Richard Feynman’s “Atoms in Motion” – Zach Eldredge

Richard Feynman the educator.

Richard Feynman the educator.

“Science is the poetry of reality,” says Richard Dawkins, speaking much truth in the process. Just as a great poem stirs emotions in a way that cannot easily be articulated, great science stirs the mind to understanding where previously it lay in ignorance. Every discipline has its own particular expressions of beauty that approach this ideal — whether mathematical proofs, philosophical elucidations, microbiological complexities, sweeping passages of prose, or the elegant nuances of song. The mark of a true performer is the ability to properly and passionately communicate these moments and this elegance to someone outside their own field. Richard Feynman, luckily, was such a performer and a genius to boot. In this, the first of his famous set of undergraduate lectures on physics, he shows the beauty of tracking a simple idea’s implications.

Newton's approximation is simple, understandable, and accurate enough to be useful.

Newton’s approximation is simple, understandable, and accurate enough to be useful.

First, though, he spends some time justifying himself to his students. If physics is the application of known laws to understand processes, why not simply provide the fundamental laws of nature and let them get on with it? Feynman points out that geometry is taught this way; however, he also notes the ways in which physics is not geometry. Starting from his definition of science (“ideas are tested by experiment”), he goes on to discuss the nature of physical laws. These laws are not known; all we actually know are approximations. And, to understand current approximations, you must understand simpler approximations, and so on. Therefore, introductory lectures on gravity teach Newton’s law, not Einsteinian general relativity, despite the fact that Newton’s law will leave students unable to calculate the proper orbit of Mercury. Here, Feynman does an excellent job of setting forth a basic philosophy of physics, and communicating degrees of approximation—it is, for instance, absolutely and completely wrong that an object’s momentum is equal to its mass times its velocity. In reality, there is a relativistic correction factor which is only noticed at speeds that are a notable fraction of the speed of light. Yet although we are factually wrong to state the law without the relativistic factor, we are practically right—it is a law which applies to nearly every situation in the world, within a small margin of error. Science is in reality a very messy business with error bars and statements like “to a first approximation.”

Einstein's theory of general relativity is more accurate but also harder to grasp, and thus more difficult to intuit.

Einstein’s theory of general relativity is more accurate but also harder to grasp, and thus more difficult to intuit.

The impressive part of this lecture starts after this introductory exposition when Feynman proposes a thought experiment: suppose that all scientific knowledge were wiped out in some cataclysm and only one sentence could be saved for the next generation. What should it be? Feynman proposes  “All things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another” and spends the rest of the lecture drawing inferences from this.

Feynman starts with his atomic hypothesis, and proceeds to discuss a droplet of water, expanded by some unfathomable factor such that we can view the individual atoms. Then he takes us on a tour of some very basic phenomena. A glass of water at rest reveals itself to be a teeming mass of activity, molecules breaking free from the water into the air while others become attached again to the liquid. Eventually the water reaches equilibrium and these processes balance—unless you sweep the water vapor off and allow more water to evaporate. So our atomic hypothesis explains why a fan will dry water faster than still air.

A critical word: Feynman is brilliant, but he is also cheating. Most of the conclusions he draws cannot—or at least would not—be drawn from that statement. He knows how matter behaves already, and so draws the correct conclusions. Nonetheless to watch him reason is exhilarating. It is somewhat like observing a magician, whose show generates such fantastic spectacles that it does not really matter how “real” the magic is. He isn’t really rediscovering modern science. What he is doing, besides putting on a show, is recasting simple events in terms of atomic phenomena. This is important. The models we use to describe the world are esoteric even to the best physicists. We know, for instance, that time slows for a moving observer—but we don’t feel it, and we won’t feel it if we spend a hundred years doing exercises manipulating space-time four-vectors. Neither does a still glass of water seem to be a teeming mass of activity, neither do we perceive ourselves to be atomic processes. We know all sorts of things that we do not believe. While these models are hard to absorb, they distinguish themselves from flights of fancy by being useful and indeed powerful, so it is important to develop some instinct for them. Feynman is attempting to bridge the gap between our minds and the models we have built.

Democritus, along with Leucippus, was among the first to propose an atomistic theory of reality. However, with his ideas being overcome by Aristotle and then the Aristotelian Church, Physics languished for centuries until atoms were again embraced.

Democritus, along with Leucippus, was among the first to propose an atomistic theory of reality. However, with his ideas being overcome by Aristotle and then the Aristotelian Church, Physics languished for centuries until atoms were again embraced.

Feynman explains that if a molecule of water is liberated by moving quickly, then it will have had higher energy than the other molecules—so the average energy should go down and, in turn, the water should cool off. Evaporation, therefore, is a cooling process—explaining both why blowing on soup cools it off, and why our bodies ooze salt water when we feel overheated.

The note about sweat is relevant, as Feynman finishes with a bold statement. “There is nothing that living things do that cannot be understood from the point of view that they are made of atoms acting according to the laws of physics.” This is a philosophical statement. But it is a statement that he has just gone to some lengths to demonstrate. From Feynman’s perspective, that of modern science, it is true. He notes that he does not find it demeaning to the human spirit, closing with a paragraph on human beings and the potential demonstrated therein by a “lump of atoms.” Feynman, in just his first lecture, has demonstrated the character of physical law, the capability and structure of an inference from physical principles, and finished with a conclusion of philosophical implications. It is a powerful introduction to both physics and the scientific worldview.

Advertisements

Contribute

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: