Q E D

A number of years ago I was visiting my friend Mauricio in Rio de Janeiro. Mauricio had a beautiful house in the neighborhood of Lagoa, looking out over the water.

It happened that Mauricio’s guest room was also his library, and what a library! During my stay I spent happy hours exploring his huge and eclectic assortment of published works.

One book in particular, a small book I had somehow never heard of, was Richard Feynmann’s QED: The Strange Theory of Light and Matter.

I found out later that this book was based on four lectures he gave in 1985 at the University of Auckland, which are now available on-line in streaming video.

It’s actually a perfect example of the kind of P-code I was talking about yesterday, in this case a P-code for discussing quantum field theory in clear and easy to understand lay terms. In this book Feynmann set out to explain, in an intuitive and non-technical way, the theory of Quantum Electrodynamics – the theory (often abbreviated to “QED”) that describes how light interacts with electrons through space and time. Feynmann shared a Nobel prize in Physics in 1965 for helping to make this theory a lot more elegant and powerful.

The title of the book is also a really clever play on words, since Q.E.D. is also shorthand for Quad erat domenstrum, or “that which was to be proved” – the thing mathematicians write at the end of a successful proof of a theorm.

Not being a quantum physicist, or really having any particular knowledge of quantum physics, I picked up this slender volume that night in Mauricio’s guestroom/library with no confidence at all that I would be able to make heads or tails of it. To my surprise, Feynmann’s beautifully clear and simple prose began to take me through a wonderful world I hadn’t known about.

Feynmann also had a meta-message – that science, even very advanced science, does not need to be incomprehensible. With care and thought, even very sophisticated concepts can be explained clearly to a general audience.

And this delightful little book amply proved the point. For example, one thing I understood after reading it, a conundrum that had puzzled me since childhood, is the question of why light always travels along the shortest path between any two points. I had always wondered how light manages to know which is the shortest path.

I mean, what would happen if some light were to guess incorrectly and take the wrong path, not realizing its mistake until it got almost all the way to its destination? Would it then need to excuse itself, go back and try again? And if not, does that mean that light is psychic, able to predict the future?

Feynmann explained that light actually goes in every direction and takes all possible paths, radiating out from any point into all headings at once, somewhat like the ripples that form when you drop a pebble into a pond. But because light has a phase, it turns out that all of these possible paths arrive at any point in space in such a way that their energies cancel out and add up to zero.

All the paths that is, except the one path that happens to be the shortest path. Along just that one path, the phases all add up constructively, rather than destructively. To an observer who doesn’t know what’s really going on, it looks as though the light has only traveled along this one shortest path.

Note that as strange as this description of reality may seem, it actually provides a cause and effect reason for why light travels the way it does, with no need to resort to the phrase “because it just does”.

Things actually get lovelier and more interesting than the way I’m describing them, but why spoil the fun? You should read it for yourself. The important thing is that Feynmann doesn’t just claim these things – he leads you, step by clear and careful step, through the why and how of everything.

And along the way he amply proves his point: That it is indeed possible to make even the most advanced science fun and accessible to a non-expert.

Q.E.D.