Nobel Prize Conversations
“You have to reinvent yourself every couple of years. It’s absolutely important. It’s necessary for me to make my life interesting. Life is too short.”
Meet physicist Anton Zeilinger in a podcast episode where he speaks about his endless curiosity, the randomness and weirdness connected to quantum mechanics and why the number 42 is so important to him. Sailing is one of his biggest hobbies – hear him speaks about the sense of freedom that he gets when sailing.
The host of this podcast is nobelprize.org’s Adam Smith, joined by Clare Brilliant. This podcast was released on 15 June, 2023.
Below you find a transcript of the podcast interview. The transcript was created using speech recognition software. While it has been reviewed by human transcribers, it may contain errors.
Anton Zeilinger: “When journalists asked me even in the 1990s what this is good for, my answer always was, I can tell you very honestly and proudly, this is good for nothing. I do it for curiosity. It helps to change our view of the world. What goes on in the head of people is quite important.”
Adam Smith: Anton Zeilinger is a joy to talk to. You might think that being, for instance, the person who was the first to realise teleportation in any sense, you might become a bit big-headed and pleased with yourself, and it really strikes me that he’s just not that. He’s clearly very confident, but he also seems very humble. Those two words might sometimes be seen as being in opposition, but maybe that’s the ideal combination: to be both confident and humble. He doesn’t seem so surprised by the strangeness of quantum mechanics – it’s such a normal reaction to quantum mechanics to say, wow, this is just far out there. He does say that. He does say, this is really odd, but that’s not so surprising. He sort of expects things to be odd, and that’s quite refreshing and probably a good way to approach the world, not to expect predictability, but rather to expect strangeness.
I always find these conversations fascinating, but perhaps more than usually, this one gave me an insight into who Anton Zeilinger is, and I very much hope that you too enjoy this conversation.
Clare Brilliant: This is Nobel Prize Conversations. Our guest is Anton Zeilinger, who received the 2022 Nobel Prize in Physics. He was awarded for experiments with entangles photons, establishing the violation of Bell inequalities and pioneering quantum information science.
He shared the prize with John Clauser and Alain Aspect.
Your host is Adam Smith, Chief Scientific Officer at Nobel Prize Outreach. This podcast was produced in cooperation with Fundación Ramón Areces.
Anton Zeilinger is professor emeritus of physics at the University of Vienna and senior scientist at the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences.
He talks to Adam about embracing randomness, contemplating the changing world through his collection of old maps, and how his life-long curiosity was sparked when he, as a child, observed the world from the window of a castle.
But we begin, with the beauty of quantum mechanics.
Smith: There are, if you like, two stars of this podcast. There’s you, of course, and there’s quantum mechanics. We should start with quantum mechanics since that’s, for most of us, quite hard to get our heads around. Obviously, to those who understand it, it’s very beautiful. Could you describe what is so enormously attractive about quantum mechanics?
Zeilinger: One is that it’s mathematically extremely beautiful. When I first heard of it, I was impressed with how you can express a lot of complexity through symbols. How the mathematics kind of imposes novel phenomena, which nobody had thought about when they wrote down the original equations.
Smith: Yes, because in its simplest form, and although it’s impenetrable to most of us, if you look at Schrödinger‘s equation in its simplest form, there are just five symbols there. It encompasses so much. It’s extraordinary.
Zeilinger: Yes, the same holds for the Heisenberg formulation, which is just a commutation relation between two operators. How can such a thing be so important in describing the physical world?
Smith: There’s that aspect. Its beauty is in its power, if you like, from that description. Is there more about it that attracts you?
Zeilinger: I think the beauty is a little bit more than the power. It’s more like, when you look at arts, there’s one line of the development of arts, and this holds for many arts. It holds for jazz, for example. There’s a development that you work with as little as possible. You hit the drum fewer and fewer times, and so on, and you still get it. That’s part of the beauty. That is the same beauty I see in, actually, not only quantum physics, but also in fundamental science. Your question whether there is more, yes, there is more. Namely, the incredible precision to which the predictions of quantum mechanics have been confirmed in experiments. This is the record. No human theory has been better confirmed than just a few symbols of quantum mechanics.
Smith: I really like this comparison of quantum mechanics and jazz. As you said, the simplicity. Could you just talk a little bit more about that parallel? That is a very nice way to think about it.
Zeilinger: Yes, a friend of mine, he was a quantum physicist, Mike Horn, a famous guy, and he was also a jazz player, and he showed it to me. He showed me that the original tune is like, do-do, do-do, do-do, and then he left out basically every second or every third tone, and so on. You still get it. You say, oh, that is beautiful. That is really something. There seems to be something going on in our heads. There is something going on in our brain, or however we call this thing up there, where we add, very often, things which are not in the beginning there, but which are justified. That could be something like that in science, but that is very speculative, you know.
Brilliant: Adam, after your recent conversation with Alain Aspect, you and I had a conversation where we tried to make sense of some of the difficult concepts in quantum mechanics.
Smith: I wonder how we did, oh dear. Anyway, yes.
Brilliant: I mean things were feeling a bit clearer but I think I might need a bit more help now. In this conversation we’ve already had Schrödinger’s equation and the Heisenberg formulation mentioned. I feel like I’ve heard of both but don’t really know what they are so it’d be great if you could explain a bit about them please.
Smith: The Schrödinger equation is a differential equation which describes the behaviour of the wave function of a particle in quantum mechanics. Now in quantum mechanics every particle can be described by a probabilistic wave which shows its probability of being somewhere in space at a particular time. It’s like a sort of bell curve shape with a greater probability of it being in the middle and a lesser probability of it being elsewhere but immediately that takes us out of the realm of what we know. If you look at your sofa you don’t say it’s got a strong likelihood of being in the centre of the room and a lesser likelihood of sort of drifting off into the corners of the room. This isn’t the world we all live in but this is how you describe the behaviour of the smallest things in the universe in quantum mechanics. The concept perhaps to take forward from the Schrödinger equation is the description that all these tiny things from which we’re made up all have probabilities of existing in particular places but that shows that you don’t necessarily know exactly where they are. The Heisenberg formulation that Zeilinger referred to, commonly known as the Heisenberg uncertainty principle, states that for any particle in quantum mechanics you cannot be absolutely sure of its position and its speed, its velocity, at the same time. The more certain about its velocity you are the less certain about where it is or the more certain about where it is the less certain you are about where it’s heading. That relates to the Schrödinger equation because again it comes down to this probabilistic description of the nature of particles seen as waves.
Brilliant: It all sounds pretty random yet the way Zeilinger was describing it was the sort of the beauty and simplicity.
Smith: You’ve obviously got a deep innate understanding of quantum mechanics to leap to randomness because that is I think the underlying principle of it all that everything that is happening is governed by statistics, by the probability of something being in one state or another or in one place or another.
Brilliant: One of the things that I wondered is I recognise Schrödinger’s equation and I’ve also come across the term Schrödinger’s cat. Is that something that helps us to understand Schrödinger’s equation a bit better? Or not at all?
Smith: If you’re a brilliant quantum physicist it probably does. For the likes of me, Schrödinger’s cat is a thought experiment designed to illustrate the oddness of one quantum mechanical phenomenon which is superposition of states. The idea that in quantum mechanics particles can exist in combinations of two or more states at the same time. This idea of existing in two or more states at once is so contrary again to what we in the universe we kind of see around us know. Schrödinger’s cat was simply a thought experiment designed to show how crazy it could be and the idea behind that experiment is that you have a cat in a box and you have a mechanism that will kill the cat releasing a deadly gas if a particular radioactive particle decays. If it decays the gas is released, the cat dies. If it doesn’t decay the gas isn’t released, the cat does not die. In quantum mechanics it is possible to describe the radioactive particle as decayed and not decayed at the same time. If that was the case then the gas would be released or not released at the same time and the cat would be dead or alive at the same time which is obviously crazy. The point of that thought experiment was that as long as you keep the box sealed and the cat is in there it is possible in quantum mechanical terms to say the cat is both dead and alive at the same time. Obviously bonkers. What it really illustrates is the difficulty of describing quantum mechanics in terms of the real world that we know and love. Possibly an easier way to think of superposition is, it all comes down to maths of course, it all comes down to equations, is a very simple equation which is x squared equals four. That’s pretty easy to solve because you know that x in that equation can either be two or minus two. Both of those values of x suit that equation and you can say in that equation therefore that two and minus two are in a state of superposition perhaps. It’s a bit of a stretch but it’s a sort of start.
Brilliant: The complexity of quantum mechanics and the way that you have to sort of suspend your belief in some ways must attract people who have quite unique perspectives on the world.
Smith: Anton Zeilinger actually speaks interestingly about that, about how people with different worldviews come to him. Let’s listen to him talk about that.
Zeilinger: As you can imagine, I am quite often asked by people with esoteric viewpoints whether what they do is supported by quantum mechanics or they actually claim that. My usual answer is, you have no idea how strange quantum mechanics is. Really, get used to it, work with it. Then you will see that your concepts are extremely naive and simplistic. Randomness is, in my eyes, a very nice feature of the universe. If you think about the universe in the old terms, where it was basically thought of as a classical machine, every generation thought that the latest theory describes how the world works, how the brain works or whatever. Sometimes this is a classical machine, very much like the planets. Now, I wouldn’t want to live in a world where everything is completely predetermined. This is a horrible idea. I love it that quantum mechanics tells us there can be randomness. Randomness is not so irrelevant. For example, the quantum randomness most certainly also plays some role in random changes in the genetic code. It’s not something out there which is not relevant for us.
Smith: The message from a deep study of quantum mechanics is embrace strangeness and randomness.
Zeilinger: Embrace it and see it as a step forward to understand this universe and our whole in it.
Zeilinger: The case of this last Nobel Prize… All three people, Clauser, Aspect and myself, we had not the slightest idea of an application. Not the slightest one. Now there seems to be a big business, quantum computation, etc. When journalists asked me even in the 1990s what this is good for – and there had been the first ideas already out for quantum cryptography and quantum computation – my answer always was, I can tell you very honestly and proudly, this is good for nothing. I do it for curiosity, and I think that it has the same use as astronomy. It helps to change our view of the world, to widen our view of the world, to understand more what is going on in the deep sense. I would say this is also an application. It’s a different kind of application than technology, but what goes on in the head of people is quite important.
Smith: Indeed. There’s that lovely quote from Robert Wilson when he went in front of the review board for building the Fermi lab’s first accelerator, and they asked him how it would help with the defense of the country. He said something like, it won’t help at all with the defense of the country, but it will make the country worth defending.
Zeilinger: Yes, exactly right.
Smith: Your own curiosity and desire to explore, can you say where that came from? I’ve read that you were brought up for a while looking out of the window of a castle at the world around you and observing. Tell us about that.
Zeilinger: It was after ’45 and Austria was in a very bad economic shape. My father got a position at a small agricultural school in the countryside in Austria as a researcher. They had this castle available, which was empty, so we got to live in this castle. We were living up on the second floor by European count, third floor by American count. They tied me to this window with some harness so that I couldn’t fall out. I looked down for hours. I saw cattle coming by, and I saw the farmers coming, and the machines, and everything. The people in the village thought that this guy is a little strange. But I was always curious, as far as I can think back, I was always curious to look behind the immediately obvious. I was never interested in a technical way. I was interested in how things work technically, but I was never interested in building something. This was in a small village, and my friends were children of farmers and so we played out in the fields and everything. I was not isolated. But these hours of looking down were obviously crucial. I know that I often ask questions, also friends or whatever, some of the questions which I thought were deep, and they said, what a silly question are you asking. Interestingly, that did not turn me off.
Smith: That is interesting, because most people just probably drop it and think, oh well, I better not go down that line. I look foolish.
Zeilinger: It was clear that the guy saying that didn’t understand the question.
Smith: There’s an interesting confidence there in you then, that you knew that you had something that you were thinking that was interesting.
Zeilinger: This seems to be a feature of my personality. It has been remarked by other people, that I seem to have a very large confidence in what happens to come out of my head. I don’t know why. This probably was crucial for my success. There were situations where I changed some direction of research in my group, and my group was not happy with that decision. But I had confidence that it was the right way to do, and it happened. The point is really that, to me, it’s absolutely clear that most of our thinking goes on subconsciously, unconsciously, and so on. Even in physics, nobody knows where the ideas come from. If you then write a paper and explain this is for that and that reason, that’s some explanation in hindsight. I learned one thing from my thesis supervisor, Helmut Rauch. He was a real leader in foundations of quantum mechanics, and I was absolutely lucky to work with him here in Vienna. I learned from him, just the way we interacted, that sometimes he had ideas, and he gave the reason why, and the reasoning was completely wrong, it was absurd. But the idea was right. That is fascinating, our brain is able to produce ideas which turn out to be right, when the reasoning is wrong. The opposite is also true, but that’s a different story, right?
Smith: Yes, it’s wonderful to think of that creativity going on inside, and ideas that one should take seriously popping out. Of course, it’s a bit dangerous as well, it can lead you in all sorts of directions.
Zeilinger: It can be dangerous and there are many cases where it was not good for the person. But, again, there’s a parallel to music. A very good friend of mine was a famous conductor, Nikolaus Harnoncourt. Nikolaus Harnoncourt was the guy who kind of brought back a lot of music by playing original instruments, and by trying to find out, by lots of study, what was really going on when these composers wrote this 200, 300 years ago, or whatsoever.
CLIP with music: ”Pièces pour la flûte traversière, 1er livre: VI. Menuet ”Le Beaulieu” by Nikolaus Harnoncourt and Concentus Musicus Wien.
Zeilinger: I asked him, how can you argue that this works? He says, in the end it’s intuition, in the end it’s creativity. In the end I have to trust that what I found is the right way, at least for me to do it. This is all over the place, this creativity is all over the place, even in daily life I would say.
Smith: This intuition that you had, and confidence, that allowed you to maintain the curiosity you had, have you any idea why you were able to do that? Most people are very nice and curious as children, and lots of people ask questions, but so many people then sort of get overwhelmed by a desire for a career or something like that, or not a desire perhaps, but just the feeling that they need to get serious and plan. Somehow much of the curiosity, not all of it, but much of it ebbs away. Do you have any feeling for why it didn’t happen to you, why you just stayed childlike, if you like?
Zeilinger: Yes, childlike is the right word. We have at the end of what we call gymnasium, in America it’s called high school, I don’t know how it is called in Sweden or in England, when you are 18 year old, you have a final exam, right? A final big exam with a committee, and it’s supposed to be very serious and so on, and you supposedly have to show a lot of respect. A friend of mine, I was so lucky, I had a friend in high school who was as curious as I was, and he was as childish as I was. Honestly, when the others started to talk about girls, we talked about the Big Bang and all this kind of thing. It’s really strange. So, this is one important ingredient. There was another one who I could talk to, so I was not completely isolated. The two of us were not completely isolated. Then came this final exam, and you are waiting in your classroom for the official verdict, okay, and you are supposed to be nervous, and the two of us were playing a childish game with coins on the table, and our class head teacher came in and said, Zeilinger, you will never grow up. I considered that a compliment. You have this curiosity, something like, I think I can say that I started some interesting subfields in quantum experiments. Not just the Bell stuff, which was started by others, but some other things. Whenever things like that became popular, and other groups did it, I made a turn. I said, let’s look for something new. Even now I am looking for some. I think I have some ideas that I will do in the next couple of years, which is a little bit different from what I did so far. You have to reinvent yourself every couple of years. It’s absolutely important.
Smith: Most people would think that was pretty brave to do so, but you don’t see it as brave, you see it as just necessary.
Zeilinger: It’s necessary for me to make my life interesting. Life is too short. It happened once that we took a turn and we buried something like 2 million euros or whatever. Because in that case, what we had planned was really too ambitious. We worked on it and we couldn’t, there was no way to understand what’s going on. Now this field is taking up again slowly. That can happen. Science has to have the possibility that sometimes the goals are too ambitious. But another thing I’d like to say is, if somebody writes down an application, writes down what he or she will do in 5 years, if after 5 years he or she does exactly what they said 5 years ago, then it was a waste of time and money. There should be something new coming out. There should be something exciting where people say, Oh my God, oh, why didn’t I think of it, and things like that.
Smith: Do you want to tell us what it is that you’re turning to now?
Smith: Fair enough.
Zeilinger: No, I would love to, but I have made the experience that when I say something like that, people can be excited and they will also do it. The ideas are very premature, maybe in a year I can say more.
Smith: Nice to have an insight into the kind of burgeoning new idea and how, as you say, you’re going for unoccupied territory.
Zeilinger: That’s right, yes. There are still so many white spots on the map. My general view about science is when people say something like that the theory of everything is just around the corner, then what they do is – maybe I’m too impolite here – in my eyes they just expose publicly the limits of their imagination. If you look at it, we do modern science, science as a mathematical science, which was started by people like Kepler, who was still somewhat esoteric, Kepler, Galilei, and finally Newton, who wrote down physics as a mathematical science. This is only a few hundred years old. To believe that we found a significant part of what can be found, I think that it must just be wrong.
Smith: Yes, isn’t that interesting? There is a huge tendency to think that we’ve kind of reached the epitome of what we are, that we’re the sort of pinnacle of everything, that we’ve thought through things, the current generation is the one that’s going to solve it – and no. It’s strange that, really, when you look at, because we also can just look out at the history of the world, how long it’s been here, and realise that this is just a moment in time, and things are progressing. Or regressing, but something’s happening anyway.
Zeilinger: I’m not so pessimistic. I don’t think that our time is significantly more regressing than other times were.
Smith: That’s good!
Zeilinger: I don’t share these negative viewpoints. I don’t know. I think the universe is just beautiful. I’m not pessimistic, I think.
Smith: I know that you collect maps, and you’re interested in the development of borders and countries. From that historical perspective, does that give you hope about the world?
Zeilinger: It tells you that we shouldn’t take today’s borders, particularly, but other situations, too seriously. Because things change a lot. If you want to learn something about how strange the world was, just look at the map around 1900, with all the colonies and so on. Today you would say that’s ridiculous. It’s impressive how that changed. Look at the development in Europe, specifically, or Eastern Europe. How many different large empires were where today Russia is. There was Lithuania, for example, a huge country. All this changes, all this is relative. One shouldn’t take the world as it is now, as given in a way that changes in itself are negative. One shouldn’t be too conservative about what is today. We can be surprised and we will be surprised. I once said I would be very surprised if the future wouldn’t surprise me. This is also a negative side, this is quite clear. This is not only the positive thing, who would have thought that Russia would make that huge mistake to attack Ukraine. It’s unbelievable. Who would have thought that? Some of my very good friends are historians who specialised in Eastern Europe. They were completely shocked and completely taken by what happens. Maybe my position is more, not a naive positive view, but more a question of humbleness. We have to accept how things develop. We have to ask ourselves what is our role here, what is going on and so on. But again, I’m a physicist, and probably very simple-minded.
Smith: You’re a physicist brought up in Austria and based in Vienna. How important do you think Vienna is and the culture of Vienna to your physics?
Zeilinger: I think I found out after some time that it was important for me. Because in Vienna you had this special culture around the turn from the, around the 1900s, even before and afterwards. In the sciences there was Ludwig Boltzmann. Boltzmann was interested in philosophy. He was the founder of thermodynamics as a molecular science. Schrödinger was about to become professor of philosophy in Czernowitz, which was the easternmost part of the Austro-Hungarian Empire, which is now Ukrainian. He said, we lost the war and therefore I turn to physics, something like that. This basic interest in Austria, in fundamental questions, be it in the sciences or be it in literature or painting or whatever, this still exists. That is an openness to foundations which I discovered that it was special when I came to America. When I came to America, I realised that this is not there. I’m pretty sure that that attitude was very important to my scientific development.
Smith: You have these conversations with the Dalai Lama, I understand. Are they revealing? Do your two worlds meld well?
Zeilinger: In a sense, yes, but in a different sense as many people in the West think. This discussion with him was not at all esoteric or mystical and so on. It was about hard facts, it was about science. For example, I asked him once, what is your evidence that karma exists? He said, that is a typical scientist question, I like it. The Dalai Lama is a very open mind.
Smith: Did he answer it, as well as liking it?
Zeilinger: No, he did not answer it. The point is that you have to go, and that is parallel to science, you go in your analysis deeper and deeper. That’s the same in Buddhism. At some point you have to say, that’s just the way it is. You cannot argue deeper. In science, it’s fundamental concepts. You cannot explain every fundamental concept. You have to start somewhere. To me, the big question in science now, is in physics, what are really the most fundamental concepts we have to use? Are we using the right concepts since Newton and so on? Or should we change somewhere? Maybe we find something and the next generation will knock on their heads and will say, oh my God, how could we have missed it? The facts of observation are not to be changed. But the fundamental concepts which we developed on the base of analysing the facts, that is flexible.
Zeilinger: A central book for me, which I recommend to everyone interested in physics, is a book called Albert Einstein, Philosopher-Scientist. It’s a collection of about 20 articles by leading minds in the 1950s, including mathematicians, and including also Einstein‘s autobiography. In that book, there are still a number of questions today open, which were addressed there. That’s quite interesting. It’s very deep. I suppose when you write an article for a collection which is for Albert Einstein, then you write down your very best.
Smith: Yes, you do. Another book that might have had an influence on you is The Hitchhiker’s Guide to the Galaxy. In particular, the number 42. Let’s just play quickly this excerpt on 42.
CLIP with reading from the book The Hitchhiker’s Guide to the Galaxy: “The answer to the ultimate question of life, the universe and everything is… 42”, said Deep Thought, with infinite majesty and calm. ”42!”, yelled Loonquall. ”Is that all you’ve got to show for seven and a half million years’ work?” ”I checked it very thoroughly, said the computer, and that quite definitely is the answer. I think the problem, to be quite honest with you, is that you’ve never actually known what the question is.”
Smith: There’s a lot of depth in that particular quote. Tell me, tell us about the meaning of 42 for you.
Zeilinger: 42 is the name of my sailboat. My sailboat is the answer. Very simply.
Smith: How is your sailboat the answer?
Zeilinger: It’s the answer to life, the universe and everything. You go there and you sail and you are happy and everything is fine. Sailing is very special. I was thinking about why sailing is so special for me. It’s probably because when you sail, you are completely occupied by that activity. Both your mind and your body. You have no time to worry about anything else. You are completely immersed in something. That’s it.
Smith: The way you describe your work, it sounds so joyous. Do you find you actually need to escape from it to be on the sailboat?
Zeilinger: I don’t know. That’s a good question. I never ask myself that question. I don’t see sailing as an escape from it. I think it’s part of myself. When you work on science, there are also different stages. There are stages where you are also very deeply immersed. Everything in your head goes on and thinks about that and so on. That could be an analogue. I don’t know.
Zeilinger: I’m also in some sense a religious person, as you probably found out. Not in the sense of following the rituals of any given religion precisely. But in my life I always had the feeling that there is a God somewhere. I cannot argue that. You cannot argue that logically. You cannot give a reason, something like that. It’s the way it is.
Smith: Just a sense of that’s the way things are.
Zeilinger: That’s the way it is. Exactly.
Smith: To those listening who would say, and this of course is a debate, a discussion had all the time all over the world. To those who would say that the scientific concepts that you study and other scientists study are at odds with that belief. Do you have any repost?
Zeilinger: There is not everyone at odds with this belief. When you talk about religion versus science, there is no way to argue scientifically pro or con whether God exists. Either way is overstepping the limits of science. I have a feeling that that position is accepted by most people.
Smith: Yes. I’ve used up all my time with you, which is a shame because this has been absolutely lovely. I’ve really enjoyed talking to you.
Zeilinger: It’s better that we run out of time than the opposite.
Smith: Yes, isn’t that true? If we were just sitting here trying desperately to think of something else to say.
Zeilinger: Exactly, yes. Absolutely, yes.
Smith: Okay, good. Let’s leave it there then. I look forward very much to the next time.
Zeilinger: Thank you for the good discussion.
Brilliant: You just heard Nobel Prize Conversations. If you’d like to learn more about Anton Zeilinger, you can go to nobel prize dot org, where you’ll find a wealth of information about the prizes and the people behind the discoveries.
Nobel Prize Conversations is a podcast series with Adam Smith, a co-production of Filt and Nobel Prize Outreach. The producer for this episode was Karin Svensson. The editorial team also includes Andrew Hart, Olivia Lundqvist, and me, Clare Brilliant. Music by Epidemic Sound.
If you want to delve deeper into the mysteries of quantum mechanics, listen to our episode with Anton Zeilinger’s co-laureate Alain Aspect.
You can find previous seasons and conversations on Acast, or wherever you listen to podcasts.
Thanks for listening.
Nobel Prize Conversations is produced in cooperation with Fundación Ramón Areces.
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