Brownian control -Reply

[Hans Blom, 960214]

(Rick Marken (960212.0810))

What do we have here, "control" or simply the result of a
combination of some laws of physics? Both, I would say.

I would say it's pretty unlikely that there is any control at all
going on here. But you have to do The Test correctly in order to
find out. If you've got this set up as a computer simulation just
add a continuous disturbance to the positions of the particles and
see what happens; I bet that the disturbance will be completely

Let me see whether I understand you. I did The Test in that I picked
up the particle, put it somewhere else, and then let it go again. It
returned to where it seemed to "want" to go again, if I may use those
words -- i.e. it resumed climbing the gradient.

You propose a continuous disturbance. Disturb what? How? Picking up
the particle and keeping it between my fingers (or miniature
tweezers) will not do, of course; I'm much too strong. But I could
measure the force with which it tried to escape, and the direction of
that force. I could also put some iron into the particle and apply a
continuous random magnetic field. Is that similar to what you have in
mind? I could also tie the particle to a piece of string and observe
the direction in which the particle strains to move. What do you
think? What kind of disturbance to apply?

I guess that even without formally performing such a Test, you would
know the answer already -- since you are familiar with the underlying
mechanics: in all cases, the particle will still try to climb the
gradient, in addition to being subject to some externally applied

_We_ don't call this control unless there is continuous resistance
to disturbance to a variable.

Why do you stress _continuous_ disturbance so much? Wouldn't a perio-
dical disturbance -- regularly picking up the particle, putting it
somewhere else, and letting it go again -- be equivalent?

I'm not sure this answer will satisfy you ;-).

It satisfies me because it helps me understand why you have been
unable to understand or accept PCT after all these years. Control is
a very clear and real phenomenon; it is only superficially similar
to stability phenomena like the one you described.

I love to investigate what some others call superficialities ;-).

Why study a theory of control if the phenomenon that the theory
explains (control) is meaningless (ie. non-existent; a word has
meaning if it refers to something; apparently the word "control"
refers to nothing, from your point of view)?

Oh no. Control _does_ refer to something -- to a range of phenomena
that have to do with stabilization in the face of disturbances --
homeostasis. But, like all words that humans have invented to refer
to something in the world, the term is not quite clear-cut. Blame it
to an aberration of mine, but I like to investigate fuzzy boundaries.
Sometimes something can very clearly be called control, and sometimes
the word control isn't applicable at all. But once in a while I
encounter situations where I have trouble classifying something as
control or no control. To me, those are the fascinating cases.

That has to do with the question of how the kind of control that
living organisms are capable of arose in the first place, out of the
physical interactions of dead matter. That was, maybe unclear to you,
what I was investigating.



[Hans Blom, 960214d]

(Martin Taylor 960213 12:30)

Hey, Martin, I feel really understood! Not that I'm much controlling
for that (I think), but when it happens it's nice nevertheless!

Now let's see whether Hans's particle is even closer to being a
control system. ... So, it would be quite easy to see the system as
a control system with a fixed reference level, the controlled
perception being of chemical concentration, the output gain being
represented by the change in bulk as a function of the change in

"Quite easy to see as", that's indeed what I tried to point out.

Incidentally, if, as you suggest, you used "f=ma" to compute the
expected movement of the pendulum, you would come to the definite
conclusion that "there must be something actively opposing that
force", and according to you there must be an external power source.
This simple illustration suggests how critical the correct _a prior_
model is, if you want to use the "expected deviation" criterion for
determining whether something is being influenced by a control

You very rightly point out that The Test cannot be more than a check
of some fully thought out hypothesis. One needs to fully know the
implications of the hypothetical law in the comparison between "what
do we see" and "what would we see if there were no control". The
latter is a purely hypothesis-driven theoretical thought experiment.
In particular, The Test is _not_ a vehicle for the _generation_ of