From Bob Clark (931217.1720 EST)

Cliff Joslyn (931215.06:13 pm EST)

Do vortices involve negative feedback?


Are vortices control systems?


Is their stability the result of attraction or control?


"Stability" has been suggested as an indicator of the presence of a
negative feedback control system. In many situations, such systems
are "stable," but not necessarily so.

A system is said to be "stable" if the disturbed variable tends to
return to its previous condition after the disturbance ceases. In
more formal terms: The magnitude of the perceived variable returns to
its previous value.

Its stability is "neutral" if it simply continues in accordance with
the effects of the disturbance, even though the disturbance has

It is "unstable" if the system acts to further increase the effects
of the disturbance, rather than opposing them.

In some cases, especially those that are unfamiliar, such as
"vortex," the concept of "momentum" (and, likewise, "angular
momentum") suggests some kind of "stability." But this usage does not
come from the language of physics.

Linear Momentum
A stone sliding on a surface continues on its way as long as long as
no disturbing forces are applied. If there are any such forces, we
have: f = ma, with a related transfer of energy. The same is true of
a thrown ball, a ballistic missile. The forces could be due to
friction, collision with another object, etc. In the event of a
collision (ignoring friction), both momentum and energy are conserved.

Angular Momentum
Vortices are treated in terms of rotational motion rather than linear
motion. The concepts of momentum and energy apply directly, being
expressed in polar or spherical coordinates rather than Cartesian..
A vortex is a collection of very small balls, each subject to the
same forces, circulating in stable orbits. The ball-in-a-bowl is
more familiar. It continues in its orbit as long as there is no
disturbance. The orbit can be changed, in any direction, in
accordance with the forces arising from a disturbance. It does not
return to its previous condition. It follows a new orbit. In the
absence of any other disturbance, it remains subject to friction,
slowing down and coming to rest at the bottom of the bowl.

As Bill points out [Bill Powers (931214.1445 MST)], the concept of
"attractor" is a metaphor. It implies the existence of some
"attractive entity." This idea may come from the mathematical concept
of a "central force." If such a force exists, it can be used to
calculate the motion resulting from its combination with other
forces, subject to the mathematics of energy, momentum, etc.
Introducing the concept of an "attractor" is a distraction at best --
a disturbance to those trying to learn and apply the methods and
concepts of physics.

Language of Physical Science
This is a special language developed by people for discussion and
prediction of the actions and reactions of material entities. It
really works quite well for those purposes.

Language of PCT
PCT is concerned with the structure of several levels of perception.
This leads to development of the specialized language needed to
communicate with other people on that subject. Physical science is
concerned only with the material world -- irrespective of the
"purposes" and "intentions" of the people using the concepts.

I hope this is helpful.

Regards, Bob Clark