James Peebles Interview: Conversations with History; Institute of International Studies, UC Berkeley

A Cosmologist’s Intellectual Journey: Conversations with James E. Peebles, Professor Emeritus of Cosmology, Princeton University; October 12, 2006 by Harry Kreisler

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Jim, welcome to Berkeley.

Thank you.

Where were you born and raised?

In Manitoba, the center of Canada, to the south of the province, born and in early life in St. Boniface, a sister city of Winnipeg; then later in St. Vitale. Public schools, small schools, and then on to the University of Manitoba.

Looking back, how do you think your parents shaped your thinking about the world, or maybe in your case I should say the universe?

We didn't talk about the universe. My father, though, was very good with hands. He built things, and that very much grabbed my attention. I, as a youth, didn't pay too much attention to the stars, although I remember being impressed by the aurora, but I did pay a lot of attention to building things. I'd build sleds, I'd build inexpensive radio receivers. I like to work with my hands, and that must have been inspired by my father.

As a young person were you drawn to science, in high school, middle school?

I didn't know what science was in high school. I shouldn't complain. It was a good school, I learned things, but I didn't learn very much about modern science, even modern mathematics. It was quite a shock to go to university.

In what way were you shocked, and what did you major in after the shock?

It was a wonderful place, so many bright people doing so many interesting things. Because I was not a diligent student in high school I didn't have a clear idea of what I wanted to do, except that I did feel I'd like to continue with education. I knew I liked to build things, so I enrolled at the university in engineering. That was okay, and I guess I could have become a mediocre engineer, but to my great good fortune friends persuaded me to transfer over to physics. I can't say it was a "eureka" moment; I just stopped complaining and started doing my homework.

So, it felt natural to you?

Somehow it felt right and I never looked back, and never have asked myself, "Should I have done something else?" No, this was right for me.

Did you have any teachers at the university that were very influential in pointing you in a particular [direction]?

Super, super [teachers]. It's not a world-famous university perhaps, but there were excellent faculty and they really inspired me in physics. I consider myself a physicist, not an astronomer. I took no courses in astronomy. I didn't even know about stars when I left Manitoba.

Where did you go to graduate school?

Princeton University in New Jersey. I came there intending to continue my interest in quantum physics, particle physics, but didn't, although there were excellent people doing that sort of thing at Princeton. Instead, I met my lifelong teacher from then on, Bob Dickie, who inspired me to follow him. He had been a great contributor to quantum optics. In the years from the Second World War into the fifties he was one of the leading figures in figuring out quantum optics, the development of masers and lasers, some wonderfully ingenious inventions in that field. But then he decided gravity physics was being very neglected as a subject for research in physics. He started working on that, and what he was doing was so fascinating, I just trailed along.

What did you wind up doing your dissertation on, I assume under his influence?

There are in physics the constants of nature, the numbers that characterize interactions. In particular, the strength of the electromagnetic interaction is measured by a number called the Fine Structure Constant. Bob was fascinated by the question: Could such numbers be not fixed numbers but rather vary? It was on his part more philosophical than based on anything firm. Somewhat ironic that these days, within superstring theory, people are convinced these numbers ought to vary with time and maybe slightly with position.

In any case, he set me the task of finding evidence that would constrain how much this number could have varied through time. It turns out there are lots of ways to do it. In particular, in those days one had pretty well developed already the concept of radioactive decay of long-lived isotopes as a method of measuring the ages of rocks. Different radioactivities decay at different rates, leave different products, you can count the products, deduce an age under the assumption that the decay rate is constant. But if the strength of the electromagnetic interaction were varying, that would change the decay rate, and so different decay change would give inconsistent answers. Kind of neat! So I learned some geology, which I'd never done before, and I learned some astronomy, because [when] you look at great distances, you see things as they were in the past, and again, make some checks. So, my thesis, in a way, was leading up to some very modern ideas. I had no idea, of course.

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