A Debate About Assembler Design


Post-debate comments by David Forrest, 10 September 2005

Richard Jones, a physicist at U. Sheffield, has challenged the notion that the vision of molecular manufacturing systems proposed by Eric Drexler in Nanosystems offers the best design for productive nanosystems. In various places in his book, Soft Machines, Jones points out three issues that he claims will "scupper the entire enterprise" (p. 159): Brownian motion, thermal noise, and surface forces (p. 161). As an alternative he proposes that biologically-inspired systems that are adapted to and exploit Brownian motion are a better approach to develop molecular machine systems (in fact, he claims this is the only approach that will work). He elaborated on this to some extent in a debate in August 2005, but has not offered any specific alternative designs.

In response, we offer the following points:


1Consider for example the complex shape of the ribosome, a natural molecular assembler, which is composed of two halves that adhere together according to matching geometries and potential energy surfaces.

2In addition to Drexler's first paper on nanotechnology there is a publication that provides a more specific approach to the concept of protein design for the construction of molecular machine components for productive nanosystems.

3Prof. Jones advocates developing systems that take advantage of Brownian motion, which is a good idea. There are certainly tradeoffs involved in terms of performance and reliability if you make the entire system dependent on Brownian motion, but there's not really much to debate--we encourage a diversity of approaches to the development of molecular manufacturing systems. Again, we need to see an actual design.

In chapter 4 of his book, Professor Jones provides a description of Brownian motion, explaining how molecules in liquids and gases are continually jostled about. He also states that one cannot engineer a system that does not contain Brownian motion (page 63). We note again that only part of the system proposed by Drexler in Nanosystems would exclude Brownian motion: the eutactic environment which is sealed from contaminants, and in which the trajectory of every atom is controlled. This is distinguished from the traditional phases of matter--solid, liquid, and gas--by the term "machine-phase."