Taken from “Surely You're Joking, Mr.
Feynman!” Adventures of a Curious Character by Richard Phillips Feynman as told to Ralph Leighton edited by
Edward Hutchings
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 he a force on it. And there must he 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 he 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.
But
then a miracle occurred, as it has occurred again and again in my life, and
it’s very lucky for me: the moment I start to think about the physics, and have
to concentrate on what I’m explaining, nothing else occupies my mind—I’m
completely immune to being nervous. So after I started to go, I just didn’t
know who was in the room. I was only explaining this idea, that’s all.
But
then the end of the seminar came, and it was time for questions. First off,
Pauli, who was sitting next to Einstein, gets up and says, “I do not sink dis
teory can be right, because of dis, and dis, and dis,” and he turns to Einstein
and says, “Don’t you agree, Professor Einstein?”
Einstein
says, “Nooooooooooooo,” a nice, German sounding “No,”—very polite. “I find only
that it would be very difficult to make a corresponding theory for
gravitational interaction.” He meant for the general theory of relativity,
which was his baby. He continued: “Since we have at this time not a great deal
of experimental evidence, I am not absolutely sure of the correct gravitational
theory.” Einstein appreciated that things might be different from what his
theory stated; he was very tolerant of other ideas.
I
wish I had remembered what Pauli said, because I discovered years later that
the theory was not satisfactory when it came to making the quantum theory. It’s
possible that that great man noticed the difficulty immediately and explained
it to me in the question, but I was so relieved at not having to answer the
questions that I didn’t really listen to them carefully. I do remember walking
up the steps of Palmer Library with Pauli, who said to me, “What is Wheeler
going to say about the quantum theory when he gives his talk?”
I
said, “I don’t know. He hasn’t told me. He’s working it out himself.”
“Oh?”
he said. “The man works and doesn’t tell his assistant what he’s doing on the
quantum theory?” He came closer to me and said in a low, secretive voice,
“Wheeler will never give that seminar.”
And
it’s true. Wheeler didn’t give the seminar. He thought it would be easy to work
out the quantum part; he thought he had it, almost. But he didn’t. And by the
time the seminar came around, he realized he didn’t know how to do it, and
therefore didn’t have anything to say.
I
never solved it, either—a quantum theory of half-advanced, half-retarded
potentials—and I worked on it for years.