Hans Bethe first of all calculated the Lamb shift with a cut-off at the electron mass, right away, right after the Shelter Island meeting, within a day. And... and then Viki [Victor Weisskopf] and his graduate student Bruce French, [Norman] Kroll and [Willis] Lamb himself, and two of the people who were working on the newer relativistic methods, Dick Feynman and Julian Schwinger, all started to calculate the relativistic Lamb shift using mass renormalization and the cancellation of the infinities in the vertex and the propagator, for the electron. And French and Weisskopf actually won the race, they got the right answer first, but because [Richard] Feynman and [Julian] Schwinger using the relativistic methods, got different answers at that moment, they were… Weisskopf was discouraged. French was not, he knew he was right, but Viki Weisskopf insisted on waiting and so Kroll and Lamb, using old-fashioned methods, were actually the first ones to publish the correct calculation. It could have been French and Weisskopf if they hadn't been put off by Feynman and Schwinger. Dick Feynman in his paper manipulated his footnotes with stars and daggers and so on, so that the footnote referring to this was numbered 13. And then he wrote, 'I had some difficulty', he wrote, 'in reconciling the relativistic method with the non-relativistic cut-off of Bethe, and therefore I made a mistake at that point. And French and Weisskopf were discouraged by that, and I'm sorry. This footnote is appropriately numbered'. Something like that. Schwinger of course never said he was sorry. So that quantum field theory was okay. Then the pion was discovered by [César] Lattes, [César] Occhialini, [Cecil] Powell and that was all fine, too, then. In the meantime, just before the pion was discovered...

[Q] That was fine because we now understood Yukawa?

Right, but just before that, Marshak had suggested that there were two different particles:  what we now call the pi, which was Yukawa's particle, more or less, and the muon, which was more like the electron. And he suggested the actual properties of the pi and the muon, and within a few months they were confirmed. So, suddenly theory wasn't so bad. The two crippling contradictions were both removed, and it was in that atmosphere that I arrived at MIT.