QED: The Strange Theory of Light and Matter, by Richard Feynman

The discussion of physics is, in my mother’s opinion, a glaring faux pas. She has always expected me to behave according to the strictest standard of Southern politeness, and recently shared this insight with me: “When people ask you what you do, they don’t actually want to hear about it.” Elaborating on my study of physics in everyday conversation is, in her opinion, a transgression equivalent to responding to a casual “how are you?” by giving an acquaintance a detailed account of one’s recent appendectomy.

Her attitude seems to be a common one that was probably no less widespread in 1983, when one of the most renowned physicists of the twentieth century, Richard Feynman, gave a series of four lectures on the subject of QED, or quantum electrodynamics. The lectures were transcribed, are available in the form of a book, QED: The Strange Theory of Light and Matter. Though even the name of this field of study sounds intimidating, these lectures were designed to deliver an explanation of QED, the most thoroughly proven result of modern physics, that was accessible to people with no previous training in physics. It is an ambitious goal, especially in the face of what may be an even larger challenge: bringing some of the most complicated ideas in physics to an audience that, ostensibly, has no desire to hear about physics. However, by the end of the book, I was convinced that if all physicists were as well-spoken as Richard Feynman, perhaps elaborating on our field of study would not be considered so uncouth.

QED is written in a casual, chatty, engaging style. Feynman takes care not to alienate his audience, and he meticulously avoids the use of jargon – one runs across only a few technical terms, which are all thoroughly explained before the author will allow himself to use them freely. He frequently reassures his audience that it will be impossible to “understand” quantum electrodynamics, since it is so unlike the way events unfold in the everyday world, but that neither he nor anyone else can understand QED in this sense, either. It is only possible to describe what is happening. QED involves no math more complicated than squaring numbers to find the probability that a photon will take a certain path. However, it gives a remarkably complete description of the subject of quantum electrodynamics. Feynman states that his ambition in the lectures is to explain what is actually happening when photons interact with matter, and to describe the basic principles that physicists use to make more complicated calculations. He is remarkably successful at developing a self-consistent conceptual explanation of what happens when photons and electrons interact. QED contains no oversimplifications: all of his initial descriptions of photons, electrons, and their properties can be extended to fully describe the theory of quantum electrodynamics.

Feynman’s informal, conversational language painlessly leads his audience thorough this tour of quantum electrodynamics. The book’s first chapter serves as a first introduction to the topic, and outlines the major ideas that Feynman will keep coming back to: light is made up of particles called photons, and the wavelength of light is related to how much energy its photons have. Photons can interact with the electrons in everyday matter, and Feynman develops the theory by exploring examples of these interactions, such as partial reflection, that any person will have observed. In the rest of the book, he goes on to show how light’s observable wavelike properties are more accurately explained by QED, and then elaborates on how electrons in matter conspire with photons to create these properties. The final lecture describes some lingering unresolved problems with QED, and finally shows how QED is related to the rest of physics.

He remains firmly within the realm of the concrete, and makes frequent analogies between the material and everyday life. His illustrations are, at times, memorable, and I imagine that even if I had not already understood the phenomenon of refraction, Feynman’s description of it would have stuck with me – he compares a photon to a lifeguard who must reach a beautiful drowning victim as quickly as possible, and will therefore choose the path that takes the least time to reach his destination as he travels through a layer of air, then a layer of water.

Perhaps most importantly, he manages to trick his listeners into visualizing a photon with wavelike and particle-like properties. Any introductory physics course will teach that light travels as a wave, and that beams of light interact with each other in the same way that water waves would. However, as Feynman points out, extensive experiments have shown that this description is a horrible oversimplification. The truth is that when only one photon is aimed at a reflecting surface, it may take many different paths, and we can only predict the probability that it will choose one path over another. Normally, this sordid fact is revealed only in advanced physics classes, and students must change the conception of light that they have used for years. I wish that I had been introduced to the concept of photons that behave in this way, rather than having to come to grips much later with the idea of light as something with both wavelike and particle-like properties.

That said, people who have had to come to grips with the theory of quantum electrodynamics in their own way may find this book less profoundly enlightening, in terms of its basic subject matter. The only real problem I had with the book was that sometimes Feynman uses numbers in his examples, and it is hard to tell if the values he is using are arbitrary, or if they are fundamental quantities somehow determined by the theory. However, I doubt that this would be an issue for people who are less accustomed to always having to keep track of where numbers are coming from, and Feynman’s conceptual explanations are always quite clear. In fact, they will be especially impressive to anyone who has made their own attempt to explain this material to people with little knowledge of physics. For those who have already studied QED, this book serves as an inspiration, and also a challenge: it is proof that even the most advanced physics concepts can be made accessible to anyone, as long as the presenter is good enough at communicating what actually takes place. For this reason, I recommend QED to anyone interested in modern physics – it will illuminate the topic for people who have no previous knowledge of it, and will give physicists an outstanding example of how to make their field of study more accessible to the general public.

It is necessary that we physicists (and aspiring physicists) reclaim the realm of casual conversation as our own. We must take Feynman’s lessons to heart, and make an effort to convince the general population that our chosen field is a vibrant and fascinating one. QED can be read by anyone as a fantastic introduction to recent developments in physics, and will hopefully inspire today’s (and tomorrow’s) physicists to make similar efforts to show that their research can and should be appreciated by the entire human race, not just a small circle of other physicists.