Remembrances of Dirac

Farmelo replies: I thank the correspondents for their illuminating points. I am especially grateful to Ted Jacobson for drawing attention to Georges Lemaître’s 1931 article on the quantum theory of the early universe; I had not previously heard of it. It is an impressive paper. Jacobson is surely correct that Paul Dirac had probably read it before he wrote his 1939 Scott Lecture, though I expect that Dirac had forgotten about it; he was in the habit of doing that and would blame his “poor memory.” That said, it seems to me that Dirac’s words are a good deal clearer and more insightful than those of Lemaître, who goes off the rails with the specifics toward the end of his piece.

It was a pleasure to read Ron Edge’s recollections of Dirac. I went to a lot of trouble to check the veracity of the Dirac stories still in circulation, including Dirac’s famous “That was not a question, it was a statement.” Dirac was not joking. He used the comment several times, beginning in the late 1920s. One of his closest friends, Leopold Halpern, told me in February 2006 that he once asked Dirac if he really did respond that way. Dirac replied, “Yes. Why do people find it funny?”

I agree with Edge about the importance of the del squared V and Kapitza clubs. I could not find detailed information about the former, but the papers of John Cockcroft in the excellent Churchill College Archive Centre in Cambridge, UK, contain a record of the meetings of the Kapitza club, along with charming photographs of its final meeting in 1966.