The Standard Model - with Harry Cliff

what is a Higgs boson you might ask and that's very reasonable question so I'm going to very briefly take you on a quick tour of particle physics to try and understand what this thing actually is so let's start with maybe something slightly more familiar this is the periodic table of the chemical elements which dates back to the 19th century so at the end of the 19th century are sort of well the understood theory of what the universe is made from is there are you know more than a hundred different chemical elements and thanks to Dalton's atomic theory what that's what he said was that for every element hydrogen helium lithium and so on there was a atom which was a fundamental indivisible indestructible little thing that and you had different atoms one for every element so that was a sort of Victorian view of the nature of matter now so here's your atom then it the turn of the twentieth century so 1897 actually the kind of oratory where I work I knew a a particle was discovered the first elementary particle that we we found called the electron and that led over the next few years to a revision of the structure of the atoms the axon as I said before was thought to be something hard indestructible indivisible when the electron was discovered that was revised and we get the model of the atom that we all learn about in school which is a nucleus which contains most of the mass of the atom and that's positively charged and around the atom go these electrons now the periodic table if you look at it in the way that the elements were arranged there are there's a certain there are certain patterns in the properties of the different chemical elements so for example if you look at the Group one elements they all tend to have react in similar ways and they get more reactive as you go down but there are clear patterns in the way the elements are arranged and that was sort of indicative of some deeper structure and this is the deeper structure so essentially you can explain the properties of all these different elements by different numbers of electrons going around the outside of atoms and electrons are what determine the chemical properties of that particular element now this isn't the end of the story so if you zoom into the nucleus it was discovered in sort of the nineteen 1930s that the nucleus itself is made of smaller things and these are called protons and neutrons so these are smaller parts smaller particles which make up most of the mass of the atom the proton is positively charged the neutron is electrically neutral they're much much heavier than electrons they're about 2,000 times more massive than electrons now this may be where you're sort of school physics ended possibly but in the 1960s if you it was discovered actually protons and neutrons themselves are not fundamental they're made of even smaller things and those smaller things what we call quarks quarks depending on your taste so the approach on is made of two up quarks which are these red triangles and one down quark and the neutron is made of two down quarks and one up quark and that's it so that basically says that all of matter every atom in the universe everything that we know about is made up actually of just three different elementary particles so you have the electron first of all discovered by JJ Thompson in Cambridge in 1897 you've got and the two quarks the up quark and the down quark so everything that exists is made of just these three things so you are just quarks and electrons arranged in a rather peculiar way essentially and these are the first three particles of what we call the standard model now the standard model of particle physics is a rather boring name for something quite extraordinary it's really the closest we have to a complete description of the universe at the fundamental level the only thing well in this is quite a few things actually but the main thing that you might be familiar with that it doesn't include his gravity but other than that is got it pretty well pinned down so you've got these three particles that make up all the matter that we're made of then there's something else that gets added to this table called a neutrino neutrinos are sort of like ghosts they're they're these invisible almost almost undetectable particles there are trillions of them going through you right now they're produced by the Sun in vast quantities that go straight through you straight through the earth and they very very rarely interact with the ordinary matter that we're made out of so that's why we're not really that aware of the existence of neutrinos most of the time so this column of four particles makes up what we call the first generation of matter now for some reason which we do not understand nature provided us with two additional copies of these particles there's something called the second generation and in the second generation all the particles are exactly the same as in the first generation set their more massive and they're unstable so for example the electron has a sort of heavy cousin called the muon which is about 200 times more massive than the electron and the reason we don't we're not made of muons and there aren't muons hanging around is because if you make a muon it will very quickly decay into an electron and some neutrinos so these second generation particles don't hang around very long they're unstable but you can make them in high-energy collisions like at the LHC for example and then force at another and then there's a third generation which is even heavier so this is these are what these are what is this four by three twelve particles are the matter particles so they make up the kind of solid stuff of the universe essentially or at least they would if they weren't all unstable apart from this first column and we do not know it is a big mystery we do not know why there are two extra columns in this table it's a bit like the periodic table in a way where you have this sort of structure and you can see these patterns but you don't actually understand yet back in the nineteenth century what underlies this but there's something suggestive here something that sort of hints that maybe there's some deeper structure that could explain why we've got this rather peculiar set of matter particles and I'll come back to that in a little bit and then the last ingredient the standard model are the force particles so there are three fundamental forces in the standard model probably the most familiar to you and one that a lot of important work was done in this building on is electromagnetism so by Faraday and Maxwell and various others so that's the force that causes electrons to stick to the nuclei of atoms it binds atoms together it's responsible for chemistry it's responsible for basically most of the stuff that is important to us and the particle that transmits the electromagnetic interaction is the photon the particle of light so light itself is also an electromagnetic phenomenon then there are two other or three other particles which you may not have heard of there's something called the gluon which is the force particle of something called a strong nuclear force which is a force that binds quarks together inside the atomic nucleus and binds protons and neutrons together it's called a glue one because it glues things essentially and then there's two rather weird ones called the w and z particles and these are particles that transmit a third force an even weirder one called the weak nuclear force now the weak nuclear force doesn't really bind things together like electromagnetism or the strong force this force is responsible for causing particles to decay so when a muon turns into an electron that happens through the weak force and I'll talk a bit more about the weak force it's very important the weak force although we don't really notice it in our daily lives if it wasn't there the Sun wouldn't be able to fuse hydrogen into helium and there would be no matter in the universe so it's very important even though it's not something we're very familiar with so this is the standard model and this was the standard model as had been sort of studied and observed on the 3rd of July 2012 and on the 3rd of July 2012 there was one piece missing which was this the the Higgs so what is this Higgs boson thing and why is it so important well to understand that we actually need to ask a slightly deeper question which is what do I actually mean by a particle so you could be forgiven I sort of did the way I've described this to you in the last few minutes you could get the idea that maybe these particles are somehow like little Lego bricks or they're a bit like the Victorian atoms they're sort of solid little points that move around and stick together but actually that's not what modern particle physics tells us particles are in fact particles aren't really what matters at all it's with our field is kind of badly named in a sense what actually we think of as being fundamental are not particles but fields so a field we've all probably if you've ever held a magnet next to a piece of steel or iron you've felt the effect of a field so field is something that can cause for example a force to be exerted over a distance where there's no physical stuff actually causing that force to be exerted so you could have something a field can be served from a magnetic field and that can you know be strongly a magnet and get weaker as you move further away or it could be a gravitational field like the one that the earth creates around it or the Sun creates around there so we believe that actually for every in particle physics every one of these particles has an Associated field so there is a field for the quarks for the electrons for the neutrinos and for all the force particles and the way we think of these particles are actually as little tiny ripples moving through these fields so this is a rather nice cartoon but my colleagues at Cambridge David Tong who is a theoretical physicist so here you've got your fields this pond a blue sheet and then here you've got some particles having a punch-up so they're kind of these little localized disturbances in these fields and that's how we think of all matter so electrons quarks everything are just little ripples moving through these cosmic energy fields that fill all of space are everywhere which is quite a sort of strange idea but that's really how we think things are so coming back to the Higgs what is the Higgs well the problem existed in the 1960s when the standard model was being put together it was discovered that if you tried to make the particles in the standard model massive then the theory broke down it gives you nonsensical answers so in particular there was a particular problem with these W and Z particles these particles that transmit the weak nuclear force it was known that if they existed they had to be extremely massive but if you gave them mass in the theory the theory gave you nonsensical answers so there had to be some solution to this and the solution was essentially to invent another field so just like the other fields that these particles are ripples moving about in or Peter Higgs essentially said and actually five other colleagues he was working with around about the same time was imagine that there is throughout the entire universe an additional cosmic quantum field and as these massive particles these things that we think are massive moved through it actually they are imbued with mass by this field so for example the electron which has a certain mass what the Higgs mechanism tells us is actually the electron is mass less but by interacting with this cosmic energy field it acquires the property of mass so Higgs wrote his paper in early 1964 and he had this idea which was written down with very elegant mathematics which looks a bit like this and I don't worry I won't try to explain what this means and he sent it off to the journal and he was rejected people was rejected they basically said this has nothing whatsoever to do with physics so Peter Higgs here's nice maths but you know nothing to do with reality so Peter Higgs went back to his paper and he said well hey I need to connect this with something that could be experimentally measured and what he added to his paper was actually basically one line that said if this cosmic energy field that gives mass to all the particles exists then you should be able to create a ripple or a disturbance in it which would show up as a new particle and that thing that ripple in the higgs field is what we call the Higgs the Higgs boson so the thing that gives mass to all of it well to the particles we're made of at least is this field and the Higgs really is the proof that this field is out there and that's why finding it was so important because the Higgs mechanism this Higgs process by which the particles get mass is absolutely fundamental to the standard model it's kind of like the keystone in an arch if you take it away the whole theory just falls in on itself so it was absolute people were almost kind of convinced actually is that this thing must be out there and that's why finding it was so so crucial and what everyone got so excited back on that day on the 4th of July you

Channel: The Royal Institution

Views: 76,491

Rating: 4.934823 out of 5

Keywords: Ri, Royal Institution, standard model, physics, particles, elementary forces

Id: MRwRNMgOGL0

Length: 12min 9sec (729 seconds)

Published: Thu Oct 11 2018