[From Tom Bourbon (950902.0115)]
Bruce Abbott [From Bruce Abbott (950901.1045 EST)], replied to my post (Tom
Bourbon [950831.1858]), about particles, physicists, fish and gods. (Who
says PCTers have narrow interests?) Bruce said that, in the physicists'
"model" for aligned movement in masses of particles,
there is no need to assume that the physicists were implicitly positing
some kind of God-of-the-Computer to explain the behavior of their
particles.
I used the metaphor of a god-in-the-computer as a way to show that the
physicists applied their "simple behavioral rule" in the form of an
irresistible external force that controlled the actions of each modeled
particle.
In their article, the physicists say the particles engage in "biologically
motivated interaction," but there is nothing, nada, in their model to
represent anything that resembles "biological motivation." They wrote the
model. In it, they did not include one term, function, operation, or
signal, that in any way represents a "biological motivation." When they
run their model, there are plenty of interactions, but not one motivation,
aside from their own.
Instead of motivations, an external "force" dictates changes in the
directions of movement of their particles. The force is in the form of a
single rule: "The only rule of the model is at each time step a given
particle driven with a constant absolute velocity assumes the average
direction of motion of the particles in its neighborhood or radius r with
some random perturbation added." The rule _assures_ that, after a
sufficient number of computational steps, each particle will be moving in
the same direction as its nearest neighbors, and if the density of
particles is great enough, all, or nearly all, of them will be moving in
one direction. The rule guarantees it; the particles do nothing but exist
as points, acted upon by a controlling force outside themselves -- by a
god-like rule.
I believe an important point is involved here, one that it easily
overlooked. The physicists' rule is a surrogate for them. When their
program runs, it (the program) applies the rule in a way that makes the
rule a stand-in for the physicists. It is as though, on every program step
(time interval), they look at each particle, one at a time, and for each
one they calculate the average direction of movement of all other particles
within radius r of the particle. Then they arbitrarily align the direction
of movement of each particle with the average direction of movement of its
immediate neighbors, within radius r.
Why do they use that rule? Why do they arbitrarily make each particle move
in the same direction as its neighbors? Because they want to see particles
moving in the same direction as their neighbors, and they will keep
tinkering with the direction of each individual particle until they (the
physicists) see particles moving in the same direction. The physicists, in
the guise of their rule, are controlling their own perceptions. They have
observed, or read about, phenomena involving large assemblages of objects
of various kinds and sizes (particles, molecules, bacteria, birds, fish,
automobiles in traffic, etc.), in which the objects "tend" to move in the
same direction. They started with phenomena observed in nature, and they
wanted to reproduce certain features of those observations in simulation;
they wanted to see large numbers of simulated particles go from a state in
which their directions of movement varied in a random manner, to a state in
which they moved in the same direction. They succeeded.
Concerning their success, in so far as it might be useful in the study of
living control systems, I say, "so what?" Bruce says,
What I _was_ trying to communicate (apparently not very well) is that a
group of autonomous control systems might in fact behave (under the right
conditions) in precisely the way that the physicists' model describes,
because at the right level of abstraction, such "particles" would interact
in much the same way that ferromagnetic atoms interact, though for very
different reasons.
Bill [From Bill Powers (950901.1430 MDT)] and Rick [From Rick Marken
(950901.1400)] have already replied to that line of discussion from Bruce.
I share their conclusions, to the effect that any resemblance between the
movements of iron filings influenced by a magnetic field, and the movements
of automobiles, with drivers inside, in traffic are spurious and trivial.
I will not argue that what the physicists did is useless in physics, where,
apparently, purely descriptive models (curve-fitting models) can play an
important role. However, I doubt their idea that the ferromagnetic model
might have, "possible applications in a wide range of biological systems
involving clustering and migration." Concerning living things, their model
could apply only at the most superficial level of description. From my
biased peerspective, to applying their model to living systems would be
akin to saying: We observe organisms moving in the same directions as
their neighbors (for reasons we do not know and about which we do not
care); we have a model in which a simple rule unfailingly assures that
simulated particles move in the same directions as their neighbors, much as
iron filings would do when exposed to a magnetic field; ergo, our model
applies to coordination and cooperation between living things. I don't
think so.
Later,
Tom