In the early 1970s I wrote a profile of Albert Einstein for the New Yorker. I had known his secretary Helen Dukas since my days at the Institute for Advanced Study. She had come with him when he emigrated from Germany and lived in the Einsteins’ house in Princeton, which after his death she shared with his stepdaughter Margot. I asked if I could visit the house. She agreed. In Einstein’s study there was an etching of James Clerk Maxwell and one of Newton which had come out of its frame. This seemed symbolically correct. Helen offered to make lunch and while she was preparing the sandwiches she gave me a book to look at. It included a letter Einstein sent from Brussels to his wife Elsa in 1930:

I went across to the station … to telephone the Kings. It was quite tedious, because the line was always busy … At 3 o’clock I drove out to the Kings, where I was received with touching warmth. These people are of a purity and kindness seldom found. First we talked for about an hour. Then an English woman musician arrived, and we played quartets and trios (a musical lady-in-waiting was also present). This went on merrily for several hours. Then they all went away and I stayed behind alone for dinner with the Kings – vegetarian style, no servants. Spinach with hard-boiled eggs and potatoes, period. (It had not been anticipated that I would stay.) I liked it very much there, and I am certain the feeling was mutual.

‘The Kings’ were King Albert I and Queen Elisabeth of Belgium. I had the beginning of my piece. (Much later I learned that Leo Szilard had asked Einstein at the beginning of the Second World War to ask the queen not to let the Germans export uranium from the Belgian Congo.) It took me many months to write the profile and the editing, by Pat Crow, was a monumental job too. Then came the fact-checking. It went smoothly until we got to Einstein’s aphorism ‘Raffiniert ist der Herrgott, aber boshaft ist er nicht’ (which I would translate as ‘God is sophisticated but not malicious,’ though it’s often rendered ‘subtle’ rather than ‘sophisticated’).

I heard the aphorism from a physicist called Max Herzberger who had come as a refugee in the 1930s to Rochester, New York where I grew up. He was employed by Eastman Kodak as a lens designer. Einstein had been one of his PhD examiners in Berlin and from time to time he went to visit him in Princeton. But the fact-checker wouldn’t let me quote the aphorism unless I could produce a source he could verify. I didn’t even know when Einstein had said it or why. In desperation I called the Princeton maths department. The secretary who answered the phone told me that the aphorism was inscribed, in German, over the fireplace outside her office in Fine Hall.

Einstein made his first visit to Princeton in 1921. He was told that Dayton Miller, a physicist at the Mount Wilson Laboratory in Pasadena, had just done an experiment which might invalidate the theory of relativity. To which Einstein commented: ‘Raffiniert ist der Herrgott…’ Miller’s experiment failed. The mathematician Oswald Veblen, who heard Einstein make the remark, in 1930 got his permission to make it part of the fireplace in Fine Hall. The mathematics department has moved (to a newer building also called Fine Hall) but the aphorism has remained where it was, as well as in my New Yorker profile.