Quirks & Quarks

Hear from Canadian-born cosmologist James Peebles about his Nobel Prize

Manitoba-born cosmologist was awarded the Nobel Prize in physics "for [his] theoretical discoveries in physical cosmology"

The Manitoba native has made major contributions to our understanding of the universe

James Peebles in his office at Princeton University the morning he was awarded the Nobel Prize (Denise Applewhite / Princeton University)

This year's Nobel Prize in physics has been awarded to Manitoba-born scientist James Peebles "for [his] theoretical discoveries in physical cosmology." He shares the prize with two Swiss researchers Michel Mayor and Didier Queloz for their work on detecting exoplanets. 

This is the third time in five years that the Nobel Prize in physics has been awarded to a Canadian-born scientist. Art McDonald won the prize in 2015, and last year, it was awarded to Donna Strickland

Dr. Peebles, the Albert Einstein Professor of Science at Princeton University, has been widely regarded as one of the world's leading theoretical cosmologists for five decades. He's credited for developing the theoretical framework that laid the foundation of our modern understanding of the universe's history —  from the Big Bang to the present day. 

Here's part of his conversation with Quirks & Quarks host Bob McDonald: 

This interview has been edited for length and clarity.

Bob McDonald: First of all, tell me about the call from Sweden. What was that like?

James Peebles: 5:00 in the morning. The first statement: 'I have decided to award you the Nobel Prize.' The second sentence: 'do you accept?' So I said yes. 

BM: Well good! Glad you accepted it. [laughs]

You were born in Manitoba and studied at the University of Manitoba before moving to Princeton University for your PhD. Why did you decide to pursue physical cosmology in the 1960s when that field was just a fledgling branch of physics? 

James Peebles in a yearbook photo from 1958 (University of Manitoba Archives & Special Collections)

JP: You're quite right. I got into this subject with some reluctance. I arrived at Princeton as a graduate student from the University of Manitoba in 1958. To my great good fortune, I fell into work with Bob Dicke, a truly great physicist who decided a few years before that that gravity is too important to ignore, as it had been in recent years in physics. 

The fact that he was doing such fascinating things, I just couldn't resist joining his group. That led from one thing to another to finally in 1964, his idea that maybe our space would be filled with radiation left from the early universe. I remember the day he said casually to two of his young experimental colleagues, 'why don't you build a radio orbiter to look for this radiation,'  and he said to me, 'why don't you think about the theoretical implications.' Those few words set the careers of my friend and colleague David Wilkinson on the experimental side, and me on the theoretical side.

BM: Wow. So it was at that point where they said, 'okay, the universe is expanding, maybe there was a Big Bang.' What were some of the theoretical problems that you were trying to solve about that whole process? 

JP: Well, of course. to begin with, the theory that is now well tested assumes Einstein's general relativity theory of gravity. In 1964, when I started working on this, there were tests in the solar system, but nothing beyond that. It was a beautiful theory, but you really didn't know whether to trust it. And the deepest concern among the concerns I had back then is that we're extrapolating it by an enormous factor to the scale of the observable universe. It made me wonder if the universe is really well-described by general relativity. The answer emerged much later that it is. But for many years, that was an open question.

The other big question is, 'do I trust this notion that the universe on the very largest scales is close to uniform — the same everywhere.' That uniformity is what makes it possible to talk about a theory of the universe as opposed to a theory of bits and pieces of it. If the universe is almost the same everywhere, then we can by looking in a few places, see what the universe has been doing. That was a spectacularly adventurous assumption to make back in the 1960s. It's become clear now that this is the way the universe is made, the reason for the claim that we can make about a theory of the evolution of the universe.

James Peebles (second from left), who earned his Ph.D. at Princeton in 1962 and taught at the University his whole career, enjoys a standing ovation during a news conference at Princeton on October, 8, 2019. (Denise Applewhite / Princeton University)

BM: One of the things that your work did lead to were new ideas about dark matter and dark energy, which actually make up most of the universe. How did those emerge from your theory? 

JP: In brief, the radiation that fills space is very smooth — only slightly disturbed from uniformity. The universe is very clumpy in its distribution of matter. It was reconciling the clumpy distribution of matter with the smooth distribution of the radiation that called for this hypothetical dark matter.

I built this theory in 1982, not as a serious theory of what the universe was like, I meant it to be an example of how the universe could work. It was one example of how the universe could work. I added the cosmological constant in 1984, again, to fit the observations that were getting tighter. In the late 1980s, early 1990s. I was very uneasy about the community acceptance of this model. You can make other models. Why are you so convinced this is the way it goes. I have to admit I was totally wrong. This model fits now a really abundant range of evidence.

BM: Well, it's interesting that we still don't know what they are —  dark matter or dark energy. It's almost like you've made the universe stranger and more mysterious with this.

JP: Yes, we don't know what it is. We only have a constraint. It better be acting much like an ideal gas — collisionless, not interacting with matter. What it is is a deep mystery, and we must leave to the next generations to discover. 

James Peebles chats with three students at an afternoon reception for all members of the greater University community in Rockefeller College Common Room at Princeton University. (Denise Applewhite / Princeton University)

BM: How rewarding is it for you to discover new mysteries like that? New questions for physicists to engage with?

JP: I don't really think in those directions. I throw out an idea. I feel nervous about it. Often, I'm surprised that the idea is right. 

BM: You've obviously had an enormously rewarding career. What is it about theoretical physics that you find so rewarding?

JP: I've always, since I was a kid, been interested in how things work. Clocks around our house were in danger because I loved to take things apart, and failed to put them back together.

One thing that sticks in my mind is when I was a kid, and I had just learned to read,  I came across one of my older sister's textbooks that explained compound pulley. I thought that was really neat, and I still do.

The entire audio interview is available to hear at the top of this page


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