Lex Fridman PodcastHarry Cliff: Particle Physics and the Large Hadron Collider | Lex Fridman Podcast #92
EVERY SPOKEN WORD
150 min read · 30,156 words- 0:00 – 3:51
Introduction
- LFLex Fridman
The following is a conversation with Harry Cliffe, 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. 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, @LexFridman, spelled F-R-I-D-M-A-N. As usual, I'll do a few minutes of ads now, 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 that works behind the scenes to create the abstraction of the fractional orders is an algorithmic marvel. So big props to the Cash App engineers for solving a hard problem that, in the end, provides an easy interface that takes a step up to the next layer of abstraction over the stock market, making trading more accessible for new investors and diversification much easier. So again, you get Cash App from the App Store or Google Play and use the code LEXPODCAST, you get $10 and Cash App will also donate $10 to FIRST, an organization that is helping advance robotics and STEM education for young people around the world. This show is sponsored by ExpressVPN. 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. 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.
- 3:51 – 13:55
LHC and particle physics
- LFLex 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?
- HCHarry Cliff
Okay. So it's essentially this gigantic, 27 kilometer circumference particle accelerator. It's this big ring. It's buried a hun- 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, and the analogy is actually fairly precise. So-
- LFLex Fridman
Gigantic microscope.
- HCHarry Cliff
Microscope. Effectively. Uh, except it's a microscope that looks at the structure of the vacuum.
- LFLex Fridman
In order for this kind of thing to study particles, uh, which are these mi- microscopic entities, it has to be huge.
- HCHarry Cliff
Yes.
- LFLex Fridman
So it's a gigantic microscope. So what do you mean by, "Studying vacuum?"
- HCHarry Cliff
Okay. So, I mean, so particle physics as a, 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, uh, like the magnetic field around a magnet that exist everywhere in space. They're always there. In fact, actually, it's funny that we're in the Royal Institution 'cause 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, if he... Well, it's a very famous, uh, experiment that he did, where he got a magnet and put it, on top of it, a piece of paper, and then sprinkled iron filings. And he found the iron filings arranged themselves into these kind of loops, uh, of, of, uh, 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 and, or two poles of a magnet and pushed them together and felt this thing, this force, pushing back. So these are real, physical objects. And, uh, 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.
- LFLex Fridman
You know, I, I don't, uh, I apologize perhaps for the ridiculous question. Are you comfortable with the idea of the fundamental nature of our reality being fields? 'Cause to me, particles, you know, uh, a bunch of different building blocks makes more sense sort of intellectually, sort of visually. Like it's-
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
... it seems to, uh, I, I seem to be able to visualize that kind of idea easier.
- HCHarry Cliff
Yeah.
- LFLex Fridman
Are you comfortable, psychologically, with the idea that the basic building block is not a block, but a field?
- HCHarry Cliff
I think it's, um, I think it's quite a magical idea. I find it quite appealing. And it, 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. Um, it's this spread out, wibbly-wobbly, wave-like thing. And we know, we've known that since, you know, the, the early 20th century thanks to quantum mechanics. So when we, 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? So in the LHC, when we collide particles together, you'll get, you know, you'll get like, uh, hundreds of particles all flying out through the detector, and they all take a, 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, um, 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. Um, 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.
- LFLex Fridman
(inhales deeply) And, uh, what, what is the story of the vacuum when it comes to LHC?
- HCHarry Cliff
I-
- LFLex Fridman
So why, why did you mention the word vacuum?
- HCHarry Cliff
Okay, so if we just, if we go back to like the physics we do know.
- LFLex Fridman
Yeah.
- HCHarry Cliff
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's 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. Now, there are potentially, we, 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, the Higgs field that we believe is the reason that electrons and quarks have mass. 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.
- LFLex Fridman
So the Large Hadron Collider, uh, in order to get that ripple in the Higgs field, you, it requires a huge amount of energy-
- HCHarry Cliff
Yeah.
- LFLex Fridman
... I suppose. And so that's why you need this huge ... That's why size matters here. So maybe there's a million questions here, but let's backtrack. Why does size matter in the context of a g- (laughs) of a particle collider? So why, um, does bigger allow you for higher energy collisions?
- HCHarry Cliff
Right, so the reason ... Well, it, 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.
- LFLex Fridman
Mm-hmm.
- HCHarry Cliff
So the advantage of, uh, 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 two million volt electric fields inside them-
- LFLex Fridman
Mm-hmm.
- HCHarry Cliff
... 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, the proton gets attracted then kicked out the other side, so it gets a bit faster. So you send it, but then you send it back around again and-
- LFLex Fridman
That's incredible, like the timing of that, the synchronization. Wait, really?
- HCHarry Cliff
Yeah. Yeah, yeah, yeah.
- 13:55 – 38:59
History of particle physics
- LFLex Fridman
maybe c- can we backtrack to the-
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
... standard model and-
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
... say what kind of particles there are, period?
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
And, uh, maybe the history of kind of assembling that, uh, the standard model of physics and then how that leads up to the hopes and dreams and the accomplishments of the Large Hadron Collider?
- HCHarry Cliff
Yeah, sure. Okay. So-
- LFLex Fridman
(laughs)
- HCHarry Cliff
... sp- all of 20th century physics in like five minutes. Let's try.
- LFLex Fridman
Yeah, please.
- HCHarry Cliff
So, 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.
- LFLex Fridman
Yeah.
- HCHarry Cliff
Um, 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, I'm still, uh, where I'm based, uh, showed that there are actually smaller particles inside the atom, which eventually became known as electrons. These are these negatively charged things that go round the outside. A few years later, Ernest Rutherford, very famous nuclear phys- one of the pioneers 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-
- LFLex Fridman
Mm-hmm.
- HCHarry Cliff
... as, 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. 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, we've got three particles, we know what the atoms are made of, that's fine. But then, uh, s- cloud chamber experiments, so 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. And in these, uh, 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. An- 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.
- LFLex Fridman
Are these discoveries on the first, uh, theoretical discoveries or are they discoveries in, in experiment? So like-
- HCHarry Cliff
E- yeah.
- LFLex Fridman
... wha- yeah, wha- what's the process of discovery for these early sets of-
- HCHarry Cliff
It- it's-
- LFLex Fridman
... of particles.
- HCHarry Cliff
... it's a mixture. I mean, the, the early stuff around the atom is really experimentally driven. It's not based on some theory. It, 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 antielectron, the positron, that was predicted from quantum mechanics and relativity by a very, uh, clever theoretical physicist called Paul Dirac-
- LFLex Fridman
Mm-hmm.
- HCHarry Cliff
... who was probably the second brightest, you know, physicist of the 20th century apart from Einstein, but isn't as w- anywhere near as well known. So he predicted the existence of the antielectron from basically a combination of the theories of quantum mechanics and relativity, and it was discovered about a year after he made the prediction.
- LFLex Fridman
What happens when an e- when an electron meets a positron?
- HCHarry Cliff
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.
- LFLex Fridman
So, um-When you have tha- that kinda situation, why, why does the universe exist at all if there's matter and antimatter?
- HCHarry Cliff
Oh God, now we're getting into the really big questions. So... (laughs)
- LFLex Fridman
K- Maybe-
- HCHarry Cliff
Depends if you... Do you wanna go there now? I mean-
- 38:59 – 57:55
Higgs particle
- HCHarry Cliff
- LFLex Fridman
So tha- so first of all, it started, uh, as a theoretical notion. Like this is some-
- HCHarry Cliff
Yeah.
- LFLex Fridman
... and then, I mean, wasn't the Higgs called the God particle at some point?
- HCHarry Cliff
It was, by a guy trying to sell popular science books, yeah. Yeah.
- LFLex Fridman
Yeah, but I mean-
- HCHarry Cliff
(laughs)
- LFLex Fridman
I mean, I remember 'cause, uh, when I was hearing it, I thought it would, um, I mean, that would solve a lot of the, unify a lot of our ideas of physics-
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
... is was was my notion. But, um, maybe you can speak to that. Was-
- HCHarry Cliff
Yeah.
- LFLex Fridman
Is it as big of a leap, is it as, is it a God particle or is it a Jesus particle?
- HCHarry Cliff
(laughs)
- LFLex Fridman
Which, uh, which, you know, what's the big contribution of Higgs in terms of this unification power?
- HCHarry Cliff
Yeah. I mean, to understand that, I, it maybe helps to know the history a little bit. So when the, what we call electroweak theory was put together, which is where you unify electromagnetism with the weak force, and the 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+ boson, the W- 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 1983, '84, the Ws and the Z particles were discovered at an accelerator at CERN called the Super Proton Synchrotron, which was a seven kilometer particle collider. So three of the bits of this theory had already been found, so people were pretty confident from the '80s 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 this question about why is the LHC the size it is-
- LFLex Fridman
Yes.
- HCHarry Cliff
... well actually, the tunnel that the LHC is in was not built for the LHC. It was built from a, for a previous accelerator called the Large Electron Positron Collider. So that f- that was b- began operation in the late '80s, early '90s. Um, they basically, they, that's when they dug the 27 kilometer tunnel and they put this accelerator into it, 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. That was one of the things it was trying to do, but didn't, man, 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 could only make a few of them at the previous accelerator. So you can, 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 '70s a- and really make sure that it worked. So actually by 1999, 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, the Higgs or something very like the Higgs had to exist, 'cause 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-
- LFLex Fridman
Is missing.
- HCHarry Cliff
... is not there. So in a way, it depends how you look at it. The discovery of the Higgs on its own, um, 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-
- LFLex Fridman
Yeah.
- HCHarry Cliff
... kind of know that that piece-
- LFLex Fridman
(laughs)
- HCHarry Cliff
... must be there somewhere, right?
- LFLex Fridman
Yeah.
- HCHarry Cliff
So if-
- LFLex Fridman
(laughs)
- HCHarry Cliff
So the discovery in itself, although it's important, is not so interesting in that sense.
- LFLex Fridman
It's like a confirmation of the obvious-
- HCHarry Cliff
Confirmation. Yeah.
- LFLex Fridman
... at th- at th- at that point.
- 57:55 – 59:48
Unknowns yet to be discovered
- HCHarry Cliff
- LFLex 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?
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
Is there other bigger efforts on the horizon, like, in this space, what are, what are the open problems, the exciting possibilities? You mentioned supersymmetry.
- HCHarry Cliff
Yeah. So, well there, 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, was supposed to solve. Um, there's the fact that 95% of the universe, we know from cosmology and 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.
- LFLex Fridman
Uh-huh.
- HCHarry Cliff
It's what Donald Rumsfeld called the known unknown.
- LFLex Fridman
(laughs)
- HCHarry Cliff
So we, we know we don't know what they are.
- LFLex Fridman
Well, that's, it's better than an unk- unknown unknown.
- HCHarry Cliff
Yeah, well, there may be some unknown unknowns, but by-
- LFLex Fridman
Within that...
- HCHarry Cliff
... definition, we don't know what those are. (laughs) So, yeah.
- LFLex Fridman
But, but, uh, the, the hope is the, uh, uh, a particle, um, accelerator could help us make sense of dark energy, dark matter? There's still, there's, uh, some hope for that?
- HCHarry Cliff
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, uh, 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 m- a lot of people would say now that, um, the chances of the LHC directly discovering new particles in the near future is quite slim. It may be that we need a decade more data before we can see something. Or we may not see anything.
- LFLex Fridman
Mm-hmm.
- HCHarry Cliff
That's the, that's where we are. So, I mean, the, the, the physics, the experiments that
- 59:48 – 1:07:38
Beauty quarks
- HCHarry Cliff
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, uh, the big guys. There's two big experiments called ATLAS and CMS, uh, 3,000 physicists and scientists and computer scientists on them each. They're 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 preference is either bottom or beauty. We tend to say beauty-
- LFLex Fridman
Beauty, yeah.
- HCHarry Cliff
... because it sounds sexier.
- LFLex Fridman
For sure.
- HCHarry Cliff
Yeah.
- LFLex Fridman
For sure.
- HCHarry Cliff
Um, but these particles, um, are interesting because they, uh, we can make lots of them, we make billions, or billy- 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, the sort of analogy they'll often use is if you imagine you're looking in, you're in a jungle and you're looking for, um, an elephant, say.
- LFLex Fridman
Mm-hmm.
- HCHarry Cliff
And you are a hunter, and you're kind of like... Let's say 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'd 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. 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 that, you've got a 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-
- LFLex Fridman
(laughs)
- HCHarry Cliff
... 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-
- LFLex Fridman
I see.
- HCHarry Cliff
... these b particles, the way they behave can be influenced by the presence of, say, superfields or dark matter fields or whatever you like. Um, and they're, the way they decay and behave can be altered slightly from what our theory tells us they ought to behave.
- LFLex Fridman
Got you. And it's easier to collect huge amounts of data on, on b-
- HCHarry Cliff
Yeah.
- LFLex Fridman
... on b quarks.
- HCHarry Cliff
We get, you know, billions and billions of these things. You can make very precise measurements. And the, 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.
- LFLex Fridman
Just to clarify, um, which, oh, 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 that were which they're collided? What's the, what's the fundamental difference between-
- HCHarry Cliff
No, it's that the-
- LFLex Fridman
... the different experiments?
- HCHarry Cliff
The collisions are the same. Um, 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, they come flying out, and it can record all of those particles. And-
- LFLex Fridman
What's the... Sorry to be interrupting, but what's the, what's the mechanism of the recording?
- HCHarry Cliff
Oh. So these detectors, I don't know if you've seen pictures of them. They're huge, like ATLAS is, uh, 25 meters high and 45 meters long. They're vast machines. Um, instruments, I guess you should call them really. Uh, they are, they're kind of like onions. So they have layers, concentric layers of detective, 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 calorimeters, which measure the energies of the particles, and on the very edge, you have, um, things called muon chambers, which basically me- 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.
- LFLex Fridman
And all of that is being recorded?
- HCHarry Cliff
That's all being fed out to, you know, computers that-
- LFLex Fridman
The data must be awesome. Okay. Uh-
- HCHarry Cliff
But L- so LHCb is different. So we, because we're looking for these b quarks-
- LFLex Fridman
Yes.
- HCHarry Cliff
... b quarks tend to be produced, uh, along the beam line. So in a collision, the b quark tend to fly sort of close to the beam pipe.
- LFLex Fridman
Mm-hmm.
- 1:07:38 – 1:10:22
Matter and antimatter
- HCHarry Cliff
- LFLex Fridman
So what can you... sort of returning to the, the question we were... before about this fundamental symmetry, it seems like if there's perfect symmetry between, uh, matter and an- antimatter, if we have the equal amount of each in our universe-
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
... it would just destroy itself.
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
And just like you mentioned, we seem to live in a very unlikely universe where it, it doesn't destroy itself.
- HCHarry Cliff
Yeah.
- LFLex Fridman
So, uh, do you have some intuition about, about why that is?
- HCHarry Cliff
I mean, (laughs) well, I, I, I'm not a theor- I don't have any particular ideas myself. I mean, I, I sort of do ex- measurements to try and test these things. But the... I mean, so in 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've got equal amounts of matter and antimatter made. 'Cause 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, 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 u- there's, 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, um, which all involve sort of physics going on in the first trillionth of a second or so of the Big Bang. So it, 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, it acquired its modern value.
- LFLex Fridman
Mm-hmm.
- HCHarry Cliff
And when that happened, um, this caused all the particles to acquire mass, and, 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, 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 early universe. So that's one idea. There's other ideas to do with neutrinos, that there are exotic types of neutrinos that can decay, uh, in a biased way to just matter and not to antimatter. So, uh, 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. So yeah, there are ideas, but at the moment, no clear evidence for which of these ideas might
- 1:10:22 – 1:17:27
Human side of the Large Hadron Collider
- HCHarry Cliff
be right.
- LFLex Fridman
S- so we're talking about some incredible ideas. By the way, never heard anyone be so eloquent about describing, uh, even just the standard model. So, uh, I'm in awe just listening.
- HCHarry Cliff
(laughs) Oh, thank you.
- LFLex Fridman
And ju- and just in- and just ha- having fun enjoying it. So the, yes, the theoretical, the, 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-
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
... 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 e- uh, ev-
- HCHarry Cliff
Mm-hmm.
- LFLex Fridman
... it's just collaboration everywhere. Could you maybe... uh, I, I don't know what the right question here to ask, but almost, what's your intuition about how it was 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? 'Cause it seems like this is a great, great illustration of us working together to do something big.
- HCHarry Cliff
Yeah. I think it's possibly the best example, maybe a- a... I can think of, of international collaboration that isn't for some unpleasant purpose, basically (laughs) . You know, I, it's, I mean, so I, 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 admirat- admiration for the people who managed that, 'cause this was a project that was first imagined in the 1970s, in the late '70s was when the first conversations about the LHC were, 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 noughties, in 2000. So when 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 800 collaborators in LHCb, but you're also competitors, because you're academics in your various universities, and you wanna be the one that gets the paper out on the most exciting, you know, new measurements. So there's this funny thing 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, um, 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, uh, maybe a decade or so ago, to try to understand how these organizations functioned.
- LFLex Fridman
Did they figure it out? (laughs)
- HCHarry Cliff
I don't think they could. I mean, (laughs) I think one of the things that's interes- one of the other interesting things about these experiments is th- you know, they're big operations. Like, say, ATLAS is 3,000 people. Now, there is a person nominally who is the head of ATLAS, they're called the spokesperson. Um, and the spokesperson is elected by, usually by the collaboration, but they have no actual power, really. I mean, they can't fire anyone. Th- they're not anyone's boss.
Episode duration: 1:38:19
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