What Is the Higgs Boson? | Sean Carroll Discusses the God Particle

where were you on july 4th 2012. i was in geneva switzerland at cern the european center for particle physics research but the vibe in the air was closer to that of a rock concert than that of a physics laboratory there were kids 19 years old 20 years old who had literally camped out overnight to get good seats much like you would camp out for a lady gaga concert except that everyone had brought along their laptops there were also distinguished 80 year old scientists who were jostling for good seats in the presentation hall but they were not there to see a concert at all they were actually there just to see a couple of powerpoint presentations of course you know why they were so excited to see some physics seminars it's because july 4th 2012 was when we announced the discovery of the higgs boson this was a massive worldwide media sensation front page news on the new york times and newspapers throughout the world the web servers that were bringing the live stream of this of the seminar announcements crash over and over again you may even have heard of a phrase that physicists sort of dread namely the god particle the god particle was a label given to the higgs boson by leon letterman a very distinguished nobel prize-winning physicist back when he was trying to make the case that the united states should be looking for this mysterious boson but the problem was that letterman wanted to give sort of a marketing label to the higgs boson he knew that if you're watching cnn and you heard higgs boson you would keep on going but if you heard god particle you might stop to listen the problem was he didn't realize that people would take him literally people would think that the higgs boson actually has something to do with the existence of god that is completely false whether you're a believer in god or whether you're not nobody actually believes that god plays favorites among the elementary particles but the higgs boson is a big deal and that is really what i want to try to explain part of the point of this course is going to be not only to explain to you what the higgs is what role it plays but why people were so excited by it and because this is a lecture course not a mystery novel i'm going to give you the answers ahead of time this is the kind of subject where it repays careful thought some in this lecture going to tell you try to explain why it was such a big deal and then in the lectures to come we'll go through all the details and fill in the story a little bit so the point is the higgs boson is a little bit hard to understand because what we call particle physics is different than what we actually think about as professional physicists i actually blame the guy named democritus democritus is an ancient greek philosopher he is really the father of what we now call particle physics we don't know what democritus look like but we do have portraits painted that are labeled democritus because since we don't know what he looked like people like to paint self-portraits and call them democritus so you'll see pictures of people like rembrandt with the label democritus in fact we have no idea what he looked like we do have a nickname that he got he was known as the laughing philosopher and democritus had the idea that you see a bunch of things around you you see water you see solids you see air and the ancient greeks would have thought these were all fundamentally different things the atomists like democritus had the idea that in fact they were just a small number of fundamental building blocks that go into creating all of these different substances they called these fundamental building blocks atoms now sadly for historical reasons in the 19th century the chemists got a hold of the word atoms and so we now use atoms in our modern language to speak of the chemical elements but these atoms that we have the chemical elements aren't really fundamental we know that atoms are made of smaller things what democritus and his colleagues were really talking about are what we would now call the elementary particles the fundamental building blocks of nature and since the 19th century physics has been trying very hard to look for to find the elementary particles particle physics is a thriving field we know that atoms are made of elementary particles called electrons they also have protons and neutrons which we thought were elementary turns out they're not protons and neutrons are made of even smaller particles called quarks and we also have gluons we have neutrinos we have muons there's a whole zoo of elementary particles we will be talking about in lecture three the reason why the higgs boson is hard to understand is because particles are actually not what the world is made of we talk about that we use that all the time and so when we talk about the higgs boson it's a particle it's a boson which as we will see is one of the two major kinds of particles however that's just sort of a sloppy approximation to the true underlying reality our modern idea the idea that is really centrally important to modern physics is that the world is not made of particles but it's made of fields a field unlike a particle is spread out everywhere throughout the universe it's a number at every point in space and time a particle has a location but a field is spread out everywhere and is vibrating is changing its value think of the temperature of the air in the room at every point in a room there's a temperature that's a number that's a field temperature is not a fundamental field it's a derived quantity that comes from the air comes from the molecules the modern point of view on the fundamental nature of reality is that quantum fields vibrating at every location in space and throughout time are the fundamental building blocks of nature you may have heard the question is light or are electrons particles or waves i will tell you the answer they are waves they are waves they are vibrating quantum mechanical fields what we call particles are just what we see when we look at the fields that is the miracle of quantum mechanics that's one of the subtle things we'll have to describe during this course now why is it such a big difference why do we care that the world is made of fields versus particles well like i said when you look at the field you see it vibrating you see a particle there so it makes perfect sense to use the language of particle physics to say there's an electron particle even though we really know there's a vibration in the electron field the one difference is the higgs boson the higgs boson is itself a particle it is a vibration in a field called the higgs field but unlike all the other particles unlike the electron which is a vibration in the electron field the photon which is a vibration in the electromagnetic field for the higgs boson the particle is beside the point for the higgs boson it's the higgs field that really matters on that day july 4th 2012 people were very excited to announce the discovery of the higgs boson but what got them excited was the knowledge that there is a higgs field that fills space you are soaking in it as the commercials used to say that is really what makes modern particle physics go the idea that everywhere around you as you walk through the universe as you wave your hand through space you are moving through the higgs field now remember i'm saying that every particle that we know about is really a field of one kind or another but there's a difference between the other fields and the higgs there's something that makes the higgs special what makes it special is even in empty space the higgs field is not zero if a field is something that has a number at every point in space when you turn things off when there are no electrons around that's a way of saying the electron field is at zero in empty space all of the fields we know about are sitting at zero undisturbed except for the higgs field that is what is making the higgs a little bit different than all the other forces of nature all the other fields we know about the higgs is there lurking and affecting things even in empty space and that higgs field plays two crucially important roles in modern particle physics one role is that it governs the action of the weak nuclear force as we will see there are four fundamental forces in nature there's gravity which we all know about there's electricity in magnetism or electromagnetism which is actually unified into one force then there are two nuclear forces that only work on very small scales they are imaginatively called the strong nuclear force and the weak nuclear force all of these forces are different in their own individual ways the higgs boson is responsible for how the weak nuclear force works and the reason why that is important as we will see is that gravity and electromagnetism are noticeable in your everyday life the reason why they're noticeable is because they stretch over long ranges the nuclear forces on the other hand are stuck there inside the nuclei of atoms they are very very short range that was a mystery for a very long time why were the nuclear forces short range even though gravity and electromagnetism stretch out over such large distances it turns out because particle physics is complicated that there are very different reasons why the strong nuclear force and the weak nuclear force are short range in particular for the weak nuclear force the answer is the higgs boson or the higgs field filling all of space the short answer to a longer question that we'll get to later why is the weak nuclear force short range because the lines of force that are trying to stretch from one particle to another are absorbed by the higgs field that higgs field lurking out there in empty space is really governing how the weak nuclear force works and as we'll see that makes a crucial difference to how our lives work to how all the elementary particles interact with each other the second main feature of the higgs boson is that it gives mass to elementary particles now this is a bit tricky we're going to have to explain this in great detail because who says that you need a field or something else to give mass why can't elementary particles just have mass if you were isaac newton talking about the mass of the earth you didn't need to know about the higgs field you didn't need to know about particle physics or bosons at all when paul dirac the famous physicist first invented an equation governing the electron he just put a mass in there he said the electron has a mass we've measured it i'm going to put a term in my equation that tells you what that means he didn't realize you needed something called the higgs boson to explain how the electron could have a mass so in lecture six we will be explaining why you should be surprised that particles have masses at all and then how the higgs boson does the work to get it right it all comes down to the fact that the weak nuclear force is complicated people tried for a long time to find the right theory to make sense of it in the end the only reason why the weak nuclear force works the way it does and the only reason why we have a theory that explains it is because of the higgs boson so if there were no higgs boson if there were no field filling space from which the higgs boson arose we would live in a very different universe we would live in a universe where the electron for example did not have mass if you had a world with the electron didn't have mass you would not have atoms because electrons would not be able to settle into atoms that means no molecules that means no chemistry that means no biology or no life without the higgs boson there will be a very different place today we have a wonderful elaborate complicated theory of particle physics which also has a very boring name it is called the standard model of particle physics it's an amazingly successful theory really worth a tremendous amount of adulation it's an amazing intellectual accomplishment in that theory all of the forces gravity electromagnetism weak and strong they're all different they all have fundamentally different properties it was the higgs boson that was the last piece of the standard model puzzle it makes the weak interactions work it gives mass to some of the other elementary particles and was the last particle that we found but because of the theoretical superstructure of the standard model we knew that the higgs boson had to be there before we had found it basically since the 1960s particle physicists had thought about this idea maybe there is a field filling space something that we now call the higgs field it seemed to make everything else fit together it seemed to make our theories of particle physics make sense all we had to do was find it and that's what we did in july of 2012 that's why there was such an excitement in the room in that lecture hall at cern it was just a couple of powerpoint presentations but they were saying that we were completing the standard model of particle physics we were completing our understanding of how the matter that you and i are made up of actually works we're made of atoms we're made of electrons and quarks and things like that the higgs boson was crucial to understanding how that worked as i said this understanding went back to ideas from the 1960s and one of the most impressive things about it was that these thinkers back in the 1960s who invented the idea of the higgs field and the higgs boson they weren't really driven by specific detailed experimental results they were really driven by trying to understand how nature could possibly work how could it possibly be the case that the weak nuclear force is such short range this was a very difficult issue at the time and it was fundamentally a mathematical problem we had good ideas about where the weak nuclear force and the strong nuclear force could come from but they didn't seem to give us the kind of theory that we really wanted that's why we were eventually driven to this dramatic idea that all of empty space is suffused with this invisible energy field called the higgs the issue was that we had this really lovely attractive picture for how forces of nature arise at all we have these four forces why why are there four forces why do they have the features that they do the answer that became popular in the 1950s and 1960s was because of symmetries again we'll have a whole lecture devoted to the idea of what a symmetry is it's the basic idea that there's stuff in the universe and you can transform the stuff you can imagine like rotating it changing one field into another without changing the fundamental nature of the object that you're considering that's what a symmetry is it's a change that doesn't make a difference so we had this brilliant idea from the 1950s that symmetries imply forces if you have the right kind of symmetries these very powerful symmetries which we're going to call gauge symmetries they give rise to forces of nature and it's a very beautiful elegant compelling mathematical structure the problem is the forces that you get out of these symmetries are always long range they're always things that stretched over huge distances which we should easily be able to detect we found gravity we found electromagnetism that wasn't that hard but we haven't seen long-range forces for the nuclear forces those are only short-range so it seemed to be a conundrum you had this wonderful idea that you wanted to be true symmetries underlie forces but they only give rise to long-range forces so maybe that idea was not going to work for the nuclear forces the idea that then came along was that these symmetries are there but symmetries are broken there's something in nature that takes these symmetries and breaks them just a little bit if you did that then you could have a symmetry giving rise to a force but that force could be confined to short range and to do that how do you break a symmetry like that you need a field that pervades empty space and has a non-zero value that is the higgs idea in a nutshell you wanted to have these symmetries that give rise to forces but you had to break the symmetry and to do that you introduced the higgs field now when this idea came along in the 1960s it was a very general principle it wasn't something that was a very specific model that was meant to do one precise thing it was an idea if you have a field filling space you can break a symmetry giving rise to a short range rather than a long range force it took a few more years for people to figure out you know what this is how the actual weak interactions of particle physics really work once that idea came along suddenly everything fit together the experiment suddenly made sense however we didn't actually see the field we had that idea of the higgs boson but we hadn't actually back in the 1960s or even 70s seen evidence for it in our data so the next step is to actually go look for it it's very nice to have a theory that fits together and makes sense but we really want to get the direct evidence that we're on the right track and in particle physics that means building new more energetic more powerful particle accelerators really the way that particle physics gets its direct evidence is by e equals m c squared einstein's famous equation relating the energy of an object at rest to its mass times the speed of light squared now you can think that the equation e equals m c squared means that energy is mass times the speed of light squared but really it's the energy a particle has when it's not moving what this does is it enables us to bring into existence new particles with heavier masses than before if we can squeeze a lot of energy into a very tiny amount of space so that's what a particle accelerator does it accelerates other particles to extremely high velocities so those particles get a tremendous amount of energy together and then it smashes them together so there's a lot of energy there you can create more massive particles it was really in the 1970s that the search for the higgs boson began in earnest the 1970s were an era when quantum field theory really became triumphant before in the 1960s even before that all the way back to the 30s we had ideas of quantum field theory but it wasn't until the late 60s early 70s that we really knew this was the right way to think about nature at a fundamental level we figured out many of the pieces of the standard model of particle physics we knew that there were quarks there were gluons there were w and z bosons out there we didn't discover the w and z's until the 1980s but we knew they had to be there even the top quark which was hypothesized back in the 1970s everyone was convinced it was there and we would eventually find it and ultimately we did find it in 1995 at a particle physics accelerator called the tevitron the tevetron was a facility right outside chicago at fermilab the flagship united states particle physics laboratory and in addition to looking for the top quark they were also looking for the higgs boson roughly speaking every major particle physics accelerator since the 1970s has been looking for the higgs there was the tavitron at fermilab there's a dedicated place called the large electron positron machine at cern but look as they may none of them were actually to a actually able to find it that led us to build the large hadron collider the lhc the lhc is not only the most impressive particle physics experiment ever built it is the largest machine ever built of any kind by human beings like i said it's just outside geneva in fact it's underground it crosses the border between france and switzerland it's a european collaboration where other countries such as the united states are sort of allowed to participate but the u.s is not part of the governing body that really runs how cern works the u.s tried to build its own particle accelerator called the superconducting supercollider but congress canceled the funding for that back in 1993 we left it up to the europeans to find the higgs boson so they built the lhc this gigantic machine is 27 kilometers in circumference 100 meters underground cost about 9 billion dollars to build it's a lot of money there's no question but it's spread out over many years many countries and then finally in 2008 we turned on the lhc there were some fits and starts at the beginning we'll tell the wonderful story of the lac being built in lectures eight and nine but finally it started running it started running once and for all in 2009 and it got better every year and finally in 2012 we found the higgs in fact we found it sooner than we had thought i was actually hoping that it would be announced late in 2012 because i had a contract to write a book about the higgs boson the book finally came out in november 2012 as the particle at the end of the universe and i was hoping that the book would be released the same day that we announced the discovery of the higgs boson but the lhc actually worked better than we thought and we discovered in july 2012. so the bad news was my book release was not timed at the same time the good news was i was there at cern i was actually able to be there listening to the announcements that the higgs boson had finally been found this was an historic event not just for particle physics but for human intellectual achievement people were really immensely moved by what they saw it was hard to find the higgs boson we knew from the theoretical construct how it should interact with other particles we knew how it should interact with quarks leptons electrons and so forth but what we didn't know is how heavy it was we didn't know what the mass of the higgs was supposed to be that was a what we call a free parameter in the theory it could have been a hundred times the mass of the proton 120 140 180 we just didn't know it could have been much lighter than that except we would have found it long ago so the trick was to build up the statistical significance of the search as we'll discuss in later lectures all of these particle physics experiments fundamentally run by the rules of quantum mechanics and quantum mechanics says that when you do an experiment when you do a particle physics collision and you look to see what comes out you can never predict with a hundred percent precision what's going to happen you can predict the probabilities of one thing happening versus another one but you can't predict for sure so what you have to do is do that experiment over again and over again and over again seeing enough of an anomaly in your data that you can say aha there's definitely a new particle there that's what took time in 2012 but in fact the experimental particle physicists did better than we expected they got the answer in july 2012 worldwide acclaim soon followed and in fact nobel prizes followed for peter higgs who the boson is named after and francois anglair another one of its discoverers so you can ask yourself why do we do this why do we spend nine billion dollars building large hadron collider why do talented young physicists devote their lives to looking for a particle that may or may not be there many times people want to know what is that going to what are going to be the technological ramifications are we going to build a better iphone are we going to cure malaria or something like that and the answer is you know when you do this kind of basic research looking for a fundamental new particle of nature there will be technological applications there will be spin-offs we have done in building the large hadron collider amazing accomplishments in computer science superconductivity cern the home of the lhc invented a little thing that we call the world wide web because it turns out that particle physicists need to share data back and forth by spending money on doing basic research we inevitably get more back per dollar than we put into the science in the first place but that is not why we do it it's nice to get spin-offs it's nice to get the world wide web or better superconducting technology but really the reason why we devote our lives and our money to something like the higgs boson and the lhc is because we want to know the answer it's simply driven by curiosity we want to discover the way the world works we are driven by the same impulse that democritus and the ancient greeks were driven by we want to know what this nature is that we live in what this world is what are the rules what are the ingredients it's part of what makes us human beings we are curious we want to know we're not content simply to exist and to live from day to day and it turns out for particle physics there is no cheaper way to do it you can't say well we spent nine billion dollars on the lhc the large hadron collider what about if we spent only half that four and a half billion would it have taken a few more years to find the higgs boson the answer is no we would not have found the higgs boson we would not have gotten half as many higgs boson by spending half the number of dollars either you spend the money and you find it or you don't and you don't so so far fortunately the human race has decided it's worth the money to look for these fundamental building blocks of nature and the higgs boson especially is a special particle as we'll see in later lectures it plays a different role than the other particles we are made of quarks and particles called leptons we're not really made of higgs boson it's not an ingredient that you can find inside our atoms but the existence of that higgs field changes the properties of the particles that we are made of and what this means is when it comes to the physics underlying the everyday world the physics of atoms and molecules the physics that underlies the biology that we're made of that describes us we now have a complete theory we have the standard model of particle physics which accounts for everything that you and i are made of it's not all of physics there's many more things out there but when it comes to people planets stars anything you've ever seen with your eyes or touched with your fingers we have a 100 complete theory of the fundamental building blocks that make that up it's the underlying theory it's not the theory of planets and stars themselves when it comes to complicated interactions of many many particles there are many things that we don't understand it's as if we have figured out what the rules of chess are that does not make us a good chess player but still it's very very important to figure out what those rules are when we think about atoms and the particles that make us up we know what the basic rules are there's no room for new particles that we haven't yet discovered to play an important role in you or me that is why the discovery of the higgs was such a big deal and now that we have found it we can move beyond everyday physics as we'll see there's dark matter out there in the universe there's dark energy there's the big bang there's black holes we're hopeful as particle physicists that the higgs boson will not simply be the end of one story the standard model of particle physics it will also be the beginning of the next era in fundamental physics it turns out for technical but believable reasons the higgs boson is a more sociable particle than any of the other ones we know about by which i mean it is easier for the higgs boson to interact with other particles we do think that there are other particles out there not ones that we touch or are made of but we think that there could be supersymmetric particles there could be extra dimensions of space there certainly is something called dark matter out there in the universe we would like to see it we would like to find it the higgs boson might be the way to do that and of course the biggest most exciting possibility is that we will be surprised we have a good theory the standard model underlying what you and i are made of but there's a lot that we're not made of we have ideas maybe super symmetry maybe dark matter other things but in the history of physics the most fun parts have always been when ideas have not been quite right when the experiments have given us something we didn't expect now that we have the higgs boson that's a tool it's something we can use it's a new way of looking at the universe we're hoping to keep looking using our new tool and if we're lucky nature will surprise us once again [Music] you

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Id: wCZr8mUsJ2s

Length: 30min 58sec (1858 seconds)

Published: Fri Jul 16 2021