there was earlier on there was a slide which showed that 5% of everything was you know us as it were the real the real world that we know how do you know it’s 5% when you don’t know what dark matter is made of yeah good question so well there are a number of different ways of working out how much dark matters out there so there’s the lensing method so you can use this lensing method across the whole sky essentially and map the distribution of dark matter by how light is being bent through space and you can compare how much bending you expect from how much visible material so that’s one way of getting at how much dark matter there is another way though actually the way dark matter was originally observed was by looking at the rotations of stars around galaxies so physicist called Vera Rubin in the 70s was looking at Andromeda and other galaxies near to the earth and she measured excuse me she measured the rotation speeds of the stars and what you expect is the close to the center of the galaxy you have lots of gravity so the star should be orbiting very quickly in order to not fall into the center essentially and then as you move out through the galaxies gravity gets weaker and you’d expect stars in the edge of the galaxy to be going around more slowly and what she found was that the speeds of the stars didn’t seem to depend on how far they were from the center so they moved they fell off a little bit but more or less they stayed constant at any distance and that again to explain that motion you need to invoke some invisible material that adds an extra gravitational attraction to hold the stars in the galaxy and you can use that again to measure how much dark matter there is in neighboring galaxies to our own for example the other way of doing it is by looking at something called the Cosmic Microwave Background which is very very faint microwave radiation left over from the Big Bang so it’s essentially the point at which just about 380,000 years after the Big Bang the universe before that point was like the Sun it was kind of a boiling mass of superheated plasma at 380,000 years it expanded enough and cooled down enough that plasma condensed into a gas and light for the first time could travel freely and that light’s being basically traveling through space ever since and we now detect it as this very faint echo and by looking at patterns that this radiation across the whole sky leaves you can calculate again how much dark matter there is in the universe and all three of these methods brought give you broadly similar answers and the dark energy one you can work out by basically how much acceleration is there in the in the way that galaxies are moving away from our own so they’re all complimentary measurements and they basically all line up so this is a fairly solid picture and particularly in terms of the dark matter that means that there isn’t like a boson for gravity ah very good question so is there a boson for gravity is that what you’re asking could you explain it okay so that’s a very good question so is part of a part there’s two a two-part question we were asked about X dimensions does that mean there’s no boson for gravity well we think there is a particle for gravity and it would be called the graviton and it would be a bit unlike the other particles in that table the problem with gravitons is that assuming they do exist and we sort of assume that they do because gravity is so weak is very very difficult to actually measure their effect so if you go down to particle level you’ve got these incredibly strong forces you’ve got the electric magnetic force you’ve got the strong nuclear force and you’ve got the weak force and they totally overwhelm gravity so if you’re trying to do some experiment where you’re measuring say the gravitational attraction between two particles that attraction is so fantastically tiny that it’s basically impossible to measure in an experiment at the moment if you wanted to find really sort of see evidence of gravitons you have to build a gigantic particle accelerator that was the size of the Milky Way unfortunately so we think those things we think gravitons are out there but we don’t have any firm evidence for their existence but it’s kind of assumed that they are but they’re very very at the moment impossible to detect directly but sometimes actually these these extra dimensional theories contain massive gravitons in them and those are things you could observe in a cool if some of these extra dimensions of space ideas are right then there could be gravitons that were detectable at the LHC for example soon we might find out maybe if we’re lucky thank you I’ve notes as a there is a question upstairs we’ll come to you as the very final question because unfortunately don’t have a microphone upstairs but is there anyone in the center but maybe on the left there fellas gentlemen right at the back there I’m sorry to send you right to the top but we’ll just watch fail

just run upstairs there we go you said the in the Large Hadron Collider there are black holes created many black holes that disintegrate into particles spontaneously but we know there are black holes in the universe at the center of galaxies why don’t they decay spontaneously – ah that’s a good question what they do actually but just very slowly so essentially a black what Stephen Hawking showed I think it was in the 60s or 70s was that a black hole if you’re not feeding it if it’s just sitting in empty space gently radiates energy away so it evaporates a very but over very very long periods of time so and the bigger the black hole the slower the evaporation is so essentially as a black hole evaporates imagine you had a bike on you left it in space for trillions and trillions and trillions of years very gradually it would give off radiation and would get smaller and smaller and smaller and as it got smaller the rate it radiated gets higher and higher so basically a black hole kind of dies very slowly but then at the last minute it kind of goes very quickly and all of its energy disappears and it be very sort of violent process so the black hole’s that we well we haven’t managed we so far there’s no evidence that black holes have been created at the LHC there’s certainly no sign of them but if you could create one of these things because it’s basically as small as it’s possible for a black hole to be it would evaporate instantaneously because of its tiny size whereas a much bigger black hole would evaporate very very slowly and the level of radiation that it gives off is extremely low I wanted to ask about the Alice experiment is a bit of a Cinderella experiment it certainly doesn’t sort of get mentioned in horrid Alice yeah poor Alice so what’s coming out of you know colliding heavy ions together you were looking and look for new states of matter can you just update us and what’s happening that and would that Lee informed our theories we just had this wonderful discovery of the neutron star merger Multi messenger astronomy would that has that informed Cerner’s that informed the way we there are theories of how nuclear synthesis takes place in neutron star really you’re getting at the edge of my knowledge here to be honest by me I do know I know I can take a bit ballots but a neutron star thing I mean whether there’s a link there I don’t know there may be but I mean what Alice does essentially it’s a heavy ion experiment so for usually for about a month of the year the LHC rather than accelerating protons accelerates lead ions so the nuclei have led they’re banged into each other and when that happens comfortable with the atomic number of letters but it’s a big number some one hundred one hundred and something at Canterbury exactly but when those two things bang into each other you get a huge amount of mess essentially so the the Alice collisions I showed you some of the collisions of CMS they say mess one maybe have a few hundred lines in them the Alice collisions just have thousands of particles going everywhere so what the objective of Alice is really trying to do is to study a state of matter that hasn’t existed in the universe since a very short fraction of a second after the Big Bang it’s something called a quark gluon plasma so the states of matter you might be familiar with if you’ve got solids liquids gases to take a gas and heat it up even more eventually the electrons will dissociate from the atoms and you get a plasma that’s what the Sun is made of mostly if you heat a plasma up even more eventually eventually at very high temperatures the nuclei will disintegrate into protons and neutrons and if you keep heating them up even more the prunes and neutrons melt effectively and they turn into a sort of soup of quarks and gluons which behaves a bit like a liquid it’s got this blob of extremely hot liquid and what Alice is trying to do is really to study the properties of this stuff so you get in there in these LED iron collisions you get little blobs of quark gluon plasma that exists for a very short period of time and then they condense effectively like a like a kind of liquid turning into a solid and the particles come flying out of that blob and you use what you see in the detector to infer the properties of that very hot blob and I think I’m getting this number wrong but Alice broke the record for the highest man-made temperature ever a few years ago I think it was something stupid like 1.5 trillion Kelvin but don’t quote me on that but it was off that order anyway so they’re doing I mean they’re doing really extraordinary things the short answer is I don’t know very much about it but it’s very exciting and it’s kind of it’s really telling us something about what the conditions in the universe would have been like very shortly after the Big Bang and it also helps us to understand this strong nuclear force because the strong force is actually very hard to study because it’s it’s impossible actually two separate quarks out from protons and the only time this happens is when you make this quiet view on plasma where you have this kind of free soup of quarks and gluons floating about and looking at how it behaves compared to what the strong force tells us or theory of the strong force tells us allows us to also understand a bit more about this force in the standard model going back to the dark matter theory he didn’t mention the modified new Newtonian gravitational theory yeah the Mondt yeah and is that falling out of favor now it’s not really been in favor for a long time I think so Mondt is

essentially one know when da Matta was discovered an attempt was made to say well actually let’s not invoke a whole new type of invisible material what if it’s just that gravity needs to be modified to mean to change the law of gravity and maybe we can explain galaxy rotation curves and various other things by just changing Einstein’s theory of relativity so general activity essentially and it’s always been a bit marginal but I think I mean really all the evidence suggests that it doesn’t really work you can’t use it to explain all these different things that you see lensing rotation curves the formation of structure in the universe is very hard to account for all these different things using these kinds of modified gravitational theories I think actually that measurement and the neutron star collisions put paid as well was a really big blow to modern theories so the reason these so this is you may have heard about it was in the news I think a couple of weeks ago LIGO which is this gravitational wave detector saw the sign of two neutron stars banging into each other in a very distant part of the universe and that causes these ripples in space-time which can be detected by these incredibly sophisticated gigantic lasers essentially on you know in in the States and what was interesting about the neutron star collision was that it didn’t just have a gravitational wave associated with it it had a light source associated with it so the two I think were two or three things that LIGO has seen before were black hole black hole collisions when black holes collide they don’t give off any light that is good they cover lots of gravitational waves but no lights neutron stars though are not black holes they’re made of matter were very strange and very dense matter so when they bang into each other you get you do get a lot of light produced so I think when LIGO detected this gravitational wave they said look at the sky quickly and telescopes pointed at the place where they thought that wave would come from and they saw a glow of light and what they found was that the time the arrival time between the light and the gravitational wave was basically exactly the same within seconds and this a lot this gravitational wave had traveled across the almost the entire universe and what that tells us is the speed of gravity and the speed of light is basically the same and usually in mond theories they’re not so as my understanding of it at least is that this really kind of this neutron neutron star collision actually is a big blow to modern theories as well so it’s there probably I mean I suspect their property but anything where you can find a way of explaining away why you haven’t seen any sign of it but they’re not really in favor at the moment okay are there any questions there’s gentlemen just Mac but no women ask questions so I’m like a woman to ask a question if that’s possible in the middle sorry it just underlines a fonzie you feel can get them like that so you took about it in tomatoes what if they are in toy food with mere possibility if it is possible worthy would it be like Oh auntie force fields so you means you mean the so like the photon yeah so the the fourth particles do have anti particles but they’re actually themselves so the photon is its own antiparticle so two photons can annihilate to make an electron and a positron for example the same with the gluons and the same with the W’s and the Zed’s so they’re all their own antiparticles essentially i mean actually the the w is one where it’s really obvious if i go back one animation not too far there we go so the w actually comes in two different types the W plus the W minus the W plus is positively charged W minus negatively charged so they are literally anti particles of each other but the photon is its own antiparticle the gluons are their own of course as well so it’s not quite the same but they do have anti versions and the lady in said sentence just past my clunky I just want to ask a question about something you mentioned at the start about cosmic energy feels giving mass to all particles was in the different particles have different fields or is it that there’s the the field is giving mass to all particles well so there is a field for every single particles so every every square in this table has a field so there is an up quark field for example and an up quark is just a ripple in the up quark field and the same for the I don’t know the muon neutrino there’s a muon neutrino field and the muon neutrino is a little ripple in the muon neutrino field so those are the fields that these particles exist in but on top of that there’s another field which is the Higgs field and that field for one thing the ripple in the Higgs field is the Higgs boson this thing but that field also imbues to these other particles the property of mass so if you like when you make a little ripple in say the up quark field that interacts with a Higgs field around it and it choirs mass through that interaction there’s not a very good analogy for it unfortunately but that’s basically what’s going on that’s how things got about five-ish minutes left as a question i’ll come up you have mine I’ll show a question about dark energy

dark energy is a field of some sort that opposes gravity but is energy really a the right name for a ship we’ll be talking about something completely different there are different I mean while everything is energy to some extent so any field is form of energy so there’s energy stored in the electromagnetic field the quark fields the electron field and so on so energy is probably fine because it basically scrubs pretty much anything you can think of there’s lots of different possibilities for what dark energy could be one of the first attempts at explaining it was that well I said that all of these particles in the standard model have associated fields and those fields even when there are no particles in them so when there’s no ripples moving about these fields have a finite amount of energy and that’s due to something called quantum uncertainty it’s because of quantum mechanics all these fields if you think about them a bit like the surface of a pond they’re all chittering slightly all the time and that jittering contains a certain amount of energy so what people tried to do was to calculate if I take a you know cubic meter of space and I calculate how much energy is stored in all the jitters in all these fields that we’ve got here how big is that energy and could it be dark energy and what you find you get a number that is something like 110 to 120 times to big so if you if you basically calculate using standard naive version of the standard model some calculation to estimate roughly how much energy is stored you find a number that is 10 with 120 times 100 zeros after it too large so if that were dark energy the universe would have ripped itself to pieces immediately essentially so it may be that it’s the energy of the vacuum which is what we’re talking about here and it’s just that we don’t really know how to calculate it properly we’re missing something it could be some additional field though so there are various ideas that it could be a field a bit like the Higgs field so I’m an additional if something’s called the in photon field or the or something else so it’s which then something that could have been involved in the expansion of the universe very shortly after the Big Bang and that’s been hanging around ever since and is still causing this expansion there’s some ideas that it even could be the Higgs field itself that the Higgs field could somehow be causing it’s universe there’s loads of ideas out there but unfortunately no real evidence for any of them just yet I’m sure I saw some other hands over there who’ve we got there’s a gentleman thank you I was wondering if it’s the Higgs field that is what’s giving all the other particles mass how is it that the Higgs boson has an Associated mass with it on the diagram there the Higgs kids it gives itself mass as the answer to the question isn’t there maybe a bit unsatisfying but yeah that the the Higgs boson also interacts with the Higgs field and gets mass through its interaction with the Higgs field you have to take my word for real fortunately and there’s a question just there as well just yes you that’s great hi can I talk a bit about the like you said that Higgs boson abused mass and it mass is in in general is quite related to the gravity but apparently it’s not so can you talk about that relation yeah okay so let’s let all about gravity first so what Einstein is well we had Newton’s law of gravity what Newton’s law of gravity says is that gravity is created by mass so if I have two masses mass m1 and mass m2 then there is a force between them which depends on how big those masses are and how far apart they are so the bigger the mass is the stronger the force that’s what Newton says Einstein says something slightly different which is that it’s not just mass but also all forms of energy and momentum so if I take a bit of space let’s say I don’t know let’s say I take a piece of the interior of the Sun that contains electrons and protons and other things whizzing about they all have mass they have rest mass but they also have kinetic energy because they’re moving and they have momentum because they’re moving about only how they have a pressure as well so in general activity basically all forms of energy are a source of gravitation not just rest mass so that means if things are moving about quickly they contain mass as well they create mass as well if they all create gravity rather so that’s the relationship between energy and mass what we talk about with a Higgs field is we’re really talking about the rest mass of these particles if I take an electron and I stop it and look at it it has this fundamental amount of energy left in it when it’s not doing anything which is its rest mass and that rest mass comes from the Higgs field but but not actually interestingly not all mass actually so not all matter only only this kind of rest mass comes from the Higgs field so if you have say you know a hot bit of the Sun a lot of the energy in that system that creates gravity is not to do with the rest mass of the particles in it actually interestingly the proton and the neutron if you then I said their masses are about 2,000 times the mass of the electron

if you proton neutrons are made of up quarks and down quarks so here are these two things here so these have a mass in this is in particle physics units of about two mega electron volts which is about four times the mass of the electron so we’ve got four times the mass of we got two of these guys in the proton so that’s about eight times the mass of the electron then you add on this and that gives you a bit more that gives you another another eight so about 16 times the mass of the electron but the proton is 2,000 times heavier so how does that work well that’s because most of the mass of the proton actually doesn’t come from the mass of the quarks at all it comes from the energy stored in the binding of the strong force that glues these quarks together inside the proton so the Higgs field only really accounts for actually a very small amount of mass most of the mass in our bodies is actually the mass of the strong force binding around inside these protons and neutrons so it explains as a particular type of mass but when there is a link to gravitation but the Higgs field itself doesn’t actually you know do anything different to say the electron or to the to the quarks in terms of adding extra energy that can create gravity so let’s take a final question from down here Mike hi I’m you said that the Higgs person was predicted from mathematical equations I was just wondering if a lot of these theories are based on mats why aren’t they all correct is and isn’t like isn’t there any one right answer from well these are I mean yeah they’re only models so I mean you like maths is the language you use but they’re not derived from first principles so any theory in physics starts with some assumptions so for example if you take if you take general relativity Einstein’s theory of gravity that starts from the assumption that acceleration and gravity are indistinguishable so that’s his assumption and if you use that you can then make with a few other things you can make progress and derive the theory of gravity but it’s not something that just emerges from mathematics by itself you could write down lots of different theories and people indeed people do that’s what theory spend all their days doing actually is coming up with some difference so the Sander model starts off with some set of assumptions basically you have to add in different sorts of symmetries of nature and different sorts of particle fields and then you can use the theory to calculate how these things would behave but you could equally well put in some different fields like supersymmetry or something else they’re not derive from some single fundamental principle and then everything comes out of it it’s you have to start somewhere which is I’m going to introduce these ingredients and then work out what the consequences are I guess what you’re describing is sort of this like dream of the final theory the Weinberg and others have talked about for a very long time there maybe there’s some basic principle that if we start with this we can work out everything and that seems rather unlikely I think you’re always going to have to make some assumption at the beginning and that assumption will determine what the theory looks like so finally you’ve been bursting to ask this question the whole time so if you could just a thank you are we in the third or fourth dimension because of time right so that’s quite a good question so again there are three dimensions of space there’s up that way in that way and there’s also time so there are four dimensions but time is quite unlike for three dimensions so spatial dimensions you can choose how you move through them so I can go this way or I can go this way or I can jump in the air but I can’t choose how I move through time that seems to just kind of happen I get carried along through time and people don’t really understand I don’t it’s it’s fair to say very well what time is and there’s lots of ideas about you know trying to explain trying to get time to emerge from some deeper principle but yes the short answer to question is yes there are four dimensions including time but we don’t necessarily really know what time is fantastic well that’s very intriguing but also tantalizing point point to end this evening I just wanted to end with a snide comment and as some of you may know and I may well get the day wrong here but I think it was 1897 when JJ Thompson at the Cavendish laboratory discovered the electron should correctly say the fundamental particle that later became known as the electron yeah which is a very long-winded way of saying he had one total at the electron where did he come to announce it but he came right here to this very lecture theater to announce the electron discovery so I like to think Harry that when you and your colleagues of the Cavendish laboratory and the LHC be experiment solve the problem of lepton universality you’ll come back here to announce that discovery but in the meantime thank you so much for a fantastic talk and an excellent [Applause] you