"This is the third of four lectures on a rather difficult subject—the theory of quantum electrodynamics—and since there are obviously more people here tonight than there were before, some of you haven't heard the other two lectures and will find this lecture incomprehensible. Those of you who have heard the other two lectures will also find this lecture incomprehensible, but you know that that's alright: as I explained in the first lecture, the way we have to describe Nature is generally incomprehensible to us."

Richard Feynman  |  QED: The Strange Theory of Light and Matter