Richard Jones lists 6 challenges for molecular nanotechnology:

1. Stability of nanoclusters and surface reconstruction. Surfaces have a tendency to “reconstruct” – seek out stable equilibria in ways not necessarily predicted by molecular dynamics simulations.
2. Thermal noise, Brownian motion and tolerance. Atoms on the nanoscale may be too wobbly to build complex machines out of. Drexler addressed this, but not in thorough detail.
3. Friction and energy dissipation. Surface area becomes much larger as machinery scales down, and high functional densities will give rise to high power densities in molecular machine systems. The friction and heat may be so intense that molecular machine systems cannot be reliably constructed.
4. Design for a motor. Richard is skeptical that the electrostatic motor as described in Drexler’s Nanosystems would actually work. More detail needs to be fleshed out and supported by experimental testing.
5. The eutactic environment and the feed-through problem. For MNT systems to work, they would need to operate in ultra-high vacuum. But, interacting with the outside, they’d be exposed to a very atomically messy environment. Valves and pumps need to be around 100% efficient to exclude foreign molecules.
6. Implementation path. How do we get there from here? If “soft” nanotechnology is all that works, how do we transition from there to hard?

These are all valid arguments, but some are a bit more interesting than others. To estimate them roughly in order of declining importance based on my own opinion, I’d list them as 3, 1, 2, 4, 5, and 6.

beats tracking down all the physical chemistry papers

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