From: Adrian Bowyer (A.Bowyer@bath.ac.uk)
Date: Thu Mar 24 2005 - 14:24:33 EET
Bathsheba Grossman wrote:
> That's not exactly my experience of how tolerance failures tend to
> work; I doubt it's a general principle that they fall on a bell curve.
> If they did, a complex part might have 20 dimensions, and if one of
> them happens to be right, you'd still rolling the dice on the other
> I'd bet a dollar that the author of that paper has never operated a
> milling machine. A vertical mill with all the trimmings is the
> closest thing I can think of to a large-scale self-replicating
> machine, and think about what would happen if you took a Harbor
> Freight mill and tried to make another one.
Not only do I operate one, I own one. It's in my workshop at home.
In all this talk of accuracy, remember this: people have been making objects
accurate to within the wavelength of light since medieval times using nothing
fancier than a knife edge and a candle...
> There are only a few types of self-replicating machine in the known
> universe, all biomolecular: DNA-based life, RNA-based machines
> contingent on the "RNA world" hypothesis proving out, and parasitic
> prions if the "protein-only" hypothesis is true.
> If I were building such a machine, I'd be looking very hard at the way
> analog and digital mechanisms interact in those systems. There's an
> entropic principle that has to be overcome, and the way DNA does it is
> an awesome hack; any other such machine would have to be built around
> an equally awesome hack. DNA relies on the uniform nature of
> elementary particles, and therefore its existence may not imply a
> useful model for larger scales. If this problem did turn out to be
> soluble on the macro scale, that would have consequences far beyond
> having cheap SLA in every household.
Hmmm. Doesn't human engineering as a whole also constitute a self-replicating
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