# Vortices are not control systems: the reason

**URL:** <http://discourse.iapct.org/t/vortices-are-not-control-systems-the-reason/12144>\
**Category:** CSG1993\
**Created:** [December 20, 1993, 4:33am UTC](http://discourse.iapct.org/t/vortices-are-not-control-systems-the-reason/12144 "1993-12-20T04:33:52Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![William\_T\_Powers2](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/w/c67d28/32.png) [@William\_T\_Powers2](http://discourse.iapct.org/u/William_T_Powers2)\
**Post date:** [December 20, 1993, 4:33am UTC](http://discourse.iapct.org/t/vortices-are-not-control-systems-the-reason/12144/1 "1993-12-20T04:33:52Z")

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[From Bill Powers (931219.1830 MST)]

Martin Taylor (931219.1730) --

> I apologize in advance for continuing this irrelevant thread on  
> vortices, but several posters have asked me to do so. I'd  
> prefer to get on with talking about real PCT.

It's not an irrelevant thread if there really is a difference  
between control systems and vortices that is not just a matter of  
a variable reference signal. I am still convinced that there is a  
difference, and that therefore control theory is not continuous  
with the "dynamical systems" approach to attractors etc.. Your  
well-organized post on vortices, for which thanks, may get us  
closer to settling this question, which is an important one. I  
think I may now have the means of saying what I've been trying to  
get across with "unidirectionality" and other less-than-clear  
arguments.

> We all agree that vortices and other self-organized structures  
> have no purpose. As such, they are not PERCEPTUAL control  
> systems.

We can't agree on this, because if vortices and such are control  
systems, they are purposive. The existence of a reference input  
is irrelevant to my concept of purpose, because even if there is  
such an input, the signal entering it can be zero. That case is  
indistinguishable from the case in which the reference input is  
missing. If the closed-loop organization is not sufficient to  
define purpose, then neither is a reference signal, because a  
reference signal means nothing without the closed loop.

The problem with treating a vortex or any similar system as a  
negative feedback system, I have finally realized, is that you  
can't separate the forward path from the feedback path. These  
paths are not physically distinct, even though you might be able  
to manipulate the equations to give the appearance of distinct  
paths. The so-called feedback effects are simply the inverse of  
the forward effects; you are separating action and reaction, but  
only through the artifice of mathematics (using superposition to  
treat the two paths as if they were independent). In fact, the  
"reaction" is identical with the "action," and separating them is  
a conceptual mistake -- unless they are in fact physically, not  
just conceptually, separate as they are in all true control  
systems.

Using this artificial separation of paths, you can treat a simple  
spring as a negative feedback system. When you disturb the  
position of one end of the spring (with the other end anchored),  
you apply a certain force. The spring quickly comes to a state in  
which it is applying a precisely equal and opposite force at the  
same point, so the net force becomes zero. The reaction force  
could be imagined to be a negative feedback phenomenon. The  
deviation of the end of the spring from its undisturbed state  
gives a measure of the loop gain: if k is the spring constant in  
stretch per unit force, then the loop gain is, by inference,  
approximately 1/k. The greater the stretch, the lower the loop  
gain.

But a spring is not a negative feedback system. Or do you say  
that it is one?

Or consider another case, a bucket with a hole in it, being  
supplied with water from a running spigot. The forward path  
consists of the incoming water, which increases the height of  
water in the bucket at a certain rate. The feedback path consists  
of the fact that as the height of the water increases, the  
outflow through the hole increases, reducing the rate at which  
the height of the water increases. This outflow effect tends to  
offset the inflow effect and bring the height of the water to a  
specific level. If you scoop out a little water, the water level  
will decrease, but will increase again to the original level; if  
you add a scoop of water, the water level will increase and then  
decrease again to the original level. You can show that there is  
an incoming flow of energy and an outgoing flow of energy, and  
that the correction process is powered by that energy.

But the bucket with a hole in it is not a negative feedback  
system. Or do you say that it is one?

My judgment in each case is justified by the fact that the  
forward and so-called feedback paths are one and the same path.  
The outflow in the bucket is produced by the inflow, not by a  
separate path that detects water height and independently acts to  
adjust the outflow. The reaction force in the spring is  
identically the applied force; the applied force, which stretches  
the spring, also creates the reaction force. In neither case is  
there a separate feedback path.

If the state of motion of the vortex were truly a controlled  
variable in a control system, then increasing the head of the  
water in the bathtub would have no effect on the vortex. In the  
bucket example, increasing or decreasing the inflow rate would  
have no effect on the final water level. In the spring example,  
applying a force to the end of the spring would have no effect on  
the final length of the spring. That is how you can tell that a  
control system is present: the physical system does not respond  
normally to changes in energy or force inputs. It comes close to  
not responding to them at all.

A physicist presented with these claims would object that each  
one is impossible. That is precisely the point. A control system  
creates impossible relationships among the variables familiar to  
the physicist. And when it is explained how each control system  
would work, the physicist would object that we are cheating. The  
vortex's spin rate could be made independent of the head if we  
simply stirred with our fingers in the direction and by the  
amount needed to keep the spin rate constant. The water level in  
the bucket would remain constant despite changes in the inflow if  
we manipulated a faucet inserted at the hole in the bottom, in  
the way needed to counteract changes in the inflow. The length of  
the spring would remain constant if we pulled on its end through  
another spring, in the appropriate direction and by the amount  
needed to keep the end from moving, while the disturbing force  
was applied.

Control systCSG-L@UIUCVMD.BITNET  
Status: O

[Martin Taylor 931005 14:00]  
(Hal Pepinsky Tue, 5 Oct 1993 12:41:55)

Sorry if I used "referent". It should read "reference" or "reference  
signal" or "reference level" depending on the context.

> do you see my point  
> about the importance of modeling two or more actors' control in  
> relation to one another?

Absolutely. That's been more or less the focus of my work for the last  
10 or 12 years, both before and after learning about PCT. That's ems work by using a feedback path that does not enter  
significantly into the energetics of the output process, and that  
is physically distinct from the output process. In a vortex, the  
forces that restore the vortex to its equilbrium state after a  
perturbation arise from the perturbation itself. The forces  
downstream subtract from or add to the upstream forces to create  
the final effect; they are part of the reaction forces, not  
separately generated forces. The vortex is simply a complex  
version of the bucket with the hole in it, complex enough to make  
the reasoning more difficult and the relationship between action  
and reaction harder to work out. But only normal physics is  
involved; only action and reaction, two ways of looking at a  
single relationship.

Control systems create abnormal physics. The four major classes  
of amplifiers (vacuum tubes, transistors, neurons, and enzymes)  
create a strong assymetry, preventing actions from producing  
equal and opposite reactions directly against their causes.  
Disturbing the output of a unity-gain amplifier has no  
the output of a unity-gain amplifier has no  
Status: RO

significant effect on the input of the amplifier. This allows the  
effect of an action to alter the action without reflecting  
directly against it; the opposing effect arises through a  
physically different pathway in which actions produce effects  
without reactions.

This is the difference between all equilibrium systems and all  
negative feedback control systems -- all purposive systems.

> **···**
>
> Subject: Re: Hal to Martin  
> ---------------------------------------------------------------  
> Best,
> 
> Bill P.