Particle Astrophysics at the Large Hadron Collider, Part I — Dr Martin White

come on yes I think I wanna thank you so this lecture is called particle astrophysics at the Large Hadron Collider and beyond so I want to start by explaining what particle physics is then I'll explain what particle astrophysics is then I will attempt to teach you what I can in two hours one of the running themes of the lecture is that actually it involves lots of hideous mathematics the physics we do nowadays and I'm going to show you the mathematics right I don't believe in in hiding anything from you or giving you lies or anything else and you're not going to understand the mass but I want you to have some idea of where you're going because there's no doubt that you will understand this in probably about five years time so the first lecture is mostly theoretical I'm going to talk about what the standard model of particle physics is now Lawrence Krauss I think told you some of this is that correct good I'll talk about special relativity I'll talk about quantum mechanics and I'll talk about very scary mats right and I will show you some very scary mats now I'm fairly unique in that I mostly started as an experimental physicist and I became the theorist that's quite rare and so I feel that in the last couple of years I've had to study very hard to learn this theory so I've proved it's possible it is possible and it's actually quite fun I mean sitting it sort of 11:00 and evening with the textbook because you can't put it down because you're really trying to understand something is a lot of fun the second lecture is mostly experimental that doesn't mean I'm going to do it in rhythmic dance or with the harmonica it means I'll focus on the experiments that we do to test the theories and of course I'm someone who does both theories and experiments and I like both right and my message to you is whatever you like doing in life there is somewhere at CERN that you can do it right and be paid money for it and that could be computing or it could be anything right so let's start with the theoretical stuff before we do I'll just explain a bit about my my background so I grew up in Cornwall in the UK has anyone ever been there right so you'll know that it still doesn't have electricity and that's that's amazing I then did my undergraduate and PhD at Cambridge no one in my family had been to university before we were the first generation to go I stayed on at Cambridge to do a research position then fell in love with an Australian and came over to Australia so I lived in Melbourne and them now based in Adelaide but the proof is that you can indeed grow up in the country in the middle of nowhere and go off and be an international scientist it's it's actually easy right it is far easier than people lead you to believe so please speak to me later after the lecture or doing this anew after the second lecture or later today about how you want to do that I can help you apply and things like this okay so let's start with what particle physics actually is I mean put your hand up if you have a rough idea of what particle physics is right Emily that's what I expect and I expect you ideas probably the same as as my idea so it's basically the science of what the fundamental building blocks of the universe actually are and the forces that act between them there's two things I need to know I need to know what stuff is made up on what the glue is that that's gluing it together now answering those questions is amusing in itself but it turns out that it also tells us about the very early universe so the universe was born you know very very small at the Big Bang and then it expanded so everything we see in the universe at the moment was originally squeezed into a tiny space of enormous energy density right and when we recreates that energy density at places like the Large Hadron Collider we're studying the state of matter in the very early universe so whatever we produce in terms of the fundamental building blocks of nature were there in the early universe when we see the history of the universe this afternoon you will see that originally you couldn't have atoms in the universe and you couldn't have nuclei even you can even have protons at one point because it was so hot it just melted everything to its constituent parts but so the reason I got into particle physics was because more than anything else it's going to tell us why we're here where the universe came from and how it came to be right it's sort of the modern equivalent of the ancient philosophers who try to think about about where we came from and it's the best answer I suspect about how to get is from particle physics and there's always this sort of particle physics religion debate there isn't a debate really they're more or less just orthogonal to each other it's quite consistent to be religious and scientific and indeed many of my colleagues are this is not yeah so if that's particle physics what is particle astrophysics basically the particles that we make in our colliders are also inspect right now they're particles that that you know we don't make an are colliders but also in specs like hydrogen for example but we found over the last few years that we really have to start studying Astrophysical observations to try and make sense of what's happening in colliders and the other way around and we'll see the explicit connection of that this afternoon did no one to tell you about Dark Matter he must have done right so we're going to talk about Dark Matter again from a slightly different angle I hope this afternoon so most people in the field called themselves particle astrophysicists nowadays partly because it sounds cool but also because we genuinely are doing astrophysics and particle physics I mean before I flew here I had one students meeting with a student who's looking at whether you can measure dark matter in the Sun from its effect on the helioseismology models right the speed of sound in the Sun would change if they start matter in it then I have another person who's trying to find things at the Large Hadron Collider so that's particle physics then I have other people who were writing quantum field theories of dark matter so that's both particle and astrophysics all right so it's really now the same thing so let's start on on what the universe is is made of what we found have you all played with Lego at some point right I mean when I was in the country we couldn't afford Lego we just had to use grass but we found in the 20th century that the universe is really just a giant Lego set you know by definition is it's the biggest Lego set that you can possibly have amazingly the universe is just made of a few different types of block and there are different ways of sticking them together so in Lego there's one way of sticking the blocks together why don't you just sort of put them together but in nature there's four there's four different ways for different types of glue and we'll see what they are in this lecture now if you zoom in the way to think into two particle physics is to start with the atom if you zoom into the atom it's made of stuff right there's a nucleus and there is an electron or a series of electrons orbiting the nucleus if you zoom into the electron there's nothing in it as far as we know right we think that's a fundamental particle in nature if you zoom into the nucleus it is made of stuff right there are protons and neutrons in the nucleus if zoom into the protons and neutrons they're made of stuff right when I was in school they never basically tell you about what's inside the proton even though it only takes another second to say that basically there's stuff in the proton called a quark and the proton is basically made of things called quarks and gluons and it's this weird complicated thing right so here is the table of the Lego blocks of nature right we see that they are we're mostly made of these things here these are called up and down quarks the first third the reason nobody knows there are heavier versions of each of these particles so your protons are mostly made of up and down quarks there's a heavier version of the up quark called the charm quark there's an even heavier version of the charm quark with the top quark there's an even heavier version of the down quark with the strange quark and then there's a heavier strange quark called the bottom quark so by that point people were really running out of ideas you would say in how to name things now it's a great mystery why we have these what we call three generations of particles right no one ordered them they just turned up right there just there in nature we also have particles called neutrinos they're very very light they're very small sort of weakly interacting but they are there we first discovered that those exist in radioactive decay right so if you look at radioactive decay there's some momentum missing when you look at the process right and we think that that's basically because there are neutrinos there then there are particles you know like the electron well if so put your hand up if you've heard of the electron right good have you heard of the muon a few hours very good so there's a heavier version of the electron called a muon and then there's an even heavier version called the tail right so that's this thing here and again these things fit very neatly into three generations right if we make these extra generations which we do at the LHC in places like that spent many happy hours in the office studying top quarks for example they decay very quickly to the particles of the lighter generation right so it's unstable this heavy matter but nevertheless it does exist and it's made whenever there's high energy in the universe so indeed much higher energy than the LHC is the upper atmosphere of the earth right that is a place where you see lots of high-energy collisions so that's the those are the Lego blocks of nature right and I say you're protons are mostly made of up and down quarks in fact they're sort of glued together with this horrible quantum mechanical soup and that includes trace elements of all of the quarks in principle right so then there's the glue and there's four forces in nature that they can glue things together now the first force that you've probably heard of is electromagnetism have you heard of this right good so something you've probably not thought about is it's actually a net to magnetism that's stopping me falling through the floor right because it's the charges in the floor repelling the charges in my feet when I first learned electromagnetism I thought it was just magnets and electric currents and stuff but it's much more fundamental than that it's extremely important that magnetism then there's something called the weak force and the weak force is a weird one to explain it it basically causes radioactive decay to happen if you heard of radioactive decay you know you get radioactive elements and things and generally you've heard about it in the context of giving you cancer if you stand too near these things which people didn't know for years I mean Marie Curie's notebooks is still too radioactive to handle basically because she was she was basically sitting next to radium for that long so you still couldn't handle them without dying horrible death a bit like Marie Curie unfortunately so the weak force makes that happen it's weird to think of a force making a decay happen but that's just what happens in quantum mechanics that may make more sense later today the third force is somewhat easier to understand it's called the strong force so you've got to ask the question what glues your protons together so have you seen the force of electrostatic have you seen the Coulomb force law some of you put your hand up if your hand I mean some will some won't have done if I have two charges here can you see this here good let's say I have a plus Q and a minus Q I'm probably gonna get the sine wrong but the force between them is minus Q squared divided by the distance squared and there's some numbers in there it's probably a 4 PI epsilon 0 zit the problem the problem with being a particle physicist is we deliberately work in units where we set all of these constants to 1 so we never had to bother with them right and it's simply because we can't be asked it's there is no other reason to do this so basically I multiply the charges together and I divide by the distance squared now think about your nuclei right the protons have one electron charge on the right and the distance between them is tiny it's absolutely tiny and then it's squared right so the electrostatic force between them is massive and it's repulsive which is probably where I've got the sign wrong so they probably want to fly apart almost immediately and inside your proton the quarks are actually charged as well so the quarks don't want to sit near each other either there has to be a force which is considerably stronger than electromagnetism which glues that stuff together and we just called it the strong force right it's the strongest force there is and thank heavens it is there because otherwise we wouldn't be okay what's so did Laurence mentioned the standard model of particle physics and I studied that for five years before having any real idea of what it actually meant because to some extent the standard model is just everything we know about particle physics so it includes the particles that we saw in the table just now and it's really built on some theoretical underpinnings so it's basically special relativity plus quantum mechanics plus lots and lots of hard math right that is the standard model we have a complete mathematical description of how the world works now if I write a novel I could write it in you know English or Spanish or Chinese I say yeah I could I could barely write it in English as has been but many of you could write it in many different languages that's one the brilliance things of this school and yeah that is a novel it's written in English if I write a theory of particle physics it's written in a different language called quantum field theory right and that's just a mathematical language but it is just a language right if I want to write a theory of particle physics I buy a textbook on quantum field theory twelve last year just for kicks because they've all got good things in them and then I learn how to use this language it's like learning French and then I'll write a theory particle physics right and bizarrely what but you know when you're studying math in school it just seems like a series of bizarre problems and sort of arbitrarily annoying things that you're given to do some of them are interesting but then eventually you just become so familiar just like oh I'll just write this out and I'll write this this equation for a theory and it just becomes second nature right so I'm going to walk through each of these things in turn okay let's start with with special relativity have you heard of special relativity at least I don't know if you've studied it yet we're not going to do the math okay good now this is one of the things that Einstein is famous for among several brilliant things and what it really does is describe what happens to the laws of physics the different observers all right so first of all I have to explain the concept of it of a different observer it's something that you're totally familiar with but you may not have ever thought about before if I do an experiment here right something will happen right now if I stand over here and do the same experiment you would be amazed if I got a different answer right the laws of physics are the same over there as they are here and indeed if you're doing an experiment at school you can go to the teacher if you've got the wrong result and say well it's because I was standing next to the bin right the laws of physics are the same everywhere so they're different observers right they're in different places in space-time effectively I mean they said there's another sort of observer which turns out to be special right if you're moving at constant velocity the laws of physics don't change for you either it's different if you accelerated and that's what Einstein went on to develop general relativity for but if you're moving at a constant velocity you're fine and the classic example you see in textbooks is let's say you on a train and you're moving a constant velocity the laws of physics are the same for you now partly because I come from Britain I've never stood on a train which is traveling at constant velocity but never they're always being accelerated in horrible directions but it's roughly true I mean I've don't cups of tea I can't stand the Australian obsession with coffee I've drunk cups of tea on trains and I wasn't amazed to find the tea just explode in front of me or go into my face right it felt a bit like drinking a slightly shaky cup of tea right the laws of physics were similar enough all right you can throw a tennis ball up and down if you walk down a you know a train so if you're moving at constant velocity it is true that the laws of physics are the same for you okay so yeah Einstein raised that to a postulate and it was it meant something slightly special at the time they'd started to discover the laws of electromagnetism and he said look it's not just mechanics that's the same for all these observers everything all the laws of physics yeah the laws of electromagnetism should also be the same for anything the second postulate is nonsense the first one you know as I've explained it to you is uncomfortable the second one is nonsense he said that the speed of light is always the same independent of the motion of the observer or the source so in other words I could have a light ray shining towards me and I measure the speed of light right and now I could run towards the light ray at a million miles an hour I can do that incidentally I won't do it for you because it scares people but I can run towards this thing at a million miles an hour and I measure the same speed of light right nonsense it's absolute nonsense but it's true right we did experiment and we found that exactly that is what happens so you just have to accept it as a fact and that's what Einstein did and then all the special relativity is is it's the theory of what that does to the universe because it's true all right so let's go through that a bit slower because we need to wrap up our heads around it you've actually done a version of relativity for your whole lives called classical relativity or Galilean relativity that was before Einstein that you're familiar with if I have a spaceship which is approaching another spaceship at a million miles an hour so a million meters per second how fast is spaceship a approaching spaceship B what's the relative speed of approach can anyone tell me louder two million is obviously two million meters per second obviously right and in fact both ships see that both ships see the other ship coming too them at two million meters per second let's say I have a spaceship now I've already told you the answer let's say that I have a spaceship at naught meters per second and the light ray comes towards it at 300 million meters per second what's the speed of light that he measures or she it's 300 million meters per second which is the speed of light you've probably already seen the speed of light I then have another spaceship which is moving at a million miles an hour towards the library what speed does he get or she it's 300 million again right so if you say three million three hundred million and one you're using classical relativity and that's true for anything that's sort of moving at speeds a lot less than the speed of light and it ceases to be true when you do start moving near the speed of light and in fact it's in the turn in terms of light it's never true that you add the speed sorry basically but you've only noticed these effects when you have anything that's moving close to the speed of light so for some reason light is singled out and you always measure the same speed and it doesn't matter how you're moving at a constant velocity you will always measure the same speed of light and in fact it's not light particularly this special it's anything that's massless we'll see eventually that the forces have particles associated with them the photon is the particle of light and the photon has no mass so that's why it travels at the speed of light so this is complete nonsense but again it's true right it's absolutely true it's it's bizarre but it's absolutely true so Einstein very carefully worked out the implications of this and what it does for you as I said it's only really noticeable these sorts of effects only become noticeable when you travel at speeds close to the speed of light and that's why you have never noticed this particularly because you travel at speeds obviously you can only walk at speeds massively less than the speed of light so one of the things that happens is pull time dilation clocks run slower as you travel very fast well if you think about it you've probably seen even without doing relativity you've probably seen this formula yep you've seen speed equals distance over time there was there was some sort of nervous giggles there or not again so I suspect you've seen this a lot but well if I start saying that speed is fixed for something I start screwing with distances in times I have to because how can speed still equal distance over time if different observers moving at different speeds see the same speed for light right so it turns out the clocks run slower as you tumble faster and again you can do it well you can just stick a clock on a plane and you can make the plane go really fast and the clock run slow right it's amazing you also get sort of length contraction links get shorter for you and things like this we also find that the speed of light is the fastest possible speed it is not possible to go faster than the speed of light and the reason is that you can only go at the speed of light at all if you're massless and if you're slightly more massive you go to slightly slower speed and you can't get negative mass right so you could never go faster than the speed of light you can also show that the energy of a particle at rest is equal to MC squared and it gets bigger right as you go to higher speeds so if we look at this formula this is the actual energy of a thing in relativity now you're used to seeing things like you know you've seen the kinetic energy for something which is half MV squared and what you're getting relativity is something has an energy even if it's at rest and that energy is called its rest energy and that's MC squared this thing here this whole denominator is always bigger than one right so this formula is always at least MC squared and it gets bigger if the particle is moving so we're going to come back to this equals MC squared of course is very famous and we'll see this terribly profound much more profound than it appears here so did any of you see last year that some people claim they've seen particles going faster than light right and they were particles called neutrinos and we actually loved the fact we were doing the Doctor Who show at the time because if this is possible time travel is possible I actually think time travel is possible because Lady Gaga approves it I have to keep updating that reference to keep down with the kids it used to be David Bowie they claimed that particles travel faster than than light right and so what they did is they were measuring the speeds of neutrinos and they measured the speed which was bigger than the speed of light and physicists so well look this is totally against anything Einstein said and he's never really been wrong right if you asked him what he had for tea last night it's the best thing you could possibly be right so everyone was doubtful and indeed eventually a few months later they said well we didn't plug in our GPS properly right so that's a huge media splash and they just didn't plug in the GPS so if you go on to be experimenters that's what I do first if I were you so indeed as far as we know nothing can go faster than the speed of light it's still true yes really so this was not Pro but I'm not aware of this did it can remember what it was cool I'll look this up because I mean there are and this is actually a good point because there are many experiments still testing this idea and we tend to call it an events violation and you can use giant Astrophysical systems to try and do this sort of thing as well and work out if you're seeing it so it's not it's not impossible that some at some point will see this everything we know now was impossible at some stage right so okay I'll look this up after the lecture and see if I can find what it is because it sounds interesting so let's come back to equals mc-squared which is the single most famous equation in science put your hand up if you haven't heard of e equals MC squared nobody right indeed so let's think about what this means I said that it says that a particle has a rest energy which is MC squared right so even when it's not moving it has this energy so really this tells us there's an equivalence between mass and energy right mass is just a super concentrated form of energy and it's basically C squared that's the conversion factor right so if I have a certain amount of mass I multiplied by the speed of light squared and I get the amount of energy that he corresponds to but energy can become mass a mass can become energy they were set concepts before this really but we then realized they were the same thing right I could just convert energy to mass and that's absolutely profound for what's happening at the Large Hadron Collider right we'll see this afternoon when you collide protons together you're not looking at the bits inside a proton you're making a reeds in a very high energy density and then by e equals mc-squared that's converted to mass and we see new particles and what and we'll say after quantum mechanics that anything can basically happen right so sometimes you collide the protons and Higgs boson comes out right and the Higgs boson was never in the proton it's made entirely new from the energy that you created because equals MC squared is true so we've done special relativity no time for the mass you'll you'll be disorderly or suspect actually in special relativity if you know Pythagoras's theorem you can do most of it to be honest so if you're interested you could go away and find some good guides to this have you at least heard of quantum mechanics yes good familiar with is classical mechanics right so what I'm going to do is introduce you to the idea of quantum mechanics by revising classical mechanics in a slightly different way than you've ever done before and then basically show why quantum mechanics is is so different and indeed what is therefore so you're mostly familiar with classical mechanics because of horrible things like this basically every arbitrarily horrible problem known to man that could be given to you pendulums on Springs masses on wraps you know missiles you know in an idea where we're trying to everyone says they want world peace we're still talking about throwing missiles of people in textbooks instead of throwing sweets at people right but nevertheless although it's often tedious the skills that you develop doing this underpin the whole of theoretical physics right so the quantum field theories I told you about actually use the same mathematical techniques as the prospers of classical mechanics so pay attention as a reason we're training you with these sorts of problems but nevertheless let's think about what classical mechanics actually involves the first I'm just going to give you some fats and you may not have thought about it in this way before but you realize it's true the first fact I don't really know how to say it any other way things are basically fini right I mean this is if they right I mean you call it a table you know but it's it's basically a thing now if I turn my back and turn round again it's still the same thing that it used to be it's not a giraffe right and that's because in in classical mechanics things are thinking so in other words most things basically involve pulling particles or rigid bodies that more or less behave like point particles so you may not have done rotational mechanics yet but you know if I have a this is not a point particle it's like a rod more or less but I can treat it as the motion of the center of mass and any rotation about the center of mass but it's still a thing right it's still a definite thing that that is you know stilt you know it's still there you know and if at the end of the lecture it's not still theirs because I've nicked it right so it's still somewhere now quantities can take continuous values right so if I throw this and this is a stupid idea because I don't have to pick it up again but it can have a continuous range of velocity right if I if I move my arms slightly different it would have a different speed but it's continuous it can have any velocity okay there's a limit to how hard I can throw but I can still then just use a machine to throw it harder there's a continuous velocity right now in theory in classical mechanics the system is deterministic if I gave you the mass of this thing already you could probably work out the parabolic trajectory right if I threw it so the thing in classical mechanics is you start with the laws of physics in the initial conditions and you can derive the rest of the behavior now philosophers of course got very excited about this for centuries because they suddenly thought we didn't have free will because because I could throw a pen and predict its motion right I actually think physics is irrelevant to the freewill argument if there even is one I used to read lots of metaphysics on planes and I stopped because I would land horribly depressed because but midway through the journey they'd already proved that the plane couldn't fly and then I'd start getting very worried ok but the system is indeed deterministic we'll see that changes in in quantum mechanics so the key point is that this works well for what I loosely want to macroscopic systems the solar system right the rotation of a galaxy cluster throwing a pen in a lecture theatre and if you think about it that's because we develop new Newton developed this and people before him in sort of I don't know help me out 1500 1600 something artists thereabouts there abouts and we didn't really have much technology in those days right and probably the most exciting thing you could do in those days was strap a piece of wood to a giraffe or a donkey and fill it with fruit and watch it move right that was the limit of our technology in the early 20th century we suddenly had the technology to probe the microscopic world we could actually zoom in to things on the scale of the Ataman we could actually sue min to very very very small things and unfortunately the laws of physics that had been developed up to then were totally wrong well they're just totally but they're just the wrong physics they're totally the wrong physics right there is nothing about the motion of an atom which you can use classical Mechanics for nothing it's just totally the wrong system and it's not a surprise surely because yeah we developed this physics somewhere else I know as a professional physicist this idea of oh we need some new physics to describe this becomes normal because there's a practicing physicist I hesitate to say you're like a poet but you just you have to say something about some problem and you have to use the language of physics you know it and that's it but it's not you know it's never the case that there is some set of truth which is being updated it's just ideas we have to describe certain things now you've probably seen this model of an atom there's the nucleus there's the electron and oh look it's just like the solar system have you seen that is it true no fasiq nature of that no it's not true right you may not have done something called synchrotron radiation but basically there's a magnetic field around this nucleus this thing is moving in it and that means it's radiating energy and that's just a fact of electromagnetism that we measured you know if I have a charged particle moving in a curve in a magnetic field it radiates energy right it's the reason we have to put so much energy into our circular colliders actually because we have to overcome the energy loss as things go around so what happens in this is if this thing immediately just spirals into the nucleus and stopped right if that's true so your atoms wouldn't exist which means that you don't exist so there's no there's no car mechanics that can describe the atom and you can't fix that using classical theory either it doesn't work so they realized they had to come up with a new system of physics to describe the microscopic world and they called it quantum mechanics we'll see why they could have called it anything yeah they could have just called it mechanics part two or something but they called it quantum mechanics and we'll see why so the first thing is that in quantum mechanics is why I labored the point earlier things aren't very thingy at all right if I have something you know I could have this bottle of water I can turn my back and I could look around again it's Tony Abbott as terrifying as that might seem particularly if you were from overseas and I hope none of you arrive by boat but you know things can basically be a superposition it's worse than that they can they're not one thing or the other there are they oscillate between superpositions of totally different things if I watch neutrinos they start off you know I served you the table earlier and there's three types of neutrino there's the electron neutrino the muon neutrino and the Tau neutrino but they just oscillate into each other so we had a problem for years where neutrinos were leaving the Sun and we weren't seeing them in Earth and it's because they were changing into different sorts of things as they float right and that's all to do with with quantum mechanics so what's really happening is that the whole idea of a thing a sort of particle that doesn't change doesn't exist in quantum mechanics there's a thing called wave particle duality particles are a little bit wavy and waves do a bit like particles but really it's not either you know there's just there's something going on in the microscopic world that we can't quite picture but we can describe it mathematically and what it is is it's a things are basically a way a sort of packet of waves so you've probably seen a wave have you looked at wave theory you've torn sort of sine curves for waves and things like this and if I add up lots of waves I sort of can get things like this well I get little packets that look a bit like particles so you can't see any of this stuff in it well that's that's quite fitting for the quantum world but never mind so you actually get a sort of bowl of waviness that over time can can sort of do all sorts of weird things but it's not a particle and it's not even away it's in the middle now I find it oh and it's the cliche is when you actually get to teaching for the first time you you understand things properly in special relativity all of the weirdness is simply from the fact that the speed of light is the same for all observers well that's nonsense but if you accept that it's true nothing about the rest of the theory should ever surprise you because all the weirdness is contained in that single state right and in quantum mechanics I realize there's a similar there's a similar thing to sort of help your understanding all of the weirdness is in the fact that things aren't thinking in the microscopic world they're sort of particle wave like objects and all of the weirdness comes from that and it comes from the mathematical description of that as well right so the fact that it's very strange and very odd it simply comes from that one fact and it is just a fad we've seen so quantum systems aren't deterministic that's the second point so you know a good example of this we've already mentioned radioactive decay if I have a hundred radioactive atoms don't worry I don't here we go then start throwing around if I have a hundred atoms in fire if I know the half-life I can tell you how many I expect to have decayed in five minutes but I can never tell you which atoms decayed because it's a random process right and that's because it's quantum mechanical yes so they're not so it's so quantum so right they're not deterministic in the sense that if I have these hundred atoms in a deterministic system I could I could tell you exactly if one atoms going to decay right in the same way if I have it's something in classical mechanics and I have the laws of physics if I have this pen I can totally predict its motion based on the laws so that's called determinism right I can basically determine what's going to happen that's why it's called determinism in quantum mechanics I can't tell you if a specific atom is going to decay I can only work out the probability that it's going to decay so if I have a hundred atoms based on that probability I can tell you how many of decayed because that's really what a probability is but I could never tell you exactly what's going to happen to one particle or one atom so in mechanics the fundamental thing that we workout is a probability you know you end up replacing this thing with a sort of hideous 3d sketch of looking like this all sorts of horrible things which if you started doing chemistry you may have seen and what I'm drawing is the probability to find an electron in a hydrogen atom and that's all I can work out right and so chemistry is simply based on the overlapping of probabilities of where I'm going to find particles at any one time right which is scary you know the whole system is just based on this sort of crumbling edifice of probability so of course philosophers got very excited about that again because they said well that's where free will comes from then isn't it because you can only determine probabilities right sadly that's irrelevant as well I think you know at this scale things are still deterministic right at this scale classical theory applies it's only in the microscopic world that we see quantum effects and they get a lot weaker as you sort of go back up to macroscopic scales so if you're on court you know in court on a murder charge you can't say I'm sorry I was a superposition of someone else that week you know you can of course you can say that I don't expect it will wash and okay quantities can only take discrete values that's why quantum mechanics is called quantum mechanics and this is a weird concept it turns out to be related to the fact that things are a little bit wavy and it's to do with actually fitting in standing waves when you model things and things like this but you can only travel at certain fixed speeds in quantum mechanics and all I can do with a quantum system is move it from one state to the other but it can't have any speed in between those values right and so everything is then quantized energy is quantized momentum is quantized like mass at some level would be quantized right I can't have any continuous value of these things I can only have discrete values of these things so the last point I guess is the most obvious everything in quantum mechanics is totally in mind-bendingly bizarre right there is no no intuition from classical mechanics at all which will help you in quantum mechanics the mathematical techniques will you know if you've done wave theory then that's basically it yes what you find is that so there is a relativistic version of quantum mechanics called relativistic quantum field theory where basically you would still have conservation of basic quantities yes although it gets slightly trickier because you shift the definition of variables to another way okay this is a common it's actually quite deeply complex question which I'll think about through the day but largely speaking things are still basically quantized yes yeah yeah so you know your relativistic effects would would effect the potential energy in the system although the way the system evolves but they wouldn't change the fundamental nature of the quantum activity right okay so the maths that you learn can help you learn quantum mechanics but but it's totally it's just totally different to classical mechanics you know and as soon as I stopped trying to make it fit with a common experience it was much plain this a it's it's actually quite easy quantum mechanics if you just think of it as a new sort of physics that you've got to learn it's quite easy now the last thing I should mention is that the you know we really do understand the quantum world absurdly precisely I mean my favorite example is the transistor right I mean it's the thing obviously that's still really underpins the computer chip and they're sort of miniaturized technology that you now have in your in your hand when I was at university sort of even early 2000s they were getting to the point where computer chips would overheat before we turned them on right and one of the things that could happen in in quantum mechanics is if I have a potential barrier here so let's say I have a chip with some coating on it the electrons in the chip that of course causing things to work and actually just tunnel through this quantum mechanics allows them to do it and they were getting to the point where to make to actually fit more of these chips into one CPU they were getting to the point where quantum tunneling would ruin the whole behavior and yet our ability to manipulate nature on those tiny scale scales of a nanometer and make an iPad that people just aren't even surprised about they're just like oh this is a bit than this thing you know it's it's just phenomenal I mean be really the proof that we understand the world is that we can we can really manipulate it on those scales it's just phenomenal so there's a very fundamental thing in quantum mechanics called the uncertainty principle right and that's really the fundamental difference between classical and quantum physics so in classical physics I can measure something in principle with arbitrary precision I mean unlimited by the precision of my instrument if you're let's go back to the sort of crime example if you're you know driving a car you can have a policeman with a radar gun measure your speed and it doesn't disturb your motion right and so you can go to court and he'll say well you were doing over the speed limit and you can't say that's because your radar gun made me go faster unless it's psychological rather than physical it's not true you know you can measure something with a particular decision in quantum mechanics you can't possibly even in principle separate a measurement from the thing you're measuring so if I was measuring this bottle of water and I turn round and it's suddenly Tony Abbot before I looked at it it was a superposition of a water bottle and Tony Abbot right the only difference of course is that a water bottle would be a much more effective prime minister I actually I actually watched the UK election recently because it caught living in Australia you could just watch it through the day and it was a monumentally depressing day I think the whole the whole world has gone mad but the thing is it's my measurement that actually caused it to appear as Tony Abbot and then if I turn away again it's a superposition again so the measurement is crucial and we still don't really understand philosophically how that works the processes of measurement what it introduces is something called the uncertainty principle and it says if I measure something you're familiar with momentum I hope and you aware that momentum is a vector is that true you've done vectors yes good so you know a vector has three components I can write them as a column or as a row or you know in lots of different ways there's different notations but there's three components so let's say that I just have a particle moving in 1d and I want to measure two things its x-coordinate and the x component of its momentum is that clear okay so there's this formula on the on the slighty the uncertainty principle that says that the error in the position times the error in the momentum coordinate has to be at least equal to this than h-bar isn't it this number now this is just a number you can look up in textbooks right there's a minimum number for the product of my uncertainty right and you know this is basically let's say that I measure the position of my particle extremely precisely so that means that I have no error at all in the position then I basically get that Delta P X must be greater than or equal to H bar over 2 times 0 what's 1 over 0 roughly it's infinity right it's infinity I was gonna make a joke about the Greek economy then but there's no Greek city ok it's actually very sad forward so in other words if I know the momentum coordinate of the particle very precisely I can know absolutely nothing about its its position why absolutely nothing and that the difference between quantum and classical physics is you're used to seeing errors in classical physics as being the error on my measurement so I'll just use a better instrument and I get a smaller error but this is actually about what we can possibly know in nature right we can't ever know anything about the momentum if we know the position precisely right and of course the same is true the other way around if I'd measured this thing totally precise which one have I done right if we know the position we can't know the momentum if I know this very precisely I can't ever know the position so it's just crazy right but it has profound consequences and interestingly this thing is very very quick to derive once you accept that things are sort of particle waves and you learn the mathematical description of a particle wave and it comes there's a branch of maths called Fourier analysis and you can learn that in your first day of the University and that basically is all of quantum mechanics yeah yeah right so yes so there's a number called age which Planck emitted which is this number in quantum mechanics and then sometimes when you do calculations you need this number which is H over 2 pi so they just conveniently define H bar as H over 2 pi and I can never remember sadly what this number is it's about H bars about 1 times 10 to the minus 34 something like that so if you look it up in a textbook you'll see a number and it'll say H equals this and then H bar is just this over 2pi and generations of students have lost marks and exams by computing the two okay right so there's another version of the uncertainty principle called the energy time uncertainty principle this is you know there's different versions of this and they all come from the same math so they have the same origin so they says if we have a time interval in which we make a measurement of the energy we can't by any method make a measurement to better accuracy than Delta e so in other words our energy uncertainty times our time uncertainty must also be at least this number right and this this to me is one the most effective metaphors for adulthood that I've ever seen if you have the energy for something you don't have the time and if you have the time you don't have the energy groans from the youth you'll get there one day so delta e delta T must be at least eight PI over two and we'll see that this has profound consequences because it's actually where forces come from so this is our sort of last topic in quantum mechanics well well understand that this gives rise to the origin of a force and it will also explain this idea that there are particles associated with the forces in nature so have you seen this sort of demonstration of a force before this sort of idea of where force comes from a sort of force field well you may have seen this oh I can see how I just can remember when I first saw this I've got a feeling it was it was later in my education than you are at the moment so you may not have seen have you seen there the field lines around a bar magnet have you done that right you've probably and that's the same thing really I mean we're just plotting magnetic field lines and this will go from the north to the South Pole this so this was a very sort of it's very Victorian area idea of a force they just built an industrial revolution out of cogs right so the idea of how the world works was well this is cogs everywhere then isn't it this cogs in space in and everywhere just filling things and and therefore one one particle influences another through a field which is a bit like having a load of really fundamentally because everything's cogs you know you've got to think of these Victorian scientists with big beers saying my wife is made of cogs you know so you basically you know you have this idea that a positive or negative charge attract each other because there's a force field and it's the force lines and the density of the force lines is related to the strength of the force and all this sort of thing the problem is as usual it makes absolutely no sense all right I could have a positive charge four billion light years that way and I can have a negative one here and I can wobble the negative charge and this thing tells me that the positive charge immediately knows I've wobbled it right it makes no sense we've already seen it nothing can travel faster than light so that means information can travel faster than light right and so basically it's going to take time for this thing to know about it well this is just an old picture it doesn't make sense there has to be some origin of a force which is not this so the answer turns out to be totally non classical I mean that was a classical picture the answer is quantum mechanical so quantum mechanics tells us that contrary to all of our experience of course in the in the classical world a virtual particle can appear right if I this is this is just as a cartoon showing a particle sort of merrily rolling along and it spits out a virtual particle right now in this case it's a photon right but but you know we'll see that it could be anything in principle so the thing is in the quantum world I said that things aren't very thingy something which naively we might treat is a particle like an electron is actually constantly spitting out virtual particles that then just disappear again and if I remove all the matter from the universe I'm left with vacuum you know we call it the vacuum but the vacuum is not empty it's comprised of particles just popping into existence and then popping away again right and it's literally true I can actually take two metal plates and I can make a vacuum between the metal plates and I actually see a force on the plates because there's particles coming from nowhere and disappearing again right it's it's just true right it's what happens so there's a virtual particle now what we now know and this was really sort of mind-bending result in quantum mechanics is that every particle in nature is emitting an absorbing virtual particles all the time right and it's not yeah this is an idealized cartoon so we have this sort of thing in fact it gets it can get much more complicated than this and I can actually have a particle which releases a photon and then the photon releases an electron and positron and then it goes back to a photon again and then this thing can do even more stuff right so it's just an endless chain all right and when you're actually a professional sort of particle physicist you learn how to calculate what this thing means for the mass of something well it actually changes the mass of particles bizarre so this is Richard Feynman who is probably the most famous physicist after Einstein a monumentally clever man so he came up with this is a fireman diagram this is just his cartoon way of showing this if I have a particle this is one particle say it's an electron say this is a positron which is an anti-electron right and this thing spits out a virtual particle and occasionally it can be absorbed by another particle right so this thing can can happen now the interesting thing to mention just as an aside is that this isn't just a doodle he's actually I mean Richard firemen came up with a set of mathematics which based on this diagram you can use to calculate the interaction rate of this so it's a complete mathematical system it's really quite cool and we're still using it today there was a paper by carnie Hartmann I think last year they claimed that it finally got a better system than Farman diagrams but no one understood him so we're still using Farman diagrams until he can explain it to us in conventional language so here's the same thing again this is just an electron and it spits out a photon and there is a positron moving at the top right now if you think about it what happens there is that the electron spits out this photon which means it loses a bit of momentum and then this positron is hit by the photon which means it gains a bit of momentum right now that's exactly what we mean by a force well what is a force it's something that changes the momentum of something right and it's even related to Newton's third law if you want to think of it that way right now the keeping is it's the uncertainty principle maybe this is something I skipped over yes it's the uncertainty principle that allows this to happen because the fact is in a small amount of time I can never be sure that there isn't a certain amount of energy there and this is just the uncertainty principle rearranged right the fact that there's this relationship between the time uncertainty in the energy uncertainty means that you know if I take a small interval of time which constitutes my uncertainty then there is a small amount of energy which I can never be sure isn't there so it is there right because that's the point in quantum mechanics it will be there effectively because of this uncertainty so this particle can exist for a time delta T if it basically has an energy consistent with this principle right so if I make really heavy things if a really heavy virtual particle popped out of the vacuum it's not going to last as long as a very light particle popping out of the vacuum so this actually allows us this is more complicated you may or may not understand this this is actually taken from the first-year University lectures but later you're getting a bit of university education today I said charging fees for that right so the range of a force can actually be calculated in terms of this so using speed equals distance over time if the particle exists for a time delta T and it's traveling at the speed of light then it's going to go a distance C delta T right and if I put that into the if I use the uncertainty principle and rearrange things I get a range of a force being this well this is the energy produced and if you sit with the formula later perhaps you can ask me after the lecture we can go through that you find the range is basically in this case this funny number again times the speed of light divided by the energy right so this is going to be the typical range of the force and again it's related to the fact that light particles can exist for a bit longer because they require less energy to produce now the key thing with a photon is its mass is zero the mass of the photon is zero and remember that the rest energy of something is MC squared all right so if something's not moving at all it's got an energy MC squared well if M is zero then the energy can basically be zero right so for a massive particle I can never get a zero energy there's always the rest energy but for a photon I can in principle get zero energy because it has no mass so if I put zero into here I get an infinite range for the force so indeed the electromagnetic force is infinite in range because you've basically got this behavior here and indeed have you seen this potential for the electromagnetic force before like maybe there's a question in the back right I mean that is the answer is basically related to quantum field theory and I'm not sure how to put it into into into language you can transfer momentum without having mass basically that's the short answer it you can you can do it right you don't actually require mass to transfer momentum right and that's because in you know what you're thinking of is that in classical mechanics the momentum is MV and if I want to transfer momentum momentum I have to basically transfer something which is a bit like an MV and the answer is in quantum mechanics it's not that simple and there are ways to transfer momentum which are entirely separate formats right and indeed in these virtual particles they're not even constrained to have a fixed mass I can have an electron that doesn't actually have the mass of an electron it has a smaller mass for example and it's just some the process can happen anyway because of quantum mechanics right another question how we get the range yeah sure I mean I mean I'm assuming I can actually pick it up I like it up if I do it which is why I was saying I would do it after the lecture if you're interested it's it's basically if we take a sort of we have what we have Delta e Delta T must be at least 8 bar over to we have a distance which is C delta T and so the range of the force is going to be haven't got a range here okay we've got delta T must be at least 8 bar over 2 times Delta e which we can just call the energy of the photon I pick nor what the factor of 2 here and then the range is 2 C times this okay that's that's a lot clearer that it was just now I hope it's probably still not transparent but is it's clear right yes no question yeah yeah this is also a very good question and the thing and the answer is that in relativity you can prove that the energy of a photon is given by its momentum times C and I can make the momentum arbitrarily small this is its relativistic momentum I can make that arbitrarily small which means I can make the energy arbitrarily small but that's not clear until you've done the maths of relativity and for vectors basically yeah yeah yes yeah with the action at a distance so the real-world implications are it's still the case that when you actually look at things at large distances you have to sort of look at the propagation of signals from one to the other but we've proved that I mean we knew that the Coulomb law was was true so we saw that the Coulomb law was you know Q squared if you have the same charge over four PI epsilon zero R squared right that means the potential is the integral of the force so that goes as 1 over R Y which is what we shown there that has to be true still in classical energies and what we've seen is that the quantum picture of a force effectively reproduces the same law when we get to classical scale yep one ball one ball and I'm with them yep you see the thing is P is no longer mV in relativity so that's why I said this is relativistic momentum right so this is this is relativistic momentum which is not MV right yep it's something else so the photon can have a momentum even though it doesn't have a mass I think me I believe off the top my head the formula for relativistic momentum is M gamma V where gamma is 1 over the square root of 1 minus V squared over C squared so the crucial point is that you won't understand this until you've done the massive special relativity sorry yes yes certainly I don't think it'll help it yes of course I think it's just oh I see what happened yeah right okay so the key thing to take forward is that this idea of a virtual particle actually explained all of the forces in nature not just electromagnetism so we just sort of walked through a cartoon for electromagnetism we saw this table at the start of the lecture you know this is these are the Lego blocks this is the glue that glues them together and so these things can be thought of as basically particles of the force so the particle of the electromagnetic force is the photon and that's also light I mean light is an electromagnetic wave right so that is the the photon we get some particles here for the weak force again this is the force that makes radioactive decay happen there's actually three of them there's two of these W bosons and there's Ed boson we call them all bosons for after Bose the scientists the strong force gets a glue on there's actually eight different types of glue on right but you get a glue on here which is that's the particle of the force which basically binds you your nuclear together yes the complete answer is the fact that these corresponds with non-abelian symmetry group in nature but that won't make any sense to you there turns out to be a amazing relationship this is really an aside now and I suspect we're gonna run over but it was something I was going to include but I took it out because I thought it wouldn't make sense so if it doesn't make sense don't worry there turns out to be a beautiful relationship between symmetry and forces in nature and indeed symmetry and lots of things there's a great mathematician I mean neither I can ever say oh they probably who realized this connection really properly mathematically to give you an example of symmetry have you ever wondered whether conservation of momentum comes from I can only hear a murmur right if people just say momentum is conserved and you expect it to accept this right it's because the laws of physics are actually translationally invariant right the fact that I get the same laws of physics here and here can be shown to demonstrate that momentum is conserved right or energy it's one of the two I think it's momentum in this case and there's a very very short mathematical proof which I was going to give you in the lecture but you have you done calculus yet oh damn I could have given it to you then I thought you wouldn't have done calculus right that's what I thought and say you can yes okay you can prove that the fact that the laws of physics are the same there is there means that momentum is conserved right that's really profound I mean it's not obvious at all but there's a simple proof that you can do this now the what happens with the forces is that I can write the equation so that's like a symmetry transformation that's telling me I can take my laws of physics I can translate all the position vectors over here and I end up with the same laws of physics and what happens with the forces is that I can take the equations of the standard model and they are invariant under other symmetries and there's various abstract symmetries that I can perform on the equations and after I've performed them I get the same I should get the same laws of physics and in doing that I derived the forces so for example it was shown that have you done complex numbers right it was shown that I can take the laws of physics you know I feels for you know I represent particles as fields in my theory and I should get the same laws of physics if I rotate all the fields and mo taking the fields is the same as multiplying this thing by this was effectively a complicated function by e to the I alpha because in the complex plane e to the I alpha rotates things and the laws of physics are the same if I just rotate the field right it doesn't matter right it's exactly the same in principle by analogy by saying if I have something moving this way I could have my coordinate system this way or I can have my coordinate system this way but I should still get the same answer right yes yes I'm coming to that you might be able to guess what it is if you can get yes yeah that's it I thought that was a disappointing actually I thought it's gonna be not good enough okay so I'll finish off this side as quick as I can right so in this case the laws of physics should be the same now remarkably that basically proves that we have photons well the existence of photons comes from the fact that this thing is invariant under rotations right and I can actually have you done group Theory you almost certainly haven't right so basically this is a certain sort of symmetry transformation which we call a u1 transformation it's just a weird name that we call it and it's called u1 because there's certain matrices you can write down that have equivalent to these complex number rotations and they have certain properties which meet them you want now for the other forces in nature it's more complicated we get for example transformations called x u2 but if I take my equations and I make this transformation and insist that I get the same laws of physics I have to introduce three bosons for the weak force Y so the fact that there's three of them actually comes from the property of the symmetry that I had to do to get the laws of physics and in this case it's an even more complicated two transformation called SU 3 right so this is a very abstract idea but exactly in the same way I can get the conservation of momentum from forcing my laws of physics to be the same in translation if I perform other bizarre transformations of the equations I can actually derive the existence of forces so nowadays you know have you heard the term grand unified theory right what a grand unified theory would be would be a theory that actually explained why we get this sort of arbitrary pattern of symmetry transformations in nature people are just trying to work out why on earth we are laws of physics seem to be invariant under certain transformations are not habit I expect in none of that made sense but I'll move on and hopefully that was interesting to the questioner okay so what we found is if we get particles for the forces and indeed the one force that's missing here is gravity we nobody still knows how to write a quantum theory of gravity string theory is an attempt to do it but it's nowhere near finished and it's unclear if it's going to succeed and there are other theories like quantum loop gravity and things like this now that's the biggest unsolved problem in theoretical physics if you if you solve that you're the most famous physicist of the next hundred years I suspect many many many people have tried and failed but it's possible you would have something you inside I suspect now there's one other particle here called the Higgs boson and I will explain quickly why that's necessary so put your hand up if you've at least heard of the Higgs boson yes good I think certain PR department did a good job on this and so the key thing is we saw that the photon was massless and that gives us a very long range force right the gluon is actually massless as well the problem is that these particles actually have a reasonable mass it's quite high and that's why the weak force is weak we saw that there was this connection between the strength of the force and the mass of the virtual particle that it corresponds to so massive virtual particles can travel very far and the weak force is weak the issue is that if we basically try and put this into the into the standard model you've got that system taunt of what's coming if you try and just put mass into the standard model it breaks the theory immediately and so I'll show you the theory and attempt to sort of rant for two minutes to explain why that's the case yet so what are the masses so that's about I it's been years since I can remember numbers off the top of my head because it seems I remember them I have to forget someone's phone number I once saw a neuroscientist give a lecture and he basically said the memory is a cupboard and when the cupboard is full that's it and you have to start taking things out the cupboard it seemed a very simple picture but it's true I mean this the mass of the electron at least is what point five only know them in weird units it's point five one one MeV isn't it right this thing is about 90 GeV so basically this thing is probably a thousand times heavier than the electron right something like that right the two first order these are all very light these are extremely light those things are extremely heavy compared to this yes yes the strong force is weirder there's a long range bit and there's a bit that grows with distance so actually the the strong force I mean the fact that it mostly worked on the scale of the nucleus and things like that it doesn't mean that that's its range it's actually got on slightly longer range than that suggests it's just that the things it tends to glue it binds very tightly because it is such a strong force yes it can be answered I think I mean if you we've seen this picture of firemen diagrams right what radioactive decay actually corresponds to at some level you're you have a proton or something which is mostly I said it was mostly comprised of up and down quarks and what could happen is if the up quark could basically spit out a W boson and a down quark and then this W boson can decay like this or something so this is how Richard Fineman were taught this process so we've seen now actually this is not a bad question we've seen now that the idea of a force is basically some sort of virtual particle exchange so my particle in the nucleus can basically spit out a virtual W boson which then decays and a down quark so when you see a radioactive decay you often see a proton turn into a neutron right that's what radioactive decay means and that's because the U u D has turned into a u D D and it's done it by spitting out electron and a neutrino and so this is how we first realized something like the neutrino how to exist because this things invisible and in radioactive decay there was some missing momentum yes sorry that you have to be louder it you can get both I mean basically because because you I can take these diagrams and turn away I mean it maybe then in most major to decay that's what's happening I can't actually remember to be honest but anytime I draw this diagram I can rotate it round so that either these possibilities could happen yep yeah so that's that's again a sort of simplification of a fireman diagram and it comes down to these weird effects of relativity in fact yeah this this particle here is much much lighter than the W boson so this is really a quantum mechanical effect there's a small probability that I can release the W boson but I haven't started with enough energy to do it so I mean to some extent sort of borrowed energy from the vacuum to do that which is then you know but but I can do that for a certain time what really happens in quantum field theory is is I mean the whole picture of viewing this is somewhat different from this simple description of physical things being emitted and things like this so we end up talking sometimes about non-physical W bosons which the sort of thing Lawrence Krauss is talking about where it's sort of like it has a negative mass or something right but that's only one way of viewing it okay I'll move on and show you this because I think we're probably running out of time so this is really the standard model of particle physics right and I wanted to show it to you not to frighten you I would hope you would sort of look at this and think this is brilliant but it's slightly sadistic to show this to you because in my view you can probably understand 1/4 and 1/8 and that's about it maybe 1/2 if you've really paid attention but I mean none of these objects are probably familiar to you from from high school mats so this is a sort of equation called a Lagrangian that's what the fancy L stands for I said that if you pay attention to classical mechanics the techniques that you develop are exactly the techniques that we use to write particle physics theories so Lagrange was an incredible mathematician and he came up with a brilliant way of doing classical mechanics which they should teach you first because it's easier than the normal way so this is a sort of equation that the grunge would write down for a theory this thing is a tensor field right so you're used to seeing problems where you have a mechanics problem and you start off by writing the momentum of something as a vector maybe and maybe you have the position of something so a vector is actually a type of tensor I could always write a matrix with some other components in it which is like a multi-dimensional vector that's called a tensor so in this sense of active is like the simplest form of tensor in some way so this is a tensor but it's a tensor field so the way that we represent particles now in our theories is the electron for example is an electron field which is filling space and it's the excitation of the field that gives us the electrons and that's because in normal quantum mechanics it turns out that you can't change number density of particles to do that you need a different way of viewing it so if I have the electron field and I sort of excited imagine now I have a you know old school mattresses just with Springs just a network of Springs put together and if I do that on the mattress and let go then some little excitation will suddenly sort of just propagate around the mattress for a brief period and that's what we think particles really are their excitations of fields so this is a tensor field so here this is what the forces of the standard model actually look like in mathematics right here they are right and you can see there's even you one su two in su 3 gauge terms right that's the post name for the fact that these are derived from a symmetry which which we discussed is now yet it's because I'm an SS that there's a sort of travel from waves in quantum mechanics to field modes in you're basically doing some sort of wave mechanics still but you've shifted the degrees of freedom into a field so it's it's a it's basically it only makes sense if you study the equations where it fits in I don't have a simple physical picture I'm afraid that's not a good answer but I don't have a simple physical picture for exactly what's happening with waves in there you can think of these excitations as sort of multi dimensional wave packets if you like this is what the yeah we're okay but we'll get that that's fine yeah we're nearly done we're nearly done okay so here we have the this is what the matter actually looks like why we have these weird things that look like vectors but they're not quite vectors they're something else there's been each we know in the electron there's the quarks and so the mystery as we get down here you start seeing the word Higgs appear right so again the mystery is that if we start with this theory we can actually what we found by about the sixties is you can write down a theory of particle physics with massless particles and everything works perfectly and as soon as you add a massive particle it breaks instantly and you might say well it's just rubbish start again in that case right but it it covers everything else really precisely so there's there must be some way to introduce mass to the system which doesn't just involve adding mass directly so it was Peter Higgs and many others who basically came up with the idea that instead of particles having an intrinsic mass they interact with the field to get their mass right so there's a Higgs field that fills space that particles interact with to gain mass so the W boson it's not true to say it's intrinsically massive it interacts with the Higgs field to get its mass so there's a rough analogy for how this might actually work imagine that you have a party of physicists which I guess it's you probably on the boat this evening and then a celebrity walks into the room and it will be the ghost of Einstein for our purposes now ghosts presumably have no intrinsic mass right there sort of corporal in that sense so the ghost of Einstein has no mass but of course everyone in the room wants to talk to it because they want to first of all find out how he rose from the dead and secondly they want to know how to put gravity into quantum mechanics now as he walks through the room of course people will bunch around him and he acquires an inertia basically for the interaction with this field so this is only a picture but it explains the concept of something interacting with the field to get inertia right and indeed that's what the Higgs field is now the Higgs boson we've just had this picture of exciting fields the Higgs boson is an excitation of the field so you can imagine that now there is no ghost of Einstein there's just a rumour of free wine or something and that clusters around the room and we've excited the field and we get this sort of propagating if it's something that looks like a particle but it's really just an excitation so what we did it CERN in 2012 and I guess in fact in the few years before 2012 several times is we indeed excited the Higgs field and observed this for the first time so Peter Higgs proposed in 1964 that there should be a Higgs boson and it took till 2012 to discover it so come up with your theories early that's my advice to you because you'll probably be just retiring mirliton they're discovered what we knew at this point this is the sort of article I wrote for the web we knew that the particle looked extremely like the Standard Model Higgs boson but it could have been something else we now think it's almost certainly the Standard Model Higgs boson what I still hope and perhaps we'll cover up this afternoon is that it's just one Higgs boson of many I mean many of our theories give us five Higgs bosons for example and that's something that I must hope to see and in those theories one of them would look like the Stan a model Higgs boson so that's good okay so we've reached the sort of end of the lecture so we've seen the standard model and what it actually am always hopefully having seen the equation you get some sense that there's some awesome mathematical power there even if you can't do it yet I hope you've understood something about the bits of special relativity in quantum mechanics that make this thing really work for us what we're going to start with this afternoon is what with the standard model you know if we discovered everything why are we still spending billions of dollars throwing protons together there is a reason and then I'll talk about how we fix it any any other questions or do we or do you want to move people you

Channel: The Professor Harry Messel International Science School

Views: 13,962

Rating: 4.8251367 out of 5

Keywords: Large Hadron Collider (Exhibition Subject), Astrophysics (Field Of Study), Particle Physics (Field Of Study), physics, Australia (Country), Sydney (City/Town/Village), ISS2015

Id: uhwuU9l10PM

Length: 78min 40sec (4720 seconds)

Published: Fri Sep 04 2015