Watson thought the stuff I had done with phages was of some interest, so he invited me to go to Harvard. I gave a talk to the biology department about the double mutations which occurred so close together. I told them my guess was that one mutation made a change in the protein, such as changing the pH of an amino acid, while the other mutation made the opposite change on a different amino acid in the same protein, so that it partially balanced the first imitation—not perfectly, but enough to let the phage operate again. I thought they were two changes in the same protein, which chemically compensated each other.
That turned out not to be the case. It was found out a few years later by people who undoubtedly developed a technique for producing and detecting the mutations faster, that what happened was, the first mutation was a mutation in which an entire DNA base was missing. Now the “code” was shifted and could not be read any more. The second mutation was either one in which an extra base was put back in, or two more were taken out. Now the code could be read again. The closer the second mutation occurred to the first, the less message would be altered by the double mutation, and the more completely the phage would recover its lost abilities. The fact that there are three “letters” to code each amino acid was thus demonstrated.
While I was at Harvard that week, Watson suggested something and we did an experiment together for a few days. It was an incomplete experiment, but I learned some new lab techniques from one of the best men in the field.
But that was my big moment: I gave a seminar in the biology department of Harvard! I always do that, get into something and see how far I can go.
I learned a lot of things in biology, and I gained a lot of experience. I got better at pronouncing the words, knowing what not to include in a paper or a seminar, and detecting a weak technique in an experiment. But I love physics, and I love to go back to it.
Monster Minds
While I was still a graduate student at Princeton, I worked as a research assistant under John Wheeler. He gave me a problem to work on, and it got hard, and I wasn’t getting anywhere. So I went back to an idea that I had had earlier, at MIT. The idea was that electrons don’t act on themselves, they only act on other electrons.
There was this problem: When you shake an electron, it radiates energy and so there’s a loss. That means there must be a force on it. And there must be a different force when it’s charged than when it’s not charged. (If the force were exactly the same when it was charged and not charged, in one case it would lose energy, and in the other it wouldn’t. You can’t have two different answers to the same problem.)
The standard theory was that it was the electron acting on itself that made that force (called the force of radiation reaction), and I had only electrons acting on other electrons. So I was in some difficulty, I realized, by that time. (When I was at MIT, I got the idea without noticing the problem, but by the time I got to Princeton, I knew that problem.)
What I thought was: I’ll shake this electron. It will make some nearby electron shake, and the effect back from the nearby electron would be the origin of the force of radiation reaction. So I did some calculations and took them to Wheeler.
Wheeler, right away said, “Well, that isn’t right because it varies inversely as the square of the distance of the other electrons, whereas it should not depend on any of these variables at all. It’ll also depend inversely upon the mass of the other electron; it’ll be proportional to the charge on the other electron.”
What bothered me was, I thought he must have done the calculation. I only realized later that a man like Wheeler could immediately see all that stuff when you give him the problem. I had to calculate, but he could see.
Then he said, “And it’ll be delayed—the wave returns late—so all you’ve described is reflected light.”
“Oh! Of course,” I said.
“But wait,” he said. “Let’s suppose it returns by advanced waves—reactions backward in time—so it comes back at the right time. We saw the effect varied inversely as the square of the distance, but suppose there are a lot of electrons, all over space: the number is proportional to the square of the distance. So maybe we can make it all compensate.”
We found out we could do that. It came out very nicely, and fit very well. It was a classical theory that could be right, even though it differed from Maxwell’s standard, or Lorentz’s standard theory. It didn’t have any trouble with the infinity of self-action, and it was ingenious. It had actions and delays, forwards and backwards in time—we called it “half-advanced and half-retarded potentials.”
Wheeler and I thought the next problem was to turn to the quantum theory of electrodynamics, which had difficulties (I thought) with the self-action of the electron. We figured if we could get rid of the difficulty first in classical physics, and then make a quantum theory out of that, we could straighten out the quantum theory as well.
Now that we had got the classical theory right, Wheeler said, “Feynman, you’re a young fella—you should give a seminar on this. You need experience in giving talks. Meanwhile, I’ll work out the quantum theory part and give a seminar on that later.”
So it was to be my first technical talk, and Wheeler made arrangements with Eugene Wigner to put it on the regular seminar schedule.
A day or two before the talk I saw Wigner in the hail. “Feynman,” he said, “I think that work you’re doing with Wheeler is very interesting, so I’ve invited Russell to the seminar.” Henry Norris Russell, the famous, great astronomer of the day, was coming to the lecture!
Wigner went on. “I think Professor von Neumann would also be interested.” Johnny von Neumann was the greatest mathematician around. “And Professor Pauli is visiting from Switzerland, it so happens, so I’ve invited Professor Pauli to come”—Pauli was a very famous physicist—and by this time, I’m turning yellow. Finally, Wigner said, “Professor Einstein only rarely comes to our weekly seminars, but your work is so interesting that I’ve invited him specially, so he’s coming, too.”
By this time I must have turned green, because Wigner said, “No, no! Don’t worry! I’ll just warn you, though: If Professor Russell falls asleep—and he will undoubtedly fall asleep—it doesn’t mean that the seminar is bad; he falls asleep in all the seminars. On the other hand, if Professor Pauli is nodding all the time, and seems to be in agreement as the seminar goes along, pay no attention. Professor Pauli has palsy.”
I went back to Wheeler and named all the big, famous people who were coming to the talk he got me to give, and told him I was uneasy about it.
“It’s all right,” he said. “Don’t worry. I’ll answer all the questions.”
So I prepared the talk, and when the day came, I went in and did something that young men who have had no experience in giving talks often do—I put too many equations up on the blackboard. You see, a young fella doesn’t know how to say, “Of course, that varies inversely, and this goes this way … because everybody listening already knows; they can see it. But he doesn’t know. He can only make it come out by actually doing the algebra—and therefore the reams of equations.
As I was writing these equations all over the blackboard ahead of time, Einstein came in and said pleasantly, “Hello, I’m coming to your seminar. But first, where is the tea?”
I told him, and continued writing the equations.
Then the time came to give the talk, and here are these monster minds in front of me, waiting! My first technical talk—and I have this audience! I mean they would put me through the wringer! I remember very clearly seeing my hands shaking as they were pulling out my notes from a brown envelope.