from the supply dump [where raw atomic material is stored] to the correct position in which to place it? How will they get their power for comminution [breaking up material] into single atoms, navigation and, above all, for massive internal computing?' The list continues before Jones concludes, 'Until these questions are properly formulated and answered, nanotechnology need not be taken seriously. It will remain just another exhibit in the freak show that is the boundless-optimism school of technical forecasting.'"

This was the summing-up paragraph of Jones' book review. As he stated these various problems in the earlier paragraphs, and as we responded paragraph by paragraph to his arguments, we here refer the reader to our response. A brief discussion of a method for dealing with the positional uncertainty caused by thermal noise in the context of an assembler is available.

"The nanoists' response to this fusillade is simple: read Drexler's technical tome Nanosystems, which contains a response to virtually any general point raised by detractors. Acoustic waves, for example, can be used to supply power to assemblers, an answer to one of Jones' objections."

The response was a point-by-point rebuttal that Scientific American was aware of and chose not to mention. A charitable attitude towards this omission might be that they simply didn't know about its existence. Unfortunately for this hypothesis, Scientific American made extensive use of resources on the web (I know -- I spent more time than I care to remember on the telephone discussing the contents of specific web pages with them). Further, when they asked for a critic, I provided them with Jones' name and suggested they look at my web page rebutting his arguments. I followed up this discussion by sending them an e-mail which said: "David Jones ... wrote a review of "Nano!" in Nature that was rather bluntly critical. I don't think much of his opinions, but I don't think he's retracted them. There's a link to my comments from the "reactions" page, along with the reference to his article."

As Jones' book review is literally the only published criticism of the feasibility of nanotechnology that Scientific American mentioned, as they devoted several paragraphs to it, and as Jones' criticism contained gross errors that should have been immediately obvious to anyone who attended the Fourth Foresight Conference on Molecular Nanotechnology, their omission of the rebuttal is ... shall we say delicately ... odd.

Of course, reading Nanosystems is excellent advice. Had Jones done so before writing his attack it might have made responding to his "questions" a bit less tedious.

"Drexler contends that his critics, with their need to focus on new products or the next grant-funding cycle, have trouble thinking far enough into the future. 'To people outside who don't understand that you're talking about the year 2020 or whatever, these ideas raise confused, unrealistic expectations about the short term,' Drexler maintains. 'That makes researchers uncomfortable because it's not a yardstick they want to be measured by. It also brings in ethics and the future of the human race, which are not the usual cool, scientific, analytical concerns.'"

As a general rule of thumb, groups or individuals that have an interest in nanotechnology have long planning horizons. NASA, for example, often plans missions many years or even decades in advance. Members of the National Space Society typically view the settlement of space as a multi-decade undertaking. The Department of Defense has internal planning documents, such as the Project 2025 report, that consider where the world might be, both politically and technically, 30 or more years from now. Medical applications of nanotechnology are of interest to individuals if they can be developed within their lifetime: many of us expect to live at least a few more decades. Many people care about the world that their children will live in. Members of the environmental movement want to preserve the beauty and majesty of nature not only for the next year or two, but for centuries and more. It's not surprising, therefore, to see interest in nanotechnology from members of these groups.

Those who express little interest in nanotechnology usually have planning horizons of ten years or less. One very good experimentalist explained to me that he wasn't interested because he wasn't going to be here in a decade. While sympathizing with his predicament, many of us both expect to be here for several more decades and also care about at least some aspect of the future even after that.

As a society we need to be thinking not only about the next month or the next year, but also the next few years, the next decade, and the next few decades.

"For engineers who build things, finding the relevant page in Nanosystems is not enough. Drexler touts his work as 'theoretical applied science': research constrained only by physical law, not by the limits of present-day laboratory or factory manufacturing capabilities. To hard-nosed engineers, though, the juxtaposition of 'theoretical' and 'applied' quickly becomes an oxymoron. Their response to the author of Nanosystems? Come back when you can tell me how to make those things."

I believe a "hard-nosed" engineer, pretty much by definition, would have a planning horizon of under 5 years. In order to motivate such individuals it is necessary to either (1) describe something that they can do in the next few years that will provide them with some direct benefit (a product that makes money, for example) or (2) pay them money to work on something that will not have any significant pay-back in 5 years.

As there are many sharp engineers who are actively looking for projects with significant short term payoffs there is little need to tell them what they should be doing -- they'll see the payoff and will work for it pretty much independent of any long term considerations. It is reasonable to expect that a great deal of useful work will be done for such reasons.

Unfortunately, it is not reasonable to assume that years or even decades of research and development motivated by nothing more than short term payoffs is the best or even a feasible way to develop a relatively complex system that has a high payoff. Anyone familiar with chess playing programs will understand this -- it's called the horizon effect. If the program looks only at the next five moves it will overlook a checkmate that is ten moves deep. Continued tactical play based on a five move look ahead might or might not ever detect the deeper strategy -- it will certainly not detect it as quickly.

"The accumulation of small details may doom the best theories for small machines. Phillip W. Barth, an engineer at Hewlett-Packard, characterizes simulations of molecular bearings as 'computer-aided speculation.' 'The holes are bigger than the substance,' he says of Nanosystems. 'There's a plausible argument for everything, but there are no detailed answers to anything.' Barth is a leading engineer in micromechanics, a field that builds microscopic sensors and machines from silicon [see "Silicon Micromechanical Devices," by James B. Angell, Stephen C. Terry and Phillip W. Barth; SCIENTIFIC AMERICAN, April 1983]. Barth observes a lack of discussion of a number of basic engineering considerations that could make many of Drexler's nanodevices impossible to build. Drexler's nanobearings may be molecularly stable. But Nanosystems, he notes, does not address the stability of structures synthesized during intermediate steps in building the bearings."

So far, the critics have provided no unanswerable (or even very difficult) problems -- small or otherwise -- to accumulate. Barth's concern that intermediate structures must be stable is a significant design constraint -- just as the concern that the intermediate states of (say) a house must be stable is also a significant design constraint. It might be prudent to assemble a wall before trying to raise it, and the roof should presumably be put in place after there are adequate supports to hold it. The argument that nanotechnology is infeasible because the stability of intermediate structures imposes a design constraint is remarkably weak, particularly when we consider the astronomically large number of intermediate structures that are possible if we wish to make a structure of any reasonable size.

We consider one approach for dealing with the stability of intermediate structures. We note, firstly, that the stability of structures with no dangling bonds and in which the strain on the bonds is relatively modest can be evaluated relatively easily. We could adopt a set of design rules enumerating a set of allowed local structures and setting explicit limits on allowed local strain. The simplest design rules would be for structures that closely resembled diamond. Such structures have been proposed in Nanosystems and elsewhere, and arouse (as Barth notes) little concern.

Next, we note that during synthesis we might create a structure which has dangling bonds. Such dangling bonds, particularly if there are many of them, can make the analysis of the stability of the structure difficult. To consider a well known example, the 7x7 reconstruction of the non-hydrogenated silicon (111) surface is not generally viewed as intuitively obvious and took considerable effort to work out. If we used intermediate structures similar to the this, we'd have our work cut out for us.

A simple strategy, therefore, is to ban intermediate structures with many dangling bonds. Thus, we deem the non-hydrogenated silicon (111) surface as "too complex to analyze."

Can we still synthesize a very wide range of structures within this constraint? One strategy for doing so follows. We start with a structure which has no dangling bonds. We make a small local modification to the structure by (if needed) first abstracting a few hydrogen atoms (or otherwise making a very small region reactive). The stability of such a small region can be analyzed adequately using current ab initio quantum chemistry methods. Further, if we are synthesizing a large structure in which there are a few common repeating and relatively small patterns, we would expect that the local structure representing the local intermediate state would also be repeated -- so we need only analyze in detail a few small "unstable" regions in great detail to ensure that they would not engage in some unexpected reconstruction. Finally, having made the desired local modifications, we determine if there are any dangling bonds. If there are, we cap them off by adding hydrogens to them.

In brief summary, this strategy changes the problem from "Start with relatively simple and stable structure X and synthesize relatively simple and stable structure Y (where Y is very different from X)" to "Start with relatively simple and stable structure X and synthesize relatively simple and stable structure X' (where X' differs from X by only a few atoms); then from X' synthesize relatively simple and stable structure X'' (where X'' differs from X' by only a few atoms); then ..... ; then from XN synthesize relatively simple and stable structure Y (where Y differs from XN by only a few atoms)."

This kind of issue has been well known in the nanotechnology research community for some years. The 1993 Foresight Conference had a demo of the MASS (Molecular Assembly Sequence Software). The purpose of this software is to provide an aid for the development of synthetic sequences intended to make diamondoid structures. The idea is to start with the final structure and work backwards to some starting structure by a sequence of steps, each one of which can be mediated by a suitable positionally controlled molecular tool. Chemists will recognize this as a variant of retrosynthetic analysis, but with the added assumptions that (a) synthesis takes place in vacuum, (b) the object being synthesized is a stiff diamondoid structure and (c) positionally controlled molecular tools are available. Discussions of the issues involved preceded 1993 by several years.

"Unresolved details, moreover, may not be so trifling. 'Energy is a fundamental concern,' Whitesides declares. 'It is no good to say it comes from somewhere - acoustic waves or whatever. If we can forget the details of energy supply, we have a perpetual motion machine.'"

An interesting series of statements. Energy is indeed important, but providing a source for it is "no good?" Followed by the implied claim that we're providing perpetual motion? To think that Drexler and myself; the researchers at Caltech, Oak Ridge, NASA Ames, NRL, NCSU and elsewhere; the students at MIT, Caltech, and other universities; and the many others who have looked over the proposals for molecular machines; would have anything to do with a proposal that either required or provided perpetual motion is not only insulting, it's ... very ... very ... dumb! Though not all that unusual for this story.

Being charitable, however, perhaps there is a concern about how to convert mechanical energy into chemical energy. A simple example of a mechanosynthetic process to do this is the conversion of a precursor to the hydrogen abstraction tool to the activated form. Consider the precursor shown to the left. Clearly, if we pull hard enough on the two handles, something will break. If we design in a "weak link," then it will break where we want it to break -- in this case, between the silicon and carbon. The result is the activated hydrogen abstraction tool, which is chemically very reactive.

This general mechanism -- pulling on a structure until something breaks -- can be used to create a wide variety of radicals. It is a simple method of converting mechanical energy into very reactive chemical structures.

"The present inability to build an assembler - coupled with elaborate speculation about what the future may hold - gives nanotechnology a decidedly ideological or even religious slant, in Barth's view. In early January he posted a message to an Internet bulletin board (sci.nanotech) suggesting that subscribers comment on whether molecular nanotechnology has the makings of a mass social/political movement or a religious faith in the traditions of Marxism or Christianity. Barth bolsters the case for nanoism as a form of salvation by citing a passage from a new magazine called NanoTechnology: 'Imagine having your body and bones woven with invisible diamond fabric. You could fall out of a building and walk away.'"

It's useful to recall, at this point, that the original question was whether or not nanotechnology, defined as the ability to inexpensively make most structures that are consistent with natural law, is or is not feasible. There are very good reasons to believe that it is. The relevance of Marxism and Christianity to this technical question is, shall we say, unclear. The inclusion of random quotes to "bolster" this red herring serves little useful purpose.

"On the Border of Science and Fiction"

The nanoists' legacy may be to stoke science-fiction writers with ideas for stories. The latest genre in science fiction employs nanotechnology as its centerpiece. A follow-on to the cybernetic fantasies of authors such as William Gibson, it is sometimes even called "nanopunk." The world depicted by nanowriters goes beyond cybernetic mind control and downloading one's brain into a computer. It postulates ultimate control over matter. "It seems like nanotech has become the magic potion, the magic dust that allows anything to happen with a pseudoscientific explanation," says Ist-van Csicsery-Ronay, Jr., an editor of the journal Science-Fiction Studies, published by DePauw University."

Again, the objective is to draw attention away from the technical issues. Space travel is feasible even if not all science fiction stories about space travel are correct or even sensible.

"A collection of 'nano' stories that appeared last year features the imaginings of noted science-fiction writers, such as Poul Anderson. The volume, Nanodreams, even contains an introductory essay by Drexler on the merits of science fiction as a means of exploring the societal implications of a nanotechnological future. 'Saying something sounds like science fiction should not be regarded as a form of dismissal,' Drexler said in a recent interview. 'Much of what science-fiction writers described in the 1950s happened, and you need to distinguish between antigravity and flying to the moon, between time travel and making a robot that works in the factory.'"

Drexler's comment about sums it up.

"Nanodreams includes a story in which the pain experienced by a fetus during an abortion is telecommunicated to nanomachines that reproduce the sensation within the father of the child - and then, finally, kill him. Another nanotale describes a company that has just achieved a breakthrough by making nanomachines that can repair tissue damaged by a bullet wound. In one scene a poster on a laboratory wall depicts Albert Einstein handing a candle to Drexler."

And the relevance of this to the technical feasibility of nanotechnology is?

"The fantasies of nanoists posted on Internet bulletin boards and World Wide Web sites often outstrip the imaginings of the best science-fiction writers. Take the often discussed idea of a utility fog: nanobots that link together to create materials and objects in a desired form and shape, from paint to furniture. 'When you got tired of that avant-garde coffee table, the robots could simply shift around a little, and you'd have an elegant Queen Anne piece instead,' reads one description on the Web."

More biased language. How would someone from 1896 react to what is common place today?

"Chemistry has distant roots in alchemy, the belief that transmutation of materials will bring health and wealth (though perhaps not ultimate mastery of interior decoration). Nanoism resembles a form of postmodern alchemy - and one that awards cash for molecular machine parts. Toward the end of November's Foresight conference, an announcement was made about a new prize, named for Feynman."

Another non-statement. If we eliminate the statements in the story that have no bearing on the technical issues, most of the story simply vanishes. The few statements that remain are easily rebutted.

"The prize of $250,000 comes courtesy of Jim Von Ehr, an executive at Macromedia, a software company in San Francisco, and Marc Arnold, a St. Louis venture capitalist. It is to be awarded for the fundamental breakthroughs that will usher in the era of molecular nanotechnology: a robot arm and a computing component for an assembler."

Historically, prizes have been very effective at motivating research in a field.

"For the time being, the nanoists can only wait for these breakthroughs to arrive, while continuing to formulate their computerized models of molecular machine parts. It may be a long time coming. In fact, Drexler himself has said that his fortitude has been weakened by jibes from critics and that he might consider a calling other than nanotechnology. "I'm tired of it," he says."

As the reader might appreciate, the kind of ad hominem attacks used in this story would make anyone tired. The fact that researchers pursuing fundamentally new and valuable objectives commonly have to endure such an ordeal is a societal problem of great significance. How many discoveries were not made, or were delayed, because the people in a position to make them decided it just wasn't worth the pain?

The "waiting for breakthroughs" theme is based on the view that science advances by unexpected and serendipitous discoveries. If the purpose of scientific research is to discover new laws of nature and unexpected phenomena, then this view is reasonable. The important event is the "breakthrough," i.e., the unexpected discovery of evidence showing that our existing understanding of nature is either incomplete or in fact incorrect.

However, the whole thrust of nanotechnology is to develop what is feasible within the framework of existing and accepted natural law. This is a very different objective from the "pure science" objective of determining what those laws are. We assume that existing natural law -- supported by a great deal of experimental evidence -- is correct. When there are serious questions about how to apply existing natural law to a particular structure, we avoid using that structure. An example of this principle was given earlier, where the 7x7 reconstruction of the silicon (111) surface was deemed "too complex," and the structure was therefore avoided. This principle has broad applicability in the design process where we are free to avoid designs that create problems.

The idea of accidentally and serendipitously discovering a Saturn V launch vehicle illustrates the absurdity of thinking that the pursuit of pure science is the only worthwhile objective. Other objectives are also worthwhile and call for other methods. In particular, if we think that nanotechnology will involve the design and manufacture of relatively complex artifacts, then the design process itself becomes a significant component of the overall effort. This is a concept well understood in computer science, where the design process entirely dominates software development.

It's also intriguing to juxtapose the criticism that greater analysis and greater detail is needed in the proposals for molecular machines in general and assemblers in particular before we can believe they are feasible with the criticism that providing greater detail and analyzing molecular machine proposals in depth by computer modeling is a waste of time. In many instances the "critics" are really saying: "I don't understand how you could do that." What they really want is not experimental evidence of a breakthrough, but a design proposal that illustrates how to achieve the desired objective within the framework of existing accepted and well understood natural law.

"Nanoists' convictions about the inevitability of a breakthrough evoke memories of another idea once posed by Feynman, their adoptive mentor. In a commencement speech given to the 1974 graduating class at Caltech, Feynman noted that some Pacific Islanders religiously awaited the return of the U.S. troops who had landed in World War II. He described the elaborate preparations the islanders made for the return of the planes that would bring them advanced technological accouterments and limitless wealth. Fires mark the sides of the runways. A man plays air-traffic controller by sitting in a hut with carved wooden headphones from which pieces of bamboo stick out, like antennas. The believers wait patiently in this preindustrial imitation of an airfield."

Scientific American has another major problem with Feynman. If Feynman is taken at face value, then nanotechnology should be feasible. Jones mentioned this as one of the arguments in favor of nanotechnology but then dropped the subject, never explaining either (a) where Feynman was wrong or (b) why Feynman's observations were inapplicable.

To get around this awkward problem it is necessary to neutralize Feynman without actually addressing the technical issues (or attacking Feynman). The paragraphs above and below are an attempt to do exactly that.

"'They're doing everything right,' Feynman said. 'The form is perfect. It looks exactly the way it looked before. But it doesn't work. No airplanes land.' Similarly, some scientific endeavors rely on wish fulfillment - and an inability to consider why something may not work, Feynman noted. 'So I call these things cargo cult science,' he concluded, 'because they follow all the apparent precepts and forms of scientific investigations, but they're missing something essential, because the planes don't land.' Until the nanoists can make an assembler and find something useful to do with it, molecular nanotechnology will remain just a latter-day cargo cult."

I think Feynman would not be pleased to have his name and words attached to this technically empty argument. Readers are invited to read There's plenty of room at the bottom and draw their own conclusions.

As noted earlier, Carl Feynman (the son of Richard Feynman) was also dismayed at the misuse of his father's essay.


What, then, are the technical arguments advanced against the feasibility of nanotechnology? One book review by David Jones -- thoroughly rebutted shortly after it came out -- was quoted. The existence of the rebuttal was conveniently omitted. A concern about the stability of intermediate structures was expressed. One strategy for dealing with this concern was presented here. A few people were quoted in a way which suggested they had a technical criticism of the feasibility of nanotechnology. The quotes were rebutted.

The story has repeated and irrelevant descriptions of Drexler, ranging from his tone of voice to how he drinks his tea to whether or not he's "tired of it." I'd certainly be tired of such biased and inaccurate journalism. In previous eras the messenger who told the king something he didn't want to hear was killed. This was no doubt momentarily pleasing to the king, but it doesn't actually deal with the substance of the message. And it ensures that no one tells the king anything he doesn't want to hear -- which can cause problems.

Scientific American should stop evading the fundamental technical question: given the currently accepted understanding of natural law, is nanotechnology feasible or is it not?

To date, all the evidence of which I am aware strongly supports the conclusion that it is. The obvious strategy, given this conclusion, is to go ahead and build molecular manufacturing systems. It is, however, difficult to build something before it has been designed, particularly when the design is itself non-trivial. Thus, we need to design such systems. The available tools of computational chemistry are sufficient to let us do this. That is, it is possible to design and computationally model both molecular components and indeed an entire (simple) assembler. While we might debate how hard it will be to build the resulting designs with our existing tools, and whether they will work perfectly the first time they are tried (unlikely), it is clear that this process will

It's likely that we'll actually have to design several such systems. More powerful systems, able to synthesize complex diamondoid structures, would seem harder to make directly with our existing capabilities. Intermediate systems also need to be designed, systems which are less powerful but more amenable to near term synthesis. Such simpler systems could then be used to build the more powerful systems.

In closing: a modest proposal. Let's go ahead and design these things. It will take a lot of work, and it seems unlikely to provide a near term payoff (say, in the next five or ten years). But if we don't design them it's very difficult to see how we can build them. Ever.

And the long term payoff is immense.

Questions for further discussion:

You might wish to send e-mail to Scientific American, with a cc to Foresight Institute ( expressing your opinion of their story. (Polite letters are more effective.) A selection of these letters has been posted at the Foresight web site.

Round 1 -- Part 1 | Letters | Part 2

Round 1 | Round 2 | Round 3 | Round 4 | Epilogue

Overview of the Debate