(gentle upbeat music begins) - Hello everyone and welcome back to Conversations at the Perimeter. I'm Lauren and I'm here as always with Colin. - Hello. - In this episode we're sharing our conversation with Savas Dimopoulos. Savas is a faculty member at Stanford University in California, and he's the Coril Holdings Archimedes Visiting Chair, here at Perimeter Institute. He's a renowned particle physicist whose career spans over four decades.
- So I've been wanting to have Savas as a guest on this podcast ever since we first launched it. So I was thrilled that we made this happen. I first met Savas nearly 10 years ago during one of his annual visits to Perimeter, and I was immediately struck by his kindness and his wisdom, and really by his undiminished passion after all these years for exploring the most puzzling mysteries in the universe.
- In this conversation, he shares his thoughts on fundamental, huge, open questions like, why is gravity so weak? - Why is the universe so big? - And is there a multiverse? And he also talks about how he remains motivated to search for answers to such huge puzzles. - Savas was also one of the scientists featured prominently in the award-winning 2013 documentary, Particle Fever, about the hunt for the Higgs boson at the LHC, CERN's Large Hadron Collider.
Savas tells us some history of collider physics and he explains how a renaissance in small-scale experiments could reshape how physics is done in the generation between the LHC and the next big super-collider. We were fascinated by this conversation and we're pretty sure that you will be too. So let's step inside the Perimeter with Savas Demopolis. (gentle upbeat music fades) Savas, thank you so much for joining us. I've been looking forward to chatting with you for a long time now.
- My pleasure. - It's been a bit of a break for you coming to Perimeter because of the pandemic, but we're glad to have you back. And I was looking at your Stanford webpage the other day, and it says that your job is to search for answers to the biggest mysteries in the universe. That's about the biggest job description. Can you tell us what does that mean? What do you do for a living? - I assure you, the job description is big,
but it is not matched by salary. (both laughing) - It would have to be an astronomical salary. - It would have, but I'm happy, because my main reward is that I'm given the time to just think about the universe, and that's the reward enough for me. - So what are the big questions about the universe that are driving you these days? - Yeah, so there are several, but I want to give you some big principles that guide the questions that we are asking.
One of the big principles is what's called, "Naturalness." And the idea of naturalness, actually, is in all of science. In the case of physics, naturalness has to do with trying to understand very large numbers. For example, if you take the size of the universe and you compare it with the size of an atomic nucleus, you get an enormous number, 10 to the 40, which is 1 with 40 decimals next to it.
With such enormous numbers it's natural to ask, "How come the fundamental particles of the theory are so much smaller than the universe?" Or conversion, "Why is the universe so big?" You can ask it in many different ways, but one of the ways it's asked, it's called a, "Cosmological constant problem."
Another question is, "Why is gravity so weak?" So for example, what I mean by the weakness of gravity, when I lift this glass of water, the electrical forces from my fingers to the glass are large enough to compensate or to overcome the gravitational attraction of the entire planet Earth. And if you think about it, - Hmm. this is amazing. The entire planet Earth is enormous compared to my fingers, - Mm-hmm (affirmative).
yet I'm able to overcome the gravity of the earth with the electrical forces, or atomic forces, that my fingers exert on on the glass. So the only reason why this is possible is because the intrinsic strength of electrical forces, or atomic forces, is far, far bigger than the strength of gravity. It's, again, it's about 40 orders of magnitude, 1 with 40 zeros bigger. That is called, "The hierarchy problem."
And these questions, the enormity of the universe and the weakness of gravity have been driving, in some ways, theoretical thinking for the last 40 some years. And much of the theoretical community in my field, which is called, "High energy physics," has been driven by these questions. Now, one of these questions, the so-called, 'hierarchy problem,' has had some possible answers.
And much of what many people did, including myself, over the last 40 years, was to search for answers to this question, the weakness of gravity. Why is gravity so much weaker than electricity? Or why is gravity so much weaker than all the other forces of nature? To answer these questions, we came up with theoretical ideas.
There is three or four, depending on how you count, but the simplest one to describe in words and with pictures is the idea of large extra dimensions, which was proposed back in 1998 by myself and a couple of collaborators, Nima Arkani-Hamed and Gia Dvali. The basic idea of that framework is that gravity, in contrast to the other forces of nature, lives in more than three dimensions.
As a result, it spreads inside a space bigger than three dimensions, maybe four, maybe five, maybe six, et cetera, dimensions. And in so doing, it dilutes its strength. It spreads itself thin in a sense. - So gravity's having an influence in the dimensions, we might not experience ourselves? - Exactly right, at least not directly. The picture there can be described as follow: Imagine the surface of this table that represents our universe.
By our universe, I mean the three-dimensional space of our universe, okay? So clearly this is not a precise... The surface of the table has two dimensions. Our universe has three dimensions, but nevertheless, imagine the surface represents our universe.
So all ordinary forces, which is electricity, magnetism, the so-called, 'strong interactions,' which keep an atomic nucleus together, or the 'weak interactions,' which are responsible for radioactivity, all of the other forces of nature stay in this three-dimensional space, and are confined to this table.
Whereas gravity can spread also perpendicular to the table in these extra dimensions that we usually call, 'height.' So because gravity spreads in more dimensions, it dilutes its intrinsic strength. It's like when a river which moves, let's say in one direction, in one dimension, spreads itself into several tributaries, it loses its strength. - Hmm (affirmative). - So it is with gravity that this extra dimensional space dilutes its strength.
And this idea received tremendous attention, both theoretically and observationally. The big experiment that we call, "The Large Hadron Collider," at CERN in Geneva is looking for signature of these theories. And I can describe to you a couple of ways you can look for this that follow from this picture of the table representing our three-dimensional universe and the vertical directions, - Mm-hmm (affirmative). the extra dimension.
So one test is the following of this hypothesis: Imagine the surface, which represents our universe, is like a pool table. The surface of the pool table represents our three dimensions. Billiard balls on the pool table represent elementary particles, like the proton or the electron, et cetera.
Now, normally when we play with billiard balls, the billiard balls collide and when they collide, of course, they still stay in two dimensions, they stay in ordinary space, but the sound that the collision creates propagate also in the third dimension, inside the space of the extra dimensions.
So even if we were not looking at the extra dimensions, just by listening to the sound that the collision of the billiard balls produces, we could infer about, well, what happened, the collision and the fact that some sound or, was emitted inside the third dimension. So we could infer about the presence of the extra dimensions. So LHC is looking for the analog of that. You collide to elementary particles, which in that case is protons.
And if there are extra dimension, some of the energy of this collision may manifest itself by particles that come into the extra dimensions. So some of the energy that was in our universe, if you wish, in our, what we thought was three-dimensional universe, will be missing before the collision and after. Some of the energy has been carried out in a new space that we are normally not aware of. This is called, "The missing energy signature."
You collide two particles or two billiard balls, and there is some energy missing because it went to new particles or to the sound waves in the case of the billiard ball. And by looking very carefully at energy imbalance before the collision and after the collision, you can look for the space of extra dimensions.
- Can you say a little bit more about where the seed of this idea comes from because, as you're saying, there are some experimental signatures that you can look for, but is that something that you come up with after the fact? Or is it these experimental signatures that inspired you to look for a theory in higher dimensions in the first place? - Well, that's a very interesting question because in some sense, for the case of extra dimensions, both played their role.
Historically, I was made aware by talking to some of my experimental colleagues at Stanford that gravity has been tested to only distances of about, back then it was about a centimeter. This means, Newton's law of gravitation that the force between two particles was like the inverse square law. Had only been tested down to a distance of a little less than a centimeter, and this was back in 1990.
So I was astonished to hear that because when I was an undergraduate, in my lab, we tested Newton's law to a distance which was maybe 15, 20 centimeters, not much larger than the 1 centimeter or so. The original measurement was done 200 years ago. How come? So that immediately planted to me the seed of an idea that I should be brave about creating theories where the law of gravity is different, distances below a centimeter.
Newton's, what's called, "Inverse square law," is not obey that shorter distances. So that sort of opened the door for me that I could contemplate such possibility without immediately being disproven by non-experimental facts. The other thing theory also played a role, in the sense that I was looking for an explanation of the weakness of gravity. However, for several years, I didn't make the connection between those two.
In fact, I wrote papers proposing new particles that would cause deviations from Newton's law of attraction, but without any reference to extra dimensions. And then finally, after a few years, my colleagues and I started making the connection and that's how the theory of large extra dimensions was proposed. In fact, your question also is related to the second test of these theories, namely, you can study Newton's law at very short distances.
So when I started talking about this possibility in 1990, several of these in particular colleagues of mine at Stanford were inspired, experimental colleagues, and we started talking about them testing Newton's law. We spoke for a long time, maybe a couple of years, with a friend of mine, Aharon Kapitulnik. And we have good friends, we have dinners together and we drink good wine together.
So it was at that setting that we started talking about these very wild and speculative ideas, and he decided to test them. And he and several other people around the world started looking and today, the force of gravity that Newton say inverse square law has been tested, done with distance of about a hundred microns. So far smaller than a centimeter, which used to be the case. And now there is enormous amount of effort to test it at shorter and shorter distances.
Now, what does this have to do with extra dimensions? Well, if there is extra dimensions, the so-called, 'inverse square law,' will be modified. For example, if instead of three spatial dimensions you have a fourth, the inverse square law will become the inverse cube law. And if it's two dimensions, it'll be the inverse fourth power law, et cetera. So that's what these experimentalists are looking for. A deviation from one over distance square to one over distance cube or fourth, et cetera.
And clearly, no such deviation has been seen, but people are looking at shorter and shorter distances now. And in fact there was a very nice workshop, or actually it was a school last week, where many of these top experimentalists were giving lectures to students from all over the world and to each other. Actually there were many professors, experiment and theory, about the new frontiers, how to look for such new dimensions.
And this is a very nice story because it shows you how a theoretical idea that can be described without too much mathematics can in fact connect with experiment. Now, part of the reason for that is 30, 40 years ago, it would be incredible for anyone to propose looking for such small forces at, let's say, below a hundred microns. Such new forces has been looked for down to distance of 40 microns. To give you an idea, a hundred microns is smaller than the width of human hair.
So it's incredible that you can even conduct an experiment, let alone a precise experiment that will measure the force between two not visible particles to such a precision. And so why was this possible? Definitely it was impossible 50 years ago. Microtechnology. In other words, there has been a driving force in part because of application to manipulate things at extremely short distances.
And over the last several decades, experimental physicists have been at the forefront of this manipulation of the very small. When they started doing that, their objective was not to test gravity. I don't think there would be enough money (Colin laughing) funding such an effort from the physics of 40, 50 years ago. Usually, physicists like to emphasize how physics makes our lives better. We have all of technology, electricity, and how useful quantum mechanics has been, lasers, et cetera.
But there is also, of course, the converse where technology allows physics to progress, and these things go hand in hand. So when I started to think about this in 1990s and started talking to my good experimental friends, partly motivator for social reasons to have a good time on the weekends, et cetera. Then I realized, "Oh my god, these people are amazing!" I couldn't believe it. They can look at a hundred microns smaller than the width of a human hair. Yeah, just by all means do it.
So they went from a centimeter, which you can visualize, to extremely small distances and they'll be progressing further. I actually think this paradigm sort of summarizes much of, I mean this is sort of at the highest level, summarizes though, the interplay between theoretical ideas and technology and experimental progress and the back and forth. - You mentioned a few minutes ago, the term, 'naturalness.' - Yes. - It's not one that I've come across very often.
Can you explain how that sort of fits into this picture? - Yeah, so the way it fits into the picture, I can explain in the context of the hierarchy problem. So let's back up. So the hierarchy problem was the problem of understanding why gravity is so weak.
So the connection is, if there are extra dimensions of space in which all elementary particles that we know of, electrons, protons, all the forces, the other forces we know, electricity, magnetism, et cetera, are constrained to this three-dimensional space. This three-dimensional space we call our universe. Now if gravity is not constrained to this three-dimensional place, but it spreads into the extra dimensions, then it'll dilute its strength and it'll become weaker.
Now how weak? Well, it depends on the size of the extra dimensions. The bigger the size of the extra dimensions or the more extra dimensions you have, the more rapidly you dilute the strength of gravity. So in fact, you can infer some relation between the size of the extra dimensions and the weakness of gravity. So that's the connection. The gravity is weak because there is a large amount of space in extra dimensions inside which gravity dilutes its strength. - Okay. - That's the connection.
So what used to be, and you know, 40 decimals now translates to how many extra dimensions you have and how big they are. They cannot be ultra small, but they can be even as small as 10 microns, a hundred microns, and still explain the dilution or the weakness of gravity. So naturalness came because you transcribe the problem, which look like a 40 decimal problem to some geometric problem that you can imagine solving. So that's an example of an approach to the natural.
Now there are, I don't want to get, because I'm not, it's not my field, but in other fields, for example, in biology, in some sense, Darwin's theory made many of the biological wonders. So what seems unimaginably complicated, like a human being, where millions of things have to work synchronously, very precisely, can think, the heart, the mind, everything, this become a natural consequence of what's called, "Evolution." - Mm-hmm (affirmative).
- Now not everybody buys that, but scientifically, I think there is no question that that's a valid theory. So that's another example where you take an incredible mystery, you look at it from a different perspective where this mystery looks more natural. - Mm-hmm (affirmative). - In physics, it usually has to do with explaining big numbers. Numbers that are about are like 1 or 10 or a 10th, we feel, "Oh, okay, well such and such is about as big as such and such, okay."
But when you have disparities of many, many, many orders of magnitude, they beg for an explanation. And the other example of this, is the enormity of the universe, or the so-called, 'cosmological constant problem.' - That's a question I've been dying to ask a physicist is, - Yes, please. why is the universe so big? - So the universe, why it's so big...
First of all, how big it is, as we were saying before, if you compare it to the size of anatomic nucleus, it's again, about 40 orders of magnitude bigger than the size of anatomic nucleus. - Mm-hmm (affirmative). Again, it begs for a mystery. You start, if you wish, with a theory that has nuclei and electrons and atoms and all of a sudden, you have this enormous universe that supposedly follows from the same equations that have this tiny nuclei, et cetera. How can this be?
This problem has many, many facets and I cannot do justice to it. I'll just tell you that there is no solution to this problem. At least there is no solution within the usual framework that science proceeds, where you write down the laws of nature which means, some equations that dictate how the universe works. And then you can derive that, "Oh, therefore, the universe is large." There is no mathematical theory of this.
There is a very controversial approach to this problem, which was proposed back in 1987 by more than one person, but in particular, a very well known physicist called, "Steven Weinberg," who just passed over a year ago. The basic idea there is embedded in what's called, "The idea of the multiverse." But before I take you back to what's the multiverse, I want to draw an analog. And this goes back again to some ancient Greek physicist called, "Aristochos."
Aristochos was one of the first people that believed there were many, many solar systems. That was not a very popular idea, either at the time of Aristochos or even in 1600, when what we call, "Modern science," emerged. Most people, even by 1600, believe that there was only one solar system. That was it.
So then, in the context of these many mysteries up here, if you believe there is one solar system, it looks amazing that that solar system, in particular, the planet Earth and the sun, the distance between the earth and the sun, were made just perfectly to allow the conditions on earth to be friendly to our existence. For example, if we were a few percent closer, a few percent further than the sun, the earth would either boil or freeze and we wouldn't be around.
The chemical compounds that we see on earth are just exactly what we need to exist and to flourish, et cetera. So it looks like, again, there is some, you know, higher intelligence that really cares for us. Ah, - Like turning a knob until they... - Turning a knob. - Just right. - Exactly right. Oh, okay. Oh, we don't have Savas, so let me go back. (all laughing) So it looks like a miracle in many ways, considering how much it takes to have life. And this point of view is very popular.
It was obviously also popular with the church. There is some deity that really cares. That's why everything was made perfectly for our existence, et cetera. Then in 1600, there was a priest called, "Giordano Bruno," from Italy, who really believed in our Aristochos's ideas, and he started discussing them in public. And eventually, he was burnt at the stake for his beliefs. He was burned at the stake in 600. Galileo was almost burned at the stake around 1630s.
Galileo died in 1642 and Newton was born in 1642. So that was really the beginning of the renaissance of science. And so many ideas in many ways they went back to Aristochos. Aristochos who actually could argue that the lights that we see in the sky are actually solar systems, and because they're so far you can't tell that they're moving, but they're moving, et cetera. So they started going back, and then Galileo, of course, invented, or co-invented, the telescope.
And people started looking at planets, which had moons around them. And then they said, "Okay, it looks like things like our solar system actually are probably out there," and they started making observations, so modern science. And now, of course, if you ask anybody yet now, of course, there is many solar systems.
In fact, if you take the number of galaxies, there is about a hundred billion galaxies, and each one has about a hundred billion stars, 10 to the 22 stars, again, and 1 with 22 zeros, stars in the universe. And most stars have planets. We are not unique. So the chance is that when you have such a huge number of stars that senses that in some of them there are friendly conditions that allow life like our own, or maybe quite different than our own, to exist is extremely likely.
It hasn't been proven because we haven't made an observation. It hasn't been proven yet, but I think most scientists believe that it's very likely that conditions similar to our own or even different, has allowed the evolution of intelligence and life in other places. - Mm-hmm (affirmative).
- So notice what happened that what used to be unnatural or required great care, namely the occurrence of life in the universe, is by changing your perspective and, of course, encouraged by observations, it became something not just palatable but very likely. So that's an example of how a change of perspective converts something that looks miraculous to something that looks natural. - That's all within our own known Universe, right? - Exactly. - Okay. - So now we are taking the next step.
- Okay. - So we go back to, why is our universe so large? Now this is correlated with, as I said, what's called a, "Cosmological constant problem." The cosmological constant is essentially the energy density that is in the vacuum of the universe. This is an energy density that we are not aware of, but in principle it's there. And in fact, if it was there, there are measurable consequences. The energy of the vacuum... If you ask any theorist, what would you think the energy of the vacuum is?
They would pull out pencil and paper and say, "Oh, it's probably this number." And the number that they would get is 120 orders of magnitude larger than what it actually is. And what it actually is, is not zero. Has been measured back in the 90s, very precisely, by astrophysicists and cosmologists because it has consequences on how the universe expands or if it expands or contracts, how rapidly.
So with cosmological observation, looking at how far away objects like supernovas recede from us, how rapidly they move away from us, you can tell if there was cosmological constant or not. And it's 120 orders of magnitude smaller than it should have been by just taking what you know in your theory and computing. So very much like, and very closely related to, the fact that the size of the universe is 40 orders of magnitude bigger than the size of an atomic nucleus.
So they're very closely connected problems. And finally, a few physicists, and together with Steven Weinberg said, "There is many, many universes." All of these universes have different value of the cosmological constant. Some are big, some are small, et cetera. When you have cosmological constant, that affects how the universe expands. So if you have too much, it expands very rapidly. So if you have small enough, then it expands slowly enough to allow for galaxies to form.
Our planetary system belongs to a galaxy, and stars and their planets are in galaxies. So galaxies are very important because they're relatively dense structures that allow stars to form. And stars are important because there are planets around stars and that's where life forms. Life benefits from having the heat of the stars provide energy, so it's important for life. Galaxies are important for life because we live on planets. Planets are near the sun.
They draw energy, and stars like our own sun belong to galaxies. So if the cosmological constant was any bigger than it is, then galaxies wouldn't form. So we wouldn't have stars and we wouldn't have planets, we wouldn't have life. So to do that, Weinberg had to postulate the existence
of many, many, many, many universes. (chuckling) And again, the number of these universes is enormous that you need, because the cosmological constant is so much smaller than its natural value, which would've been 120 orders of magnitude bigger. So this was the proposal in '87.
And in fact, using this idea, he derived a prediction for how big the cosmological constant should be, because if it's any bigger than that, galaxies cannot form, but there is no reason why it should be smaller than the maximum it could be to allow for our existence.
So he made the prediction in '87 and the prediction sure enough was confirmed within a factor of an order of magnitude, which is not considering the range of the prediction that it predicts a quantity that is off by 120 orders of magnitude. But it did something within a factor of 10 and it turned out to be what the cosmological constant. So it looks like our universe is tuned. It doesn't have as big a cosmological constant as it could because it would be crazy.
The universe would be expanding at an enormous speed. We wouldn't, not even atoms would form, let alone galaxies and stars, et cetera. So it's not as big as it could be. It's smaller and smaller and smaller, far smaller. It's 120 orders of magnitude smaller, but that's when you stop. The moment it's 120 orders magnitude smaller, you form life and that's you stop.
So in fact, he proposed it as a way to test his theory just about 10 years before it was tested, because the idea was exceedingly unpopular in 1987. In fact, I remember 'cause I was visiting him. It was October 19th, 1987, 'cause the same day I was visiting him, there was a big stock market crash. And I was giving a talk (both laughing) at the University of Texas where he was. So he showed me his theory and I said, of course, I was very polite, "Oh interesting," et cetera.
But I said, "Oh, the old man has completely lost it." (all chuckling) My definition of old back then, I think he was like 56 or 50. Yeah, he was in fact, yeah, 55 back then. Old by my then standards and I think he was ultra young. But he tells me this thing, "Many universe in my head is spinning." And I say, "Oh, I understand." He's about to die pretty soon. He wants this big questions answered. (laughing) And what can you do? Yes, sleep a lot.
And I wasn't alone, I think everybody thought, "Hey, Weinberg has lost it." (chuckling) He was viewed until the end of his life as a major, if not thee major physicist of his time. So he seems to have been right, at least with the numerical prediction. Whether the multiverse exists is exceedingly controversial for several reasons. One is, the number of universes you need to explain this cosmological constant is enormous.
Now we are talking about really enormous, like 10 to the 120, 10 to the hundred 30 universes, you know, one with the hundred 20. This is sort of the minimum number you need to begin to explain the cosmology. - This sounds like the opposite of naturalness. - Exactly, so in a sense the complaint is, "My God, you transcribe the problem to a different large number, and unless you have a sort of theory, how are so many universes created, you haven't made progress. It's a great point.
That's one of the reasons. And then the controversy get even stronger because there is a very speculative, again, controversial theory called, "String theory," which turns out, it can predict the existence of so many universes. However, it's already a controversial theory, the fact that...
So it's very much an open question and the question in the end in science are not decided by conversation or writing down formula or the prestige of the person who made the proposal and whether they have a Nobel Prize or not. This don't count for anything. It has to be experiment in the end. The one piece of experimental evidence for Weinberg's multiverse was, of course, the fact that the cosmological constant was measured to be what he had predicted.
But you need more than that in science, especially with such big ideas. So there are some proposals on how to test this idea. One is called, "Split supersymmetry," that I was involved with. However, even if you see split supersymmetry, I don't think it'll be enough to prove the multiverse. You need many more data. And the problem is the idea, it's not obvious what to go and measure.
For example, when Aristochos and Giordano Bruno, et cetera, postulated the many solar systems hypothesis, multi solar systems, eventually there was a discovery of the telescope which allowed you to begin this path towards discovering that there is much more in the universe out there. Those sort of blinking lights are not there for decor. In fact, they're a world like us. (Colin chuckling) Many of them are whole galaxies so they have 10 to 11 stars.
But there was a way to progress through experiment, through observation. And there is no clear path through experiment, through observation to prove the multiverse so far. So I think it'll remain controversial for, I would say maybe, decades if I'm optimistic if not more than a century, which is a very long time scale. But maybe I'll be proven wrong. There are other predictions. There is another idea which is called, "The axiverse." I don't want to get into it.
There are other predictions of having many universes. - Mm-hmm (affirmative). - In particular, the axiverse is the idea that if there are many universes, there's also many particles in our universe, that again, the conference that we had last week here touched upon how you can go out to discover this many particles. So if you see many particles, you see split supersymmetry, maybe people will start believing. I'll be convert very rapidly because I'm psychologically prepared for wild ideas.
And that's why I worked on trying to find, I mean I was involved both with split supersymmetry and the axiverse ideas because I still want to see how you could test the existence of many universes and... - So I really love this point you've raised a couple of times about how the types of questions we can hope to answer in our theories really depends on the technology that we have.
And when I read about your work online, I've seen the line a few times that your career in particle physics spans four decades. So I would assume that the types of questions that you've been able to answer have evolved a lot throughout your career. So can you tell us a little bit about this and how the types of questions you've been able to study have changed with technology? - Yes, yes. I was trained in the late 70s as a particle physicist.
Again, to give you a perspective, I'll sort of zoom out to tell you what, how particle physics started. So a key day in the history of science, a key year is 1945. That's when the public and politicians and everybody realized that actually science has consequences. It can be used in a bad or in good ways, but knowledge allows you to do things. So they started funding the science very heavily and that led immediately to what we call, "Big science."
Big science means, for example, what are called, "Colliders." Colliders are, essentially, you take two beams of particles, one from the left and one from the right, and you collide them and you see what comes out. And the more the energy, the more, the faster the particles go towards each other, the more energy you have to produce new particles. By new, I mean, things that we are not familiar with, like the electron or the proton are familiar particles. We know them from...
Because we are made out of nuclei and electrons. New particles, I mean, things that live for a very, the briefest amount of time. You create them and then they decay into other particles, familiar particles. - Are these collisions that happen in nature as well or are you creating things that only exist in the lab? - They can happen both in nature and the lab. In nature, they happen very far away from, you need very violent conditions.
Or they happen in what are called, "Cosmic rays," very energetic particles that have been accelerated somewhere in the universe. And they come towards us, not by intelligent life, but by astrophysical processes. But we study them on earth because you need a lot of collisions to be able to study what you predict. And in the universe, definitely in our location, there is not a lot of collisions. You have an occasional cosmic ray come and hit, but it'll hit something in the atmosphere.
You won't know it, but they can happen also naturally. So you have these collisions, you study the decay, the product of these collisions and that's how you find out, in some sense, new particles. Sometimes you find out what something is made out of. If you collide nuclei or an electron, a nucleus, you find out what's inside the nucleus. Sometimes you produce a new particle that was not inside, but the energy that you produced allowed you to create new particles, et cetera.
That's called, "The colliders." Colliders are very big projects. An example is a certain collider, the most recent one in the Large Hadron Collider at CERN. And they involve hundreds of people now working for decades. It started out working for years now. The colliders have been getting bigger and bigger. To give you an idea, the Large Hadron Collider at CERN has a circumference of 26 or so kilometers.
It's about a couple of hundred meters underground and it involves magnets going all around these 26 kilometers. And these magnets are very important because they navigate the protons that are accelerated to go on a very precise trajectories. Again, within microns, things have to be exactly where they are within tiny, tiny distance or else they will miss each other, they won't collide.
So half the protons go clockwise, the other half counterclockwise and then magnets navigate them and eventually, they collide in four different spots where you have detectors. They are huge, like a 5-story building that are instrumented with very sophisticated machines, versions of the human eye. You can see what happens. You can see what particles you produced. And just like the eye has to go to connect to the brain, so there is then cables that take these events, they analyze them, computers.
And then they tell you, "Okay, you produced it." It's beyond my imagination that humans have been able to do such complicated things. It all started with the willingness to support science that was started in 1945. In the beginning, colliders would take a few months to a few years to be built, only a fraction of the cost that they are now. Now they have reached the point, for example, the Large Hadron Collider is about a billion per year to run, and so it was like 10 billion to build.
It's a big project and the money is not the main problem. The problem is that it takes time and expertise to build it, to have 27 kilometers worth of magnets. These are huge magnets, where it is they have to be ultra cold and they have... It's a miracle that you can have control to this level. It's even, as a European, for me, it's even more of a miracle. It was created, in a sense, as a result of the Second World War, where European countries were fighting each other.
At least that's how it started. And then the same European countries collaborated at this spectacularly precise accomplishment. One of the great accomplishments of, I think, humans to create this machine. Work so well and we've learned so much from it and all the predecessors. LHC is only the last example, and there have been tens of colliders, you know, various sizes, et cetera, since then. So we've been on this large science road over 70 years.
Now we've reached the point where the next collider, the next upgrade that will take us to even bigger energies, may take, if we are lucky, 20 to 30 years to build. - And why is it that long? Is that because of the technology needed or the investment? - Or how big it has to be? - I think all of the above. - Hmm (affirmative). - Plus it takes time. Even if Bezos gives you all his money saying, "Okay go build it," (chuckling) the money would be plenty in his case.
However, it would still take a long time to assemble the people. And then the technology, even if the technology exists because the technology does exist. If you make it long enough, you can have enough magnets and enough to accelerate particles to very high energies, the next energy frontier. 10 times bigger energy than the LHC. So the technology exists, but the time it would take, I would guess at least 15 years, probably much more.
Even with all the money, I think it would take couple of decades. - Well this comes across in the movie, Particle Fever, the documentary that you're in, which is largely set at the Large Hadron Collider. 'Cause you personally had to wait how many years of your career for that to to be completed and be brought online? That was a long wait for... - That was a long wait. By the way, I didn't think it was going to be a long wait (chuckling) when I started.
You know, humans tend to be optimistic by nature. That's why we've evolved so well. (Colin laughing) I can tell you, anecdotally, in 1983, there was the first study group of what was then called, "The Superconducting Super Collider," which was a very similar collider. Actually would have higher energy than the LHC that was going to be built in the US, the SSC, Superconducting Super Collider. And the date that was discussed was well by 1990 we should be running. This was the first study.
So it took much longer and it wasn't even, the SSC was canceled in '93 for political reasons. The moment a site was chosen, which was Texas, to build it, then a support from the rest of the states diminished. And in the end it was not built, which is really a shame because it would be very good for the world to have two colliders in the same competition and at any rate, so it took much longer. So I didn't think it would take from '83 until 2008 when it first started.
So this time scale, it seems like it was getting longer. I anticipated this in the 90s. That's why I started thinking about small-scale experiments. I didn't anticipate exactly dates, but I said, "Well there is a lot of technology happening, so what can we do with it?" Because I was learning these things from my friends that I have dinners and wine tasting, et cetera. So I could see that there was a whole other field of experimentation. So that inspired me to start thinking about this.
And now it's a major part of what's happening. Because the next collider will take so many decades, many people have started doing it, especially in the last five years. There has been what is called, "The golden age of small, doing fundamental physics with small-scale experiments." - So you don't have to wait three decades for a collider to be built? - You don't have... - I think colliders are still very important.
You are not looking for exactly the same physics if you do small-scale, high precision experiments and collider experiments. Collider experiments, eventually you produce new particles. When you produce them, even though they live for very short time, you can study them. You can see what are their decay products and from there you learn a lot.
You learn all there is to know about their fundamental properties, their mask, their electric charts, and what's called, 'their spin,' and how they couple to other particles. You learn a lot in detail. And the moment you've produced a particle, the signature of that is fairly clean. With small-scale experiments, the discoveries are more indirect. You see a new effect, and then you have to infer from that effect what it is that produced this effect.
And it could be the same particle that you would have discovered in a collider, but you'll see it more indirectly. So usually it takes more than one small-scale experiment to study, let's say the same particle or the same phenomenon. Nevertheless, I think these are complimentary. So there is a lot that can be done thanks to the amazing technological developments for what's can be called, "The high precision frontier."
So there is a lot that can be done and now it is a golden era for this many experimentalists have turned their attention to this. Many of these people, what they were doing for technological purposes, and now they're doing it to make major new discoveries about the laws of nature new. So it's very exciting. - I remember in that documentary, Particle Fever, which is largely about the search for and discovery of the Higgs boson, sort of the most famous outcome of the Large Hadron Collider.
I've always wanted to ask you, that movie, it shows people packing an auditorium for the big announcement of the Higgs boson and you couldn't get past security, they locked you out. What happened? - I was late. (all laughing) So what happened was, I had several students and posts docs that went there early and they kept a seat.
In fact, they showed in Particle Fever, the empty seat for me. (all laughing) But even though there was a seat available, I couldn't go in because there was a big backlog and they didn't... Anyway, so I had to watch it from a TV outside. - Yeah. But you were there at the LHC at CERN when the discovery was announced. How did that feel for you for that milestone? - Oh, it felt fanta... You know, it's like when something amazing happens, you feel that you live in a dream. That's how it was.
That was, by the way, December of 2011. That actual first announcement, that was the incident that was shown. July 4th, 2012 was the official announcement. And at the time of the official announcement, I was actually in Santorini on vacation looking at the announcement and some beautiful views of the sea. - That sounds nice. It's better than being locked out by security. - Exactly, but the first... I'm glad I was there though for the first announcement.
- Mm-hmm (affirmative). - And it was amazing. It was amazing. Scientists are like humans. (both laughing) So the moment you dream of something, it happens. You accomplish and say, "Okay, what's next?" Very soon, you get used to now we are looking forward to seeing what may be beyond what's called, "New physics," beyond what we call, "The standard model," now. With the discovery of the Higgs, marks the end of what we call the standard model and we are now on a path to discover new particles.
That's what we are looking forward to. - We have a student question submitted that's about the standard model, by Felicity. And maybe we could play that for you? - Yeah, sure. - Hello Savas, I'm Felicity in grade eight. What are the discrepancies in the standard model for physics, and what makes them as such? - Okay, that's an interesting question bec... (chuckling) the word 'discrepancies' suggest that there is something wrong with the standard model, that something doesn't work.
That 'by doesn't work,' I mean it's contradicted. The standard model makes a prediction that when you do experiment X, you'll find A, but you don't find A, when you do it, you find B. So there is no discrepancy of the standard model in that sense. If there was, it wouldn't be the standard model of particle physics. It would be a theory that has some problems. So there is no real discrepancy.
What I described to you, the hierarchy problem, the cosmological constant problem, are not logical contradictions with the standard model. In a sense, they're a static criteria, that in the same theory, you have two numbers that differ by 40 orders of magnitude. There must be a reason for it. The standard model is not fundamental enough to address these questions of, why is the universe so much bigger than an atomic nucleus, or why is gravity so much weaker than the other forces.
It is, essentially, the naturalness criteria and aesthetic criteria. - I remember once, you saying something like, "The biggest mystery is that the universe is comprehensible to us at all." - That is, in a sense, a meta question. It's almost in the realm of philosophy.
Indeed, several big philosophers and physicists have said the same thing in different ways that the most, (I forgot, maybe it was Einstein), who said that, "The most incomprehensible thing about the universe is that it's comprehensible." The fact that there is a language for the universe, which is called, "Mathematics." The fact that the universe obeys mathematical laws is just astonishing, what's called, "The unreasonable effectiveness of mathematics."
In mathematics, you can ask a question and no matter how hard it is, if it's within the realm of mathematics and physics, and it may involve millions of steps, but you arrive at something that's true. Now it's very rare you start, you have a starting point, some question, and then a million steps later you arrive at a conclusion that's still true.
Because a million steps is a lot of steps and all it takes is few missteps to be led to the wrong direction, and mathematics that doesn't do that if you ask the right question. I think it was Pythagoras who said that, "O Theós geometreí," which means in English, (chuckling) that, "God geometrizes everything." By geometry, he meant mathematics, that God speaks the language of mathematics, if you want to paraphrase. - Mm-hmm (affirmative). That's an incredible mystery.
And the fact that mathematics is a precise language, like one plus one equal two, there is no if, but, approximate. Well, it's a matter of opinion, (Colin laughing) and there is left wingers and right. - Now that's fake news. - Yeah, fake news. There is no... And, of course, that's an exceedingly simple example, but with math you can have very complicated examples that describe what happens in a complicated situation in nature. You know, how the sun works and creates energy for us.
And there is trillions of steps and to do, but before you figure out how the sun works, how come it produces all this energy? What will it do next? Or the loss of gravity, you don't have to go... Newton told us, gave us equations, you can use these equations to predict where any planet will be at any point in the future, and where it has been any point in the past, 10 billion years ago or 10 billion years from now. And you can tell exactly, if you'll have an eclipse and what it'll be.
So this power of extrapolation gives a new meaning to the concept of truth that, "Oh my God, this is real true. There is no fake stuff." It's amazing that such a thing exists, and in fact, it's what drove me into physics, what I told you about Newton's equations. When I was, I think I was 13 years old, one of my classmates back in Greece told me that, "There is these equations that do exactly what I told you.
You can predict the position and speed of a planet any point in the future if you know it today or any point." I said, "Impossible. No way." It's so complicated. There are all these other planets and there is so much happening at the same time. And that's when I said, "I want to do this. What is it called?" I know, I knew it was called, "Physics," because... - Mm-hmm (affirmative). - And this comes up in the movie also. I was interested in the concept of truth.
When I went to Greece for the first time, I was age 12. I was born in Constantinople, but then my family was expelled because they were Greeks to go to Greece and we went there. And all of a sudden, it was a free country. There was left and right, and I would hear a speech by the left leaning politicians. "Well that makes perfect sense." Then I would go to the same topic, a speech from the right leaning. I said, "Oh that makes sense too, but they are opposite conclusions." So I was confused.
What does it mean to be true? And then I realized that with language you can play games, whereas with mathematics, it's such a precise language that you don't play games. If you ask a precise question, you get a precise answer. So I said, "I want to do that." And then I was, for about a year, I was wondering, if I should do mathematics or physics. And it was that comment by my classmate that, because you can predict precisely what will happen in the future.
And then I realized that physics has an advantage over mathematics. That in physics it's not just the logic and what two or three mathematicians think, or a million mathematicians think. It is nature that goes and tests your theory to see if it's actually realized in nature or not. So that gives an additional foundation to the concept of truth. And I said, "Ah, no." In math, there is truth. In physics, it's super true because even nature agrees with you.
The truth does not depend on the eloquence of the speaker. And in fact, nature can answer what the truth is in physics. So those were very attractive ideas for me. So I decided to spend my life on it. I'm glad I did. - So you decided at that stage to spend your life on this and you haven't looked back since? - No, for sure, I haven't looked back. It's very funny because many of my relatives would tell me, "You know, with your brain you can make a lot of money." Said, "I know. I don't want money.
I want time to do what I enjoy doing." And they thought I was a bit strange. True. (all laughing) - But you're still enjoying what you're doing? - I'm still enjoying, yeah. Yeah, there is this childlike curiosity and joy that you discover. You know how children, they're excited because they discover new things. And in science, there's so many interesting questions that even now, there's interesting questions. When you understand something, you get the joy of understanding.
You see connections and... - Well, Savas, we're delighted that you still enjoy your work, and we're very excited that you stopped to chat with us. This has just been fascinating. - Thank you. (gentle upbeat music begins) It has been a pleasure for me too. - Thanks so much for listening. Be sure to subscribe so you don't miss any of our conversations. We've interviewed so many brilliant scientists whose research spans from the quantum to the cosmos, and we can't wait for you to hear more.
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