 So, please find some seats. I hope everyone had a great lunch. I know I did. It was fun seeing old friends and meeting some new ones. We have an exciting afternoon planned, and we're going to get it started here. It's my pleasure now to introduce my colleague, Professor Josh Brown from our Philosophy Department. So, our next speaker is Dr. Tara Shears. She's Professor of Physics at the University of Liverpool and a member of the LHCB experiment at CERN's Large Hadron Collider, the LHC, where she initiated the QCD Electro-Week and Exotica Physics Working Group. She's also one of the world's foremost public ambassadors for the LHC and for the science of particle physics more generally. Now, I am really, really, really, really excited to introduce Dr. Shears, because she's got the coolest job in the world. She smashes protons together at just shy of the speed of light and then shifts through the wreckage in order to look for clues about the nature of matter and about the evolution of the early universe. It's a little bit like this. Let's get down to business. Are you ready? I'm ready. Go for it. This is compact, compact rocket sled in three, two, one. As I said, it's a little bit like this, but really, it's even cooler, because protons, of course, are much, much smaller than the Mythbusters rocket sled. But the protons that Dr. Shears smashes together are also moving much, much faster. The rocket sled is moving at about 650 miles an hour. That's faster than most passenger jets, and were you riding that sled? You could get here, from here, on Gustavus' campus to downtown Minneapolis in about six and a half minutes, or from the LHC in Geneva to Stockholm in about two hours. The protons in the LHC are traveling over a million times faster, roughly 670,616,600 miles per hour. In your six-and-a-half-minute rocket sled ride to the Twin Cities, an LHC proton could travel to Mars and halfway back, over 71 million miles. The proton gets from the LHC to Stockholm in 7 1-thousandths of a second. Now, when two of these protons collide, they don't just disintegrate like the car in the video. They briefly recreate the conditions that prevailed in the universe right after the Big Bang, a stew of particles with a temperature of over two-and-a-half trillion degrees Fahrenheit, hotter even than the center of the sun. Dr. Shears studies the birth and behavior of fundamental particles in this stew. Just this past spring in April, Dr. Shears' LHCB experiment announced exciting results concerning a type of particle called a strange beauty meson. Now, what's really fascinating about strange beauty mesons is that they spontaneously can flip from being matter to being antimatter. The LHCB experiment looked at 70 trillion proton-proton collisions, isolated 1,000 or so strange beauty mesons, and discovered that matter mesons outnumbered antimatter mesons by about 25%. This is the first observation of what's called a charge parity or CP violation in strange beauty mesons, and it's one important experimental step in helping us understand why when we look out to the farthest reaches of the universe, and so back in time towards the Big Bang, we see only matter and not antimatter. Dr. Shears' work thus reaches towards all of the disparate limits of the universe. By probing its smallest, most fundamental parts, she's helping explain its largest features and discover what it was like at its very beginning. Please join me in welcoming Dr. Tara Shears. Thank you, everyone. So, in this talk, we're going to explore the universe right at the innermost frontiers. We're going to look at what matter is made of and how it behaves at the very smallest, the very deepest scales, the scales of particle physics. Now, what I want to do is to show you what particle physics has shown us, but I don't just want to talk about what we understand about the universe at these very tiny distance scales, because I also want to show you, in a sense, how little we understand and where the frontiers of our understanding lie. So, I'm going to tell you about some of the biggest open questions in our subject. These are questions that drive us to do our research. They drive us to build enormous experimental facilities to try and find answers. And I'm going to tell you about one of those. I'm going to tell you a little bit about the Large Hadron Collider, because I work on it, it's most familiar to me. I'll show you what it looks like, how it works, but most importantly, I'll show you our latest results, because already the Large Hadron Collider is starting to fill in the gaps in our understanding of matter and the universe at these innermost scales. And so you'll see for yourselves just how far we've come and where the frontiers of our understanding have stretched to. Now, let me start at the beginning, because I should tell you really what particle physics is and how it fits into the history of the entire universe. So, in brief, particle physics, well, in particle physics, we have an idea that everything that we see around us is made of the same basic stuff, the same ingredients, the same fundamental particles and make everything. And we think that only if we could identify these and understand their behavior, well, then that would allow us to understand the behavior of the universe at larger scales. And that's the approach we take. Now, behind me, you can see almost everything we know about the universe through physics, encapsulated in one picture, very simplistically. So, on the left, we have the Big Bang, where we think everything started. The Big Bang was this, if you like to imagine it, was a hugely tremendously energetic fireball that brought everything in the universe into existence. And the early universe was a very different place to the universe that we know now. It didn't have stars in, it didn't have planets, it didn't even have atoms. Instead, it was populated just by the ingredients of atoms, the fundamental particles that I just talked about. Now, as time marched on, the universe expanded and cooled down until, at various points as it cooled, it became, energetically speaking, more effective for matter to start to clump together into new forms. So, after a few fractions of a second, we start getting neutrons, protons. After a few hundred thousand years, we have the first atoms. And then, as time marches on, we get larger and larger structures, stars, galaxies. And then, here we are, almost 14 billion years later. Well, that's what we think happened. But of course, how we know any of this, and I say this because I'm an experimental physicist, is through experiment. It's the only way to be sure. And to work out what the universe is made of now, it's quite straightforward. You can just look at it. You look at it through telescopes. You can send out probes to take measurements of anything if it's close enough to you. But if you really, really want to understand the universe, you also have to understand how it got from the Big Bang to now. And that's a problem. Because you can't look at the very early universe through telescopes. It's opaque. You can't see into the universe before it was about 300,000 years old when atoms formed. So instead, if you want to work out what was going on just after the Big Bang, you have to recreate those incredibly hot conditions in the laboratory. And that's what we do in particle physics. That's what we do in our particle accelerators. So that's the angle, if you like, that particle physics brings to our understanding of the universe. It tells us what matter is made of at the very tiniest scales, what the universe is made of. But also, what the universe was doing in the first brief seconds of its existence. Now, already our experiments have shown us an awful lot about what the universe is made of. So we've realized that matter is made of no more than 12 fundamental types of particles. Six quarks, six leptons. Now, these particles are really amazingly small. They're at least as small compared to atoms as atoms are compared to you. I say at least as small because they're so small we've never been able to measure them. That's just the limit of technology. They are incredibly small. Now, in your everyday lives on Earth, you don't even see this many particles. You don't come across them. You just come across a fraction of them. The first two quarks up there, the up-and-down quarks, they're familiar to us in everyday life because collections of those form the neutrons and protons in our nuclei, which are orbited by electrons to make atoms. And the neutrino associated with the electron we often see in radioactive decay. We don't even come across these other more exotic particles unless we go to higher energies and we typically have around us on Earth. But they exist and we've seen them in our experiments. We know they're an ingredient of the universe. Okay, so that's matter. That was easy. Now, what makes this matter a set of fundamental particles stick together to form matter that looks and behaves in the way it does to us are a small number of fundamental forces. Not very many, just a small number. There's a weak force, for example. Now, it's the weak force's job to give us radioactive decay. The weak force describes radioactive decay. And it affects every single one of our matter particles. And we think that we have a picture for the way this force works. We think it's communicated by the exchange of other types of particles that carry the force, force carrying particles, called W and Z bosons in this case. And this idea of a force working by exchanging a force carrying particle between matter particles isn't just peculiar to the weak force. It's the idea we have for how forces work for really any of the forces that we can describe. So, besides the weak force, we have another couple to get through. There's the electromagnetic force, which is much more familiar to us. It's driving the lights, it's driving the projector. You use it at home an awful lot. You know it acts on anything with an electrical charge. And that means it acts on any of our fundamental particles that are electrically charged, too. And it's communicated by photons of light. And then quarks, and this is what makes them different from leptons, as Frank was telling us in his talk before, experience the strong force. And it's the strong force that keeps atomic nuclei stable because it's an attractive force. And it's strong enough to overcome the electrostatic repulsion between the protons that you have in the nucleus that would otherwise drive it apart. And that's communicated by a number of force carrying particles called gluons. Fantastic. And I have to say, that's almost all we consider in particle physics. That's almost all the ingredients of the universe that we've come across. Now, there is one more fundamental force that I haven't mentioned. And I don't know if you can think of what that might be, but it's a force that's responsible for the large-scale structure of the universe. It's gravity, of course. Gravity is incredibly important. Gravity acts on mass. It's what is keeping you stuck to your seats, stuck to the Earth. And we know that all of our fundamental particles have mass as well because we've measured it, so therefore they must also feel gravity too. However, gravity is so much weaker than the other forces that we can just neglect its effects when we're describing what goes on in the very small distance scales that we look at in particle physics. So I have it here with a question mark because gravity, although we know it exists, it clearly does, is something that in our subject we have yet to fully understand. Okay, so we have matter. We have forces. And there's just one more ingredient left in the universe. And it's an ingredient that was only verified by a discovery last year. It's a very timely piece of information. And this extra piece of the universe goes back to this idea of mass that I just mentioned for gravity. Why do particles have mass? What causes them to have the value of mass that they do? Well, we think the explanation lies in something called the Higgs field. Now, the Higgs field is like a type of energy field which is present throughout the universe. It's part of the universe's structure. And fundamental particles, we think, obtain mass as they move through the universe and move through the Higgs field. And the amount of mass they get just depends on how strong their interaction with that field is. And this field also has a particle associated with it which is the Higgs boson which was what was discovered last year which is what allowed us to verify that this particular idea was correct. So in this idea, if you are a massless particle like a photon, you zip through the universe completely unaware of the Higgs field. But if you are a massive particle like the top quark, your path through the universe is impeded by your interaction with this field all around you. You are a heavy object. Now, we don't see the Higgs field. It's invisible. But we should be able to see the Higgs boson that's predicted to accompany it. We should be able to make it in our experiments. We should be able to detect it by the characteristic way it decays and leaves a signature behind. And indeed, that is the layer of logic that we followed in order to make the discovery. And I'll tell you a little bit about how that worked later on. Okay. We have mass, force, and an explanation for mass. And we even have a picture for how this all works together. And what's even better than that is to encapsulate this picture in mathematics. We can write it down in equations. And the equations that we write down form our theory of particle physics. And our theory of particle physics is so succinct, so elegant that you can write it on the front of a t-shirt. And if you go to CERN over in Europe, you can even buy the t-shirt. It is a retail opportunity that awaits you as you go in the front door. I've always wanted one of these. And the reason that this equation is so beautiful harks back to what Frank was saying in his talk, because it's founded on the principles of mathematical beauty that he was talking about. So now you're starting to see where the frontiers of mathematics and geometric structure start to impinge on the world of reality and what we can measure. Now, not only is this equation really, really beautiful, it's also really, really good, because we haven't yet made any measurement at all that disagrees with any of its predictions. It's so good that we call it the standard model of particle physics. And that's brilliant. But it's not the whole story. It's not the whole story because we know that this theory is incomplete. For a start, it doesn't describe gravity. And that's not because we've been lazy and we think it doesn't matter. It's because we can't put gravity in the same type of equations as the other forces. It just doesn't work. It gives us rubbish out as answers. And besides not describing that, we know that there are many phenomena in the universe that we have observed, but which cannot be explained or predicted inside our theory. And for that reason, we think there must be a deeper, underlying understanding of the universe to be had if only we can find it. And it's that that drives our research to learn more and to understand more about this innermost layer of the universe. So, having told you about what we understand, I'm now going to move on to what we don't understand. And so, the very fact that I've spent such a small fraction of my talk on what we understand should tell you that the entire universe is up for grabs when it comes for understanding it. There's so much to find out. I'm just going to tell you about some of the bigger questions that we have. The first one is such a basic question that I've given it number zero, not even number one. And that's, is the standard model even correct? We know it's incomplete, but where it can describe data? Is it even a correct description of data? Now, this was a much more leading question before the LHC started, because the standard model had a prediction for finding the Higgs boson. The Higgs boson hadn't been found, and the whole correctness of the standard model hinged on this particle being discovered and being known to be there, and being known to be the particle associated with the standard model. So, how do we find a way to verify this? Well, we have found Higgs, and not just the theorist, Peter Higgs himself, we have found a Higgs boson, but we still don't know very much about it. We still don't know if it's a Higgs boson we expect to see in the standard model, or a Higgs boson that's associated with some more exotic theory of nature. So, that's why I've kept this question in my talk, and I'm not sure if it's needed, not knowing if the theory is correct or not yet, because although we're close to the answer here, we don't entirely know, and I'll show you how close we've got later on. Okay, so let me talk about something that we really don't understand, and in fact, Josh beat me to it in his introduction. And this is the phenomena of antimatter. Now, antimatter sounds great. It sounds like science fiction, but it's not science fiction. It's science fact. It's just incredibly rare. Now, every type of particle I've told you about in the standard model has an antimatter counterpart, a type of mirror image, oppositely charged version. Now, we just don't see very much antimatter on Earth, and we know this, because if I have antimatter and it meets its matter equivalent, it annihilates, and the resulting annihilation is huge. If I have a quarter of a gram of antimatter meeting a quarter of a gram of normal matter, this annihilation has the explosive force of five kilotons of TNT. It's a very good diagnostic tool if you have antimatter in the room. You immediately discover it. Well, we haven't seen that. We haven't seen it on Earth. We haven't seen it out in the universe anywhere we've looked. And so, for that reason, we don't think there's very much antimatter around. And that is the problem, because when the universe started in the Big Bang, we think that half of it was made of antimatter. And just after the Big Bang, matter and antimatter would meet, annihilate, releasing photons of light that then would split into new pairs of matter and antimatter that would meet, annihilate, and this whole process carried on as the universe expanded and cooled. Until eventually, when the universe was a matter of seconds old, the universe had expanded so much and cooled so much that these annihilation photons no longer had enough energy to make new pairs of matter, antimatter particles. And this whole battle between matter and antimatter stopped at that point. And what remains in the universe now, today, is a consequence of a very tiny difference between the amount of matter and antimatter that we had at that point. A very tiny difference, something like one part in a billion. But that very tiny difference is the reason why we're here. We're the leftovers, because if there were equal amounts of matter and antimatter at that time, the universe now would just be full of light. It would be a very, very different place. So if we really need to, we really do need to understand how the universe evolved, and that means we really do need to understand what made antimatter that little bit different to normal matter, what the difference in behavior is. And that is one of the leading questions in particle physics today that we have to solve. But it's not the only one. So not only are we not 100% sure that our theory is correct, not only do we still have to understand how the universe evolved, everything I've told you about concerns visible matter. And cosmologists tell us that's a mere 4% or so of the whole thing. So in fact, what I've described to you is a small fraction of the universe. There's far more out there, and you'll be hearing about it and talks after mine. The vast majority of the universe's energy budget consists of mysterious dark energy and mysterious dark matter. Now in particle physics, we have absolutely no idea what dark energy is. We have no idea what dark matter is either, if I'm perfectly honest, but at least we have some ways of testing what dark matter might be made of. We have ideas. We have possible alternative theories of matter that hypothesize what it could be composed of that we can test in our experiments. And one of the most popular versions of theories that could explain this is a theory called supersymmetry. We talked about it very briefly in the discussion after Frank's talk. Supersymmetry is a theory that takes the standard model and extends it, and it brings in deep, intimate connections between force and matter. And in the process, it predicts the existence of a whole new raft of particles, supersymmetrical, Susie particles, partners of the particles that we know about, and the supersymmetric partners of matter particles, behave like force-carrying particles, and the supersymmetric partners of force-carrying particles behave like matter particles. Now, the really great thing about supersymmetry from the point of view of trying to work out what dark matter might be made of is that in many versions of supersymmetry theory, the lightest one of these new particles is a really good candidate for dark matter. It's a really good candidate because it's massive, so it experiences the gravitational effects that led us to infer the existence of dark matter in the first place. And it's also a really good candidate because it's completely, experimentally unseeable, just like dark matter. Well, that seems rubbish. Why would you explain something you can't see by predicting something you can't see, either? But it's not that bad, because if supersymmetry is the right way to view the universe, although we wouldn't see the dark matter particle, we would expect to see the other supersymmetric particles predicted by the theory. We should be able to discover them in our experiments, measure their behavior, match that behavior up to what we expect to see with supersymmetry. And if we can do that, we can infer the existence of this lightest dark matter particle. We can infer what dark matter would be composed of, and that would be wonderful. So these are pretty big questions, but they're by no means the only questions. There are many, many fundamental questions, and these are just the known unknowns. We don't even know what the unknown unknowns are yet, because what we've found out is the more we discover about the universe, the more we find out that is to know about it. And it's questions like this that make us want to research the answers. It's questions like this that made me want to become an experimental particle physicist, because I wanted to know why. So how do you find answers? Well, if you're an experimental particle physicist, you need an experiment to work on. And there aren't many particle physics experiments in the world. I have a map of the globe here with some of the main ones, and I stress this is the personal selections. If I've missed out your favorite experiment, I'm very sorry. So the places in red are where we have particle accelerators. So there's Fermilab and Brookhaven in the States, CERN in Europe, KEK in Japan. Some of these have neutrino facilities as well. Neutrinos, we don't know very much about. They need specialist detections, specialist experiments. And I've put some other facilities where neutrino experiments take place in blue on the map as well. So you pick one of these places. You pick the experiment that's going to give you access to the data that you need to explore these questions. And I work at CERN, which I'll tell you about now. It's a European center for particle physics. And it's been researching fundamental physics now for almost 60 years. And during that time, it's moved from being a European center set up just after the Second World War to allow physicists from different countries to be able to collaborate together when normally politics would not allow them to, to now being something more of a world center because particle physicists from all over the world, from here, from Australia, from Africa, from India, all come to CERN to collaborate together and perform their experiments. And that's because CERN is an incredibly exciting place at the moment, because it's the home of our largest, most powerful particle accelerator. It's the home of the LHC, the Large Hadron Collider. Now, you may have heard of this before, but if you haven't, I'm going to tell you all about it. So the LHC, you can see it in this picture behind me. Actually, on either side, I've just realized there's two screens, so I should stand in the middle. On this aerial view, in red, you can see the outline of the LHC itself. It's a circular accelerator, and I'm mixing up my units here between metric and imperial. It's about 16 miles long, 27 kilometers. And it straddles the French-Swiss border near Geneva. So if you can see a dark area just above the ring, that's Lake Geneva, the city of Geneva is just at the right-hand end of that before you get to the mountains. And in the background, you see the snowy Alps, a Mont Blanc, the tallest mountain in Europe is Slap Bang in the middle there. Now, the LHC is situated 100 meters under the ground, 110 yards. I looked it up. I did the translation. If you go to CERN ever, if you find yourself in that area of Europe, you can go and visit it. As long as we're not running, you can actually go underground and visit it. And by the way, this year and the next year is a very good time because we're not running. And if you do that, you'll find yourself standing in a tunnel like this. And it's only by standing in this tunnel that you really appreciate just how very large the LHC is. You can just see it curving away in the distance, hardly at all. It's almost like a straight line. The circle is that big. And you find yourself standing next to a long chain of blue magnets. Well, these magnets are the heart of the particle accelerator. It's their job to keep our particle beams bent round in this circular path. Because what happens when the LHC operates is that we have two beams of protons, hydrogen nuclei, circulating in opposite directions around the accelerator, and then accelerated to enormous energies. Until it designs spec, these beams will be going just a few miles an hour less than the speed of light. Incredible. Now, I have to add, we haven't reached design spec yet. We're only halfway there, but it's still extremely fast. And when we've made the beams go this fast, we bring them together and we smash them into each other at four points around the ring. It's not quite as good visually as Josh's video, but it's still pretty effective. And we don't just do this once or twice. This process goes on 40 million times a second. And what's so amazing about that, what's so fascinating and compelling if you're a particle physicist, is that in every one of those collisions, for a tiny instance of time, in the tiniest area of space, what you've done is recreate the very hot conditions of the very early universe. And that means you can study matter as it existed at that point in the universe in terms of fundamental particles. That's how we get them to study them. And when I say very early universe, I do mean incredibly early. We're talking billions of a second after the Big Bang. This is where we can access experimentally. Now, around these collision points, we build our experiments. And our experiments are like gigantic, three-dimensional digital cameras. And they allow us to take a snapshot of what happens during a collision. They allow us to take a snapshot of the fundamental particles that are produced and what happens as they fly outwards. We record their paths, their energies, everything we need to be able to deduce what's going on there. And the idea is if we keep on taking snapshots of what goes on in the early universe and what goes on at matter at these very tiny levels, we can start to build up a bigger picture of what's happening. And we can compare it to our theory of what should be happening. And if it matches, great, fantastic, we understand what we're looking at. And if it doesn't, it's even better. We're going to make a discovery. You can't lose in particle physics. Now, just like the LHC, our experiments are huge as well. This is a picture that you may have seen sometimes in stories in the media, often where certain stories come up. It's a picture of the Atlas experiment, one of the two big experiments. CMS is the other one. America works on both of them. But it's a picture taken during construction. So all you can see here are the orange-striped rings of the magnet held up by scaffolding. The important point here, which I wanted to show you this picture, is to take note of the normal-sized man in the yellow heart hat standing at the front. That gives you the sense of scale for just how very large this experiment is. It's 20 metres high. It's 45 metres long. Now, if you see it, that entire volume is filled with precision particle detection equipment with some 100 million channels of electronic information to read out every time we take a snapshot. It's extremely high-tech, extremely complex. Now, every experiment at the LHC is instrumented in the same way, using the same sort of ideas. So what we do immediately around the collision point is have a series of detectors that can tell us where particles go. Incredibly precise detectors, like this silicon-based detector we built for my experiment, LHCB. The silicon is a silver semi-circle, and it's the size that would just fit in the palm of your hand. And it's so precise, it can tell you the position of a charged particle going through it within a tenth of the thickness of your hair. And every experiment has its own version of this, the whole series of them that provide the dots we join together to trace out the paths of particles. Around this, we have other detectors that measure other features of the particles, how much energy they have, what type of particles they are, until by the time you get out to the edge of the experiment, these detectors get very large indeed. And what you see behind me here is a picture of one of the outermost detectors in the Atlas experiment being cabled up, finished off before we started data-taking. Now, I wanted to show you this just to prove that we had filled the middle of Atlas with particle detection equipment, and we hadn't left it empty. Turn your brain around from where you saw the detector before. You're looking at it end-on now, but you can still see those orange stripy magnets. But now they're buried inside lots and lots of detector material. You can also see two physicists cabling up the last part of this detector, but note to get there, they're on a platform. And the platform is suspended by a crane, 20 meters above the surface of the cavern that the experiment sits on. You really need a good head for heights if you're going to work on a particle physics experiment. Now, not every experiment is as big as Atlas, but as I say, they all work on the same principles. The LHC gives us a collision that makes the fundamental particles that we study. The experiments take a snapshot and different particles leave different traces inside the experiment, depending on how far they travel before they're absorbed, and that's what allows us to recognize them. So if we read this out, we can write software programs to analyze what we're seeing. And then, if we do that, we can compare what we get out of these software programs to our theory to see if we're on the right track or not. So there's one extra ingredient we need before we can look at the data, of course, and that's the computers needed to manipulate the vast amount of data that these experiments produce. They produce petabytes of data. In one year, they should produce a thousand times more information than the world annual book production. You know, no one's got enough computers to analyze that, and that presents a bit of a problem because you do have to analyze a data set of that size. If you're going to research any of the big questions I told you about in the beginning, if you want to find the hicks, if you want to look for dark matter, you need to look through every single bit of that data. But we have a solution, and it was developed by computer scientists. The solution's called the grid, and it's like the next step up from the World Wide Web. It's a layer of software that we put on our computers that make it from the outside to the user look like all of our computers in particle physics are joined together in a way we just are completely unaware of, and it makes our computing facilities behave like a geographically distributed supercomputer that is powerful enough to meet our data processing needs. And this map of the world, wherever it has a blob, shows you where we've put computers and connected them onto the grid. Wherever you see a little line, that's where someone's written a program, a software program, and it's travelling around the computer looking for the data, or it's sending back its results. We spend hours looking at maps like this, wondering how our programs manage to get to exotic places when we don't. But it's the last step in our puzzle. So the LHC gives us fundamental particles. The experiments give us snapshots like this. And it's the grid that gives us the computing power to be able to turn this snapshot into an analysis that tells us that this is a candidate, for example, as it is, to be a Higgs boson. So that's how we do it. That's how we perform our research. That's the idea behind it. And the LHC has been running, really seriously running since about 2010, and it's given us a huge amount of data, hundreds of trillions of proton-proton collisions. So now I want to go back to the big questions that I told you about at the beginning of the talk, and I want to show you how much progress the LHC has helped us make into finding out more about the universe. Let's tie it back and see how we're doing. So remember the first question, was the theory correct? And that was all tied up with whether the Higgs boson existed, and if it did exist, was it a Higgs boson? Was it the sort of particle we expected to see in the standard model? Well, prior to the LHC, nobody had discovered the Higgs. Lots of experiments had looked for it, including at the Tevatron here in Chicago. But no one had seen it. All these experiments could do could home in on a certain region where if the Higgs boson did exist, well, that would be where we'd expect to see it. It would have a mass in this region here. And that's what allowed the LHC to be designed in such a way that if that Higgs boson existed, then it should be discovered. So up until the LHC, your best chance of finding the Higgs if you didn't bump into the man himself to buy the soft toy version. And I dread to think how this got started. I have this awful vision of a hundred or so PhD students who are so fed up by having a PhD on finding the Higgs and then failing to do it. They're driven to doing things like this. But at least... Well, at least it was less expensive than a genuine Higgs boson. But all that changed when the LHC started because the LHC had enough energy and produced enough data to be able to disentangle traces of the Higgs boson from all the many backgrounds that mimicked the signal that messed up the signal for other experiments that went before it. And just over a year ago, on a date that Europeans now refer to is Higgs Dependence Day. I can say this because I'm European. Then CERN held a public seminar where the Atlas and CMS experiments that were driving the search for the Higgs publicly announced their latest findings. And this is what they said. Now, I'm going to have to do a little bit of translation from particle physics language, I think. So what had happened was hundreds of trillions of proton-proton collisions had been analyzed and a new particle had genuinely been seen. And it had a mass of about 125 times the mass of the proton where nothing else existed before. And it was seen at 4.9 standard deviation significance. Now, in particle physics, I have to explain this. It's a little bit embarrassing. We have a threshold where we officially define when something has been discovered and when it hasn't yet been discovered. Our threshold is really a matter of statistical precision. And our threshold happens to be five standard deviations. And so no particle physicist could really put the word discovery on that slide there. Now, the difference is five standard deviations just corresponds to a chance of one in 1.7 million that nature has somehow conspired to look like the thing that you're looking for without it being there. 4.9 standard deviations is only a chance of one in 1 million. You know, quite different. But luckily, luckily, the media were on hand to translate for us. And this was widely reported as a discovery as indeed it should have been because both experiments independently saw the same behavior. They saw the same signal from independent data sets analyzed independently. That's a very strong confirmation that something new has happened. And indeed, no particle physicist present at CERN at that time was in any doubt that the Higgs had been discovered. And CERN weren't in any doubt either because sneakily they had invited some of the theorists responsible for predicting the Higgs mechanism along to the seminar just in case they were interested. Now, there's more theorists than just Higgs who predicted this. In fact, there are a set of six theorists who all worked relatively independently in three groups that all came up with the same idea. And here's a picture of Peter Higgs on the right meeting one of those other theorists, François Anglère from Belgium. And would you believe these people wrote their papers back in 1965? And this was the first time they had ever met in person. You'd think that would be impossible nowadays with a number of conferences and workshops and trips to CERN where people always meet each other, but they'd never met before. So there are many firsts going on on that day for Higgs. Now, the reason it took us so long to find the Higgs is like, as I say, it's incredibly rare. And let me show you how rare by showing you an animation of the signal from Atlas building up. So what you see here points to data. The red area is what we expect to see from things that aren't the Higgs. So for a discovery, you want to see an accumulation of data at a place, a particular mass that isn't described by the red curve. And you can just see it becoming apparent now. Well, that's more data than was used for the discovery. And just coming up now is our entire data set that's been delivered. There we go. There's a discrepancy. The next thing to do is to see if it's consistent with what we expect from the Higgs boson. Here in light blue is what we expect. It matches up. That's great. But it matches up within the statistics that we've been able to measure. And there's not many of them. And for that reason, this question is still slightly open. What we've seen for everything we've measured so far is that this Higgs is consistent with the one we expected in the standard model, but we can't be absolutely sure yet. And to test that, we do things like look to see how often we see Higgs in different experimental signatures. We compare that to how often we should see it from the standard model. We compare how often we should see it to how often we do see it as a ratio. And all these different ways of seeing the Higgs, if it is a standard model Higgs, should give you a point that lines up at one. We see it as often as we expect to. You can see there's a bit of fluctuation. And you can see from the size of the horizontal error band there's still quite a lot of uncertainty. And it's at this level, we think we've seen the standard model Higgs. But we need more data to be absolutely precise. And that's going to come in the future. Now, I have to say that that hasn't stopped people just working out things just in case it's not a standard model Higgs. I had a look on the archive where we put our preprints before our papers are submitted to journal. And I counted from the start of 2012 the number of papers with Higgs in the title. Now bear in mind there can only be a handful of experimental papers with Higgs in the title. I counted 1,946 papers, all due, well, the majority due to theoretical physicists coming up with really wacky ways in which this Higgs could be something completely different. Those are the sorts of things we have available to us to test. Okay, so for the first question, we've made progress, tremendous progress. We're pretty sure that the theory is correct insofar as the Higgs boson exists and it looks like the one we expect to see. What about the other questions? Okay, let's go on to the next one, antimatter. Antimatter is really investigated at the LHC by the LHCB experiment. It's what it was designed to do. And I have to point out that the B in our name doesn't come for coming second or being second best. The B is there because we study the properties of the B quark, one of the fundamental particles. And we do that because the reasons we really don't understand, the effects of matter and antimatter for that particular fundamental particle are most different, and that makes it easier to study experimentally. And that affects the whole design of the shape of our experiment. You can see from this cartoon that it's a very different shape to the Atlas experiment. And that's because B quarks, when they're produced, preferentially travel in the same direction as the beam. So we just instrument the area immediately around the beam. So this is a cone-shaped detector where the collision between protons takes part at the left-hand end of the experiment. We just make measurements of particles going forward. Now, to investigate antimatter and matter and their differences, the approach we take here is to isolate a sample of particles containing B quarks, like the B sub-s mesons Josh was talking about. And we can do this from picking out a particular way that they leave a signature behind in our experiment, a signature that looks something like that picture, where in this case, the B sub-s meson has decayed to two particles, a kaon and a pion. We obtain them from our data set, and then we subdivide them into matter and antimatter, depending on the electrical charge of those kaons and pions they've decayed to. And essentially, all we do is count how many of one we have compared to the other, because we expect B and anti-B quarks to be produced in equal amounts. So if we don't have equal amounts by the time they've decayed, that tells us something a bit strange is going on with antimatter, and it's that bit strange behavior that is what we want to understand. Now, as Josh mentioned, we made our first measurement of this difference earlier this summer. And here is an extract from the experimental paper. What it shows you is a number of B sub-s mesons we reconstructed, we found out from our data. The matter version on the left, the antimatter version on the right. And the B sub-s mesons, I'm afraid, don't correspond to the great big thing that goes off the top of the graph. They correspond to the little green area next to it. There's only about a thousand of these things that we found in our data, despite looking at over 70 trillion proton-proton collisions to get them. That's why you need something like the LHC to generate the huge data sets for you to find them. It's very, very rare. Anyway, as you can see from the relative heights of those green peaks, we saw more matter than antimatter. And as Josh said, it was about 25% more. And that was great. So let's go back to our quarks between matter and antimatter. So we made a measurement of it for the B quark. And it was a measurement that had a value of what we expected to see. And that was very good news and very bad news at the same time. I'll tell you what is bad news in a moment. And other experiments have investigated the B quark, the strange quark. LHCB can also investigate the charm quark where we don't expect to see any differences between matter and antimatter. We can make measurements of that. And we don't see any differences between matter and antimatter. So that agrees with what we expect to see too, which is bad news as well. Now, why is this bad news? Well, the bad news is that we don't have an underlying theory of antimatter that gives us predictions about how it behaves that we can test to see if we're on the right track. We only have experimental measurements that matter and antimatter are different. And that means we have to describe this somehow in the standard model because it's an experimentally observed phenomena. It means essentially we have to patch up this very beautiful, elegant theory with something quite ugly to just try and fit what we see. And the way that the standard model does that is by four numbers. It's quite simple. And of these four numbers, one of them directly describes the difference between matter and antimatter and matter, and the other three describe differences in quark behaviour with the weak force where we see matter and antimatter behaving differently as opposed to the other forces where they don't. And we take all the measurements we ever made in any of our experiments that are sensitive to differences in matter and antimatter and using our theory we extract values for these four numbers from them from our experimental results and we compare the numbers that we get. So if these four numbers are a good way of describing antimatter we should expect the numbers that we extract from all our experimental measurements to all match up and be consistent. If it's a really rubbish way of doing it then they're not going to match at all and that's going to tell us we have to think again. But in fact what we find in this somewhat colourful plot is that it all works really well. So what you can see here are lots of different coloured areas. These different coloured areas are the allowed values for this standard model parameter that describes the difference between matter and antimatter from a huge variety of different experimental results direct measurements of matter and antimatter differences measurements of matter mixing into antimatter and back again measurements of matter decaying, antimatter decaying it all goes into here but what we see is that all these allowed values coincide at one point and that means that although there's no understanding no deep reason to have this particular way of describing matter and antimatter in the standard model it does the job it describes what we see in our experiments really well so perhaps that gives us a clue to its deep nature. Well we can think about that and we can look at the amount of matter we see around in the universe and we can look at the difference between matter and antimatter that the standard model describes and we can work back to see how much antimatter that implies at the start of the universe, that's a really good test and what we find is that we don't end up with half a universe of antimatter in fact it's nowhere near that we fall well short we have found that we only describe something like a galaxy's worth of antimatter and that's the problem because we've described matter and antimatter behaving differently in the way we can test it with quarks but this explanation does not explain how the universe evolved we've made progress in understanding this question but there's more to it there has to be another way of tackling this problem and indeed there are other experiments that try to work on measuring antimatter in different ways to try and work out where the extra antimatter went there's another experiment at CERN that isn't situated on the LHC it's situated on an accelerator called the antiproton decelerator lovely name and what this does is it makes samples of anti-atoms you have antiprotons slow down cool down in this accelerator bombarded by positons which are anti-electrons until some of them are captured into an anti-atom and there's one experiment there called alpha that tries to hold these anti-atoms in one place for long enough to make measurements of their quantities and their behaviour to compare directly to hydrogen atoms and this is the only way we have of looking at antimatter directly but it's really tricky because as soon as you make an anti-atom and it hits an atom or it hits protons or electrons it just annihilates it's very difficult to keep it in one place long enough to study it and what alpha have worked out is a way of doing that and it's called a magnetic trap it's very very strong magnetic fields that can hold these anti-atoms in suspension by the subtle interplay between the magnetic field that's applied and the magnetic effects that go on inside the atoms and that holds them in suspension it stops them touching the walls of the tube and annihilating and that means you can make tests of them well so far alpha has only really done a technology prover about 400 anti-atoms and hold them in one place for about 15 minutes but it allows you to make some tests you can test for example the effect of gravity on antimatter and this is a question does antimatter fall down under gravity or does it fall up who knows antimatter is weird you'd think it would fall down but you really really have to test it and in this case you can just turn off the magnetic field and see if your anti-atoms can stop and annihilate or just fall down and annihilate well that test has been done but without much in the way of statistical precision and it will be done in the future with more precision and also we want to study the structure of anti-atoms the energy levels the positrons can have in them compare them to the energy levels electrons have in hydrogen atoms and so forth and this is an area of investigation that's really going to start going next year 2014 when an upgraded version of this trap is going to be commissioned so that larger samples can be studied again it's not the only handle we have on antimatter these are just experiments on earth there's also a really good experiment out in space that you're going to hear about later on from Sam it's the AMS experiment and that is out in space looking for dark matter and antimatter now there are sources of antimatter that we know about in space that just are a by-product of protons moving around in the interstellar gas and scattering they produce positrons as a by-product low energy positrons so we'd expect to see those but there are other potential causes of antimatter dark matter maybe annihilating now that would be really good because then we could understand maybe a bit more about dark matter and we'd understand where extra sources of antimatter are in the universe that aren't described by quarks you can have astrophysical sources that accelerate up positrons to enormous energies too it's a really intriguing subject and I was going to put the results here but I'm not because you can all wait for Sam's talk this evening because I'm sure he's going to show you what they've seen so far and it's really interesting and the last way you can look at antimatter is a way we haven't managed to yet I've told you about quarks and antimatter neutrinos because we know so little about neutrinos and the next generation of neutrino experiments hopes to make the first measurements of matter and antimatter versions of neutrinos that's in the future so antimatter we're making progress and there's many avenues of research going on what about beyond the standard model what about dark matter my second big question what about supersymmetry have we seen any evidence for supersymmetry yet in our experiments well no we're in the dark about dark matter still and that's not for want of looking for evidence of supersymmetry to try and see if this theory is correct or not let me show you this list of investigations that the ATLAS experiment have done looking for different supersymmetric particles behaving in different ways in the experiment in each one you see a coloured line that coloured line corresponds to where we haven't seen that particle where if it existed we would have seen it we've drawn a blank everywhere so much so that when CMS who also looked for supersymmetry presented their latest reports in an open report to CERN last week they retitled this plot instead of calling it the CMS supersymmetry searches plot they called it the CMS we did not find supersymmetry plot and here is their version again the coloured region shown you where we've looked for supersymmetry and not found any evidence for it now just because we don't see it directly in front of our eyes that doesn't mean to say it's not there and that we can't look for it in a more clever way and we can also look for it let me give you an analogy it's akin to flying an aircraft and just looking to see what's in the sky in front of you, you can look with your eyes at what's visible, that's direct you can use radar to see what's hiding out there behind clouds that's indirect well we have our own version of this sort of indirect radar search for supersymmetry going on as well and it comes back to this very popular B-sub-es-mes on this study, a very rare process where three out of every billion times this B-sub-es-mes on is produced it will give us an experimental signature when it decays a pair of muons very rare in the standard model however this rate can be enhanced or suppressed, changed about generally by any new physics that's out there that can participate in this reaction so that makes it a very delicate, sensitive probe of new physics because it can reach out to higher masses than we can access directly now with our entire data set at the LHC LHCB and the CMS experiment have made their first measurements of this process and it's bang on the standard model value yet again there's no smoking gun for a signal of supersymmetry and this always makes the press in Britain at least get incredibly excited every time a new result fails to come out and they have a whole variety of phrases and hyperbole that gets more and more extreme so to start with supersymmetry was being put on the spot awkward questions were being asked of the theory and now it's got so bad that every time a new result comes out we have headlines like supersymmetry in hospital supersymmetry badly damaged but the point about supersymmetry is it's an immensely elastic theory because there are so many unknowns inside it what these results have done have ruled out classes of possible versions of supersymmetry but by no means have they ruled out every type of supersymmetry there's still much out there to test and so because we failed to see supersymmetry so far doesn't mean to say that we're not going to be able to describe dark matter than it doesn't exist just means to say that we need to go to higher energies to look further in order to find it and of course supersymmetry itself might not be the deep underlying theory of the universe that we've been looking for Frank mentioned extra dimensions in the universe we're looking for evidence of those experimentally we're looking for evidence of new types of fundamental particles that we haven't thought of yet we're looking for evidence for anything and as you can see behind me with all these colored lines we haven't found any evidence of anything untoward or unexpected yet we haven't even found evidence for the one thing we assured you would not be produced when the LHC started back in 2008 we've looked for them in our data and we failed to find black holes being produced as well which I must say is quite a reassuring thing however it doesn't really answer that question dark matter is still a huge mystery to us the true nature of our understanding of the universe at this innermost level this innermost frontier is still a mystery to us but research never ever stops so what I've shown you here is what we understand about the universe at the subatomic level what our big questions are our areas of uncertainty are and where we've made our latest progress but there's still more progress going on what's happening now although we're in a rest period with the LHC is that we're performing maintenance on it so we can run at higher energies when we start up again in 2015 we hope to run at the design specifications the design energies and that will give us a much greater reach to look for super symmetry and evidence of dark matter and evidence of really bizarre stuff that would be great if we could find something that would just show us beyond the standard model and it will also give us the extra Higgs events that we need to fully pin down whether that Higgs is a standard model Higgs or perhaps one associated with another theory like super symmetry Alpha and AMS are just at the start of their respective investigations and they're going to continue to give us really interesting results that will hopefully give us progress in our understanding of dark matter and antimatter and then beyond this in the future we're already thinking of the next generation of particle facilities and this is important because it takes an immensely long time to design and build these facilities you're looking at a lead time of something like 30 years from the decision to do something to the development of the technology to make it happen the construction, the commissioning to get to data taking so that means that we have to plan now even though we plan to run the LHC until 2030 and there are many many many discussions about what might come afterwards but whatever comes afterwards we're in a really, really incredibly exciting time because we're in a phase of particle physics where almost every year we push the amount of universe that we're able to see, we push our horizons out further where we can make more discoveries or where we don't make discoveries but in so doing we just learn more about the universe and its behavior than we knew before and what's incredibly exciting at the moment is we're just about to take another one of those steps by going up to full energy at the LHC and we could find anything there because it's in a part of the universe that we've never been able to study before it's completely open and I hope very much we'll find the answers to some of the open questions that I've been telling you about we may not, that's the beauty of research we have no idea so this is a subject in flux you're going to have to wait to see how we push the frontiers of our understanding of the innermost universe out in the next few years thank you thank you Professor Shears for that smashing talk sorry I couldn't resist at this time I would like to invite our panelists to come up to the front and we'll begin to collect questions from our audience remember, find an usher with a sheet to write your questions on and then get them back to them and we'll begin the question and answer period in a short time thanks George Kline, nice to meet you thank you thank you you realize I'm going to pass all the difficult questions onto my esteemed theoretical colleagues oh you're so nice thank you Tara but it's fine, anyway does it it doesn't matter thank you okay folks please find a seat and we'll begin the question and answer period in just a second okay Professor Meloma you can start the questioning alright we'll begin as always with any questions from our panel for Professor Shears anybody want to start? Jim I have a question first of all I wanted to thank Tara for a fantastic brief on what's going on at the LHC it was just stunning it was super shall we say absolutely thank you a lot of people know that I wrote the first PhD thesis at MIT on supersymmetry in 1977 so I've been watching this idea for forever in my life and I noticed that on one of your transparencies the one where you were talking about the decays of the Higgs where you had the red arrow bars there was one which I believe was the Higgs go to 2W where the red line did not line up with the rest of the data sets can you speak to that for the audience? I can indeed how I would reply to this is that I showed five different signatures the Higgs leaves behind and statistically speaking if you look at how you would expect to see your data line up that difference is completely probable if you work out the probability of seeing that distribution there's nothing wrong with it it's not a sign that there's anything wrong only it might be interesting to motivate looking for it in the future there's nothing about that that says it's inconsistent those arrow bars one or three or two sigma one sigma that wasn't very far away from the line really one and a half sigma I wanted to make sure that that point was made clearly to the audience for the equalize out there watching the line as a theorist it's even more important there's an old maxim that no theory should agree with all the data because some of the data is wrong sure I don't know that I agree with that but my serious question is actually this you actually in the latter part of your presentation really kept returning to supersymmetry and for a lot of people who follow the literature the popular discussion they keep hearing the supersymmetry is dead so can you speak a little bit more about why in your eyes it was so important to come back and tell this more nuanced version of the story well it's impossible to kill off supersymmetry as a theory and I said when I described supersymmetry that was because there were a large number of unknowns in the theory it's not very tightly known there are many different values different parameters and it can take and that affects the masses of these new particles that are predicted so they could be much more massive than we've seen so far that's and that would still be perfectly allowable so the LHC has ruled out masses and that's great so it's ruled out versions of those theories that predicted masses in that region but it can't rule out everything in supersymmetry I must say you must be very proud if it was your thesis it's a theory that keeps on giving you have predictions all the time but we would like to mention that there is one bit of circumstantial evidence that's in favor of supersymmetry is this the Higgs? No I mean no way he's going maybe we should count that as 1.5 so I'll mention that also that's good so when you consider unification of the forces of the standard model which is based on strong electromagnetic and weak forces with different strengths we'd like to unify those into one force that has just one strength of course however as observed they have different strengths fortunately this phenomenon of asymptotic freedom that was mentioned predicts that the effective power of forces changes depending on what distance at which you measure them and we expect the underlying simplicity and unity to emerge only at short distances so you can calculate with the stroke of a pen how the forces will behave at much shorter distances if you do that without including supersymmetry the unification fails but if you do it with supersymmetry the unification works so to me that's very strong circumstantial evidence that supersymmetry is a feature of the physical world furthermore the calculation relies on particles not being too heavy so I think there's an excellent chance that they will be found at CERN Frank I'd like to thank you also I won a couple of bets based on faith and supersymmetry because before the Higgs particle was discovered nothing was known about its mass its mass could have been well nothing is too strong but its mass could have been anything say between 80G EV and 800G EV an enormous range of possibilities but supersymmetry predicted the mass would be on the low side less than 150G EV so I put some bets at very long odds like 10 to 1 against that supersymmetry would be found at the LHC with the mass I'm sorry the Higgs particle would be found at the LHC with the mass less than 150G EV and I won and now if I may have my say this is a commercial you guys don't know this but what Frank just did was give you a commercial for my talk you want to go first yeah Tara you expressed some relief that miniature black holes had not been found even had they been produced they wouldn't pose any danger to us for a number of reasons and moreover had they been produced it would have indicated the possibility of an extra macroscopically big dimension so astrophysicists would love this kind of thing you know I do apologize I was quite relieved simply because of the first at the start of the LHC and you're perfectly right it's a really easy logical way to understand that this isn't a problem with black hole production at LHC because the energies involved in LHC even though they're massive and much really energetic compared to other accelerators we've built they're still tiny on the cosmic scale and much harder interactions go on out in outer space so if this is a mechanism it would be happening all the time but still it makes our lives easier when we explain what we've done and that's what gave me relief even though I appreciate your concern I just wanted to add to the play between Jim and Frank there's an interesting sociological phenomenon with experimental physics which is usually wanting to try to prove the theorist wrong which is a good thing but it's interesting that in the case of the Higgs for example before it was found the main thing about the LHC and the machines before it is that it ruled it out from all but a very small region and I remember the experiment saying we're going to show it's not there and of course that was the region it was in and so I think it's important to realize that the experimental nondiscovery of supersymmetry will only be a nondiscovery until it's discovered if it's there so it's really important to constrain it I'd like to make a related point actually broader which is when you report that you're not discovering something what you're actually reporting is that you're discovering that the standard model works extremely well much better than its original evidence would have indicated so we did well and not only did we do well in formulating the theory but enormous amounts of work and ingenuity have gone on into calculating its consequences and one wouldn't be able to make sense of anything that happens at the LHC without tremendous control on how things usually behave in the standard model which usually means as you mentioned parts per billion or parts per trillion you're looking for discrepancy from the standard model you're looking for very small effects haystacks for little bitty needles so you'd better understand hay very well and it turns out that we do in fact as I know you're proud of Frank the thing you won the Nobel Prize for is now the background that's right there used to be an enterprise called testing QCD which was to test whether the theory was right but now after well depending on how you count perhaps I don't know 10,000 sigma evidence in favor of QCD now we have pretty good faith in it so now instead of talking about testing QCD people talk about calculating backgrounds it's exactly the same activity there is one point there's a point however that I think is really important for Americans to understand we salute the great triumph in place at the LHC with the discovery of the Higgs I should point out it's a triumph that belongs to everybody and I agree and that's exactly where I'm going with my comment on the occasion of my previous presentation here at the Nobel conference I spoke about the fact that we Americans stepped back from supporting something that didn't happen which was the SSC which you're very well aware of the SSC would have operated at three times the initial design energies of the LHC and a lot of the technologies as you just alluded to that go into the operation and the detection of the Higgs is made in America however it shows the danger of what bad choices can do when it goes out in the political realm and we look for questions where we ask the American people for their support in science so there's a slightly cautionary tale here actually it's worse because I remember when that happened and it just looks as crazy haha hahahaha ouch sir professor coin was a question could I ask laurence a question are they any crazier oh yeah I mean it would they seem like geniuses now I mean if I may change the topics from super syntax smashing discussion as Chuck said of supersymmetry. I'm wondering, Sarah, it may have been buried in your talk, but I didn't hear it. Are WIMPs still a candidate for a fairly good fraction of dark matter? Well, yes, they are, but we just haven't seen any evidence for them yet. The lightest supersymmetric particle is a WIMP. Is it WIMP? Yes. They're the one and the same. Oh, I see. WIMPs is weekly interacting massive particles. Yes. Did I get that right? Yeah, absolutely. Since the subject of WIMPs, can I chime in just a little bit here? Because a lot of us are real fans of WIMPs, and we don't mean the guys that walk down the street, right? We mean the weekly interacting massive particles. In Frank's talk earlier today, he did something rather beautiful that I'd like to illustrate for the audience. He talked about interspace. Now, we physicists have been talking about this forever. We almost never talk about this to the public, and so this was actually a brave choice. But the thing that's really interesting that follows from us is that if you take the idea of interspace and combine it with string theory, you figure out that there are two forms of dark matter, WIMP dark matter, and another form of dark matter called hidden dark matter. So it's rather interesting that this extension speaks to things that we still don't know about yet. Well, I've got a question here from the internet that maybe accompanies that. This is from a Gustave student named Jen, but she submitted it over the internet. What do you think needs to be done or invented before dark matter is something that can be discovered in the lab, and how close do you think scientists and physicists are to study dark matter in the lab? Well, it all depends what dark matter actually is. So that's a very good question, and if I knew the answer, I would put bets on and then rake in the money. People are exploring all many, many different possible signatures or signals for dark matter. Professor Ting will tell us later about cosmic rays, which are one promising way, searches at accelerators. Another contender for dark matter that I'm very fond of that I think is the best, actually. It's not a wimp at all. It's this so-called axion that I introduced a long time ago, and certainly it has a much better name than wimps, and important experiments to look for that are also being done that are quite different. They are more like the experiments used to search for the microwave background radiation and explore its properties. They use very special kind of antennas, because in some ways the axions are like photons, but more elusive. Then it's also possible, and in fact, such evidence, I mean such, well, I should say over the last few years, and especially over in the recent couple of years, there's been one rumor after another of possible dark matter signals, and I think there are probably even five or six now different groups that claim to have some kind of hint for dark matter. The problem is that these different hints all disagree with each other and basically rule each other out, but none of them has fit very well into any of the existing paradigms of wimps or supersymmetry or axions, so they're probably all wrong, but people are looking very hard for any non-gravitational effect of dark matter. Let me say the other thing that makes it very exciting, and I may talk about this tomorrow, is that there's this competition because there are direct, there's two ways to look for dark matter. One is to create a lab, as Tara talked about. The other one is to look at the dark matter left over from the universe, which is in this room, as I'll talk about, and that means that you can actually build direct detectors, and it's a kind of a neat competition because the existing direct detectors, some of which are underground, near here in fact, are sensitive to almost the same kind of scale of physics that the LHC, that Tara talked about, and so there's this really neat competition. You don't know who's going to do it first, and anytime there's competition in physics, it's a great thing. Anybody else on the panel? I've got another question from the internet from Brad in Sioux Falls for Professor Shears about the LHC. He asks, what are some of the limiting factors in the energy produced by the LHC? Why is the design spec 13 TeV and perhaps probably not beyond that? Oh, that's just a function of the engineering and of the magnets that we use to be able to control the beam and the devices that we use to accelerate the beam. Now, when charged particles go around in a circle, they actually lose energy. They radiate all the time, and it means you have to keep on pumping energy into them, especially if you want them to go faster. This has two effects. One is that you need to pick a type of particle that you'll be able to do that efficiently with, and that's why we use protons, but then that has a side effect. Protons are really hard to keep on bending round in a circle because they've got a lot of momentum. You need very strong magnetic fields to keep those beams going round when you have a circle of the diameter of the LHC. Now, why we run at 14 TeV was because that was the strength of the magnets that could be manufactured industrially at the time. It's the limit of the superconducting technology that was accessible at the time, which I guess we thank you for. But progress could be made if we could find higher temperature superconductors that are possible to manufacture magnets from over the same scales, and that would help us push up the energy. The other alternative, and this is on the table for a future facility at CERN, is to build a bigger ring. Because if you have a ring of a larger diameter, then you could use the same strength magnets, but just make everything go faster. And people have already started making gestures towards the potential digging out of another ring at CERN that instead of being 27 kilometers long, it's 80 kilometers long, and it goes up completely under mountains and completely under the lake. It's quite speculative at the moment. But those are the only ways in which you can change your effective energy scale, and that's why we picked 14 TeV, because it was a limit of what was available. And of course, that's why the SSC would have gotten to greater energies, because there's a much bigger scale. Can I ask a question? Of course. Frank, you talk about Paxium. What is the most unique feature of Paxium? Well, the axion is a very, very light particle. The theory has one parameter, so when I speak of axions, there's a range of possible properties. But given this one, it was like the Higgs particle before the mass was discovered. We know everything about it except one parameter, which could be thought of as its mass. But in this case, the mass instead of being 125 GeV or there are abouts is more like 10 to the minus 5 electron volts. So really, really small. It's a spin-zero bosonic particle, very, very, very feebly interacting. And we believe, well, if you take the consequences of the theory, it would be produced in great abundance in the early universe in a kind of boson-steined condensate that we could hope to detect as a relic of today. Depending on what the mass is, you could hope to detect it either with appropriate kinds of fancy antennas, and that kind of experiment is underway at Livermore. They have a very ambitious program. But if the parameter is in another regime, very large, the most promising ways involve either looking for unusual effects around black holes, where axions could form atmospheres around black holes, or very sensitive, magnetic resonance experiments that could detect it. Does it have a limit on its speed? On speed? Yeah. But its speed would be, it would be cold, dark matter. So, so would the speed. No, no, no. The speed would be faster than the speed of light, or less than the speed of light? The speed of, of axial. Oh, no, much less. It's cold, dark matter. It's cold by now. So, it cools off. And its mass would be just the mass of things that fall into the galaxy and are subject to its gravitational field. So, 200 meters per second or thereabouts. I've got one last question from the audience here for Professor Shears, which is, is there a project in the works at CERN that you're aware of to look for the force particle responsible for gravity. For gravity? Oh! Well, the problem with gravity is that we don't have a good testable theory to make predictions to look how best to look for it. We do have some theories that are testable at the LHC, like the theory of extra dimensions, which can help explain why gravity is so weak in our four-dimensional space by allowing there to be extra dimensions in space where it can be a lot stronger, and where we can see detectable experimental signatures from that feature. So we can test those models at the LHC, although we haven't seen any evidence yet. Other experiments at CERN, I don't believe there's any others that are testing that sort of physics. There are other experiments at CERN that are testing antimatter that are making very precise measurements of particular processes to try and deduce new physics beyond the standard model. I would have put it a different way. We do have quite a good theory of what gravitational effects should be produced at the LHC. It predicts you shouldn't find any. Yeah, I mean, one thing we should really make clear that we maybe haven't is that you sort of been implicitly said, and I guess once earlier too, that gravity is unbelievably weak. It's the first force we get to know of when we wake up and try and get out of bed, but that's because the whole earth is acting on us, and in every particle sense, gravity is essentially irrelevant. The gravitational force between two elementary particles is so small, as Frank pointed out, that there's no conceivable laboratory experiment that could measure that. And that makes it very difficult because we have this really wonderful classical theory of gravity, and we'd like to understand if it can be made like the other theories as a quantum theory. But if we can't even test at a fundamental level the classical theory of gravity acting between particles, you can imagine how much harder it is to try and measure the quantum theory, and that's part of the conundrum of the forefront of physics. But this alternative theory that would include gravity at the same level as the other forces also isn't at the level of sophistication yet to provide predictions that we can test elsewhere, so it's... It's very speculative. It's very... Yeah. It's undoubtedly wrong. As I mentioned, if there were at least one additional dimension that's macroscopically big at the 0.1 millimeter level, something like that, then gravity is strong enough to produce a black hole under the 14 TeV collisions that you hope to achieve. So, I mean, that to me would be a really fantastic discovery because it would imply or suggest the possibility of extra dimensions, which are so important to string theory and everything, right? It also demonstrates the complementarity, which I'm sure will come up at a number of times in the rest of these talks, between particle physics and cosmology. The universe is a laboratory, which is one of the reasons I spend a lot of time thinking about it as a particle physicist, and there are many experiments you can do with the universe that you can't do in a laboratory, and vice versa. And so the universe does allow us to test many things that we can't test at the large outrun collider, the discovery of dark energy, and in fact, it may allow us to test, even at some level, the quantization of gravity, because the universe has certain properties. So that complementarity allows us to do things that's really important. We need both areas. If I may, I want to make sure the audience is aware that there is a classical test of gravity underway right now. Everyone on this panel knows about it. It's called LIGO. It's a ground-based observation system where people are looking for waves of gravity. It's located in two states here in the United States, in the state of Washington, and in the state of Louisiana. And so it's not that we physicists are sort of sitting back saying we can't test gravity classically at all. There is a test underway right now. And well, and to expand upon that, we're also looking for gravitational waves from the early universe, which will be another great test of classical gravity, but in fact, as actually Frank and I just showed, it may even allow us to test quantum gravity. Actually, well, there are many tests of gravity. Things fall down, after all. And I mean, astrophysicists combine gravity in their calculations with quantum theory every day. That's what they do. So despite a lot of loose talk, there's really no conflict between gravity and quantum mechanics. The conflicts arise only under much more extreme conditions than are practically realized or realizable in laboratories, or certainly most, maybe all, astrophysical situations. So you have to work very hard to find any evidence for quantum gravity. And in fact, none has been found so far, an effect that you couldn't ascribe to classical gravity. People have looked for all kinds of things. People have looked for fifth forces, which would be significant deviations from Einstein's theory of gravity, and briefly found them, but those were discredited. People test very carefully the equivalence principle, the perihelion shift of mercury. Many, many experiments are done to test gravity. The people, modern cosmology is based on general relativity. So it provides many indirect tests of Einstein gravity. The trouble, if you want to call it trouble, is that Einstein gravity always works. It works very, very well. It's just like the standard model. And I don't think it should be considered as distinct from the standard model. It really is part of the standard model. If you take the standard model, it gives you a unique prescription for how you should incorporate gravity. That's the prescription we use, and it works. Well, Frank, I would take issue with that. The back of the envelope calculation predicts a vacuum energy that's 120 orders of magnitude larger than what is actually seen. Well, I think that's the biggest error ever in theoretical physics. No, but that's not a legitimate calculation. No, it is, though. The real thing. It's the Planck scale to the fourth power. The real answer that you get from that, well, the real answer you get from that calculation is no answer, because the ingredients that go into it are undetermined. So if you actually did the calculation, you'd find infinity, which definitely shows that your theory has failed. In other cases where you encounter infinities, we invoke a procedure called renormalization, which sweeps them under the rug, which has succeeded in the past. And certainly, although it's inelegant, succeeds also in this case. You're just, OK, so it's smaller than it should be. But if you take its value and put in that very small determination, nothing goes wrong. The theory still works. It's perfectly fine. In fact, the canonical theoretical argument was that because it's infinite, it must be zero. Yes. Yeah. OK, folks. I think we're going to have to cut off the discussion at this point. We will have an opportunity if we're continuing the discussion after Alex Filipenko's talk at 3 o'clock. Thank you.