Retired University of Pennsylvania physicist Gino Segré has carved out a second career as a historian of science, with lively, accessible books about physics, including

Ordinary Geniuses


Faust in Copenhagen


He joins forces with his wife of 31 years, former Philadelphia health commissioner Bettina Hoerlin, for The Pope of Physics: Enrico Fermi and the Birth of the Atomic Age, a biography of the Nobel-winning physicist and Manhattan Project team leader who has been dubbed the architect of the Nuclear Age.

The couple will talk about their book with Penn physics professor Larry Gladney at 7:30 p.m. Wednesday at the Free Library.

Fermi assembled the world's first nuclear reactor in 1942 and was a major figure in the development of the atomic bomb. You call this merely a tiny part of his overall contribution to science. In fact, he had already earned his Nobel in 1938.

Segré: Physics has two major divisions, theoretical and experimental, and there's a very firm line between them. Fermi was the only physicist to have reached the peak in both. He was . . . the first physicist to appreciate computing, and he's the father of what's called computational physics. He was the last physicist to work in all areas of the field: He worked in astrophysics, molecular physics, nuclear physics, particle fission, relativity theory. That work is worth a whole basketful of Nobel Prizes. He shaped how we live today in a way that's never been surpassed since.

You don't come to Fermi merely as academics. Both of you have family connections to him.

Segré: My uncle [Nobel laureate Emilio Segré] was his first student in Rome, and they worked closely together for 20 years, including at Los Alamos [with the Manhattan Project].

Hoerlin: My father [German émigré Hermann Hoerlin] was a physicist, and we moved to Los Alamos in 1953. . . . It was the last summer Fermi was there, too. . . . Fermi died prematurely a year later [at the age of 53].

You write about him in your memoir "Steps of Courage: My Parents' Journey from Nazi Germany to America." You were 13 at the time?

Hoerlin: I remember Fermi quite well. I was a teenager, and I remember how all the Europeans there did this whole European thing. They had hikes on Sunday mornings, and they'd go mushroom-picking. . . . Physicists are an interesting bunch, but some of them are quite eccentric, and he seemed quite normal through my teenage eyes, which was quite a welcome thing for me.

Segré: She's a graduate of Los Alamos High. You should definitely mention that.

You did extensive research on his early life and his most formative childhood experiences.

Hoerlin: Like some people at the time, his parents farmed him out after birth. Literally. They gave him to a farming family to raise until he was 21/2. So he returned to his family at 21/2 into this strange place he's never known, and he burst into tears. His mother just said, "We don't do that here." That was one of the biggest influences in shaping his whole life - the fact that he must suppress all his emotions.

Segré: The second has to do with the extraordinarily close relationship he had to his brother Giulio, who was a year older. When [Enrico] was 13, Giulio . . . died as a result of freak medical accident. That's when Fermi developed this intense interest in mathematics and physics.

So what was he like as a person - say, as a husband to Laura and a father to his two kids, Nella and Giulio?

Hoerlin: People called him "The Pope of Physics" because he was infallible, maybe not always, but usually, when it came to physics. But he was fallible in other respects, including family life. . . . His two children had the same problem as the children of other famous parents: having to learn to live with people who are always put on a pedestal by others. . . . Later in life, his daughter said that the problem wasn't that her father didn't have emotions, but that he never knew how to express them.

Fermi famously used his 1938 trip to the Nobel ceremony in Sweden as a gesture of protest that insulted Benito Mussolini.

Hoerlin: He went without the uniform members of the Royal Academy wore. . . . And he didn't give the fascist salute.

Yet, wasn't he a member of Italy's National Fascist Party?

Hoerlin: He was a very apolitical guy. He wanted physics, just physics, pure and simple. But he joined the fascist party in Italy, which coincided with Mussolini inviting him to join the Italian Royal Academy. So on paper he was a fascist. But he was very wary of them, and he was married to a Jewish woman. He had been to the United States a number of times in the 1930s, and he really regarded it as a land of the free. . . . So even though Laura was very hooked into life in Rome and her family, he finally convinced her they needed to leave Italy.