King's College London: Physics

so my name is Malcolm Ferber I’m the admissions tutor for physics so I can give you a talk about our course or I can tell you first a little bit about my research into cosmology and then give you a talk about our course so who wants to just the course one the boring one I knew once the cosmology one yeah okay so I tell you today about cosmic inflation okay cosmic inflation not to be confused with inflation which is just boring so where is scientific thinking taken us on small scales we had chemistry and then we got to atomic physics and then we discovered nuclear physics and now we’re at the stage of particle physics you know so we know that what the nucleus is made of and we’re trying to work out what’s going on in the smallest scales on the on large scales we started looking at the motion of planets going around the Sun and then later on we refined that to general relativity so you’ve got this physics of the very large and this physics of the very small and what I’m going to be talking about today is what happens when you smash those two things together and use them to do the same thing so particle physics when we do particle physics you probably think of particles there’s lots of little balls flying around and bouncing off each other you shouldn’t really if you do the mathematics of particle physics then you need to use something called quantum field theory okay and then what what that tells you is that this room is full of fields each different particle corresponds to a different field and you can think of fields as been lots of pendulums so you imagine this room is full of pendulums but they’re invisible and they’re connected to each other with Springs so if I if I take one of the pendulums and I move it a little bit then it’ll make the pendulum next to it move and you’ll be able to create a wave that moves through the room and that’s the way that you should think of particles really as waves in a set of pendulums so you take one pendulum and make it oscillate and the other ones are connected to it they will also start oscillating and that’s the way you should think of particles so how does a pendulum work well force is a derivative of a potential some of you know this consciously you all actually know this you might not know that you know it but you do some of you aware of it consciously but you all know it subconsciously so this is Snowdonia if you want to find out how you’re going to roll down the hill in Snowdonia what you do is you look at a map and you look at the equal height lines the contour lines and you see when they’re steepest that’s going to be the steepest direction so you’re going to be you’re going to roll down the hill in that direction and that’s because the force corresponds to where the potential the height is gravitational potential where it’s changing the most rapidly so where it’s steepest you get a bigger force so force is the derivative of potential so here when you’ve got a pendulum you’ve always got a situation where as you pull the pendulum away from the minimum it’s a bit higher so it’s got more potential energy so the force is in the opposite direction because the potential energy goes down in that direction so that’s what’s responsible for a pendulum operating okay whether it’s a spring or whether it’s a gravitational potential now in quantum field theory you’ve got exactly the same thing so when we talk about Springs oscillating sorry when we talk about pendulums oscillating when we’re pulling them away from the minimum when we’re displacing them from the minimum taking their position to be a bit away from the minimum they’ve got a bigger potential energy which means there’s a force pointing about in the other direction which means they’re going to oscillate around and it’s the same with quantum field theory which is why I said that you can think of particle physics as being lots and lots of pendulums each of these fields so this is a scalar field so for example this would be like the Higgs boson each of these fields if you distort them a little bit away from their minimum then there’s a potential which is bigger which means they want to go back to their minimum which is why they oscillate and that’s why you can have waves moving out through the room because these things are so late so this here’s all the particles that were aware of we’ve got six quarks we’ve got three neutrinos we’ve got an electron and it’s big brothers and sisters the muon and the Tau particle and those are the fermions so that I like to think of those as being the things that we are made of and in particle physics are tickle physics in quantum field theory everything is particles including forces so every single force between stuff that were made of the things that keep us stuck together also have to be mediated by particles and those are the bosons do that job those are the force particles so we’ve got photons and we’ve got the gluons which keep quarks together inside nucleus in neutrons and protons and then we’ve got the W and Z bosons that are the big brother and sisters of the

photon and then we’ve got the Higgs boson of course which is actually finally been discovered which is incredible now each of these has got a pendulum associated with so you should think of the room is having lots of different sets of pendulums in the room so you’ve got one pendulum for the up quarks one pendulum for the each shell for the electron and they oscillate with each other and electron is if you take the electron pendulums and oscillate them a bit you’ll get a wave moving through the electron pendulums and that corresponds to an actual electron moving through the room and that’s the way that you should think about it in particle physics and also the different sets of pendulums are connected to each other with more Springs which is why you can get different particles interacting with each other okay so that’s what that’s what we call the Standard Model of particle physics this is Einstein what’s Einstein’s most important equation equals MC squared no so mu nu minus 1/2 R G mu nu equals 8 pi G over C to the fourth T mu nu so the first one he came up with in 1905 that’s the special theory of relativity the second one he came up with in his head in 1908 but he couldn’t write it down for seven years because he found mass genuinely difficult ok so that’s the general theory of relativity which he came up with in 1915 general relativity is extremely successful now what is general relativity I’m going to come back to the particle physics in the pendulums so that was a small stuff now let’s talk about the big stuff for a minute general relativity he came along and he started with the idea that the laws of physics have to be the same for all observers in all reference frames basically Einstein was very clever and very stubborn and he said there has to be true and he thought about it a lot and he thought if that’s true then we’re thinking of gravity the wrong way we normally think of gravity as being a force but actually and that’s what makes the the the Sun go around the earth because there’s a force between the Sun and the earth but he said you shouldn’t think of gravity as a force you should think of gravity as being due to the curvature of space-time so a planet goes around the Sun because space-time is curved which means that this the straightest line that it’s able to take is a curved line through space-time and space-time is curved because the sun’s massive and and his equation here you’ve got you put this mass of the Sun in on the right hand side and you get the curvature of space-time coming out on the left hand side now you might think well that’s just silly why do you want to take a perfectly good theory like Newton’s theory and turn it into something really weird what’s the point actually it does make so out here indeed when you’re talking about the earth going around the Sun there’s no difference between Newton’s theory of gravity and Einstein’s theory of general relativity you get the same answer 365 days you know but when you get closer to the Sun you’re moving into a stronger gravitational field and you start to see very small differences between the two theories pop up so for example the orbit of mercury around the Sun when people use Newton’s theory they found they got the wrong answer for the particular way that mercury was spiraling around the Sun but when they used Einstein’s theory of general relativity and instead of a force they said as a curvature of space-time they got exactly the right answer and also Einstein’s theory predicts that light gets bent around massive objects like the Sun so what you do is because you can’t stare at the Sun because it’s too bright you wait until there’s a total eclipse and then you can look at the Sun and you know that you’re a stars – are actually behind the Sun because you know where the stars are but you can still see them because the light from those stars has been bent around the Sun and it works it works really really well this guy came along fairly quickly after he’d come up with his theory so well yes professor Einstein that’s a really nice theory but you know that it makes the universe expand now for Einstein this was a disaster you should think of the universe as being a big cake with lots of chocolate chips in it I think that’s the best way to think of the universe and it’s there are some conceptual problems it’s an infinite cake and you need an infinite oven etc etc etc but just go with me for a while okay so the the chocolate chips are galaxies if you’ve got two chocolate chips in your cake dog that are quite close to each other and then you put it in the oven as the cake rises the two chocolate chips will not move away from each other very quickly but two chocolate chips that are far away from each other in the cake dough they will move away from each other more quickly as the cake grows and that’s the way that you should think of the universe and this guy said well Einstein theory predicts that this cake the rate at which the cake is going to grow which is given by the typical separation between two chocolate chips a so da by DT which we call a dot divided by a squared the rate at which the cake is expanding is going to be equal to 8 pi times Newton’s constant divided by 3 times the density of the universe and of course there is some density in the universe because there’s stuff around us so any density in the universe is going to make the universe expand so Einstein thought this was a complete disaster because of course the universe is not expanding we’re now sort of 19:20 19:30

the universe is obviously not expanding so he actually started bashing his theory with a hammer to try and stop the universe from expanding by sticking this thing in called the cosmological constant but then this guy Edwin Hubble who had this telescope in the hills above Los Angeles he started making observations of galaxies and fairly quickly he realized that galaxies that are further away from us or are moving away from us faster and the universe is actually expanding and this is a nice picture of Hubble showing and span up his telescope and so Einstein changed his theory got rid of the cosmological constant he never won the Nobel Prize for this it’s a remarkable prediction nobody did and that’s because nobody did I just press some things made the lights go down well somebody did fine he never won the prize for this um and that’s because nobody really took it seriously even until the 1950s when he died nobody really it was only in the 1960s when people started getting really good data and then the 1970s and 80s that we really became convinced that the universe is absolutely expanding so it’s a remarkable prediction so the universe expands in general relativity so this theory that he came up with because he was a stubborn guy wanted the laws of physics to be the same for all in all reference frames it turns out it works in the solar system and it explains the expansion of the universe it’s a great theory however there’s some problems so the input in cosmology and that is that the universe looks exactly the same in all directions so if you go backwards in time everything used to be closer together everything was hotter the pressure was higher the temperature was higher if you go back far enough the temperature was high enough that electrons and protons because everything was closer together is the precious how the temperatures how electrons and protons are so hot that the electrons are stripped off the protons and the universe is full of plasma it’s full of fire so for the first four hundred thousand years after the Big Bang the universe is full of fire so before so this is before so then we run the clock forwards again so when it’s on fire you’ve got electrons and and positive nuclei flying around and photons that are moving around they get stopped they bounce around because they bounce off charged particles afterwards the electrons join up with the ions and you get atoms so you just the universe the fire goes out and you get a gas instead and then all the photons are free to move in all directions okay so if you imagine you’ve all been camp most of you will have been camping right have any of you ever made a fire when you went camping you put the fire out before he went to sleep right presumably or you made sure it was out in the morning have you ever thought about what happened to the photons that were made by the fire they’re still moving off into space in all directions you haven’t thought about these years you’re very selfish people these poor photons are all moving off into the universe they’re still going in all directions nobody cares because there’s so few of them but they moved out into space and they’re going out now imagine the entire universe is on fire and then you put the fire out you’re going to get photons moving out in all directions from all directions and the universe is just going to be full of this light and that’s what the CMB was and this is how the CMB looks on the largest scales it was detected as this was measured in the early 90s and the thing is that what they noticed was yes we can see the light from the fire over there since then the universe has expanded so it started off being orange but since then the universe is expanding so this light is from being orange to being red to being infrared and now it’s microwave light okay and you can see this microwave light from the fire after the Big Bang all across the sky but the trouble is if you look in that direction it’s got exactly the same temperature as if you look in that direction now what’s the problem with that if we say that direction over there is a and that direction over there is B the place where the photons are coming from where we’re seeing the light from the fire that if you’re at a four hundred thousand years after the Big Bang when when that fire went out there wasn’t enough time to send a signal to somebody at B over there 400,000 years after the Big Bang when that fire went out a and B and not in contact with each other there isn’t enough time in that four hundred thousand years for them to send a signal to each other there’s only enough time for them to send a signal to earth so not to each other so why if they got exactly the same temperature and that’s called the horizon problem now the clever ones amongst you’ll be thinking well hold on the universe is expanding so it used to be closer together so they could have sent a signal there but even when you take that into account there’s no possibility for a signal to go between a and B so why have they got exactly the same temperature so now we’re going to take the particle physics all this pendulum nonsense and we’re going to talk about general relativity and we’re going to smash them together and I’m going to tell you about the theory of cosmic inflation which explains this okay so remember we think that all particles are like pendulums and they’re oscillating around in these potential these they’re like pendulums

in a in a potential well now so if we set a particle in motion if we send a particle through the room what we’re doing is we’re taking these Springs and oscillating them so we’re taking the field away from the bottom of its potential and it oscillates around the bottom of its potential and that corresponds to a particle now what happens now that has got some potential energy and it’s got some kinetic energy and that energy is energy density both of those things are I’ve got energy associated with them and so they are energy density so now you remember in general relativity what makes the universe expand quickly is the density of stuff in the universe so here the density of stuff is the potential energy and the kinetic energy of these fields oscillating so the oscillation of the fields makes the universe expand because the density that goes into Einstein’s equations of the expansion of the universe is the potential and the kinetic energy added together now conversely the expansion of the universe has an effect on the way that these quantum fields oscillate on the way that these pendulums oscillate and he acts like a friction so it’s if you imagine a pendulum and I let it go then it’s going to go like that but then if you imagine here that I’ve got a fish tank full of oil and I put the pendulum in the oil and I let it go it’s still going to oscillate but it’s going to be damped and it’s going to go like that the expansion of the universe acts like an oily friction on the oscillation of these pendulums okay so here’s his here’s your oscillating field and you see that because of the expansion of the universe what it does is it makes the oscillation die down all the time and if the unit if the universe is expanding really really quickly the oil is thicker and at some point it doesn’t even oscillate it’s just completely damp and the pendulum just slowly slide down towards the bottom so now what happens let’s say we’ve got a big density so we get these pendulums oscillating we take all the pendulums and we pull them away from the minimum now they want to that means they’ve got a big potential energy because they’re far from the minimum that corresponds to a big energy density that makes the universe expand really really quickly because the universe is expanding really really quickly the motion these guys these pendulums that want to go down and oscillate around and act like particles and not like quantum fields they can’t because their motion has been damped by the rapid expansion of the universe so the field remains frozen very very far away from the minimum and it only slowly moves down but of course as it slowly moves down it’s got a very big potential energy which is making the universe expand very quickly so you get trapped in a cycle which makes the universe expand really really quickly and it doesn’t stop for a while until these fields slowly get to the bottom and the potential energy switches off and then as it gets closer to the bottom the expansion’s reducing and reducing they’re moving faster and faster because the frictions going away and eventually at the bottom it starts oscillating around and they’re hot it stops and then the universe starts expanding normally but this first phase where it’s trapped that’s called inflation now at the end of inflation when it starts oscillating around the bottom I remember I told you that all these sets of Springs so this is this is going to be the thing that is responsible for inflation is going to be one field called the in photon field we don’t know what it is yet but we know that it we think that it exists okay now at the end of inflation what it’s going to do as it oscillates around the bottom it’s connected to all the other fields and it’s going to make them oscillate to so once it starts oscillating at the bottom everything’s going to become excited that means it’s gonna be particles flying everywhere with lots of energy the universe will be full of fire and that’s how the bit that’s how we think the universe began we had this period of cosmic inflation which ended then the universe it oscillated around and filled the universe with fire by making all the pendulums oscillate because they’re all connected to each other so now we’re cooking on gas or rather plasma quark-gluon knew on tau neutrino dharma you know that was what was around so typically after inflation once the universe is reheated everywhere in the universe is like the center of the LHC except it’s probably about a million times hotter okay then we get quiet gluon phase transitions so all the gluons and quartz come together to form neutrons and protons then we start getting nuclear reactions occurring between about one second to one minute after the Big Bang that gives us everything that we know that there’s left over after the Big Bang bit of helium hydrogen lithium deuterium then you wait nothing really happens the universe is just full of fire for 400 thousand years then the fire goes out the recombination then nothing happens for a while not sure why how long probably about eight hundred million years then you get the first stars inflation solves the horizon problem because during this period when the universe is expanding really really quickly because the fields are trapped you get two regions that are very very close to each other and they get stretched very very far apart across the universe okay so two points a and B that started off very very close to each other so the high a high B they come into thermal equilibrium with each other

they exchange information then this then this period of cosmic inflation occurs where the fields get trapped because of the expansion of the universe and you get this rapid exponential expansion and point a and point B had taken very very far away from each other in the universe effect it appears today that they’ve moved apart from each other faster than the speed of light they haven’t really it’s a subtlety of general relativity but that’s what it feels like and that’s how we think that a the light that comes from position a over there and the like the cosmic background light that comes from position B over there that’s how we think they’ve both got exactly the same temperature because of this thing called inflation and some of our research here is based upon trying to figure out what could be responsible for inflation and whether we can understand what this in photon field is based upon what’s happening right now at the LHC and also we do inflation for example there’s a third year project on this for example it also explains where the universe is so flat and it also as its rolling down to the bottom the little quantum fluctuations in it we think that’s the origin of structure I don’t have time to talk about this properly today but we think that these tiny little fluctuations in the fire left over from the Big Bang based on the quantum fluctuations of this in photon field as its as it slowly moves down to the bottom most potential so that’s an example of the kind of research we do in the theoretical particle physics and cosmology department subgroup of the physics department let me now let me talk about other research in Kings physics so we’ve been talking about two different scales in the universe the very largest things and the very smallest things but let’s talk about something a bit more familiar the size of cells one of the things that we’re very strong at in the physics department is biological imaging so some of my colleagues spend a lot of time trying to do biological imaging essentially one of the key things that they want to do is make movies of cells interacting that’s a problem because cells are very small so they don’t produce a lot of light and they interact very quickly so you have to make them shine you have to make them glow up and then you have to make highs high speed you have to make and then you have to make sure that you catch every single photon that comes off them and then you have to do that at high speed as well so they make them glow up by using fluorescence so you can either insert nanoparticles into the cells or you can change the DNA of the cells themselves by inserting things like the kind of DNA that makes fluorescent green coral floressa fluoresce and then you’ve got you can make your cells fluoresce so that when you shine light on them they keep it for a little while then they give it back they sort of glow in the dark cells and you can make them light up more then you have to catch every single photon that comes off the cells so you have to have a super-duper night-vision equipment the equivalent of a super-duper night-vision equipment and then you have to have a super high-speed camera so this is the typical rate of which you have to take a picture of a cell if you want to get a movie of it and this is a glass which is smashing due to sound okay so you need a very very high-speed camera my colleagues have got all these things and they put them all together and they make images of cells and they use that to try and understand how cells attack each other and interact with each other and and they’re trying to and then they help medics medical people some doctors and people in the pharmaceutical industry create new treatments for things like cancer and asthma and epilepsy and things like that and this is an example of a fourth-year project which used nanoparticles to make cells grow up so you could make movies of them and this was this fourth year project resulted in the paper that was in an international journal so that’s an example I’ll talk more about the fourth year projects in a moment but that’s an example of successful fourth year project which ends up in truly research level research let’s go a bit smaller the third group they basically take all the atoms that we have in the universe and they try and understand how they interact with each other using quantum physics this is the Schrodinger equation which is an equation that you will come to know and love as physicists it’s basically the most important one of the most important equations in quantum physics and on the very small scales it determines how particles interact with each other and they use they stick all this into a computer and they work out structures and properties and processes and the different ways that atoms interact with each other see this quantum physics it sounds a bit highfalutin you know it’s probably some weird metaphysical thing but of course quantum physics these days is being just being used by everybody to do very very down-to-earth things so for example this is a quantum mechanical model that they’re using to model the way that stone fractures and they’re using quantum mechanics to actually work out how you can build better drill bits for industry or for example here’s another thing they’ve done they’ve done enormous

computer simulations to work out how you can stop the surface of hip replacements which you want to if you get your hip replaced you’ve got a nice smooth metal surface on the hip replacement and you want it to stay nice and smooth you don’t want it to start growing bone so they’ve used quantum mechanics to work out how you can stop bone from growing on hip replacements there’s another group which I’m not gonna have time to talk about today working on things like plasmonics so what they are doing is they’re trying to replace they’re doing lots of very very cutting-edge things with photons okay the basic goal one of their main goals is to try and build a computer that doesn’t operate using electrons moving around circuits they want to replace the electrons with photons the reason they want to do that is because you might have noticed that computers have stopped getting faster you can get a computer with more and more cores in it but they’re all kind of three gigahertz we’re not we’re not seeing 10 gigahertz cores and that’s because the the cores are getting too hot and they’re getting hot because there’s electrons moving around you’ve got resistance so if you can build a computer that’s made out of photons instead you’ll be able to get it I don’t know 100 gigahertz without any problems because it won’t heat up so what they’re doing is trying to work out I mean obviously this is in the very early stages but they’re doing some of the work to manipulate photons for applications such as building a computer out of photons okay the history of Kings physics this is charles wheatstone he invented the concertina perhaps more importantly invented the Telegraph and the first Telegraph went between Houston and Camden this is the most important physicist who’s worked Kings is James Clark Maxwell I think most people agreed that he was the most important physicist in the 19th century and the most important part of his work he actually did when he was at Kings and that is formulating the Maxwell equations now what he did was he realized that electricity and magnetism were both part of the same thing which is electromagnetism and in the process of doing that he explained how you can get waves electromagnetic waves moving through a vacuum so that’s that’s everything from radio waves to microwaves infrared optical light all these things x-rays gamma rays they’re all photons they’re all particles of light and all of them are just different solutions of Maxwell’s wave equation and he basically took electricity and he took magnetism and he stuck it together instead of selectra magnetism and since then you know people have been trying to realize that electromagnetism and one of the other forces the weak nuclear force is part of the electroweak force of course eventually we want to understand how all these different things are unified into one grand unified theory and that’s that of course is something that we spend time worrying about today for example one of my colleagues here at King’s John Ellis he’s working at the CERN and here trying to understand the next stage of this unification Barker he when he was here he won the Nobel Prize for his discovery about x-rays Oh in Richardson was here you won the Nobel Prize for his work on valves valves the things that people used before transistors and this was Appleton he was here he won the Nobel Prize for his work on the upper atmosphere bouncing radio waves off the affair atmosphere basically and this is Maurice Wilkins now he shared the Nobel Prize for the discovery of the double helix nature of DNA and that was in the physics department at Kings so they shone x-rays fruit DNA and they figured out from the diffraction of the x-rays what shape the DNA was of course the person who did most work on that project was rosalind Franklin but unfortunately she died when she was 38 so she couldn’t receive the Nobel Prize she died of cancer and of course people are now using DNA to kill cancer which is some famous X undergraduates arthur c– clark was here Peter Higgs was here as an undergraduate he did his PhD here as well so that’s a super-fast tour of the history of Kings how do we teach okay so we’ve got lectures about nine hours a week supported by tutorials so the tutorial groups will be an hour a week that will typically be by a postdoctoral researcher that’s somebody who’s got a PhD the groups for the tutorials will be about five people but there’ll also be problem classes in the lectures so the everybody does lectures differently so my lecture course is three hours a week two of those hours I’m lecturing at you the third hour you’re doing problems in class and I’m running around making sure that you’re keeping up with the things with two or three PhD students so that that works though that’s enough cover we were actually redundant that’s more than enough people and then you’ve got a personal tutor who’s a full member of staff and you see them whenever you need

to about patek you know problems and everywhere all students have problems you know financial problems personal problems in the first year and the second year you do lab one day a week on that day you just do lab so basically the entire day is given over to lab we won’t be able to show you the labs today because they’re just actually on the other side of the river there so just over the bridge so on that day you go there and you don’t come to the strong campus all the other four days your lectures are here on the Strand campus and then of course you do personal study what courses do we offer well your choice starts limited because we have to teach you to walk before you can run but then as you move through you get to a point where your choice is really huge so in the first year you do feels ways and matter master mechanics thermal physics lab and computing physics skills and culture which is about giving presentations and making YouTube videos and things like that then in the second year you start to see some choices appearing everybody has to do electromagnetism modern physics but you can do a choice of astrophysics medical engineering then in the third year you do stop met quantum mechanics optics third year project a literature review and then you get a choice general relativity particle physics medical imaging the University ambassador scheme is where you get an opportunity to go into a school and give a couple of hours teaching so that’s a module so you teach in a school you do classroom assisting but sometimes and then you do a project which is like you take a lesson or you do some kind of extracurricular activity with the students but it gives you an example of what teaching is like and then in the fourth year I know I’ve got to finish soon don’t worry in the fourth year because we’re part of the University of London you’ve got a huge number of courses that you can choose from you can do physics courses from King’s College London a Queen Mary Royal Holloway or UCL and you can take courses in any subject you want so there’s a huge choice of subject if your interests role physics you can do astrophysics if you into particle physics you know string through nano physics Medical Physics any nuclear physics any kind of physics that you’re interested in because you’ve got those four departments you can choose courses from any of them and then you’ve got a fourth-year project which is a hefty project and that’s really supposed to be a research level so that if you’re here if you’re at Kings the research projects will be taken you’ll be doing it at Kings with one of the members of staff and that’ll be twenty five percent of your fourth year and that’s supposed to be a research level and we get scientific papers out of these projects what if we got to offer you were slightly smaller than other London universities we’ve got about 90 students in the first year we’ve got about thirty to thirty three staff it fluctuates a little bit always going up it’s a recent it’s a decent stuff student ratio we like to keep things such that we sort of know who our students are and they feel that they can come and talk to us and we know who they are they’re more than just the number the Maxwell society they do Maxwell it normally I wouldn’t talk about a physics society but the Maxwell society is really good we do Maxwell lectures every week which is an opportunity for students to think about what they might want to do when they finish their degree and once a year they all got to the park in Windsor to to have a weekend where they get more detailed lectures on a particular theme I’m gonna have to finish now but if any of you’ve got more questions you can come to the hub where incidentally there’s tea coffee and some cakes and so next people are coming in here in about ten minutes right right okay so I suggest that you’ve probably all got lots of questions but you go down to the hub and I’ll be waiting for you down there and we discuss it down there okay thanks very much you