Over at Soft Machines, debate continues among Richard Jones, Chris Phoenix, Philip Moriarty, and me on the feasibility of molecular manufacturing. Click on Read More below for my response. Richard: My point is that by becoming so enamoured with one particular manufacturing technique, we run the risk of choosing materials to suit the manufacturing process rather than the function that we want our artefact to accomplish…Will MNT similarly limit the materials choices that you can make? I believe so."
Christine: This would seem to depend on what stage of MNT we are looking at. Surely in the beginning we will be very constrained — heck, we'll be thrilled to be building with atomic precision at all. But over time, the range of materials we can build using artificial molecular machine systems should broaden. It is unclear why there should be classes of materials that can exist but cannot be made using artificial molecular machine systems. [Possible exceptions noted below. –CP]
Richard: "Certainly we can represent structures virtually in code; the issue is whether we can output that code to form physical matter. For this we need some basic, low level machine code procedures from which complex algorthms can be built up. Such a procedure would look something like: depassivate point A on a surface. Pick up building block from resevoir B. Move it to point A. Carry out mechanosynthesis step to bond it to point A. Repassivate if necessary. Much of the debate between Chris Phoenix and Philip Moriarty concerned the constraints that surface physics put on the sorts of procedures you might use. In particular, note the importance of the idea of surface reconstructions."
Christine: OK, duly noted. I assume we can regard the representation question as resolved. Perhaps I missed something, but the above doesn't seem to make the case that we are blocked in principle from coming up with procedures for doing molecular manufacturing.
Richard: "The absence of such reconstructions is one of the main reasons why hydrogen passivated diamond is by far the best candidate for a working material for mechanosynthesis. This begins to answer Chris Petersonís next questionÖ[How did we get into the position of needing to use only one material here?]Öwhich is further answered by Chris Phoenixís explanation of why matter can be treated with digital design principles, which focuses on the non-linear nature of covalent bonding:"
Christine: Avoiding reconstructions sounds like a valuable feature, but it may not be the dominant one in choosing a material to build. Chris Phoenix's point about the non-linear nature of covalent bonding is interesting, but it doesn't appear to restrict molecular manufacturing to covalent bonding only.
Richard: "So it looks like weíre having to restrict ourselves to covalently bonded solids. Goodbye to metals, ionic solids, molecular solids, macromolecular solidsÖ it looks like weíre now stuck with choosing among the group 4 elements, the classical compound semiconductors and other compounds of elements in groups 3-6."
Christine: I don't see how this follows. Again, if a structure can be made at all, it's unclear from the above why it would be impossible to construct it using artificial molecular machine systems, which could (eventually) make use of whatever chemical techniques are used when the structure is made in other ways. Perhaps some exceptions would be extremely high pressures and temperatures, which would damage the molecular machinery…
Richard: "If the bonds donít behave in the same way, a mechanosynthetic step which works with one bond wonít work with another, and your simple assembly language becomes a rapidly proliferating babel of different operations all of which need to be individually optimised."
Christine: Yes, this does indeed sound very difficult, very complex. But what a fun challenge! ; ^)
Richard: "The idea of being able to manipulate atoms in the same way as we manipulate bits is seductive, but ultimately itís going to prove very limiting. To get the most out of nanotechnology, weíll need to embrace the complexities of real condensed matter, both hard and soft."
Christine: Yes, it's true that thinking of atoms in simplistic ways is very limiting. We have no choice but to do as Richard says, embrace the complexities of matter both hard and soft. No way around it.
Philip Moriarty, in the comments, expresses disapproval of MNT advocates' attitude of ìif ëxí doesnít work, well weíll just try ëyí".
Christine: I am new to this discussion, and can well believe that such a comment could be annoying if receiving in response to a specific chemical critique of a specific chemical proposal. But to me, coming in new, that attitude is simply one normally found in engineering. Always, in engineering, there is an original plan, which generally is found to have some flaws, necessitating tweaking or sometimes major revisions. The only way to find out is to try the plan, and learn as one goes. The MNT goal is to reach a general capability to build with atomic precision using artificial molecular machine systems. A very ambitious goal, but a very powerful capability once reached. Getting there will be a mind-boggling amount of work, requiring many many changes of plan. So we do need to take a flexible attitude. The plan is in its earliest stages.–CP