From: Peter C. McCluskey (pcm@rahul.net)
Date: Thu Nov 28 2002 - 23:20:14 MST
mez@apexnano.com (Ramez Naam) writes:
>2) Assemblers make and break chemical bonds. From a molecular
>modeling standpoint, this automatically forces you to use more
>expensive simulation methods, as the cheapest methods simply do not
>handle the breaking or formation of chemical bonds. In addition, a
>chemical interaction at one end of the assembler may end up having
>surprising effects on previously "isolated" subsystems. How does a
>subsystem react when the assembler a whole temporarily picks up or
>loses an electrical charge, for example?
For pure diamondoid systems, people who try to model this plan to
mainly use the Brenner Potential, which scales up pretty well (I don't
know much about its accuracy). Extending this to handle many atom types
sounds pretty hard, but my impression is that it will get done if
enough money depends on it.
There will be some use of quantum-level modeling of very small subsets
of the system to improve on that modeling - there probably won't be very
many places in an assembler where the bonds are made and broken.
Yes, there will still be some surprises due to long-range interactions
not accurately modeled by the Brenner Potential - so what?
I think you underestimate what can be accomplished via trial and error,
and how valuable an assembler can be if it can only make a handfull of
bond types.
>3) Perhaps most problematically, in at least some proposals assemblers
>reproduce. This gets into an additional level of modeling and
>simulation which I haven't even mentioned up to this point.
>Essentially you start dealing with population biology, an area where
>modeling is now being applied but where our ability to predict exact
>outcomes is essentially zero.
Population biology? Computer virus designers frequently accomplish
what they want without thinking about population biology. They rarely
make a virus that infects an OS it wasn't designed to infect, and
assembler designers will probably only make their system work on
one or two specialized feedtstocks for much the same reasons.
>I agree. At the same time I think this has risks (you're doing trial
>and error experimentation with replicators) and limits our ability to
>directly control and program our creations.
>
>Finally, this approach undermines the goals of Foresight. If the goal
>is to understand what it may be possible to create before we actually
>gain the ability to create such things, then modeling and simulation
>are crucial. As far as I can see, our modeling and simulation
>capabilities will not be up to the task for quite a long time to come.
We can make many important predictions without a precise enough design
for molecular modeling to be relevant, such as whether a large class of
designs can reproduce in the wild, what legal restrictions would be good,
and how assemblers will affect military power. Or maybe we won't be able
to make predictions because the designs that matter will be kept secret.
If you think that Foresight expects to predict many things that require
molecular simulations, you've probably overestimated Foresight's goals.
-- ------------------------------------------------------------------------------ Peter McCluskey | Free Jon Johansen! http://www.rahul.net/pcm |
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