Author: Richard Jones

In part 1 of this series I talked about the growing importance of Richard Feynman’s famous lecture There’s plenty of room at the bottom as a foundational document for nanotechnology of all flavours, and hinted at the tensions that arise as different groups claim Feynman’s vision as an endorsement for their own particular views. Here I want to go back to Feynman’s own words to try and unpick exactly what Feynman’s vision was, and how it looks more than forty years on.

Feynman’s lecture actually covers a number of different topics related to miniaturisation. We can break up the lecture into a number of themes:

Writing small

Feynman starts with the typically direct and compelling question “Why cannot we write the entire 24 volumes of the Encyclopedia Brittanica on the head of a pin?” Simple arithmetic convinces us that this is possible in principle; using a pixel size of 8 nm gives us enough resolution. So how in practise can it be done? Reading such small writing is no problem, and would have been possible even with the electron microscopy techniques available in 1959. Writing on this scale is more challenging, and Feynman threw out some ideas about using focused electron and ion beams. Although Feynman didn’t mention it, the basic work to enable this was already in progress at the time he was speaking. Cambridge was one of the places at which the scanning electron microscope was being developed (history here), and only a year a two later the first steps were being made in using focused beams to make tiny structures. The young graduate student who worked on this was the same Alec Broers who (now enobled) recently attracted the wrath of Drexler. This was the beginning of the technique of electron-beam lithography, now the most widely used method of making nanoscale structures in industry and academia.

Better microscopes

Electron microscopes in 1959 couldn’t resolve features smaller than 1 nm. This is impressively small, but it was still not quite good enough to see individual atoms. Feynman knew that there were no fundamental reasons preventing the resolution of electron microscopes being improved by a factor of 100, and he identified the problem that needed to be overcome (the numerical aperture of the lenses). Feynman’s goal of obtaining sub-atomic resolution in electron microscopes has now been achieved, but for various rather interesting reasons this development has had less impact than he anticipated.

Feynman, above all, saw microscopy with sub-atomic resolution as a direct way of solving the mysteries of biology. “It is very easy to answer many of these fundamental biological questions; you just look at the thing! You will see the order of bases in the [DNA] chain; you will see the structure of the microsome”. But although microscopes are 100 times better, we still can’t directly sequence DNA microscopically. It turns out that the practical resolution isn’t limited by the instrument, but by the characteristics of biological molecules – particularly their tendency to get damaged by electron beams. This situation hasn’t been materially altered by the remarkable and exciting discovery of a whole new class of microscopy techniques with the potential to achieve atomic resolution – the scanning probe techniques like scanning tunneling microscopy and atomic force microscopy. Meanwhile many of the problems of structural biology have been solved, not by microscopy, but by x-ray diffraction.

Miniaturising the computer

The natural reaction of anyone under forty reading this section is shock, and that’s a measure of how far we’ve come since 1959. Feynman writes “I do know that computing machines are very large; they fill rooms” … younger readers need to be reminded that the time when a computer wasn’t a box on a desktop or a slab on a laptop is within living memory. In discussing the problems of making a computer powerful enough to solve a difficult problem like recognizing a face, Feynman comments ” there may not be enough germanium in the world for all the transistors which would have to be put into this enormous thing”. Now our transistors are made of silicon, but more importantly they aren’t discrete elements that need to be soldered together, they are patterned on a single piece of silicon as part of a planar integrated circuit. It’s this move to this new kind of manufacturing, based on a combination of lithographic patterning, etching and depositing very thin layers, that has permitted the extraordinary progress in the miniaturization of computers

Feynman asks “Why can’t we manufacture these small computers somewhat like we manufacture the big ones?” The question has been superseded, to some extent, by the discovery of this better way of doing things. This discovery was already in sight at the time Feynman was writing; the two crucial patents for integrated circuits were filed by Jack Kilby and Robert Noyce early in 1959, but their significance didn’t become apparent for a few more years. This has been so effective that Feynman’s miniaturization goal – “the circuits should be a few thousand angstroms across” – has already been met, not just in the laboratory, but in consumer goods costing a few hundred dollars apiece.

So far, then, we can see that much of Feynman’s vision has actually been realised, though some things haven’t worked out the way he anticipated. In the next section of this series I’ll consider what he said about miniature machines and rearranging matter atom by atom. It’s here, of course, that the controversy over Feynman’s legacy becomes most pointed.

Every movement has its founding texts; for nanotechnology there’s general agreement that Richard Feynman’s lecture There’s plenty of room at the bottom is where the subject started, at least as a concept. The lecture is more than forty years old, but I sense that its perceived significance has been growing in recent years. Not least of the reasons for this is that, as the rift between the mainstream of academic and commercial nano- science and technology and the supporters of Drexler has been growing, both sides, for different reasons, find it convenient to emphasis the foundational role of Richard Feynman. Drexler himself often refers to his vision of nanotechnology as the “Feynman vision”, thus explicitly claiming the endorsement of someone many regard as the greatest native-born American scientist of all time. For mainstream nanoscientists, on the other hand, increasing the prominence given to Feynman has the welcome side-effect of diminishing the influence of Drexler.

Many such founding documents easily slip into the category of papers that are “much-cited, but seldom read”, particularly when they were published in obscure publications that aren’t archived on the web. Feynman’s lecture is easily available, so there’s no excuse for this fate befalling it now. Nonetheless, one doesn’t often read very much about what Feynman actually said. This is a pity, not because his predictions of the future were flawless, nor because he presented a coherent plan that nanotechnologists today should be trying to follow. Feynman was a brilliant theoretical physicist observing science and technology as it was in 1959. It’s fascinating, as we try to grope towards an understanding of where technology might lead us in the next forty years, to look back at these predictions and suggestions. Some of what he predicted has already happened, to an extent that probably would have astonished him at the time. In other cases, things haven’t turned out the way he thought they would. We’ve seen some spectacular breakthroughs that were completely unanticipated. Finally, Feynman suggested some directions that as yet have not happened, and whose feasibility isn’t yet established. In my next post in this series, I’ll use the luxury of hindsight to look in detail at Plenty of Room at the Bottom, to ask just how well Feynman’s predictions and hunches have stood the test of time.

The recent comments by Alec Broers in his Reith Lecture about the feasibility or otherwise of the Drexlerian flavour of molecular nanotechnology have sparked off a debate that seems to have picked up some of the character of the British general election campaign (Liar! Vampire!! Drunkard!!! ). See here for Howard Lovy’s take, here for TNTlogs view. All of this prompted an intervention by Drexler himself (channeled through Howard Lovy), which was treated with less than total respect by TNTlog. Meanwhile, Howard Lovy visited Soft Machines to tell us that “when it comes to being blatantly political, you scientists are just as clumsy about it as any corrupt city politician I’ve covered in my career. The only difference is that you (I don’t mean you, personally) can sound incredibly smart while you lie and distort to get your way.” Time, I think (as a politician would say), to return to the issues.

Philip Moriarty, in his comment on Drexler’s letter, makes, as usual, some very important points about the practicalities of mechanosynthesis. Here I want to look at what I think is the strongest argument that supporters of radical nanotechnologies have, the argument that the very existence of the amazing contrivances of cell biology shows us that radical nanotechnology must be possible. I’ve written on this theme often before (for example here), but it’s so important it’s worth returning to.

In Drexler’s own words, in this essay for the AAAS, “Biology shows that molecular machines can exist, can be programmed with genetic data, and can build more molecular machines”. This argument is clearly absolutely correct, and Drexler deserves credit for highlighting this important idea in his book Engines of Creation. But we need to pursue the argument a little bit further than the proponents of molecular manufacturing generally take it.

Cell biology shows us that it is possible to make sophisticated molecular machines that can operate, in some circumstances, with atomic precision, and which can replicate themselves. What it does not show is that the approach to making molecular machines outlined in Drexler’s book Nanosystems, an approach that Drexler describes in that book as “the principles of mechanical engineering applied to chemistry”, will work. The crucial point is that the molecular machines of biology work on very different principles to those used by our macroscopic products of mechanical engineering. This is much clearer now than it was when Engines of Creation was written, because in the ensuing 20 years there’s been spectacular progress in structural biology and single molecule biophysics; this progress has unravelled the operating details of many biological molecular machines and has allowed us to understand much more deeply the design philosophy that underlies them. I’ve tried to explain this design philosophy in my book Soft Machines; for a much more technical account, with full mathematical and physical details, the excellent textbook by Phil Nelson, Biological Physics: Energy, Information, Life, is the place to go.

Where Drexler takes the argument next is to say that, if nature can achieve such marvelous devices using materials whose properties, constrained by the accidents of evolution, are far from optimal, and using essentially random design principles, then how much more effective will our synthetic nano-machines be. We can use hard, stiff materials like diamond, rather than the soft, wet and jelly-like components of biology, and we can use the rationally designed products of a mechanical engineering approach rather than the ramshackle and jury-rigged contrivances of biology. In Drexler’s own words, we can expect “molecular machine systems that are as far from the biological model as a jet aircraft is from a bird, or a telescope is from an eye”.

There’s something wrong with this argument, though. The shortcomings of biological design are very obvious at the macroscopic scale – 747s are more effective at flying than crows, and, like many over-40 year olds, I can personally testify to the inadequacy of the tendon arrangements in the knee-joint. But the smaller we go in biology, the better things seem to work. My favourite example of this is ATP-synthase. This remarkable nanoscale machine is an energy conversion device that is shared by living creatures as different as bacteria and elephants (and indeed, ourselves). It converts the chemical energy of a hydrogen ion gradient, first into mechanical energy of rotation, and then into chemical energy again, in the form of the energy molecular ATP, and it does this with an efficiency approaching 100%.

Why does biology work so well at the nanoscale? I think the reason is related to the by now well-known fact that physics looks very different on the nanoscale than it does at the macroscale. In the environment we live in – with temperatures around 300 K and a lot of water around – what dominates the physics of the nanoscale is ubiquitous Brownian motion (the continuous jostling of everything by thermal motion), strong surface forces (which tend to make most things stick together), and, in water, the complete dominance of viscosity over inertia, making water behave at the nanoscale in the way molasses behaves on human scales. The kind of nanotechnology biology uses exploits these peculiarly nanoscale phenomena. It uses design principles which are completely unknown in the macroscopic world of mechanical engineering. These principles include self-assembly, in which strong surface forces and Brownian motion combine to allow complex structures to form spontaneously from their component parts. The lack of stiffness of biological molecules, and the importance of Brownian motion in continuously buffeting them, is exploited in the principle of molecular shape change as a mechanism for doing mechanical work in the molecular motors that make our muscles function. These biological nanomachines are exquisitely optimised for the nanoscale world in which they operate.

It’s important to be clear that I’m not accusing Drexler of failing to appreciate the importance of nanoscale phenomena like Brownian motion; they’re treated in some detail in Nanosystems. But the mechanical engineering approach to nanotechnology – the Nanosystems approach – treats these phenomena as problems to be engineered around. Biology doesn’t engineer around them, though, it’s found ways of exploiting them.

My view, then, is that the mechanical engineering approach to nanotechnology that underlies MNT is less likely to succeed than an approach that seeks to emulate the design principles of nature. MNT is working against the grain of nanoscale physics, while the biological approach – the soft, wet, and flexible approach, works with the grain of the way the nanoscale works. Appealing to biology to prove the possibility of radical nanotechnology of some kind is absolutely legitimate, but the logic of this argument doesn’t lead to MNT.