From: snodgras@crash.cts.com (John Snodgrass)
Newsgroups: sci.philosophy.tech
Subject: Re: nano-replicator assumptions
Date: 4 Sep 92 17:31:22 GMT

In <BILL.92Sep2120437@ca3.nsma.arizona.edu> bill@nsma.arizona.edu (Bill Skaggs) writes:



>Well, *I* can.  He gave a mathematical proof that a self-duplicating
>structure exists in the Game of Life (which is a finite-state
>automaton).  He proved it by showing how to construct one.  The
>structure he describes is very large.

      The Game of Life is a program which updates cells on the screen
based on the relations of a given cell to other cells. Even the notion
that certain conglomerations of cells in certain states are reasonably
called "entities" or "units" certainly debatable. (Endlessly,
I'm sure.) Such novelties can hardly be considered programs, nevermind
self-reproducing machines.

      Besides, all programs are ruled out: they
require a processor to function, which is not part of the
program. Programs in themselves are not equivalent to 3-D machines: they
are part of machines.

      If you want to talk computers, what we're looking for is a 3-D
model of a working machine -- a manufacturing plan. Nothing else will
do.

   >> Moreover, whatever the type of logic he utilizied, the only real
   >> proof would be to build one.

>No, Life is a mathematical structure, so the existence can be shown by
>a mathematical proof.

      It's only computer program. It's only a computer program.

>But this is mostly a historical curiosity nowadays.  The workings of
>DNA are now understood sufficiently to make it clear how
>self-replication can arise.

      The discoveries you are referring to deal with how
DNA is duplicated, and how information is read from
DNA and used to synthesize proteins etc. Not how the cell
reproduces. DNA represents stored data. In an informational sense,
data stored here may control many of the functions of the cell
(though probably less than you think), but it cannot actually
carry out these functions because it is only coded
information. This concept is very easy for computer scientists to
grasp, but apparently not for molecular biologists. DNA can no
more control the cell than a disk drive or memory chip
can control a computer. The cell must therefore have a great
deal of structure which has not been found and identified, equivalent
to the CPU and all the other hardware necessary to read, write, and
execute instructions in memory. But the difference with a computer is
that in the cell it is much more complicated, since the cell is not
doing it all with informational bits, but with physical structures.

      This was where we started on this thread. The question was, could
anyone justify self-reproducing machines without reverting to the argument
that "life does it, therefore a machine can do it". (This is the argument
used by nano-replicator enthusiasts.) The point of the discussion is
whether or not life IS a machine. But instead of getting directly into
that, the challenge was raised that, if life _is_ a machine, then
explain how a machine can be built which can do what life does.


>	-- Bill

      John E. Snodgrass
      -----------------
      snodgras@crash.cts.com
Newsgroups: sci.philosophy.tech