Philip, I’ve been thinking about your comment on simple models giving rise to rich dynamic behavior. I think that we were actually referring to the same kind of system, though I may have used the wrong language to do it. If I can select values for three analog parameters and get a wide range of structures in five distinct families (e.g. diblock copolymers), then we could say that the variables are a handful and the physical model/computation/behavior is simple. But we could also say that the relationship between inputs and outputs is, maybe not mathematically complex, but certainly non-obvious.

I suspect that familiarity with this kind of nanoscale system, in which “simple computational models (e.g. the Ising model) can give rise to complicated and rich dynamic behaviour” is what makes some scientists say the molecular manufacturing approach is “too mechanistic” or “too simplistic,” and then start looking for the complexity they assume we’re trying to sweep under the rug.

But there may be a deeper point. If the system’s behavior is accurately described by analog values and continuous equations, doesn’t that imply that it must involve relatively large numbers of atoms? And if there are far more atoms (more precisely, far more degrees of freedom) than can be directly specified by the precision of the input variables, doesn’t that imply that the output probably isn’t atom-precise? An exception could be if the atoms self-organize according to strong forces like ionic crystallization (e.g. salt crystals), but can that be compatible with rich dynamic behavior in self-assembly?

To relate this to the Ideas Factory’s purpose: Are there classes of analog-behaving system that, while they form interesting nanoscale structures, can be excluded from consideration as goals and/or methods because their analog nature must preclude atom-precision?



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