After abandoning family plans to go into the heating business, Leonard Susskind went on to become a founder of string theory. He is the director of the Stanford Institute for Theoretical Physics in California. His latest book, with George Hrabovsky, is The Theoretical Minimum: What You Need To Know To Start Doing Physics. Now he is teaching physics to people in their 90s. He talks to Anil Ananthaswamy about the language of physics and why new thinking is pushing experiments into the impossible.
Anil Ananthaswamy: You teach physics at Stanford University's continuing studies program. Who are the people that attend your classes?
Leonard Susskind: They are in their 40s to 90s, and I mean that literally. There's a lady in a wheelchair who was close to 95, and she was following the technical lectures. They are people who had other careers and I think are a little sorry that they never became physicists.
AA: Are these the type of people you've written your new book for, which is not really popular science nor a physics textbook?
LS: Over the years, I began to understand that there were a lot of people out there reading physics in popular literature that they could not understand—not because it was too advanced, but because it wasn't advanced enough.
At the same time, they were not about to plough through a big fat textbook. I wanted to give them a book from which they could learn easily and efficiently. It's not for complete beginners; it represents the bare minimum you need to know to honestly and truly learn the subject and move on to the next step.
AA: Hence the title The Theoretical Minimum?
LS: Yes. The title goes back to Russian physicist Lev Landau, who did not suffer fools gladly. To him, the theoretical minimum was what a young physicist had to know to work with him, which was everything. That name stuck with me.
AA: You are now in your 70s yourself. How did you get into physics as a young man?
LS: I did not come from an academic background. My father was a smart man, but he had a fifth-grade education. He and all his friends were plumbers. They were all born around 1905 in great poverty in New York City and had to go to work when they were 12 or 13 years old. But sitting around the kitchen in our house, they had all sorts of interesting conversations. There was a funny intellectuality to them.
I went to college because my father thought that I should learn engineering, because he wanted to go into the heating business with me. There I realized I wanted to be a physicist. I had to tell him, which was a somewhat traumatic experience.
AA: What happened when you told your father?
LS: For months I had been trying to figure out how to tell him. One day I drove over to his house. This is emblazoned in my memory: It was a terrible, terrible feeling.
He had a plumbing shop in the basement and was there cutting pipe for the next day's job. I went down and said, "I'm not going to be an engineer." He got upset. Though he almost never used bad language, he said, "What the fuck are you going to be? A ballet dancer?"
I said, "No, I want to be a physicist." He said, "No, you ain't gonna work in no drugstore." I said, "No, no, a physicist, not a pharmacist." And then I can't remember the exact conversation, but I do remember the magic word was Einstein. I said I wanted to do what Einstein did. That just shocked him.
Something snapped, and he decided right then and there that that is what I had to do. That was the end of it. From then on, my father tried very hard to learn a little about physics.
AA: Did the experience of watching your father learn physics lead you to teaching older people and to write The Theoretical Minimum?
LS: That's an interesting question. I have some sympathy for people like that. And there is some similarity between my father's friends who would sit around the kitchen table talking about everything and the people who come to my classes to learn physics. So, maybe an unconscious influence.