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Re: CAUSATION IN PHYSICS



This illustration is not physics but I will use it. After running
my pulse rate is higher than it would be if I were not running.
Most people would agree that running (internal and external
work) is the cause of the higher pulse rate. Why? Because of
the time sequence; first we run then we measure the pulse rate.
What happens later can not be a cause of an earlier occurence,
in classical physics.

But is it not true that the pulse rate increases gradually when
we are running? I suspect that a smooth curve can be drawn
to display the pulse rate versus the work done. How does
this differ from "more positive work done on a particle larger
its final acceleration"? Thus F is the cause and a is the effect.

In my opinion natural laws are cause and effect relations.
Understanding is a process by which such relations are
discovered by humans. My definition of "to understand"
includes the "ability to identify true causes and effects".
Our brains "want to know what causes what". I am not
saying that a smooth mathematical relation, for example
y=k*x, implies that x is a cause of y. It can be the other
way around. And it is possible that x and y are strongly
correlated because both of them are caused by z. I will be
willing to accept a good explanation in which the net force
and the acceleration are correlated because of some hidden
variable z. But for the time being I am comfortable with F
being a cause of acceleration. What is wrong with this?
Ludwik Kowalski

Brian McInnes wrote:

In his reply to John Clement's well-stated points, John Denker writes

"There is every reason to believe they (acceleration and force) are
simultaneous, and no reason to believe otherwise. If anybody has
theoretical or experimental evidence to the contrary, please let us
know."

I think we should remember the distinction between the real world and
the models we construct to explain that world. Our model is based
around point particles and rigid bodies, neither of which exist in the
real world.

In the model we expect the unbalanced applied net force (John
Clement's push) and the acceleration of the point particle or the
rigid body to be simultaneous.

However in the real world, where elastic forces come into play as
existence of the unbalanced force is "communicated" to all parts of
the non-rigid body, simultaneity is not obvious.

But Leigh said all of this far better a few days ago:

"By hypothesis this equation applies strictly to a model. The model
closely resembles the phenomenon of a a physical body moving under the
influence of an applied force. It is in the details which distinguish
the model from the physical system that the causal relation between
force and acceleration is to be found. The gradual buildup of the
force over a very short time after its initial application and the
slight compression of the body over this same time interval will
corroborate the causal relation we naturally assign. In light of what
is really happening the metaphysical questions are readily seen to be
trivial."