Our expanding universe

Dr. James Peebles, the Albert Einstein Professor of Science at Princeton University, has earned global recognition as a theoretical cosmologist during his career spanning over five decades. The Manitoba-born researcher received the 2019 Nobel Prize in Physics for his groundbreaking theoretical contributions to the field of physical cosmology, marking the third time that a Canadian had secured the illustrious prize since 2015 – Queen’s own Art McDonald received the prize in 2015 and Donna Strickland, University of Waterloo, won in 2017.

Peebles’ theoretical framework underpins our contemporary understanding of the evolution of the cosmos, spanning from the inception of the Big Bang to the current era. Building upon this foundation, researchers at Queen’s working at SNOLAB are hunting for the illusive dark matter particle, which Peebles showed plays a critical role in shaping the early evolution of galaxies. This work is propelling the scientific community toward the adoption of innovative methodologies aimed at extremely sensitive particle detection, tools that have applications well beyond particle astrophysics.

Recently, Dr. Peebles met with colleagues and collaborators at the Arthur B. McDonald Canadian Astroparticle Physics Research Institute (McDonald Institute) and delivered his lecture, “Our Expanding Universe,” to a sold-out public audience. His talk delved into the intricacies of our cosmos, shedding light on how we’ve come to understand the universe and our place within it. The Queen's Gazette had the opportunity to catch up with Dr. Peebles and learn more about his research contributions.

*This interview has been edited for length and clarity.

Queen’s Gazette: Your Nobel Prize-winning work opened various new avenues for future research. Looking ahead, what do you think are the most promising areas of exploration for researchers, or what comes to mind when thinking about the most exciting questions or biggest mysteries surrounding cosmology?

Dr. Peebles: It's always the case in history, and I’d say even in my own personal experience, that when you solve a problem you open a new set of even deeper problems. This is happening in cosmology, the study of the large-scale nature of the universe. The universe is complicated; we must make progress by successive approximations. For example, in cosmology, physicists have discovered a new form of matter – dark matter. We don't know what it is, and we have little understanding of its properties. Naturally, scientists are wondering about the nature of dark matter. This is only one of many questions about cosmology that scientists are pondering, and seeking better theories that might pass tests. Some of these theories are looking to be more promising than others because they pass promising tests of predictions. This is our standard criterion for a good theory, though never a guarantee. In short, we have an abundance of evidence that makes a compelling case that we're on the right track in the theory that the universe is expanding and cooling, but we still have a lot of open questions to resolve.

Among the open questions is how the galaxies formed. I'm convinced that the theory we have now is a good first approximation to the way they formed. It has taken many years of effort to apply the theory we have now to a prediction of how the things we call galaxies formed. The results come close but still miss the mark. Maybe that is because the formation of galaxies is complicated, so people need to work even harder with the theory we have now, or maybe we don't quite have the right theory. Maybe we're missing something interesting. It would not be surprising; the universe is large and full of interesting things.

Dr. Peebles is renowned for his pioneering contributions to the field of theoretical physics.

Queen’s Gazette: As you know, the Nobel Prize in Physics was awarded to Canadian-born scientists three times between 2015 and 2019, to yourself, Arthur B. McDonald, and Donna Strickland. What do you think is contributing to this remarkable success of Canadian physicists on the international stage?

Dr. Peebles: One of Canada’s most valuable assets is its scientific researchers. We love to have Canadian students come to graduate school at Princeton; they're good at what they do. Why are they good? I expect that in Canada there is a little more emphasis on the basic principles of physical science, more than what one sees in the United States. The basics, which I learned at the University of Manitoba, are deeply valuable to me.

When I was an undergraduate at the University of Manitoba I learned a lot of basic concepts from the professors of physics and mathematics. One of them, Ken Standing taught a particularly interesting physics course. Ken told me “Go to Princeton for graduate studies.” He thought it would be just right for me, almost as if he knew it would work out. I never realized it at the time, but he did a spectacularly good job of mentoring me. We kept in touch, and I had the deep pleasure of visiting him on many occasions when I went back to visit the University of Manitoba.

At Princeton, as a graduate student, I joined a research group run by Professor Robert Henry Dicke – Bob Dicke. He was an experimentalist, and I’m a theorist, but he did experimental work that I admired. He greatly influenced me in graduate school by showing by example what physical science is all about and by giving me interesting problems and leaving me to find my own way through them. These two people played a big role in making me who I am.

Queen’s Gazette: Beyond your scientific contributions, you’ve also been an educator and a mentor yourself. What advice would you give to young researchers or aspiring physicists who are interested in pursuing a career in cosmology?

Dr. Peebles: I’m often asked that question by young people, and truthfully, I don’t have much in the way of answers, at best only hints. I wasn’t a focused student in high school: I didn’t pay attention, I didn’t participate in any activities, I was what you could call a “dreamer.” Then I went to the University of Manitoba, where I discovered what I wanted to do. I discovered it mostly through lectures and reading materials that grabbed me. So, to students, my advice is “pay attention.” Specifically, pay attention to the interesting things you run across, and ask yourself, “is this something I would like to study for a long period of time?” I got a clear answer - it was physics. Others get other answers.

Another thing I always caution is not to jump into anything without thought at leisure, particularly when you’re 20 years old. Many students enter university with definite ideas of what they want to do. That can change in a university environment where people are exposed to other people with many different interests in fields of research and inquiry. They learn still more in lectures. All of this leads many to change their plans in the first year or two. This is healthy. I would say that as you enter university try to broaden your vision, and leave room for new directions. Things are going to happen that may cause you to change direction. That’s good.

Queen’s Gazette: I am hoping you could share with me what inspires or motivates you to continue in your scientific work, even after achieving such a significant milestone like the Nobel Prize in Physics?

Dr Peebles: Well, I’ve committed my life to physics, even now I'm retired. How shall I fill my days? I don’t particularly like golf; to me, it’s a nice walk spoiled.

But I do enjoy working on physics research. I’m fortunate that I can keep my office at Princeton University, and I go in three or four times a week to work – but I can't call it work because I’m not paid. I like presenting public lectures such as the one we did at Queen’s. You gave me an audience of lively young people, I guess many of whom are students, older people, and children. I liked that. I hope the people in that wonderfully diverse audience came away with a better understanding of what we are doing in natural science, and maybe even doing something about it. I think Queen’s is doing a great job of maintaining its research curiosity and keeping students driven towards this great mission to solve the world’s greatest problems.

Note: This story originally appeared in the Queen's Gazette.