Chapter 4: Our Newtonian Worldview: A universal equation of motion

In Chapter 4 (and 5) we cover that little bit of classical physics needed to appreciate the quantum enigma. In our conceptual physics course, in addition to dealing with the “straight physics,” we emphasize classical physics concepts that are often just assumed. Namely: determinism, physical reality, separability, and reduction. Our point is, of course, to prepare for our eventual contrast of these concepts with what will be seen in quantum mechanics. But including this material is also motivating of the technical aspects. And it makes for interesting discussion. Students appreciate seeing how these concepts, arising from Newtonian mechanics, shaped thinking in areas far beyond physics–including their own thinking.

In QE, the “scientific method” gets only about one page. It has a much bigger part in our conceptual physics course. We want to get students to explicitly accept scientific criteria for whether or not they consider a theory or hypothesis to be reliable science. We have two reasons for this. An obvious one: We want students to reject (or at least hold in some doubt) the kinds of things we consider pseudo-science. Our other reason for emphasizing the scientific method is to show how we are logically compelled to accept quantum mechanics as reliable science–in spite of it being so counterintuitive.

We use a diagrammatic representation of the method of science. We call it a “filter” to see which theories can come through to become (tentatively) reliable science.

TH = The theory (or hypothesis) that is a candidate for becoming reliable science.
BP = The “Bold Prediction” test: Does the theory make a testable prediction?
NT = Not taken. The theory makes no testable prediction. (E.g., a religion)
P = Pass. The theory passes the BP (or CE) test.
CE = The “Challenging Experiment” test: In an experimental test of the prediction that trys to falsify it, is the theory’s prediction correct?
F = The CE falsifies the prediction. A theory (or hypothesis) that fails even a single CE test must be abandoned, modified, or have its domain restricted.
INC = The CE was inconclusive.
tRS = tentatively Reliable Science.

To become increasingly reliable science, a theory must make many Bold Predictions that pass every Challenging Experiment.

This brief description of our representation of the method of science does not do it justice. A several page treatment is available on request. Another advantage of this diagram is that it provides a sound, and easy-to-grade, set of exam questions (fill in the blanks with words).

In our treatment of the Newtonian worldview in our conceptual physics course, we emphasize the way its mechanical picture (the “clockwork universe”) still shapes the way we think, including in areas well beyond physics.

To stress conceptual ideas in our conceptual physics course, we, for example, treat F = Ma and F = Gmm/r^2 together. After all, for Newton to arrive at his universal equation of motion, he had to postulate the law of gravity at the same time. (Most conceptual physics books present the law of motion early on, and only much later deal with the law of gravity.)

We practice calculation techniques with, for example, one-dimensional motion, projectiles, and planetary motion.  We treat orbital potential energy in connection with the Bohr atom, where a relation to quantum mechanics motivates this rather tricky material.