Followers of the Drexlerian flavour of radical nanotechnology often accuse nanoscientists of ignoring their approach for reasons of politics or prejudice, and take the lack of detailed critiques of books like Nanosystems as evidence that the whole Drexlerian program is feasible, and indeed imminent. Scientists, on the hand, find the Drexlerian proposals too futuristic and too lacking in practical implementation details to be even worth criticising. The result is an ever-widening gulf between the increasingly bitter Drexlerites and a dismissive and contemptuous mainstream nanoscience community, which does neither side any good. So it’s a very positive development that Robert Freitas has presented a detailed scheme for achieving the first steps towards the mechanosynthesis of diamondoid nanostructures, and even more positive that Philip Moriarty has made a detailed critique of these proposals, based on his deep practical knowledge of scanning tunneling microscopy and surface growth processes.
Philip’s critique is contained in an 8-page letter to The Center for Responsible Nanotechnology‘s Chris Phoenix. The letter was prompted by an approach from Chris, asking Philip to expand on the criticisms of the Drexlerian vision that I reported him making at our joint appearance at the Institute of Contemporary Arts. Chris has, in turn, replied to the letter, and will be publishing the whole correspondence on the CRN web-site in due course.
The letter covers a lot of ground; at its heart is an exploration of some fundamental problems with the Freitas scheme – just how will a diamondoid cluster grow, and is the assumption that the mechanosynthesis tool-tip will grow in the necessary pyramid shape at all realistic? The answer to this seems to be, in all probability, no.
Just as important as this critique of one specific proposal are the general comments Philip makes about the importance of proof-of-principle experiments and of the theory-experiment feedback loop. This gets to the heart of the gulf between conventional nanoscience and the followers of Drexler. To the latter, theoretical demonstrations of feasibility in principle are primary, and considerations of how one is going to achieve the goals are secondary engineering issues that don’t need detailed consideration now. But to nanoscientists like Philip, the devil is in the details. It’s these details that determine whether a theoretically possible outcome will in practise be achieved in 10 years, in 50 years, or never. The Drexlerites tend to say “if x doesn’t work, then we’ll just try y”. But the more and more specific systems we try out and have to discard, the further away we get from the MNT dream of a system that can make any combination of atoms consistent with chemistry.
Freitas and Merkle have taken a very positive step in addressing these issues of implementation and experimental detail. The fact that the proposals can be criticised is positive too; in science this type of criticism isn’t destructive. It’s at the heart of the process by which science moves forward.
Update – 26th January. The whole correspondence between Moriarty and Phoenix, including the original letter, is now available for download here.