I had, at that time, a student who was working on exciting things with me, and that took all my imagination. Richard Feynman had been graduated from Massachusetts Institute of Technology, and he arrived in the fall of 1938, as a graduate student. By some freak of fate or good luck, in his task, he was assigned for me as somebody to grade papers of the students in my courses. So every week, at a certain time, he'd come in with the papers graded, so I could give them back to the students, and we'd go over what the students' difficulties and premises were. And then we got off on other things. And I can recall talking to him about the idea, how unnatural it is that a particle that is jiggled here should lose energy only to a particle some distance away later, why not also earlier? Little by little, as we got into these questions, we found ourselves getting more excited. I recall sitting one day in the living room at home, on a Sunday afternoon, figuring on the back of an envelope; look, if a particle here radiates energy outward, and jiggles all the particles far away, what will be the effect of these Far Away Particles back on this particle? According to views then current, it couldn't have any effect then because the effect had to go out, that'd take time, a million years, say, and then another million years to come back. So this particle would never see the consequences until two million years later. But I said to Feynman- suppose, if the effect comes back before it starts, so-called Advanced Potentials, and I found that the effect was of the right order of magnitude to explain the observed loss of energy of this particle, the force acting on it, it slowed it down and took energy away from it, coming from the effect produced by these far away particles. That seemed a big contradiction to the normal order of time, but Feynman was happy to go along with this. But I came out with an answer off by a factor of two. Can you figure out what I did wrong? Well, he figured it out. And then we thought these ideas were sufficiently interesting, why not go round and see what Einstein could contribute on it. So he and I went round to 112 Mercer Street, and Einstein was kind enough to talk about this, things with us, and he told us how years ago he had written a paper with a German physicist, Walther Ritz. To me it's the height of the ideal of science, two people considering a problem as carefully as they can, they come out with opposite views, but they write down what they agree on, what they disagree on, and what should be done to settle the disagreement, and here were Ritz and Einstein. Ritz said the world was built so that forces only act later than the action. And Einstein said the asymmetry in time that we observe in nature is not due to the forces, it's due to statistics, the fact there are large numbers of particles out there, somehow or other. So he was sympathetic to the point of view that Feynman and I had developed. And that gave us great encouragement to go ahead and publish this.