The following is a conversation with Don Lincoln, a particle physicist at Fermilab, who has spent decades working at the frontier of high energy physics. This was a mind-blowing and inspiring conversation. Don turned out to be one of my favorite people to talk to about physics. Truly a unique mind with that Richard Feynman ability of taking very complicated ideas and explaining them simply without losing any of the essential brilliant insights at the core of those ideas. This is the Lex Fridman podcast. To support it, please check out our sponsors in the description where you can also find ways to contact me, ask questions, give feedback, and so on. And now, dear friends, here's Don Lincoln.
In describing the search for a theory of everything in physics, you describe the history of physics can be told effectively as a kind of history of unifications. There's this centuries-long quest to show that these distinct phenomena are actually linked by some unified underlying principles. Even starting with Newton, that you can think of the effort of physics as one as trying to unify the laws of nature. So I was wondering if we could talk through the history of unification, that lens of physics.
There are, of course, lots of different ways to do physics, but the way that I would say that particle physicists, cosmologists do is they are trying to really find basically the underlying principles that govern the laws of nature. If we go back, say, to the, I don't know, 1650s or so, you're the most brilliant person around and you've noticed two things. One you've noticed is that when you trip, you fall. That is the nature of gravity that we all experience day-to-day. But then there's sort of astronomy where you look out at the heavens and you see the stars march across the sky. You see the planets move through the stars and there that seems to have absolutely nothing to do with what happens when you drop your sandwich and the dog grabs it from you.
Yeah, the brilliant thing was when Newton looked at that and he thought about maybe the moon is falling but it's missing the earth. So what we had is that in maybe 1650 you had what we might call the laws of celestial gravity, the gravity that governs the heavens, and terrestrial gravity, the gravity that is here on Earth. Now we don't think of it that way anymore. We think of it as just gravity. But at that time that wasn't at all obvious. And in fact, if you look in the books, Newton's theory is Newton's law of universal gravity. The universal is there. And the reason is because he realized these two things that seem to have nothing to do with one another were indeed one and the same. I mean, this is absolutely brilliant. I mean, Newton is arguably one of the most brilliant humans of which I'm ever aware. But at any rate, it is the first sort of easily describable unification of physics that you can state in a way that sort of makes sense to modern humans.
I mean, you can go back farther than that where people are talking about chemistry, the nature of atoms. You go back to Democritus who was wrong about very many things, but the idea that there was a smallest particulate form of matter is right. So, it's kind of funny. You read the chemistry books and they say that the idea of atoms goes back to Democritus and you know his idea was that like there was a smallest atom of oil which was smooth and it was smooth of course because well oil is smooth. There was a smallest atom of vinegar because vinegar is tart and it pricks your tongue so therefore atoms were little sharp pointy things. And so he was wrong about a lot but he was right about the idea that there was a small particle and we now know we have a very different concept than he did. So you can go back farther than that but getting to unification there are more examples.
For instance, if you go back to say 1830 or so, scientists were trying to understand electricity for instance and there was a lot going on. People really understood things. But at the time you would have two phenomena that are familiar to us now. One is a magnet which you know at the time mostly magnets were simply little pieces of iron that had been magnetized and they could stick to steel. And then you had electricity which was at the time they were generating little sparks that they could play and have fun with or more broadly a lightning bolt blazing across the sky. And so when you think about this, that lightning bolt and that little magnet seemed to be really unrelated.
Mhm. But over the 1800s, a number of scientists were exploring little aspects of it. What happens when you run electricity through a wire? It seems to make a magnetic field. You know, there was a whole bunch of experiments and there were a lot of names. But in about the 1860s or so, James Clerk Maxwell took all of those ideas that had been percolating around for the previous 50 years and wrote his laws of electromagnetism.
And they're really fascinating. If you look at the laws of electromagnetism, they are differential equations or integral equations. But basically what they say is on one side you have a bunch of terms that have electricity in them and then you have equals on the other side a magnetism thing. So forgetting all of the mathematical symbols you have electricity side equals a magnetism side. Electricity equals magnetism. And that is a staggering concept. The fact that these two things, a lightning bolt and the magnet that holds your kid's art to the refrigerator, are one and the same. And this was another case where electricity and magnetism became unified into electromagnetism. So now we have two examples. One, gravity being unified, terrestrial and celestial gravity, and then electricity and magnetism. So I'll tell you about some more in a moment. But one thing that's kind of important because the goal is of course to unify everything, that if I could do what I want to do, I would have some unified theory that would explain all the behavior of all energy, matter, space and time, which is a grand goal.
And we should say that maybe one of the goals of science more broadly outside of physics even is to construct models that can generalize the world. So if you look at Darwinian evolution, that was a very beautiful theory that captures another layer of reality of like how this particular thing that we see here on earth happens, right? So when we talk about theory of everything in physics, that's capturing a different layer of abstraction about the functioning of the universe.
Right, the whole Darwinian evolution, the fact that our genetics has significant overlap with the genetics of a banana is pretty staggering, is astonishing that that works. So that is amazing. But for at least the class of scientists that I am, what we think of is well sure biology is interesting and all but when you get right down to it it's caused whatever happens in biology is caused by the movement of molecules. And then you say, well that's great and all, but molecules, they do what they do because they're made of atoms.
And then the next step is, well, you know, atoms, that's great, but atoms work the way they do because of the nucleus and the electrons. And then the nucleus is protons and neutrons. And so there are those of us, myself included, who want to dig down to the very very bottom and find out what is the smallest building block of nature from which all of these other far more complex and interesting and abstract things are, but what is at the very very bottom? And also that's great, but if you know what the smallest building blocks are, that doesn't tell you the story. That's like having a whole bunch of Legos but not knowing how to put them together. You also need to know how they interact, how they work. And so that's what we study, forces. So there are the various subatomic forces of which we're familiar. And for instance, electricity and magnetism are components of electromagnetism which then governs the behavior of things like this is amazing. Electromagnetism explains of course electricity and magnetism but it explains how light works. It explains how much of chemistry works.
So electromagnetism, 1860 or 70, the wonderful thing about that is if you take Maxwell's equations and you apply a little bit of calculus it's very easy to see that the laws of electricity and the laws of magnetism combined together make what's called a wave equation which shows that these electric and magnetic fields oscillate. They vary. And if you have something that's varied, that's a wave. And the wave then moves. And if you do the math, you find out that the speed at which these waves move is the speed of light. And so people said, wow, the speed of light comes out of those equations. And that had to be, I think, very persuasive. And of course, electromagnetism also plays a really significant role in chemistry because after all, atoms are held together by electromagnetic forces. There's more to how atoms work. There is all the quantum mechanics stuff. But if you did not have electromagnetism or if electromagnetism was very different, then atoms would be very different. So it plays a very big role in holding us together. So it's a staggering advance in science to have a good behavior on that.
And of course being able to tame electromagnetism is why people can hear you when you do your podcast because through the miracles of the internet or just electricity running the computers. I mean, this is a case, if I can get on a small soapbox, where people back then said, well, why are you messing around with magnets and sparks and who cares? Well, that very fundamental digging into the laws of nature has spin-offs. And it has spin-offs. One of the big spin-offs is our entire technological society. Without being able to govern electricity, we'd still be farmers and shoemakers in cities, but we certainly would not have everything that we do. So, off my soapbox, but it's really a lovely thing to show how this digging into deep fundamental, not understood, mysterious things can 100 or 200 years later transform the world.
And the type of science I do now, people often ask, well, what good is knowing about how the inside of atoms work, how the inside of quarks work. And I don't know the answer to that. But just being a little more pragmatic, if I go back, say, a hundred years, where people were trying to understand how the protons and neutrons inside atoms held together, how they split, how you could combine them and so forth. This has led to nuclear power. Now, whatever you think about nuclear power and some people like it and some people don't, but it is powerful. It will generate energy for humanity and it may be that is the path that we take as we move away from digging fossil fuels out of the ground. Humanity is going to need power no matter what. Nobody is going to go back to the way things were in the 1700s. And one enormous source of energy that is there for us to take if we so choose is the modification of the nucleus of atoms, which seem to have absolutely nothing to do with anything. And yet it provides humanity with an opportunity which of course requires that we think carefully of how we do that and if we want to, but it gives us something that we didn't have before.
Yeah, it's very clear that nuclear fusion and nuclear fission will unlock huge amount of energy that's required for a civilization to flourish. But that's almost like near-term. Mhm. Longer term, you can think about things like we'll talk about dark energy crisis and antimatter. Maybe if you figure out some of the mysteries around antimatter, that too would lead to energy sources, how to produce energy, that too might lead to counterintuitive propulsion systems for us humans to travel through the universe. Now, right now it seems far-fetched, too expensive, too complicated, too difficult. But breakthroughs in the fundamentals of theoretical physics might lead us to unlock some incredible energy sources, incredible technologies that will allow humans to explore the universe. And of course, we should also mention that as always with technology, it's a double-edged sword. It will most likely lead to the development of more dangerous weapons or other sources of harm. And then we as a civilization kind of have to walk that line and hope we figure out how to do more good than bad with the technologies we build.
Right? But we have to really remember while people worry about nuclear weapons which are admittedly very dangerous and even nuclear power which has waste that has to be dealt with. What science is doing is working out finding power that nature has presented to us. This is not new. Fire is like that too. Fire can burn down your house or it can cook your steak. Power is like that. And that's just something that we have to understand as humanity. And that's why this needs to be a, you know, when we talk about science it has to be a broad conversation by all of society because what scientists can do is figure out how the world works. Society has to figure out how we wish to apply that or not apply that.
Also solving the mysteries and the puzzles of the universe in itself is effing awesome.
It is. It is. So, I mean that's the thing that makes us human in part is looking at a thing and saying, how does this work? And then together, a bunch of apes get together like poke the thing, kind of shake the thing, and then over time you have rockets going out into space, you build roads and bridges, you build the internet.
Anyway, so we talked about Newton, we talked about Maxwell. That takes us in the 20th century in terms of unification. There's a guy named Einstein on whom you wrote a book who did quite a lot of progress on the effort of unification.
Sure. So Einstein, he's a pretty amazing guy. In 1905, he had his miracle year where he wrote multiple papers. The one that most people know about is special relativity where he showed something that makes no sense to anybody who's not really dug into it very hard. And that is that two people experience time differently. Time, you know, is a fascinating thing. We don't really understand what time is, which is weird. You think that that'd be something we'd understand very well, but we really don't. We know a lot about it, but really understanding it, not so much. But, Newton thought that time was just universal for everyone. So my time, your time, some person's time on Mars or on Alpha Centauri, everybody experienced time the same. What Einstein showed was that that wasn't the case. That different people moving at different speeds with respect to one another experience time differently, which is absolutely a mind-blowing concept.
Now, most people think that Einstein then said, well, he invented spacetime, that space and time are the same thing, and he was behind that. But that actual insight came from one of his teachers, a guy by the name of Minkowski, who looked at Einstein's equations. Minkowski was a little bit more mathematically inclined than Einstein. And he saw that if you look at the equations, you have basically one person's space and time equals some numbers times this person's space and time. And so that's kind of a staggering thing. So that is where Einstein and Minkowski really did this unbelievable concept that space and time are actually pretty much the same thing, that runs afoul of our understanding of how the world works because time just moves. It's continuous. We know what it is at a visceral level and an experiential level. We might not understand it at a formal level, but we know what time is. It's what keeps makes today today and not yesterday or tomorrow. Space is a little different. You can walk somewhere, you can walk back, you can move around. You have more freedom to move in space than you have to move in time. You can always move forward in time. It's just moving backwards. It turns out to be a little more difficult. But yeah, Einstein's understanding that that is the case, it caused everybody to think about the world very very differently. And that was in 1908 when Minkowski really laid it out in the strict spacetime.
And that also led to the work on special relativity led to the speed limit, the speed of light.
Well, it was a premise. He had two premises. One was that the laws of nature are the same for everybody. So if you're moving at some speed or if I'm moving at some speed, I can say I'm not moving and saying you're moving at some speed. That's not controversial. That is what we call Galilean relativity. It's from hundreds of years ago. But what Einstein said that was controversial was that everybody measures that the speed of light is the same irrespective of how we're moving with respect to each other. You'll measure the speed of light to be a number. I'll measure the speed of light to a number. And that's very very different from what Newton would have said or Galileo or any of the old guys. And it was taking those two things together that caused all of the weirdnesses of special relativity.
Now you could then very easily say, well that second premise that everybody measures the speed of light to the same is just dumb and that you know you could test that. So that's where testing relativity comes in and Einstein's equations which include those two assumptions it predicts the behavior of everything perfectly well. Now we've actually measured, done experiments where we can say that the speed of light is the same for everybody. That's not how that's been in the beginning. It was really that assumption leads to predictions. The predictions are true. So the assumption is true. Now there is a, for those people, for your viewers who want to say well how do you measure that the speed of light is the same for everyone, the particle physicists do this and the way you do this is the following. There are some subatomic particles that when they decay they emit light that's their decay product and so you collide two things together so you know when the particle was created then you have surround your collision point by a detector and you measure how long it takes for light to get to your detector and by God it's the speed of light which it should be.
However, sometimes in these collisions some of these subatomic particles you make are coming out at very high speed. They might be coming out at 95 or 97 or very large fraction of the speed of light and then they decay into photons. And so you measure how long it takes for the photon to get to your detector and it says light travels at the speed of light. Now if it were that if Einstein's conjecture was incorrect, you'd have a particle coming out at near the speed of light. It would be decaying into a particle traveling at the speed of light. Then that particle should have traveled at say two times the speed of light or something like that. So it should have taken half as much time to get to the detector. But it doesn't. So this is a hard serious measurement that shows that something, you know, we can measure the speed at which light comes out of this stationary created particle and it's the speed of light then we can measure what the speed is of it coming out of something that's moving and it's still the speed of light. So that is an actual measurement but that is not something that was possible in Einstein's day but it is now.
Just to take a small tangent. How weird is it in the full ranking of weirdness that is physics? How weird is it that there's that speed limit of this speed of light?
Well, I have to tell you, when I first encountered this, it's pretty freaking weird. It's like pegs the weird meter. But as you become more familiar with it, as you become more comfortable with the idea, the thing to remember is the speed of light. It's the speed of light through spacetime. Once you embrace that, that makes a whole ton of sense. It all of a sudden makes everything fall much more into place. I think that there is an ultimate speed isn't that shocking. It just simply says that it's a property of space in the same way that there is, you know, space can transmit a certain strength electric field. It can support certain things, whatever space is and we don't know what space is but whatever it is it has the capability of transmitting these things at that one speed through space or time and everything else comes from our insisting that we keep space and time different. That's how I view it and at least for me that once I accepted that it all became very comfortable.
So the nature of my question actually here that will apply over and over is trying to empathize, trying to put ourselves in the shoes of the people before space and time are unified into spacetime and really experience and think through how difficult of a leap is that.
The reason I sort of say that is we are now in the modern day in the 21st century and of course we're going to have to make leaps like that in our future. Mhm. So what are the unifications we're not seeing in front of our eyes? So for example, there's so many examples through your work, through your lectures of Paul Dirac taking antimatter seriously. Looking at what the math shows and saying, I really think this thing exists, right? I mean, it just sounds insane.
And so I think this is a good warm-up. The spacetime unification is a good warm-up as we march through the 20th century because it gets in my view at least weirder and weirder even with Einstein himself.
Well, let me give you an even more basic example. Sodium and chloride. Sodium is an explosive metal. You put it in water and it's kind of neat. You put it in water and it just it doesn't quite explode, but it gets hot and it pops around. Chlorine, it's a gas. It's going to kill you. So these two things are deadly. They're awful. And yet when you mix them, you put it on your food at night. Salt, right? And so this is a case where this whole a unification and b this deeper understanding in this case of chemistry of how two things that are dangerous can be brought together and turned into something not only innocuous but necessary for human life. And so this is not unusual that what you're describing. I mean when you think about it, forget about everything else. Just the fact that you know we tell little kids that the world is made of atoms. Now that's crazy. Most people have never seen atoms and yet nobody really doubts it anymore. And I think it's just a case of familiarity and then the culture slowly accepts it and then it's real even without the evidence.
In fact, one of the courses you described there, how we know what we know. I think that's a valid question. How do we know there are atoms? And of course, there are ways we do. And by the way, on that front, I would love to go through how we know the building blocks in the universe as we march towards quarks. That in the course that you mentioned is one of the most fascinating things of this philosophy of atoms being around for a very long time. Then you concretize and you actually can prove or have strong observations that indicate that there are atoms and then there is a nucleus, there are electrons, there are photons, there are quarks and I mean it gets weirder and weirder and now we're facing the mystery. Is there building blocks even smaller than that? But anyway, Einstein turns out didn't just do special relativity. By the way, I really think he deserves three Nobel prizes. He got it for photoelectric effect. The fact that he didn't get it for general relativity is a crime against humanity. I don't understand. Obviously should have gotten it for general relativity and special relativity. I mean I think special relativity is separate from general relativity as far as Nobel prizes go. So general relativity is another unification.
Yes, that's right. What Einstein realized was that if you were in a rocket ship and the rocket ship was a very quiet rocket ship and it was accelerating, it would feel like you're experiencing gravity. And so, as you say, it's one of his happiest moments when he realized that acceleration and gravity feel very much the same. What I'm impressed by is that idea, which is already a pretty neat idea, somehow led him to take his spacetime idea, take this acceleration gravity idea and realize that he could describe gravity as the bending of spacetime. Spacetime being constant like east, west, north, south, that's already hard enough. But now he's saying, well, you know, take your map and crinkle it and bend it and so forth and that's gravity. That is a staggering mind-blowing idea.
I guess I wonder if you can comment on what do you think is the idea generation process that leads to that. So it probably in Einstein's case has to start with what if gravity is itself spacetime geometry. You have to have a thought like that, right?
Yes, I think so. There's a lot about science. There's of course knowing what went before. There is knowing the mathematics that allows you to figure out the implications of your theory. There is the discipline to argue with yourself and other people because most ideas are wrong. But then there's what you just described, that intuitive spark, and that is something that is very very difficult to create. There's a reason that we venerate these people is because it is an unusual feature and most people only have that aha moment once in their lifetime if they have it at all. Mhm.
And then there's a tricky business because I'm sure you do and I get a lot of letters from creative thinkers who don't have all of the history and the mathematical discipline and the self-critique that's necessary. And so they come up with these ideas and often it's easy to see where they just don't play out. So in order to be that person who changes the way we see the world, ideas themselves are not enough. These creative ideas, that's not enough. You need it with the discipline and the critique. And it's that amalgam of those things that make you a genius that history remembers.
But it's hard to know in a field of people you might be tempted to call crazy, there could be geniuses there. And it's hard to know which is which. We should mention that Einstein himself couldn't see the genius in quantum mechanics initially. Couldn't see the correctness, I should say. So he could see the insanity of gravity bending spacetime, but quantum mechanics was too weird for Einstein.
In all fairness, it's weird for me, too. But...
But the thing is even while that is true and Einstein maybe spent the last few years of his life trying to blend electricity and magnetism, gravity in a single thing and he was unsuccessful but he still was a very very valuable critic of quantum mechanics. It's not that he didn't understand it because he did understand it. He thought about the implications and all this quantum entanglement business. Well, not all of it, but he was responsible for saying, well, if you're right, then this. And of course, then people went out and found out that Einstein's implication of quantum mechanics was real. And so they could say, see, quantum mechanics is real. So, you know, he was thinking deeply about it. And he was doing exactly that thing I said. There's that spark idea, but there's that critique idea. And if you're able to critique an idea, you might kill it. And that is it's always depressing when I have this brilliant idea and it gets killed, but it's better to be killed than to keep it around and waste time on it. And so he was in that case not generating the aha, but he was saying is, all right, let's take your aha. Let's see it's right. What does it mean? It means this. That allows people to go test it. And so he was contributing very crucially to that other part of scientific advancement, which is not just the aha moment, but the beat it to death, test it, critique it, and make sure it's real. And it's only after all of that has been done that you really are sure you're right. And that's why science is such a powerful tool. It is that combative just downright kind of jerky critique that most people don't like. They don't like people saying your ideas, you know, might be wrong. But that is it is crucial. It is crucial part of the scientific process.
Plus, there's that quote on the other side of it that I've heard you mention which is, you know, I believe your idea is crazy, but is it crazy enough? Was that...
Yes. Yes. We all agree that your idea is crazy, but is it crazy enough?
And there is some degree of taking those leaps of crazy, but it has to be backed with rigor, right? And the unifications continue that as we take steps towards the standard model, which is such an incredible part of physics in the 20th century. So, can you describe that unification?
So, you know, we're sort of jumping forward here now to the 1930s or thereabout. And by that time people had realized that there are four distinct forces that do not seem to be connected. One is gravity, two is electromagnetism, and those are things people are relatively familiar with. But there are two other forces that only have any real importance inside the nucleus of atoms, which is why most people have no experience with them. One is the strong nuclear force which holds the nucleus of the atoms together and the other one is what we call the weak nuclear force which is responsible for some types of radioactivity. And since most people don't play around with nuclei and most people don't play around with radioactivity, they don't know what that is. But by the 30s scientists had done enough experiments, done enough theorizing to say that there were these four forces and that was already a triumph. I mean we in our goal for a theory of everything we'd like to think that there is one force which is what we're talking about the unification. Maybe these four forces are just different ways of looking at a single underlying force. But in the 30s that's where we were. There were the four forces.
So we move ahead and in the late 50s and early 60s some people were thinking that maybe the weak nuclear force and electromagnetism actually were the same. So they were working on trying to bring together these two forces to show that they're connected. And it came true. They were able to show that electricity and magnetism were actually two different facets of a single force that we now call the electroweak force. Mhm.
Now, the story that you're told in articles about this about what people have called the Higgs boson or the God particle, the story is very very simplified because in 1964 there were three groups with six individuals who came up with important papers talking about what's called the Higgs field. I'll get back to what that is in a minute. But the Higgs field is important. But it wasn't until 1967, so 3 years later, that Steven Weinberg and some others actually unified electromagnetism and the weak force. Sheldon Glashow, Abdus Salam and Steven Weinberg successfully unified electromagnetism and the weak nuclear force showing that at high energies these two forces were merged into a single electroweak force, right? And that was in '67. All right. Everybody talks about this thing happening in '64, but it really wasn't. It happened over quite a few years actually. But all right. So now let's what you said is true. So Weinberg, Glashow and Salam showed that electromagnetism and the weak force at high energies were the same. There was a problem however and the problem is that electromagnetism has an infinite range. And we know that because we can see stars that are millions of light years away. I mean that shows you that the range of that force is essentially infinite.
The weak force however basically becomes non-existent on distances much smaller than the size of a proton. Mhm. So that you know to say oh they're the same and yet one can reach across the universe and one can't reach out of an atom. Well that's just dumb. I mean the obvious thought here is well we just proved that that whole idea is stupid so throw it away, ridiculous. And that is where these ideas from 1964 came in and saved the day. So how can it be true that the electroweak force is real and electromagnetism and the weak force act so differently? The way that could happen is if these forces were transmitted by a particle moving from one subatomic particle to the other. In the case of electromagnetism, it's the photon. In the case of the weak force, we call them now the W and Z particles. So the idea is that Higgs and his colleagues came up with is saying all right electroweak force is real. The way we make it so that there is now an electromagnetic force and a weak force is the force carrying particle of electromagnetism has no mass. The force carrying particle of the weak force has a mass. And so what was done is a field was postulated that there was this additional field that was kind of distinct from this electroweak field and we call it the Higgs field. And the Higgs field permeates all of space.
And here's the kicker, some particles interact with a field and some particles don't interact with a field. The ones that interact with the field get mass and the ones that don't interact with the field don't have mass. And so that's the idea is that the Higgs field gives the weak force particles mass. However, the photon laughs at the Higgs field, doesn't see it, and it has no mass. And I should say here, going to perplexity, the big picture view, the Higgs field is a quantum field that fills all of space and gives many elementary particles, just as you're saying, their mass through their interaction with it. The Higgs boson is the particle associated with ripples or excitations of this field. In modern particle physics, every type of particle corresponds to a field that exists everywhere. The Higgs field is one such scalar field, meaning at each point in space, it has a single numerical value rather than a direction. The Higgs field differs from most other fields because even in empty space, empty in quotes by the way, empty space, its average value is not zero. This nonzero vacuum value is what enables it to endow particles with mass.
Right? So let's talk about something a little more familiar just to try and hang some intuition on those words. All right? So right in front of us there is a gravitational field. Now, you can't see it, but right there. Right there. Check it out.
If I were to take something, a pen or whatever, and put it there, it feels a force and it falls.
Very insightful. I know. So, we have the gravity field and we have the pen that has a mass. And the mass and the gravity field interact and it drops. Now, if we had another...
I have an object for you demonstration purposes.
Performance art. Here we go. This is great. This thing has mass and we drop it. How remarkable. It falls. But when we step back and think about what really happens, it's the mass of this thing and the interaction with this invisible field we see here. That's what gives this weight.
Now, I have this particle here that you can't see, but it's there. It has no mass and I leave it there. Well, since it has no mass, it doesn't feel gravity. It's still floating there. And that is really all the Higgs field is. Some particles have effectively what you could call the Higgs charge that interacts and sees the field and other particles don't. And that is really what you read just basically means. Now it's kind of neat because in the ordinary day there is a Higgs field right there and the Higgs field is not zero just like gravity is not zero and things will get mass but at super high energies the Higgs field, the strength of the Higgs field goes to zero so whether things have mass, whether they have a Higgs charge or not, they have no charge or they have the Higgs charge, Higgs field zero, they don't interact, it has no mass. So that's kind of what Weinberg and Salam, Glashow said is at very high energies, the Higgs field is zero. Since the Higgs field is zero, the weak force particles don't feel mass and therefore they can travel at the speed of light just like the photon does and everything's happy.
It is when the universe cooled down after the big bang. It was very hot, very high energy. Nothing had mass. The universe cooled and at a certain temperature what happened is the Higgs field turned on and at the moment it turned on it gave mass to the weak force particles, did not give mass to the photons. So that's what we call electroweak symmetry breaking. So, it's a mouthful, but all it says is there was a moment in time early in the history of the universe at 10 to the minus 12 seconds after the big bang, the Higgs field turned on and particles got mass. So, that's the whole idea. So, this is another really neat thing. So, the electroweak symmetry theory doesn't need Higgs because that only really applies at very very high energies. But in order to make it work at low energies, you need to fix the theory. And you need to fix the theory by effectively putting a band-aid on the theory. Higgs theory is just a band-aid on top of electroweak symmetry theory. And that is the band-aid that fixes it because it gives mass to particles at low energy.
Well, how does then Higgs, this band-aid, the field and the Higgs boson come into play on the experimental front, on the evidence? Okay. Discovery front. So, what is this Higgs boson?
Okay. Excellent. So, we have never seen the Higgs field. Higgs field is a hypothetical theoretical thing. But that is true of most of our fields. We've never seen the electromagnetic field. We've never seen the gravity field. We've seen the effect of the field. And so all of these theories are now what we call quantum field theories. And the whole idea of quantum fields, if you have a quantum field, that field can vibrate like a drum head. And so it doesn't vibrate just exactly like a drum head, but it vibrates locally. So you can have specific localized vibrations. And those specific localized vibrations are the particles. In the electromagnetic field, the vibration is the photon. In the Higgs field, the vibration is the Higgs boson.
And so what we can do is not see the field, but we can actually excite the field, make it vibrate and detect the vibrations. So the Higgs boson idea was predicted in '64. It became useful in '67. And then scientists started looking for it. So in the early 2000s, people were starting to think that we had built particle accelerators more powerful or powerful enough to actually be able to create these vibrations and detect them. So the accelerator that was working at the time was a large particle accelerator outside Chicago at Fermilab called the Tevatron.
And we were colliding protons and antimatter protons at near the speed of light at very high energy. And that was the accelerator at which the top quark was discovered in '95. But we had upgraded our apparatus. We had 10 times the number of collisions per second. We had slightly more energy and we were banging the protons and the antimatter protons together hoping that we would actually find the Higgs boson.
Can you actually back up a little bit and look at the bigger picture? So, Fermilab has this legendary accelerator that there's also a personal story with you connected to it because I mean there's a million questions I want to ask you and we'll ask you about some aspects of that. So, this idea of an accelerator, the design and the physics of an accelerator, how is that productive for understanding and discovering different aspects of particle physics?
Well, I'm so glad you asked. I mean, this is fascinating. All right, everybody has heard Einstein's equation E=MC². Nobody knows what it means. Maybe they heard that energy equals mass and mass equals energy. I don't know, you know, but they've heard the equation, the most famous equation in all of science.
But buried inside that equation is a really thoroughly fascinating concept that energy and matter are equivalent. And you can in fact convert movement energy into mass. And so this is something that we've known for a long time. This was predicted back in basically 1928. So a long time ago, actually almost 100 years ago. And it is not in the slightest bit controversial. We can do this all the time. So the simplest thing is to take two particles that have no structure. So you know the closest thing you can have to BB's that are just true mathematical BB's. If you smash those two things together, it's coming in with a huge amount of energy from one direction, a huge amount of energy from the other direction, the directions cancel. So the net momentum, the net energy of this has no motion. So you have these two things coming in with a you know exactly balanced energy and if they collide they could stop. Well that energy has to go somewhere and that energy can literally create mass create particles. Now there are special rules about what happens if you have two things coming together and it creates a particle. It has to create an antimatter particle to balance it. That's just kind of the rules of the laws of nature. Why is that the case? Well, we have some ideas, but in many respects the answer is because those are the laws of the universe and that's the things that we try to understand. But this is absolutely true. So what particle accelerators do among other things is simply transform energy into particles. And so basically any particle that doesn't exist in nature we can make in this way. You can make the antimatter electron by taking two particles, smashing them together. The energy sits there and it will make an electron and an antimatter electron and it just does. And we know that the antimatter electron was discovered in 1932.
This is all pretty easy. The antimatter proton was discovered in 1955 at the Berkeley Bevatron. And so this is just what you do. You can convert energy into a matter antimatter particle. Now the converse goes true and that's something we might talk about. You can take matter and antimatter and bring it together and it'll make energy. It's the process can go both ways. Energy can make matter and antimatter. Matter and antimatter can make energy. And this is just true. We do it all the time. There's no question that this is the case. We should also mention that this is the reason why Fermilab had a nice stash of antimatter particles. So as a side effect, you can also collect antimatter in this kind of way.
You can produce antimatter, but it's an extremely costly...
Well, very, very costly. In order at the Fermilab machine, we would have to smash 100,000 protons into something to make one antimatter proton. So I mean it took some work.
Is there some extremely precise recipe of being able to produce particular kinds of particles and all this kind of stuff when you smash two things together? Is there like how can you control accurately which kind of particles you're trying to produce? If you want to make antimatter electrons, you smash together energy at a certain...
It's just easier with electrons because the electrons to the best of our knowledge have nothing inside them. So they're simple. They have a certain mass and that's that. So if you smash particles together with the right energy, you can make them very very easily because you can it's like a old style radio back in the day where you had to dial it in. You could get right on the station and you could hear the signal and if you were off a little it didn't work. The problem for things like protons and so forth is they're not pointlike particles. They're kind of like garbage cans full of stuff and so it's very difficult to make antimatter protons. Now you can get more of them by increasing the energy at which you collide two particles together. If you're at below a certain energy, and you collide, say you collide two protons together at kind of low energy, you just don't have enough energy to make an antiproton.
And so it doesn't happen. You get to a certain energy and you can just barely make them. The more energy you collide them together, the more you make. So that is just sort of how it works. More is better.
And then with CERN, if you compare maybe CERN and Fermilab, going to perplexity here, CERN's accelerator, the Large Hadron Collider, LHC, is the world's highest energy proton collider, while Fermilab's current and planned accelerators focus on intense proton beams for neutrino physics rather than pushing the absolute energy frontier. Absolute energy frontier meaning highest possible energy smashing of protons together.
Correct. So one we were talking about like accumulating antimatter. Yes. All right. And so there that is typically making antiprotons as opposed to making all particles in general. So let's focus on the antiproton side to begin with. All right.
So Fermilab doesn't make antiprotons anymore. We stopped making them in 2011 and it's because we shut our big accelerator down to concentrate on a different facet of particle physics. However, at the time we would smash protons with an energy of 120 GeV and in that we would make antiprotons. So that's a ton of energy. It's true that the CERN accelerator, the big accelerator, is now much higher energy than the Fermilab accelerator was. No problem. But that's not how they make antiprotons. All of these big beam laboratories, it's not one accelerator. At Fermilab, there were five distinct accelerators and it was basically like shifting an old standard car because you couldn't just go zero to super speed in one accelerator. You had to go from one to another getting higher and higher. Well, at CERN, they use one of the basically their second gear in their very big accelerator complex to make antimatter protons. And their accelerator is only 26 GeV compared to the 120 GeV at Fermilab. Fermilab's not operating, but when it was operating, it operated at an energy of about four times higher than what CERN is doing now. And why is that? Well, it's because what CERN needs to do is to not make as many antiprotons as Fermilab did. They are doing a very different current experimental program. They're doing a fascinating experimental program including trying to figure out does anti-gravity fall up or down, which is kind of neat and we sort of know the answer to that different that's separate. But anyways, so getting back to the antiproton business.
Well, Fermilab doesn't do it now. It was top dog. It's not anymore. The only really big antiproton accelerator creator is a small accelerator at CERN. Okay, so that's the antiproton thing. And if we get back to antimatter, we could talk about that because that is way cool.
Now the other side of your thing about making high energy unknown particles, bigger is better. And it is true that the LHC is a very high energy machine. It is about seven times more powerful in terms of energy per collision. It is also about a hundred times more collisions per second than the Fermilab machine. So it is true that the LHC can make bigger heavier particles that the old Fermilab, the Tevatron, ever couldn't and that is true. So if you want to look at high energy stuff, yeah, you go to CERN now. Which is why many of my colleagues including myself once we had measured all of the sort of frontier measurements we thought we could make with the Fermilab accelerator, we saw this bigger, more powerful machine with seven times the energy and 100 times more collisions per second. We said, "Heck yeah, let's go work on that." And to give you a sense of scale, the top quark, which is the heaviest particle ever discovered, discovered at Fermilab in 1995. There were two discovery papers and the one on which I was a co-author. We had worked for a good chunk of between 6 months and a year of collecting collisions and there were a lot of collisions and our paper had 38 top quark candidates. 38. And we knew that half of them were crap because when you make a detector like that, there's what you call background. So you have the background and the good stuff. And we know it was about 50/50. So we had maybe 19 top quarks after working for between 6 months and a year of collecting data. But now at the LHC, we make a top quark every second.
And that's what higher energy and more collisions per second will do for you. That extra energy, you're above threshold. You make a ton of them. And when you compare the 1995 Fermilab accelerator to the current CERN accelerator, it's probably a thousand times of collisions per second. So it went from painstaking, pulling teeth to, yeah, now top quarks are a background. We try to get rid of them. There's just too many of them. They get in the way of searching for the stuff we really want to search. They are like so 30 years ago.
By the way, is there something to be said about the kind of sort of signal processing here? How you remove the noise, how you remove the background, how you determine which particle is which. There's probably some like incredible nuance there even outside of the scope of this conversation.
So, let me just throw some numbers out. All right. So, at the CERN accelerator when it's operating, the collisions occur at a prodigious rate. We get about a billion with a B collisions per second. Now each one of those...
Yeah. Yeah. That's what I said. Wow.
Now it turns out some of them are happening at the same time. So there's about of order 40 million moments in time per second where you would take a shot and inside that moment there might be 20 collisions.
So that's why where we get to the billion.
But can you individually pinpoint the collisions?
Sort of to a degree. So the beams are, you know, when people think of beams, they think of like laser beams, but that's not really what particle beams look like. Particle beams look like little tiny sticks of spaghetti, except they're much thinner. They're not as fat as a stick of spaghetti, and they're at the LHC. Different accelerators are different. They're about this long. And so you have one of them going one way full of protons and another one going the other way full of protons. And they pass through each other. And as they pass through each other, you should think of this as like a swarm of bees. And this is like a swarm of bees. And mostly the bees pass through each other and don't do anything. But every so often some of the bees hit nose on and stripes and wings and everything everywhere.
And so as they collide through each other, you know, one collision's here and one's here and one's here and you can't tell too much side to side because the beams are really small. They're sort of the thickness of a human hair. But you can see along the direction and there, you know, this is about the right size. And so we have detectors around them and we can actually see, oh, particles came from here and particles came from here. And that's amazing. All right. So at any one crossing, there's maybe 20 collisions. Now, most collisions are absolutely boring. They're boring because they exemplify physics that we know a great deal about already. We've tested it for decades. We know all about it. We don't care. I mean, it's kind of blas that we can say, "Oh, yeah, yeah, we're making a billion subatomic particles every second, but who cares?" Because, you know, but that's just the way of, you know, frontier scientists. So, what you need is you need to pick out the cool ones, the weird ones, the ones that nobody's seen before. And so what happens is these things these beams collide and we surround the collision point with an enormous detector. There are two absolutely ginormous detectors at the LHC. One of them called CMS which is the one I'm on and the other one is called ATLAS.
Which is the other one and we don't speak of because well no they're both really amazing.
Okay. It's good to know that there's friendly competition even inside...
I mean the fact is they are both amazing absolutely amazing detectors.
But CMS is just a little cooler than...
Oh yeah. Yeah. I mean you know in particle physics we really absolutely want our competitors to do extremely well just not quite as well as we do.
Got it. All right. So these two giant detectors...
Right. So but one of them our detector the CMS detector it's the small one. It is 70 ft long, 50 ft high, 50 ft wide. It's 5 stories tall. It weighs 14,000 tons.
Small. ATLAS experiment is 150 ft long, 80 ft across. It weighs only 7,000 tons. Just piece of cake. You could take the ATLAS detector and you could put four of them on a soccer or football field and it would fill the field up with just enough room on the sidelines for the cheerleaders and the water boy and the coaches and stuff. That's how big they are. So these are absolutely ginormous detectors and basically they're cameras and what they can do is they can take pictures 40 million times per second. Now all the data comes streaming off that detector and we can't record it all. It would just fill up all of our tapes and it would be full of all these boring things we don't care about. So what we do is as the beams pass through one another, we teach our detectors to say we only want one where there are certain configurations that might be interesting like there's gobs of energy in the detector or there's a gob of energy on one side and nothing on the other side or there's four gobs of energy or whatever. These are called triggers. And so what we have is fast electronics that take the 40 million possible pictures per second and it says you know about a 100,000 of those are really cool. We should think about them. And then it passes not all of the 40 million but those 100,000 to the next level which are commercial processors that have basically our final analysis code but optimized to run very very quickly. And what they do is they do a really quick and dirty analysis to further refine what's good and what's not. And that computer farm then accepts about a thousand collisions per second and we record those for further analysis. So that's what's really happening of the 40 million possible collisions per second the fast electronics and then the computers pick the thousand and then we pass those through analysis software and hand them to the graduate students and they pick through them looking and finding the handful that are the next Nobel Prize. So that's how that works and that is truly astonishing. I'm hats off to the accelerator builders, the detector builders, the people who make the software work, the people who make the not gigabytes, not terabytes, but petabytes of data flow around the world seamlessly. It's really amazing. I'm very grateful.
So take me to July 4th, 2012, the discovery of Higgs boson.
So this is really fun because the people searching for the Higgs, it's a community and the entire community knew that the LHC was coming online. So even though many of us had been working on the Fermilab accelerators, a lot of us were transitioning to the CERN accelerator. So we were in the very funny business of wearing our Fermilab detector people hats trying desperately to find the Higgs boson at Fermilab while simultaneously wearing our CERN hats knowing that CERN was going to be able to find it if it existed. And so you know we were a little neurotic kind of wanted you know our old stuff to work and there was an awful lot of people on both experiments.
Did you have a sense that one of the two places would be able to find the Higgs? First, did you think the Higgs boson existed? And second, did you think that these accelerators have the chance to find them?
So, I was cognizant of the fact that the Higgs boson might not exist, but there was a lot of evidence pointing in the direction that it might be. I knew that both experiments, the Fermilab accelerator and the CERN accelerator would either find or rule out the Higgs if it existed.
Well, that's a possibility. I mean, maybe the Higgs theory was wrong.
Right. Until you know it's there, it might be wrong. It's like dark matter. People talk about dark matter. It might not be real. I mean, it probably is, but it might not be.
So, you knew at these energy levels, you should be able to find the Higgs boson.
Yes. So that's the nice thing about this kind of physics because there was a theory that theory made predictions. Now there were parameters in the theory we didn't know if the mass was this we'd get this thing. If the mass was this we get this thing. But we could do the calculation for every conceivable Higgs mass. And so then we could search look well let's say the Higgs mass is 100 in some units. Did we see it there? No. Then it's not 100. Well, let's look at 103. Is it there? No. So, we could do that. Both accelerators could either find it or definitively rule out the predictions of simple Higgs theory. 100% guaranteed.
However, the CERN accelerator had 10 times the collisions per second and three and a half times the energy. So remember when I said it with the top quarks it was like 6 months for 19 versus one a second. There's no question the writing is on the wall. The LHC was going to have an easier time of it if it was real.
However, so but you know I'm a Fermilab scientist and we wanted Fermilab you know come on we want Fermilab to win not you know. So we were busting our butt and we had done what I said. We had ruled out this region. And we had certain mass ranges. We knew it wasn't there. And we finally said if there was a Higgs boson, if it existed, which we didn't know at the time, its mass was somewhere between, if I recall, between like 120 and 145. All right, we'd ruled out all the other stuff. And so, wearing our CERN hat, we said, "Okay, we're going to find that." But we were really, really, really trying to do it. Now, if we had had another 2 years or maybe 3 years of running the Fermilab accelerator, Fermilab would have discovered or ruled out or in this case turning out discovered the Higgs boson because it's a real thing. We would have found it without a question, but we didn't have enough data in July of 2012. We needed a couple more years. Unfortunately, in 2008, or fortunately, the LHC had turned on. It broke. They had to fix it. Turned on again in 2010. It ran poorly in 2011. In 2012, they pushed up their sleeves and said, "Let's do this." And it turned on. And so, you know, there was this the Fermilab knew if it didn't have it now, it was too late. Anyways, come 2012 rolls around and like two days before the announcement at CERN was July 4th. So two days before that, Fermilab made a measurement and said we can rule out certain regions but certain regions we can't rule out but what we know and this is important. If the Higgs boson exists, it must be in this region for which we are not capable yet of ruling out. So that's where we were 2 days before the LHC said we got it. That was July 4th, 2012.
So detecting the Higgs boson confirmed the existence of the Higgs field, the mechanism through which fundamental particles like electrons and quarks acquire mass in the standard model. Correct?
Although let's be very specific of what we did then we found a particle consistent with the existence of the Higgs boson. There were alternative theories at the time that predicted not one but multiple Higgs bosons. So there's a theory called supersymmetry which said that there was not one but five Higgs bosons. The standard original 1964 Higgs theory says there were one. And so all we really knew at the time was we found a theory. We did not necessarily confirm that Higgs was right. We found data that said that it looked like Higgs was right. But until we ran for longer, we were unable to rule out other alternative theories. So that's the deal. Now in the fullness of time, it is after all what 14 years now later, we have been able to basically rule out some of those other things. And by now we have validated things. We found the mass of the particle. We know the spin of the Higgs boson. It has a spin of zero. We have discovered Higgs boson decays. It preferentially decays into the heaviest particles. It can through energy conservation can't decay into top quarks. It's too light to decay into top quarks, but it can decay into bottom quarks. It can decay into W and Z particles. Can decay into a weird way into photons. And we have looked for all of the hypothesized decays of the original Higgs theory. And we have validated that it decays in those ways at the rates that theory predicted. And so now in the fullness of time, I'm pretty comfortable saying Peter Higgs and Robert Brout and François and his colleagues, they were right back in the 60s. But we weren't sure on July 4th. All we knew is we found a particle consistent. But the thing is with these discoveries, they're often just barely discoveries. It takes a while to go and do the more complex detailed measurements and that's what we've done.
So at the time I remember being called referred to as the god particle.
You also had a minor in theology. So throwing that all together. So calling it the god particle is speaking to the importance the potential importance of discovering this particle.
Do you think that is in some degree justified like if we look at the big impact of it on the history of physics? How important was it to find and show that the Higgs field is real?
Well, I don't think it is as important as for instance some of Einstein's stuff. I mean it was it's an important prediction like the prediction of quarks was very important and interesting in validating this. The Higgs was kind of like validating that quarks existed. It's an important stepping stone and I do not wish to denigrate it in any way but there's ones that change the way we thought about the world like Einstein did it wasn't that sort of thing and there is a funny story so the reason they call it the God particle is this book by Leon Lederman and if you read his book he says well you know we call it the god particle but we should call it the goddamn particle because it's been causing us so much trouble trying to find it. And Leon ran Fermilab. So, and he wrote a foreword for one of my books. And you know, I talked to him. He was a really funny guy. And the real truth was the book was called The God Particle because his publisher thought it would sell more copies. But you know, then that got into the mindset of the reporters and so forth and we called it the God Particle. Leon never really thought of it as anything to do with a religious or even I mean he was an incredible jokester. The goddamn particle.
It is a really important part of our model of the universe. It is that there's this field that it gives mass to some particles and not others. That's...
Right. It's a huge thing but it was part of the standard model. The standard model had known forces. It had known particles. It had all that. The Higgs boson the one thing that is true is it was the last unvalidated piece of the standard model. The standard model does not answer all questions which is why we have unanswered questions in physics. But it was a punctuation point end of about 50 years of discovery and searching where we finally were able to say the standard model while incomplete, it's mostly right as far as it goes.
Quick 10-second thank you to our sponsors. Check them out in the description. It really is the best way to support this podcast. Go to lexfridman.com/sponsors. And now, dear friends, back to my conversation with Don Lincoln. We did a whirlwind tour of the history of physics and took a little tangent on this incredible discovery of the Higgs boson. But we didn't go all the way yet. There's this dream of the grand unified theory, the GUT that is a step towards the TOE theory of everything. So can we talk about the GUT first? So what's entailed in the GUT?
So the GUT is short for grand unified theory. We talked about that there were four known subatomic forces. The electromagnetic force, gravity, the strong force and the weak force and electroweak symmetry unification merged the weak force and electromagnetism into the electroweak force. So what GUT hopes to do is to merge the electroweak force and the strong force into one grand unified force. Now that leaves gravity outside because gravity is seemingly fundamentally significantly different. Then subsequently it is hoped that at a higher energy we will be able to blend the theory of everything together with all of the known subatomic forces the strong weak and electromagnetic forces and then gravity but so as you say GUT is sort of a way station along the way that's the goal and at this point I would have to say that I do not see a fast progress in the immediate future. I think we're a ways away from that at this point.
You mean on the gravity front?
Maybe we'll come up with something really cool. We certainly had some ideas back in the early 80s that we tested and they didn't pan out.
Speaking of which, string theory is the thing you're referring to.
So string theory posits that particles are tiny vibrating strings and by tiny we mean extremely tiny at the scale of a Planck length.
Then there's other leading candidates like loop quantum gravity. Maybe there's some alternate theories in the works. So can you linger on that a little bit more? Do you think a theory of everything exists?
So I hold personally that there are rules that govern matter and energy space time and they probably are rules that I don't know. There are probably phenomena I'm not aware of. But I do believe that there is a rule that governs reality. And so in that sense once we understand the rules that govern reality, the fundamental rules that would be a theory of everything. You know there are things that are unknowable like for instance inside black holes we don't know what's inside there but that doesn't mean that there's not something inside there. So there's a distinction between what we can know and truth. So I do believe that there are the rules and I do believe that with sufficient time, technology, effort, we will be able to figure this all out. Now, this isn't a thing in my lifetime. It's not a thing in my grandchildren's lifetime or even their grandchildren's lifetime.
Whoa, whoa, whoa. That's a pretty strong statement, right? That's a pretty strong statement saying we're...
We're 50 to 100 years out from finding a theory of everything. It took 200 years to go from unifying gravity to unifying electromagnetism. It took a hundred years to go from unifying electromagnetism to unifying the electroweak force. Now you could say, well, gee, that went from 200 to 100. So it's getting faster, but it's also getting harder because the unification scale is of order 10 to the 15, which we can do the math. That's a quadrillion times higher than the highest energy accelerator we can build today. And it was one thing to, you know, we are reaching diminishing returns. We get something like a factor of seven increase in particle accelerator energy every 20 years. And so we have to get to a quadrillion times. Now, you know, if you really did believe a factor of seven every 20 years, then that's we're talking like 500 years, but you know, this is like Moore's law that it doesn't continue forever. We're not going to every 20 years get another factor of seven. So, yes, I think it's a very long time. That's my prediction. You know, some people are far more optimistic and we can talk about that. We should also actually mention...
That I guess your intuition behind that is not just the part where you come up with a theory that's beautiful and seems to be internally consistent, but you have to have a theory that's making falsifiable testable predictions.
Correct? And you have to have a feasible engineering construction a methodology for creating an experiment that tests that prediction.
So I think a lot of your this is 50 100 200 years from now. Intuition is maybe about the second part of that which is like you need to have an experiment.
Yeah. Yes. Yes. But you know let's say I mean you alluded to superstrings. I haven't answered that question. And I'll table that for a moment. Superstrings is a fascinating idea. I don't believe it. But I love it. I hope it's true. And there's a real, you know, aphorism and it says you should absolutely never believe what you think. So even if you think Superstrings is true, you shouldn't believe it because it hasn't been tested.
Now let's say superstring is correct. I mean hypothesis it's correct. 100% correct.
I don't know it's correct. So I don't care. I mean, you know, it could be correct, but I don't, you know, until it's validated, it's just a wild ass guess, you know. So we have to have a way of validating it. So, yes, the empirical side of it is important. I mean, you could wake up tomorrow and have the theory that is the perfect theory, but if I can't prove it, I don't care.
If we were to think, this is going back to the great courses on the evidence for modern physics, we're talking about energy levels and tiny particles to the degree where the kind of prediction we would be making is not accelerator type predictions. So it's probably going to be impossible to build an accelerator that detects something like a string. So you have to make predictions about macro scale behaviors.
That's another alternative.
It's a different kind of prediction.
Do we even have intuitions about what kind of predictions they would be? So one of course one of the lines of intuitions has to do with black holes where in the singularity the physics of black holes combine certain elements of general relativity and quantum mechanics. So there you could see some kind of predictions you can make.
But you can't really mess with a black hole. It's not like you can create a black hole in the lab.
And the energies that you were talking about, the sizes we're talking about are inside a black hole, which you can intrinsically never see.
So you know, you can only see the outside of a black hole, not the inside of a black hole. So what you said, you did say something that was incredibly important and incredibly correct and probably won't happen, but that's still good.
Okay. So we have two choices when you talk about superstrings. Either superstrings are correct and they're making predictions up at the Planck energy scale at which point we have to somehow build facilities that can generate Planck energies. That's possibility one. Possibility two is this theory which is currently only applicable at Planck energy scales. Someone figures out a way to take those equations and solve them in a way that say predicts the mass of the electron.
Right. And that is a tricky business. I am not a string theorist, so I can't tell you that that's likely, but I can tell you that they've been working on it since the 80s, and they haven't gotten very far. Furthermore, I think it's fair to characterize that string theory is still a vague idea, and that's unfair. But let me tell you why I say that. Because what they have are approximate solutions to approximate equations. And that is already saying that we're a ways away from really getting a handle on that. So yes, if there could be some bright young lad or lass out there, someone listening to this podcast right now who figures out a way to take superstring theory and solve them in tractable ways that makes predictions from the scale at which they currently apply down to measurable scale today. And if that happens, well, then I might retract my concept. There's a reason why I think that probably isn't true. That's probably not valid.
So let me I love this. All right, so let's back up. I'm going to pitch. I wrote this book for Oxford, Einstein's Unfinished Dream. And Einstein's unfinished dream was to come up with a theory of everything. It was unfinished because, well, it's unfinished. And so the second part the tagline of that book is practical progress towards a theory of everything with the emphasis on practical. Because when you read books about theories of everything, when you see podcasts, when you listen to YouTube videos or whatever, they are often written by theorists. And theorists are they're big idea people. They're very very smart. But there's a pragmatism that is often missing in the sense that they say well superstrings look you know have these little vibrating things and wouldn't it be cool and you know but you got to get to the do you know it. So let's pretend superstring theory or something like it is correct. The energy scale at which that should occur is of order 10 to the 15 times higher 10 to the 19 GeV. We can currently do things at 10 to the 4th GeV give or take. So that is 10 to the 15 that's a quadrillion times higher energy. So what we are doing now is we are looking at the world with our very best measurements and we are trying to project out a quadrillion times higher and figure out a theory that explains everything. Now I have a couple of analogies but I like this. Suppose that you were some, you know, Joe Australopithecus 2 million years ago or something in Africa wandering around somewhere in Kenya.
All right. You're about a meter in size. So you can walk a meter meter scale is like your scale.
You can walk 10 meters in every direction. That's 30 ft. No problem. You can walk 100 meters, 300 feet. You can walk a thousand meters, that's half a mile. You can walk 10,000 meters, that's 60 miles. 100,000 meters is 10 to the 5th. And that's unlikely. But the distance that we need to go from what we can see to the Planck scale, it's not 10 to the 5th, it's 10 to the 15th. So that means in my analogy, think about this guy who's walking around Africa. Now, if he walks, you know, 100 ft or something, it looks a lot like what it is now. He can make a prediction about what he sees, and when he goes to that new place, it's probably going to be okay. But if he starts walking 500 miles east, well, he walking around the center of Africa has no concept of, for instance, the Indian Ocean, he would never predict sperm whales or Kraken. He would never predict what it's like the bottom of the ocean is going north. He's in Africa. He would never ever have a clue about the Alps or Antarctica. Going even smaller distances, going a mile up, things wouldn't be very different. But if he goes 10 miles up, he wouldn't breathe and he'd freeze. If he goes 100 miles up, he would die. If he goes two miles down, he would roast. The point being is we are like that Australopithecus. We have a realm that we can study and we can even predict to some validity what would happen if we go some distance away. But the farther away we go, the less and less our local prediction really represents the reality of those more distant times. And so basically his theory about the world would be totally bogus. So even if he had the best theory, his theory would not have anticipated the Alps. It would not have anticipated penguins, right? Flamingos not there, you know, and that is just the case. So now that's what we're doing. We are taking something and we have reason to understand what we know and we can predict a factor of 10 or 100. But I think it is the absolute the pinnacle of arrogance to think that what we can do given the understanding that we have from what we've measured now and predict it out a quadrillion times higher than we can see now. So my opinion and this is partly because I'm an experimentalist. The correct way to make progress, practical progress towards a theory of everything, is to look around at the things that we don't have answers to right now. For instance, are there something smaller than quarks? I don't know. Is dark matter real? I don't know. If it's real, what is it? I don't know. Is dark energy real? Yes, probably. But I don't know. What is the nature of space and time? I don't know. But these are questions we can explore. And I would expect, and this is my prediction, that all right, we're going to figure things out at a factor of 10 or 100 times better than we can do now. And we might be able to do that in my kids' lifetime or something like that. But in order for us to predict a quadrillion times higher, I'm pretty sure superstring theory is wrong. Not because people aren't smart, but because...
Something new is going to happen. I mean, if you were talking about chemistry, you would have never predicted nuclear physics. And that's a small increase in energy, right? The idea that there is something in the nucleus of atoms that causes the sun to burn. There's a reason why people didn't believe, you know, they calculated how old the sun should be and it should only be 10 million years old because otherwise it would burn out. Well, that's clearly wrong. And it's wrong because of nuclear physics. That is why I feel fairly confident to say while someone could think, well, superstring might be right or something and maybe it's right and I hope it's right. It would be awesome if it's right, but what are the odds when you're making something with that tiny lever arm, predicting it out a quadrillion away and say, oh yeah, we got it right. What are the odds? And my answer is, you got to be kidding me. Now I could be wrong and I admit that I could be wrong, but that's why I think the real issue is not the brilliance of humanity. It's the stuff we haven't found. We don't know. I mean, the simple one, and I say simple and it's not, but what is dark matter?
We don't have a bleeping clue. Not a clue. We know a lot of what it isn't, but we don't know what it is. And so, you know, talk about superstrings. All right. Well, maybe dark matter fits in superstrings. Or maybe dark matter is governed by a physics that is completely diametrically opposed to the superstring concept.
And allow me a bit of a thought experiment here. A brief thought. My intuition says that when you propose a theory of everything, the kind of prediction you want to make involves a kind of leap of conceptual understanding that Einstein did. So, for example, you want to come up with something like spacetime and then gravity bends spacetime.
So it's not merely that you have this beautiful mathematical framework, but that framework allows you to rethink how you see reality enough to make a prediction that's about the macro world.
I mean, to come up with something like spacetime, you know, there's one idea, for instance, to say that space and time aren't real, they emerge from entropy. Yeah, that's a way of a new way of thinking and maybe there's some validity and I want people to think about it, but in the end it's just an idea and that's the real key thing. And as you say, it has to tie to a macro world. You have to validate. If you don't validate, it's a crazy idea. Theorists are incredibly creative, smart, wonderfully interesting people. But I don't care. I want a measurement that validates the idea because there are so many. I mean, if you read the journals, there are so many theoretical papers with all these nifty ideas that die. You know, one that was recently I liked and might still be true was that dark matter, that, you know, our simple model of dark matter is that there's a subatomic particle out there that's heavy and it's floating around and it's causing gravity. But someone said, well, you know, maybe there's complex dark matter, which means there's a whole dark sector. So there are dark atoms and they interact with one another. And that is a nifty idea and I love it. And that was all the rage for a while. And we looked at it and it may still be true, but the simple ideas have been mostly invalidated because we've tested it and it doesn't work. Same thing, there was a talk about large extra dimensions. The reason that gravity is so much weaker than the other forces was, well, maybe gravity can sneak into more dimensions than the other forces.
It leaks into those dimensions.
That was a cool idea. I mean, but that's the point is you have these lovely, cool, interesting ideas that constantly die.
And so, you know, I would love for a new nifty idea to be the idea, but I don't know how to pick it out of the hurricane of wrong ideas.
I mean, that's the real beauty of science. It really is. I mean, the theories kind of get some of the glory sometimes, but the real beauty emerges from the experiment and the demonstration that the theory is correct.
And there are two directions. You're talking a top-down. Someone comes up with this big idea that's testable. But you also have the other way that science advances and it's not with a theory that is then tested. It's with the, huh, that's weird. For instance, either in the 1930s with Fritz Zwicky or in the 1970s with Vera Rubin, she did a simple thing. She said, how fast are galaxies rotating? Because it's an easy thing to calculate. You can literally calculate that with high school physics and you get an answer and then you measure it and it's wrong. And so all that, that's the wow. Huh. I don't know what that is. And that led to the hypothesis of dark matter. Now, dark matter is not a theory of everything, but it's a clue. It's a powerful clue. We should pull, tug at that thread. Maybe our entire theoretical edifice unravels. Or maybe it doesn't. Maybe it's just a snag and we can fix what we have now. I'm not sure. So that's another option is to simply look at many measurements that are very precise and find ones where the outcome and the prediction with established theory disagree and that is a clue.
