Interview with James Peebles on 6 December 2019 during the Nobel Week in Stockholm, Sweden.

What did you want to be when you were younger?

James Peebles: Until I reached university, I was rather directionless. Never a rebel but rather a dreamer. I didn’t pay too much attention to classes, I am sure I annoyed my teachers, or to what I would want to do after I graduated from high school. So, I didn’t have a direction until I reached the University of Manitoba. There I learned that I love physics. I’m sure there were signs before I reached the university that I loved physics, for example I do remember as a youth I would read anything that was before me, the cereal boxes. I read in one of my older sister’s schoolbooks how compound pendulum works, and I still remember thinking how wonderful that is, and it was a hint, and I liked to build models. Because I liked to build models, I entered the university in engineering. I enjoyed it. I guess I could have made my ways through life as a mediocre engineer, but to my eternal gratitude of friend who I can name, Dale Loveridge, since I complained to him that we were running out of physics courses to take in engineering: “Why don’t you transfer to physics?”

Perhaps you know the phrase a “Duh” moment? Well, that was a “Duh” moment. Why didn’t I think of that? So, I entered physics and loved it from the start. I owe a lot to the faculty and I owe a lot to the students too. You know, students learn a lot from fellow students, we don’t give that enough attention, I think. Nothing I like better than to see students arguing over how to work a problem. Also, my fellow students introduced me to Allison. So I was married and off to Princeton university as graduate student. The faculty member who told me I would go to graduate school in physics to Princeton, Ken Standing, died just a year or so ago. It was a great pleasure to meet him prior to that. He had his own distinguished career in the structures of large biological molecules, biochemical molecules, I am not sure the phrase. Anyway, I love physics, it’s just grabs me and still does.

What do you enjoy about physics?

James Peebles: One way to put it, I think, is that event with the compound pulley. A compound pulley is that the one in the same time rather subtle, but yet explicit within the framework of the game. Similarly, physics is layer upon layer of concepts such as a compound pulley. Each compound, complex, what am I trying to say? Each element of physics is, when looked at from afar, a compound pulley. It’s a simple concept, well defined and subtle but yet direct straightforward in many ways. And physics is just a hierarchy of such things. I find that neat. I suppose I am also satisfied by the fact that in physics you get to settle arguments, because you can do experiments and you can find out whether or not this concept make sense. It’s also relative to say, oh, biology much simpler and I do treasure that simplicity. Again, my impression of a biologist is someone who’s waiting through depths and complications, it’s just so subtle. Whereas in basic physics, which is the kind I enjoy, you can actually start from the fundamentals and work your way up, layer upon layer of compound pulleys. You can’t do that with biophysics because it is just too, too complicated. I guess I could have made my way through life as a biophysicist too, but I wouldn’t has been as happy.

Was there a particular person that influenced you?

James Peebles: Yes, I can mention two. I have already mentioned one, Ken Standing, at the University of Manitoba. You know I reflect back, and I don’t remember him ever saying: “I suggest you go to the University of Manitoba, Princeton for graduate study”. He was rather: “You will of course go to Princeton”. It set my life. If I hadn’t gone to Princeton I wouldn’t have met my second and really top adviser, professor Robert Henry Dicke, Bob to everyone, who was an inspiration when I arrived. He has doing gravity physics which of course lead to cosmology. He has just the sort of skills that I really take a delight in. He understands physics very well, but he understands also how to apply it and to be very, very much a person who likes the combination of theory and practice which totally grabbed me and still does. Bob Dicke I have called for many years my professor of continuing education. He’s alas no longer with us but through the years he taught me so much. Not only about physics, but also, don’t be messy with your physics. The one time he would get hostile was when you were sloppy in your thinking. And that certain cured me of being sloppy.

Can you tell us how you discovered you’d been awarded the Nobel Prize?

James Peebles: Do you know that in the US, perhaps around the world, there are sites in which you can place money, wagers, on events, such as who will get the Nobel Prize and it turns out that these sites have a pretty good record. You understand that the more money placed on a candidate for the Nobel Prize, the lower the pay-off. So, my university and I think many others, keep track of the odds on faculty members and so, for the last two years I have had an enigmatic message from our department of public relations: “If you need help with publicity we will come to your aid”. No explanation, no mention of Nobel, but at this time of year you wonder, so I was slightly prepared, and you know, to be honest, I think it was a good choice. I’ve been riding this wave my entire career, so, that was great. They called at a definite hour here in Sweden, which may be a very different hour at the Laureate’s home. So, five o’clock, the call, and you know at that hour either it’s something really bad or something really good, so, I was somewhat prepared when I picked up the telephone. Allison’s … my first words were: “Oh God!”. The university was prepared, and they had laid on elaborate celebrations through the day. Totally exhausting. But still, utterly rewarding.

Do you have any advice for young scientists?

James Peebles: There is one piece of advice that I keep advising, keep offering: “Don’t judge your career by the number of prizes and awards. I have so many. It’s wonderful and the Nobel Prize is absolutely spectacularly wonderful, but to get such a prize requires not only dedication and creativity, it requires eventualities. The cards must line up just so, in order to make it appropriate for a prize-winning committee to recommend you, don’t count on those eventualities. Judge your career by how well you did at it. And of course, don’t be sloppy.

Do you have any advice for young people entering science?

James Peebles: My advice, my central advice to a young person considering entering science of any sort, say in natural science: look around, discover what really interests you. It may not be the first thing that you notice, you may find something mildly interesting, but if you look a little harder, you’ll find something even better. Don’t jump into a particular line of research until you have looked around quite carefully and discover that which really fascinates you. If you are fascinated, you’ll do well.

Why do you like teaching?

James Peebles: You understand that teaching, the students learn from a good teacher and the teacher learns from the students. Also, you know, there is the comment of Samuel Johnson, “Nothing quite concentrates the mind like a prospect of being hanged” and that quite a serious, but the prospect of having a student ask a question that you haven’t anticipated, is something that makes me very uneasy. So, of course, when I teach, I prepare, and I try to think of all of those odd little side issues that I never perhaps thought through. They happen and I learn from that. Also, of course, it’s so lovely to see young people who are interested in something, so interested so they sit here and take notes from what I say. And, of course, I emphasize time and again, they are learning from each other. Nothing I love more than to see a group of students arguing over how to work a problem, so that’s rewarding. And because I love physics, you are not surprised to learn I enjoy talking about it and so, yes, I have taught both students who are advanced in physics, who are deeply interested in physics and those who take the course as a requirement.

The last is a far by far the most difficult. How do you persuade these people that physics is not simply a hurdle to pass so they can get on to do something they really want to do, perhaps medicine? How do you convince them that this is a fascinating subject? In part, you know, I think we have to be fatalistic about that, some people are charmed by compound pulley and some are not. Perhaps you don’t particularly care about compound pulleys, but they are neat, and perhaps not neat for you, but some for they are. So, I guess I do have the seat-of-the-pants feeling, feeling that different people are suited for very different activities, that’s obvious isn’t it, must be. So, my test might be, offer them a compound pulley, do you think that is neat or would you rather that I would stop talking about it. So, most of the time I have taught people who think compound pulley is neat even though they’ve never considered that before. By far, as I say, the most difficult is teaching those who’s not so sure compound pulleys are neat. The most depressing question is: “Is this going to be on the exam?”

What are the most important qualities for being a teacher?

James Peebles: The most important quality of being a teacher, I think, surely is the enthusiasm for what you are trying to teach. And perhaps it’s equally important, you should pay attention to the students. That seems pretty obvious, but I suppose if you are a teacher who don’t enjoy your job, then I think it would be good of you to find another line of work. If you enjoy your job it means you are just love transforming, transmitting information to the student. And you will notice the student either understanding what you’re saying or not and if the latter you’re going to try hard to get the student’s attention. That was when we used to have an hour and a half long lectures, to stop half way in between was a good way, not only to get them awake, because it’s rather hard to sit for an hour and a half, but also I found, there are students who have questions but they don’t want to ask them, because they don’t want to be the subject of attention and the breaks were a wonderful way for a student who was diffident to approach me. I don’t know how to encourage these people to speak up, no one is going to bite them, some people are just like that. The break was always a good way, not only to refresh all of the students but also to give the diffident ones to get a chance to talk to me.

What do you enjoy doing in your free time?

James Peebles: As I have reached the golden years, I find that I enjoy physics, so I don’t often take much time off. I love going into the laboratory and writing and calculating or reading. I used to enjoy gardening quite a lot. In recent years physical effort is becoming more difficult. The fact that the market gardens have tomatoes in immense abundance when I have my pitiful few tomatoes, I stopped gardening. However, I spent the last two years full time on a book on how we got from where we were in the past to now in cosmology. The book is now done. It will be out next spring. I have still some deep jobs to do in checking proofs, but that labour is pretty much over and I think I will not get myself involved in another project that is quite that intense and that maybe I will start gardening again. I think maybe flowers rather than vegetables.

Where do you do your best thinking?

James Peebles: I’m deeply fortunate that we live just one mile from my office. It’s a mile through almost entirely quiet residential streets, so walking to and from the lab is to me refreshing and a chance to let my mind wander. I’ve always, when walking, paid very little attention to where I put my feet and so the mind can wander in totally random, irrelevant silly directions, but sometimes it will land on a little point: “Why didn’t I think of this?”, rather a “Duh”-trip moment. Though it’s interesting, I discovered a few years ago that I was tripping and, you know, a face-plant when you fall, it happened to me three times in one year. No injuries at any time but it’s such a chock to suddenly find yourself prone. So, I’ve started looking where I put my feet to the detriment of my thinking. Which should I do? I think I will continue to watch where I put my feet, I will put a little more attention to that, but I also will continue to enjoy walking and letting my mind wander. I hate running. I can’t imagine operating a treadmill or pumping weights, that’s sounds so dull. But to me a walk in the woods or in the city is pleasant – always is.

What do we still have to discover?

James Peebles: In our field we are leaving to the future generations a lot of interesting research problems. It is rather difficult to convince non-scientists of the fact that we at the same time have a reliable science, well-established and yet there are simple questions they can ask of you that you can’t answer. It’s particularly notable in cosmology when you consider that we postulate this dark matter, we postulate this cosmological constant or dark energy. They surely have deep physical meaning, that we do not understand, what a glorious opportunity, explain this. It is as I say, a subtle business to explain that we have both great open problems and yet a securely established physics. The point is, of course, all of our physics are approximations, we have no complete theory in any branch of physics or in any other natural science. We instead have approximations that are good or more or less well-established depending on the evidence. We have so much evidence for cosmology that I think it is almost a dead cert that the dark matter’s there. We know that its properties must be in a defined range, but that range is pretty broad. We’re sure that there must be there and the great triumph would be to identify it. Lots of experiments are going on attempting to do that, watch your local newspaper, for announcements.

Watch the interview

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