Who can ever tire of learning about the great discoveries in physics during the first forty years of the twentieth century, and about the men and women who were responsible? The benchmark texts are the surveys and biographies written by the late physicist and historian Abraham Pais, though all the essentials are gathered in a more condensed—and, to my taste, somewhat more digestible—form in the relevant chapters in William H. Cropper’s Great Physicists (2001). Now here is Gino Segrè with an original and worthwhile contribution to the field.
Faust in Copenhagen is an exceptionally thorough account of the emergence of modern quantum mechanics over the years from 1925 to 1933, aimed at a general reader—which is to say, there are no equations. This is a difficult story to tell in any straightforward way. So many different and concurrent threads have to be woven together that a simply chronological narrative can’t be given. Some more subtle organizing principle is called for. Segrè has used the Copenhagen conference of April 1932 as his focus, returning repeatedly to it, and to its participants, as a way of keeping us oriented.
These Copenhagen gatherings were held annually from 1929 to the onset of the Second World War, so the 1932 conference was the fourth. One participant at the 1937 Copenhagen meeting was Emilio Segrè, the author’s uncle, and Gino Segrè has himself had a long career as a theoretical physicist. He understands the science as well as anyone, and has a close knowledge of all the great players, in some cases from first-hand acquaintance. He is just the right person to write a book like this, and has done a fine job, occasionally weaving in some small details of his own family, but in a way that is not self-indulgent or obtrusive.
“Writing this book has been a labor of love,” the author tells us, “allowing me to spend time in the company of many of the intellectual heroes of my youth.” The love shows. Through a skillfully designed narrative and many personal insights, Segrè brings to his reader the warmth of his admiration and reverence for some towering figures of our civilization.
Segrè has placed at the heart of his story seven key physicists. One of them, Wolfgang Pauli, did not actually attend the 1932 meeting. Three others of Pauli’s generation (ages 25 to 31) were present in Copenhagen: Paul Dirac, Werner Heisenberg, and Max Delbrück. To balance these four young revolutionaries, Segrè includes three older (ages 46 to 53) participants among his magnificent seven: Niels Bohr, Paul Ehrenfest, and Lise Meitner. There were of course others present at the gathering—close to forty altogether, Segrè tells us—and we hear about some of them in passing.
The reason Segrè has taken the 1932 conference as his focus is that this was a pivotal year in the development of modern quantum mechanics. The theoretical foundations of the subject had been laid down in the first three decades of the century, from Max Planck’s great 1900 paper implying the quantization of energy through Pauli’s postulating of the neutrino (Gino Segrè’s research specialty) at the end of 1930. Now the experimentalists were beginning to take over from the theorists. Mere weeks before the 1932 conference, James Chadwick had become the first person to observe neutrons in experiment. In the summer of that year, bracketing the conference, Carl Anderson at Caltech observed the positron, which had been postulated by Dirac in 1928. Experimental results then came thick and fast, culminating in July 1945 with a dramatic event in the desert outside Alamogordo.
The year 1932 was the pivot. It was preceded by the long theoretical slog that had culminated with a sensational burst of creativity from 1925 to 1930: Heisenberg’s matrix mechanics, Schrödinger’s wave mechanics, Pauli’s exclusion principle, Heisenberg’s uncertainty principle, and Dirac’s relativistic equation. It was followed by the great experiments: Anderson’s positron, the “splitting of the atom” (actually of the atomic nucleus) by Hahn and Strassmann, Fermi’s chain reaction, the Bomb. The Faust in Copenhagen year, the year 1932, was the eye of the storm.
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