From: Bathsheba Grossman (email@example.com)
Date: Thu Mar 24 2005 - 01:27:43 EET
On Wed, 23 Mar 2005, John Walmsley wrote:
> I agree that if a machine was building copies of itself, the
> accuracy could be a problem, but I think that most of the parts
> would be within a specified tolerance, since in theory more parts
> would fall within a bell-curve than at the ends, no? Therefore we
> should get mostly usable parts.
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.
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.
-- Bathsheba Grossman (831)429-8224 Sculpting geometry bathsheba.com
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