What Does it Take to Make a Universe? - with Harry Cliff

[Music] [Applause] well thanks martin for that very generous introduction and thank you all for coming it's so nice to be back in the royal institution it's a place that's very close to my heart talking to real live humans for the first time in ages is fantastic and thank you also if you're listening online at home as well um so i'm here to talk tonight about my my new book how to make an apple pie from scratch and this book is essentially the story of the search for the answer to what i think is one of the most profound and most important questions that human beings have ever asked and and it's this what are we made from what is the world around us made from and where did it come from now this is a question that people have been thinking about for thousands of years and over the last few centuries hundreds of different people chemists physicists astrophysicists cosmologists have been working in one way or another to answer this question and we've unravelled a huge amount of this story over the last few centuries and as far as i'm concerned at least this is one of the most exciting stories that i've ever ever heard um and it's one of i think one of the most exciting intellectual adventures that human beings have ever been on and this is the story that i'll be telling about tonight and it's also the story that's in my book now i should probably start by saying just in case some of you have come along for a cookery lesson i should probably explain the title so i spent a long time thinking about this book it's been sort of gestating for about 10 years as my long-suffering friends and family will tell you and um but i spent quite a while trying to find the right way into the story this this story contains a lot of at times quite challenging concepts from particle physics cosmology astrophysics and chemistry and various other things and i wanted a relatable way of keeping uh the audience reminded that ultimately no matter how sort of abstract and far off into the distant parts of the universe we get we are still talking about ordinary physical stuff the stuff that the world is made from and uh this the title is actually inspired by a quote from from this man uh carl sagan who is a mythic figure in the pantheon of science communication he spoke in this lecture theater i think at least once if not more than that um and it's this line he spoke at the start of episode nine of the blockbuster 1980s science documentary series cosmos and in a slightly strange scene uh an apple pie is brought out to carl sagan and he's sitting in the grand dining hall of trinity college cambridge and as the pie is set down in front of him he turns to camera with a little twinkle in his eye and apologies for the accent and says something like if you wish to make an apple pie from scratch you must first invent the universe and what sagan is saying really that is that even an object like an apple pie even this very ordinary mundane object its ingredients go back far farther than just the kitchen where it was made they go back all the way to the very first moments of the universe so if we want to understand how to make even this rather ordinary object that we will probably at least have a go at making in our kitchens we've got to understand the entire cosmic history of the universe so this is how how the story is framed um so this talk and the book is really about starting with an apple pie and tracing its origins uh back all the way as far as we can go to the big bang and then the big question we're trying to answer is how far can we go how far back can we go and do we eventually reach a point where our understanding breaks down um so this talk is actually going to be in two halves uh the first half i'm going to be telling you the story of what we have already found out what we already know um and this uh in the book i tell this story i tell the story of the the the people through history have helped to unravel uh unravel this story i won't do all of that in this lecture because we actually would be here for 13.8 billion years so i'll just summarize the key science points and in the second half i'm going to discuss the big open questions because uh to give you a spoiler we don't yet know the full story there are still bits of this recipe that are missing and that's going to be the focus of the second half but um to begin um i'm going to start to do i'm going to do something which i've never done at the ri before which is very exciting because i'm a particle physicist normally uh well as my boss val who's here will tell you our equipment is far too big to fit into the royal institution so i usually have to contend myself with some slightly crappy powerpoint animation so instead uh today i'm actually going to do a little experiment this is um this could go horribly wrong hopefully it won't so what i am going to do is this is actually how i began the book so i started writing this book i took the train down to my parents house in suburban south east london armed with some glassware and a a mr kipling bramley apple pie other apple pies are available and did probably what is the silliest scientific experiment i've ever attempted which is the reason i went down to my parents house is my dad who's just sitting over there as a young young teenage boy was a very keen amateur chemist and he still has his old bunsen burner so i wanted to use that to essentially thermally decompose an apple pie or as someone uh susie sheehy pointed out to me recently is um known as pyrolysis which is just a pun that's too good to be true really so what i'm now going to do is use this blowtorch and hopefully not set myself on fire um so what what we did what we're seeing here basically i hope you can still hear me over the noise of the blowtorch is gradually as we heat up the apple pie you see that various vapors start to come off so the heat is causing the the carbohydrates and the sugars and the fats in the apple pie to break down and we start to get this rather unpleasant smelling mist that comes down this condenser and then pours into the flask at the end and if you keep doing this for long enough eventually what happens is you end up with more or less carbon solid carbon at the end in the form of charcoal this is a very similar process to actually how charcoal is made traditionally i think i'll stop there because you're probably all going to get overwhelmed by the fumes but you get the idea um so in sort of true blue peter style right i'd have to do this about 10 minutes to really get down to proper carbon so i'm not going to let you make you watch that so instead i just i've got some stuff that um jenna very very kindly prepared earlier so what you end up with if you do this is a little bit of carbonized apple pie um and so this is the physical stuff that we're after where does this stuff come from the physical matter that makes up the apple pie and that's the story i'm going to be telling you um in this lecture let me take off my very attractive lab coat um and i didn't i didn't set myself on fire maybe that's disappointing um so carl sagan actually straight after this this scene he starts actually by picking up a knife and saying what happens if i cut a piece out of this apple pie and then another and then another and keep going how far can i go so this is the question that lies behind one of the most important ideas in science which is the atomic hypothesis the idea that matter ultimately if you go far enough is made of small indivisible points which you can't divide anymore now in giving a talk like this traditionally what you do is refer to the ancient greeks and you give credit to democritus who's supposed to be the first person who suggested that the universe might be made from atoms now i think democracy is the most overrated person in history right i mean he he never actually did anything to check whether this was right he just went hmm i wonder if the world is made of atoms and that's it so we don't we're not going to give the credit to democritus i think the person we should really credit for the modern idea of the atom is this man this is john dalton um john dalton was born in 1766 in eagles field in the northwest of england he was the son of a weaver from quite a poor background but because he was a quaker he got a good education moved to manchester which at the time was the beating heart of the burgeoning industrial revolution and did various chemical experiments and during his investigations of the chemical world dalton noticed that if you react two different chemical elements together they always react in fixed proportions so for example if you take the carbon that i just produced and burn it in oxygen that carbon always combines in oxygen in fixed ratios you can get carbon what we know is carbon monoxide or carbon dioxide for example and dalton took this as evidence of the fact that matter is made of atoms the basic logic is if you have an atom a and atom b you can only join them together in a certain way and therefore you get these fixed proportions in your chemical reactions so dalton is really where we get the idea of atoms from and in the 19th century the view was that for every element in the periodic table there was a small indivisible atom and there was about so about 90 or so of these different atoms and that was all you needed to make everything in the universe and if you think about it all the complexity that we see around us this is a pretty economical view of things just 90 building blocks now the question is then well where did these atoms come from well someone else who also suggested the idea of atoms was isaac newton and this was newton's definition of an atom he said it seems probable to me that god in the beginning formed mata in solid massy hard impenetrable movable particles so what newton's vision of the atom and indeed dalton's is that atoms are indestructible they're immutable they were made by god in the beginning of time and we're just left with them when we can assemble them like lego bricks but that's actually a lot but of course we know that atoms actually are not indivisible and over the course at the very end of the 19th century and over the first few decades of the 20th century physicists doing experiments in university laboratories gradually took the atom apart and they found that the atom is not an indivisible nugget it's got a nucleus at the center which is positively charged surrounded by these orbiting electrons these negatively charged particles and then in the 20s and 30s more experiments were done where physicists started to fire projectiles at atoms first using radioactive elements that spit out particles and then later using particle accelerators and they found that if they fired bits of atoms other atoms they could knock things out of the nucleus and they discovered that the nucleus is indeed made of even smaller things called protons and neutrons and once you with it so by about 1932 we have this picture of the atom as being made of three particles protons neutrons and electrons and in this way you can start to explain the chemical elements of the periodic table so you all know this i'm sure but hydrogen for example is one proton and one electron helium the next simplest element is two protons two neutrons and two electrons and carbon the next uh carbon for example this carbon from apple pie is six protons six neutrons and six electrons and once we know that atoms are made of these smaller building blocks this then allows people to think well presumably if they're made of building blocks you can assemble them and the question then is where did atoms come from and over the course of the the middle part of the 20th century it's realized that ultimately most of the chemical elements are forged inside stars and the problem here is that if you want to say force two protons together let's say you want to make helium from hydrogen protons are positively charged in order to get them to fuse you have to get them to within a thousandth of a trillionth of a meter of each other but the electrical force the repulsion between them increases as the square of the distance so as they get closer and closer that force gets bigger and bigger until there's an absolute tremendous repulsive force trying to prevent them from joining together so in order to get these two protons to fuse they have to be going incredibly quickly you can think of it a bit like running up a very steep slided ramp and the place in the universe astronomers and physicists realized that was hot enough where these protons were moving out fast enough was inside stars so we now know that the sun for example is its power comes from the fusion of hydrogen into helium and at the end of its life eventually when the hydrogen the core of the sun runs out in about five billion years when the fuel source of the sun is exhausted it will the center will contract and heat up even more and then helium will start to fuse together to make carbon and when this happens the sun will swell to a red giant engulfing the earth and scorching everything at least if we haven't done it ourselves by then um and finally at the end of its life once the once the once the core has been turned mostly into carbon and oxygen it will waft its outer layers out into space and what you end up with something like this this is a planetary nebula it's um this is actually the bowtie nebula and what you can see here is the sort of vision of our own solar system five or six billion years in the future at the center of this is a white dwarf which is a cold dead well not cold actually quite hot the hot dead husk of the star that was there at the beginning which is mostly made of carbon and oxygen and then around it you have clouds of carbon helium and hydrogen that were wafted away in the star's atmosphere and it's these kinds of stars that are responsible stars like our own sun for making the the carbon in our apple pie and indeed in all of us so we are all made of bits of stars or as carl sagan said we are made of star stuff um which is a lovely a lovely thing and we i say it's kind of a familiar fact we all know this i guess but it and i think when it was discovered in the 60s and 50s and 60s it was a really magical idea it's almost become too familiar that we forget about it so it's worth remembering that is really an extraordinary thing so that's the carbon but actually it's interesting if you want to know where oxygen comes from it doesn't actually come from sunlight stars and the reason is that although sunlight stars at the end of their lives will make oxygen it stays locked up in this white dwarf this very small dead remnant at the center from the center of the star the oxygen or apple pie actually comes from much more violent processes so for stars much bigger than our sun say beetlejuice which is a star in orion which is about 10 to 20 times heavier than the sun when much heavier stars when they get to the end of their lives something much more dramatic happens which is once the core is being turned into carbon and oxygen the core keeps collapsing and that's because the weight of the gravity of the star allows to collapse and heat up more and then you start burning carbon into heavier elements like silicon and eventually you get all the way to iron and nickel when this happens the star's core runs out of energy you get this awesome explosion known as a supernova which will then spread a huge range of different chemical elements out into space and in particular this is where the oxygen in our apple pie comes from um still working so when i was researching this book i had the great opportunity to visit various uh observer observatories and experiments around the world in particular one of the most memorable ones was visiting this place this is apache point observatory 3000 metres up a mountain in new mexico what you can see here is the sloan telescope opening up uh for a night of scar gazing against this incredible sunset backdrop i have to say i came away from this trip thinking i've picked the wrong area of science like most of when i was a phd student my office was in um i have to be careful with sake my boss is here my office was in a in a windowless room uh underneath the men's first floor toilets um which frequently leaked and the feeling of water dripping unexpectedly onto my head still gives me sort of panic attacks um but uh but this is really science as it's most romantic this incredible sunset but um what the what the sloan telescope does it has connected to it uh into a spec a spectrometer which analyzes the stars from across the milky way galaxy in order to unravel the cosmic history of the chemical elements and actually this story although we've known the rough outline of this story about where the elements come from inside stars since about the 1950s there are still parts of it that aren't yet fully fully filled in and we're still learning more and more as time goes by um one of the lovely things i came across when i was writing this book was um was this periodic table so this is a periodic table produced by jennifer johnson who is an astrophysicist at ohio state university and what you can see is a familiar periodic table but the colors tell you where all the different chemical elements come from so for example if we take carbon you can see that carbon mostly is shaded in yellow which means it comes from dying low-mass stars that's like our sun our sun is quite a small star by cosmic standards and then if we look at oxygen say well that comes mostly as i said from exploding massive stars these supernova explosions but one of the interesting things that's happened recently in in this area what's called stellar nucleosynthesis which is essentially the cooking of elements inside stars people have realized that some of the story wasn't quite right so it was thought for a lot of the latter half the 20th century that the very heavy elements like gold and platinum were also made inside supernova explosions but thanks to a very exciting discovery that was made in 2017 um by an observatory called ligo in the united states we now think they actually come from an even more extraordinary place which is from the collisions of neutron stars so oops sorry too far a neutron star is the possible end product of a supernova it's an even denser basically dead husk made entirely of neutrons from the center of a supernova explosion and in 2017 ligo which is a gravitational wave observatory detected ripples in spacetime produced by the collisions between two neutron stars in a very different very distant part of the universe and it was and they alerted various optical telescopes around the world who then swung and pointed at the point of the sky where this signal had come from and what they detected was the telltale characteristic signature of huge quantities of gold being made i think it was something like 30 solid gold earth's worth of gold was produced in this collision um but i should add before you get on the phone to elon musk with a get rich quick scheme if you flooded the earth market with that much gold the value would plummet so don't bother it's also very far away um but um i mean admittedly i should also say i suppose that there isn't actually gold at an apple pie um but it could be one of those fancy ones with some gold leaf on top so there you go but anyways the point really is this story is not a done deal and there's still really exciting science being done in this area um so then we have this we have another question then which is if we look at the composition of the universe this is a pie chart that represents what the universe is made from in terms of the different chemical elements and you can see the vast majority of it about 73 is hydrogen 25 of it is helium and then the rest about one and a half percent or so but just under two percent is everything else so all the all the other elements apart from helium and that's a tiny fraction so that's all the sort of solid material basically that makes up the earth and everything else now there's this rather peculiar thing though if you look there's a huge amount of helium but we know that helium is made inside stars and all this stuff is also made inside stars so why is there so much helium and so little of everything else and this is a question that puzzled astrophysicists in the 1950s and 60s and it was eventually realized that actually stars are not the only cosmic oven that cooks the chemical elements there's another one and that other one is the big oops excuse me the big bang itself so the universe began as i'm sure you will know about 13.8 billion years ago in this awesome expansion and explosion of space and time and energy and if you go back far enough to the first few minutes of the universe's history the temperatures were incredibly high and at this time the universe was mostly made of protons and neutrons that were just flying about freely in this boiling plasma but on for after about a minute or so after the big bang for about 15 minutes the basically all the helium in the universe was cooked so that's where the helium really comes from it doesn't come from stars that stars are contributed a bit but most of it was made in this nuclear fireball at the very very beginning of the universe and this is actually one of the big triumphs of the big bang theory one of the strongest pieces of evidence we have for the big bang is the fact that if you take what we assume about the beginning of the universe which was there was roughly an equal number of protons and neutrons you work out the temperatures and densities and you calculate how much helium should be made you get pretty much exactly what we observe in the night sky and this is this really supports the idea the universe really did begin with a big bang so this is the reaction that took place nuclear fusion of protons and neutrons to make helium um and then we have okay we can keep going those we've got quite a long way now we've figured out where helium and all the other chemical elements come from but because because i'm a physicist you're so bloody-minded and you see it saying why so what happened what happened before this what was the previous step where did the protons and neutrons the ingredients that make up all the other elements ultimately come from well in the 1960s experiments were done particularly using a large particle accelerator called the stanford linear accelerator just based outside san francisco and what the linear accelerator did was it was essentially a three kilometer electron gun it fired electrons very very close to speed of light at protons and neutrons and then they use big detectors to see what angles the electrons come bouncing off the protons and neutrons and what they found is the angles that the electrons came off at suggested that the existence of smaller objects inside protons and neutrons the proton neutrons were not fundamental they actually had substructure and they're made of particles called quarks and there are two types of quarks that are important there's the up quark which is these uh red triangles they have a chart an electric charge of plus two-thirds quark's a bit odd they have a fractional electric charge unlike electrons and then the down quark this blue thing which has a charge of minus one-third if protozoa neutrons the same logic applies if protons neutrons are made of quarks then that suggests that perhaps they were assembled from quarks and indeed remarkably in fact there are experiments going on uh right now on earth that recreate the conditions when protons and neutrons formed in the very early universe so we're now talking about conditions that existed in the universe about a millionth of a second after the big bang when the universe had a temperature in the trillions of degrees so incredibly high temperatures and there's an extraordinary experiment based actually just outside new york on long island at brookhaven called the relativistic heavy ion collider this is a big particle accelerator and what they do is they fire nuclei of atoms quite often gold atoms they whizz them around the circle they smash them into each other and when these gold atoms collide they briefly recreate temperatures and densities that haven't been seen in the universe since about a millionth of a second after the big bang reaching temperatures of trillions of degrees and under these temperatures the protons and neutrons get so hot that they effectively melt so they melt and what you end up with is this very strange sort of incredibly it's a super fluid super hot soup made of free quarks and gluons called a quark gluon plasma and when i was researching the book i went to brookhaven and one of the things that's really interesting is that they're currently targeting there's a there's a phase transition that happened in the early universe this is a phase transition very similar to say water freezing into ice where this quark gluon soup this super hot soup condensed to form protons and neutrons and they're getting very close to understanding that phase transition so we have hopefully very soon hone in on the moment that protons and neutrons formed in the early universe in experiments here on earth which is pretty extraordinary right so let's see where we are so we've got to this point we have now three basic building blocks three particles that make up all the matter or at least all the visible matter in the universe the electron the up quark and the down quark and with these three things you can make anything you like you can make an apple pie you can make a human being you can make a supernova and that's amazing really when you think about it that all the complexity in the world can be reduced to this incredible simplicity but we're going to do the same thing now okay where do these guys come from where do we have these three particles well it may surprise you to know given that i'm a particle physicist and the subject's called particle physics that we don't actually think of particles as being the fundamental building blocks of the universe they're not actually thought to be truly fundamental they're manifestations of something even deeper something more fundamental and these are rather strange objects called oops excuse me why does this keep happening called quantum fields so it sounds like a slightly scary word but you're probably you're very familiar with the idea of a field i'm sure so a lot of work was done defining the idea of a field in in this building by michael faraday in the 19th century and faraday did lots of experiments with coils of wire and magnets and if you've ever held a magnet say say you take two magnets and you push their north poles together you can feel this repulsion this this physical thing and you can almost feel like you're tracing out the outline of some real tangible object what you're feeling there is a magnetic field it's invisible but it has a real physical presence and quantum the magnetic field is just one example of these types of field and in modern particle physics we actually think of every particle the electron the various quarks all the other particles as being little disturbances little vibrations in these underlying fields so these fields are everywhere so there is an electron field for example this the electron field is throughout this room and every electron in your body is a little knot of energy a little vibration a ripple moving about in this electron field which rather which rather beautifully or scarily depending on how you want to look at it means that you're all we are all connected to each other we're all part of the same underlying fluid-like substance that fills the whole universe and the same thing goes for the quarks and for everything else so once you have this view of particles well in order to create a particle all you have to do is put some energy into a quantum field make a little ripple and you've made a particle you can make an electron you can make a quark so we now have a mechanism at least by which you can start to think about how you make the basic building blocks that make up our universe oops and our best description of how all these quantum fields behave and their associated particles is encapsulated in this theory known as the standard model of particle physics which is an incredibly boring name for one of the most exciting and important intellectual discoveries as human beings have ever made i think and the standard model is a theory of these quantum fields and it describes for example including it the up quark and the down quark and the electron that makes up ordinary matter it also includes a bunch of other particles which i won't really get into we don't really understand why these things exist but we just see that we can make them in experiments there are also fields associated with the various forces of nature you have the photon which is associated with the electromagnetic force the force that holds atoms together the force that's responsible for light for electricity and magnetism um they're all and there are particles called gluons which are associated with a strong force which binds quarks together inside protons and neutrons and then you also have these rather odd things called w and z bosons which are the quantum fields of the weak force which is a force responsible for causing particles to decay to transform from one type into another and finally and perhaps most famously of the lot is the higgs boson which i'll talk about a bit more in a second so the standard model is a fantastically successful theory it describes all the visible matter that we can see in the universe with absolutely stunning accuracy and pretty much there is no experiment in existence that has contradicted its predictions it's probably the most successful scientific theory ever written down it's the closest we've come really to a theory of everything but we know this theory must be incomplete and in the second half of the talk i will tell you why we think it must be incomplete so just as a little a little health warning we are now moving off the edge of the known world into the unknown so here there'd be monsters in other words um we're getting to a point where our understanding is partial and speculation sort of comes in and this is where all the big questions of modern physics uh really live and where a lot of the exciting work is currently being done so with that caveat side so we've got to this point we have these basic ingredients of our universe and we have this beautiful theory that describes how they behave how they interact but as we go back further in the history of the universe beyond the point when protons and neutrons form we start to find that there are places where our recipe for mata has gaps in it where there are holes things that we don't understand and one of the biggest holes is to do with something called antimatter so antimatter is a stuff beloved of science fiction writers um you may have encountered antimatter for example in the terrible novel angels and demons by dan brown where some uh some nefarious organizations steal some antimatter from cern in order to blow up the vatican um for no reasons that aren't really explained particularly well um so just there is actually an experiment at cern called alpha where they do actually make antimatter they make atoms of anti-hydrogen and they study in the laboratory and i went to visit alpha when i was researching the book and jeffrey hankst who is the um the spokesperson of alpha basically the head of the experiment pointed out that the cost of the amount of antimatter you would need to block the vatican is so huge that it would be much more cost efficient to pay a team of builders to dismantle the vatican by hand bring by brick so and it will also take basically the age of the universe to make enough antimatter to do it in the first place so we're not going to use antimatter to do anything nefarious i can i can promise you that but what is anti-matter i should probably explain that so every particle that we in every matter particle that we know about in the standard model which are these 12 things there are six quarks and six things called leptons and the electron is one of these these leptons has a kind of mirror image which has exactly the same properties the same mass the same interactions with the different forces but they have opposite charges so there is an anti-version of the electron the electron is negatively charged called the positron or the anti-electron which is positively charged there there's a version of the up quark called the up antiquark which instead of being positively charged is negatively charged now in the standard model whenever we create a particle of matter you also create a particle of antimatter so at the large hadron collider when you smash protons into each other for example you make particles and anti-particles and if you count up all the particles that you put into reaction and then the number of particles minus the number of anti-particles you get at the end those two numbers will always be the same in other words you can't make more matter than antimatter now this is a bit of a problem because if we go back and think about the very earliest moments of our universe in the very early universe the universe had incredibly high temperatures and matter antimatter were being created continuously in this sort of seething broiling plasma and because of this symmetry between matter and antimatter we would have expected equal numbers of particles and anti-particles to be present at any one time so you then let the clock run forward a bit more and about a millionth of a second after the big bang the universe has expanded enough that it cools down that there's no longer enough energy to keep making particles and anti-particles and what then happens is an event that frank close calls the great annihilation which sounds exciting um so this is basically when all the matter and antimatter in the universe meet up and they annihilate each other so when matter antimatter meet they wipe each other out releasing light and various other forms of radiation so this suggests that if our understanding of antimatter is correct that we should not be here that after very shortly after the big bang everything should have been wiped out and we would live in a cold dark lifeless universe with just a few photons coasting through the infinite blackness but of course we know the universe looks like this it's full of stuff so the fact that the universe is full of stuff the fact that we are here the fact that apple pies are here tells us there is something wrong about our understanding of antimatter or there is something missing so this is one of the big questions we have to answer how did mata survive the big bang there's another question too so this is related to um the higgs boson so i should explain to you what higgs boson is so um the higgs boson is really evidence for the existence of something called the higgs field like all the other particles that we know about the higgs boson is a little ripple in an underlying quantum field and that quantum field is called the higgs field and the reason that we well the reason the theorists believed the higgs field existed was when the standard model was being assembled in the 1960s and 70s they found that if you gave mass to the particles in the standard model the theory broke down it gave you nonsensical answers in other words the the mathematics the theory seemed to be suggesting that if particles had mass then the theory was inconsistent but of course we know electrons for example have mass we know a lot of the particles in the table i showed you have mass and the solution to this problem which was uh discovered by peter higgs and actually about five other theorists around the same time was that well let us actually assume that the particles in the standard model actually don't have a mass they're massless but they get their mass from somewhere else and the somewhere else that they get their mass from is this thing called the higgs field now there's been various competitions run to try to come up with a good explanation of how this works and none of them are really very good um so i'll give one that's sort of they're all wrong in various different ways but i'll give one that's sort of at least you can get your head around and it isn't totally misleading you can kind of think of the higgs field as a bit like molasses or honey like some kind of thick gloopy substance and the idea is that as electrons move through this higgs field say take electrons for example they get slowed down and they get given the the property of mass through their interaction with this gloopy higgsy fluid now that's wrong but that's if you can hang on to that idea that's sort of what's going on very very roughly now the other thing that's unique about the higgs field is that unlike all the other quantum fields that we know about it has a non-zero value so what i mean by that if if we were to go into a very very distant part of space far away from any sources of radiation and were to sort of close it off remove out remove all the atoms remove all the particles and then study the quantum fields that are left we would find that all the quantum fields in nature had more or less zero energy in them they had a zero value apart from some little quantum jitters the higgs field is different it has a fixed value throughout all of space and it's this fixed value that is responsible for giving the mass to the other particles the fact it has this non-zero value is crucial and in fact the value the higgs field takes uh is it completely determines the properties of all the other particles and if you change the strength of the higgs field you change the way the universe is in essence now we believe that about a trillionth of a second after the big bang the higgs field switched on so it before about a trillionth of a second it was off it was had a value of zero particles had no mass they all flew around at the speed of light and then about a trillionth of a second in the higgs field switched on for the first time and acquired its modern value and particles took on the properties that they they have today but the thing that's very curious is that if you do a calculation and figure out what the likely values of the higgs field ought to have been you get two rather disturbing results the first oops got a given game away the first possibility is that the higgs field is fully on it's like a it's almost like a switch it acquires a value of 10 billion billion giga electron volts this is what we call the planck energy it's the energy at which we believe gravity uh becomes a quantum mechanical phenomena it's the sort of upper limit of energy that we can really imagine so it's basically as far as you can go now if the higgs field had this enormous value it would be very very bad because what this would mean is that every particle would become so massive that ordinary mata would just collapse into a black hole and we wouldn't be here the universe would be filled with black holes and not much else it wouldn't be a very nice place to to live the other possibility is that it goes off the extra just remains off stays at zero and if that happens that's also very bad because if a higgs field is off then particles don't have mass and among other rather unpleasant consequences of this is that electrons don't have mass they don't bind to atoms and there's therefore no structure there's if there's no atoms then there's no wobbly flesh colored things made of atoms either so we don't exist these are seem to be the only two probable possibilities but because of what we've experiments that we've done cern and other places we know now that the higgs field has a value not of 10 billion billion or of zero but of 246 giga electron volts which is very odd it's a very very long way away from this number but it's also not zero and the thing that's really fishy is that it turns out that if you change this number by even a little bit very quickly the universe becomes uninhabitable and the only way to get this number to come out successfully is to effectively gerrymander the standard model or fiddle about with all of the sort of properties of the particles of various constants of nature until you find one particular setting where the higgs field has this lovely goldilocks value where we can exist now this looks very suspicious and physicists really don't like this very much because it sort of suggests that some cosmic tinker has set everything up in just the right way we would like an explanation of why we have this very peculiar number that is not 10 billion billion and not zero either so we have our second question why didn't the higgs field kill us so these are the two two of the big gaps in their current attempts to understand the origins of mata and they're two of the big questions that motivated the construction of the largest scientific instrument that's ever been built by the human race this this is the large hadron collider what you can see here is a an aerial shot taken from a plane i think of the area just outside geneva so you can see lake geneva or la la man here this is the city of geneva you've got the alps in the background that's mon blanc at the top and then marked in yellow on the countryside is the route of the lhc 27 kilometers in circumference and what this machine does i should add actually you can't see this in real life it's 100 meters underground because it would have annoyed lots of farmers if we painted a big yellow line on the fields um what happens is all the lhc does is really kind of simple and brutal somewhere over here cern there is an ordinary bottle of hydrogen gas the gas is extracted it's put into a little box which rips the electrons off the protons and the protons then sent through a series of accelerators and then injected into the lhc and the lhc accelerates them to 99.99999 one percent of the speed of light and then they're smashed into each other inside four big uh detectors that are also known as experiments these are marked around the route so lhcb this is the one that i work on over by the airport and the reason we do this is because we want to understand we want to try to find answers some of these questions so this gives you an idea of what these detectors look like this is a photograph of cms which stands for compact muon solenoid experiment now this is a very strange use of the word compact given this thing is 15 meters high weighs about 14 000 tons and you can make two eiffel towers out of the iron it contains this is a big thing here's a guy for scale down the bottom if you want another example of here's me as a student age 21 a summer student standing next to the end cap of cms so i haven't grown very much since then so this is pretty much you get a sense of how big this machine is although my hair's a bit shorter now thankfully right um so what happens when two protons collide with each other the end the reason we accelerate them is because we want to give them huge amounts of energy and when they collide the energy they're carrying is converted into new particles so the lhc doesn't smash atoms to bits as such although it does smash protons to bits but a lot of what you're seeing here is not what was inside the proton it's stuff that's being made you're knocking these quantum fields that are always there you're creating new particles and they come flying out from the collision this is a representative image of one of these collisions you can see hundreds of particles being produced and the job of people like me is to scour through these collisions analyze the data and try to find evidence of new particles new forces of nature new phenomena that might help to explain for example why there is matter in the universe and it wasn't all annihilated with antimatter or in particular why the higgs field has this weird peculiar value now the first great triumph of the lhc took place on the 4th of july 2012 what became known as cern as higgs dependence day so this was the day that they announced that atlas and cms too the two big general purpose experiments announced the discovery of the higgs boson this ripple in the higgs field that had been predicted back in 1964. this was a tremendously exciting day a huge achievement and the hope was that soon after this discovery we were going to start to see evidence of new particles new phenomena that would help address some of these big open questions in some ways the discovery of the higgs was a sort of confirmation of the standard model which has been around in its current form more or less since the 70s what we really then wanted to know was what comes next what answers the what fills these gaps in our in our current understanding but if you followed the news from the lhc over the last decade or so you'll know that the basic story is this we haven't seen anything nothing new there'd be lots of things now i don't want to pretend i don't want to say that there's not been great stuff going on lots of interesting physics has been done we understand the standard model far better than we did before new states new states involving quarks have been discovered particularly by the experiment that i'm a member of so there's lots of great stuff that's happened the higgs boson itself has been studied and understood but in terms of the new things super particles micro black holes all kinds of exotic objects that we might have seen we haven't seen them so far and i think if you speak to particle physicists and they're feeling sort of candid they'll probably say this has been a little bit worrying a little anxious making but there has been just in very recently the first signs of possibly and i should say that this is very possibly in capital letters the signs we might be about to discover something new and this these results come from the lhcb experiment this is an experiment that i'm a member of i'm one of 1400 people that work on this instrument and lhcb um the b in lhcb stands for beauty and beauty refers to one of the six quarks in the standard model this thing here you'll see actually it's labeled bottom quark not beauty confusingly um now the reason for this is when the bottom quark and its part of the top quark were discovered there was an effort to call them truth and beauty sounded rather poetic but physicists went for the more prosaic top and bottom but on lhcv we'd rather be beauty physicists than bottom physicists so it's for us it's beauty and these particles are really interesting to study because if you study them in in detail then you can get evidence of the existence of for example new forces of nature new particles that we haven't seen before now the lhc is a great place to study bottoms you get billions of bottoms made every year in the collisions this is an example of one of the collisions produced by lhcb and the detector allows you to reconstruct uh the tracks of the various particles and see if you made a beauty quark somewhere back here at the collision point these beauty quarks i should say they don't live for very long so they only live for about one and a half trillionths of a second and then they very quickly decay into other things so you never actually see the beauty quarks directly you see the things that they turn into and those are the things that hit your experiment um so the the reason these things are interesting as i said is if you make precise measurements of them you can get indirect evidence for the existence of new phenomena and the way this works is a bit like this so here's our beauty quark now as i said it doesn't live very long it lives about trillionth of a second and it then decays let's say it decays into a bunch of other particles in the standard model well we know how this happens in the standard model it happens through the other quantum fields that we know about so because the standard model is very well understood you can make a prediction using the standard model of how often a given decay ought to happen for example now the trick is that let's say that there's a new force of nature a fifth force of nature if beauty quarks interact with this fifth force that fifth force can provide an alternative route for this decay to happen so if you make your very precise prediction with a standard model then you make a very precise measurement you compare them and you find that they're different that difference can be indirect evidence that there's a new quantum field possibly a new force that's changing how these beauty quarks behave so that's the game we play precise prediction precise measurement compare them and if they disagree that could be the sign of something exciting so here's the something possibly exciting so what my colleagues at lhcb have done recently is a series of measurements that look at processes a bit like this so this is a decay of the beauty quark where it turns into something called a strange quark which is a basically a slightly lighter version of the same thing and an electron and an anti-electron and what my colleagues did is they measured this process and they compared it to a very similar related process where instead of having electrons you have particles called muons apologies for all the jargon is flying about but muons are in essence copies of the electron they're very very similar the only difference is that they have a larger mass and they're unstable but otherwise they're identical to electrons in every way and because they're identical to electrons in every way the forces in the standard model treat muons and electrons the same so if you compare how often a beauty quark decays into an electron and how often it decays into muons these two processes should happen at exactly the same rate but that isn't what my colleagues have seen what since about 2014 we've been getting increasing evidence that the muon decay happens less often than the standard model predicts now these results still come with on so all of these measurements come with uncertainties which means we only know the rate of these decays within certain precision and for at least for a few years these sort of results they're quite intriguing they were a little bit away from the standard model prediction but as we've added more data the thing that's really exciting is that these anomalies these deviations have got bigger and bigger and stronger and stronger as our measurement has got more and more precise and this culminated in a very exciting day uh back on the 23rd of march this year if you follow the the science news you may have seen some headlines particle physics briefly re-emerged into the sort of the public domain after the discovery of the higgs with stories like this so what happened on this day was an update of this measurement was made using all the data that's currently been recorded by lhcb and this deviation crossed a slightly arbitrary but nonetheless important threshold which basically means there is now about a one in a thousand chance of getting a deviation like this just because of random statistics so you've just been a bit unlucky a bit like tossing lots of heads in a row on a coin for example so this is this is this caused enormous excitement and this if this is real if this effect is real and not a statistical blip um then it could be the first evidence we've ever seen of a new force of nature beyond the standard model something that lies outside our current understanding um and this is this would be such a this would be a huge deal because the standard model as i said has existed in its current form more or less since the 1970s this will be the first really genuinely new thing we've seen in particle physics since then then something even more remarkable happened about two or three weeks later on the 7th of april another big announcement was made from a completely different experiment this is an experiment at fermilab in the united states called the muon g minus two experiment um and what they announced is they again had seen evidence potentially for you'll see a new force of nature um so sort of discover monumental discoveries seem to be turning up like buses so this is a bit strange they all arrived at once um but what this experiment does uh it's based just a fermilab just outside chicago is it measures the particular property of the muons this is the heavy version of the electron in particular it measures its magnetic field the muon behaves a bit like a little bar magnet has its own magnetic field and again using the standard model you can predict how strong the muon's magnetic field ought to be and then if you do a very clever experiment like they did at fermilab you can also make a very precise measurement of the magnetic field of the muon and again what they found is that their measurement didn't agree with the standard model prediction and it didn't agree by an even larger factor in fact it didn't agree to the extent that there's about a 140 000 chance of this one being a statistical blip so again it's not yet at the point where we can say for sure definitively that we're seeing signs of new physics but i think these two results in particular are the most promising evidence we've seen of something really genuinely new for a very very long time and they could well be connected to these questions how did mata survive the big bang why didn't the higgs field kill us or they might have nothing to do with them they might be they might be answering questions we haven't even thought to ask yet or they may be related to some of the other big outstanding problems in physics but if we are really seeing the signs of something new then it will surely tell us a lot more about the world we live in and it could well help us unravel some of these questions so there are definitely gaps in our recipe for our apple pie but there's there's at least a chance that in the next few years we're going to start to fill in some more of those gaps so i'm just going to finish by going even further back now so we kind of i've been discussing here these are sort of the physics that existed around about a trillionth of a second after the big bang but let's go back even further let's say how far back can we go ultimately and what happened at the moment of the big bang so if we really want to make an apple pie from scratch we need in principle to understand the very first moments of the universe so this is a diagram of the cosmic history of the universe with the big bang over here and apple pies over here um it's not usually how it's presented i should add but um so what we can see if we go backwards in time through the history of the universe the universe gets is the universe is expanding so as we go back in time we get smaller we go back and back and back eventually there are no stars they haven't formed yet we go back and then atoms haven't atoms haven't yet formed we enter the fireball of the big bang and then a tiny moment after the big bang and i'm going to get this wrong but i think it's something like 10 billionths of a trillionth of a trillionth of a second after the big bang this process known as cosmic inflation took place so this was a period right at the very beginning of the universe where the universe expanded exponentially now thanks to the last years we're probably all familiar more familiar with the idea of exponential growth than we used to be this basically means it expanded very very quickly to give you a sense of how quickly it expanded if you take in this very short period of time fraction and fraction of billionths per second the universe grew in size so if you were to take a full stop at the end of a sentence and blow it up by the same amount it would end up 100 times bigger than the milky way galaxy so the universe underwent this incredibly rapid period of expansion and well at least we believe it did and the reason we believe this or cosmologist i should say believe this is if you look out at the universe at very very large distances if you look over there so if you get telescope and look as far as you can in that direction then you look as far as you can in that direction those two bits of the sky look eerily similar they have the same temperature the same density the same amount of stuff but according to the classic big bang theory these two bits of the sky these two places were never in contact with each other so how on earth are they the same how do they know uh to be the same temperature and density well the answer is they were all actually once at the same place and then they got spread apart by this incredibly rapid expansion called inflation and ultimately inflation is where we believe the the matter that makes up our universe came from so this very first moment there's huge amounts of energy in something called the inflaton field which is another field and this is the field that's driving this incredibly rapid expansion and then what happens is as inflation switches off inflation basically comes to an end and all this energy in the inflaton field gets dumped into the other quantum fields that we know about in the standard model and you get electrons and quarks neutrinos and higgs bosons all other kinds of things so this is the moment really when mata gets created this and this is actually as far back as we can even go in principle because if inflation is right basically what it means is if we want to go back any earlier let's imagine there are events before inflation where we'll never see them because any information from that earlier time would have been carried way out of sight by this incredibly rapid expansion of the universe so inflation really is if it's right that's the end of the story that's as far as we can go there's a hard limit on what we can know so the question is you know did inflation happen well there's there's lots of evidence that it did um it explains properties it explains lots of properties of the universe for example the fact that it looks the same in every direction it also explains the fact that there is structure in the universe one of the really amazing things that inflation says is that when you look out in space you see these structures you see galaxies and you see you see that galaxies are arranged in what are called filaments so these kind of like web-like structures that thread the universe made up of galaxies that kind of look a bit like a spider's web and it's believed that these structures ultimately came from quantum fluctuations down at scales far far smaller than an atom so just little quantum jitters that got blown up by inflation to the size of the entire sky and these little quantum jitters were the seeds of all the structure we see around us so these are these quantum jitters cause the formation of galaxies and the large scale structure of the universe so there's lots of indirect evidence that inflation happened but the question is how can we ever directly know that it happened well one of the problems is that if you go back to about 380 000 years after the big bang times earlier than that the whole universe was so hot that it was filled with this fireball it was essentially like the sun and that meant light couldn't travel if you try and send a particle of light through that fireball it bounces off atoms and it doesn't get anywhere and so we can only look back to about 380 000 years after the big bang with optical telescopes and if you do that this is what you see this is called the cosmic microwave background which is the oldest light in the universe it's the faint microwave remnant of the light that existed around this time when the universe was filled with a fireball and this kind of acts like a fire wall it's a barrier we can't look through this you go back there you can't see any further but just the last few years we now actually have a brand new way of looking at the universe and this new way of looking at the universe might allow us to penetrate the cosmic microwave background and look right back to the moment of inflation and you do this using things called gravitational waves so this is a photograph of an instrument called ligo which is a very strange observatory it's actually it's an observatory that studies the universe just like any telescope but it's made up of two uh parallel three kilometer arms which fire laser beams back and forward um i went to visit this instrument when i was searching the book it's in this pine forest in southern louisiana and there's another instrument up in washington as well and what this instrument essentially does is it listens for vibrations in the fabric of space and time itself so these are ripples in space-time created by incredibly violent processes in the distant universe and in 2015 after decades of work decades of refining their instruments ligo picked up the first sign of gravitational wave and it was produced by two black holes uh billions of light years away and in the past that collided with each other and as these two black holes spiraled around each other and merged they create these they create these ripples in space-time that traveled out and were eventually picked up by the ligo instrument now inflation would have done something to space-time very like these black holes inflation was incredibly violent so if inflation happened it would have roiled space-time it would have sent these ripples cascading out through the universe now today these ripples would be incredibly faint uh far far too faint for ligo to pick them up but in the future there are experiments planned at the south pole high in the atacama desert and even observatories orbiting up in space that may be able to pick up the gravitational waves left over from the very earliest moments of the universe and if we were to get evidence of that would really complete the recipe that would tell us ultimately where the the physical stuff in our apple pie came from so we've reached the end of the story so i suppose to summarize to say um one of the things i i got from writing this book is an incredible appreciation over hundreds of years how different people chemist physicists astronomers all working on different parts of the puzzle ultimately we're actually all working on the same puzzle which is where does stuff come from and why are we here and this is a story that excites me hugely as a teenager it's why i became a scientist and it's a story that i hope i've tried to share some of the excitement with you tonight and i hope you enjoy the book if indeed you do pick it up but thank you very much for your attention it's been lovely talking to you [Applause] you

Channel: The Royal Institution

Views: 247,373

Keywords: Ri, Royal Institution, harry cliff, large hadron collider, particle physics, standard model, particle physics lecture, particle physics explained, a recipe for a universe, how to bake an apple pie, how to make an apple pie from scratch, universe, big bang, origins, cosmic history, cosmos, carl sagan

Id: bzV4O85n2y8

Length: 57min 14sec (3434 seconds)

Published: Thu Oct 28 2021