The Joy of Insight: Passions of a Physicist
In the fall of 1950, when I was a senior at Harvard, I decided that I wanted to study the quantum theory. This was only moderately unreasonable. I was a mathematics major and had taken a solid course in freshman physics given by the theoretical physicist Wendell Furry. I had also read some popular books and had a great many philosophical talks about the quantum theory with my teacher Philipp Frank. While I knew some higher mathematics, when it came to physics I knew next to nothing. Nonetheless, I decided to enroll in the first-year graduate course in quantum theory taught by the then reigning genius in theoretical physics at Harvard, Julian Schwinger.
To say that Schwinger’s lectures were both brilliant and impenetrable would be an understatement. They were very brilliant and impenetrable. Schwinger was, it turned out, trying out an entirely new formulation of the theory on us—the old one would have been hard enough—and since he lectured from memory questions were discouraged. (Years later Robert Oppenheimer once said to me of Schwinger that when most people discuss a problem they show you how to solve it, but when Schwinger discusses a problem he shows you that only he can solve it.) After a few weeks I was lost. I was commiserating with a friend, a physical chemist, who was also taking Schwinger’s course. He said, what you should do is come with me to MIT and audit “Viki.” Viki, I learned, was Victor Weisskopf, who was Schwinger’s analogue—I am tempted to say antiparticle—at MIT.
My visits to Viki’s class in quantum mechanics at MIT were, in every way, a culture shock. The class and the classroom were both huge—at least a hundred students. Weisskopf was also huge, at least he was tall compared to the diminutive Schwinger. I do not think he wore a jacket, or if he did, it must have been rumpled. Schwinger was what we used to call a spiffy dresser. Weisskopf’s first remark on entering the classroom, was “Boys [there were no women in the class], I just had a wonderful night!” There were raucous catcalls of “Yeah Viki!” along with assorted outbursts of applause. When things had quieted down Weisskopf said, “No, no it’s not what you think. Last night, for the first time, I really understood the Born approximation.” This was a reference to an important approximation method in quantum mechanics that had been invented in the late 1920s by the German physicist Max Born, with whom Weisskopf studied in Göttingen. Weisskopf then proceeded to derive the principal formulas of the Born approximation, using notes that looked as if they had been written on the back of an envelope. Along the way, he got nearly every factor of two and pi wrong. At each of these mistakes there would be a general outcry from the class; at the end of the process, a correct formula emerged, along with the sense, perhaps …
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