Path: utzoo!attcan!uunet!jarthur!usc!zaphod.mps.ohio-state.edu!rpi!sci.ccny.cuny.edu!phri!marob!cowan
From: cowan@marob.masa.com (John Cowan)
Newsgroups: comp.ai
Subject: Re: Emergent properties (was: What AI is exactly)
Message-ID: <270363E7.15B1@marob.masa.com>
Date: 28 Sep 90 14:53:26 GMT
References: <15132@venera.isi.edu> <84118@tut.cis.ohio-state.edu> <1990Sep27.185805.21493@ncsuvx.ncsu.edu>
Organization: ESCC, New York City
Lines: 107

In article <1990Sep27.185805.21493@ncsuvx.ncsu.edu>,
	fostel@eos.ncsu.edu (Gary Fostel) writes:
>
>  Some of the recent posts have criticised the term "emergent property"
>  as a euphamism for "we don't understand" and some have defended the
>  term by examples of the application of the term and some have tried
>  to justify the term as a valid one more abstractly.

I'm not sure which camp I fall into, as I gave both an abstract definition
and a concrete example (aqua regia).

>  If I assemble a device from wheels, pedals, metal tubes and such,
>  and it happens to become the most efficient transportation device
>  around, is that an emergent property of the parts?

Not exactly.  It is an emergent property of the whole transportation system,
because "most efficient ... around" is a notion that depends critically
on what else is around.  You certainly cannot (on the explanatory level of
common understanding) point to any part of the transportation system and say
"This part makes bicycles the most efficient".  You can only do that on
the explanatory levels of mechanics + thermodynamics.

>  I doubt that
>  defenders of the term would like it to be so.  But why not?  Probably
>  because the transportation property was a goal of the design process
>  that controlled the assembly.  Now suppose a Venusian engineer viewed
>  this as a process of putting wheels, metals tubes, pedals, and an
>  engineer, and a few tools, in a room.  These "parts" may well have
>  an emergent property, from the perspective of the Venusian, since
>  they had no expectation of a transportation function arising from
>  the collection of parts.  (Yes the engineer is a part in this view.)
>  I identify this as an emergent property because I believe it would
>  satisfy most of the ad hoc definitions I have heard.  

I agree.  On the explanatory level of the Cytherean ("Venusian" is a barbarism,
on all fours with "Marsian", "Earthian", or "Jupiterian"), who does not
recognize the human engineer as a purposeful system.  Again, the concept
"emergent property" makes no sense without reference to a level of explanation.

>  I do not expect most supporters of the "emergent property" term to
>  like this use of the term.  They will not like it (I am guessing of
>  course) becuase they will feel that they can identify the source
>  of the property which has emerged ... but of course the Venusian,
>  having utmost contempt for the large water based carbon compound in
>  with the metal parts, will not be able to identify the source and
>  the "emergence" is viewed from that creatures perspective.

Right.

>  A second example: if you put large pine forrests, rabbits and foxes
>  together in northern Canada, you will get a 10 year cycle of boom
>  and bust in the populations of rabbits, foxes and young pine trees.
>  (Rabbits LOVE to eat pine needles, far more than carrots.)  Is this
>  pattern an emergent property?  From the perspective of a naive and
>  innumerate individual, the answer is certainly yes.  The cycle is
>  there, it was not predicable (by them) and it is not easy to 
>  identify the source in myopic analysis of rabbits, foxes, or pines.
>  From the perspective of an ecologist or someone versed in simple
>  dynamical systems theory, it is not an emergent property.  It can
>  be predicted, modeled, and well explained, based on properties of
>  the constituent elements, e.g. kilocalories needed, supplied, 
>  gestation period, etc.

Exactly.  This fits in with my original statement about aqua regia.  At the
level of commonplace understanding of mixtures, "aqua regia dissolves gold"
is an emergent property.  At the same level, OTOH, "salt water dissolves
sugar" is a resultant (non-emergent) property, because it depends on the
minor premise "water dissolves sugar" and the major premise "the properties
of mixtures are a mixture of the properties of the things mixed".

At the level of acid-base chemistry, to say nothing of more detailed levels
(quantum mechanics, e.g.) this property of aqua regia is resultant, because
there is a complete explanation at the component level.

In your example, the corresponding levels of explanation are "naive" and
"dynamical systems theory".

Consider Hofstadter's joke about how to fix the timesharing system that
works fine with 35 on-line users but starts thrashing with more:  poke
around in the kernel, find the "35" and change it to a "60"!
That this procedure does not work is evidence that the number 35 is an
emergent property; it cannot be explained at the level of "kernel tuning
parameters".

OTOH, at the level of "tuning parameters" you can fix such superficially
analogous problems as "this system provides 20 files per process fine, but
chokes when 21 are required".  In this case, we really do just need to
change the 20 to a 21 (and recompile the kernel).

This obviously does NOT mean that there is no explanation at ANY level of 
why 35 is the simultaneous user limit.  It simply means that AT THE SPECIFIED
LEVEL OF EXPLANATION, we don't know why.  So you are correct that "emergent
property" states a negative, but the negative is by no means absolute.
Someone who understands the kernel time-slicing algorithms, the speed of the
disk drives, the details of the various simultaneous jobs, etc. etc. will
come up with a very good understanding -- perhaps even an analytic model --
that predicts the onset of thrashing.  It's just that that kind of information
is hard to gather and harder to validate.

Most precisely, the claim that "P is an emergent property" states a limitation
on the power of a given explanatory framework, to wit: it cannot account for
P.  Whether one looks for a more powerful framework, shrugs and accepts the
unexplained fact, or just buys a faster disk drive depends on one's purposes,
a matter outside the scope of this discussion.
-- 
cowan@marob.masa.com			(aka ...!hombre!marob!cowan)
			e'osai ko sarji la lojban