What Happened At The Beginning Of Time? - with Dan Hooper

Thanks thanks everyone for coming out I want to start by saying it's really exciting to see such a packed room full of science enthusiasts at least in my country people are constantly lamenting the lack of the public's support or interest in science and yet when I come out to give talks like this you all show up so they're wrong and thank you for helping me to prove them wrong tonight so when you think back across history people of all times and all cultures have something in common they all looked up at the night sky and they all wondered about their universe and how it came to be in this respect we have a lot in common with with our ancient ancestors but in one way we're very different indeed we're different because we live at a very special time in history where for the first time when we look up at the night sky we more or less understand what it is we're looking at it's a privileged time in this sense take this image for example this is an image from the space telescope called Hubble it's part of the program we know as the Hubble Deep Field most of the blotches you see in this image these blotches of light are pictures of galaxies similar in size and shape to our own Milky Way but because it takes time for light to travel across space this image doesn't accurately depict what those galaxies are like today but rather what they looked like more than 13 billion years ago only a few hundred million years after the Big Bang our universe was a very different place then it's much more compact and much hotter filled with different kinds of things and we more or less understand how and why it has evolved and changed in the ways it has to become the universe we live in a little over a hundred years ago physicists didn't even have the foggiest idea how to ask these sorts of questions much less how to answer them we didn't know how our universe had changed or evolved or began in fact we didn't even know how to ask a question like how could space change we thought of space as an unchanging backdrop something that objects could move through but we didn't ever use verbs in connection with space space never did anything in Newtonian physics but now we think of space as something that can change and evolve expand contract warp curve and we can think that change or give that give thanks for that change to the ideas of Albert Einstein so he thought he was the one who taught us that space was more exciting than the static backdrop that Isaac Newton told us about in 1915 with his general theory of relativity he taught us that space can change it can do things it can be dynamic and in fact you can use these equations the ones he published in 1915 to show that the space that makes up our universe can do a lot of things but it can't stay the same if you take those equations you and picture a more or less uniform body of space filled with some amount of matter you fight invariably without exception that it has to either be expanding or contracting and in 1929 the great astronomer Edwin Hubble observed for the first time that our universe is in fact expanding points in space are getting farther apart from each other as time progresses causing the universe to steadily become colder and less dense and bigger than it was in the past so my guess is that everybody in this room has at some point heard that space is expanding that our universe is expanding with time but my other guests is that most of you don't really know what that means you're probably picturing a situation where there's a bunch of stuff in space or a part of space it is slowly moving out of it occupying a bigger volume I want to remove that image from your brains that is not what cosmologists mean when they say space is expanding what Hubble actually saw through his telescope in the 1920s was that all the galaxies he could see were moving away from us they were receding and the farther away a given galaxy was the faster he observed it to be moving away now it's possible that that data would be consistent with an idea that we were like in the middle of some big cosmic explosion everything's just moving away from us but in fact that's not the case if you look at the universe as a whole combined all the data we have what you find is that if you were in a different galaxy and looked out at your neighboring galaxies you would see the same thing Hubble did everything is moving away from every other point in space all the time if you're like most people you're probably asking yourself what I find to be a very predictable question around this time it's predictable guys I've given enough talks like this to know that that's probably what's going through 7-3 80% of your your minds right now and you're asking what is space expanding into right show me your hand if you are kind of wondering that yeah okay I told you so it sounds like a reasonable question but it doesn't have a good answer it doesn't have a good answer because if space were expanding into something what would we call that something space all right that's not what we mean when I tell you that space is expanding when a cosmologists says that space is expanding what they mean is that all of space not some of it is expanding the volume of any pieces face is bigger in hell than it was in the past and will be bigger still in the future if you have a hard time picturing space expanding without something for it to expand into I'll teach you a trick this is something I came up with when I was a grad student and I was struggling with these ideas like I imagine a lot of you are right now so the mental trick involves this so I say I look at this room I want to measure the size of this room so I what I do I find myself a meter stick I run over there I lay the meter stick down one after the other until I find out that this is uh you know 15 meters from side to side did I wait a little while I do it again make same similar measurement but this time I find it takes 16 meter stick links how do I interpret this information live two ways I could do it I could say ah I've just measured that the room is expanding it's growing in time or equally well I can say ah the meter stick is shrinking both are completely compatible with the data I've just described but I could imagine objections you could say well you can tell whether this meter stick is shrinking by comparing it I can go over here and see does this take two meter sticks or two and a half or something and does that change because if the meter stick is shrinking then you could tell by comparing it to other things so I say okay I'm gonna refine my hypothesis saying that everything in this room is together shrinking in unison that will look just like the room expanding so taking this back to cosmology if you're uncomfortable with the idea of space expanding without expanding into something you can conveniently instead think of everything in space including the constants like the speed of light are all shrinking together at the same time so if space is expanding which it is and it has been for a long time we can deduce that in the past and he given space must have been smaller and since it contains the same kinds of matter and stuff it must have been denser in the past and when you take a gas of particles say and compress it it gets hotter so Hubble's observation carried with it profound implications about our universes past this is at the heart of what we mean by the big bang theory the idea that over billions of years our universe expanded and evolved from a hot dense state into the universe that we see all around us today now when you think about the Big Bang or when it's usually described you're probably tempted to picture something like a cosmic explosion when somebody says the temperature a trillionth of a second after the Big Bang was something or other or the density a minute after the Big Bang was whatever or nuclear fusion was taking place a second after the Big Bang you might think it happened somewhere in space that's not what we mean when I tell you that the Big Bang was at a certain temperature the universe was a certain temperature just after the Big Bang what I mean is all of space that temperature was everywhere those densities were everywhere there was extreme mind-boggling conditions that the Big Bang describes were a state that persisted throughout all of space everywhere in the universe it's not an explosion it's not an event it's not a location it's not an object it's a state that our entire universe was in 13.8 billion years ago all right so let's take a step back and walk through a timeline of our universe's cosmic history so on this scale you see a couple of key events you can start a couple of hundred million years after the Big Bang that's when the first stars begin to form those stars were pretty different from the ones we see in our universe today the first stars were much bigger and they were shorter lived they were very hot volatile objects and exploded in a short period of time seeding the conditions for the next generations of stars to begin for him we are just now acquiring the technology we think it will take to image some of these stars to see the first pictures of these stars with our telescopes something like 9 billion years later our star the Sun and the various planets formed to make our solar system then over the next say five or so billion years after that four-and-a-half billion years or so life evolved on the earth and if you look at that image all of human history is contained in approximately one pixel in this sense human Humanity has played a very insignificant role in our cosmic universe in other ways of course we played the only important role so there's nothing wrong with this timeline it's fine it's not wrong but a cosmologists looks at this and they say this is a really boring way to describe our universes history it's a terrible way to show it because all of the most interesting stuff happened way way way on the left on on the far left side you can't see it on this scale so let's change the scale instead of showing it on a linear axis let's do it on a logarithmic one so now when you stretch everything out in powers of 10 you can look back towards much earlier times closer and closer to the Big Bang in particular you can see the special moment about 380,000 years after the Big Bang when the first atoms formed this transition was really important for a lot of reasons I will explain but the reason it happened had everything to do with the temperature of the universe today our universe is filled with a background of radiation that's only two point seven degrees above absolute zero very very cold but if you go back you compress that radiation the expansion of space done in Reverse makes those photons shorter and hotter and if you go back to this 380,000 year point you find a point in our history where the whole universe was filled of the background of 3,000 degree radiation this is comparable to the temperature of the surface of a red star okay but it filled all of space this isn't just any old temperature it's a particularly important one because because it is what I like to call the melting point of atoms what do I mean by that I mean that if I took a box full of a gas of some particles there's some some atoms it doesn't really matter what kind and I started to heat it up right around the time they got to 3,000 degrees the electrons would start to fall off instead of having a gas of electrically neutral atoms you would have a plasma of electrons protons and other nuclei so in our universe's history prior to this transition the universe was didn't contain any atoms it instead consisted of electrons protons and other nuclei and then around 380,000 years those electrons become bound to those nuclei forming the first atoms in our history the reason that cosmologists are so excited about this is that before that transition when the universe was still a plasma all of space was opaque to light if you had a flashlight only 200,000 years after the Big Bang and you tried to turn it on all those photons would just kind of bounce around they wouldn't get anywhere it'd be about as successful as if I tried to shine a flashlight and through the earth they just wouldn't make it any distance at all but as those atoms began to form light became or the space became increasingly transparent and suddenly a huge amount of light was liberated into space and it's been traveling through the universe ever since more or less unabated now I'm a scientist and intrinsically in my heart of hearts I'm a skeptic if you want to convince me something that something like I just described actually took place isn't just a speculation but that it really took place you're probably going to have to provide me with some pretty compelling empirical evidence some sort of measurement or some sort of observation that I just think ok this is clearly settles the matter at hand and you might think that since this happened 13.8 billion years ago evidence like that is just not going to be possible to acquire after all something so dis in the past so far away there's just no way we could plausibly measure that sort of thing but in that respect you'd be wrong because this is an image of that light that was released into our universe only 380,000 years after the Big Bang we call it the Cosmic Microwave Background it was 3,000 degrees when it was released but then as the universe expanded those photons were stretched and cooled and today it's that 2.7 degree radiation that fills all space we're bathed in it right now every cubic centimeter has 411 or so photons from that transition it's all around it so if you take an old old television set you know the kind with rabbit ears and you turn it well least in the States if you turn it to channel one where there's no broadcast maybe you have a channel one here I don't know you'll find that you just get this white static some few percent of that is coming from the Big Bang this was measured for the first time were detected for the first time in the mid-1960s and since then cosmologists have been eagerly measuring it with higher and higher precision this is an image taking from the Planck satellite that's a telescope designed to study this radiation in particular and it provides our highest resolution most detailed map of this era of our cosmic history those tiny little blotches of orange yellow and blue you see is a depiction of the tiny little variations in temperature in this radiation the hottest spots are about one part in a hundred thousand hotter than the coldest spots are about one part in a hundred thousand cooler than average that maps on to a distribution of matter and energy that existed during the time when these atoms were forming so by studying this we know what our universe was like that close to the Big Bang only a few hundred thousand years after the origin of time let's go back to our timeline let's go back even further this time we're gonna go back to the first minutes and seconds after the Big Bang we're the first nuclei were forming prior to this time the universe had things like protons and neutrons in it but kind of like the melting point of atoms it was too hot for the nuclei to bind together to form nuclei but at this point about a billion degrees in temperature those nuclei began to undergo nuclear fusion the way I like to think about this is that this was a point where the universe was so dense and so hot that the entire universe all of space functioned like an incredibly efficient nuclear fusion reactor doing the sort of stuff you find in the mast and in the in the cores of massive stars today except a lot faster because there were a lot more neutrons those protons and neutrons bound up into things like deuterium tritium helium-3 and eventually helium as we know it in the universe today in fact about a quarter of all of the protons and neutrons found their way into helium during this period of time along with the smattering of heavier elements like lithium and beryllium we can use the equations of general relativity and some equations dictating the behavior of nuclear physics to calculate how much helium lithium beryllium we think should have been formed in this way and we can go out into the universe and try to measure it and see if we find those quantities and we do to the best of our ability to measure this process of nucleosynthesis occurred in exactly the way the theory does and that gives us a lot of confidence that we understand how are you has evolved from the first seconds after the Big Bang all the way to the present let's go back even farther now we're gonna go back to this point something like a millionth of a second after the Big Bang this is when the first protons and neutrons were forming before this point there weren't any protons and neutrons instead there were just the particles that that make up protons and neutrons things we call quarks along with things we call gluons a proton after all is nothing more than a few quarks held together by gluons as is a neutron as universe cooled these quarks begin to bind together forming the first protons and neutrons at an incredible temperature of about 10 trillion degrees now when I described the formation of the first atoms in the formation the first nuclei I told you what we observed about the earth from the early universe to kind of convince you that we knew this really happened and in those two cases we are quite confident they really happened but we have no way of observing the proton and neutron formation epoch we don't know of any way with current technology that enables us to see back to the first millionth of a second of cosmic history but that doesn't mean we can't make any progress what we do instead what we have to rely on for the time being with our current technology is to instead try to recreate the conditions that were found in our universe in these early times and we do that using these fantastic machines we call particle accelerators this is an image of the Large Hadron Collider the Large Hadron Collider is an enormous 17 mile underground tunnel goes beneath the city of Geneva Switzerland and then it passes into nearby France it's too big to fit under Switzer under under Geneva and throughout that tunnel we have 21st century magnets super powerful magnets superconducting magnets that accelerate protons to just under the speed of light and when I say just under the speed of light I mean 99.999999 7% of the speed of light I think I got the right number of 9s sir sometimes I get it one or two wrong but awfully close the speed of light and then those beams of particles are directed head-on to each other in key locations inside these devices called particle detectors they're roughly the size of a gymnasium and they're all built of 21st century electronics in those detectors of the particle beams collide and about 600 million times every second protons collide and are their energy is transformed into new forms of matter and energy the reason we do this the reason we collide particles together isn't immediately obvious if I wanted to learn more about automotive mechanics I don't get to cars and drive them into one another as fast as I possibly can that would not be a very effective technique but when it comes to particle physics this is our best tool we're taking advantage here of einstein's most famous equation equals MC squared what Einstein equation really means is that mass as a form of energy and if you put enough energy in one place at one time you can convert that energy at least in principle to other sorts of things that carry lots of mass so in the collisions at the Large Hadron Collider we're able to create a long a large variety of particles in forms a matter in energy to carry a lot of mass that we don't find in our universe otherwise today at least not in any appreciable quantity we produce things like top quarks and W bosons and Higgs bosons and tau leptons and the list goes on and on and on these particles are all explosive these particles are really rare in our world today but a trillionth of a second after the Big Bang the universe was teeming with them all of them that's because the kind of collisions that the Large Hadron Collider produces and we have study yet when we use to study the kind of collisions that were going on a trillionth of a second after the Big Bang under those sorts of temperature and density conditions this is a chart showing you all of the particles that we've observed and studied at the Large Hadron Collider and at other particle accelerators and the upper left are the six quarks the up and down quarks are the kinds that make up protons and neutrons the others are more short-lived and exotic matter the top quark was discovered at my own Fermilab long before I worked there in the bottom left are the six leptons this includes the electron that's very well known and it's heavier cousins the muon and tau they're also three neutrinos the neutrinos are kind of exceptional because they're so feebly interacting that they can pass through the entire Earth without knowing it's there but we can still study them we know how to do that and then on the right we have the force communicating particles for example the reason that there is an electromagnetic force the force that Michael Faraday presented here in this very stage more than a century and a half ago that force exists we now understand because of photons being passed back and forth through space between charged particles the gluon brings into existence too strong nuclear force and the particles known as the W and Z bosons bring into existence the weak nuclear force in the early universe a trillionth of a second after the Big Bang any particle that exists in space was constantly interacting with its neighbors in a flurry of activity being created and destroyed in rapid succession one after the other an electron would become a top quark which would become a gluon which become a photon which become a neutrino and then all over again it was an incredibly active time full of creation full of transformation and all of everything we know about that period of time we can thank Large Hadron Collider and other accelerator experiments for for helping us build and understand okay so at this point in the lecture you might be under the impression that I'm trying to tell you that we really understand a lot about our universes first fraction of a second but that's not true we have a wonderful theory a spectacularly successful theory when we combine everything that Einstein taught us about space and time with everything we've learned about particle physics and quantum physics from particle accelerators and other experiments we can explain a lot of what we see we can explain the detailed patterns of light we see from the formation the first atoms we can understand how galaxies formed and clusters of galaxies and why they carry that kind of characteristics we observe we can understand how the light nuclear elements formed only the few seconds after the Big Bang but when we get to an earlier time than that there are lots of reasons to think our theories may be incomplete or just wrong for one we can't observe those eras so there's a lot of opportunity to get things wrong and then secondly there are series of puzzles or problems that cosmologists have uncovered in the recent decades which turn out to be really difficult to solve and they all seem to point back to this early era these puzzles make me at least suspicious that we've got it right I don't know maybe we'll tie up these loose ends as history progresses with better measurements and better observations may be a little theorizing or maybe these puzzles are indications that we've gone about this all wrong and we need to radically rewrite the first second of our universes history book let me describe some of these puzzles that I'm talking about for you the first of these puzzles has to do with the simple fact that matter exists in our universe when we study matter at particle accelerators we learn that every kind of matter is accompanied by something that's a equal and opposite version of that matter that we call antimatter example the electron exists alongside something called a positron they have the same mass all the same properties basically except that the electron has a negative electric charge and the positron has a positive electric charge quarks have their antimatter counterparts and anti quarks neutrinos antineutrinos so on and so forth there seems to be a perfect symmetry between the laws that describe matter and antimatter you can't have one without the other and best we can tell you can't create antimatter without creating along sided an equal amount of matter and you can't destroy antimatter without destroying an equal amount of matter they come into and out of existence in unison their fates are intertwined so when cosmologists think about this they run into a big problem they have every reason to think from the laws of physics as we currently understand that the early universe should have been filled with equal quantities of matter and antimatter they follow the same laws of physics whatever created the matter would have created alongside at the same quantity of antimatter but then as a universe expands and cools the matter and antimatter should have destroyed each other but this would have left us in a universe without any electrons without any protons without any neutrons without any atoms without any stars without any planets without any galaxies and without any life that's clearly not the universe we live in so we know we've got something wrong about how this played out in the early universe but we don't know what the answer is we have a bunch of guesses but we don't know which ones right the second problem also has to do with matter but not the kind of matter that consists of atoms something else what I'm showing you here is an image of the Andromeda galaxy it's one of ours our nearest neighbor to the Milky Way we can look at an object like that and we can look at how any stars that contains how much gas it contains basically we can get a pretty good inventory of all of its visible matter when we do that we can work out just using the laws of gravity how stars should move around a galaxy like this and you get something like this this is a predicted rotation curve of the galaxy like Andromeda as you move away from the middle of the galaxy we find that stars should be moving in slower and slower orbits because they're farther and farther away from the concentration of mass this is the same reason basically that Pluto moves in a really slow orbit and we move in a much faster one it's the same basic idea in the 70s though astronomers begin to measure rotation curves look that looked more like this upper line these galaxies seem to harbor a lot more mass than we could account for in terms of stars gas dust and planets furthermore the mass we couldn't observe seem to be puffier extending out to much greater distances from the middle of the galaxies we had a lot of arguments and debates but ultimately a consensus form that what was going on here is that most of the mass and galaxies isn't made of luminous material it's not made of things that appreciably radiate absorb or reflect light instead it's made of something else something that for a lack of a better name we just called dark matter we don't know what dark matter is just because we can give it a name doesn't mean we understand it furthermore as time went on we became convinced that the dark matter must consist of one or more new kinds of substances maybe some kind of new elements root particle or particles that fill all space and basically act interact under the force of gravity if that were true we could begin to understand how our universe came to have the structures in it that it does this is a sequence of images taken from a computer simulation of dark matter particles evolving from an early time shortly after the Big Bang on the for left and then in a sequence allowing the universe to expand and the force of gravity to pull on the Dark Matter collapsing it collapse again into things we call halos when we look at the distribution of those halos in the lower right panel we see a distribution that looks the same as the distribution of galaxies and clusters of galaxies in our universe today so in a universe its mass is dominated by dark matter by which I mean about 5/6 of the total matter is made of dark matter we can explain why the distribution of galaxies and clusters of galaxies in our universe look the way they do so if you ask me 10 years ago what the dark matter was likely to consist of I would have given you a pretty confident sounding speech about how wimps are the most likely class of candidates wimp stands for a weakly interacting massive particle and we thought they were really compelling because if particles like that existed then we could calculate how many would have been produced in the Big Bang how many would have been destroyed and how many was survived and lo and behold the number that survived was about the right quantity you needed to explain things like this in those rotation curves of galaxies so left us thinking that that's probably the answer is pretty simple it's really easy to write down a particle physics theory that behaves this way that's probably it and the better thing about it yet was that if it were true we knew how to test it we could build these really sensitive underground dark matter detectors we knew how to do it or at least thought we could figure it out and you know we thought in another you know 5 10 years we discover this stuff it was it was a no brainer so we went to deep underground laboratories and when I say we I mean the people doing experimental physics they don't let me anywhere near the experiments for good reason so this is an example of an underground laboratory in Italy the Gran Sasso laboratory and in this little kind of chart you can see xenon and dark side and dama and crest all of those are dark matter detectors there are many others in other laboratories scattered around the world and they have performed really well the science off to the scientists who built and designed these things operated them they have exceeded all expectations in terms of their sensitivity and performance they are something like a hundred million times more sensitive than they were when I started working on dark matter when I was a grad student 100 million is a big number but they haven't seen anything no one can blame the experimentalist a theorist told them this is what you need to find this is how you use the kind of experiment you'd have to pull off in order to do it they said okay we're up for that challenge they went out and they did it they did it well but the things we told them to look for weren't their best we can tell wimps are either harder to look for than we thought and that's possible I can write down some theories of wimps that can evade these constraints I have to work a little bit but so it's a little harder than used to be but it can be done or maybe it's telling us that the dark matter wasn't produced in the early universe in the way we have long imagined maybe things played out differently in the universe maybe space expanded at a different rate maybe there were other forms of matter and energy present maybe Dark Matters origin wasn't in this thermal baths like we imagined but maybe was produced in some other way any of those could be possible and I would just say that the elusiveness of dark matter that's been surprising to me and others is at least suggestive of some events in the early universe we weren't expecting there it's not part of the standard story all right the third puzzle I'll talk about has to do with the rate at which space has been expanding over time if you take Einstein's theory of relativity and deduce how an expanding universe should be changing over time you wind up with predictions like this depending on exactly how much matter there is in universe and the universe it might be that it gets bigger for a while reaches a maximum size and then begins to contract ultimately undergoing something like a big bang and verse which we call a big crunch that's the lower line it could also be like in the upper line the universe just gets bigger without limit slowing down but still steadily increasing in size as time goes on and then there's kind of an intermediate case where it gets bigger and it kind of plateaus to a more or less maximum size ultimately those are all logical possibilities in throughout most of the 20th century cosmologists were out there trying to find out which of these universes we lived in they thought of this as a multiple choice question a B or C in the 90s we finally had the kind of telescopes it took to definitively answer this question once and for all and what did they find D none of the above that's approximately the sort of curve that we learned was the case indeed all right all right so in the 90s we learned that space isn't just expanding its expanding at an accelerating rate space is expanding faster today than it was a billion years ago and by all indications it will be expanding even faster a billion years from now this doesn't make any sense it's it makes about as much sense as if I took a rock and I threw it upward and it just kept going faster away from the earth something's propelling it gravity should be pulling on it slowing it down but it's not happening the only way we have to understand this at all is if we pause it the space itself contains intrinsic to space a fixed quantity of energy a fixed density of energy we call the sub dark energy and that energy has to be have about the same density at every place in the universe and about the same density at every time in universe in our universes history so that means as a cubic meter of space turns into two cubic meters of space as it expands everything else gets diluted all the matters density goes down by a factor to all the energy density light goes down and the energy density in dark energy stays the same that means that over time a bigger and bigger fraction of our universes total energy is in the form of dark energy and when it becomes the main component accelerated expansion is predicted to take place so today we think about 70% of the energy dense interior universes in form of dark energy we don't understand what it is we certainly don't understand why it exists in the quantity it does and I don't know how we're gonna change that all right the fourth and final cosmological puzzle I'll mention is an effort to solve the fact that if I look as far back as I can in that direction with a telescope and I look far back in that direction as I can with the telescope and I compare what I see I basically see the same thing our universe on the grandest biggest scales is remarkably homogeneous same amount of stuff everywhere same temperature everywhere in fact the Cosmic Microwave Background in that direction is within one part and a hundred thousand the same temperature as a Cosmic Microwave Background in that direction and it shouldn't be because that part of space never had a chance to be in contact with that part of space it's like to people who have never met or otherwise communicated with each other just wrote the same song if you found two people to both claim to have written the same song you'd say one of them or both of them maybe learned it from a common source if you don't want accuse them of being a liar you say you heard it somewhere and it got in your head subconsciously but these people these parts of our universe never had a chance to meet or interact in fact from what we understand about the laws of physics even if you travel to the speed of light that thing could never have contacted that thing just not possible so to address this we've been forced in Alan Guth and others in the 1980s began to contemplate the possibility that shortly after the Big Bang space may have had a period of hyper fast expansion that we call cosmic inflation the idea here is that you take two points in space in contact with each other and you have them expand way way way faster than the speed of light apart from each other that space grows so fast it carries them to very different places being driven by an energy field kind of like dark energy but a lot more intense and then that energy converts itself into normal radiation and particles kind of starting off the Big Bang as we know it and then you have an explanation for why that part of the universe in that part of the universe got to be so much alike because once they were neighbors but you need something like this bursts of hyper fast expansion that we call cosmic inflation if you're trying to try to explain that one particularly cool in my opinion facet or outcome of considering inflation is that it doesn't tend to end if I have a piece of space and it's inflating there'll be a little patch of it that stops inflating and it's gets filled of matter and energy and it starts to expand like a normal universe and it becomes a normal universe but the rest of the inflating space continues to inflate and then a patch of that stops inflating and makes a universe and then another patch in another passion forever it never ends you produce a unbelievably large number of universes in this way so in other words if inflation happened we have every reason to think our universe is one of very very many within a greater multiverse I wouldn't say a multiverse is a scientific fact that's certainly not true but the more we learn about inflation the more likely it seems to be that our universe is one of many all right so let me pivot a little bit here we have an incredibly successful theory we can explain the details of the Cosmic Microwave Background the expansion history of our universe and the formation of light nuclei we understand this stuff really well and yet there are these puzzling loose ends dark matter dark energy what happened to all the antimatter and why did cosmic inflation happen all of this stuff are kind of the impossible or really challenging outstanding questions that we've been struggling with for the last years and decades and as time goes on they haven't proven to become easier if anything the experiments we've done have only made these questions more difficult to address so when I want to frustrate and/or entertain my colleagues I like to ask them a following question and you'll come back to this it will seem like a departure but it will come back to this in a moment I like to ask them what they think it would be like to have been a physicist in 1904 why 1904 I could have picked any year you think but no no 1904 special 1904 was the year that businesses had the greatest confidence in their ability to understand the universe at that point Newtonian physics had been successful for 200 years new discoveries kept being made like electricity and magnetism and heat and other things like this and from the Newtonian mindset or paradigm we kept being able to tackle it we explained more and more with these ideas of mass and force and acceleration and velocity and in geometry space all this stuff we that was introduced by Newton two centuries earlier just kept working in most physicists the vast majority of physicists in 1904 were confident that the Newtonian framework would continue to thrive into the distant future maybe forever of course there were a few loose ends in 1904 as well one of those loose ends had to do with the nature of light it had been measured that light always travels at the same speed in any frame of reference that's different from other kinds of waves if I tell you there's a water wave moving across the ocean at 20 miles an hour and I put myself in a boat moving along with the wave at 10 miles an hour I'll measure the wave to be moving 10 miles an hour in my frame of reference everyone expected light to be like this too but it turns out that light travels at the same speed 3 times 10 to the 8th meters per second in every frame of reference and no one could understand why the second of these puzzles had to do with the planet Mercury in its orbit like any other planet mercury moves along an ellipse and the orientation of that ellipse changes a little bit from year to year it processes over the course of the 19th century the precession of the perihelion of mercury was measured very accurately that the rate at which it processed was measured very accurately and it was just a little bit different than what Newton had predicted best we could tell Newtonian physics didn't accurately describe Mercury's orbit now one hypothesis that was popular at the time is there might be some other planet out there something called Vulcan that's where the name came from and maybe it was just tugging gently on Mercury screwing up its orbit a little bit but astronomers looked for Vulcan and they didn't find it no one had a good explanation for why mercury was behaving the way it was perhaps the biggest outstanding problem had to do with the Sun in fact physicists could not explain how something the size of the Sun could be emitting so much sunlight for so long for billions of years this thing had been putting out about the same amount of energy in sunlight we knew that from geology but even if the whole Sun were made of gasoline or coal it should have run out of fuel after only a couple of tens of thousands of years people also imagined that maybe was contracting converting gravitational potential energy in the sunlight but that would last millions not billions of years so no one had a clue why the Sun was doing what it was doing and then lastly physicists had no way of even approaching the problem of how atoms worked atoms were known to give off these peculiar spectral lines these kinds of light no one knew why no one could even begin to calculate it furthermore when we tried to calculate what an electron should do in an orbit around a proton we found that those electrons should spiral inward and crash into the nucleus and almost no time at all in other words atoms shouldn't be stable and yet here we are of course these didn't turn out to be loose ends in 1905 Einstein came out with a number a sequence of incredibly revolutionary papers he introduced a theory of relativity and he wrote the first paper introducing some of the ideas that would eventually become quantum physics these papers didn't build upon the Newtonian paradigm they tore it down and built up something else in its place the theory of relativity explained why speed of light was the same to all observers and all frame of references it's because space and time were not the way that Newton imagined them the general theory of relativity offered equals mc-squared which could explain how the Sun could convert a very small fraction of its mass into enough energy to power sunlight for ten or more billion years the theory of quantum physics that Einsteins worked started off could explain not only the spectral lines we observed from atoms but why they were stable and eventually Einstein's general theory of relativity would explain with high precision why Mercury's orbit behaved the way it did so I find myself asking the following question is 2020 the 1904 of cosmology we have a wonderful theories been successful for a long time and yet there are things we cannot explain at least haven't been able to so so far maybe it will turn out that these are just loose ends that we will neatly resolve with further observation experiment or maybe we will find out that the only way to resolve these lingering problems and puzzles is with a new paradigm one that I can't even imagine what it looks like yet because it hasn't been written alright thanks this has been a lot of fun I look forward to taking a bunch of your questions and then afterwards we'll come out here and we'll sign some books and you can ask me some questions in person Thanks [Applause]

Channel: The Royal Institution

Views: 398,332

Rating: 4.5791841 out of 5

Keywords: Ri, Royal Institution, Universe, Cosmology, Big Bang, Astrophysics, Particle accelerators, large hadron collider, cosmic background radiation, particle physics, antimatter

Id: dB7d89-YHjM

Length: 51min 33sec (3093 seconds)

Published: Thu Mar 05 2020