From: ghsvax!hal@uunet.uu.net (Hal Finney)
Newsgroups: sci.nanotech
Subject: Some questions re "Nanosystems".
Date: 18 Dec 92 01:26:16 GMT

Here are a few responses to the points raised by Hudson Hayes Luce on
the WELL, quoted in Robert M. Solovay's posting.

  For starters, let's look at p259, figs. 9.2a-e. Drexler terms these structures
  "diamondoid" and ascribes the properties of diamond to them.
  [...] 
  However, in structure 9.2c, there are fused 3- and 4-membered rings, which
  have bond angles of 60 degrees and 90 degrees, respectively, and whose
  C-C-C-C dihedral angles, in some cases, are 0 degrees. This structure is
  highly strained due to bond angle deformation and non-bonded steric
  interactions. Compound 9.2c can thus be assumed to be highly unstable
  at room temperatures, and is probably subject to thermodynamically-
  driven rearrangement.

Drexler's figure 9.2 is not claimed to consist entirely of
"diamondoid" structures.  9.2a, for example, is polyethylene, and has
no rings at all.  The caption explicitly says "The structure of rod
[9.2c] departs from the diamond pattern...".

Drexler does not appear to discuss bond strain in the specific design
of figure 9.2c.  He does discuss it in the context of other
similar designs, such as in figure 9.5 and 9.6, so presumably he is
aware of the issue.  I don't think he is claiming that his book
represents the last word on any of these designs, and more detailed
analysis is certainly appropriate.

  On p265 Drexler states "acquiring and processing molecules from solution.."
  in reference to a possible use of nanosystems, but on p5 he states that "The
  operating environment assumed for the nanomechanical and mechano-
  synthetic systems discussed in Part II is high vacuum"
 
  Describe a high-vacuum/solvent interface.

The p265 quote goes on to reference section 13.2.  There Drexler
discusses this issue in detail.  In that section, see Figure 13.5,
p384, for a diagram of a high-vacuum/fluid interface.  Also see
section 11.4 for a discussion of fluids, seals, and pumps.

  On p 196 it is stated, "In solution-phase chemistry, when molecular potential
  energy is transformed into mechanical energy, this promptly appears as heat
  Reactions that reduce potential energy are accordingly termed exothermic,
  those that increase it, endothermic. In mechanochemical systems, however,
  potential energy released by a reaction can often be stored elsewhere in the
  mechanical system, either as potential energy or as kinetic energy in the form
  of orderly motion"
  [...]
  Analyse Drexler's statement in light of the 2nd Law of Thermodynamics. If this
  statement is true, perpetual motion is possible.

There are different kinds of perpetual motion machines.  Some are said
to produce energy spontaneously.  I think here we are instead talking
about the kind that simply consume no energy but continue to run
forever - basically, zero-friction machines.  The 2nd Law says that
zero friction is impossible.

I think it is a serious misreading of Drexler to say that he is
claiming that nanotech will allow such machines to exist.  Instead, he
is simply saying that with nanotech we will have more opportunities to
capture energy which is dissipated in normal chemical reactions.

He goes to great length in the book to analyze friction and energy
dissipation.  Much of chapter 10 is devoted to this analysis.  It's
clear that Drexler is not proposing perpetual motion machines.

Hal Finney
hal@ghs.com