#92 – Harry Cliff: Particle Physics and the Large Hadron Collider

Harry Cliff is a particle physicist at the University of Cambridge working on the Large Hadron Collider beauty experiment that specializes in searching for hints of new particles and forces by studying a type of particle called the “beauty quark”, or “b quark”. In this way, he is part of the group of physicists who are searching answers to some of the biggest questions in modern physics. He is also an exceptional communicator of science with some of the clearest and most captivating explanations of basic concepts in particle physics I’ve ever heard. Support this podcast by signing up with these sponsors: – ExpressVPN at https://www.expressvpn.com/lexpod – Cash App – use code “LexPodcast” and download: – Cash App (App Store): https://apple.co/2sPrUHe – Cash App (Google Play): https://bit.ly/2MlvP5w EPISODE LINKS: Harry’s Website: https://www.harrycliff.co.uk/ Harry’s Twitter: https://twitter.com/harryvcliff Beyond the Higgs Lecture: https://www.youtube.com/watch?v=edvdzh9Pggg Harry’s stand-up: https://www.youtube.com/watch?v=dnediKM_Sts This conversation is part of the Artificial Intelligence podcast. If you would like to get more information about this podcast go to https://lexfridman.com/ai or connect with @lexfridman on Twitter https://twitter.com/lexfridman, LinkedIn https://www.linkedin.com/in/lexfridman/, Facebook https://www.facebook.com/lexfridman, Medium https://medium.com/@lexfridman, or YouTube https://www.youtube.com/lexfridman where you can watch the video versions of these conversations. If you enjoy the podcast, please rate it 5 stars on Apple Podcasts https://podcasts.apple.com/us/podcast/artificial-intelligence/id1434243584, follow on Spotify https://open.spotify.com/show/2MAi0BvDc6GTFvKFPXnkCL, or support it on Patreon https://www.patreon.com/lexfridman. Here’s the outline of the episode. On some podcast players you should be able to click the timestamp to jump to that time. OUTLINE: 00:00 – Introduction 03:51 – LHC and particle physics 13:55 – History of particle physics 38:59 – Higgs particle 57:55 – Unknowns yet to be discovered 59:48 – Beauty quarks 1:07:38 – Matter and antimatter 1:10:22 – Human side of the Large Hadron Collider 1:17:27 – Future of large particle colliders 1:24:09 – Data science with particle physics 1:27:17 – Science communication 1:33:36 – Most beautiful idea in physics

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Lex Fridman?

  The following is a conversation with Harry Cliff, a particle physicist at the University of Cambridge, working on the Large Hadron Collider beauty experiment that specializes in investigating the slight differences between matter and antimatter by studying a type of particle called the beauty quark, or B-quark. In this way, he's part of the group of physicists who are searching for the evidence of new particles that can answer some of the biggest questions in modern physics. He's also an exceptional communicator of science, with some of the clearest and most captivating explanations of basic concepts in particle physics that I've ever heard. So when I visited London, I knew I had to talk to him.

• 0:42Lex Fridman?

  And we did this conversation at the Royal Institute Lecture Theatre, which has hosted lectures for over two centuries from some of the greatest scientists and science communicators in history, from Michael Faraday to Carl Sagan. This conversation was recorded before the outbreak of the pandemic. For everyone feeling the medical and psychological and financial burden of this crisis, I'm sending love your way. Stay strong. We're in this together. We'll beat this thing. This is the Artificial Intelligence Podcast. If you enjoy it, subscribe on YouTube, review it with five stars on Apple Podcasts, support it on Patreon, or simply connect with me on Twitter, at LexFriedman, spelled F-R-I-D-M-A-N. As usual, I'll do a few minutes of ads now

• 1:27Lex Fridman?

  and never any ads in the middle that can break the flow of the conversation. I hope that works for you and doesn't hurt the listening experience. Quick summary of the ads. Two sponsors, ExpressVPN and Cash App. Please consider supporting the podcast by getting ExpressVPN at expressvpn.com/lexpod and downloading Cash App and using code LexPodcast. This show is presented by Cash App, the number one finance app in the App Store. When you get it, use code LEXPODCAST. Cash App lets you send money to friends, buy Bitcoin, and invest in the stock market with as little as $1. Since Cash App does fractional share trading, let me mention that the order execution algorithm

• 2:09Lex Fridman?

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• 2:50Lex Fridman?

  Get it at expressvpn.com/lexpod to get a discount and to support this podcast. I've been using ExpressVPN for many years. I love it. It's easy to use, press the big power on button and your privacy is protected. And if you like, you can make it look like your location is anywhere else in the world. I might be in Boston now, but I can make it look like I'm in New York, London, Paris, or anywhere else. This has a large number of obvious benefits. Certainly, it allows you to access international versions of streaming websites like the Japanese Netflix or the UK Hulu. ExpressVPN works on any device you can imagine.

• 3:32Lex Fridman?

  I use it on Linux, shout out to Ubuntu, Windows, Android, but it is available everywhere else too. Once again, get it at expressvpn.com/lexpod to get a discount and to support this podcast. And now, here's my conversation with Harry Cliffe.

• 4:08Lex Fridman?

  Let's start with probably one of the coolest things that human beings have ever created, the Large Hadron Collider, LHC. What is it? How does it work?

• 4:19Speaker 01

  Okay, so it's essentially this gigantic 27-kilometer circumference particle accelerator. It's this big ring buried about 100 meters underneath the surface in the countryside just outside Geneva in Switzerland. And really, what it's for ultimately is to try to understand what are the basic building blocks of the universe. So you can think of it in a way as like a gigantic microscope, and the analogy is actually fairly precise, so.

• 4:45Lex Fridman?

  Gigantic microscope?

• 4:46Speaker 01

  Effectively, except it's a microscope that looks at the structure of the vacuum.

• 4:53Lex Fridman?

  In order for this kind of thing to study particles, which are the microscopic entities, it has to be huge, a gigantic microscope. So what do you mean by studying vacuum?

• 5:05Speaker 01

  Okay, so I mean, so particle physics as a field is kind of badly named in a way because particles are not the fundamental ingredients of the universe. They're not fundamental at all. So the things that we believe are the real building blocks of the universe are objects, invisible, fluid-like objects called quantum fields. So these are fields like the magnetic field around a magnet that exists everywhere in space, that are always there. In fact, actually, it's funny that we're in the Royal Institution because this is where the idea of the field was effectively invented by Michael Faraday doing experiments with magnets and coils of wire. So he noticed that, you know, it was a very famous experiment that he did where he got a magnet and put on top of it a piece of paper and then sprinkled iron filings.

• 5:49Speaker 01

  And he found the iron filings arranged themselves into these kind of loops, which was actually mapping out the invisible influence of this magnetic field, which is a thing, you know, we've all experienced, we've all felt, held a magnet or two poles of magnet and pushed them together and felt this thing, this force pushing back. So these are real physical objects. And the way we think of particles in modern physics is that they are essentially little vibrations, little ripples in these otherwise invisible fields that are everywhere. They fill the whole universe.

• 6:20Lex Fridman?

  You know, I don't, I apologize perhaps for the ridiculous question. Are you comfortable with the idea of the fundamental nature of our reality being fields? Because to me, particles, you know, a bunch of different building blocks makes more sense sort of intellectually, sort of visually. Like it seems to, I seem to be able to visualize that kind of idea easier.

• 6:45Speaker 01

  Yeah.

• 6:45Lex Fridman?

  Are you comfortable psychologically with the idea that the basic building block is not a block, but a field?

• 6:52Speaker 01

  I think it's, I think it's quite a magical idea. I find it quite appealing and it's, well, it comes from a misunderstanding of what particles are. So like when you, when we do science at school and we draw a picture of an atom, you draw like, you know, a nucleus with some protons and neutrons, these little spheres in the middle, and then you have some electrons that are like little flies flying around the atom. And that is a completely misleading picture of what an atom is like. It's nothing like that. The electron is not like a little planet orbiting the atom. It's this spread out, wibbly wobbly, wave-like thing. And we know, we've known that since, you know, the early 20th century, thanks to quantum mechanics. So when we, we carry on using this word particle because sometimes when we do experiments, particles do behave like they're little marbles or little bullets, you know?

• 7:36Speaker 01

  So in the LHC, when we collide particles together, you'll get, you know, you'll get like hundreds of particles all flying out through the detector and they all take a trajectory and you can see from the detector where they've gone and they look like they're little bullets. So they behave that way, you know, a lot of the time. But when you really study them carefully, you'll see that they are not little spheres. They are these ethereal disturbances in, in these underlying fields. So this is, this is really how we think nature is, which is surprising, but also I think kind of magic. So, you know, we are, our bodies are basically made up of like little knots of energy in these invisible objects that are all around us.

• 8:18Lex Fridman?

  And what is the story of the vacuum when it comes to LHC? So why did you mention the word vacuum?

• 8:26Speaker 01

  Okay, so if we just, if we go back to like the physics we do know. So atoms are made of electrons, which were discovered a hundred or so years ago. And then in the nucleus of the atom, you have two other types of particles. There's an up, something called an up quark and a down quark. And those three particles make up every atom in the universe. So we think of these as ripples in fields. So there is something called the electron field. And every electron in the universe is a ripple moving about in this electron field. The electron field is all around us. We can't see it, but every electron in our body is a little ripple in this thing that's there all the time. And the quark field is the same. So there's an up quark field and an up quark is a little ripple in the up quark field. And the down quark is a little ripple in something else called the down quark field. So these fields are always there.

• 9:11Speaker 01

  Now, there are potentially, we know about a certain number of fields in what we call the standard model of particle physics. And the most recent one we discovered was the Higgs field. And the way we discovered the Higgs field was to make a little ripple in it. So what the LHC did, it fired two protons into each other very, very hard with enough energy that you could create a disturbance in this Higgs field. And that's what shows up as what we call the Higgs boson. So this particle that everyone was going on about eight or so years ago is proof really. The particle in itself is, I mean, it's interesting, but the thing that's really interesting is the field. Because it's the Higgs field that we believe is the reason that electrons and quarks have mass.

• 9:55Speaker 01

  And it's that invisible field that's always there that gives mass to the particles. The Higgs boson is just our way of checking it's there, basically.

• 10:03Lex Fridman?

  And so the Large Hadron Collider, in order to get that ripple in the Higgs field, you, it requires a huge amount of energy.

• 10:11Speaker 01

  Yeah.

• 10:11Lex Fridman?

  I suppose. And so that's why you need this huge, that's why size matters here. So maybe.

• 10:17Lex Fridman?

  There's a million questions here, but let's backtrack. Why does size matter in the context of a particle collider? So why does bigger allow you for higher energy collisions?

• 10:32Speaker 01

  Right, so the reason, well, it's kind of simple really, which is that there are two types of particle accelerator that you can build. One is circular, which is like the LHC, the other is a great long line. So the advantage of a circular machine is that you can send particles around a ring and you can give them a kick every time they go around. So imagine you have a, there's actually a bit of the LHC, that's about only 30 meters long, where you have a bunch of metal boxes which have oscillating 2 million volt electric fields inside them, which are timed so that when a proton goes through one of these boxes, the field it sees as it approaches is attractive. And then as it leaves the box, it flips and becomes repulsive and the proton gets attracted, then kicked out the other side. So it gets a bit faster. So you send it, then you send it back around again.

• 11:14Lex Fridman?

  That's incredible, like the timing of that, the synchronization, wait, really?

• 11:18Speaker 01

  Yeah, yeah, yeah, yeah.

• 11:19Lex Fridman?

  That's, I think there's going to be a multiplicative effect on the questions I have. Is, okay, let me just take that tension for a second. How, the orchestration of that, is that fundamentally a hardware problem or a software problem? Like what, how do you get that?

• 11:37Speaker 01

  I mean, I should first of all say, I'm not an engineer, so the guy is, I did not build the LHC. So there are people much, much better at this stuff than I could.

• 11:43Lex Fridman?

  For sure, but maybe, but from your sort of intuition, from the echoes of what you understand, what you heard of how it's designed, what's your sense, what's the engineering aspects of it?

• 12:00Speaker 01

  The acceleration bit is not challenging, okay? I mean, okay, there is always challenges with everything, but basically you have these.

• 12:07Speaker 01

  The beams that go around the LHC, the beams of particles are divided into little bunches. So they're called, they're a bit like swarms of bees, if you like. And there are around, I think it's something of the order 2,000 bunches spaced around the ring. And they, if you're, if you're at a given point on the ring, counting bunches, you get 40 million bunches passing you every second. So they come in like, you know, like cars going past on a very fast motorway. So you need to have, if you're electric field that you're using to accelerate the particles, that needs to be timed so that as a bunch of protons arrives, it's got the right sign to attract them and then flips at the right moment. But I think the, the voltage in those boxes oscillates at hundreds of megahertz. So the beams are like 40 megahertz, but it's oscillating much more quickly than the beams.

• 12:52Speaker 01

  So I, I think, you know, it's difficult engineering, but in principle, it's not, you know, a really serious challenge. The bigger problem. There's probably engineers like screaming at you right now. Probably. Yeah. Well, I mean, okay, so in terms of coming back to this thing, why is it so big? Well, the reason is you want to get the particles through that accelerating element over and over again. So you want to bring them back around. That's why it's round. The question is, why couldn't you make it smaller? Well, the, the basic answer is that these particles are going unbelievably quickly. So they travel at 99.9999991% of the speed of light in the LHC. And if you think about, say, driving your car around a corner at a high speed. If you go fast, you need a very, you need a lot of friction in the tyres to make sure you don't slide off the road.

• 13:38Speaker 01

  So the, the limiting factor is how powerful a magnet can you make? Cause it's what we do is magnets are used to bend the particles around the ring. And essentially the LHC, when it was designed, was designed with the most powerful magnets that could conceivably be built at the time. And so that's your kind of limiting factor. So if you wanted to make the machines smaller, that means a tighter bend, you need to have a more powerful magnet. So it's this toss up between how strong are your magnets versus how big a tunnel can you afford? The bigger the tunnel, the weaker the magnets can be, the smaller the tunnel, the stronger they've got to be.

• 14:10Lex Fridman?

  Okay, so maybe can we backtrack to the standard model and say what kind of particles there are, period? And maybe the history of kind of assembling that the standard model of physics and then how that leads up to the hopes and dreams and the accomplishments of the Large Hadron Collider?

• 14:29Speaker 01

  Yeah, sure. Okay. So all of 20th century physics in like five minutes.

• 14:33Lex Fridman?

  Yeah, please.

• 14:34Speaker 01

  Okay, so, okay, the story really begins properly, end of the 19th century. The basic view of matter is that matter is made of atoms and that atoms are indestructible, immutable little spheres, like the things we were talking about that don't really exist. And there's, you know, one atom for every chemical element. So there's an atom for hydrogen, for helium, for carbon, for iron, et cetera, and they're all different. Then in 1897, experiments done at the Cavendish Laboratory in Cambridge, which is where I'm still, where I'm based, showed that there are actually smaller particles inside the atom, which eventually became known as electrons. So these are these negatively charged things that go around the outside. A few years later, Ernest Rutherford, very famous nuclear physicist, one of the pioneers

• 15:16Speaker 01

  of nuclear physics, shows that the atom has a tiny nugget in the center, which we call the nucleus, which is a positively charged object. So then by like 1910, 11, we have this model of the atom that we learn in school, which is you've got a nucleus, electrons go around it. Fast forward, you know, a few years, the nucleus, people start doing experiments with radioactivity where they use alpha particles that are spat out of radioactive elements as bullets and they fire them at other atoms. And by banging things into each other, they see that they can knock bits out of the nucleus. So these things come out called protons, first of all, which are positively charged particles, about 2,000 times heavier than the electron. And then 10 years later, more or less, a neutral particle is discovered called the neutron.

• 16:00Speaker 01

  So those are the three basic building blocks of atoms. You have protons and neutrons in the nucleus that are stuck together by something called the strong force, the strong nuclear force, and you have electrons in orbit around that, held in by the electromagnetic force, which is one of the, you know, the forces of nature. That's sort of where we get to by like 1932, more or less. Then what happens is physics is nice and neat. In 1932, everything looks great. Got three particles and all the atoms are made of. That's fine. But then cloud chamber experiments. These are devices that can be used to. The first device is capable of imaging subatomic particles. So you can see their tracks and they're used to study cosmic rays. Particles that come from outer space and bang into the atmosphere.

• 16:42Speaker 01

  And in these experiments, people start to see a whole load of new particles. So they discover for one thing antimatter, which is a sort of a mirror image of the particles. So we discover that there's also, as well as a negatively charged electron, there's something called a positron, which is a positively charged version of the electron. And there's an antiproton, which is negatively charged. And then a whole load of other weird particles start to get discovered and no one really knows what they are. This is known as the zoo of particles.

• 17:07Lex Fridman?

  Are these discoveries fundamentally first theoretical discoveries? Or are they discoveries in experiment? So like, yeah, what's the process of discovery for these early sets of?

• 17:19Speaker 01

  It's a mixture. I mean, the early stuff around the atom is really experimentally driven. It's not based on some theory. It's exploration in the lab using equipment. So it's really people just figuring out, getting hands on with the phenomena, figuring out what these things are. And the theory comes a bit later. That there is, that's not always the case. So in the discovery of the anti-electron, the positron, that was predicted from quantum mechanics and relativity by a very clever theoretical physicist called Paul Dirac, who was probably the second brightest physicist of the 20th century, apart from Einstein, but isn't anywhere near as well known. So he predicted the existence of the anti-electron from basically a combination of the theories of quantum mechanics and relativity. And it was discovered about a year after he made the prediction.

• 18:02Lex Fridman?

  What happens when an electron meets a positron?

• 18:06Speaker 01

  They annihilate each other. So if you, when you bring a particle and its antiparticle together, they, they react. Well, they react, they just wipe each other out and they turn, their mass is turned into energy, usually in the form of photons. So you get light produced.

• 18:20Lex Fridman?

  So when you have that kind of situation, why, why does the universe exist at all if there's matter and any matter?

• 18:27Speaker 01

  Oh God, now we're getting into really big questions. So.

• 18:31Speaker 01

  Do you want to go there now?

• 18:32Lex Fridman?

  Yeah, let's maybe let's go there later.

• 18:35Speaker 01

  Because I mean, that is a very big question.

• 18:37Lex Fridman?

  Yeah, let's let's let's take it slow with the standard model. So, OK, so there's there's matter and antimatter in the 30s. So what else?

• 18:46Speaker 01

  So matter antimatter and then a load of new particles start turning up in these cosmic ray experiments, first of all. And they don't seem to be particles that make up atoms. They're something else. They all mostly interact with a strong nuclear force. So they're a bit like protons and neutrons. And by in the 1960s, in America particularly, but also in Europe and Russia, scientists started to build particle accelerators. So these are the forerunners of the LHC. So big ring shaped machines that were, you know, hundreds of meters long, which in those days was enormous. You never, you know, most physics up until that point had been done in labs in universities, you know, with small bits of kit. So this is a big change. And when these accelerators are built, they start to find they can produce even more of these particles.

• 19:29Speaker 01

  So I don't know the exact numbers, but by around 1960, there are of order 100 of these things that have been discovered. And physicists are kind of tearing their hair out because physics is all about simplification. And suddenly what was simple has become messy and complicated. And everyone sort of wants to understand what's going on.

• 19:48Lex Fridman?

  As a quick kind of aside and probably really dumb question, but

• 19:53Lex Fridman?

  how is it possible to take something like a like a photon or electron? And be able to control it enough, like to be able to

• 20:04Lex Fridman?

  do a controlled experiment where you collide it against something else?

• 20:08Speaker 01

  Yeah.

• 20:09Lex Fridman?

  Is that is that that seems like an exceptionally difficult

• 20:14Lex Fridman?

  engineering challenge because you mentioned vacuum too. So you basically want to remove every other distraction and really focus on this collision. How difficult of an engineering challenge is that? Just to get a sense.

• 20:24Speaker 01

  It is very hard. I mean, in the early days, particularly when the first accelerators are being built in like 1932, Ernest Lawrence builds the first what we call a cyclotron, which is like a little accelerator this big or so.

• 20:38Lex Fridman?

  Literally that big?

• 20:39Speaker 01

  This tiny. Little thing. Yeah. I mean, so most of the first accelerators were what we call fixed target experiments. So you had a ring, you accelerate particles around the ring and then you fire them out the side into some target. So it's that makes the kind of the colliding bit is relatively straightforward because you just fire it. Whatever it is you want to fire it at. The hard bit is the steering the beams with the magnetic fields, getting, you know, strong enough electric fields to accelerate them, all that kind of stuff. The first colliders where you have two beams colliding head on, that comes later. And I don't think it's done until maybe the nineteen eighties. I'm not entirely sure, but it takes it's a much harder problem.

• 21:22Lex Fridman?

  That's crazy because you have to like perfectly get them to hit each other. I mean, we're talking about, I mean, what scale it takes, what's the, I mean, the temporal thing is a giant mess. But the spatially, like the size is tiny.

• 21:40Speaker 01

  Well, to give you a sense, so the LHC beams, the cross sectional diameter is, I think, around a dozen or so microns. So, you know, ten, ten millionths of a, of a meter.

• 21:53Lex Fridman?

  And a beam, sorry, just to clarify, a beam contains how many, is it the bunches that you mentioned? Is it multiple parts or is it just one part?

• 22:01Speaker 01

  Oh, no, no, the bunches contain, say, a hundred billion protons each. So a bunch is, it's not really bunch shaped, they're actually quite long. They're like thirty centimeters long, but thinner than a human hair. So like very, very narrow, long sort of objects. Those are the things. So what happens in the LHC is you steer the beams so that they cross in the middle of the detector. So they basically have these swarms of protons that are flying through each other. And most of the, you have to have a hundred billion coming one way, a hundred billion another way, maybe. Ten of them will hit each other.

• 22:34Lex Fridman?

  Okay, so this, okay, that makes a lot more sense. So that's nice. So you're trying to use sort of, it's like probabilistically, you're not.

• 22:41Speaker 01

  You can't make a single particle collide with a single other particle. That's not an efficient way to do it. You'd be waiting a very long time to get anything. Yeah.

• 22:47Lex Fridman?

  So you're basically right. So you're relying on probability to me that some fraction of them are going to collide.

• 22:55Speaker 01

  Yeah.

• 22:55Lex Fridman?

  And then you know which, because it's, it's a, it's a swarm of the same kind of particle.

• 23:01Speaker 01

  So it doesn't matter which ones hit each other exactly. I mean, that's not to say it's not hard. You've got a, one of the challenges to make the collisions work is you have to squash these beams to very, very, basically the narrower they are, the better, because the higher the chances of them colliding. If you think about two flocks of birds flying through each other, the birds are all far apart in the flocks. There's not much chance that they'll collide. If they're all flying densely together and they're much more likely to collide with each other. So that's the sort of problem. And it's tuning those magnetic fields, getting the magnetic fields powerful enough that you squash the beams and focus them so that you get enough collisions.

• 23:33Lex Fridman?

  That's super cool. Do you know how much software is involved here? I mean, sort of, I come from the software world and it's fascinating. This, this seems like, this software is buggy and messy and so like you, you almost don't want to rely on software too much. Like if you do, it has to be like low level, like for trans style programming. Do you know how much software is in the Large Hadron Collider?

• 23:56Speaker 01

  I mean, it depends at which level, a lot. I mean, the whole thing is obviously computer controlled. So, I mean, I, I don't know a huge amount about how the software for the actual accelerator works. But, you know, I've been in the control center. So that's, there's this big control room, which is like a bit like a NASA mission control with big banks of, you know, desks where the engineers sit and they monitor the LHC because you obviously can't be in the tunnel when it's running. So everything's remote. I mean, one sort of anecdote about the sort of software side, in 2008, when the LHC first switched on, they had this big launch event and then, you know, big press conference, party to inaugurate the machine. And about 10 days after that, they were doing some tests and the, this dramatic event happened where

• 24:39Speaker 01

  a huge explosion basically took place in the tunnel that destroyed. Or damaged, badly damaged about about half a kilometer of the machine. But the stories, the engineers are in the control room that day, they, I would, one guy told me this story about, you know, basically, all these screens they have in the control room. Started going red, so all these alarms like, you know, kind of in software going off and then they assumed that there's something wrong with the software because there's no way.

• 25:02Lex Fridman?

  Yeah.

• 25:02Speaker 01

  Something this catastrophic could have, could have happened.

• 25:04Lex Fridman?

  Yeah.

• 25:05Speaker 01

  Um, but I mean, when I worked on, when I was a PhD student, one of my jobs was to. Help to maintain the software that's used to control the detector that we work on. And that was, it's relatively robust, not such, you don't want it to be too fancy, you don't want it to sort of fall over too easily. The more clever stuff comes when you're talking about analyzing the data and that's where the sort of, you know.

• 25:27Lex Fridman?

  Are we jumping around too much? Do we finish with the standard model?

• 25:30Speaker 01

  We didn't, no.

• 25:30Lex Fridman?

  We didn't, so have we even started talking about quarks?

• 25:33Speaker 01

  We haven't talked about them yet, no, we got, we got to the messy zoo of particles.

• 25:37Lex Fridman?

  Let me, uh, let's, let's go back there if it's okay.

• 25:39Speaker 01

  Okay, that's fine.

• 25:40Lex Fridman?

  Can you take us to the rest of the history of physics in the 20th century?

• 25:44Speaker 01

  Okay, sure. Okay, so circa 1960, you have this, you have these a hundred or so particles, it's a bit like the periodic table all over again. So you've got like, like having a hundred elements, sort of a bit like that. And people start to try to impose some order. So Murray Gelman, uh, he's a theoretical physicist, American from New York. He realizes that there are these symmetries in these particles that if you arrange them in certain ways, they're, they relate to each other. And he uses these symmetry principles to predict the existence of particles that haven't been discovered, which are then discovered in accelerators. So this starts to suggest there's not just random collections of crap, there's like, you know, actually some order to this underlying it.

• 26:25Speaker 01

  A little bit later in 1960, again, it's around the 1960s. Um, he proposes, along with another physicist called George Zweig, that these symmetries arise because. Just like the patterns in the periodic table arise because atoms are made of electrons and protons. That these patterns are due to the fact that these particles are made of smaller things and they are called quarks. So these are the particles, they're predicted from theory for a long time. No one really believes they're real. A lot of people think that they're a kind of theoretical convenience that happen to fit the data, but there's no evidence. No one's ever seen a quark in any experiment.

• 27:02Speaker 01

  And lots of experiments are done to try to find quarks, to try to knock a quark out of a, so the idea, if protons and neutrons, say, are made of quarks, you should be able to knock a quark out and see the quark. That never happens. And we still have never actually managed to do that.

• 27:15Lex Fridman?

  Wait, really?

• 27:16Speaker 01

  No. So the way, but the, the way that it's done in the end is there's a machine that's built in California at the Stanford lab, Stanford Linear Accelerator. Which is essentially a gigantic, three kilometer long electron gun. It fires electrons almost the speed of light at protons. And when you do these experiments, what you find is at very high energy, the electrons bounce off small, hard objects inside the proton. So it's a bit like taking an X-ray of the proton. You're firing these very light, high-energy particles. And they're pinging off little things inside the proton that are like ball bearings, if you like.

• 27:53Speaker 01

  So you actually, that way, they resolve that there are three things inside the proton, which are quarks, the quarks that Gellman and Zweig had predicted. So that's really the evidence that convinces people that these things are real. The fact that we've never seen one in an experiment directly, they're always stuck inside other particles. And the reason for that is essentially to do with the strong force. The strong force is the force that holds quarks together. And it's so strong, it's impossible to actually liberate a quark. So if you try and pull a quark out of a proton, what actually ends up happening is that the, you kind of create this, this spring-like bond in the strong force. You imagine two quarks that are held together by a very powerful spring.

• 28:35Speaker 01

  You pull and pull and pull, more and more energy gets stored in that bond, like stretching a spring. And eventually the tension gets so great, the spring snaps. And the energy in that bond gets turned into two new quarks that go on the broken ends. So you started with two quarks, you end up with four quarks. So you never actually get to take a quark out. You just end up making loads more quarks in the process.

• 28:56Lex Fridman?

  So how do we? Again, forgive the dumb question. How do we know quarks are real then?

• 29:01Speaker 01

  Well, A, from these experiments where we can scatter, you fire electrons into the protons. They can burrow into the proton and knock off, and they can bounce off these quarks. So you can see from the angles the electrons come out.

• 29:15Lex Fridman?

  I see, you can infer.

• 29:16Speaker 01

  You can infer that these things are there.

• 29:19Speaker 01

  The quark model can also be used. It has a lot of successes. You can use it to predict the existence of new particles that hadn't been seen. So, and it basically, there's lots of data basically showing from, you know, when we fire protons at each other at the LHC,

• 29:33Speaker 01

  a lot of quarks get knocked all over the place. And every time they try and escape from, say, one of their protons, they make a whole jet of quarks that go flying off, as bound up in other sorts of particles made of quarks. So the, all the sort of the theoretical predictions from the basic theory of the strong force and the quarks, all agrees with what we are seeing in experiments. We've just never seen a, an actual quark on its own, because unfortunately, it's impossible to get them out on their own.

• 29:58Lex Fridman?

  So quarks, these crazy, smaller things that are hard to imagine are real. So what else? What else is part of the story here?

• 30:06Speaker 01

  So the other thing that's going on at the, at the time, around the sixties, is an attempt to understand the forces that make these particles interact with each other. So you have the electromagnetic force, which is the force that was sort of discovered to some extent in this room, or at least in this building. So the first, what we call quantum field theory of the electromagnetic force is developed in the 1940s and 50s by Feynman, Richard Feynman amongst other people, Julian Schwinger, Tomonaga, who come up with the first, what we call a quantum field theory of the electromagnetic force. And this is where this description of, which I gave you at the beginning, that particles are ripples in fields. Well, in this theory, the photon, the particle of light,

• 30:50Speaker 01

  is described as a ripple in this quantum field called the electromagnetic field. And the attempt then is made to try, well, can we come up with a quantum field theory of the other forces, of the strong force and the weak, the other, the third force, which we haven't discussed, which is the weak force, which is a nuclear force. We don't really experience it in our everyday lives, but it's responsible for radioactive decay. It's the force that allows, you know, a radioactive atom to turn into a different element, for example.

• 31:17Lex Fridman?

  And I don't know if you explicitly mentioned, but so there's. Technically, four forces.

• 31:22Speaker 01

  Yes.

• 31:23Lex Fridman?

  I guess three of them would be in the standard model, like the weak, the strong, and the electromagnetic, and then there's gravity.

• 31:31Speaker 01

  And there's gravity, which we don't worry about that because it's too hard. No, maybe we bring that up at the end, but yeah. Gravity, so far, we don't have a quantum theory of, and if you can solve that problem, you'll win a Nobel Prize.

• 31:42Lex Fridman?

  Well, we're gonna have to bring up the graviton at some point, I'm gonna ask you, but let's leave that to the side for now. So those three, okay, Feynman electromagnetic force, the quantum field.

• 31:55Speaker 01

  Yeah.

• 31:56Lex Fridman?

  And where does the weak force come in?

• 31:58Speaker 01

  So, yeah, well, first of all, I mean, the strong force is a bit easier. So the strong force is a little bit like the electromagnetic force. It's a force that binds things together. So that's the force that holds quarks together inside the proton, for example. So a quantum field theory of that force is discovered in the, I think it's in the 60s, and it predicts the existence of new force particles called gluons. So gluons are a bit like the photon. The photon is the particle of electromagnetism. Gluons are the particles of the strong force. And so there's, just like there's an electromagnetic field, there's something called a gluon field, which is also all around us.

• 32:36Lex Fridman?

  So these particles, some of these particles, I guess, are the force carriers or whatever. They carry the.

• 32:41Speaker 01

  Well, it depends how you want to think about it. I mean, really, the field, the strong force field, the gluon field is the thing that binds the quarks together. The gluons are the little ripples in that field. So that like, in the same way that the photon is a ripple in the electromagnetic field. But the thing that really does the binding is the field. I mean, you may have heard people talk about things like, have you heard the phrase virtual particle? So sometimes, if you hear people describing how forces are exchanged between particles, they quite often talk about the idea that, you know, if you have an electron and another electron, say, and they're repelling each other through the electromagnetic force, you can think of that as if they're exchanging photons. So they're kind of firing photons backwards and forwards between each other, and that

• 33:25Speaker 01

  causes them to repel.

• 33:28Lex Fridman?

  That photon is then a virtual particle.

• 33:30Speaker 01

  Yes, that's what we call a virtual particle. In other words, it's not a real thing, it doesn't actually exist. So it's an artifact of the way theorists do calculations. So when they do calculations in quantum field theory, rather than there's no, no one's discovered a way of just treating the whole field. You have to break the field down into simpler things. So you can basically treat the field as if it's made up of lots of these virtual photons. But there's no experiment that you can do that can detect these particles being exchanged. What's really happening in reality is that the electromagnetic field is warped by the charge of the electron and that causes the force. But the way we do calculations involves particles. So it's a bit confusing, but it's really a mathematical technique. It's not something that corresponds to reality.

• 34:12Lex Fridman?

  I mean, that's part, I guess, of the Feynman diagrams.

• 34:15Speaker 01

  Yes.

• 34:15Lex Fridman?

  Is this these virtual particles? Okay.

• 34:17Speaker 01

  That's right, yeah.

• 34:18Lex Fridman?

  Some of these have mass, some of them don't. Is that, is that, what, what does that even mean not to have mass? And maybe you can say which one of them has mass and which don't.

• 34:29Speaker 01

  Okay, so.

• 34:31Lex Fridman?

  And why is mass important or relevant in this, in this, in this field view of the universe?

• 34:38Speaker 01

  Well, there are, there are actually only two particles in the standard model that don't have mass, which are the photon and the gluons. So they are massless particles. But the electron, the quarks, and there are a bunch of other particles I haven't discussed. There's something called a muon and a tau, which are basically heavy versions of the electron that are unstable. You can make them in accelerators, but they, they don't form atoms or anything. They don't exist for long enough. But all the matter particles, there are 12 of them, six quarks and six, what we call leptons, which includes the electron and its two heavy versions and three neutrinos. All of them have mass. And so do, this is the critical bit. So the weak force, which is the third of these quantum forces, which is one of the hardest to understand.

• 35:24Speaker 01

  The, the force particles of that force have very large masses. And there are three of them. They're called the W plus, the W minus and the Z boson. And they have masses of between 80 and 90 times that of the, the proton. So they're very heavy.

• 35:42Lex Fridman?

  Wow.

• 35:43Speaker 01

  They're very heavy things.

• 35:43Lex Fridman?

  So they're what, the heaviest, I guess?

• 35:46Speaker 01

  They're not the heaviest. The heaviest particle is the top quark. Which has a mass of about one hundred and seventy five ish protons. So that's really massive and we don't know why it's so massive. But coming back to the weak force, so that the the problem in the sixties and seventies was that the reason that the electromagnetic force is a force that we can experience in our everyday lives. So if you have a magnet and a piece of metal, you can hold it, you know, a meter apart if it's powerful enough and you'll feel a force. Whereas the weak force only is becomes apparent when you basically have two particles touching at the scale of a nucleus. So we should get to very short distances before this force becomes manifest. It's not, doesn't, we don't get weak forces going on in this room. We don't notice them.

• 36:30Speaker 01

  And the reason for that is that the particle, well, the the field that transmits the weak force, the particle that's associated with that field has a very large mass, which means that the field dies off very quickly. So as you, whereas an electric charge, if you were to look at the shape of the electromagnetic field, it would fall off with this. You have this thing called the inverse square law, which is the idea that the force halves every time you double the distance. No, sorry, it doesn't halve, it quarters every time you see, every time you double the distance between, say, the two particles. Whereas the weak force kind of, you move a little bit away from the nucleus and just disappears. The reason for that is because these these fields, the particles that go with them have a very large mass.

• 37:12Speaker 01

  But the problem that was that theorists faced in the sixties was that if you tried to introduce massive force fields, the theory gave you nonsensical answers. So you end up with infinite results for a lot of the calculations you tried to do. So the basically it turned, it seemed that quantum field theory was incompatible with having massive particles. Not just the force particles actually, but even the electron was a problem. So this is where the Higgs that we sort of alluded to comes in. And the solution was to say, okay, well, actually, all the particles in the standard model are mass, they have no mass. So the quarks, the electron, they don't have a mass, neither do these weak particles, they don't have mass either.

• 37:53Speaker 01

  What happens is they actually acquire mass through another process, they get it from somewhere else, they don't actually have it intrinsically. So this idea that was introduced by, well, Peter Higgs is the most famous, but actually there are about six people that came up with the idea more or less at the same time. Is that you introduce a new quantum field. Which is another one of these invisible things that's everywhere. And it's through the interaction with this field that particles get mass. So you can think of, say, an electron in the Higgs field. The Higgs field kind of bunches around the electron. It's sort of drawn towards the electron. And that energy that's stored in that field around the electron is what we see as the mass of the electron.

• 38:36Speaker 01

  But if you could somehow turn off the Higgs field, then all the particles in nature would become massless and fly around at the speed of light. So this idea of the Higgs field allowed other people, other theorists, to come up with a, well, it was another, basically a unified theory of the electromagnetic force and the weak force. So once you bring in the Higgs field, you can combine two of the forces into one. So it turns out the electromagnetic force and the weak force are just two aspects of the same fundamental force. And at the LHC, we go to high enough energies that you see these two forces unifying effectively.

• 39:16Lex Fridman?

  So first of all, it started as a theoretical notion, like this is something. And then, I mean, wasn't the Higgs called the God particle at some point?

• 39:27Speaker 01

  It was by a guy trying to sell popular science books, yeah.

• 39:30Lex Fridman?

  Yeah, but I mean, I remember, because when I was hearing it, I thought it would, I mean, that would solve a lot of, that unified a lot of our ideas of physics, was my notion. But maybe you can speak to that. Was it as big of a leap? Is it a God particle or is it a Jesus particle? Which, you know, what's the big contribution of Higgs in terms of this unification power?

• 39:57Speaker 01

  Yeah, I mean, to understand that, it maybe helps to know the history a little bit. So when the, what we call electro-weak theory was put together, which is where you unify electromagnetism with the weak force, and Higgs is involved in all of that. So that theory, which was written in the mid 70s, predicted the existence of four new particles, the W plus boson, the W minus boson, the Z boson, and the Higgs boson. So there were these four particles. That came with the theory that were predicted by the theory. In nineteen eighty three, eighty four, the Ws and the Z particles were discovered at an accelerator at CERN called the Superproton Synchrotron, which was a seven kilometre particle collider. So three of the bits of this theory had already been found.

• 40:39Speaker 01

  So people were pretty confident from the eighties that the Higgs must exist because it was a part of this family of particles that this theoretical structure only works if the Higgs is there. So what then happens? So you this question about why is the LHC the size it is? Yes. Well, actually, the tunnel that the LHC is in was not built for the LHC. It was built for a previous accelerator called the Large Electron Positron Collider. So that that was began operation in the late eighties, early nineties. They basically, that's when they dug the twenty seven kilometre tunnel. They put this accelerator into it, the collider, that fires electrons and anti electrons at each other, electrons and positrons. So the purpose of that machine was, well, it was actually to look for the Higgs.

• 41:23Speaker 01

  That was one of the things it was trying to do. It didn't have enough energy to do it in the end. But the main thing it achieved was it studied the W and the Z particles at very high precision. So it made loads of these things. Previously, you can only make a few of them at the previous accelerator. So you could study these really, really precisely. And by studying their properties, you could really test this electroweak theory that had been invented in the seventies and really make sure that it worked. So actually, by nineteen ninety nine, when this machine turned off, people knew, well, okay, you never know until you until you find the thing. But people were really confident this electroweak theory was right and that the Higgs almost,

• 42:03Speaker 01

  the Higgs or something very like the Higgs had to exist because otherwise the whole thing doesn't work. It'd be really weird if you could discover and these particles, they all behave exactly as your theory tells you they should. But somehow this key piece of the picture is not there. So in a way, it depends how you look at it. The discovery of the Higgs on its own is is obviously a huge achievement in many, both experimentally and theoretically. On the other hand, it's this, it's like having a jigsaw puzzle where every piece has been filled in. You have this beautiful image, there's one gap and you kind of know that that piece must be there somewhere, right? So so the discovery in itself, although it's important.

• 42:45Speaker 01

  Is not so interesting.

• 42:47Lex Fridman?

  It's like a confirmation of the obvious at that point.

• 42:51Speaker 01

  But what makes it interesting is not that it just completes the standard model, which is a theory that we've known had the basic layout of for 40 years or more now. It's that the Higgs actually is a is a unique particle. It's very different to any of the other particles in the standard model. And it's a theoretically very troublesome particle. There are a lot of nasty things to do with the Higgs, but also opportunities. So that we basically, we don't really understand how such an object can exist in the form that it does. So there are lots of reasons for thinking that the Higgs must come with a bunch of other particles or that it's perhaps made of other things. So it's not a fundamental particle, that it's made of smaller things. I can talk about that if you like a bit.

• 43:36Lex Fridman?

  That's that's still a notion. So yeah, so the Higgs might not be a fundamental particle. There might be some, it might, oh, man.

• 43:44Speaker 01

  So that that is an idea. It's not, you know, it's not been demonstrated to be true. But I mean, this, this, all of these ideas basically come from the fact that it's a, this is, this is a problem that motivated a lot of development in physics in the last 30 years or so. And there's this basic fact that the the Higgs field, which is this field that's everywhere in the universe. This is the thing that gives mass to the particles. And the Higgs field is different from every all the other fields in that. Let's say you take the electromagnetic field, which is, you know, if we actually were to measure the electromagnetic field in this room, we would measure all kinds of stuff going on because there's light. There's going to be microwaves and radio waves and stuff. But let's say we could go to a really, really remote part of empty space and shield it and put a big box around it and then measure the electromagnetic field in that box.

• 44:26Speaker 01

  The field would be almost zero, apart from some little quantum fluctuations. But basically it goes to naught. The Higgs field has a value everywhere. So it's a bit like the whole, it's like the entire of space has got this energy stored in the Higgs field, which is not zero, it's it's finite. It's got some, it's a bit like having the the temperature of space raised to, you know, some background temperature. And it's that energy that gives mass to the particles. So the reason that electrons and quarks have mass is through the interaction with this energy that's stored in the Higgs field. Now, it turns out that the precise value this energy has has to be very carefully tuned

• 45:10Speaker 01

  if you want a universe where interesting stuff can happen. So if you push the Higgs field down, it has a tendency to collapse to, well, there's a tendency, if you do your sort of naive calculations, there are basically two possible likely configurations for the Higgs field, which is either it's zero everywhere, in which case you have a universe which is just particles with no mass that can't form atoms and just fly about at the speed of light, or it explodes to an enormous value, what we call the Planck scale, which is the scale of quantum gravity. And at that point, if the Higgs field was that strong, even an electron would become so massive that it would collapse into a black hole. And then you have a universe made of black holes and nothing like us.

• 45:51Speaker 01

  So it seems that the strength of the Higgs field is to achieve the value that we see requires what we call fine tuning of the laws of physics. You have to fiddle around with the other fields in the standard model and their properties to just get it to this right sort of Goldilocks value that allows atoms to exist. This is deeply fishy. People really dislike this.

• 46:14Lex Fridman?

  Well, yeah, I guess, so what would be, so two explanations. One, there's a God that designed this perfectly. And two is there's an infinite number of alternate universes and we're just happen to be in the one in which life is possible.

• 46:28Speaker 01

  Yeah.

• 46:28Lex Fridman?

  Complexity. So when you say, I mean, life, any kind of complexity, that's not either complete chaos or black holes.

• 46:36Speaker 01

  Yeah, yeah.

• 46:38Lex Fridman?

  I mean, how does that make you feel? What do you make of that? That's such a fascinating notion, that this perfectly tuned field that's the same everywhere is there. What do you make of that? Yeah, what do you make of that?

• 46:51Speaker 01

  I mean, yeah, so you laid out two of the possible explanations.

• 46:53Lex Fridman?

  Really?

• 46:54Speaker 01

  Some, well, yeah, I mean, well, someone, you know, some cosmic creator went, yeah, let's fix that to be at the right level. That's one possibility, I guess. It's not a scientifically testable one, but, you know, theoretically, I guess, it's possible.

• 47:05Lex Fridman?

  Sorry to interrupt, but there could also be not a designer, but couldn't there be just, I guess, I'm not sure what that would be, but some kind of force that.

• 47:17Lex Fridman?

  That some kind of mechanism by which this this um this kind of field is enforced in order to create complexity, basically basically forces that

• 47:32Lex Fridman?

  pull the universe towards an interesting complexity.

• 47:36Speaker 01

  I mean, yeah, I mean, there are people who have those ideas. I don't really subscribe to them.

• 47:40Lex Fridman?

  As I'm saying, it sounds really stupid.

• 47:42Speaker 01

  No, I mean, I there are definitely people that make those kind of arguments. Um, you know, there's ideas that I think it's Lee Smolin's idea, one, I think, that, you know, universes are born inside black holes. And so universes, they basically have like Darwinian evolution of the universe where universes give birth to other universes. And if universes where black holes can form are more likely to give birth to more universes. So you end up with universes which have similar laws. I mean, I don't know, whatever.

• 48:09Lex Fridman?

  Well, I talked to I talked to Lee recently on this on this podcast and he's he's a reminder to me that the physics community has like so many interesting characters.

• 48:22Speaker 01

  Yeah.

• 48:22Lex Fridman?

  It's fascinating.

• 48:23Speaker 01

  Yeah.

• 48:23Lex Fridman?

  Anyway, sorry. So.

• 48:24Speaker 01

  I mean, as an experimentalist, I tend to sort of think, these are interesting ideas, but they're not really testable. So I tend not to think about them very much. So, I mean, going back to the science of this, there wasn't, there is an explanation. There is a possible solution to this problem of the Higgs, which doesn't involve multiverses or creators fiddling about with the laws of physics. If the the most popular solution was something called supersymmetry, which is a theory, which is involve involves a new type of symmetry of the universe. In fact, it's one of the last types of symmetries that is possible to have that we haven't already seen in nature, which is a symmetry between force particles and matter particles. So what we call fermions, which are the force, the matter particles and bosons, which are force particles.

• 49:06Speaker 01

  And if you have supersymmetry, then there is a super partner for every particle in the standard model. And the, without going into the details, the effect of this basically is that you have a whole bunch of other fields. And these fields cancel out the effect of the standard model fields, and they stabilize the Higgs field at a nice sensible value. So in supersymmetry. You naturally, without any tinkering about with the constants of nature or anything, you get a Higgs field with a nice value, which is the one we see. So this is one of the, and supersymmetry has also got lots of other things going for it. It predicts the existence of a dark matter particle, which would be great. It, you know, it potentially suggests that the, the strong force and the, the electron weak force unify at high energy.

• 49:49Speaker 01

  So lots of reasons people thought this was a productive idea. And when the LHC was, just before it was turned on, there was a lot of hype, I guess, a lot of, an expectation that we would discover these super partners because, and particularly the main reason was that if, if supersymmetry stabilizes the Higgs field at this nice Goldilocks value, these super particles should have a mass around the energy that we're probing at the LHC, around the energy of the Higgs. So it was kind of thought, you discover the Higgs, you probably discover super partners as well.

• 50:20Lex Fridman?

  So once you start creating ripples in this Higgs field, you should be able to see these kinds of, you should be, yeah.

• 50:26Speaker 01

  The super fields would be there. When I, at the very beginning, I said, we're probing the vacuum. What I mean is really that, you know, okay, let's say these super fields exist. The vacuum contains super fields, they're there, these supersymmetric fields. If we hit them hard enough, we can make them vibrate. We see super particles come flying out. That's the sort of, that's the idea.

• 50:43Lex Fridman?

  That's the hope.

• 50:43Speaker 01

  That's the whole point.

• 50:46Lex Fridman?

  But we haven't.

• 50:47Speaker 01

  But we haven't. So, so far at least, I mean, we've had now a decade of data taking at the LHC. No signs of super partners, have supersymmetric particles have been found. In fact, no signs of any physics, any new particles beyond the standard model have been found. So supersymmetry is not the only thing that can do this. There are other theories that involve additional dimensions of space or potentially involve the Higgs boson being made of smaller things, being made of other particles.

• 51:15Lex Fridman?

  That's an interesting, you know, I haven't heard that before. That's really, that's an interesting, but could you maybe linger on that? Like what? What could be, what could the Higgs particle be made of?

• 51:25Speaker 01

  Well, so the oldest, I think the original ideas about this was these theories called technicolor, which were basically like an analogy with the strong force. So the idea was the Higgs boson was a bound state of two very strongly interacting particles that were a bit like quarks. So like quarks, but I guess higher energy things with a super strong force. So not the strong force, but a new force that was very strong. And the Higgs was a bound state of these, these objects. And the Higgs would in principle, if that was right, would be the first in a series of technicolor particles. Technicolor, I think, not being a theorist, but it's not, it's basically not done very well. Particularly since the LHC found the Higgs, that kind of, it rules out, you know, a lot of these technicolor theories.

• 52:10Speaker 01

  But there are other things that are a bit like technicolor. So there's a theory called partial compositeness, which is an idea that some of my colleagues at Cambridge have worked on, which is a similar sort of idea, that the Higgs is a bound state of some strongly interacting particles and that the standard model particles themselves, the more exotic ones like the top quark, are also sort of mixtures of these composite particles. So it's a kind of an extension to the standard model, which explains this problem with the Higgs boson's Goldilocks value, but also helps us understand, we have, we're in this situation now, again, a bit like the periodic table,

• 52:51Speaker 01

  where we have six quarks, six leptons in this kind of, you can range in this nice table and you can see these columns where the patterns repeat and you go, hmm, okay, maybe there's something deeper going on here, as you know. And, and so this would potentially be something, this partial compositeness theory could explain, sort of enlarge this picture that allows us to see the whole symmetrical pattern and understand what the ingredients, why do we have, so one of the big questions in particle physics is,

• 53:19Speaker 01

  Why are there three copies of the matter particles? So in what we call the first generation, which is what we're made of, there's the electron, the electron neutrino, the up quark and the down quark. They're the most common matter particles in the universe. But then there are copies of these four particles in the second and the third generations. So things like muons and top quarks and other stuff. We don't know why. We see these patterns. We have no idea where it comes from. So that's another big question. You know, can we find out the deeper order that explains this particular periodic table of particles that we see?

• 53:53Lex Fridman?

  Is it possible that the deeper order includes like almost a single entity? So like something that I guess like string theory dreams about. Is this, is this, is this, is this essentially the dream? Is to discover something simple, beautiful and unifying?

• 54:10Speaker 01

  Yeah, I mean, that is the dream. And it will, and I think for some people, for a lot of people, it still is the dream. So there's a great book by Stephen Weinberg, who is one of the theoretical physicists who was instrumental in building the standard model. So he came up with some others with the electroweak theory, the theory that unified electromagnetism and the weak force. And he wrote this book, I think it was towards the end of the eighties, early nineties called Dreams of a Final Theory, which is a very lovely, quite short book about this idea of a final unifying theory that brings everything together. And I think you get a sense from reading his book written at the end of the eighties, early nineties, that there was this feeling that such a theory was coming.

• 54:54Speaker 01

  And that was the time when string theory had been, was, was very exciting. So string theory, there's been this thing called the superstring revolution and theoretical physicists getting very excited. They discovered these theoretical objects, these little vibrating loops of string that in principle not only was a quantum theory of gravity, but could explain all the particles in the standard model and bring it all together. And you, as you say, you have one object, the string, and you can pluck it. And the way it vibrates gives you these different notes, each of which is a different particle. So it's a very lovely idea, but. The problem is that, well, there's a few, people discover that mathematics is very difficult. So people have spent three decades or more trying to understand string theory. And I think, you know, if you spoke to most string theorists, they would probably freely admit

• 55:39Speaker 01

  that no one really knows what string theory is yet. I mean, there's been a lot of work, but it's not really understood. And the other problem is that string theory mostly makes predictions about physics that occurs at energies far beyond what we will ever be able to probe in the laboratory. Yeah, probably ever.

• 55:59Lex Fridman?

  By the way, so sorry, I take a million tangents, but is there room for complete innovation of how to build a particle collider that could give us an order of magnitude increase in, in the kind of energies? Or do we need to keep just increasing the size of thing?

• 56:15Speaker 01

  I mean, maybe, yeah, I mean, there are ideas, but to give you a sense of the gulf that has to be bridged. So the LHC collides particles at an energy of what we call 14 tera electron volts. So that's basically the equivalent of you've accelerated a proton through 14 trillion volts. That gets us to the energies where the Higgs and these weak particles live. They're very massive. The, the scale where strings become manifest is something called the Planck scale, which I think is of the order 10 to the, uh, hang on, get this right. It's 10 to the 18 giga electron volts, so about 10 to the 15, um, tera electron volts.

• 56:57Speaker 01

  So you're talking, you know, trillions of times more energy, more than.

• 57:02Lex Fridman?

  Yeah, 10 to the 15, or 10 to the 14th larger.

• 57:05Speaker 01

  I may have been slightly wrong, but it's of that order. It's a very big number. So, you know, we're not talking just an order of magnitude increase in energy. We're talking 14 orders of magnitude energy increase. So to give you a sense of what that would look like, were you to build a particle accelerator with today's technology?

• 57:21Lex Fridman?

  Bigger or smaller than, than our solar system?

• 57:24Speaker 01

  As the size of the galaxy.

• 57:26Lex Fridman?

  The galaxy.

• 57:27Speaker 01

  So you'd need to put a particle accelerator that circled the Milky Way to to get to the energies where you would see strings, if they exist. So that is a fundamental problem, which is that most of the predictions of the unified, these unified theories, quantum theories of gravity, only make statements that are testable, energies that we will not be able to probe, and barring some unbelievable, you know, completely unexpected technological or scientific breakthrough, which is almost impossible to imagine. You never, never say never, but it seems very unlikely.

• 57:59Lex Fridman?

  Yeah, I can just see the news story. Elon Musk decides to build particle collider the size of our.

• 58:07Speaker 01

  It would have to be, we'd have to get together with all our galactic neighbors to to pay for it, I think.

• 58:12Lex Fridman?

  What is the exciting possibilities of the Large Hadron Collider? What is there to be discovered in this, in this order of magnitude of scale? Is there other bigger efforts on the horizon in this space? What are the open problems, the exciting possibilities? You mentioned supersymmetry.

• 58:31Speaker 01

  Yeah. So, well, there are lots of new ideas. Well, there are lots of problems that we're facing. So there's a problem with the Higgs field, which supersymmetry was supposed to solve. There's the fact that 95% of the universe, we know from cosmology, astrophysics, is invisible, that it's made of dark matter and dark energy, which are really just words for things that we don't know what they are. It's what Donald Rumsfeld called a known unknown. So we know we don't know what they are.

• 58:56Lex Fridman?

  Well, that's, that's better than unknown, unknown, unknown.

• 58:59Speaker 01

  Yeah, well, there may be some unknown unknowns, but by definition, we don't know what those are. So, yeah.

• 59:04Lex Fridman?

  But, but the, the hope is the, a particle accelerator could help us make sense of dark energy, dark matter. There's still, there's some hope for that?

• 59:14Speaker 01

  There's hope for that. Yeah. So one of the hopes is the LHC could produce a dark matter particle in its collisions. And, you know, it may be that the LHC will still discover new particles, that it might still, supersymmetry could still be there. We just, it's just maybe more difficult to to find than we thought originally. And, and, you know, dark matter. Particles might be being produced, but we're just not looking in the right part of the data for them. That that's possible. It might be that we need more data, that these processes are very rare and we need to collect lots and lots of data before we see them. But I think a lot of people would say now that the chances of the LHC directly discovering new particles in the near future is quite slim.

• 59:54Speaker 01

  It may be that we need a decade more data before we can see something, or we may not see anything. That's the, that's where we are. So, I mean, the physics, the experiments that I work on. So I work on a detector called LHCB, which is one of these four big detectors that are spaced around the ring. And we do slightly different stuff to the big guys. There's two big experiments called Atlas and CMS. Three thousand physicists and scientists and computer scientists on them each. They are the ones that discovered the Higgs and they look for supersymmetry and dark matter and so on. What we look at are standard model particles called B quarks, which depending on your your preferences, either bottom or beauty, we tend to say beauty because it sounds sexy. Sure, for sure.

• 1:00:37Speaker 01

  But these particles are interesting because they, we can make lots of them. We make billions or billions, hundreds of billions of these things. You can therefore measure their properties very precisely. So you can make these really lovely precision measurements. And what we are doing really is a sort of complementary thing to the other big experiments, which is they, if you think of the analogy they often use is, if you imagine you're looking, you're in a jungle and you're looking for an elephant, say. And you are a hunter and you're kind of like, they said, there's the elephant's very rare. You don't know where in the jungle. The jungle's big. So there's two ways you go about this. Either you can go wandering around the jungle and try and find the elephant. The problem is if the elephant, if there's only one elephant and the jungle's big, the chances of running into it are very small.

• 1:01:21Speaker 01

  Or you could look on the ground and see if you see footprints left by the elephant. And if the elephant's moving around, you've got a chance, your better chance maybe of seeing the elephant's footprints. If you see the footprints, you go, okay, there's an elephant. I maybe don't know what kind of elephant it is, but I got a sense there's something out there. So that's sort of what we do. We are the footprint people. We, we are, we're looking for the footprints, the impressions that Quantum fields that we haven't managed to directly create the particle of, the effects these quantum fields have on the ordinary standard model fields that we already know about. So these these B particles, the way they behave can be influenced by the presence of, say, superfields or dark matter fields or whatever you like.

• 1:02:02Speaker 01

  And the way they decay and behave can be altered slightly from what our theory tells us they ought to behave.

• 1:02:08Lex Fridman?

  Got you. And it's easier to collect huge amounts of data on on B quarks.

• 1:02:13Speaker 01

  We get billions and billions of these things. You can make very precise measurements. And the only place really at the LHC or in really in high energy physics at the moment, where there's fairly compelling evidence that there might be something beyond the standard model is in these B, these beauty quarks decays.

• 1:02:32Lex Fridman?

  Just to clarify, which is the difference between the different, the four experiments, for example, that you mentioned, is it the kind of particles that are being collided? Is it the energies which they're collided? What's the fundamental difference between the different experiments?

• 1:02:47Speaker 01

  The collisions are the same. What's different is the design of the detectors. So Atlas and CMS are called, they're called what are called general purpose detectors. And they are basically barrel shaped machines and the collisions happen in the middle of the barrel. And the barrel captures all the particles that go flying out in every direction. So in a sphere effectively that can fly out and it can record all of those particles and.

• 1:03:09Lex Fridman?

  What's the, sorry to be interrupting, but what's the, what's the mechanism of the recording?

• 1:03:14Speaker 01

  Oh, so these detectors, if you've seen pictures of them, they're huge. Like Atlas is 25 meters high and 45 meters long. They're vast machines. Instruments, I guess you should call them really. They are, they're kind of like onions. So they have layers, concentric layers of detectors, different sorts of detectors. So close into the beam pipe, you have what are called, usually made of silicon, they're tracking detectors. So they're little, made of strips of silicon or pixels of silicon. And when a particle goes through the silicon, it gives a little electrical signal. And you get these dots, you know, electrical dots through your detector, which allows you to reconstruct the trajectory of the particle. So that's the middle. And then the outsides of these detectors, you have things called calorimetric.

• 1:03:54Speaker 01

  Emitters which measure the energies of the particles and on the very edge you have things called muon chambers which basically these muon particles which are the heavy version of the electron they are they're like high velocity bullets and they can get right to the edge of the detector so if you see something at the edge that's a muon so that's broadly how they work.

• 1:04:10Lex Fridman?

  And all of that is being recorded.

• 1:04:12Speaker 01

  That's all being fed out to you know computers.

• 1:04:15Lex Fridman?

  That data must be awesome, okay.

• 1:04:17Speaker 01

  So LHCB is different so we because we're looking for these B quarks.

• 1:04:21Lex Fridman?

  Yes.

• 1:04:21Speaker 01

  B quarks tend to be produced along the beam line so in a collision the B quark tend to fly sort of close to the beam pipe so we built a detector that's sort of pyramid cone shaped basically that just looks in one direction so we ignore if you have your collision stuff goes everywhere we ignore all the stuff over here and going off sideways we're just looking in this little region close to the beam pipe where most of these B quarks are made so.

• 1:04:46Lex Fridman?

  Is there a different aspect of the sensors involved in the collection of the B quark trajectories?

• 1:04:54Speaker 01

  There are some differences so one of the differences is that one of the ways you know you've seen a B quark is that B quarks are actually quite long-lived by particle standards so they live for 1.5 trillionths of a second which is if you're if you're a fundamental particle is a very long time because you know the Higgs boson I think lives for about a trillionth of a trillionth of a second or maybe even less than that so these are quite long-lived things and they will actually fly a little distance before they decay so they will fly you know a few centimeters maybe if you're lucky then they'll decay into other stuff so what we need to do in the middle of the detector you want to be able to see you have your place where the protons crash into each other and that produces loads of particles that come flying out so you have loads of lines loads of tracks that point back

• 1:05:37Speaker 01

  to that proton collision and then you're looking for a couple of other tracks maybe two or three that point back to a different place that's maybe a few centimeters away from the proton collision and that's the sign that a little B particle has flown a few centimeters and decayed somewhere else so we need to be able to very accurately resolve the proton collision from the B particle decay so we are the middle of our detector is very sensitive and it gets very close to the collision so you have this really beautiful delicate silicon detector. That sits, I think it's seven millimeters from the beam. And the LHC beam has as much energy as a jumbo jet at takeoff, so it's enough to melt a ton of copper. So you have this furiously powerful thing sitting next to this tiny delicate, you know, silicon sensor.

• 1:06:20Speaker 01

  So those aspects of our detector that are specialized to measure these particular B quarks that we're interested in.

• 1:06:27Lex Fridman?

  And is there, I mean, I remember seeing somewhere that there is some mention of matter and antimatter connected to the B, these beautiful quarks. Is that, what's the connection?

• 1:06:40Lex Fridman?

  Yeah, what's the connection there?

• 1:06:42Speaker 01

  Yeah, so there is a connection, which is that when you produce these B particles, these particles, because you don't see the B quark, you see the thing the B quark is inside. So they're bound up inside what we call beauty particles, where the B quark is joined together with another quark or two, maybe two other quarks, depending on what it is. There are a particular set of these B particles that exhibit this property called oscillation. So if you make, for the sake of argument, a matter version of one of these B particles, as it travels, because of the magic of quantum mechanics, it oscillates backwards and forwards between its matter and antimatter versions. So it does this weird flipping about backwards and forwards.

• 1:07:23Speaker 01

  And what we can use this for is a laboratory for testing the symmetry between matter and antimatter. So if the symmetry between antimatter is precise, it's exact, then we should see these B particles decaying as often as matter as they do as antimatter, because this oscillation should be even. It should spend as much time in each state. But what we actually see is that one of the states it spends more time in, it's more likely to decay in one state than the other. So this gives us a way of testing this fundamental symmetry between matter and antimatter.

• 1:07:56Lex Fridman?

  So what can you, sort of returning to the question before about this fundamental symmetry? It seems like if there's perfect symmetry between. Matter and antimatter, if we have the equal amount of each in our universe, it would just destroy itself. And just like you mentioned, we seem to live in a very unlikely universe where it doesn't destroy itself.

• 1:08:19Speaker 01

  Yeah.

• 1:08:20Lex Fridman?

  So do you have some intuition about why that is?

• 1:08:24Speaker 01

  I mean, well, I'm not a theor- I don't have any particular ideas myself. I mean, I sort of do measurements to try and test these things. But the, I mean, so the terms of the basic problem is that in the Big Bang, if you use the standard model to figure out what ought to have happened, you should have got equal amounts of matter and antimatter made. Because whenever you make a particle in our coll- collisions, for example, when we collide stuff together, you make a particle, you make an antiparticle. They always come together, they always annihilate together. So there's no way of making more matter than antimatter that we've discovered so far. So that means in the Big Bang, you get equal amounts of matter and antimatter. As the universe expands and cools down during the Big Bang, not very long after the Big Bang, I think a few seconds after the Big Bang, you have this event called the Great Annihilation, which is where all the particles and antiparticles smack into each other,

• 1:09:07Speaker 01

  annihilate, turn into light mostly. And you end up with a universe later on. If that was what happened, then the universe we live in today would be black and empty, apart from some photons, that would be it. So there's stuff in the, there is stuff in the universe. It appears to be just made of matter. So there's this big mystery as to where the, how did this happen? And there are various ideas which all involve sort of physics going on in the first trillionth of a second or so of the Big Bang. So it could be that, one possibility is that the Higgs field is somehow implicated in this, that there was this event that took place in the early universe where the Higgs field basically switched on, it acquired its modern value. And when that happened, this caused all the particles to acquire mass

• 1:09:52Speaker 01

  and the universe basically went through a phase transition where you had a hot plasma of massless particles. And then in that plasma, it's almost like a gas turning into droplets of water. You get kind of these little bubbles forming in the universe where the Higgs field has acquired its modern value, the particles have got mass. And this phase transition in some models can cause more matter than antimatter to be Produced depending on how matter bounces off these bubbles in the universe. So that's one idea. There's other ideas to do with neutrinos, that there are exotic types of neutrinos that can decay in a biased way to just matter and not to antimatter. So and people are trying to test these ideas. That's what we're trying to do at LHCB. It's there's neutrino experiments planned that are trying to do these sorts of things as well.

• 1:10:34Speaker 01

  So, yeah, there are ideas, but at the moment, no clear evidence for which of these ideas might be right.

• 1:10:39Lex Fridman?

  So we're talking about some incredible ideas. By the way, never heard anyone be so eloquent about describing even just the standard model. So I'm in awe just listening. Interesting, just have having fun enjoying it. So the, yes, the theoretical, the particle physics is fascinating here. To me, one of the most fascinating things about the Large Hadron Collider is the human side of it, that a bunch of sort of brilliant people that probably have egos got together and were collaborate together and countries, I guess, collaborate together, you know, for the funds and everything, just collaboration everywhere.

• 1:11:19Lex Fridman?

  Could you maybe, I don't know what the right question here to ask, but almost, what's your intuition about how it's possible to make this happen? And what are the lessons we should learn for the future of human civilization in terms of our scientific progress? Because it seems like this is a great, great illustration of us working together to do something big.

• 1:11:41Speaker 01

  Yeah, I think it's possibly the best example maybe I can think of of international collaboration that isn't for some unpleasant purpose, basically, you know. It's, I mean, so I, when I started out in the field in 2008, I, as a new PhD student, the LHC was basically finished. So I didn't have to go around asking for money for it or trying to make the case. So I have huge admiration for the people who managed that. Because this was a project that was first imagined in the 1970s. In the late 70s was when the first conversations about the LHC were mooted. And it took two and a half decades of campaigning and fundraising and persuasion until they started breaking ground and building the thing in the early 90s and 2000. So.

• 1:12:26Speaker 01

  I mean, I think the reason, just from a sort of, from the point of view of the sort of science, the scientists there, I think the reason it works ultimately is that everywhere, everyone there is there for the same reason, which is, well, in principle at least, they're there because they're interested in the world. They want to find out, you know, what are the basic ingredients of our universe? What are the laws of nature? And so everyone is pulling in the same direction. Now, of course, everyone has their own things they're interested in, everyone has their own careers to consider and, you know, I wouldn't pretend that there isn't also a lot of competition. So there's this funny thing in these experiments where your collaborators, your eight hundred collaborators in LHCB, but you're also competitors because your academics in your various universities and you want to be the one that gets the paper out on the most exciting, you know, new measurements. So there's this funny thing

• 1:13:11Speaker 01

  where you're kind of trying to stake out your territory while also collaborating and having to work together to make the experiments work. And it does work amazingly well, actually, considering all of that. And I think there was actually, I think McKinsey or one of these big management consultancy firms went into CERN, maybe a decade or so ago, to try to understand how these organizations function.

• 1:13:31Lex Fridman?

  Did they figure it out?

• 1:13:32Speaker 01

  I don't think they could. I mean, I think one of the things is, so one of the other interesting things about these experiments is, you know, they're big operations, like, say Atlas is three thousand people. Now, there was a person nominally who is the head of Atlas, they're called the spokesperson. And the spokesperson is elected by, usually by the collaboration, but they have no actual power, really. I mean, they can't fire anyone. They're not anyone's boss. So, you know, my boss is a professor, is a professor at Cambridge, not the head of my experiments. The head of my experiment can't tell me what to do, really. And there's all, you've got these independent academics who are their own bosses, who, you know, so that somehow, nonetheless, by kind of consensus and discussion and lots

• 1:14:14Speaker 01

  of meetings, these, you know, things do happen and it does get done, but.

• 1:14:18Lex Fridman?

  It's like the queen here in the UK is the spokesperson.

• 1:14:21Speaker 01

  I guess so.

• 1:14:22Lex Fridman?

  No actual power.

• 1:14:23Speaker 01

  Except we don't elect her, no.

• 1:14:24Lex Fridman?

  No, they don't elect her. But ever, everybody seems to love her. I don't, I don't know, from the, my outside perspective.

• 1:14:33Lex Fridman?

  But yeah, giant egos, brilliant people. And moving forward, do you think there's?

• 1:14:39Speaker 01

  Actually, I would pick up on one thing you said, just the brilliant people thing. Because I'm not saying that people aren't great.

• 1:14:44Lex Fridman?

  Yeah.

• 1:14:45Speaker 01

  But I think there is this sort of impression that physicists all have to be brilliant or geniuses, which is not true, actually. And you have to be relatively bright, for sure. But a lot of people, a lot of the most successful experimental physicists are not necessarily the people with the biggest brains. They're the people who, particularly, one of the skills that's most important in particle physics is the ability to work with others and to collaborate and exchange ideas, and also to work hard. And it's a sort of, often it's more a determination or a sort of other set of skills. It's not just being kind of some great brain.

• 1:15:18Lex Fridman?

  Very true. So I mean, there's parallels to that in the machine learning world. If you want to solve any real world problems, which I see as the particle accelerator is essentially a real world instantiation of theoretical physics. And for that, you have to not necessarily be brilliant, but be sort of obsessed, systematic, rigorous, sort of unbearable, stubborn, all those kind of qualities that make for a great engineer. So scientists, purely speaking, that practitioner of the scientific method. So you're right. But nevertheless, to me, that's brilliant. My dad's a physicist. I argue with him all the time.

• 1:16:00Lex Fridman?

  To me, engineering is the highest form of science, and he thinks that's all nonsense, that the real work is done by the theoretician. So in fact, we have arguments about people like Elon Musk, for example, because I think his work is quite brilliant, but he's fundamentally not coming up with any serious breakthroughs. He's just creating in this world, implementing, like making ideas happen that have a huge impact. To me, that is, that's the Edison.

• 1:16:30Lex Fridman?

  That to me is is a brilliant work, but to him, it's, you know, it's messy details that somebody will figure out anyway.

• 1:16:42Speaker 01

  I mean, I don't know whether you think there is a actual difference in temperament between, say, a physicist and engineer, whether it's just what you got interested in. I don't know. I mean, because, you know, a lot of what experimental physicists do is, to some extent, engineering. I mean, it's not what I do. I mostly do data stuff, but, you know, a lot of people would be called electrical engineers, but they trained as physicists, but they learned electrical engineering, for example, because they were building detectors. So there's not such a clear divide, I think.

• 1:17:09Lex Fridman?

  Yeah, it's interesting. I mean, but there does seem to be like you work with data. There does seem to be a certain, like, I love data collection. There might be an OCD element or something that you're more naturally predisposed to as opposed to theory. Like, I'm not afraid of data. I love data. And there's a lot of people in machine learning who are more like, they're basically afraid of data collection, afraid of data sets, afraid of all of that. They just want to stay in more of the theoretical, and they're really good at it space. I don't know if that's a genetic, that's your upbringing, the way you, the way you go to school. But looking into the future of LHC and other colliders.

• 1:17:50Lex Fridman?

  So there's in America, there's the, whatever it was called, the super, there's a lot of super.

• 1:17:55Speaker 01

  Superconducting supercollider.

• 1:17:56Lex Fridman?

  Yeah, superconducting.

• 1:17:57Speaker 01

  The desatron, yeah.

• 1:17:58Lex Fridman?

  Desatron.

• 1:17:59Speaker 01

  Yeah.

• 1:17:59Lex Fridman?

  So that was canceled, the construction of that.

• 1:18:02Speaker 01

  Yeah.

• 1:18:05Lex Fridman?

  Which is a sad thing. But what do you think is the future of these efforts? Will a bigger collider be built? Will LHC be expanded? What do you think?

• 1:18:16Speaker 01

  Well, in the near future, the LHC is going to get an upgrade. So that's pretty much confirmed. I think it is confirmed. Which is, it's not an energy upgrade. It's what we call a luminosity upgrade. So it basically means increasing the data collection rate. So more collisions per second, basically. Because after a few years of data taking, you get this law of diminishing returns, where each year's worth of data is a smaller and smaller fraction of the lot. You've already got. So to get a real improvement in sensitivity, you need to increase the data rate by an order of magnitude. So that's what this upgrade is going to do. And LHCB, at the moment, the whole detector is basically being rebuilt to allow it to record data at a much larger rate than we could before. So that will make us sensitive to whole loads of new processes that we weren't able to study before.

• 1:18:59Speaker 01

  And, you know, I mentioned briefly these anomalies that we've seen. So we've seen a bunch of very intriguing anomalies in these B quark decays, which may be hinting at the first signs of this kind of the elephant, you know, that the signs of some new quantum field or fields maybe beyond the standard model. It's not yet at the statistical threshold where you can say that you've observed something. But there's lots of anomalies in many measurements that all seem to be consistent with each other. So it's quite interesting. So, you know, the upgrade will allow us to really home in on these things and see whether these anomalies are real. Because if they are real, and this kind of connects to your point about the next generation of machines.

• 1:19:40Speaker 01

  What we would have seen then is, you know, we would have seen the tail end of some quantum field influencing these B quarks. What we then need to do is to build a bigger collider to actually make the particle of that field. So if these things really do exist. So that would be one argument. I mean, so at the moment, Europe is going through this process of thinking about the strategy for the future. So there are a number of different proposals on the table. One is for a sort of higher energy upgrade of the LHC, where you just build more powerful magnets and put them in the same tunnel. That's a sort of cheaper, less ambitious possibility. Most people don't really like it because it's sort of a bit of a dead end. Because once you've done that, there's nowhere to go. There's a machine called Click, which is a compact linear collider,

• 1:20:25Speaker 01

  which is an electron positron collider that uses a novel type of acceleration technology to accelerate at shorter distances. We're still talking kilometers long, but not like 100 kilometers long. And then probably the project that is, I think, getting the most support, it'll be interesting to see what happens, something called the Future Circular Collider. Which is a really ambitious, long-term, multi-decade project to build a 100-kilometer circumference tunnel under the Geneva region. The LHC would become a kind of feeding machine. It would just feed.

• 1:20:58Lex Fridman?

  So the same area, so it would be a feeder for the?

• 1:21:00Speaker 01

  Yeah, so it would kind of, the edge of this machine would be where the LHC is, but it would sort of go under Lake Geneva and round to the Alps, basically, since, you know, up to the edge of the Geneva Basin. So it's basically the biggest, it's the biggest tunnel you can fit in the region, based on the geology.

• 1:21:14Lex Fridman?

  Kilometers.

• 1:21:14Speaker 01

  Yeah, so it's big. It'd be a long drive if you're, you know, you're making experiments on one side, you've got to go back to CERN for lunch, so that would be a pain. But, you know, so this project is, in principle, is actually two accelerators. The first thing you would do is put an electron-positron machine in the 100-kilometer tunnel to study the Higgs. So you'd make lots of Higgs bosons, study it really precisely, in the hope that you see it misbehaving and doing something it's not supposed to. And then, in the much longer term, 100, that machine gets taken out, you put in a proton-proton machine, so it's like the LHC but much bigger. And that's the way you start going and looking for dark matter, or you're trying to recreate this phase transition that I talked about in the early universe, where you can see matter/anti-matter being made, for example. So there's lots

• 1:21:56Speaker 01

  of things you can do with these machines. The problem is that they will take, you know, the most optimistic, you're not going to have any data from any of these machines until 2040, or, you know, because they take such a long time to build and they're so expensive. So you'll have, there'll be a process of R&D design, but also the political case being made.

• 1:22:14Lex Fridman?

  So LHC, what, costs a few billion?

• 1:22:18Speaker 01

  Depends how you count it. I think most of the sort of more reasonable estimates that take everything into account properly, it's around the sort of 10, 11, 12 billion euro mark.

• 1:22:27Lex Fridman?

  What would be the future, sorry, I forgot the name already?

• 1:22:30Speaker 01

  Future Circular Collider.

• 1:22:31Lex Fridman?

  Future Circular?

• 1:22:32Speaker 01

  Presumably they won't call it that when it's built, because it won't be the future anymore, but I don't know what they'll call it then.

• 1:22:39Speaker 01

  Very big Hadron Collider, I don't know, but that will, now I should know the numbers, but I think the whole project is estimated at about thirty billion euros, but that's money spent over between now and twenty seventy probably, which is when the last bit of it would be sort of finishing up, I guess. So you're talking a half a century of science coming out of this thing, shared by many countries. So the actual cost, the arguments that are made is that you could make this project fit within the existing budget of CERN, if you didn't do anything else.

• 1:23:14Lex Fridman?

  And CERN, by the way, we didn't mention, what is CERN?

• 1:23:17Speaker 01

  CERN is the European Organisation for Nuclear Research. It's an international organisation that was established in the nineteen fifty's in the wake of the Second World War as a kind of, it was sort of like a scientific Marshall Plan for Europe. The idea was that you bring European science back together for peaceful purposes, because what happened in the forty's was, you know, a lot of particularly a lot of Jewish scientists, but a lot of scientists from Central Europe had fled to the United States, and Europe had sort of seen this brain drain. So there was a desire to bring the community back together for a project that wasn't building nasty bombs, but was doing something that was curiosity driven. So, and that has continued since then. So it's kind of a unique organisation. It's you, to be a member as a country, you sort of sign up as a member, and then you

• 1:24:00Speaker 01

  have to pay a fraction of your GEP each year as a subscription. I mean, it's a very small fraction, relatively speaking. I think it's like, I think the UK's contribution is hundred or two hundred million quid, or something like that a year, which is quite a lot, but not, not, not.

• 1:24:14Lex Fridman?

  That's fascinating. I mean, just the whole thing that it is possible, it's beautiful, it's a beautiful idea, especially when there's no wars on the line. It's not like we're freaking out, as we're actually legitimately collaborating to do good science. One of the things I don't think we really mentioned is on the final side, that's sort of the data analysis side. Is there breakthroughs possible there? And the machine learning side, like, is there? Is there a lot more signal to be mined in more effective ways from the actual raw data?

• 1:24:42Speaker 01

  Yeah, a lot of people are looking into that. I mean, so, you know, I use machine learning in my data analysis, but pretty noddy, you know, basic stuff because I'm not a machine learning expert. I'm just a physicist who had to learn to do this stuff for my day job. So what a lot of people do is they use kind of off the shelf packages that you can train to do signal noise, you know.

• 1:25:03Lex Fridman?

  Just clean up all the data.

• 1:25:04Speaker 01

  Yeah, but one of the big challenges, you know, the big challenge of the data is A, it's volume, there's huge amounts of data. So the LHC generates, now, okay, I try to remember what the actual numbers are, but if you, we don't record all our data, we record a tiny fraction of the data. It's like of order one ten thousandth or something, I think. Is that right? Around that. So it's, most of it gets thrown away. You couldn't record all the LHC data because it would fill up every computer in the world in a matter of days, basically. So there's this process that happens on live on the detector, something called a trigger, which in real time, forty million times every second, has to make a decision about whether this collision is likely to contain an interesting object like a pig's boson or a dark matter

• 1:25:44Speaker 01

  particle. And it has to do that very fast. And the software algorithms in the past were quite relatively basic, you know, they did things like measure mementas and energies of particles and put some requirements. So you would say, if there's a particle with an energy above some threshold, then record this collision, but if there isn't, don't. Whereas now the attempt is to get more and more machine learning in at the earliest possible stage because.

• 1:26:08Lex Fridman?

  That's cool. At the stage of deciding whether we want to keep this data or not.

• 1:26:12Speaker 01

  But also even, even maybe even lower down than that, which is the point where there's this, you know, so generally how the data is reconstructed is you start off with a digital, a set of digital hits in your detector. So channels saying, did you see something? Did you not see something? That has to be then turned into tracks, particles going in different directions. And that's done by using fits that fit through the data points. And then that's passed to the algorithms that then go, is this interesting or not? What would be better is if you could train machine learning to just look at the raw hits, the basic, real base level information, not have any of the reconstruction done, and it just goes. Goes and it can learn to do pattern recognition on this strange three dimensional image that you get. And potentially that's where you could get really big gains because our triggers tend to be quite inefficient because they

• 1:26:56Speaker 01

  don't have time to do the full whiz bang processing to get all the information out that we would like. Because you have to do the decision very quickly. So if you can come up with some clever machine learning technique, then potentially you can massively increase the amount of useful data you record and you know, get rid of more of the background earlier in the process.

• 1:27:16Lex Fridman?

  Yeah, to me, that's an exciting possibility because then you don't have to build a sort of, you can get a gain without having to.

• 1:27:25Speaker 01

  Without having to build any hardware, I suppose.

• 1:27:27Lex Fridman?

  Hardware, yeah.

• 1:27:27Speaker 01

  Although you'll need, you'll need lots of new GPU farms, I guess.

• 1:27:30Lex Fridman?

  So hardware still helps, but uh, the, you know, I gotta talk to you. Sort of, I'm not sure how to ask, but you're clearly an incredible science communicator. I don't know if that's the right term. But you're basically a younger Neil deGrasse Tyson with a British accent. So, and you've, I mean, can you say where we are today, actually?

• 1:27:56Speaker 01

  Yeah, so today we're in the Royal Institution in London, which is an old, a very old organization. It's been around for about 200 years now, I think, maybe even, I should know when it was founded, but sort of early 19th century. It was set up to basically communicate science to the public. So it was one of the first places in the world where scientists, famous scientists would come and give talks. So very famously Humphry Davy, who you may know of, who was the person who discovered nitrous oxide. He was a very famous chemist and scientist, also discovered electrolysis. So he used to do these fantastic, he was a very charismatic speaker. So he used to appear here. There was a, there's a big desk that they usually have in the, in the theater and he would do demonstrations to the sort of the, the folk of London back in the early 19th century.

• 1:28:40Speaker 01

  And Michael Faraday, who I talked about, who was the person who did so much work on electromagnism, he used, he lectured here. He also did experiments in the basement. So this place has got a long history of both scientific research, but also

• 1:28:50Lex Fridman?

  And the communication.

• 1:28:51Speaker 01

  Communication of scientific research.

• 1:28:52Lex Fridman?

  So you gave a few lectures here, how many, two?

• 1:28:56Speaker 01

  I've given, yeah, I've given a couple of lectures in this theater before, so.

• 1:28:59Lex Fridman?

  I mean, that's, so people should definitely go watch online. It's just the explanation of particle physics, all the, I mean, it's incredible. Like your, your lectures are just incredible. I can't sing it enough praise. So it was awesome. But maybe, can you say?

• 1:29:15Lex Fridman?

  What did that feel like? What does it feel like to lecture here to talk about that? And maybe from a different perspective, more kind of like how the sausage is made is, how do you prepare for that kind of thing? How do you think about communication? The process of communicating these ideas in a way that's inspiring to what I would say, your talks are inspiring to like the general audience. You don't actually have to be a scientist. You can still be inspired without really knowing much of the, you start from the very basics. So what's the preparation process? And then the romantic question is, what did that feel like to perform here?

• 1:29:54Speaker 01

  I mean, profession, yeah. I mean, the process, I mean, the talk, my favorite talk that I gave here was one called Beyond the Higgs, which you can find on the Royal Institute's YouTube channel, which you should go and check out. I mean, and their channel's got loads of great talks for loads of great people as well. I mean, that one, I'd sort of given a version of it many times. So part of it is just practice, right? And actually, I don't have some great theory of how to communicate with people. It's more just that I'm really interested and excited by those ideas and I like talking about them. And through the process of doing that, I guess I figured out stories that work and explanations that work.

• 1:30:27Lex Fridman?

  When you say practice, you mean legitimately just giving?

• 1:30:30Speaker 01

  Just giving talks. I started off, you know, when I was a PhD student, doing talks in schools. And I still do that as well some of the time and doing things. I've even done a bit of standup comedy, which was sort of went reasonably well, even if it was terrifying.

• 1:30:43Lex Fridman?

  And that's on YouTube as well.

• 1:30:44Speaker 01

  That's also on you. I wouldn't necessarily recommend you check that out.

• 1:30:48Lex Fridman?

  I'm going to post the links several places to make sure people click on it.

• 1:30:52Speaker 01

  But it's basically, I kind of have a story in my head and I, you know, I kind of, I have to think about what I want to say. I usually have some images to support what I'm saying and I get up and do it. And it's not really, I wish there was some kind of, I probably should have some proper process. This is probably sounds like I'm just making up as I go along and I sort of am.

• 1:31:09Lex Fridman?

  Well, I think the fundamental thing that you said, I think. It's like, I don't know if you know who a guy named Joe Rogan is?

• 1:31:18Speaker 01

  Yes, I do.

• 1:31:19Lex Fridman?

  So he's also kind of sounds like you in a sense that he's not very introspective about his process, but he's an incredibly engaging conversationalist. And I think one of the things that you and him share that I could see is like a genuine curiosity and passion for the topic. I think that could be systematically cultivated. I'm sure there's a process to it, but you come to it naturally somehow.

• 1:31:47Speaker 01

  I think maybe there's something else as well, which is to understand something. There's this quote by Feynman, which I really like, which is what I cannot create, I do not understand. So like, I'm not, I'm not particularly super bright. Like, so for me to understand something, I have to break it down into its simplest elements. And that, you know, and if I can then tell people about that, that helps me understand it as well. So I've actually, I've learned, I've learned to understand physics a lot more from the process of communication. Because it forces you to really scrutinize the ideas that you're communicating. Again, it often makes you realize you don't really understand the ideas you're talking about. And I'm writing a book at the moment. And I had this experience yesterday where I realized I didn't really understand a pretty fundamental theoretical aspect of my own subject.

• 1:32:31Speaker 01

  And I had to go and I had to sort of spend a couple of days reading textbooks and thinking about it in order to make sure that the explanation I gave captured the, got as close to what is actually happening in the theory. And to do that, you have to really understand it properly.

• 1:32:45Lex Fridman?

  And there's layers to understanding. Like, it seems like the more, there must be some kind of Feynman law. I mean, the more you, the more you understand, sort of the simpler you're able to really convey the, you know, the essence of the idea, right? So it's like this reverse, reverse effect that it's like, the more you understand, the simpler the final thing that you actually convey. And so the more accessible somehow it becomes. That's why Feynman's lectures are really accessible. It was just counterintuitive.

• 1:33:21Speaker 01

  Yeah, although there are some ideas that.

• 1:33:25Speaker 01

  Are very difficult to explain, no matter how well or badly you understand them. Like, I still can't really properly explain the Higgs mechanism.

• 1:33:33Lex Fridman?

  Yeah.

• 1:33:33Speaker 01

  With, because some of these ideas only exist in mathematics, really. And the only way to really develop an understanding is to go, unfortunately, to a graduate degree in physics. But you can get kind of a flavor of what's happening, I think. And it's trying to do that in a way that isn't misleading, but was also intelligible.

• 1:33:53Lex Fridman?

  So let me ask them the romantic question of, what do you is the most, perhaps an unfair question? What is the most beautiful idea in physics? One that fills you with awe, is the most surprising, the strangest, the weirdest? There's a lot of different definitions of beauty. And I'm sure there's several for you, but is there something that just jumps to mind that you think is just especially?

• 1:34:21Speaker 01

  I mean, I, well.

• 1:34:23Lex Fridman?

  Beautiful.

• 1:34:23Speaker 01

  There's a specific thing and a more general thing. So maybe the specific thing first, which is, when I first came across this as an undergraduate, I found this amazing. So this idea that the forces of nature, electromagnetism, the strong force, the weak force, they arise in our theories as a consequence of symmetries. So symmetries in the laws of nature, in the equations, essentially, that you use to describe these ideas.

• 1:34:49Speaker 01

  The process whereby theories come up with these sorts of models is they say, imagine the universe obeys this particular type of symmetry. It's a symmetry that isn't so far removed from a geometrical symmetry, like the rotations of a cube. It's not, you can't think of it quite that way, but it's sort of a similar sort of idea. And you say, okay, if the universe respects this symmetry, you find that you have to introduce a force which has the properties of electromagnetism. Or a different symmetry, you get the strong force, or a different symmetry, you get the weak force. So these interactions seem to come from some deeper, it suggests that they come from some deeper symmetry principle. I mean, depends a bit how you look at it, because it could be that we're actually just recognizing symmetries in the things that we see. But there's something rather lovely about that. But I mean, I suppose a bigger thing that makes me wonder is actually.

• 1:35:35Speaker 01

  If you look at the laws of nature, you look at how particles interact when you get really close down, they're basically pretty simple things. They bounce off each other by exchanging through force fields and they move around in very simple ways. And somehow, these basic ingredients, these few particles that we know about and the forces creates this universe which is unbelievably complicated and has things like you and me in it and the earth and stars that make matter in their cores by from the gravitational energy of their own bulk that then gets sprayed into the universe that forms other things. I mean, the fact that there's this incredibly long story that goes right back to, we can take this story right back to a trillionth of a second after the big bang. We can trace the origins of the stuff that we're made from. And it all ultimately comes from these

• 1:36:20Speaker 01

  simple ingredients with these simple rules. And the fact you can generate such complexity from that is really mysterious, I think, and strange. And it's not even a question that physicists can really tackle because we are sort of trying to find these really elementary laws. But it turns out that going from elementary laws and a few particles to something even as complicated as a molecule becomes very difficult. So going from a molecule to a human being is a problem that just can't be tackled, at least not at the moment. So...

• 1:36:50Lex Fridman?

  Yeah, the emergence of complexity from simple rules is so beautiful and so mysterious. We don't have good mathematics to even try to approach that emergent phenomenon.

• 1:37:03Speaker 01

  That's why we have chemistry and biology and all the other subjects.

• 1:37:08Lex Fridman?

  I don't think there's a better way to end it, Harry. I can't. I mean, I think I speak for a lot of people that can't wait to see what happens in the next five, 10, 20 years with you. I think you're one of the great communicators of our time. So I hope you continue that and I hope that grows. And I'm definitely a huge fan. So it was an honor to talk to you today. Thanks so much.

• 1:37:31Speaker 01

  Thanks very much.

• 1:37:33Lex Fridman?

  Thanks for listening to this conversation with Harry Cliff. And thank you to our sponsors, ExpressVPN and Cash App. Please consider supporting the podcast by getting ExpressVPN at expressvpn.com/lexpod and downloading Cash App and using code LexPodcast. If you enjoy this podcast, subscribe on YouTube, review it with five stars on Apple Podcasts, support it on Patreon, or simply connect with me on Twitter at LexFriedman.

• 1:38:02Lex Fridman?

  And now, let me leave you with some words from Harry Clift. "You and I are leftovers. Every particle in our bodies is a survivor from an almighty shootout between matter and antimatter that happened a little after the Big Bang. In fact, only one in a billion particles created at the beginning of time have survived to the present day." Thank you for listening and hope to see you next time.