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Feynman’s Path to Nanotech (part 6)

Open Questions

Taking Feynman’s Path to nanotech, or even studying it seriously, would require finding answers to a number of open questions. These questions, however, are quite important and knowing the answers will be invaluable in understanding the envelope of possibilities for future manufacturing technology.

  1. Is it in fact possible to build a compact self-replicating machine using macroscopic parts fabricators and manipulators? We know that a non-compact one is possible — the world industrial infrastructure can replicate itself — and we know that a compact microscopic replicator can work, e.g. a bacterium. But the bacterium uses diffusive transport, associative recognition of parts by shape-based docking, and other complexity-reducing techniques that are not available at the macroscale.
  2. Not quite the same question: how much cheating can we get away with? In KSRM theory, it’s common to specify an environment for the machine to replicate in and some “vitamins,” bits that the machine can’t make and have to be provided, just as our bodies can’t synthesize some of the molecules we need and must get them pre-made in our diets. For the purpose of the Feynman Path, we can cheat in a very legitimate way: any part or capability that can be provided on whatever scale it’s needed from the outside, is fine. We start with control signals — no autonomous AI necessary! If we synthesize molecular gears by chemistry, wonderful. If we can provide single-crystal chunks of silicon or diamond to carve, do it. If we can polish surfaces with low-angle e-beams, wonderful. What’s left for out machine to have to make?
  3. What are the roadblocks we’ll have to invent our way around? The classic example is that electromagnetic motors work poorly at small scales, so we have to shift to electrostatic ones. Here are some others (by no means a complete list):
    • Near the atomic scale, we hit an “ontological phase boundary” where we have to quit thinking of our material as continuous (and able to assume arbitrary shapes, like circles) and start treating it as discrete and lumpy.
    • Gravity essentially vanishes, but the adhesion of parts to each other increases tremendously.
    • Lubrication by oily fluids quits working.
    • Heat dissipation rates increase as surface/volume ratios do.

    … and so forth.

  4. What kinds of forming techniques will work? There are a number of solid free-form fabrication technologies at the macroscale, which can in theory be adapted to smaller-scale forms where molten droplets, or whatever, are replaced by mechanochemical deposition tips. At larger scales, for decent surface tolerance, SFF must be followed by surface finishing. Will this work all the way down?
  5. And finally, how do we see what we’re doing? It’s all very well for Heinlein to talk about scanners, but existing techniques like scanning probes only work over relatively flat surfaces, not in the crowded interior of a milling machine or the like. We’ll probably have to build physical surface scanners — but existing shop practice makes extensive use of physical contact measurement anyway, so this probably won’t be such a major change.

3 Responses to “Feynman’s Path to Nanotech (part 6)”

  1. Trent Waddington Says:

    To answer the last question.. you do a simulation of the system a-prior and calculate a timeline macroscopic effects that can be measured (typically heat or acidity in biological systems) and then require the running system to provide the same signals. Thus you get a “heartbeat” and can shutdown any system that beats irregularly.

  2. Dr. Victor Pinks II Says:

    I concur with Trent Waddington, however, he doesn’t answer the core question – How do you “require the running system to provide the same signals” as the experimentally measured ones? If he told us that, then we could answer all of the open questions. What he is actually asking us to do is to solve the n-body problem in a quip. As a molecular dynamics coding author and paradigm developer with the theoretical training specific for, and fundamental understanding of this problem, I will add to his response. An inductive feedback mechanism from the real world to the model world (simulations) is the next critical step. All of the rest will fall in place if we have a way for the real world to correct the models in a manner that causes realism convergence and thus realistic behavior in simulation (yes, that includes realistic self-assembly). There is such a mechanism that has been successfully prototyped. In my opinion, if “experts” continue to sidestep the realism question the credibility of the nanotech promise will progressively erode.

  3. Accelerating Future » J. Storrs Hall’s Feynman Path Proposal to MNT Says:

    [...] studied and analyzed? 4. The Feynman path involves more than MEMS 5. Is it worth starting now? 6. Some of the Open Questions 7. Outline of the steps to make a Feynman Path roadmap. 8. An example of prior work which suggests [...]

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