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From: fostel@eos.ncsu.edu (Gary Fostel)
Newsgroups: comp.ai.philosophy
Subject: Re: emergent properties
Message-ID: <1990Oct30.220248.20784@ncsuvx.ncsu.edu>
Date: 30 Oct 90 22:02:48 GMT
References: <1990Sep29.213139.2876@watdragon.waterloo.edu> <3499@media-lab.MEDIA.MIT.EDU> <1990Oct26.220658.11281@ncsuvx.ncsu.edu> <3841@media-lab.MEDIA.MIT.EDU>
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Reply-To: fostel@eos.ncsu.edu (Gary Fostel)
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In a previous note, I said:

   I was discussing the idea of emergence with a physicist recently and 
   something he said rings very true with this view of emergence.  He suggested
   that gravity might be considered an emergent property of collections of
   elementary particles.  In fact the "inexplicable emergent" property
   of gravity and the effort to make it more explicable has been a dominant
   influence on the direction of 20th century physics. 

To which Minsky, at MIT replied:

   Well, at least to first order -- that is, in Newtonian physics --
   gravity is a simple property of single particles; a simple
   inverse-square attractive force.  So there is nothing new when you
   have larger collections of particles - elementary or otherwise.  We
   usually use the term "irreducible" for such phenomena, rather than
   "emergent" because nothing new happens (once we have the superposition
   theory) with larger collections of particles.

The trouble with this dismissal of the "emergence" of gravity is that 
the dismissal is predicated upon a theory that has never been demonstrated.
I thought we were discussing observed properties of systems.  Unless I am
mistaken, there has never, ever, been a demonstration of the existence of
a gravitational field due to a single particle.  Not only is this far beyond
the sensitivity of current instrumentation, but in fact depending on the
theory of gravitation you like, it might not be true anyway. 

Minsky dismissed gravity as an emergent property of collections of 
particles by presuming a theory that may explain the  observations; that
seems to be a bit of a cheat.  As Minsky noted himself recently,
"emergence" is a three fold thing, involving the objects,
the observations, and the apriori understanding of the observer. 

There *are* new things that happen when there are collections of particles:
gravity can actually be observed, rather than theorized.  The emergent
property called gravity is fairly well understood, i.e. inverse square
laws etc, in a behavioral sense,  but just why it emerges remains an 
unsolved question -- or one might say "an inexplicable emergent".

My own low esteem for the term "emergent" is related to the sort of
trouble gravity caused: people may begin to think that descriptions
of behavior constitute an explanation of the behavior.  This is especially
true when the observer is quite similar to the objects being observed,
as will often be true in cognitive science or Artificial Intelligence.

----GaryFostel----                          Department of Computer Science
                                            North Carolina State University