The Pleasure of Finding Things Out

by Richard P. Feynman

He was happy with me, I believe. Once, though, when I came back from MIT–I’d been there a few years–he said to me, “Now,” he said, “you’ve become educated about these things and there’s one question I’ve always had that I’ve never understood very well and I’d like to ask you, now that you’ve studied this, to explain it to me,” and I asked him what it was. And he said that he understood that when an atom made a transition from one state to another it emits a particle of light called a photon. I said, “That’s right.” And he says, “Well, now, is the photon in the atom ahead of time that it comes out, or is there no photon in it to start with?” I says, “There’s no photon in, it’s just that when the electron makes a transition it comes” and he says “Well, where does it come from then, how does it come out?” So I couldn’t just say, “The view is that photon numbers aren’t conserved, they’re just created by the motion of the electron.” I couldn’t try to explain to him something like: the sound that I’m making now wasn’t in me.