[From Bruce Abbott (951121.2105 EST)]
Bill Powers (951121.1240 MST) --
Gravitation _is_ an empirical
observation. Newton hypothesized no cause; only Einstein has ever
proposed one (distortion of space).
You seem to have missed one. One line of thinking current in physics says
that the appearance of forces "acting at a distance" is mediated by an
exchange of subatomic particles between the interacting bodies. Different
particles mediate different forces in this scheme; I believe the one for
gravity is the "graviton."
What Newton proposed was a _model_ that accounted for the phenomenon of
gravitation. He said that each particle of matter is subject to an
apparent force in the direction of each other particle in the universe
in the way described by his formula. By summing all the calculated
forces between each particle of one object and each particle of another
object, the net force could be computed; This computed force could then
be compared with the actual force necessary to maintain a planet in its
observed orbit, or to make an object accelerate downward toward the
center of the Earth (in a vacuum).
This merely follows from the observations. If every object attracts every
other object according to its mass and inversely with the square of its
distance, then if you divide an object into two equal masses, each will
attract the other (at a given distance) with a force half that of the
original mass. Keep applying this division until you get to the "particle"
level and you have the pull exerted by each particle. The hard part, which
Newton achieved, was to develop the mathematics that would allow one to
derive the observed gravitational attraction from the sum of the pulls of
the individual particles. From this one could show, for example, that the
gravitational pull of a spherical mass could be represented as if
originating from a point at its center (if I recall correctly). But what
does this add to the empirical observation that g = m/d2? Only that this
law applies all the way down to the level of particles. It still doesn't
explain why the law holds; it does not derive the law from more fundamental
principles.
The difference between Newton and the reinforcement theorists is that
Newton proposed a model from which gravitation could be deduced, while
the reinforcement theorists did not proposed a model from which
reinforcement could be deduced. Newton's law is not a generalization
from observations: it is a leap of the imagination that goes beyond what
anyone had been able to observe, and indeed contradicts all earthly
measurements made in an atmosphere.
Now you are claiming that Newton proposed a model from which gravitation
could be deduced, which is clearly wrong. He proposed a way to apply the
empirical law to get the gravitational effect of objects composed of
nonuniformly distributed masses. This is hardly a method for "deducing"
gravitational attraction from first principles. It remains an effect of
unknown origin.
The reinforcement theorists remained at the level of gross observation,
not positing any underlying organization of which reinforcement is the
observable consequence.
And Newton did not posit any underlying organization of which gravitational
attraction is the observable consequence. What it comes down to is this:
for Newton, gravitational attraction is a property of objects with mass.
Why this is so, he had no idea. Not a clue. He said so.
Furthermore, reinforcement theorists did what
Newton refused to do: they proposed a cause of the phenomenon of
reinforcement, a cause which is seen in the term "reinforcer." The name
of the process has become a noun; one variable involved in the process
has become an agency, just as the Earth becomes an agency when it is
said to "attract" objects to itself.
Newton wasn't faced with the problem of differentiating objects for which
gravitational attraction was an observable fact from other massive objects
not subject to gravitational attraction. It's not so much that Newton
"refused" to do so as that he had no need to. Psychologists, on the other
hand, had to deal with the fact that some objects under some conditions
could serve to reinforce the responses they followed, whereas others could
not. The hungry rat would work for food but not for BBs. The same problem
was encountered by physicists, who found some materials that seem to produce
an attractive force on certain metal objects. The force was called
"magnetic attraction" and the objects doing the attracting were labeled
"magnets."
The parallel between "reinforcer" and "magnet" is quite good, although I
will grant you that for the parallel to be direct, we would have to call
material attracted to magnets "magnets" rather than the magnets themselves.
Perhaps the better equivalent is between reinforcer and "ferromagnetic
material." Dispite your assertions to the contrary, reinforcement theorists
have always been fully aware that the attractiveness of the reinforcer
resides, not in the "reinforcer," but in the relationship between the
properties of the reinforcer and the effects of those properties on the
organism as mediated by the organism's senses.
Newton would have been in exactly the same fix if he had used the same
empirical approach. By studying the way objects fly through the air and
fall to earth, he, too, would have come up with a bewildering complexity
of relationships involving such factors as composition, weight, shape,
orientation, moving parts, wind velocity, air temperature, extra-
experimental sources of force, delayed effects, collisions, and so on.
This is the state in which the science of ballistics was _before_
Newton.
Yes, I recognize that fact; this is not the source of our dispute. To make
progress, Newton had to arrive at conception of the underlying organization
that differed in important ways from the empirically-derived laws _of
motion_. (The law of universal gravitation could be very well approximated
with the right equipment, so I exempt it from this statement.) Newton
conjectured that the empirically-established slowing of objects in motion
must result from external forces acting on the objects to dissipate their
energy. The steady loss of motion shown by ordinary objects had been
misconstrued (by Aristotle) to mean that their energy (impetus) is somehow
"used up" by their mere motion; Newton's genius lay in his ability to see a
different explanation beneath the surface phenomenon. The question is, how
did Newton reach this conception? Certainly he had access to lots of good
information to help him with his thinking, such as Galileo's data on the
motions of marbles down an inclined plain, and Kepler's empirical laws of
planetary motion. Reinforcement theorists were not in the same position.
If reinforcement theorists failed to achieve results comparable to
Newton's, it was not because they failed to adopt his approach.
Newton was a modeler. Reinforcement theorists are not. To me, that makes
their approaches completely different.
But this takes us away from my original argument. When I said that
reinforcement theorists were following Newton's approach, I was specifically
talking about his use of gravitational attraction as an empirical law which
itself was not given an explanation in terms of anything more fundamental.
By assuming--without explaining--that masses attract, Newton could go on to
apply this fact to explain a number of phenomena. Reinforcement theorists
likewise began with an empirical law (the law of effect), and then used that
fact to explain a number of phenomena. Newton's law of universal
gravitation was quantitative; the law of effect was not, but only because
the observations that would provide the quantitative formula had not been
made as yet; theorists were confident that a few carefully controlled
studies would yield them. From there, they would be only a step or two away
from the sort of models Newton had developed.
That is the parallel I have been arguing for. It has seemed to me that in
prevous posts you have asserted that this use of the reinforcement principle
is somehow illegitimate, yet here is Newton doing the same thing with
gravitational attraction. If reinforcement theorists did not follow
Newton's approach far enough, they did follow it this far. The question
then becomes, why didn't they continue?
At least part of the answer, I think, was empirical. When the studies were
done to discover the quantitative relationships on which a model might be
constructed, the relationships were far from clear and nowhere near as
stable as those found in the equivalent studies undertaken in physics. It
looked to theorists that a large number of variables would have to be
investigated before something as quantitatively stable as g = m/d2 might be
found; the history of research in this area might be fairly characterized as
a search for such relationships. And when the behaviorist revolution set in
with its proscription against inferences about brain/mental processes, it
effectively prevented the development of models of the type Newton would
have approved.
Regards,
Bruce