(light electronic music) - Hi, everyone. Welcome to Conversations at the Perimeter. Today, Colin and I are so excited to bring you this conversation with Carlo Rovelli. Carlo is a theoretical physicist, with expertise in both physics and philosophy, and his research interests include loop quantum gravity, the nature of time, and the relational interpretation of quantum theory. - And Carlo is also a bestselling author of popular science books.
His "Seven Brief Lessons on Physics" was a breakout success, sold more than a million copies, has been translated into more than 40 languages. I've been a fan for years, so it was just a thrill for me to talk to him, not just about his research, but how and why he translates these difficult scientific topics into concepts that people like me can understand.
- He also has some other great books called "Reality Is Not What It Seems", there's also "The Order of Time", and "Helgoland: Making Sense of the Quantum Revolution". And he has another new book coming out called "There are Places in the World Where Rules Are Less Important than Kindness: And Other Thoughts on Physics, Philosophy, and The World", and I have to say, I just love the title of this upcoming book, and I can't wait to read it.
- And I loved this conversation that we had with Carlos, so let's have a listen. (light electronic music) Thank you for joining us, it's lovely to have you here. - Thank you, it's wonderful finally being back at the PI after this long absence. - I was struggling with ways to introduce you to our audience because there are so many things, you know, theoretical physicist, and author, and world traveler, and philosopher, so I decided I didn't want to introduce you.
Pretend I'm a stranger on a plane and I've just sat down next to you, and I've buckled up, and I say, "Hey, what do you do for a living?" - I would say, "Hi, my name is Carlo. I was born in Italy, and I go around and talk with people. I have ideas, I try to do them. What about you?" - (laughs) I talk to people like you, trying to figure out what they do, so it's a good thing we sat next to each other on this plane. You didn't mention theoretical physics.
Is that because what you consider yourself doing is more just talking to people about a variety of subjects? - No, if you have to define me, what I am primarily, I'm definitely a theoretical physicist. The rest of the things that I do are part motivating, part around that. My competency, if I have any, it's in theoretical physics. I don't like to define myself, even in front of myself. I like to keep things open.
And when I started writing books for the large public, there was a moment in which I was telling myself, "Wait a moment, are you just turning into a writer instead of a scientist," and then I realized that this is a meaningless question. I'm just doing what I'm doing, and things are connected. The only meaningful question is how many hours I devote for one and the other, that might be it.
- I ask partly because you're currently, you have a position in London, Ontario, at the Rotman School of Philosophy, which seems, at least on the surface, to be a strange place for a theoretical physicist to be. Can you explain what you're doing at a school of philosophy? - (chuckles) I talk with philosophers. I love to talk with philosophers because I think it's useful for physics. I have this convention since a long time. I've been interested in philosophy since I was a kid.
When I was a student studying physics, I also continued to study philosophy, and I think that a clear-cut separation is a bit artificial and is damaging for both disciplines. - How so? - Not all physics needs to talk with philosophy. If you have to solve the Maxwell's equations for a certain antenna, you just happily ignore philosophers, and a lot of physics is just concrete, specific problems. - Right.
- But, of course, there's a part of physics which is not to apply knowledge that we have for solving problems, it's to find out what is the knowledge we have at the basis, and that part, it's the kind of things that, you know, Einstein, Maxwell, or Newton, or Galileo, or Boltzmann were doing, or Heisenberg, and that kind of activity, traditionally, was done by people who were schooled in philosophy. I mean, Einstein had a deep knowledge of philosophy, and so Heisenberg, and certainly Newton.
Galileo, he was an avid reader of Aristotle. There's a mistake in the understanding of physics, and science in general. Science is just collecting data and writing equations that predict this data. I mean, that's just a little part of it. The largest part of it is figuring out a set of notions, concepts, a conceptual structure, how to think about that.
When you go from, you know, the Ptolemaic to the Copernican system, you don't just collect data, you rearrange the order of the world in a different way. That's what Einstein did, that's what Maxwell and Faraday did, that's what Heisenberg did, and Boltzmann, and so on.
So, the core problems in fundamental physics today, like quantum gravity, the problem in which I am, do require the same kind of rethinking the conceptual basis of a discipline, and the philosophers are very good in that, not because they solve the problem of physics. I mean, relativity was found by Einstein, who was a physicist, but he's a physicist who was listening to what the philosophers were saying. Philosophy has a capacity of critical thinking, which is very deep, has imagination.
Philosophers come out with completely different ways of thinking about reality, sometimes crazy, and we don't care about them, but that's not the point, sometimes very useful. - Sometimes I think theoretical physicists come up with ideas of reality that strike me as crazy too. - Sometimes they do, sometimes even perhaps too much crazy, and they should listen to philosophers who say, "Wait, come on, don't exaggerate, guys."
- Are there certain open questions in physics that you think would most benefit from input from philosophers? - Yes, and they change, of course, because physics is a process, and right now, the number of open questions where philosophical thinking and philosophical clarity is useful, some of them, for instance, have to do with time. In trying to write a quantum theory of gravity, of course, space and time have to change because now we're looking at the quantum property of space and time.
We have so many prejudices about how space should be and how time should be. A careful philosophical analysis of what we know, I find it useful, even in simple things. One very well-known problem about time is that the past is different from the future, and so, what's the root of this difference between past and future? Is that something intrinsic in time itself, or not? And the answer is not just academic.
Well, yeah, it is academic, but (chuckles) the question is important because if we want to understand more, understand how quantum gravity works, we have to get clarity about these things. The nature of observer is another one. We now are in this funny situation with quantum mechanics, which is a fantastically good theory, but it's formulated in terms of an observer. So, why? Do we need a guy with a PhD in physics to understand how the things work?
No, I mean, things work by themself, without an observer, so how to make sense of that, and these are questions that physicists have been struggling with, and they are, and they will come up with a solution. I think solutions are being debated around the table. Philosophers can listen, contribute, and provide perspective.
- I have your book here, "Reality Is Not What It Seems", about quantum gravity, and we'll get more into quantum gravity, but what struck me most was the book essentially begins with the ancient Greeks. Quantum gravity and loop quantum gravity are relatively new fields of physics, but to explain them, you went back thousands of years. What inspired you to go so far back to bring us to the present of quantum gravity?
- "Reality Is Not What It Seems", it's actually the first popular book that I wrote about science.
I wrote it quite late, after so many people had told me, "Why don't you write a popular book about quantum gravity?" It was at least 20 years that people were telling me that, and pushing, and some publishers also, like, "Come on, Carlo, you have this beautiful science, why don't you write about that?" Also because people were sick and tired with string theory, I mean, just can't stand string theory anymore, so let's do some good quantum gravity.
But I didn't know how to do it, because how do you tell quantum gravity to people, right? I mean, you have to digest general relativity, you have to digest quantum mechanics, so it's a long story. For long, I hesitated because I wanted to do physics and not waste time writing. Then I started considering the idea, but I couldn't find the right way, and then there was a flash. I had so many things to do, but I couldn't organize them.
I mentioned, in one of the prefaces of my books, and I don't remember which edition, I was driving from Italy to France, where I had moved at the time, in the middle of the night. And then I said, "Well, I need to explain this concept, I need to explain this concept, I need to explain this concept." I need to tell the reader what is a field, an electric field. It's not clear. I need to tell the reader what exactly we mean by geometry. It's subtle.
I need to tell the reader that particles are not precisely particles, so there's some discreteness, there's some granularity. And then I started thinking, well, maybe I should say when these ideas were born, so the ideas needed to understand, if I tell how they were born, and suddenly the entire history, the narration, came in front of my mind. I said, "Of course, I just talk about Democritus."
- Right. - I talk about Galileo, I talk about Faraday, I talk about Maxwell, what problems they were addressing, how they came out with that particular solution, and why we're using this notion now, and how this notion built up, changed, and came all the way to a point of reality. No, and this is the evolution of the world. In the Renaissance, there's this idea that this is res extensa.
Then Newton comes and says, "Okay, I go out the world, it's space, time passes, and there are some little stones that move around with forces." And then Faraday comes, "Wait, wait, wait, you're missing something, there's a field," okay, and Maxwell put the order in the field. And then, Einstein comes and says, "Look, the space and the time are actually mixed, so you should not have two different things. You should- - Spacetime.
- Spacetime, and then I instantaneously realized that spacetime is a field. Wow, okay, now we connect the notion of field with spacetime, and quantum mechanics connect the notion of a particle with a field. So, unless you go through the way that things developed, you don't get them, so I decided to write a book without details, but with the core flow of ideas. - When that epiphany hit you while driving, I know what happened after that. - You know what happened after that, I got a ticket.
- Yeah, because you were driving too fast 'cause you were- - I was driving too fast. It was an empty in the night highway. I was so excited, so excited. - You had the pedal to the metal. - Yes, the first chapter is gonna be saying this, and then (imitates siren). I said, "Shit," and then I looked at the speedometer or whatever, don't know how you call it in English, and I'm going, you know, 180 kilometers per hour on the highways.
Oh, no. So, I had to pull on the side, and the policeman said, "What the hell are you doing," and I was, you know, I just told him. I said, "I'm sorry, I just was going extremely fast. The reality was I was not even in a hurry. I just got an idea how to write a book (chuckles) and was so happy with that, I just was excited, excited." And the policeman said, "Okay, good luck with your book," and let me go. - He let you go. I'm dying to use that excuse someday, you know.
No, I was speeding because I figured out how to write a book about quantum gravity. I don't think it will work for me, but I'm glad it worked for you. - Yeah, it's good to know that works. (chuckles) I have a question. A lot of what you're talking about, it seems that it's very fundamental, this idea of unlearning things, both when you're writing a book, to encourage your readers to unlearn some things, or even in your research.
I think that when we're thinking about something, we can be stuck in certain ways of conceptual thinking or be making some assumptions and not even realize it. Are there certain strategies that you've learned, perhaps from philosophers, that encourage you to challenge your conceptual ways of thinking? - Oh, that's a very good question. I don't know the answer.
I think the most fundamental point about learning, that difficulty of learning is not to learn something new, that's easy, the difficulty of learning is to unlearn what we think we know. We are all deeply convinced that we are right about the way (chuckles) we see the world, everybody, including myself, so we just don't give up easily the ideas we have, and we don't learn unless we give up the ideas we have. - You wrote once that science is born from an act of humility.
Is that true? - Yeah. Do you mean, by humility, the idea that we can accept that we don't know everything? - That, but even stronger. The idea that what we think we know, we might be wrong, and so what we don't know is so much more and so large that we shouldn't rely so much on what we know. Yeah, I think, humility, there is this beautiful letter by Newton.
Newton was arrogant, pretentious, perfectly aware that he was the greatest thinker of his time, and three centuries later, we still think he's the greatest thinker, maybe in science, of all the times. He was aware of that, and at the end of his life, he writes this letter. He says, "I don't know how the others are looking at me or will be looking at me, but I myself look at myself like a kid playing with little pebbles on the shore in front of the ocean of our ignorance."
That's why he succeeded in being Newton, I think, because he was perfectly aware that there was everything to be discovered. - So, he was both arrogant and humble at the same time. - Humble, exactly. Arrogant and humble, there's a mix, the mixture of the two. - Right. - You can be arrogant with respect to the others, humble with respect to your work and your ignorance, and the fact that we might be wrong.
I've been reading this summer, because we're doing an audio book in English, Galileo's greatest book. It's the dialogue of the massive systems of the world. It's a fantastic book. It's a book that convinced humankind, in fact, that the earth is moving, spinning, and is going around the sun. It has all the arguments for the earth to move, but when reading it, a surprise is that the arguments are just a few pages.
A large part of the book is to convince a reader that it's possible to question what he took for granted. It's all about, look, you think that, but that might not be right. It's only when, three quarters into the book, he said, okay, now you're open to the book, I haven't argued anything. Only at that point, he brings argument for the movement of the earth, which, by the way, are wrong.
- (laughs) Yeah. - Are mistaken, we know that, but nevertheless, he convinced the world that, not by giving good argument, in fact, he is wrong, but by showing that there's nothing wrong in accepting that something completely obvious to you, it's not right. But that was not your question. Your question, well, what's a strategy we can go to for not being trapped in our own beliefs, and I don't know. Scientists are like everybody else.
- Right. - Is it more than being aware of that, keep repeating it to ourself? (chuckles) That, I don't know what's the right way of doing so. - Yeah. - Do you remember a moment in your earlier life when maybe physics, or science itself, sort of revealed to you this new way of looking or unlearning things you may have known and opened your eyes to new possibilities? Was there an epiphany there, or was it a series of happenings? - It was a series of happenings, starting from when I was a student.
I fell in love with science late, when I was already a university student in physics. In studying modern physics, it was a series of shocks, like, oh, my God, somehow reality is not what it seems. That became the title of my book. So, it was a strong experience at that time. - Is that a phrase that you've had in your mind for a long time before the book came out, that reality is not what it seems? Is that sort of the realization you had those years ago? - The concept, yes. - Yeah.
- For sure, somehow it grew with me in various manners. The phrase itself, I'm not sure. I think it came from the text of the book, and then I picked it up because it represented what was going on. - You mentioned quantum gravity before, and there's a line in your book, "Seven Brief Lessons on Physics". It's just such a simple short line, "There is a paradox at the heart of our understanding of the physical world."
That paradox is essentially, I think, the root of quantum gravity, that paradox between general relativity and quantum mechanics. Can you elaborate a bit more on why that's a paradox, what paradox we're struggling with, and why we need a solution to it? - I believe it is an apparent paradox, that it's strikingly paradoxical, the way it looks.
It's what a student of physics learns when he goes to school at the university and he just minimally thinks, because you go to classes on quantum mechanics and you get your explanation of the world, and the world is all about discreteness. Light is photons, and it's just discrete particles. They're minute particle bits of things. Everything is in bits and chunks. It's probabilistic.
There is this strange, interactive thing from which, in quantum mechanics, you predict how things interact with one another. So, you say, okay, that's the way reality is. I mean, okay, God did reality like that, I mean, we don't know what she thinks or why, but that's the way reality is.
And then you go to the other class, with this other teacher that teaches you about general relativity, and this is, you know, an equally immense, fundamental, successful theory, and the universe is perfectly continuous. There's nothing probabilistic, deterministic equations of motion. Everything is perfectly objective out there. You can write the history of spacetime in a single equation. And then I think, wait a minute.
I mean, either one or the other, there cannot be, I mean, my teachers stopped talking to one another, (chuckles) haven't talked to one another for 30 years. So, it's really two totally different images of how reality works. God can be complicated, I don't know, but not so self-contradictory. The world is either this way or the other way, or some way which is compatible with both. - And is that the question of quantum gravity? - That's quantum gravity.
Exactly. - Speaking of quantum gravity, as part of this show, we collect questions from other listeners, and a mutual friend of ours, Carlo, Lin-Qing Chen, she's a postdoctoral researcher in Brussels, Belgium, she sent in a question for you. - Oh, fantastic. - Hi, Carlo, this is Lin-Qing.
So, in our quest for a theory of quantum gravity, do you think we will need new fundamental principles that both quantum mechanics or general relativity have not yet revealed to us, and what is your strategy for finding them out? Thank you. - The answer I have, I'm not sure, but that answer on which I'm working is no. No to the question, do you think there is some fundamental principle that we'll be missing?
I think that the idea that, oh, we are missing something crucial, fundamental down there is just wrong. The point is that we have to take seriously what we learn with quantum mechanics and seriously what we learn about general relativity, and bring them together, and they do go together. I'm a very conservative guy from this perspective. I don't believe we need something new, a supersymmetry with other worlds, many dimensions, breaking the Lorentz invariance, of correction to quantum mechanics.
Nature has been saying no to all the attempts to test this alternative hypothesis so far, so I don't see any evidence that we're missing something. General relativity, it's about spacetime, so it's a shape of spacetime, a shape of space and a shape of time, which means how different clocks move with respect to one another and how meters measure jobs, and that's quantum, and so we have to understand the quantum properties of time and the quantum property of space. That's radical.
So, the assumption is conservative, but if you follow up, this is completely radical because it means this continuous space that you thought it was, forget about it. The time evolution in a single variable, forget about it. You have to replace the usual way of thinking space, the usual way of thinking time with something consistent with quantum mechanics, but not this quantum mechanics in spacetime, quantum mechanics off spacetime.
So, for instance, you have to have mathematics and a physical intuition that allows you for having quantum superposition of spacetimes, plural, of geometries. Like, there is shooting a cat that can be both awake and asleep, or somebody said dead and alive. - I like your version better. - (laughs) Yeah. - I like cats, so. - Yeah, exactly. So, shooting a cat in quantum mechanics is it can be both awake and sleeping.
And so, in the same sense, space can have a shape and also another shape in a superposition of the two, and, of course, this requires imagination, finding the right concept to talk about that. That's also where philosophy comes in useful, and the right mathematics, and I think there are, I mean, loop quantum gravity is an example of a theory that attempts to do that. We don't know if it is right.
It's very conservative, and that's why the answer to Lin-Qing's question is no. So, there's no other principle to be added, but it's completely radical then because it forces us to rethink the basic notions. - And you mentioned evidence when you were giving this explanation, looking for evidence to support various theories of quantum gravity. What kind of evidence would you be looking for?
- Recently, there has been a lot of evidence that helps us, and in science, evidence is never definitive, it's always indications, like in life, by the way. (laughs) It's not that you kill a theory. It's very rarely that you really, really kill a theory with an experiment, but you create problems to a theory, and when a theory has too many problems, you look somewhere else, and there have been a lot of these things recently.
The strongest and the most unexpected for many people has been the absence of low-energy supersymmetry. There was a big part of the community that was completely convinced, sort of 99.9%, that supersymmetry was going to be detected- - By the Large Hadron Collider? - At CERN, right. - Yeah. - It was LHC, and it wasn't. It was a shock, there were titles of the journals, like, you know, this is a crisis of physics. Of course, it's not the crisis of physics.
It's only the crisis for those who expected it, which is not physics, it's just a particular school of thought. But that's nature talking, and when nature is talking, we should listen. Another example is breaking the Lorentz invariance, the symmetry at the basis of Einstein special relativity, which is Lorentz invariance. Some people thought, also, that was like supersymmetry. It was a very nice idea. You can make the point of quantum gravity easier if you don't have Lorentz invariance.
So, people try to provide theories which break Lorentz invariance and might be quantum gravity theories. So, this was tested, 15 years now of astrophysical observations, and all the expected signs of breaking Lorentz invariance, zero. Once again, nature talks. As far as we know, nature is saying, "No, no, no, no, guys, that's not the right way to look for the solution." So, I think nature is giving indication, I mean, a lot of people expect a negative cosmological constant.
Even today, there is a large part of the community that continues to do calculations and calculations and calculations with a negative cosmological constant, or AdS/CFT. AdS means anti-de Sitter, which means there's a space with an effective negative cosmological constant, and you accept that the cosmological constant has been measured by the astronomers, by the cosmologists. In a very convincing way, they got the Nobel Prize, the ones who did that, and it's positive.
So, once again, I think my interpretation, my reading of that as a scientist, I mean, I might be wrong, but my reading of that is that nature is talking, listen. That's not the right direction. - How will nature speak to you to advance loop quantum gravity, say. - There are two or three directions where me and many of my colleagues are looking into. For the moment, zero, so we have no negative response from nature, but we don't have any positive response
(laughing) from nature. - Can you explain that a bit? - We don't know, so there's nothing that has come as a contradiction to what we expected, but there's nothing that has come to confirm predictions of the theory either, so I cannot say that quantum gravity is confirmed in any sense. So, where could the confirmation come from? I see three possible directions. One is the early cosmology. There's a lot of literature, papers, and papers written.
So, the universe, we know, came out in the Big Bang, the very early moment, at the beginning of its life, deep into quantum gravity regime, so that's where quantum gravity should appear. A lot of colleagues have applied loop quantum gravity to describe what happens there. It seems to be working, and to see if one can predict effects of what happened there that can be tested in the cosmic background radiation, it's possible, measurements getting more precise.
I hope they will convert it with something useful, but for the moment, there's nothing. That's one, the second one is black holes. I'm working on black holes. Loop quantum gravity is consistent very much with the idea that a black hole evaporates. That's Hawking's realization, that black holes evaporate. They become smaller, smaller, smaller, and then, at the end, they don't just disappear, pop out of existence, but there's a remnant, which is a white hole.
So, there's a quantum gravity transition jump from a black hole to a white hole, with a little throat, but a huge inside. And then this white hole, slowly, things come out, where the information slowly comes out, lives for a very long time. So, this is a scenario, it might have astrophysical consequences. These have been explored by this group, including London and the people I'm working with.
There's one of these possibilities, which I'm particularly attracted to, which is that these little things that float around in the universe are actually dark matter, or a component of dark matter. If so, it might be that we have already observed something, we just haven't recognized it. - Dark matter being another great puzzle
of modern physics. - Dark matter, it's a big puzzle, and that's the opposite of the quantum gravity puzzle, because it's not a puzzle in our understanding, it's a puzzle in what we see. You look at the universe around us and we see galaxies, starts, clouds of hydrogen, all sorts of stuff, and then there is this stuff out there, something that produces effect out there. We see the gravitational effect of these things. We have quite convincing evidence that it's not usual matter.
It's not just atoms or molecules or protons or neutrinos or photons, it's something else, and it's a lot. There's quite as much normal matter and dark matter, even more dark matter, and nobody knows what it is, so it's fantastic. People who say that we're close to the end of physics and close to the theory of everything, come on, guys, we don't even know what we see around us. So, dark matter is really an important question.
We have a lot of possible explanations, but many are non, confirmed non, really, credible. I like the black hole ones because it does not rely on any new assumption. Well, if there's black holes, it's just nothing we know exists. - It's funny, you said it's a mystery, we don't know, and that's fantastic. That's not always the case in a lot of professions, where the lack of knowledge about something is something you're excited about. Are you glad that physics is nowhere near being complete?
- Oh, infinitely so, of course, otherwise it would be boring, right? Imagine what a disaster if somebody wrote, "Okay, I got it, everything, this is the final equation of everything." - But that's what you're going for. - No. - No? - No, zero. - Is quantum gravity not sort of that grand, unifying theory? - No, it's a step on the way. It's just figuring out what is the quantum property of space and time.
I'm not working for material of everything, I'm working just for a next step in understanding what's around. - Once we've figured out the quantum nature of spacetime, does that open up new questions or help us answer old ones? - I suppose loop quantum gravity is confirmed. With a colleague, Marios Christodoulou, we have an experiment which we proposed, which might even be doable in 10 years or so, which would actually test the discreteness of time predicted by loop quantum gravity.
So, suppose this can be done, and bingo, the right numbers, because loop quantum gravity predicts that space is discrete, right? It's granular, like light is made by photons, spaces make this grain of space, but also time, I expect it has this granularity. We have an idea of, perhaps, with some slight advances in technology, not excessive, it could be tested. Now, suppose this comes out right. Loop quantum gravity is correct, perfect, the right numbers are there, now what?
Well, now we still have a universe described by a funny standard model, where the weak interactions and the strong interactions are completely separated, described by similar theories, but not really unified in any way. Gravity described by still another theory. 19 parameters for the standard model. Who chose them? Why? Three generations. Suppose with quantum gravity, we figure out the Big Bang, and what seems likely is that it was not, that the initial exposure was a bounce.
It's an idea studied by various people. - That our universe is the result of a previous one collapsing and expanding again? - Some universe was collapsing, in some sense, under its own weight. It gets to the sort of maximum compression, where quantum gravity comes in. It bounces, and then what we see as the Big Bang is this bounce. I think it's a reasonable hypothesis. It seems to be more reasonable than the Big Bang. Suppose we figured this out. Have we solved everything?
No, of course, I mean, where was the collapsing universe coming from? (chuckles) I mean, what was there? It seems, today, so impossibly difficult to figure out what was in the collapsing universe, but at the time of my great-grandfather, it seemed impossible to discover what was the chemical composition of Jupiter. I mean, it was considered an unsolvable problem. I mean, now we know, in Jupiter, everything, even, you know, if there were ants there, we would've seen that.
So, science finds new problems and grows at all levels if the mystery is not a reason of sadness, it's a reason of joy because a new thing's discovered. It's the beauty of understanding. - You're still, like Isaac Newton, playing with pebbles on the vast sea of what we don't know?
- Absolutely. - And regarding this, you know, general idea of working in a field, where you maybe don't yet have evidence for or against it, it just reminds me of something you write about in your book, "Seven Brief Lessons". When you're talking about Einstein's theory, you write about how, a lot of times, something very important is kind of considered useless at the time when it's developed.
One example you gave is that Rehman's work, that was generalizing Gauss's explanations, was considered useless at the time, but it was then a fundamental piece of Einstein's theory.
So, it seems that this is very crucial, to work on things where we don't actually know exactly what the application will be or exactly how long it will be, but I'm wondering if you think that physicists need to find, in general, some kind of a balance between working on problems where we have an idea of the time horizon for the applications versus working on these problems where we don't really know where it will lead. - Yes, obviously there is a balance to be searched there.
If you look at this from the main whole of Perimeter, as this is the same city, hard to find balance, but if you look at it on a large scale, 99.9% of the money put into research worldwide is to practical applications. Of course, we need practical applications, right? We need people who study chemistry of materials because we need the certain materials for something, healing people and replacing bones. I'm just defending.
Applied science is great, but to concentrate resources toward applied science so much, as is done today, I think, it's a disaster. We need people who do the kind of pure science or fundamental science or basic science, I mean, all these words are imprecise, all of them, namely who don't think about application. Our science is built upon a number of key results obtained through the same tests.
If you look at each one, no one was looking for application, and if he had looked for application at his own time, he wouldn't have got there. So, it's obvious that we need to just ask the question, what's behind things? How can I understand better at the fundamental level? Applications will come out, sometimes fortunately, sometimes unfortunately because sometimes applications are to kill people and to make war.
- So, you're the organizer of a research initiative called The Quantum Information Structure of Spacetime, and this brings together theorists, experimentalists, and philosophers. Can you tell us why you think it's so useful to bring together that group of people and what you're trying to answer through this initiative? - Thank you for this question.
The Quantum Information Structure of Spacetime, the short name is QISS, QISS, written with a Q. It's a big consortium with big grants, mostly used for supporting young people. A group of PI here, in fact, two groups of PIs are part of it, and there are about dozens of group all over the world, from Hong Kong to Mexico, to California, and the aim is to bring together two communities, or actually three communities.
The two communities are quantum information and quantum gravity, and the idea is that quantum gravity people have been using quantum information notions, or beginning to use it in various ways, and quantum information people are starting to think about how quantum information works in space and time. Let me say it this way, and so the same problems are being addressed, but from a completely different perspective.
And the third community is philosophers because this dialogue opens fundamental questions, like what we were saying before, the direction of time or the nature of what is information, what we mean by information, and in quantum gravity, it's a theory which is not written in spacetime. So, in some sense, spacetime has to be rethought to come out on the theory in some way, and these are philosophical questions.
So, these are different communities which are being brought together, and in June this year, they will be not far from PI in London, Ontario, so it's just a short drive from PI, a conference bringing together this, and it's a conference that we have organized.
It's not a standard conference with, you know, speeches and a few questions, and, "Why do you say that?" Each half-day, we'll have a few 10/15 minutes very short flash presentations, and then a couple of hours of open discussion, everybody with everybody, with a good chair, who sort of likes balance and follows.
Discussion compares all points of view because there are these communities, quantum information, quantum gravity, and philosophers who look at these things, which have different ways of viewing the same thing. So, we want to compare and, of course, learn from these differences. - Are there frustrations that tend to come up when people with such different backgrounds and education are trying to discuss a topic with each other?
- Yeah, there are things you take for granted, then a person who's a good scientist comes to you and says, "You're wrong." You say, "Wait, (chuckles) what do you mean I'm wrong, you are wrong," and that's frustrating, but that's great because I think that's how the process of knowledge works.
You know, we learn from experiments, but we even more learn from continuous exchange of perspective, and the more we listen to other perspectives, and that's a great opportunity, I think, because quantum information has boomed for various reasons in the last decade, probably, and there are very good ideas there, which I think are relevant for quantum gravity.
On the other hand, the people of quantum information are not aware that some of the things that they are struggling with have already been addressed by quantum gravity, right? So, there's really a dialogue to start here, and the philosopher has an interest in both and have things to say about both. So, I hope that this dialogue in three, based not just in presentation, but in discussion, will work, and I look forward to that.
- After two years of lockdown, of pandemics and people staying at home, have you felt, distinctly, the absence of in-person gatherings with other researchers and scientists, you know, getting together in the same place? - A little bit, yes. For me, this has not been dramatic because we are all on the internet, we're on Zoom, but being always on Zoom is also painful. This morning, finally, it's the first day I'm back in PI after so long, finally!
I was with a young colleague in front of a blackboard, writing things, and I said, "No, wait, this is not," as, oh, what a pleasure. (chuckles) It was so long that this didn't happen. - And from reading the website for this QISS initiative, it seems that a major goal is to deepen the understanding of information. Could you just tell us what you think of information as meaning and why you think that information is so fundamental?
- Information is a very tricky world 'cause the spectral of meanings is very wide, extremely wide. When you talk about information, people often get confused because in a debate, in a dialogue, people mean different things, and it goes from the most complex one, I mean, do you have information about your father? Of course, I know a lot about my father, to the most basic one, my little card here contains so many megabytes of information.
Obviously, the two are connected somehow, but the two are very different, completely different. About your father is something that has to do with meaning. In that case, with rather even emotions, (chuckles) but certainly is interpreted information in some sense, so it has to do with something that needs to be decoded, that has to be translated. In the case of the memory card, just counting something, it's a number of counting something.
It's like counting the number of atoms, so counting the number of something. In this spectrum, what is interesting is exactly the spectrum, that it has so many possible meanings, but what's most interesting is the basic one, and the basic one, there's a very simple notion of information which is purely physical, which is correlation, when two things know about one another. If you glue two things, if one points in one direction, the other also points in that direction.
If you know one, you know the other one. So, one has information about that, meaning that there is a correlation between the two. That's the basic notion of information, it's purely physical, nothing mental, no meaning, no significance.
That's the basic notion of information, and I think this notion of information is fundamental, not because the world is made by information, the world is made by stuff, by variables, by things which are, but because the world is made by relations, the properties of things are relative to something else. So, if you want to describe the structure of the world, you're always talking about how one thing affects another one, so how they get correlated to the other one.
So, immediately, you can quantify how much things affect one another by using the notion of information, and this means, not information as an ingredient of the world, but as a key ingredient of our thinking about the world. I think quantum mechanics itself can be largely thought of in this way.
I've been thinking this since back in the '90s, when I started thinking about the notion of quantum mechanics, and because of that, I think, in quantum gravity, it also could be a fundamental role to thinking about information systems helping out one another, but once we go into this way of thinking about physics, not as how systems are, but how systems have information about all of that, how they're correlated, then it's easier to understand that there's a continuity
to the most complicated notion of information. So, the mental is not so far away from the physical now 'cause we start taking the physical from the right perspective, from which it's easier to reconstruct the more complicated notion of information, meaning, for instance, we talk about memory traces, and we build it up more and more complicated. So, it's a very versatile, rich, confusing, but key notion for understanding the world information because the world is made by relations, not by things.
- In reality, it's not what it seems. There's a passage that I love, and I even told you about it after I read it, because you go through so much of the book explaining the historical context of quantum gravity and explaining the concepts in very easy-to-follow terms, which I appreciate, and then later in the book, you say, "If, dear reader, you have found the journey so far a little rough, hold on tighter because we're now flying between voids of air."
And then you get into your new ideas, which you said, "If the ideas seem confused, it's because the person with the confused mind is me." First of all, that's something I don't often see in popular science books, is the warning to the reader, like, it's okay to be shaken by this, it's okay to not fully get it. So, you gave this warning, and then you expressed ideas that you personally don't have a full concept of.
Can you explain a little bit about what that's like, going into territory that is less historically sound and more speculative, and putting your own ideas out on the line like that? - There is a lot about the world we understand, and there's a lot we don't understand. It doesn't make much sense what we too often do, in my opinion, which is to pretend that we understand the part we don't understand.
University professors that teach and lecture on physics, they shouldn't pretend that they know everything about it. They don't know about it, and they may be wrong. I mean, they might be teaching things which are wrong, so they should say, look, this is what we understand, this is what I understand, and be aware that there might be something wrong, and if there's something confusing, it might well be because it is confusing or because a person is confused or because the community is confused.
A good example is quantum mechanics. Quantum mechanics is a hundred years old, spectacularly successful, used in technological applications everywhere, but it's still confusing, and the fact it's confusing may be good because it may be that we still haven't got something, some right way of looking at it, so let's say it's confusing.
I think this makes, also, things easier for the student at university or for the reader of a book who is not presented this, you know, both white, clean piece of stone saying, this is it, period. We are humans. Science is a human activity, like everything else. It's dirty, it's imprecise, there are holes, so I think it's better to present what it is.
- I connected with the idea that you yourself are struggling with these ideas, and when you read a book by an expert on any subject, you assume the expert knows everything, and for you to say later in the book, you know, here's what I'm grappling with, it helps. I think it helps the reader understand that this is a difficult,
complex pursuit. - Yeah, my book, my books are a little bit different in spirit from most popular science books because they also are aimed at a slightly different audience, and in fact, I've remarked, from the reactions that I get, that the typical reader of science books likes my books less, and the people who like my book are a little on the extreme sides, are either people who know zero about science or people who know a lot about science.
And I understand the reason because I think, at these two extreme categories, when I'm talking about them, the typical science book, it's written for somebody who wants to know more and more and more and more and more about some domain, so you give more details, you give more information.
You say, "Oh, and we know that, and we know that, and we know that," and you know, there are kids, nerds that really want to know more and more and more about the neutrinos and all the possible details about that. I don't do that, I do the opposite. I take away, I take away, I take away.
I strip away as much as possible, trying to reduce to what seems to be the core that we have understood about something and to present it in a way that it stays together, it holds on, and allows the reader to understand what it is and what seems to me the real thing we have understood.
And then, of course, those who know nothing about science, they like it, because they say, "Oh, great, I get to that, yeah," and those who know a lot about science also like it, because they say, "Oh, wow, that's a good way of doing things, maybe I didn't think this way, maybe I was thinking the other way. That's a new perspective on things." And a lot of my best colleagues tell me, "Ah, I have read your book, wow! I didn't think about this way of putting it. Great, great, I learned something."
Even my greatest enemy, the chief of the opposite, you know, band theoretical physics, who is a Nobel Prize winner, sent a message to me and said, "Fantastic, I loved it." But the students of physics, who've just studied that at school, reads what I'm saying and knows, because they say, "Wait a minute, I mean, there's all missing here." I got an email saying, "You talk about quantum mechanics in the seven lessons. You don't even mention the Schrödinger equation."
I thought, yeah, that's right, I don't mention the Schrödinger equation, but that's not the core. - The right story. - Right, so yes, and this connects to your question, what you were saying before, because to do that, you need to understand something all the way through. So, once we have totally digested something, then you can just, bingo, you know, in one phrase. - You can whittle it down to the essence. - To the essence, right? - Yeah. - I mean, take Copernicus.
If you read the book of Copernicus, 300 pages of calculations, detail, geometry, perspective. It's horrendously complicated, then the equant, the epicycles still, and then this and this and that, and to make this complicated, and the moon is complicated. What is it, 400 years have gone from Copernicus? Now we have digested everything, can say it in two lines, the earth is spinning and is orbiting around the sun. That's what Copernicus has qualified, so it's totally clear.
It's strange if you think about we are actually moving. It's revolutionary. It changes everything. The earth isn't violent, like the others, but it can be said in two lines. Once we have really understood something, at the end, we can say it in two lines in a way that has it, has it really, and the people understand what it is.
So, my ambition, but we're not there, would be to do the same I just did with Copernicus, the same with, you know, the standard models, special relativity, general relativity, quantum mechanics, quantum field theory, quantum gravity. - You said in one piece you wrote, "Sometimes dreams come true. I felt there was a story about the adventure of physics that had to be told, but I thought people were not interested," but you were wrong. You were dead wrong because a lot of people were interested.
You know, millions of people have read your book. It's translated into dozens of languages. What do you think you got wrong about estimating people's interest in this subject matter? - (laughs) It was not just me wrong, the "Seven Brief Lessons on Physics" was printed in about 5,000 copies. That was the estimate of the publisher that was going to sell. - Yeah. Do you think it was because you whittled down to the essence and you left out the equations?
- No, I think it's because, mostly because of the last chapter of the seventh. I think that's what made the book. It's a book that is not just about physics, it's a book that tries to go down to the essence and then asks the question, all right, so what does it mean for us? How does it reflect on the way we see ourself and the way we think about the material, the physical world, and our, let me use a strong word, spiritual world. Let me tell you my interpretation of that.
I and my friends, and many people around me, share a view of the world which is not much known by a large majority of the population, and it's a view of the world that is neither the world is made by little atoms bouncing with one another and that's it, emotions, the sense of lives, whatever, that's bullshit that comes later. It's neither that, but it's neither the material world is irrelevant, there is a spiritual world, with God, morality and things, that's what the reality is.
Somehow, a lot of people are unhappy with both because they don't believe the spiritual world too much anymore because we're in a secular society, which doesn't hold anymore for a large number of people, but neither people find convincing, a sort of cold and ground cynicism, which has no hold for meaning, for emotion, for our aim, for what we are thinking and desiring and suffering.
So, the fact that somehow people find in my book a perspective where the two things can very well stay together, and there's no contradiction between one another, is when a lot of people jump in and say, "Oh," but then there are people who can think that what matters for me is my emotions, but also, there's nothing in contradiction with fundamental science there. I think that this is the bringing together that made people react.
- And regarding this goal that you have in your writing of getting to the essence of a concept, I would think this would be uniquely challenging when you're talking about something like time because the average person will probably talk about time at least once in a typical day. So, there must be a lot that you need to strip away because the average person has a lot of assumptions that they're making about this word, time.
Can you tell us about what that process was like when you're describing time? - I wrote a book just uniquely, entirely about time, and that was not an easy-to-write book because exactly for the reason you're asking. When I decided how to write this book, I exactly asked myself this question. And so, the first half, the longest half of the book, one chapter after chapter demolishing something we take for granted, our time, and on good grounds, on things we know.
So, we think that time has this property, and you know, it seems obvious to be that, that's the way we think, and now I tell you it's not the case, and I show why we know it's not the case. So, the first part of the book, in part, it's just a way of telling Boltzmann's theory, of telling Einstein's special relativity, putting the various pieces of the story together, but not just for talking about physics, for talking, look, what this implies with respect to our notion of time.
Special relativity definitely changes our notion of time. Notion of present everywhere in the universe doesn't hold, but it's hard to think of the world without a notion of present everywhere in the universe. The question, what is going on right now on Andromeda, the galaxy, is meaningless. There's no meaning, what is going on right now. There's no now in Andromeda. It's like asking, what is going on here in Beijing? We're not in Beijing, so it's not here in Beijing, Beijing is elsewhere.
The book was designed exactly to address what you are saying, to take away, one by one, the suppositions of people that the people give for granted in science. Some of my colleagues which are very reflective, a written book, there's absolutely nothing they learn because they have gone through that, but there are a lot of my colleagues that teach special relativity and never have stopped in thinking what, actually, they're teaching, and I think that's wrong.
I mean, physics is interesting because it tells us something about the world, not just because you write equations, and then you make a prediction and it matches with what you measured. - Are you yet at a stage where you can give just this one or two sentence definitions that's the core of what time is? - No, with time, it's very complicated, (laughs) and the reason is because we haven't got to the end of understanding it. There are things about time which I think were generally confused.
A lot of things we have figured out with total clarity, like the nonexistence of a present everywhere in the universe, but there are issues about how to think about time in a wholly consistent way with everything we know, which I don't think we'll figure out. Even the direction of time is implicated because we have connected it to entropy, to the microscopic description, but there are definitely holes in our understanding, in my opinion.
- I found that book, "The Order of Time", to really make my brain meld and squish in other directions. I was listening to the audio book, and at one point, I was rushing somewhere, and something you wrote about time made me think, why am I rushing anywhere, a rush is an illusion. (Carlo laughing) So, I appreciated your writing of that book. I also really liked Benedict Cumberbatch reading it to me. That was a nice experience. Boy, it helps when these concepts are-
- He's astonishingly good. - Are so mind-bending. - Yeah, he's really good. - Yes, yes, I've been listening to his voice and saying, "Wow, who wrote these wonderful things," because it's too good for, it's certainly not me. He has a way of making it a principle, but also, it's like it's talking to you and telling you like a friend- - Yeah, but we actually have another student question about your books. - Yeah. This question was sent in by a PhD student here at Perimeter.
- This is Mac Du Shen, a student at IQC in Perimeter, writing, how did you first get started into writing science books, and how has that writing helped your own research? Do you find writing a technical paper or a more accessible book more challenging? - Probably a book for a general audience. You write a paper, a scientific paper, after you've figured something out.
So, you just get confused in a problem, and either alone or with some somebody else in physics, we worked mostly in little groups, two or three in theoretical physics, you sort of come out, and at some point, it's clear, and then you write it down, and you write down what you've understood. So, the writing is relatively easy. I'm picky, I'm complicated in writing scientific articles.
I try to write them clear, so I spend time writing and rewriting and rewriting, perhaps more than what I should or could. But the writing is, you know what you're saying exactly, while when you're writing a book, you still don't know what you're saying. You're picking up what you're saying in the writing itself, and writing, for me, is a complicated process.
My books are the result of a large number of revisions and a large number of cancellations, because I say, no, this is not useful for what comes, and that's just superfluous. So, the same phrase, I rewrite it 10 times and say, "No, that's not clear, I mean, is there a way to say it better?" That's the heart of writing for me. - I was just gonna say, for you, it seems that this must be particularly challenging because you're not just writing a book for the general public.
As you said, you're hoping that your book will be influential for the general public, and also for experts in the field, even though the material is not technical or maybe doesn't rely on math. So, I would assume writing something that can be a good fit for both of those audiences must be very challenging.
- Yes, it is, and I have these two readers in mind, the super expert one who knows everything, and the one who knows nothing, which is good because thinking like the super expert one is what, you know, warns me from not saying something, which is, oh, if I say that, he's gonna complain, (chuckles) and thinking about the typical grandmother who doesn't know anything stops me from saying things, oh, but that's too complicated, I mean, how can anybody get this point?
So, I always have these struggles, so this simplifies because it gives me guidance, but yes, it's also a complication to try because I'm putting my own ideas in the books, mostly because it's my own perspective of things, writing a book of quantum mechanics, which is entirely from the perspectives of Heisenberg, Born, Dirac, rather than from the perspective of Schrödinger. So, it's taken quantum mechanics because I think it's the most interesting thing.
I'm not the only one, but there are people who think different, who think, no, no, no, no, quantum mechanics is all about the Schrödinger equation and the wave function evolving, that's all there is. I think that's wrong. My books are a way of defending a perspective, but the two things help one another because in the moment in which you try to explain something simple, you get clarity yourself. I mean, for me, it's an exercise of science.
I feel I'm doing science when I'm doing that and clarifying my mind, and reading of the great masters, who were infinitely better than me, I mean, reading Galileo, when he wrote these books, it seems to me he's doing exactly the same thing. I mean, he's talking to people.
That's a book written for the cultivated person of the European Renaissance in the 17th Century, not for his colleagues, astronomers, because it explain things one by one, but obviously it's debating with his colleagues, astronomers, in the book. It's making the subtle points of the argumentation, proving him right and them wrong, and that's what makes that book so great.
Now, of course, I'm not Galileo, and I'm not writing the dialogue of the two great systems, but it's this kind of popular science, which other people are doing, which is presenting ideas in a way which are comprehensible to defend these ideas, which I'm trying to do. - Are you working on any books now? - Yeah, I am, but I'm not sure I should talk about that. - (laughs) Are you always working on one book or another? - No, no, I have not been writing for one year, or more.
I just stopped completely. I am under strong pressure, of course, from publishers and things for writing more. Let me just give you this, I'm not covering a large portion of physics, I want to do the narration, tell the story of how a theoretical physicist like me gets into a specific problem, gets fascinated by the problem, works through and comes out with some ideas, and is struggling on. So, whether this particular thing is right or wrong is irrelevant.
I want to tell how is theoretical science in the doing. - Sort of humanizing the process or putting a- - Yes, yes. - Making it relatable to non-science. - Yes, so what is actually going on, including changing minds and realizing things didn't work, and so on and so forth. - I don't actually have any further questions. We've kept you for more than an hour, I believe. - Wonderful. - So, thank you so much for chatting with us. - Thank you.
- I'll just ask a question I always ask people when I interview them, what keeps you up at night these days? - Last night, I was awake with (laughing) my going away. - It was a relevant question. - Yeah. There is a beautiful experiment in quantum gravity, in fact, that's been proposed. There are some people who are questioning the way to think about that, and I think they're wrong.
So, I'm trying to find out a right theoretical description of this experiment, and in doing that, it's fun because it's basic physics, but it's the writing and thinking I do in new ways, and there are technical issues, technical problems, so I keep going around these things here. So, it's not a big, huge question, it's a very small, specific question. - Well, we'll have to have you back another time so you can tell us, tell us the results of that.
So, thank you again, this has just been a pleasure. - Thank you very much. - Thank you. - That was very nice. (light electronic music) - Thanks for listening to Conversations at the Perimeter. If you like what you hear, please help us spread the word. Rate, review and subscribe to Conversations at the Perimeter wherever you get your podcasts. Every review helps us out a lot, and it helps more science enthusiasts find us. Thanks for being part of the equation. (light electronic music)