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From: doom@PORTIA.STANFORD.EDU (Joseph Brenner)
Newsgroups: sci.nanotech
Subject: Barriers and Bottlenecks
Message-ID: <8904180627.AA19496@athos.rutgers.edu>
Date: 31 Mar 89 03:26:23 GMT
Sender: nanotech@aramis.rutgers.edu
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Approved: nanotech@aramis.rutgers.edu


We are people who have largely been convinced by Drexler's arguments.
I'd like to pose a question: What if we're wrong?  

Drexler typically argues:
(1) If life can do something, then it is physically possible
    to do the same thing artificially. 
(2) Human capability is quickly expanding to the limits of the 
    physically possible. 

I'm tentatively suggesting that point (2) may be wrong.  It's at least
conceivable that there could be a barrier we can't break, a human limit
that humans can't overcome.  For example, it *could* be that we're not
smart enough to write programs as smart as we are.  NOTE: I HAVE NO 
INTEREST IN DEFENDING THIS EXAMPLE.  I don't think this is a great
place to debate the feasibility of artificial intelligence. 

There is another way in which (2) could be wrong: there could be 
one or more bottlenecks to the development of nanotech which will 
slow things down radically (diamond is an unstable form of graphite,
but the transformation is so slow no one cares).  The future may
not be described by a smoothly rising curve: instead, imagine a
series of steep curves "punctuated" by plateaus.  

I propose that it may be worthwhile to try and identify possible
hard barriers or slow bottlenecks to various nanotech applications.

For example, consider genetic proofreading.  Drexler considers it a 
fairly simple process: each assembler meanders around until it finds 
a DNA strand.  It moves back and forth along it until it has the entire 
structure in memory. It compares the structure to the expected 
structure, and chooses to kill the cell if it differs (due to mutation or
infection).  There's an important caveat: the assembler must be able
to distinguish between the host's damaged cells, and the cells of
another human being (or any other plant or animal) otherwise it
would become a deadly virus if it escaped the host and wound up in
someone else's body.  Exactly how tough is this pattern recognition
job?  I don't think we know enough biology to say for sure. 
Note that this is a very simple application compared to a full-featured
cell repair machine. 

If there are problems in the development of atomic scale manipulation,
nanocomputers, self-replication, or a number of other areas it would be
devastating for the prospects of Drexler-style nanotech.  If you 
assume the problems do exist, what would they be like?

-- Joe Brenner 

(J.JBRENNER@MACBETH.STANFORD.EDU  Materials Science Dept/Stanford, CA 94306)