QED: The Strange Theory of Light and Matter Book

My reaction upon finishing this book:



(Any excuse for a Breaking Bad reference.)

Seriously, though, this is one of the best pop science books I've yet encountered. I read Surely You're Joking, Mr. Feynman!: Adventures of a Curious Character last year, and was thoroughly impressed by Feynman's animated personality and his passion for physics. Now I find myself even more impressed by his exceptional teaching ability. QED: The Strange Theory of Light and Matter is a collection of 4 lectures he gave to the general public on the subject of quantum electrodynamics. The book is intended for laypeople, is written in very accessible language, and provides "Feynman diagrams" instead of advanced mathematical formulae. A rather lengthy summary of these fascinating lectures follows. If you don't want any spoilers, or whatever you want to call them, then skip ahead to the final paragraph.

The first lecture deals with photons, and how light behaves like particles. This is discussed in detail w.r.t. the partial reflection of monochrome light by glass. There's already some fascinating shit right here, let me tell you! See, physicists can't predict which photons will get reflected and which will pass through the glass. All they can tell you is the overall probability that it will happen. In other words, "identical photons are always coming down in the same direction to the same piece of glass," and this somehow winds up "producing different results" each time. Who knew that "partial reflection by a single surface" was a "deep mystery and a difficult problem"?! Bizarre.

Feynman then teaches us how to calculate the probability of photons bouncing off either the front or the back surface of sheets of glass of varying thickness. The lecture concludes with a discussion of iridescence (the colors produced by the reflection of white light by two surfaces). Neat-o.

In the second lecture, Feynman uses QED to explain why, when light reflects off a mirror, the angle of incidence is equal to the angle of reflection. This is weirder than you might assume. (Actually, "weirder than you'd assume" sums up the entire book remarkably well!) The phenomenon discussed here is also the basis for diffraction gratings. Then he covers how light travels from air into water, and what causes mirages.

Feynman goes on to explain why light appears to travel in straight lines. Incredibly, it behaves as such only when you give it enough wiggle room, so to speak. For "when you try to squeeze light [or restrict its path] too much to make sure it's going in only a straight line, it refuses to cooperate and begins to spread out." This is not altogether dissimilar to the behavior of surly teenagers. Perhaps we can reasonably refer to them as "little rays of sunshine" in an unironic fashion from now on! :D Bad joke, sorry. Anyway, the manner in which focusing lenses work is next revealed, and the lecture concludes with how quantum theory calculates the probability of compound events.

The third lecture introduces electrons, which behave similarly to photons: somewhat like waves, somewhat like particles. (Feynman jokes about "wavicles," a term I actually love to death, and will enthusiastically champion from now on!) We learn of the three basic actions from which all the phenomena of light and electrons arise: 1) photons rollicking about, 2) electrons rollicking about, and 3) electrons emitting or absorbing photons. As per the first item, we learn that "light doesn't go only at the speed of light." So yeah, that happens. It's anarchy, I tell you! Madness! And the third action is even stranger. Hint: time travel may or may not be involved. Oh, you beautiful, depraved little positrons, you.

Next, Feynman covers how electrons behave in atoms. He re-examines the partial reflection of light from glass in far greater detail than he did earlier, and we can now see why the former simplification was in fact warranted. (We previously treated light as reflecting from the "front" and "back" surfaces of a sheet of glass, as opposed to what light actually does, which is to be scattered by the electrons inside the glass.) This scattering is also the reason light appears to move more slowly in glass or water than it does in a vacuum or in air. Also of interest is how lasers work: photons tend to go to the same point in space-time. (These lunatics are predisposed to travel in packs!) It turns out the reverse is true for electrons. Their aversion to one another is known as the "Exclusion Principle," and helps explain chemical properties of atoms.

Before finishing the lecture by discussing polarization, Feynman examines the complexity of the magnetic moments of electrons. This is fairly bananas, even considering the fact that the entire book is pretty much out to lunch. Here is what can happen: an "electron goes along for a while and suddenly emits a photon; then (horrors!) it absorbs its own photon. Perhaps there's something 'immoral' about that, but the electron does it!" (You really have to love his sense of humor.) I've included some Feynman diagrams which depict this wanton immorality:



The fourth and final lecture deals with some problems associated with quantum theory. It also looks at the relation of QED to the rest of physics, and includes a discussion of fundamental particles such as quarks and gluons, to name but a couple.

Overall, this short book is packed full of mind-blowing information. I really appreciated all of the helpful diagrams that illustrate the very peculiar concepts under discussion. Also, Feynman is an excellent teacher. I just loved his occasional bursts of exuberance and humor. His enthusiasm for his subject is irresistible, his subject itself truly extraordinary.