The Strange Theory of Light and Matter

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I was a physics major in college (I suppose I need to keep repeating that for newcomers), but I fell off that holy path a few years later, finding myself more interested in playing with computers than I was in pursuing actual research. But I still enjoy reading "popular" science books every now and again, and this is one of the best: Richard Feynman's four-lecture series on quantum electrodynamics, QED. He won the Nobel (with Julian Schwinger and Shin’ichirō Tomonaga) for his work in this field, so this book is as definitive as it gets.

QED sounds as if it might be obscure, but it's really all about … well, everything: the interplay of photons with matter. Which, for one big example, holds atoms together. (Where would we be without that? Nowhere, that's where.)

Feynman's lecturing style is wonderfully down-to-earth and colorful, with flashes of wry humor. There are videos out there. If that's your thing, check them out. He prefers pictures to math; eponymous "Feynman diagrams" eventually make their appearance, although I don't think he ever calls them that.

At one point he talks about multiplying amplitudes, represented by arrows: this involves (he says) a "shrink" (you multiply the lengths of the arrows, and they're less than one) and a "twist" (adding one arrow's angle to the other's).

And it took me (sadly) more than a few minutes to remember those old math and physics courses, and realize he's just multiplying two complex numbers represented in polar notation.

Feynman draws insightful lessons from something as simple as light reflecting off a glass plate. (Or an thin film of oil on water: see the cover.) He avoids the "easy" explanation of interfering light waves, noting you get the same effects if you crank the intensity of the light way down—this is quantum electrodynamics, after all—and only send one photon at a time. Somehow, that shiny little ball interferes with itself!

Well, see the subtitle: it's a strange theory. Here's what he tells his (civilian) audience in the first lecture:

What I am going to tell you about is what we teach our physics students in the third or fourth year of graduate school—and you think I'm going to explain it to you so you can understand it? No, you're not going to be able to understand it. Why, then, and I going to bother you with all this? Why are you going to sit here all this time, when you won't be able to understand what I'm going to say? It is my task to convince you not to turn away because you don't understand it. You see, my physics students don't understand it either. That is because I don't understand it. Nobody does.

So don't worry about making sense out of QED; Feynman's describing the way it works, not why it works that way. Nobody knows why it works that "absurd" way, and you'll just make your head hurt thinking about it. As he says, it's absurd, but he finds it "delightful", and maybe you will too.

I got an older edition of this book from the UNH Physics Library, in it, Feynman mentions that the mass of the neutrino is zero. I don't know if that's been corrected in newer editions. Get the latest one you can find.

Last Modified 2024-01-13 1:00 PM EDT