A few days ago, we talked about Wigner's friend. But who was he?
Edwin Steiner told us about a remarkable interview with Paul Dirac that was done by one of Dirac's few friends (and brothers-in-law), Eugene Wigner, and by Thomas "paradigm shift" Kuhn:
Interview with P. A. M. Dirac By Thomas S. Kuhn and Eugene Paul Wigner At Wigner’s home, Princeton, New Jersey April 1, l962Spoilers
Dirac talks about the absence of any social life during his childhood. He lived with his parents in an isolated house. The parents didn't sleep with each other and didn't even eat with each other. He could only talk to his father in French. He had one younger and one older sibling. One of them committed suicide at age of 24.
Concerning mathematics and physics, we learn that Dirac has had almost no exposure to algebra – although his greatest contributions to physics seem to be all about algebra. He would notice the quaternions but he was an autodidact in all these matters.
When it comes to calculus and differential equations, among other things, he would be affected by his training in engineering. You know, books on engineering want to get the right results and ignore rigor as long as one may reliably learn to do the important things correctly.
Dirac would soon adopt this pragmatic attitude – and he also began to appreciate all approximate theories – although his natural inclination would be very rigorous ("only exact, rigorous insights matter"), of course. I must say that my built-in attitudes as well as experiences had been virtually identical. My natural desire would be to care about rigorous exact insights only but due to the random features of the environment, I would actually be influenced by lots of practical and pragmatic books (maybe my father's manual/practical orientation helped as well). For example, I first learned about Taylor expansions, Fourier expansions, as well as the matrix multiplication from a book dedicated to engineers.
(It was a bit surprising that even non-smooth functions admitted Fourier expansions which are composed of smooth sines and cosines; it was strange to hear that the inner and matrix products based on simple products of entries in table were "fundamental" in any sense, and so on. But of course that I would understand the validity and depth of all these things rather soon afterwards.)
The interview covers lots of the social circumstances, the effect of the First World War, Dirac's move from Bristol to Cambridge etc. At some point, he starts to study the Bohr theory of the atom. Heisenberg visits Cambridge, too.
He also says that in the Continental Europe, Heisenberg's paper would be viewed as a minor improvement of the Bohr-Sommerfeld quantization conditions etc. The fact that it was a revolution wasn't appreciated. It's doubly remarkable given the fact that even now, 90 years later, many people – including professionals (in the sense of being paid for physics, not in the sense of being truly competent experts) – still have a trouble with the new picture of the world that Heisenberg, Dirac, and others would discover in the 1920s.
BTW quarks are celebrating 50th birthday these days. Congratulations to Murray Gell-Mann, too.