Interview, November 2020

Carl Wieman was awarded the Nobel Prize in Physics for his work on super cooled atoms but over the last three decades he has also been applying a scientific approach to something different: improving education. In this interview he talks about better teaching methods, what COVID-19 has taught us and how we could all benefit from a scientific way of thinking.

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Interview transcript

Eric Cornell, Carl Wieman and Wolfgang Ketterle welcome to this Nobel interview. You have been in Stockholm now for a few days and yesterday you got the Nobel Prize and this was for your discovery of Bose-Einstein condensate – the coldest piece of material in the whole universe. Do you still remember the day of this discovery, Eric?

Eric Cornell: Very very clearly. It’s etched in my memory. The excitement of the people in the lab, the images coming up on our computerised camera. Very vividly.

When was it?

Eric Cornell: It was June 5th 1995 and things had been happening over the last day or so but I would say it was on that morning, about 11 o’clock in the morning, when I said: Yes, this is …

Carl Wieman: Before 11. We remember it pretty well.

You were there too?

Carl Wieman: No actually, I was on an advisory board but I would have to listen to talks and then I would rush to the telephone and call in and get the latest results and talk to them about what was happening.

Eric Cornell: A combination of phone calls from Carl and that day we were scheduled to have an official visit from a regulatory commission that overlooks NIST and they wanted to make sure my agency were doing sensible things. Usually for these occasions we clean up the laboratory, we put up posters, the lights are bright. But on this day we thought we can’t stop for the visit and so the lights were dark, there were no posters, everything was a mess. We were working very hard, and no one would talk. The commission came in and no one would talk to them. At the time I was thinking, if this doesn’t work I’m going to have something to answer to the director of NIST but in fact a few days later things were working very well and later I heard from members of this commission who said it made a favourable impression on them because they could realise something was going on if we hadn’t cleaned up the lab and hadn’t put up posters for them.

Can you describe the feeling of seeing this big thing?

Carl Wieman: The initial feeling was of course a lot of excitement trying to get this … But there was also considerable nervousness in it. What we saw looked so much like the best we had hoped for, it’s often the case you fooled you. When things work better than you almost can expect then oftentimes it means you’re fooling yourself. I remember forcing myself to say Wait a minute, don’t get too excited here. You could be just fooling yourselves. Let’s think hard about what extra tests we can do. How can we check this? We can’t get too wrapped up in until you are absolutely certain.

Wolfgang, you were working at another laboratory in parallel and also chasing the Bose-Einstein condensate. Do you remember when you got the news from Boulder?

Wolfgang Ketterle: I remember that day. I guess I was at MIT and probably Dan Kleppner was informed over the telephone and he shared it with us. We were quite impressed. It’s always nice as a scientist to see that science moves on. On the other hand, we were the tightest competitors and for several years we had put all our efforts, invested all our resources on the goal of achieving Bose-Einstein condensation. We were just about to get ready for the next round of experiments and I remember there was feverish activity in the lab because we knew we were ready to observe it. If you have worked for something for several years, if the final result is obtained within a few days or weeks this is almost simultaneously and we were running our experiments feverishly and we thought we would also have a shot at it.

When did you arrive at the condensate?

Wolfgang Ketterle: We arrived at the condensate in a memorable night September 30th about four months later. In between it was a very traumatic time because for a few days or weeks we thought we had the experiment ready. We knew now of course that there would be a signal, it can be observed and we had everything ready to observe it, but somehow we had some problems, we couldn’t get the atoms cold enough. Then we tried in the following weeks to implement some improvements and unfortunately we lost the /- – -/ vacuum which is a major disaster and it takes weeks or a couple of months to get it back. We were ready to respond but we couldn’t. We had to wait for pumps to evacuate the chamber, to clean the surfaces, and it took a long time. Then we were ready to go and then in the next – I don’t remember – days or weeks of experimentation it happened on this night.

Dramatic months.

Eric Cornell: It must be said that when they did observe it it was with condensate a hundred times larger, a thousand times larger. It was in some sense an even much more dramatic event.

This is why you’re sitting here, I understand. How important is competition for research?

Wolfgang Ketterle: It was absolutely crucial. I have to say this competition was for me a scientific competition at its best. There was cause for realisation. I learned from things you did. We were inspired and people were working harder.

No secrets?

Wolfgang Ketterle: Small secrets. It got the best out of us.

Eric Cornell: It really focuses the mind. It’s often emphasised as a negative aspect: Oh, we’re fighting together when we should be cooperating. But in fact in the long run there is cooperation. We publish ideas. We exchange. But momentarily when it’s focused on the idea of making something work I really think it does in fact provide a set of rules to the game that as Wolfgang says really bring out ones best.

Carl Wieman: I tend to think that it doesn’t make people particularly smarter but it does make you, just like competition in any other area, it makes people just try that extra harder. The students work with a little more effort and are little less likely to go off skiing.

Day and night?

Carl Wieman: Yes. It’s just that little extra push of effort.

Blood, sweat and tears … This expression, can one apply it to research? Which of these is the most adequate?

Eric Cornell: Our chambers are different from Wolfgang’s. Our experiments are done in glass chambers and if one isn’t careful they break and in fact blood is not out of the question in these circumstances. The /- – -/ of materials these come naturally.

I understand when you arrived to the discovery that people were working through years because nobody was lucky enough to get it before you. I understand also that they had lots of failures behind them, so you must also have had it. How can you psychologically overcome all those failures you meet in your life as a scientist?

Carl Wieman: I always think that one of the most important aspects for being a good scientist is the capacity to have a large threshold for frustration because it’s not just the big experiments that run for a couple of years and then fail. Sometimes the previous work you referred to, it’s been working … it’s polarised hydrogen, they were failures in that they didn’t achieve Bose-Einstein condensation, but they weren’t failures in that no results came out. They came out with results showing paths that don’t work and we learned a great deal from those experiments. That’s failure in one sense but success on another.

Eric Cornell: More success than failure, I would say.

You turned a failure into success.

Carl Wieman: It’s not even failure at all. The point I wanted to make was that the frustration is much more not on those kind of things. It’s the frustration of all of these things that have only been made once, all the equipments never functioned before, some little component somewhere goes wrong and you have to spend days and days trying to understand why it won’t work. That’s where frustration comes in, in tracking down these things.

Eric Cornell: Millions of details.

Wolfgang Ketterle: I want to make two more points. One is when I became an assistant professor at MIT and I decided to put the focus on getting cold and /- – -/ atoms. I had the feeling I could not lose because this was new territory and everything /- – -/ if I tried it intelligently was a contribution to the knowledge of science. As Carl said if something failed it was new, if something worked it was new. I never felt I was wasting my time and neither did the people around me. If you set yourself a big goal even if you don’t accomplish it or if you accomplish it all in many years it motivates you to do good research and work at the frontier of your field.

Eric Cornell: I completely agree with Wolfgang, but I think it also must be said that there was beginning to come up around those Bose-Einstein condensation almost a dark superstition. Of course scientists aren’t really superstitious, but many …

Carl Wieman: Yes, they are, they just don’t call it that.

Eric Cornell: Many of the best scientists of our generation have put a lot of effort into this problem and for one reason or another they hadn’t seen Bose-Einstein condensation and there were a few people saying it just can’t happen, we don’t know why but some day we’ll know, and this had occurred in several other systems. Hydrogen, yes, but also in a solid state system which is discussed less often in exotons and we didn’t listen to that voice of gloom. But there were people I know who were working on Bose-Einstein condensation, but again, bordering on superstition wouldn’t say so because this was as close as you can get to bad luck. Not that we believe in bad luck.

Why was it so important to get this Bose-Einstein condensate? Was this existing already in the minds of physicists and in science?

Carl Wieman: But there’s a big difference between existing in the mind and being there. A nice dinner is very different whether you think about it or whether you can eat it.

Wolfgang Ketterle: Once you get to into the world then nature tells you what the properties are. There were some ideas how the Bose condensate would behave but some of those ideas were controversial. And if you can produce it and you can do real experiments then you learn something about nature. It’s important to do things to create things and not just speculate or have theories about it.

Carl Wieman: Another side of this is it didn’t have to exist. It existed for an ideal system. Whether it could exist with real atoms in a real world, that was a very much open question.

So it does exist at some level at least?

Carl Wieman: For real atoms, yes.

Eric Cornell: At a great many laboratories, it’s one of the things that adds to the excitement of the field is that a lot of people have moved into exploring different directions. There are more than 30 laboratories all around the world, on four continents, that can make the Bose-Einstein condensation and there have been 5,000 papers published in this field.

Carl Wieman: An astronomical amount.

Eric Cornell: It’s all of these people thinking about it, bringing new angles to the problem. That adds to the turmoil.

Carl Wieman: And that adds to its significance in physics. If it was just us that had been working on this we would never have a Nobel Prize today.

This adds something to physics and physics adds something to other humans that are not physicists. How do you view the role of physics as a part of science in shaping our world view, answering the eternal questions of humans?

Wolfgang Ketterle: There are definitely questions of humans that go beyond physics and they are treated in biology, in philosophy and in religion.

Eric Cornell: And in literature.

Wolfgang Ketterle: But what physics does it attempts to describe the world around us in terms of physical laws, particles, their interactions. What happens if you put many particles together and form different forms of matter? At this level of complexity, if you put many particles together things happen that you can’t really imagine by just knowing what the constituents are. There is enormous richness and new phenomena emerging if you put many particles together. This is the category in which the discoveries about Bose-Einstein condensates and the properties fit in.

By realising this condensate you have shown that Einstein was right.

Wolfgang Ketterle: This wasn’t necessary to show that Einstein was right.

It wasn’t necessary – but you did. Einstein’s work for almost 100 years ago it has shaken the way people lood at the world and the universe around them. Do you think there are questions in physics, and answers of course, that can play the same role now?

Carl Wieman: Absolutely. One of the big issues of the last few years is for example what’s the material in the universe. Physicists have now discovered and have quite convincing evidence that most of the matter in the universe isn’t the stuff we see, for example. That has to revolutionise our view of our existence. It means somewhere all around us most of what’s there is something entirely different than what we’re used to. That’s just one small example from the last few years.

Wolfgang Ketterle: Physics has not lost anything of its excitement. There are fundamental questions to be addressed and there are new questions being discovered.

Which questions?

Wolfgang Ketterle: The fundamental questions about particle physics. There are fundamental questions in cosmology. You just mentioned, Carl, that we don’t really know what is the major constituent of the universe.

Carl Wieman: But at the same time I think that physicists would like to maintain that they’re pursuing great questions. I don’t actually believe that. I think they’re mostly tinkering, like to manipulate control, tinker with things and that opens up – like with Bose condensation – opens up questions and then they say Yes, I really was, after answering this great question. A lot of the time it’s not exactly playing but it’s not pursuing great goals. It’s pursuing more modest questions.

Wolfgang Ketterle: But I assume this has always been like that and if scientists make discoveries which we now regard as very fundamental – when Max Planck explained the black body law – I think the general implication of those discoveries was not even imagined by the people who did it.

Carl Wieman: Sure. Both Einstein’s prediction of Bose-Einstein condensation was clearly that, he was playing with these things: Look at this. I’ve got these cohesions that describe matter, if I add this idea of Bose to that what happens. Oh this happens. It goes to a funny solution. I wonder what that means.

But when you see those equations and laws the physicists used to say that they also see the beauty in mathematics or the beauty of this coldest piece of matter. Can you see it too?

Eric Cornell: Physicists like everyone else come in different philosophical strengths. There are people who take a more aesthetic approach to their work. People who take a more practical approach. People who take a more competitive approach. I think that oftentimes the physicists who have the most aesthetic take on things they’re very quotable. They talk about I see God of the stars and so on. I don’t say that I don’t see God in the stars but in fact I don’t think of my daily work as a search for God or even for something which is lovely. Instead I’m looking for something which is interesting. Something I can get my fingers on which somehow has broader implications.

Carl Wieman: I think we’re all looking for something that is new and different but that doesn’t mean it’s the grand picture.

Wolfgang Ketterle: I think I feel we show the beauty of nature and especially the experiments we have been involved in, they have been very beautiful and I think they have inspired other people.

Eric Cornell: I don’t disagree.

Wolfgang Ketterle: They have offered new glimpses into the quantum world in an almost emotional beautiful way. I think I agree with you that beauty is not a goal in itself but when we try to do the impactful important physics it means we don’t try to go for the little details, we try to go for some sort of bigger things, things which are really new and if we explain that well in an elegant way it shows the beauty.

Carl Wieman: I think Bose-Einstein condensation is something that does not exist in nature or certainly not with that. Nature is millions times too hot. It owes its existence to Einstein noticing these equations, had these strange properties, and then developing all these decades of learning to control things. How the atoms interact. And now these extraordinarily low temperatures could meet and now it’s formed, so now there’s this totally new form of matter whose existence only came because of physicists understanding nature and realising that it could exist and that making it exists. Somehow there is something grand about that, no matter how you figure it. This came out of simply human intellectual effort.

Eric Cornell: I think something which adds to that is that in turn through the efforts of human kind going through this extreme conditions, as Carl says, really beyond the conventional natural limits, we see this effect of quantum mechanics. The underlying equations which usually govern matter on the tiniest scale within the atom. We see quantum mechanics written large over the entire sample something the size you can almost touch. We see the laws of nature amplified in this way, very much by having gone beyond what lives in the natural world. It’s a strange paradox.

In some way you see the link between the smallest things to the very large. The Nobel Prize is regarded as the highest award in the world of science. You are quite young people, you have a long future in front of you. How will you find the motivation to continue with your science?

Carl Wieman: The first thing you have to realise is I don’t think any of us started in this with that goal. Our goal wasn’t winning the Nobel Prize. It was interesting science. The science hasn’t gone away just because you get the Nobel Prize. Maybe some of the time to work on it has. At least for me and I think it’s true, although Eric and Wolfgang can answer for themselves, but it really hasn’t changed anything about the motivation.

Wolfgang Ketterle: I have to say myself after the discovery of Bose-Einstein condensation in -95 and a year later we showed that condensates are coherent just one single wave. This was very traumatic. I had to say to myself that we may not be able to repeat that in my lifetime because it was a unique combination of there was something to be discovered, I was just ready with my team, I had an apparatus which could be used for that. Such breakthroughs in science are so unique or so that it would be presumptuous to assume that you could repeat that. What I expect for me is just to do good science, to do the very best science I could. I was quite happy with what we did in the last few years exploring the properties of a condensate. Things went very well. It wasn’t as dramatic as those discoveries but that’s what I want to continue. I’m not expecting for myself to do another major discovery of that kind because maybe I’m trying but I am not putting myself under pressure.

You can try to identify another subject or another field that is quite virgin, so to say.

Carl Wieman: I’ve been warned about the … I can’t remember the exact term used, but a very prominent Nobel Prize winner who went on to do lots of wonderful stuff, Hans Bethe … the “Nobel Prize disease” is that some people figure they can’t work on any problem after that, that’s not of another Nobel Prize quality, and as a result they don’t get much time from then on.

Eric Cornell: I think that is a danger and really the three of us had our great successes working on things which had individual steps which seemed to be leading somewhere but we took pleasure and joy and derived a sense of satisfaction from achieving these smaller steps. Publishing papers about them. Bethe’s advise I think is very solid.

Wolfgang Ketterle: My motivation /- – -/ of doing science is of course linked to having some successes but the satisfaction really comes from what we do every day or every week. It’s a scientific process of exploration, failure is a part of that. Some smaller results are nice, sometimes there are bigger results, but this is what motivates me, this is what I enjoy and that’s easier to continue than aiming for the next big goal. But if you take it serious maybe you stumble over something else and it will be great again.

I have a final question: what kind of reward would you expect from the next years of your research, next years in science? What is the question that you would like to approach now?

Eric Cornell: I’m sorry I didn’t understand the question.

Wolfgang Ketterle:  think what we are going to do next year is pretty much already on the drawing board because the experiments which are being planned and experiments which are in focus. That would also get us into some technicalities. What are the goals for next year? Of course there is more exploration of Bose-Einstein condensation.

My last question would be what kind of science would you like to do now? What is the question that you would like to have answered in the coming years?

Carl Wieman: As a purely personal view I have to say that I’m somewhat older than Wolfgang or Eric and have done several other things before Bose-Einstein condensation. I actually, although I still plan to keep working on Bose-Einstein condensation because I see lots of interesting experiments to do there, I see the next few years getting a lot more involved in something that I’ve been spending quite a bit of time on which is general science education. I have a feeling that the Nobel Prize will actually push me more in that direction and it will give me more opportunities.

Wolfgang Ketterle: I have a very active research group exploiting and exploring this new form of matter in different directions. We hope to discover new properties of the condensate or demonstrate that the condensate offers even more profound and deeper views into the quantum world. On the other hand we try to use the condensate to build very sensitive sensors. These are two directions which are both exciting and I’m hoping that we have new results in the next year.

You hope for surprises?

Eric Cornell: You always hope for surprises.

Carl Wieman: Surprises other than your vacuum system just developed a big leak.

Eric Cornell: It’s hard to say at this moment but we have in my labs three interesting projects going on. One of them a little bit more applied using condensates, not studying condensates in themselves, but as a way of sensing rotation and inertial motion. That’s a more applied project. I’m very interested in the role of temperature in all this. This may be a little technical for your viewers, but we’re doing experiments which are very close to either slightly above or slightly below the temperature at which the condensate forms. A lot of the work done so far has been done at much colder temperatures. You make the condensate and you go colder yet. and in some senses we’re taking a step backwards. This is an area that I think needs to be so to speak filled in, but I think again one hopes for surprises and it may be that in filling in you’re not merely filling in but really discovering something surprising.

Carl Wieman: Just add another thing which is that for quite a few years what I’ve learned is that I can’t plan my research that carefully because it’s not done very much by me. I can contribute ideas, but so much of it is done by students and post docs and it depends on what directions, what students I have, what directions they want to go, and I nudge some, but there’s a lot of other people involved in all these efforts.

Eric Cornell: I learned from experience that when a student or a post doc is very excited about his or her project and wants to go that way passionately and in contradiction to my own directions the best thing to do is to let them go there, because they know something I don’t know. In case the passion is there you have to let them take that and I’m happy to put my name on their papers.

So you let people be driven by intuition?

Eric Cornell: When you see it there, when you sense it, it’s exactly that, you have to let them go with it.

Carl Wieman: That’s the ideal to bring them to the level that they’re now taking off on their own and that’s when you stand back.

Wolfgang Ketterle: We’re not just doing research we are educating and guiding the next generation of scientists. And it’s just a wonderful feeling for me to observe how those young scientists become mature, become independent. I just want to motivate and encourage them to do that. It pays back. It pays back in their later life as a researcher, but it already pays back now because they are the people who make discoveries and drive the research.

Thank you very much. Thank you for taking your time.

Eric Cornell: It’s been a pleasure.

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