“Ralph Merkle (of public key cryptograpy fame) has done some recent theoretical work”
Animation of Merkle's nanofactory concept
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Drexler's name is synonymous with the idea of a nano-robots and self-replication. I think he also coined the term "clanking replicator" to describe a traditional robotic approach to replication (eg. RepRaps, robot arms, etc.) Ralph Merkle (of public key cryptograpy fame) has done some recent theoretical work, eg. his on "nanofactory", which consists of exponentially-smaller gantry-like systems (a bit like the print head on a cartesian 3D printer). He's also looked at "mechanochemistry" (forming molecules by moving specific atoms together in the right ways) and concrete studies of particular molecules, the energy levels and forces required, etc. His most recent work I can find on Google Scholar are patents from a few years ago. Some links: link link this video link link Those are all "grey goo" ideas, ie. 'real' machines. There's also the "green goo" approach, repurposing biological systems like DNA, proteins and ribosomes, eg. link
