Someone once said that a book is never finished; it is merely abandoned. As the truth of it began to sink in, I sometimes wondered what on earth made me start upon this one!

I first met Richard Eden while visiting Jacques Mandelbrojt in Marseilles, in the late 1960s or early 1970s. We were next thrown together in 2000–2001 in Clare Hall, Cambridge, where he was one of the presiding deities and I a visiting fellow. In the intervening decades we had both moved from one production line to another. Richard's questioning about what I had been doing compelled me to organize my thoughts, and this book is the result; it would not have come into being without the encouragement offered by Richard, and by Jamal Nazrul Islam.

The influence of Wigner, whom I barely knew, permeates almost every page of this book. I first met him in 1961, at the Weizmann Institute. I was then working for my Ph.D. under Professor Giulio Racah on a group-theoretical problem of nuclear spectroscopy, and in awe of Wigner. As I was introduced to him, he blew my self-confidence to smithereens by asking for my opinion about the unreasonable effectiveness of mathematics in physics – I had none – but he had the kindness to send me a typescript of his article when he returned to Princeton. That question has haunted me ever since.