 A major talking point at the conference was the discovery by Willis Lamb and his graduate student Robert Retherford shortly before the conference began that one of the two possible quantum states of hydrogen atoms had slightly more energy than predicted by the Paul Dirac's theory; this became known as the Lamb shift. Oppenheimer and Weisskopf suggested that this was a result of quantum fluctuations of the electromagnetic field. Pre-war quantum electrodynamics (QED) gave absurd, infinite values for this; but the Lamb shift showed that it was both real and finite. Hans Kramers proposed renormalization as a solution, but no one knew how to do the calculation.
