Jeremy Bernstein, a physicist and science writer whose books I like, has a blog on the death of Paul Samuelson at blogs.nybooks.com…

I had some brief correspondence with Samuelson a couple of times almost ten years ago, and he seemed to be a real gentleman in the old-fashioned sense of the word, courteous and open.

Bernstein writes that “the use of complex mathematical models to make risky investments that, taken to extremes (which Samuelson himself never did), nearly caused the collapse of our financial system in the fall of 2008.”

I’ve more and more come to disbelieve that financial models “caused” the near collapse of our financial system. They weren’t blameless, and I don’t excuse them, but people and society are too complex to be brought down by one thing. The physical world can be turned upside down by one link in the chain but, with the mental, causality is not so straightforward.

Re the mental: I have just finished reading the biography of Dirac, “The Strangest Man”, by Graham Farmelo, which I enjoyed, partly because I have been studying and writing about the Dirac equation. Dirac was an espouser — perhaps only in retrospect, after he had done his great works on the the foundations of quantum mechanics, the electron, and the quantization of fields, as well as pointing the way to Feynman’s path integral Lagrangian treatment of quantum mechanics — of the efficacy of mathematical beauty as a guide to correct theories of the physical world. He thought experiments should be disregarded if they disagreed with beautiful theories, roughly speaking.

Theory and experiment seem to play leapfrog — with Maxwell, theory led experiment; then, with early quantum mechanics, experiment led theory; then with Dirac and the prediction of the positron, theory was the stimulus; with the particle zoo, experiment tossed up puzzles which Gell-Mann solved; then with gauge theory, mathematical instinct and beauty ruled again. Now string theory is begging for a lead from experiment.

Personally, I think that great equations and theories come from an unknown place which isn’t rational: Farmelo quotes Dyson on Dirac as follows:

“His great discoveries were like exquisitely carved marble statues falling from out of the sky, one after another. He seemed to be able to conjure laws of nature from pure thought — it was this purity that made him unique.”

I think I may have heard Dirac talk once at Columbia in the Seventies. (I know for sure I heard Heisenberg give a seminar there.) It’s interesting to read how by the 1950s his colleagues disrespected him as a has-been and pushed him into retirement from Cambridge as he lost interest in the latest developments in physics. It happens to (almost) everyone — it apparently didn’t happen to Pauli — but somehow I hadn’t realized it happened to Dirac.

That didn’t happen to Fischer Black, but there is something about some of the anecdotes about Dirac in the book — his awkward directness and lack of manners, his willingness to keep absolutely silent when he had nothing to say — that reminds me in a small way of Fischer.

Farmelo quotes the priest-cosmologist Georges Lema?tre (what better scientific interest for a priest than cosmology? And how do you like the effort that went into that i-hat?) on science vs. religion:

“The Friedmann-Lema?tre picture of the universe’s birth seemed to be at odds with the account of creation in Genesis, but this did not bother Lema?tre, who believed that the Bible teaches not science but the way to salvation. ‘The science-religion controversy is really a joke on the scientists’, he said: ‘They are a literal-minded lot.'”