Particle Accelerators

Misha Glenny and guests discuss the machines that are described as the world’s largest experiments: Particle Accelerators. A famous example of a Particle Accelerator is the Large Hadron Collider, a device which stretches for nearly 30km, deep beneath the ground in a tunnel between France and Switzerland. This enormous scale enables the particles within to be propelled to incredible speeds, reaching almost the speed of light before they smash together. The resulting debris offers insights into the fundamental building blocks of our universe, such as the Higgs Boson Particle. These Colliders are international scientific projects costing billions of pounds, but thousands of other particle accelerators exist around the world. The process has remarkable applications in medicine, archaeology and technology. With Harry Cliff, Particle Physicist at the University of Cambridge Victoria Martin Professor of Collider Physics at the University of Edinburgh Joseph Martin Professor of the History of Science and Technology at Durham University. Producer: Sam Peach Reading list: Jon Butterworth, A Map of the Invisible: Journeys into Particle Physics (William Heinemann Ltd, 2017) Jon Butterworth, Smashing Physics: Inside the World’s Biggest Experiment (John Murray, 2014) Brian Cathcart, The Fly in the Cathedral: How a Small Group of Cambridge Scientists Won the Race to Split the Atom (Viking, 2004) Panagiotis Charitos, Theodore Arabatzis, Harry Cliff, Günther Dissertori, Juliette Forneris, and Jason Li-Ying (eds.), Big Science in the 21st Century: Economic and Societal Impacts (IOP Publishing, 2023) Harry Cliff, Space Oddities: The Mysterious Anomalies Challenging Our Understanding of the Universe (Picador, 2024) Harry Cliff, How to Make an Apple Pie from Scratch: In Search of the Recipe for Our Universe (Picador, 2021) Frank Close, Elusive: How Peter Higgs Solved the Mystery of Mass (Allen Lane, 2022) Allan Franklin, Shifting Standards: Experiments in Particle Physics in the Twentieth Century (University of Pittsburgh Press, 2013) John L. Heilbron, Ernest Rutherford and the Explosion of Atoms (Oxford University Press, 2003) John L. Heilbron and Robert W. Seidel, Lawrence and His Laboratory: A History of the Lawrence Berkeley Laboratory (University of California Press, 2023) Lillian Hoddeson, Adrienne W. Kolb, and Catherine Westfall, Fermilab: Physics, the Frontier, and Megascience (University of Chicago Press, 2011) Joseph D. Martin, Solid State Insurrection: How the Science of Substance Made American Physics Matter (University of Pittsburgh Press, 2019) Michael Riordan, The Hunting of the Quark: A True Story of Modern Physics (Touchstone Books, 1987) Michael Riordan, Lillian Hoddeson, and Adrienne W. Kolb, Tunnel Visions: The Rise and Fall of the Superconducting Super Collider (University of Chicago Press, 2018) Suzie Sheehy, The Matter of Everything: A History of Discovery (Bloomsbury Publishing, 2023) Sharon Traweek, Beamtimes and Lifetimes: The World of High Energy Physicists (Harvard University Press, 1992) A world-class seminar every week. Spanning history, religion, culture, science and philosophy, In Our Time celebrates the pursuit of knowledge and the enduring power of ideas. In each episode, host Misha Glenny and expert guests explore the characters, events and discoveries that have shaped our world. In Our Time is a BBC Studios production

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  Hello. It's been described as the world's biggest experiment, and it sits deep beneath the ground in a tunnel between France and Switzerland. The Large Hadron Collider, an international scientific project costing billions of pounds, a machine that stretches almost 30 kilometres and was built with the aim of answering some of the most fundamental questions about our universe. It's an example of a particle accelerator, devices developed over the last century that are capable of propelling the building blocks of matter to incredible speeds and then smashing them apart.

• 3:06Speaker 03

  Well, with me to discuss particle accelerators are Harry Cliff, particle physicist from the University of Cambridge, Victoria Martin, professor of collider physics at the University of Edinburgh, and Joseph Martin, professor of the history of science and technology at Durham University. Welcome to my guests. And Harry, I would like to go to you first. Can you tell us why particle accelerators are so important? What is it that they, what do they reveal to us?

• 3:39Speaker 04

  Particle accelerators are our primary tool for understanding the deep structure of matter. They're sort of what telescopes are to the universe, they are to the subatomic world. So that's how we look down, how we understand the basic building blocks of matter, what the universe is ultimately made up from. And over the last century, they have revealed a huge amount about the deep structure of matter. So they began tearing nuclei apart, understanding what's inside the atomic nucleus. Today, with the Large Hadron Collider, we're exploring energy scales and distance scales that are unimaginable, incredibly tiny, probing particles that are being created in these colliders, but also conditions that existed in the very early universe. So there are these incredible tools for exploring the world.

• 4:22Speaker 04

  We know about 17 fundamental particles in nature. Of those 17, 14 were found by using particle accelerators. So there's only a very small number that were managed to be found using other techniques early in the 20th century, really. So they're incredibly important scientific instruments. But actually, much more than that, there are tens of thousands of particle accelerators across the world. Only a very small number of those are really used for fundamental particle physics. Most of them are used in hospitals, in cancer treatment, they're used in semiconductor manufacturers and making computer chips. They're even used for detecting art forgeries. So they have a wide use of different applications. But as a particle physicist, I'm most interested in their use for fundamental research.

• 5:01Speaker 03

  So when does the story of modern particle acceleration begin? When do we start getting interested in breaking atoms apart and breaking them down?

• 5:11Speaker 04

  It really, I mean, I'm gonna, I would sort of say it begins with a physicist called Ernest Rutherford. So Rutherford is a New Zealander, and he begins his career, actually, a very exciting time in science in the 1890s. He's at the Cavendish Laboratory in Cambridge, where I work. And at that time, it's when radioactivity is discovered, it's when his supervisor, J.J. Thompson, discovers the electron. And he does this, this is the first subatomic particle, the first evidence that atoms have substructure. And this is done, in a way, is using a very, very small particle accelerator. It's a glass tube about 30 centimetres long. It uses an electric voltage to accelerate these electrons down the tube, and then they're detected at the other end. And Rutherford is there kind of at the beginning of this exploration of the substructure of the atom.

• 5:53Speaker 04

  But you can kind of trace the, what we really mean by particle accelerators begins in the 1920s. And by this point, Rutherford is actually back at Cambridge as the professor in charge of the laboratory, he's replaced Thompson. And he's also the president of the Royal Society, so he's incredibly eminent figure. And he gives this speech in 1927 at the Royal Society, basically saying, we need a way of accelerating particles at will to high energies. Because up until this point, all the experiments that Rutherford has done through his career understanding the structure of atoms has used natural radioactivity. So particularly radium and polonium, these radioactive atoms that spit out subatomic particles, primarily these things called alpha particles, which are like these tiny sub-nuclear bullets.

• 6:34Speaker 03

  How do you actually detect those particles?

• 6:36Speaker 04

  Well, in the early days, the way it was done was sitting in a very, very dark room, and you would have a piece of material called a scintillator, which is a screen covered in zinc sulphide. And you would watch through a microscope for tiny flickers of light. So when one of these alpha particles hits the screen, it creates this tiny flicker, like a little camera bulb going off, and you would sit and count them by, sort of by eye in the dark. So that's how these things were sort of observed in the early days. It was really eye-straining, difficult work. But the problem with radium as a source is, although you get kind of high-energy particles out of it, you're limited in the intensity, you can't control the energy. And what Rutherford wants is a machine where you can at will produce intense beams of particles, because what he's really interested in is probing the structure of the atomic nucleus.

• 7:21Speaker 04

  He wants to get inside the nucleus and find out what it's made of.

• 7:23Speaker 03

  Okay, well, with that, I can turn to Victoria Martin. Victoria, can you walk us through the science? And please be gentle, slowly. What actually happens when we accelerate particles?

• 7:37Speaker 05

  Okay, so what we're doing is we're taking one of the fundamental subatomic constituents that we know about. Typically, we take electrons or protons. So electrons and protons are constituents of atoms. So most people probably know the electrons are kind of whizzing around the outside of the nucleus, and the protons are inside the nucleus along with the neutrons. But we choose the protons and the neutrons for acceleration because they are charged. And it means therefore we can more easily control their behaviour. So what we're doing in an accelerator is we're basically using a voltage, we're using what we also call an electric field.

• 8:20Speaker 05

  And we are setting up a situation where we have, for example, two electrodes, we have one negatively charged and one positively charged. And that sets up a voltage, an electric field. And if we put a charged particle in there, for example, an electron, the electron, we say it has a negative charge, and it will be attracted towards the positively charged electrode. And if we put a proton there, it's positively charged, it would be charged, it would be attracted towards the negatively charged electrode, and it would speed up, it would accelerate and go towards that. So that's how we start with acceleration. And that's how we add energy to particles, because that's what we're trying to do.

• 9:02Speaker 05

  We're trying to get them up to very fast, very high energies. The second element that we often use is a magnetic field, so using a magnet. And a magnet can't speed a particle up typically, but it can steer it, it can change its direction. So if we put a magnetic field there, if we align it in the right kind of way, we can steer the particle where it might go through the accelerator.

• 9:28Speaker 03

  So do you combine those two techniques?

• 9:30Speaker 05

  We do combine the two techniques together. I mean, early accelerators might just use one or the other, but the modern big accelerators, we need to use both electric and magnetic fields.

• 9:42Speaker 03

  Well, talking about big accelerators, we've mentioned the Large Hadron Collider a little earlier. Is a collider and a particle accelerator the same thing?

• 9:53Speaker 05

  Well, yes and no. A collider uses accelerator technology. So accelerator, I mean, does what it, it sounds, we are accelerating them, we're speeding them up, we're changing direction. But a collider, I think a great term for it, is an atom smasher. So typically, we take a piece of an atom, so the Large Hadron Collider takes a proton, which is a hadron is a kind of technical term, but a proton would be a kind of hadron. And we basically speed them up as fast as we can go, given the constraints of the size of the Large Hadron Collider and the magnetic fields that we have. So as fast

• 10:36Speaker 05

  as they go, they're almost going at the speed of light. And then we we simply smash them into each other. And then we observe what happens. And to do that, we surround the points on the Large Hadron Collider ring with detecting equipment at four points along the ring. And they're the four points where we have the atoms smashing, the protons smashing into each other. And we simply look, observe what happens there.

• 11:06Speaker 03

  Just briefly, that detecting equipment, is that, I mean, are those cameras, are they are they measuring sound, are they measuring what, but how do you actually say, yes, we can see what's happening?

• 11:19Speaker 05

  They're basically very, very sophisticated, custom-built digital cameras.

• 11:24Speaker 03

  Joseph Martin, taking us back now, Harry began with the story of Ernest Rutherford in 1927. But how had we thought about particles before that breakthrough?

• 11:36Speaker 06

  So Rutherford by 1927 is working within a research program that is trying to understand how the fundamental constituents of matter are put together. That research program is defined partly by Rutherford himself in 1911, when he discovers the atomic nucleus, doing one of these sorts of, one of the sorts of experiments that Harry described with a scintillating screen, firing alpha particles at a very thin sheet of gold foil, and noticing that some of them were ricocheting off at very odd angles, which he could only explain by assuming that there was a very small, very dense part of the atom, and the rest of it was filled largely with empty space. Those, those alpha particles by that time

• 12:20Speaker 06

  are particles, they're established research tools. So there's a, there's a great quote by the philosopher of science, Ian Hacking, about when we should believe in particles. And he says, well, if you can spray them, then they're real. All right. So by the time Rutherford is working, particles are of various types, electrons, alpha particles, which we later come to understand as helium nuclei, are well-understood, manipulable, experimental tools to try to better understand the microscopic world. So Rutherford is really squarely in the middle of an established research tradition that's increasingly, by that point, defined by quantum mechanics, which has been articulated in 1925 to 1926.

• 13:03Speaker 03

  So what did particle accelerators look like in the second half of the 19th century?

• 13:09Speaker 06

  In the second half of the 19th century, we're looking at glass tubes, very much of the type that that Harry described. Going back to 1850, you have the invention of the discharge tube, where you take a glass tube, you suck as much air out of it as you can, you put two electrodes in it, and you run a current through it, either using a battery or a little bit later, a dynamo. When you do that, what you see is really stunning visual effects. It's the same principle that we use to powerful arson tubes these days. The gases that are left in there are ionized, they give off light. And these were popular scientific curiosities, parlor curiosities from the 1850s. By the 1860s, 1870s, they

• 13:53Speaker 06

  start to become research tools. So this is William Crook in Britain, Johann Hittorf in Germany.

• 13:59Speaker 03

  So they start off as sort of games and novelties and things you take to circuses and stuff like that?

• 14:06Speaker 06

  Exactly. Yeah, they, they're striking, they're impressive, they're taking advantage of new phenomena that people are aware of, electricity, and showing the broad range of interesting effects that they can have. When people become more curious about what exactly is happening inside, they develop into into research tools. And if you do that, if you start investigating what's happening inside a tube like that, you quickly notice it looks like something is being projected from the cathode of the, of cathode terminal to the anode. So these become known as cathode rays. So before the turn of the 20th century, people are talking less about particles and more about rays, something that's being projected, whose effects that you can detect.

• 14:46Speaker 03

  So these are the same things which we then use in televisions, cathode rays?

• 14:52Speaker 06

  Exactly. So a cathode ray tube is essentially what used to be a television. You don't, you don't encounter too many of them these days. But in my childhood, certainly, our televisions.

• 15:03Speaker 03

  Harry, so around the time of Rutherford, how did particle accelerators then begin to develop?

• 15:10Speaker 04

  So Rutherford lays down this challenge in 1927 to the scientific community, can we find a way of accelerating particles? And the reason he wants to do this is because he wants to break the atomic nucleus, this tiny, dense core of the atom that Joe talked about, into pieces. The problem is, the atomic nucleus is positively charged. And so if you want to fire, say, another particle, like a proton, at it, that's also positively charged. And there's a kind of electrical repulsive barrier around the nucleus. So you have to get to very high energy before the particle can penetrate that barrier, get into nucleus, and break it apart. And that's why you need to get these particles going very, very fast. It's almost like the nucleus is surrounded by a steeply rising wall that you've got to sort of jump over effectively. And he begins a research program

• 15:52Speaker 04

  in Cambridge at the Cavendish, where John Cockcroft, who's a more senior scientist, and Ernest Walton, an Irish PhD student, start to assemble a particle accelerator in the basement of the lab. And they are attempting to reach voltages of several hundred thousand volts. And this is kind of driven actually by the developing technology of electrical transmission. So to transmit electricity through power lines, you have to get to high voltages. And industrial manufacturing companies like Metropolitan Vickers have started to make transformers that can reach millions of volts. And so Rutherford is really using this technology developed in industry to build an accelerator at the Cavendish. They have all kinds of problems. The transformers are too big to fit through the Neogothic archway of the laboratory. There's no health and safety. So they do, at one point, they

• 16:34Speaker 04

  think maybe we should see what happens with these high voltages. They discover they can burn a massive hole in a dead rat. And they go, all right, maybe we should take some precautions. So Cockcroft and Walton start to crawl around the floor of their laboratory to avoid getting smacked in the head by an electrical arc off one of their bits of equipment. But so there's, there's essentially this race that develops in the late 1920s, where you have Cockcroft, Walton, and Rutherford in Cambridge. But you also have other scientists, particularly in the United States. You've got Merle Tuves at Carnegie in Washington, who's trying to build an accelerator for the same reason. And in California, you have Ernest Lawrence, who is building a very different type of accelerator, a ring-shaped machine, what we call the cyclotron. And so there's this race really to get to millions of volts and break the atoms apart. And the race is ultimately won by Cockcroft and Walton in

• 17:19Speaker 04

  1932. They, they eventually find the basement is too small, they requisition this lecture room, and they build this, what for the time is an enormous machine, several meters high. And finally, in 32, they'd been tinkering with their instrument for a while, and Rutherford kind of famously comes in and gets very annoyed and say, you know, you've got to put these protons to use, stop fiddling with your experiment. And they fire protons through several hundred thousand volts down this tube. And just to give you a sense how different science was in those days, the detector for this accelerator is a T-chest lined with lead, inside of which is one of these microscopes and a scintillating screen. And your detector is your PhD student. So Ernest Walton is inside this lead-lined box with a curtain

• 17:59Speaker 04

  drawn, looking through a microscope, looking for scintillating flashes. And what he sees, they're bombarding lithium with protons at high energy, and they see characteristic scintillations of alpha particles. And what that tells them is that the lithium nucleus is being cloven in two, into two equally sized bits, and the atom is being split. And this is a tremendous sort of achievement. Rutherford is like absolutely delighted because this has kind of been realized by his team.

• 18:24Speaker 03

  Is this the moment when Rutherford splits the atom for the first time?

• 18:28Speaker 04

  Yeah, I mean, it's referred to as the splitting of the atom, though Rutherford himself has a real problem with this term, because you could argue the atom was split in the 1890s, when they discovered the electron. So it's really about breaking the nucleus apart. That's kind of what is achieved. But the implications are kind of pretty profound. It's also the first time that the most famous equation in science equals mc squared is experimentally demonstrated. So they show by breaking nuclei apart, you can actually get energy out. And that foreshadows what will happen later in the 30s and 40s.

• 18:56Speaker 03

  Well, that brings me on to my next question, Victoria. Why is energy so important in particle acceleration?

• 19:05Speaker 05

  Um, well, the reason it's important in particularly in colliders in what we're trying to do in a collider is create particles that weren't there before. So if we at the Large Hadron Collider, for example, when we're colliding protons and protons, what we want to see the outcome of that collision is not protons, it's one of the other fundamental subatomic particles, the ones that that Harry's mentioned. And all of those particles are heavier than the proton. So, um, and the other thing we have to consider here is that energy is conserved. So the total amount of energy that goes into the collision is going to be the same amount of energy that

• 19:47Speaker 05

  comes out of the collision. If we give a lot of energy to the protons, therefore, we have a lot of energy to come out of the collision. And using E equals mc squared, this this equivalence between mass and energy, we will therefore have enough energy to make these new, much more massive particles. So that's why energy is very important and particularly in our colliders.

• 20:10Speaker 03

  Joe, I want to take us on from where we were with Rutherford and on to, Harry just mentioned it, on to World War Two. What happens with World War Two? How does this change things for particle physicists?

• 20:25Speaker 06

  Well, even before the war is over, people are beginning to refer to the Second World War as the physicists' war. There's a massive mobilization of physical labor in service of the war effort. And for nuclear physicists in particular, that means trying to understand the properties of uranium, or later plutonium, as part of the Manhattan Project. So just before the war breaks out, it becomes clear to nuclear physicists that it's possible, in principle, to liberate great quantities of energy by splitting apart very large nuclei. And that raises the possibility, if you do a lot of that, release a lot of energy very quickly, that's a bomb. It's clear that uranium offers this possibility. But uranium

• 21:09Speaker 06

  comes in multiple isotopes, and only some of them are fissionable. So one of the earliest applications of the type of machines that emerged out of this tradition is the use of the mass spectrometer to try to sort out the understanding of the isotope. So Al Neer, a mass spectroscopist named Al Neer at the University of Minnesota, is trying to figure out which isotope of uranium will fission, will break apart easily. He takes a mass spectrometer, which is a machine, it uses, as Victoria described, a magnetic field to bend particles. If that particle weighs more, it will bend less. So if you put two particles through that field and they weigh different amounts, when you collect them at the end,

• 21:53Speaker 06

  they will have split apart a little bit. So he does that with uranium. And folks like Rutherford realized the tools that they have developed in the development of the cyclotron can be adapted to this purpose. So they built essentially what are called calutrons. They were nicknamed calutrons. These are a series of many, many, many mass spectrometers based on Rutherford's cyclotron principle that are put to work to separate uranium 235 from uranium 238. And that's one of the principal ways in which this physics of working with particulate matter is mobilized in service of the war effort.

• 22:30Speaker 03

  And we'll come on a little later to try and understand how physicists felt about this new application for the research they've been doing. In the midst of all this, we see a model for particle physics emerge. Can you tell us about that?

• 22:46Speaker 04

  So the model we currently are working with in particle physics is this almost complete description of the basic building blocks of the universe. And it describes more or less every experiment we've ever done. It has a really boring name. It's called the Standard Model of Particle Physics. It emerges somewhere later. So this emerges really in the 1960s and 70s, so sometime after the war. But it is based on experimental discoveries that are made with machines that evolve out of that sort of wartime period. In particular, machines called synchrotrons, which are basically enable you to get to extremely high energy. So before the war, we're sort of building million volt accelerators. With these synchrotrons, you can reach billions of volts. And in the process, physicists start to create all kinds of new particles in these experiments. You end up with this proliferation of apparently

• 23:30Speaker 04

  fundamental particles that becomes known as the particle zoo. And this is really dismaying for particle physicists, because physicists almost wear as a badge of honor their inability to remember anything, because the idea is in physics, you have some simple principles, you can just work everything out, you don't have to remember anything. But, you know, I think, I think, I think it might be Enrico Fermi, who says, in this period, he's very dismayed by what's happening. And he said, if I could remember the name of all these particles, I would have been a botanist. So there's an attempt to make sense of this, because we've gone from this understanding of matter, very simple, you have electrons going around the atom, protons and neutrons, and now you have dozens of particles. And what are they for? No one really knows. And in the 1960s, Murray Gelman and George Vai come up with a proposal, which is actually, this huge number of particles is actually

• 24:11Speaker 04

  made of smaller, a small number of smaller particles called quarks. Well, they're also, because Vai calls them aces, but quarks is what sticks. And people look for quarks. They try to, using accelerators, they try to break these particles apart to see if you can get quarks out, and they fail to. Eventually, though, so Gelman almost gives up on the idea, because they've not been able to see these things experimentally. But the idea is rescued by this very large, three kilometer long accelerator that's built in California, the Stanford Linear Accelerator, which accelerates electrons to very, very high energies, just below the speed of light. And they fire them at protons and neutrons. And in doing this, they see that the electrons are scattered off small objects inside protons and neutrons. So this shows that actually protons, neutrons, and all this, this zoo of particles are made

• 24:56Speaker 04

  of a small number of particles called quarks.

• 24:58Speaker 03

  So, so the quarks, when we get to quarks, that is a fundamental particle, i.e. it cannot be broken down, is that right?

• 25:07Speaker 04

  As far as we know, yeah.

• 25:08Speaker 03

  Please don't say that.

• 25:09Speaker 04

  As best, as best we've tried, you can't break a quark apart.

• 25:13Speaker 03

  I had reached a moment of certainty there, and now I have uncertainty hovering over. Victoria, what comes to mind when we talk about the Large Hadron Collider? I mentioned it at the beginning, but what, what is it? Why was it, why was it built? And what has it revealed?

• 25:35Speaker 05

  Okay, so I mean, I would pick up where Harry left off to kind of prelude this. So one set of particles within the standard model that Harry's mentioned are the interaction particles. So they would, for example, help us explain why quarks do certain things, why electrons do certain things. And one set of those interaction particles are called the W and Z bosons. And back in the 70s, it was a proposal, it was just an idea that would make this standard model fit together very nicely. And then these were found at CERN in a collider in 1983. But the problem when they were found is they're very heavy.

• 26:20Speaker 05

  They're about 80 to 90 times as heavy as a proton. And, and this is fine, it's almost what we expected. But theoretically, that's quite difficult to fit into the standard model at that point. So

• 26:35Speaker 03

  Sorry, just so I can be clear, is a boson a quark, or is it something

• 26:40Speaker 05

  No, it's something else.

• 26:41Speaker 03

  Is it fundamental, though? I, can it be broken down?

• 26:45Speaker 05

  Again, as far as we know, no, it cannot be broken down. It is fundamental. But it does play a kind of different role than the quarks.

• 26:55Speaker 04

  Maybe it's worth saying, in particle physics, there are two categories of particles. You have what are called the matter particles, or fermions technically. So that's the quarks, the electron, things like that. And then you have the force particles, colloquially, they're usually referred to, which are bosons. So that's things like the photon, the particle of light is a boson, the W and Z boson that Victoria is talking about. You have things called gluons as well. And so you're kind of either in one camp or the other. You're either matter and you kind of form physical stuff, or you're a force particle and you communicate interactions between those particles.

• 27:25Speaker 03

  Okay, I think I get that. Victoria, carry on.

• 27:27Speaker 05

  Good. So that these very heavy W and Z bosons, it, there isn't an easy way to explain why they're so heavy, except there was some earlier work by Peter Higgs and some other scientists from 1964. So Peter Higgs had come up with this concept of the Higgs field. And if the Higgs field exists, and it interacts with the other particles, the W and Z bosons, we have a way to explain why they're so heavy. So now we had an explanation of why the W and the Z bosons were very heavy.

• 28:08Speaker 03

  Posited on the existence of the Higgs field.

• 28:11Speaker 05

  Of the Higgs field. And there was one other prediction that Peter Higgs made at the same time was if you have a Higgs field, you will also have this extra new particle called the Higgs boson. And when we were building the LHC, and foremost in people's minds was can we find the Higgs boson? Because if we find the Higgs boson with all the other particles that we found, the quarks and the electrons and the other bosons, then finally, the standard model would would make complete sense. It's maybe not the full picture of everything, but it would be a very nice story. And we'd really understand what's going on to a certain extent down at that subatomic level.

• 28:52Speaker 03

  Just, I know there was a lot of coverage at the time when the Higgs boson was discovered. But can you tell us how it's actually identified? I mean, are you looking at these digital cameras and saying, oh, it's got Higgs written on it?

• 29:08Speaker 05

  Unfortunately, it's not that easy. So the Higgs boson, actually, we can make it in the proton-proton collisions. The way that the LHC is set up, about two in a billion of these proton-proton collisions will create a Higgs boson. But the Higgs boson decays almost instantaneously. But we had very good predictions about what it would decay into.

• 29:37Speaker 05

  So one thing that we-

• 29:38Speaker 03

  So those were spotted?

• 29:39Speaker 05

  Those were spotted. So one example is it can decay into two photons, into two particles of light. Our detectors are essentially digital cameras and we can detect light very well. And we can also measure the amount of energy of that. So basically, that's what we were looking for. We were looking for the signatures of the decay of the Higgs boson.

• 30:03Speaker 05

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• 31:14Speaker 02

  Hey, it's Niall Rogers, host of Before the Moment, a Lincoln original series. I'm driving across the country, meeting some of today's most fascinating artists. We're exploring the stories before the moment that changed everything. This week, I'm joined by breakout singer-songwriter Alex Warren. To this day, Ordinary would not have done anything, and I would have not been able to put it out if Book Talk didn't back it up, and if my wife and her friend didn't back it up. So- Amazing. Pretty crazy how like, just one thing. Right. I mean, I bet we could point to nine different things in our careers where it's just one thing, all of a sudden, if that one thing didn't happen, then I wouldn't be here. What you're talking about right now- Yeah. -is what I've been talking about since the beginning of my career. There's these

• 31:58Speaker 02

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• 32:22Speaker 02

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• 33:32Speaker 03

  Joe Martin, so we have this huge hadron collider, 27 kilometers or whatever it is. And yet scientists, physicists, want to build bigger and bigger machines. What are they aiming to do with that?

• 33:52Speaker 06

  Yeah, the obsession with bigness. So I think there are a number of explanations for this. There's an intellectual reason, which I think Victoria has outlined very well, which is that you find new phenomena when you accelerate particles to higher energies. You get more intense and sometimes more complex interactions. I think there are also cultural reasons for this, and why this strand of high-energy physics takes hold, especially in the post-war United States. And part of that has to do with the way in which physicists reacted to working on the Manhattan Project. In one sense, it sensitized them to working at much larger scales than they were accustomed to. This was in contemporary dollars, a $2 billion project, the Manhattan Project. It had essentially a blank check from the

• 34:33Speaker 06

  United States government to pursue whatever avenues of inquiry it thought might be productive. And that taught a lot of physicists what they could do with that level of resource. But many of them also reacted quite strongly to having been involved in creating such a fearsome weapon. One of them was Robert Wilson, who eventually became director of Fermilab, the big particle accelerator laboratory in the United States outside of Chicago. When he was testifying before Congress in support of funds for this in 1969, he is being pushed by Senator John Pastore, a Democrat from Rhode Island, who wants him to give up something about what it's going to do for the economy, what it's going to

• 35:14Speaker 06

  do for national defense. And famously, Wilson says, it has nothing to do with defending the country except to make it worth defending. This is fantastic, soaring rhetoric that has really worked its way into the culture of particle physics. And so it is partly about being remote from applications, finding the most basic, the most fundamental knowledge you can.

• 35:35Speaker 03

  Victoria, talking about pure science and going back to Peter Higgs, you studied with him, I gather. How was he, how did he respond to confirmation that the Higgs boson exists?

• 35:48Speaker 05

  Yeah, I took a couple of final year undergraduate classes with him just before he was retiring. On the day that the Higgs boson discovery was announced, that was the 4th of July, 2012, he was invited to go to CERN and sit in the big seminar. There was queues outside the door, there was overflow rooms, but he obviously had a reserved seat.

• 36:15Speaker 05

  And after the seminar, they asked for him for a few words, also from Francois Anglert, who was one of the other scientists that came up with the very similar idea to Higgs at the same time. And anyway, Peter said, it's like watching your football team win the league. Now, as far as I know, he wasn't a big football fan, but I think he was trying to describe it to the masses, although they were all physicists in that room. And I think he was a little bit overwhelmed as well, because he flew back to Scotland, to Edinburgh the same day. But he was with one of my colleagues, and my colleagues had called me just to say

• 36:57Speaker 05

  how the day had been. And I got to speak to Peter on the phone, and I can't actually remember what I said, but I think he was feeling just a little bit overwhelmed with all that had happened. And as if he had felt, you know, all the glory was going to him, he was very kind to keep reminding people that actually it was a huge effort over 48 years since he came up with this idea of experimental physics, and also some theoretical physics, and a lot of technology development to get there.

• 37:28Speaker 03

  Harry, how accurate were Higgs's predictions? And what does the confirmation of the Higgs boson mean for physics?

• 37:39Speaker 04

  I mean, his predictions were clearly accurate. I mean, one of the things that is amazing, I think, and almost unique about fundamental physics is this ability to predict the existence of phenomena or objects that have never been seen, and then you see them. And this happened in the 1920s and 30s, when antimatter was predicted purely on theoretical grounds. And similarly, the Higgs boson was predicted by Higgs and others in the 1960s. What it didn't tell us was what the mass of the Higgs boson was. So when the LHC switched on, physicists were very confident they would find it if it was there, but they didn't know exactly at what energy scale. So it would decay in different ways if it had different masses. So that made the search a bit more complicated. But what the discovery really does is it's the last missing particle of the standard model, and it ties the standard model together.

• 38:22Speaker 04

  So it was rather hyperbolically described as the God particle by a physicist trying to sell popular science books. But what they were getting at with that is without it, this whole theoretical edifice that was built over 50 years would just disintegrate. But actually, the Higgs isn't really the end of the story, because as a fundamental particle, it's deeply mysterious. And there are theoretical reasons why such a thing should not exist, essentially, in the form that it does. And so the next stage of research in this area is really to actually understand the Higgs boson in much finer detail. And I sort of said the LHC is a bit like a microscope, that it's like looking down and getting a better, better picture. At the moment, we have quite a fuzzy view of the Higgs. It's like we've seen some new object. It looks roughly like the thing that Peter Higgs predicted, but we don't know if it's

• 39:06Speaker 04

  exactly the same object that he predicted, or if it's something more exotic. And so at the LHC at the moment, people are working very hard to get a better picture of the Higgs. But ultimately, to answer this question, there will need to be a future, another collider after the LHC.

• 39:18Speaker 03

  An even bigger one.

• 39:19Speaker 04

  An even bigger one.

• 39:20Speaker 03

  And do you think that that's likely to happen?

• 39:24Speaker 04

  I mean, so in the last few years, the European particle physics community have been coming up with a strategy about what comes after the LHC. And the LHC actually has a long way to go. It's going to run until the end of the next decade into the early 2040s. But after that, we'll have got everything we can out of that machine, and you have to ask, well, what's the future? And the community is coalescing around a project that's called the Future Circular Collider. I assume it will get renamed if it actually gets built. It can't be a future machine forever. But this is a 90-kilometer ring that would sit in the same region in the Geneva Basin.

• 39:57Speaker 03

  So three times the length.

• 39:58Speaker 04

  Three times the size, but it would allow us to get to much, much higher energies and also to produce huge numbers of Higgs bosons and study them at very high precision. And this isn't, it sounds a bit sort of technical, you know, what exactly is the Higgs boson? But this is a question that's actually bound up with, why does matter exist in the universe? Why is the universe as it is? The Higgs, if you change the properties of the Higgs, the universe that we live in ceases to exist, and it would be a very, very different place. So this is really a question about, what are the origins of the world we live in? Why are the laws of nature the way they are? And that's the kind of argument for why you go to this next machine.

• 40:32Speaker 03

  So, Joe, apart from the fact that, if I understood it correctly, if the Higgs boson was interfered with, the universe would cease to exist. How important is the Higgs boson discovery to the wider world? Where is the connection that people like me might be able to understand and grasp?

• 40:51Speaker 06

  Yeah, so Leon Letterman, who wrote the book The God Particle, also liked to quip that he should have called the book The Goddamn Particle, because he claimed it was under pressure from his publisher, but also because it was very elusive. And I think that's, if you consider that a prophecy, it's sort of come true a little bit in that I think a lot of physicists were hoping that it would have properties that would give us a clearer sense of where the research program should go. And it remains sort of elusive, conceptually elusive. In terms of the broader community, I think this has to do with how physics as a whole, and high-energy physics in particular, positioned itself during the second half of the 20th

• 41:33Speaker 06

  century as something that creates fundamental knowledge about our world that gives us a deeper and more profound understanding of the sort of universe we live in.

• 41:45Speaker 03

  Thank you. Victoria, you've worked and still work at the Large Hadron Collider. So tell me, we've found the Higgs boson, hooray. But what are you looking for now? Are you just studying more Higgs boson, or are there other paths that your research is taking you down?

• 42:06Speaker 05

  So personally, I am looking for more Higgs bosons. But let me tell you about what the great thing about working at CERN with so many collaborators is that we can all look for different aspects of particle physics at the same time, because the proton collisions, something different happens in each collision. So one of the big mysteries that we still have is dark matter. So dark matter is something that we know exists from astronomical observations. So when astronomers look out beyond our galaxy, that they can see that there's more matter, more heavy stuff there than shiny stuff, in very simple terms.

• 42:50Speaker 05

  So they can see more gravitational interactions, they know there's a lot of matter there, but it's not stars. The starlight won't account for it. So this is dark matter. And dark matter very probably is a particle, but we know it's none of those particles in the standard model. All the particles in the standard model are either too shiny, so they interact with photons, or they're too light, and they wouldn't coalesce to make kind of heavy objects out in other galaxies. So we are looking inside the proton-proton collisions to see if we can see dark matter. Are we making it? How heavy is it? What does it behave like? We don't really have any indications of that yet.

• 43:34Speaker 03

  Do we know roughly what percentage of the universe dark matter makes up?

• 43:40Speaker 05

  Yes, a huge percentage. I think it's, I'm going to look at Harry for the exact number.

• 43:45Speaker 04

  So if you take the total energy budget of the universe, 5% is atoms, so visible stuff, shiny stuff. 27% is dark matter, and 68% is something called dark energy, which don't even get started on that.

• 43:59Speaker 05

  We don't want to talk about. I mean, it's enormous. And then suddenly, I feel really embarrassed that I only look at this tiny sliver of the 5% of the universe, when I really wanted to understand it all.

• 44:10Speaker 03

  Harry, I'm afraid you've piqued my interest there with dark energy. What on earth is dark? I think I get dark matter, but dark energy?

• 44:20Speaker 04

  No one knows, is the honest answer. I mean, the evidence for dark energy was discovered in the late 90s by astronomers, where they found that contrary to expectations, the expansion of the universe is accelerating. So people thought that after the Big Bang, the universe is expanding, gravity would gradually slow that down. In fact, it seems to be speeding up. And to explain that, you need some kind of anti-gravitational repulsive force that pushes the universe to get bigger and bigger, faster and faster. And we call that force, whatever it is, dark energy, but no one really knows what it is.

• 44:51Speaker 03

  So it's perfectly clear, Joe, that there is huge potential for further discovery and further research. But can you give us the basic applications of this technology in other fields?

• 45:06Speaker 06

  Sure. So in the march to higher energies that we've discussed, there are a lot of perfectly serviceable machines that get left in their wake. So if you have the forefront high-energy accelerator and somebody builds a bigger one, you're no longer going to get the physicists coming to your machine to do the forefront research. That leads to an opportunity to do something else with that machine. And one of the most prominent things that's been done is to create what's called a synchrotron light source. So if you're, I'll explain what that means. So if you're designing a very high-energy accelerator, you're trying to get the particles moving as fast as possible. If you accelerate the particles, if you curve them, they give off light. And so that takes away some other energy.

• 45:49Speaker 06

  So when you're designing a very high-energy accelerator, you want to minimize the amount of energy you're giving off by curving your particles around. What, really in the 60s, what some other types of scientists thought is, that energy that's being emitted when we move the particles around is actually really useful for us. You can get very coherent beams of X-rays or of UV light that you can use for things like scattering experiments. So this is sort of, it's analogous to taking a handful of pebbles and throwing it into a well to determine how deep it is, whether there's water in it. You shoot your photons, your X-rays, your UV rays at a sample, and you watch what comes out, and you make inferences about what's happening at the microscale on that sample

• 46:34Speaker 06

  from that. Now, that is something that you can do in a huge range of fields. It's structural biology. This is how the structure of DNA was discerned because of X-ray photographs taken by Rosalind Franklin. This early X-ray crystallography was done by the father-and-son Bragg team at the Royal Institution, Kathleen Lonsdale in structural biology. But also, as Harry was alluding to earlier, if you want to look at underpainting on a painting without doing any destructive testing, if you found a really old violin and you want to find out if it's safe to play, you can gain information from these sorts of scattering experiments. So a lot of these older particle accelerators have been converted into synchrotron light sources, where you might have 50 experimental stations with a bunch of different teams

• 47:19Speaker 06

  doing different experiments. So it's a really lovely example of how scientific instruments, even really big ones, start out being tied very closely to one theoretical program, and then they become research technologies that can be adapted to questions in a huge variety of fields. And that's, I think, one of the most interesting trajectories we've seen particle accelerators undergo in the late 20th and early 21st centuries.

• 47:42Speaker 03

  Harry, something that I'd like you to try and answer, if you can tell us in a bit more detail what antimatter is.

• 47:53Speaker 04

  So antimatter is exactly like matter, but it's a sort of mirror image. So the idea of antimatter first emerged from some theoretical work done by a British theoretical physicist called Paul Dirac. He was the first person to combine the two big revolutionary ideas of the 20th century, early 20th century, quantum mechanics, which describes the behaviour of atoms and electrons and photons, and special relativity, which is Einstein's theory of what happens when you go very fast, close to the speed of light. By bringing these two things together, he got this equation that predicted the existence of a positively charged electron. And this is something that no one had ever seen in nature before. And Dirac actually struggled for several years trying to eliminate this positively charged electron because he thought it must be wrong.

• 48:37Speaker 04

  But then, and this is kind of amazingly eerie event, in 1930, so this prediction was made in 1928. In 1932, Karl Anderson, an American physicist, discovered a positively charged electron using an instrument called a cloud chamber, which is a sort of early particle detector. So it had been predicted purely on theoretical grounds. And we now know that, so the positron, as we know it, is exactly the same as an electron, it just has an opposite charge. And if you bring it together with an electron, it will annihilate the electron and turn into light. And this is true for all the matter particles. So the quarks have antiversions with opposite charges, the neutrinos have antiversions, we think, as well.

• 49:13Speaker 03

  So that positron is antimatter?

• 49:17Speaker 04

  Is a form, it's a particle that would make up antimatter. So now, actually, at CERN, there are experiments where they make atoms of antimatter, so antiatoms, where you bring antiprotons, which are made in an accelerator, and positrons together, and you make an anti-hydrogen atom.

• 49:31Speaker 03

  And what happens?

• 49:32Speaker 04

  Well, the challenge is, antimatter cannot be stored in a vessel like ordinary matter because it will annihilate with the vessel. So it would destroy itself immediately. So you have to find a clever way of storing it in a vacuum and keeping it away from the walls of the container. And so you have these, essentially electromagnetic bottles that are built, where you trap the atoms, and now they can trap thousands of anti-hydrogen atoms indefinitely, almost, and then do experiments on them. So you can shine light at them, see how they behave, do they behave the same as ordinary hydrogen? And this is, this is tied up with actually a really fundamental question that we're also trying to answer, the experiment that I work on at the LHC, which is, why is there matter in the universe at all? Because according to the standard model, what should have happened in the Big Bang

• 50:14Speaker 04

  is you make huge quantities of matter and antimatter, and then they would have annihilated each other.

• 50:20Speaker 03

  They'd cancel each other out.

• 50:21Speaker 04

  Completely, and you get the universe with nothing in it, apart from a few lonely photons whizzing through the infinite blackness.

• 50:25Speaker 03

  So why didn't that happen?

• 50:26Speaker 04

  We don't know. And that's what we're, you know, so the experiment I work on is called LHCb, and we make precision studies of the behaviour of particles and antiparticles to try to get an answer to this question. But it's also a question, I think, that motivates the next generation of experiments as well that we've been discussing.

• 50:42Speaker 03

  That really is fascinating. Joe, Victoria, anything else that you feel it's important to emphasise that we might have missed?

• 50:51Speaker 05

  Yeah, I wanted to talk a little bit about why we're still trying to measure the Higgs boson, although we've already discovered it. And it's back to this idea of the Higgs field. So because the Higgs boson is heavy itself, we now know that it's about 125 times as heavy as a proton. So it's up there with these W and Z bosons. It means that the Higgs boson itself interacts with the Higgs field, because that's the way that we make things heavy. And the consequence of that is that we predict, we think, that there's a way for a Higgs boson to decay. So you start with one Higgs boson, and it decays into two Higgs bosons, which sounds nuts, it sounds mad.

• 51:35Speaker 05

  And I think, Harry, you almost alluded to this, like the Higgs boson almost sounds like it shouldn't exist.

• 51:40Speaker 03

  Hold it, are these two Higgs boson into which it decays the same mass as the original Higgs boson? Or are they, you know, little baby versions of the Higgs boson?

• 51:52Speaker 05

  That's a very good question. So you can have a particle that's heavier than it normally is. So you would either have a heavier than it normally is, decaying to two of the same mass, or more likely, you would start with a regular mass one, and they would be a bit lighter. It's, yeah, that's a tricky, that's a tricky question. We don't actually know the, well, we don't precisely know the answer to that. But that is one thing that we are looking for. So we're looking for it with the LHC data that we've got now, and with the future circular collider project. That is definitely one of the things we really want to test to see if this does happen,

• 52:36Speaker 05

  because that will tell us if this idea of the Higgs field is really the right one for understanding the Higgs boson and the other heavy particles.

• 52:44Speaker 03

  I visited the Almer Telescope Network in Chile, and they explained that scientists have to put in a project, astronomers have to put in a project, and wait and see whether it gets approved, and then they say, well, you can come in 10 months' time or whatever and do your project. Is that the same with the Large Hadron Collider, that you sort of put in an idea and say, I'd like to do this? How does it, how does it work?

• 53:13Speaker 04

  It's quite different. I mean, they are like telescopes in the sense that you can use a collider to study a huge range of different phenomena, but it's simultaneous. So a telescope, you point it usually at the bit of the sky, it's not always true, but most telescopes, you say, look over here, look over there, I want to look at this planetary system or this galaxy. At the LHC, the protons collide, and it's like rolling a kind of trillion-sided dice, because it's quantum mechanical, more or less anything you, you know, physically can happen will happen. And so people can look in that huge dataset for the things that they're interested in. So you don't apply for time on the experiment per se, you do build, so there are these four digital cameras that Victoria talked about. One thing to get across, these are not camera-sized, these things are the size of cathedrals,

• 53:55Speaker 04

  these are gigantic instruments that are used to detect these particles. So we're not talking about a little tabletop thing, we're talking about these vast machines. There are four different experiments that look at different aspects of the collisions, broadly speaking. But within that, there are teams within the experiments who have completely different research questions they're trying to ask.

• 54:14Speaker 03

  Joe, anything you'd like to add?

• 54:15Speaker 06

  Yeah, if you look at what's happening at CERN, it's not just a lot of people, it's multinational, there are a lot of governments involved, it's a diplomatic exercise as much as it's a scientific exercise. And this is one of the reasons, one of the things we haven't talked about is, there was a proposal in the United States in the 1990s for a very large machine called the Superconducting Super Collider, which was not built because the United States Congress pulled funding. One of the reasons that failed is that it was essentially a monument to national pride. The organisers, early on, the organisers and the politicians sort of staved off international investment, avoided making it a collaborative project, they wanted it to cement American supremacy in high energy physics.

• 54:59Speaker 06

  And at the end of the Cold War, when priorities shifted, budgetary constraints changed, the project no longer seemed viable to the policymakers who were charged with funding it. So that is, that was the moment of a shift toward the CERN model of organising this type of labour across countries, working collaboratively towards this shared goal.

• 55:20Speaker 03

  As a diplomatic experiment, as you described it, it's been pretty successful, hasn't it?

• 55:25Speaker 06

  It has. CERN, as an institution, it does more than just the LHC, right, it's a broadly invested scientific laboratory. But within the high energy physics community, you don't have the sort of user system as you might have at a synchrotron light source, where you apply with a project and it gets funded or it doesn't. You have a very large, complex community working together to coordinate the research priorities of that community, and going back to the respective governments and getting buy-in for that shared project.

• 55:55Speaker 03

  Victoria?

• 55:56Speaker 05

  I did want to pick on something maybe that Joe, well, was maybe not alluding to, but I think it was useful to think about, which is another reason I feel that CERN has been quite successful. So I mentioned the W and the Z boson, they were, found a previous collider at CERN. We actually still use that collider as a feed-in to feed into the Large Hadron Collider. And if we go ahead and build the future circular collider...

• 56:27Speaker 03

  The same will apply to the Large Hadron Collider feeding into the circular.

• 56:31Speaker 05

  Yes, exactly. So we keep reusing and reusing the old systems that are there, and that does make it much more cost-effective than, for example, building an entirely new collider in Texas, the Superconducting Super Collider would be, was planned to be, because there was no infrastructure there. So you have a huge infrastructure in terms of previous experiments that you can reuse, and also the knowledge and expertise kind of based there.

• 56:56Speaker 03

  My thanks to Joe Martin, Victoria Martin and Harry Cliff. Next week, Casablanca, how the great film of Hollywood's golden age convinced Americans that the Second World War was worth fighting. Thank you for joining us.

• 57:11Speaker 04

  Do you have coffee?

• 57:14Speaker 03

  Oh, Sam, fantastic. Cup of tea for me with milk.

• 57:18Speaker 04

  Tea with milk, yes, please.

• 57:19Speaker 05

  Tea with milk, please.

• 57:20Speaker 06

  I'll be the contrarian and have a coffee.

• 57:24Speaker 00

  Zandi, happy anniversary. Oh, what are you talking about? Have I missed something? Yes, Zandi, you have. We are over a year into making WhatsApp docs, you didn't even get me a card. Is it really over a year? It is. Think of all the episodes we've done, how to look after our feet, our shoulders, our hips, our teeth. We've explored snoring, cholesterol, the immune system, endometriosis. All with the help of expert guests. I think it's fair to say we have plundered the world of health and wellbeing, equipping ourselves... And our listeners. ...with the best information out there on how to look after our minds, our bodies, our souls even. And we're not stopping, are we, Chris? We must certainly not, Zandi. We have a lot of new topics coming up, from tinnitus to acne, crying, male fertility.

• 58:07Speaker 00

  We are holding steadfast in our mission to sort facts from fiction, debunking wellness myths along the way. And you can find all of our previous episodes of WhatsApp Docs in the feed on BBC Sounds. And don't forget to subscribe on BBC Sounds. And turn on the notifications so you don't miss any of these upcoming episodes.

• 58:31Speaker 00

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