Nevertheless, most physicists are (probably) “reductionists.” This means that they believe that all that happens in the large-scale world—even the very large-scale world of the entire universe—can ultimately be explained by what is going on in the submicroscopic world. We understand the “emergent” concept of temperature, for instance, to be a manifestation of the kinetic energy of submicroscopic bits of matter. We understand that the flood of light and energy from the Sun results from the interactions of atomic nuclei (mainly protons) at the Sun’s center. We understand energy to be conserved in the cosmos because it is conserved in individual interactions of fundamental particles.
This point of view suggests that basic aspects of the submicroscopic world can usefully be taught in introductory physics course—even taught at the beginning of a course. There are two reasons to consider doing so. First, beginning students may find that electrons, photons, and neutrinos are more exciting than are pendulums, inclined planes, and falling objects. Second, and in some ways more important, the basics of particle physics are actually simpler than the basics of classical mechanics. This may seem like an odd statement to the average teacher, who, in his or her own studies, probably reached modern physics only after trudging through classical mechanics. But consider, say, teaching about charge conservation vs. teaching about Newton’s second law. Or discussing the spin and orbital angular momentum of an electron vs. discussing the angular momentum of rigid bodies. For me, at least, in my own classroom, this port of entry to physics seemed to work. To sum it up in a motto: Smaller is greater.
There is about the fundamental particles the paradoxical fact that, although their discovery rested upon all the earlier developments of science, they are themselves rather easily visualizable, and some of their main properties can be understood with no scientific background at all. We can think of a golf ball or a marble, and, extrapolating downward many orders of magnitude, picture a fundamental particle as a tiny speck of matter, a basic building block of the universe.
Not just physicists, but also chemists and biologists, are microscopically oriented. They picture the large-scale world as put together from smaller and smaller units, down to the fundamental particles of physics and perhaps, one day, to a still deeper unit. In short, they are reductionists. If Aristotelian physics was a science of final causes, modern physics is a science of microscopic causes. “Explanation” in physical science is, as often as not, the description of something larger in terms of something smaller. To look at the fundamental particles in an introductory physics class is to examine the basis of physical science as well as one of its frontiers.
To the scientist, the fundamental particles provide the greatest challenge in modern physics. To the student they provide important insight into the scientist’s view of the world. It is well to recall that the most familiar points of impact of physical science on humankind—our satellite communications, our detergents, our bombs, our mobile phones—form only a sideline off the mainstream of scientific advance. The true frontiers of science lie far more remote from everyday life, and one of these is the submicroscopic frontier inhabited by the particles. An open question: Will the particles one day give way and allow the frontier to be extended to a still smaller domain?
1 At age 88, Anderson gathered his thoughts and recollections together in an essay collection, More and Different: Notes from a Thoughtful Curmudgeon (World Scientific, 2012).