Why Eric Drexler’s critics are right

Alyssa Vance wrote a blog post urging people to ignore one of Eliezer Yudkowsky’s critics (who goes by the handle su3su2u1), entirely based on said critic dismissing Eric Drexler as a crackpot. I think Vance has already gotten a lot of spot-on pushback, both in her blog comments and elsewhere (see e.g. here, here, and here), but coincidentally I’d been thinking about writing a post on Drexler recently, and “ignore people who think Drexler is a crackpot” is a hilariously terrible heuristic.

At best, Drexler is someone whose ideas are highly speculative, based on problematic assumptions, and have yet to yield a fruitful research program; and whose understanding of the relevant science appears superficial. At worst, he’s been called a crackpot by many scientists who know what they’re talking about. I’ll let my readers decide whether the label is appropriate.

Some background: Drexler was originally an engineer who had worked for NASA and gotten a master’s degree in aerospace engineering. He got the idea that you might be able to build little robots and factories at atomic scales, and wrote a book on the subject called Engines of Creation, published in 1986. In 1992, he got a Ph.D. under computer scientist Marvin Minsky. You can read his dissertation online.

Eliezer Yudkowsky has claimed that, “if you say that nanomachines cannot work, you must be inventing new physics.” This is a good example of Yudkowsky spouting off on scientific topics without knowing what he’s talking about.

In reality, you can’t derive chemistry from physics. I mean, we can conjecture that in principle you could, given unlimited computing power, but we don’t have unlimited computing power. Wikipedia’s article on computational chemistry is a good introduction here. (Edit: see note below.)

Wikipedia mentions calculating the properties of molecules with 40 electrons, and I’ve heard of doing quantum models of a few hundred atoms with good approximation techniques. But you’re not going to deduce molecular biology from first principles, as a protein can easily have tens of thousands of atoms.

A lot of tech nerds don’t pay much attention to chemistry because it’s not as pure as math or physics, but I think chemistry is the relevant domain of expertise to apply here–Drexler’s claims about molecular assemblers are basically claims about a radical new way to do chemistry.

(I was a biochem major in college for two years before I realized I didn’t want to be a doctor, and it improved my general understanding of the world in ways just studying physics never would have.)

So physicist Richard A.L. Jones is correct when he says:

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

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

Similarly, Nobel-prize winning chemist Richard Smalley’s criticisms of Drexler are right on target. Vance dismisses Smalley’s criticisms as “centered around a silly analogy comparing molecular chemistry to romance,” but what’s actually going on is Smalley explaining basic chemical principles in a way laypeople can understand. As Smalley says in one of his replies to Drexler:

You cannot make precise chemistry occur as desired between two molecular objects with simple mechanical motion along a few degrees of freedom in the assembler-fixed frame of reference. Chemistry, like love, is more subtle than that. You need to guide the reactants down a particular reaction coordinate, and this coordinate treads through a many-dimensional hyperspace.

Describing this motion through hyperspace as a waltz, as Smalley does, is as good an analogy as any.

To give another not-literally-true, but still illuminating analogy, imagine chemical bonds as springs rather than the sticks you often get in molecular modeling kits. The hyperspace Smalley mentions is the many mathematical degrees of freedom a contraption built from these springs is going to have. Each spring can not only be stretched and bent, they can bounce about chaotically as you’re trying to make your chemical reaction happen.

That’s why Smalley says that in order to have the kind of control of chemical reactions that Drexler envisions, you can’t just have one nanobot arm for each molecule. You’re going to need to control the movement of many atoms all at once. Hence the “fat fingers” problem. Drexler’s reply to Smalley on this point suggests he doesn’t understand chemistry well enough to understand what Smalley is saying.

Smalley, by the way, got his Nobel for discovering so-called “buckyballs”, tiny spheres made out of exactly 60 carbon atoms arranged in a soccer-ball pattern. But these molecules are synthesized by vaporizing graphite, not with nanobots. Today, serious scientific work in “nanotechnology” generally has a lot more in common with Smalley’s work than Drexler’s. That’s why I say Drexler’s ideas haven’t yielded a fruitful research program.

As for whether Drexler is a crackpot, well, different people have different views. From a Wired article on Drexler:

“It’s very impressive, there is no question,” said MIT chemist Rick Danheiser, who served as Drexler’s thesis adviser, in 1992. “I couldn’t have done a better job.”

“It showed utter contempt for chemistry,” countered Danheiser’s colleague Julius Rebek. “And the mechanosynthesis stuff I saw in that thesis might as well have been written by somebody on controlled substances.”

The first paragraph contains a mistake, Danheiser was on Drexler’s committee but Minsky was Drexler’s adviser. Danheiser was the only chemist on the committee, so my guess is that Drexler did not get an especially well-rounded chemistry education when getting his doctorate. I’m speculating, but it’s possible Drexler did impressive work with molecular modeling software, yet his ideas about the significance of his models look, well, to a chemist at least, like something you’d come up with while on controlled substances.

If this sounds implausible, imagine a mathematician who was firmly convinced that P=NP. He did his dissertation on all the astonishing implications this would have! And let’s assume the thesis is technically correct, impressive even. But when he starts saying that the only thing holding back all kinds of technological miracles is the misrepresentations of his ideas being spread by malicious computer scientists… a Ph.D. would be no proof of sanity. Nor would a lack of peer-reviewed journal articles refuting his ideas.

If Vance wants technical publications, chapter 5 of this report essentially says, in very formal language, that we can’t know that Drexler’s theoretical calculations have anything to do with reality. If she’s not satisfied by that, unfortunately the truth is there’s just not much more to say about the issue.

Note: bartlebyshop tells me the Wikipedia article is bad. Sorry, I was looking for a source that vaguely backed up things I’d learned in undergrad. But if anything, the above discussion may actually understate how hard computational chemistry is.


23 thoughts on “Why Eric Drexler’s critics are right

  1. I find it odd that Drexler apparently got his “doctorate” from MIT’s Media Lab, a division of that university’s School of Architecture and Planning. Why didn’t he get it from one of MIT’s real departments of science or engineering?

    The Wikipedia page on the Media Lab also doesn’t mention Drexler or a “nano” anything among its professors’ and students’ accomplishments. Do the people who currently run the Media Lab, and who presumably have a say in its portrayal in how its Wiki page portrays it, want to downplay its role in Drexler’s career for some reason?


  2. Not sure what’s causing it but, viewed in chrome your blog has a bunch of words that overlap each other weirdly. Hope you can get your style sheet fixed!


  3. I’ve never heard of Eric Drexler before and I’m not qualified to judge him. However, as a general rule, it’s completely fine to judge a lay person a crackpot while judging a scientist with similar views as possibly not a crackpot. In my field, every theorist advocates at least one unusual theory. It’s a professional necessity if you want to be published. And it’s a socially necessity, because having everyone argue on the same side isn’t going to produce progress. What matters is not the positions of individual researchers, but who is able to convince their peers.

    On the other hand, lay people should usually just go with the consensus, if there is one. Let’s be honest, the lay person is probably not intimately familiar with the field. They’re not in constant discussion with scientists who disagree with them. They’re just picking experts.


    • Siggy– Out of curiosity, what is your field? And, if you don’t mind giving a longer answer, what are some of the more interesting (for your preferred definition of “interesting”) unusual theories that are being advocate in your field?


    • Have you actually looked at the respirocyte paper? There is no evidence such a thing would be stable. Most of the “parts” are based on designs from nanosystems that are 10^5 atoms and asymmetric.


      • Diamondoid structures have been studied and produced to various degrees though and while I agree that the understanding of how to produce these is currently limited, there is considerable theoretical potential and theoretical potential behind these structures if we could understand how to atomically manufacture them.


      • Look at the large “turbine” like structures in the respirocyte. There is no reason to think those wouldn’t spontaneously rearrange into simpler, more symmetric structures. This is basically the same criticism Richard Jones is making above. Why would this thing be stable?

        Liked by 1 person

      • Are you saying it is physically impossible to create it as in the laws of chemistry, physics, mathematics absolutely prevents it? Or that we do not yet have the ability to manipulate atoms with the precision necessary to create these arrangements because of a lack of a number of specific synergies at this time? You are, effectively, trying to prove a negative.


      • As a reply to Respirocyte:

        Physical chemist here (admittedly not a graduate yet, though), it may be that you are thinking about nanoscale structures in the wrong way. At the scales we are talking about (the scales of polymers and large proteins) a “nano-machine” can be thought of more as an oscillating collection of bound atoms, similar to a complex protein or enzyme. At these scales quantum effects are very relevant, so not only are the various bonds vibrating and Larmor precessing, in the scales of the finer parts of the mechanism the uncertainty principle means the positions of the atoms aren’t even well defined.

        In the same way that proteins can spontaneously refold into prions on a large enough timescale (and proteins are very stable), there’s a very good chance more complex nano-machine structures will not be stable. If there’s a suitable path, the nano-machine will fall into a lower energy state of a more natural and symmetrical formation over time. Given the properties of many of the proposed “parts”, the time scale (similar somewhat to a radioactive half-life) may be very short.

        “Are you saying it is physically impossible to create it as in the laws of chemistry, physics, mathematics absolutely prevents it?”

        It’s a rather large leap to think he was claiming something that strong. However, even if the part were created, it may be that it wouldn’t last very long. Maybe at extreme low-temperature conditions?

        “Or that we do not yet have the ability to manipulate atoms with the precision necessary to create these arrangements because of a lack of a number of specific synergies at this time?”

        This is the case at the moment, yes.


  4. You wanna hear something really nutty? I heard of a couple guys who wanna build something called an “airplane,” you know you get people to go in, and fly around like birds, it’s ridiculous, right? And what about breaking the sound barrier, or rockets to the moon, or atomic energy, or a mission to Mars? Science fiction, right? Look, all I’m asking, is for you to just have the tiniest bit of vision. You know, to just sit back for one minute and look at the big picture. To take a chance on something that just might end up being the most profoundly impactful moment for humanity, for the history… of history.


    • Is that really the best argument to make? It seems to me like “This seems impossible by presently-known laws, but so did the airplane” could be used for crystal healing as easily as for nanobots.


      • Life uses molecular scale machines to manipulate reactive building blocks with (near) atomic precision to manufacture macro-scale objects. Just like fusion, nature has already proved the concept. And just like flight, the “man made” version won’t follow nature perfectly (our planes don’t flap their wings) but both birds and planes fly. DNA origami has already been used to make molecular scale machines, we are getting much better at manipulating and making measurements at the nanoscale, and computers will soon be powerful enough to control millions of processes simultaneously. And for those that think nanobots are like Borg nanoprobes or Chrichton’s “Prey,” you got caught in the same line of thinking I did when I first heard of nanotechnology. The molecular machines Drexler proposes (like those described above with DNA origami) do follow physical presently known laws. Crystal healing relies on METAphysical reasoning. You really can’t compare the two. Hell, even EMdrive (and I’m not a proponent) can’t be categorized with crystal healing.

        Liked by 1 person

    • The “vision” has to make physical sense, and Drexler’s ideas generally don’t because he engages in a kind of quantum-mechanics denialism.

      By contrast, the technologies which get the physical principles right from the beginning practically invent themselves. Hence we have seen real progress in areas which exploit quantum mechanics, from computing to medical imaging to LED lighting. A medically knowledgeable friend of mine says that current medical imaging looks like technology from an advanced, post-singularity civilization right out of science fiction, but it exists and works in the here and now. But we can’t say that about Drexler’s “nanoassemblers” or whatever he calls his computer graphic fantasies these days.

      I kinda feel bad for Drexler, BTW. He seems like a pretty smart guy, but he devoted his life to several dud ideas, starting with space colonization in the 1970’s, when he could have had a more productive career.

      I also don’t share the idolatry for Richard Feynman because of his partly-baked speculations which seem to anticipate Drexler’s ideas. If you read biographies of intellectually productive people, you’ll notice that they generate plenty of bad ideas long with some really good ones. Feynman’s throwaway talk in 1959 – “There’s Plenty of Room at the Bottom” – apparently falls into the former category.

      Liked by 1 person

  5. To summarize the meat: You think Drexler’s work relies on two crucial false assumptions (1) mechanosynthesis is possible and (2) all the little machine parts that have been designed will be unsalvagably unstable or have crazy properties that make them unusable. Is this an accurate summary? Also, I read Chapter 5 of that report and don’t understand why you think it’s such a slam dunk. It basically just says a bunch of positive things about the possibility of advanced nanotech and then concludes that experimentation will be required.


  6. I recommend this summary of the debate between the nobel-prize winning young-earth-creationist Richard Smalley and Eric Drexler : http://www.kurzweilai.net/the-drexler-smalley-debate-on-molecular-assembly

    For those who are interested in the story of why the nanotechnology research program didn’t end up pursuing atomically precise manufactoring, the story is told in Drexlers book Radical Abundance: http://www.amazon.com/Radical-Abundance-Revolution-Nanotechnology-Civilization/dp/1610391136. In this book he also writes about the methodology for reaching certain conclusions where we, as you correctly say, cannot calculate everything with precision, with the use of conservative confidence intervals, etc.

    “At best, Drexler is someone whose ideas are highly speculative, based on problematic assumptions”
    What are Drexlers problematic assumptions?

    “In reality, you can’t derive chemistry from physics. I mean, we can conjecture that in principle you could, given unlimited computing power, but we don’t have unlimited computing power.

    Wikipedia mentions calculating the properties of molecules with 40 electrons, and I’ve heard of doing quantum models of a few hundred atoms with good approximation techniques. But you’re not going to deduce molecular biology from first principles, as a protein can easily have tens of thousands of atoms.”

    Is Drexler saying anything different from this or making assumptions that are in logical contradiction with this?


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