So I continued in mathematics in graduate school but I was drifting toward physics at that time and I hadn't taken any physics but I was drifting in that direction.

So I took my first course in quantum mechanics from Schwinger. And it was an extraordinary course, though I didn't appreciate it really at the time, because I just didn't know anything but I certainly appreciate it now. I mean it was fine, the first part, where he talked about the reasons for there being a quantum theory, but then he had his own development. He was in rivalry with Feynman. Feynman had a quantum theory, Schwinger had a quantum theory and so Schwinger's personal quantum theory was abstract and, I think powerful and abstract, and completely the wrong thing to teach to students.

So we used to go down to MIT and listen to [Victor] Weisskopf lecture on quantum theory. Weisskopf was completely different. I remember the first lecture I heard of Weisskopf. He came in and there was a big class, all men, and he said, 'Boys, I had a wonderful night last night.' And everybody said, 'Yay, Vicky, bravo, bravo.' He said, 'No, no, it's not what you think. I finally understood the Born approximation.' Then he explained the Born approximation