From: Forrest Bishop (forrestb@ix.netcom.com)
Date: Mon Dec 08 1997 - 19:40:42 MST
DOUG.BAILEY@EY.COM wrote:
>
>
> Has anyone (Drexler, et al) addressed Dr. Smalley's objection to the
> feasibility of MNT?
Yes, but the jury is (obviously) still out on this. Merkle and Smalley
had
a somewhat productive debate on this at Foresight 5, which I hear was
continued over dinner.
> His problem is with thermal resolution and can be found at
> http://cnst.rice.edu/NanoWelch.html
>
> I'd appreciate anyone's informed opinion on Dr. Smalley's assertions.
The crux of Smalley's argument:
"On a length scale of more than one nanometer, the mechanical robot
assembler metaphor envisioned by Drexler almost certainly will work,
but within the 1 nm3 volume surrounding the reaction site there
is a subtlety and complexity that is often not fully appreciated even
by practicing chemists. In any chemical reaction for all but the most
trivial of molecules, the detailed mechanism takes place on a potential
energy surface in an N-dimensional hyperspace, where N is of the order
of 10-30 (three dimensions for each atom in the near vicinity of the
reaction site). In order for a robot assembler to be completely
universal,
it would have to be able to control the detailed movement of not only
the
atom(s) to be added or removed, but also the detailed motion of all the
atoms within a few bond lengths of the reaction site. Unless the motion
of all the atoms is controlled in this reaction nanospace, there is no
way of insuring that only the desired reaction product is obtained.
Since
the manipulator "fingers" of the robot would have to be made of atoms as
well, there appears to be at least one fatal problem with the concept of
a universal assembler: there simply is not enough room inside the 1 nm3
reaction volume both for the atoms desired in the final structure and
the
atomic fingers necessary to control their movement."
In the very next section he talks about catalysis, which narrows this
search to essentially zero. Much current work is directed towards
mounting
catalysts on proximal probes.
Incidentally, Drexler doesn't particularly advocate a "Universal"
assembler,
Merkle and Smalley hashed through this at a panel at Foresight 5.
Smalley's latest objection is to the size of an assembler (leaving
"universal
out of it)- he thinks it would have a minimum volume on the order of 1
cm^3 to
do useful work. Though I think this estimate is wildly inaccurate, it is
also
pointless, in that the absolute size of an assembler doesn't matter.
What matters
is {number of atoms added to a structure per unit time}/{number of atoms
comprising
the assembler}.
Please don't construe this as an attack on Smalley- he is a wonderful
guy, does
top-flight work, wins prizes, etc. He's just not an engineer.
Forrest Bishop
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