apparently you're interested in time so it seemed appropriate to talk about going to the beginning of time and I want to talk about the efforts we've made to go back and to the earliest moments of the Big Bang and and we are on the threshold of potentially a revolution in that regard so that's what I want to talk about and I hope my my remote will work well that's the one thing we haven't checked before usually requires to two or three times before it there we go okay this is the universe we live in this is the most recent Hubble Space Telescope picture the multi chromatic image which means the colors are real every image in this every dot in this image is a galaxy except for that one so there are a hundred billion galaxies in the observable universe approximately each containing a hundred billion stars and it is and in this case that the faint blue galaxies are the darkest are the the most distant galaxies so the most distant galaxies in this image would go back to maybe about ten billion light years away so we go back ten billion light years into a universe that's 13.8 billion years old so it takes us some of the ways back and with the with the successor to the Hubble Space Telescope that James Webb Space Telescope will but go back to the earliest form eight star formation the first light in the universe which probably happened between a few hundred million years and a billion years after the Big Bang but with light that's just with visible light that's as far as we can go back when you look at this image by the way there the fact that there are many galaxies is interesting you might ask where is this picture taken which direction and it doesn't really matter because the universe is the same in all directions roughly the same number of galaxies and the same in all directions that is a surprise because of time in a sense because if you look at light from the most the universe in that direction in that direction then now is the first time in the history of the universe that those regions can communicate causally since no signal can travel faster than light so if now is the first time that they could causally communicate the question is how do they know to be exactly the same that's been a puzzle that has driven much of the theory in trying to understand the early universe why is the universe the same in all directions and we'll come back to that perhaps because we we have an explanation that we can test but with visible light this is as far back as we can go we can go back further and the farthest we can go with electromagnetic radiation is the cosmic microwave background radiation when the universe was about 300 thousand years old it became transparent to visible light essentially electromagnetic radiation because before that before the time of three hundred thousand years the temperature of the universe was was greater than three thousand degrees Kelvin and when the temperature was higher than that then basically hydrogen would be dissociated into protons electrons and you'd have a plasma and a plasma is opaque to radiation so the universe was opaque to electromagnetic radiation and then it be and then when it cooled below 3,000 degrees hydrogen combined became neutral and the neutral matter became transparent so we can just as I my laser can go out as far as the that wall when we look out we can see back to a wall essentially the moment when the universe became transparent and the radiation that it was emitted from that surface we called the Cosmic Microwave Background because that radiation which was a temperature of 3000 degrees has no cool to a temperature of 3 degrees approximately and that radiation is in the microwave band was discovered by accident in 1965 by two people who didn't know what that they were doing but they won the Nobel Prize anyway you don't have to know what you're doing to win the Nobel Prize you just have to do it anyway this is an image of the of that cosmic microwave background and it is it is has false colors the colors represent temperature now the so you can see that it's hotter in some spots and colder in some spots therefore it certainly doesn't look completely uniform across the entire sky now before I explain that let me just explain this as a projection of that - of that surface at 300,000 light years it's essentially the same projection as we would have projecting the surface of the earth although that's upside down there we go my wife is from Australia so I try not to be northern hemisphere centric and and and so the projection I just gave is is this one here is the same so this is up and that's down looking at the sky this is where our galaxy is the plane of the galaxy so this is this is just a pollution in the in between us and that microwave background surface 300,000 light years after the Big Bang this is a baby picture of the universe at least two Nobel prizes have been given for it because this radiation the light that's observed from in this case came from the universe when it was three hundred thousand years old well before any structure any stars had formed and you see that there are primordial lumps there's hot spots and cold spots now as I say the the variation here is somewhat an illusion because it's extremely uniform the hot spots are roughly one one one hundred thousandth of a degree hotter than the cold spots so this is the universe is uniform at that time in temperature to almost one part in a hundred thousand that uniformity is as again striking and unexpected in some sense because there's no reason within the context to the standard Big Bang picture though it shouldn't be uniform because these this region here could never have communicated with that region there yet to one part in a hundred thousand their uniform now as I say this is the pollution from our galaxy and by by measuring this over different frequencies this radiation has it looks like a blackbody the radiation emitted from the galaxy doesn't and by comparing the two you can try and get rid of the galaxy this is the best current picture taken with a satellite called the Planck satellite and launched by Europe in fact and where the galaxies been removed so this is the baby best baby picture we have of the universe and and you can see the hot spots and the cold spots the question is first of all why is it so uniform and secondly what created the small lumps because without these hot spots and cold spots the hot spots and cold spots represent regions where there's a little more matter and a little less matter than average without that there'd be no structure in the universe today if the universe were exactly uniform then there'd be nothing around but the hot spot the regions actually in this case the cold spots represent regions where there was a little excess of matter and and that matter would collapse to form all the stars and galaxies and aliens and everything else in the universe so that these this is these would later on to form all basically all this structure that I showed you in that other picture and we have a we have an understanding potentially how that can happen in fact it requires lots of exotic physics including dark matter and dark energy which I won't talk about but I'll be happy to answer questions about but this is as far back as we can see 300,000 years after the Big Bang which is not bad but we'd like to get back earlier but this is as far back as will ever be able to see an electromagnetic radiation because of that wall because at earlier times there's no way electromagnetic radiation can propagate through that dense plasma that was the early universe if we want to look back to earlier times we have to look for a signal that can propagate from maybe earlier times to today and that means we look have to look at some sort of radiation that can that is less strongly coupled to matter than electromagnetism okay and of course what we use is gravity because gravity is by far the weakest force in nature and we use a signal from gravity that was first predicted by Einstein in 1916 which is the fact that because of course general relativity tells us that space and time depend upon the nature of matter and energy within the universe in that relationship the fact that matter and energy determines the nature of space and time which then determine the evolution of matter and energy that nonlinear relationship is what makes general relativity more complicated than SPECT then than Newtonian gravity but because matter radiation affect the properties of space every time I do this I'm curving space around me in a time-dependent way all of us curved space around us but when I curved space in a time-dependent way I produce a disturbance and it's that the and it's essentially the same as the disturbance that Maxwell first wrote down when I shake an electromagnet an electric charge I produce an electromagnetic wave I produce a disturbance in electric and magnetic fields when I move a piece of matter around I produce a disturbance in space and time in the fabric of space and time and it propagates out at the speed of light and we call that a gravitational wave Einstein called it a gravitational wave if he actually predicted in 1916 in 1936 he wrote a paper saying he was wrong he submitted it for publication he'd moved to the United States at that time he submitted it to him an American Physical Journal and it was rejected because the it was wrong actually he was very upset he wrote to the editor saying ice turns out in Germany he'd never been subjected to refereeing before and he wrote to the editor saying I sent this for publication not to be refereed and you should try that and anyway but happily it turns out that the error was discovered he discovered the error again before it was published so he that erroneous paper never appeared but but eventually that prediction came true and in fact the gravitational waves do this if this is a gravitational wave coming out of the screen then what it what it represents the fact is that when there are many gravitational waves moving throughout this room right now and as they move throughout the room the distance between the walls gets a little bit shorter and that isn't seeing the floor and ceiling gets a little bit longer and and it oscillates back and forth and these are occurring right now all the time but gravity is so weak when when I do this I produce a gravitational wave but the gravitational wave is so weak that we will never measure that it is a challenge to measure gravitational waves this is the two-dimensional version this is the three dimensional version of a with three dimensional animations have no information but they look good and anyway so this so this is meant to hypnotize you I think as I talk the question is can we measure these and it is truly amazing that anyone ever thought we'd be able to measure these because while we'll never measure the gravitational waves from my hand moving we can look for more extreme phenomena cataclysmic events in our universe because the intensity the amplitude of the gravitational waves will depend directly both on the amount of mass and and and how quickly it's moving those two factors will determine whether you'll have a an observable gravitational wave and the most cataclysmic events we can think of in the universe are the collision of black holes large solar mass black holes if they exist would produce an abundance of gravitational waves that you might hope to measure and so a brave set of experimentalists over 50 years 40 years assembled what it was what is now the largest gravitational wave Observatory in the world this is the one part of it this is the LIGO the laser interferometer gravitational-wave Observatory this is Hanford Washington there's an identical version of this in Livingston Louisiana and what it consists of it's an interferometer it consists of two perpendicular tunnels each four kilometers long and one wants to measure that and it's very simply if a gravitational wave comes down from above the length of this tunnel will get shorter and this one will get longer and then this one will get shorter and that one longer so it's very simple you just measure the length of the tunnels it's not so simple of course what you do is you you hang mirror here and we use lasers we use interferometry we as I'll show you in a second and we reflect light back and forth to try and determine the length of those tunnels but the challenge is worth noting and this is the reason I'm happy I'm a theorist not an experimentalist if two solar mass black holes were to collide in a nearby galaxy producing the most intense gravitational waves you can expect being produced in our universe today then we can calculate how much this length will change and this by the way is a time measurement too so you should be relevant it's relevant we can calculate that if such an event happened the length of this four kilometer long tunnel compared to this four kilometer tante long tunnel would vary would change by an amount equal to one one thousandth the size of a proton and that's the challenge to measure a four kilometer long tunnel to an accuracy of one one thousandth the size of proton this requires the most advanced optical technology you can imagine because the well talk about quantum mechanical vibrations later in a different context but even if you're reflecting light off the surface of mirror even the quantum mechanical vibrations in the mirror generally exceed that so we have to use squeezing we have to use we have to use sophisticated quantum optics that basically caused the quantum fluctuations in the mirror to be in this direction and not that direction one of many many bits and we send incredibly intense lasers with a very high vacuum and bounce them many times off one another and schematically this is what what it's what one does which is what one does in interferometry one has a mirror and and one one basically separates the light rays into two into two and one looks for interference here and one very carefully arranges things so that it's a null so that these the waves when they reflect come back out of phase and and so there's no signal on the mirror and when see dark so they're exactly out of phase and then with small changes in this length one can look for a signal on the mirror that that basically it's brighter and darker that's the idea okay now you can imagine that this is a challenge because of the fact that the we're looking for a variation in an amount equal to one one thousandth the size of a proton there are many things that cause vibrations in this system if a truck hits a pothole 20 miles away from this machine it will cause a vibration that will exceed the the the signal you're looking for so there's lots of background and that's one of the reasons why we have two detectors because if a gravitational wave comes by hand for Washington one could calculate it takes eight milliseconds for it to pass through the earth to get to Livingston Louisiana so we look for signals that are identical and of course we have to have very good time resolution we look for signals that are identical in Livingston Louisiana and Hanford Washington but separated by 8 milliseconds but even that is is not the only way we can do this now it we need more than that now this this detector required was originally built in 2000 and it didn't have it had only the resolution of 1/100 the size of a proton we it was operated because who knew maybe there were bigger events than we expected nothing was seen the detector was upgraded over a course of 15 years and on September 14th in 2015 it was now on it went online with an act with a resolution precision of one one thousandth the size of proton and Ray Weiss who was involved in in the original proposal said that there should be an engineering run no data should be taken as the machine was tuned up which is what you do I'm sure those of you who do frequency standards do a tuning period before you actually take measurements happily the graduate students didn't listen because so the machine was turned on and with and one hour later a signal was observed an unambiguous signal of gravitational wave the first observation of gravitational waves in history now here here are the observations now before I go into them just having the the experimental technology is not good enough because there's still lots of background you have to know what the signal is you're looking for if you didn't know what the signal what you were looking for there's no way you'd be able to extract the signal from background and while the experimental technology was not available till 2015 the theoretical technology was also not available till the early parts of this century because when two black holes collide you're in a region of very strong gravity and the calculations are extremely the space itself is bending and boiling and bubbling like a turbulent sea and it required new methodology theoretical technology to calculate what the gravitational wave signal would be in required supercomputers that was all put together and being able to interpret do time intervals basically understand what time was in the context of general relativity all that came together also at the same time and those two things came together so this was the first time in human history that we could have possibly even measured a gravitational wave and it's amazing that within one hour of putting all those things together one kindly occurred that was measurable here is the here is the signal in Hanford here's a signal eight milliseconds later in in Livingston Louisiana the two superimposing each other identical and you can see this somewhat smoother curve is the prediction if two black holes 136 times the mass of the Sun 129 times the mass of the Sun collided and coalesced in a galaxy 1.3 billion light-years away so it's kind of amazing that this this coalescence occurred 1.3 billion years ago and if they'd waited an hour to turn on the detector you would have missed it it's incredible it's an amazing story in that sense so this is the a platinum signal we've detected gravitational waves now what happens when I gravitate when these gravitational waves come in is as interesting and as daunting as that a technic technology is the observation itself is remarkable I'm going to show you a video of this is an artist's rendering clearly of what it would look like here are the two black holes they're bending space around them so you can see the light is distorted around them and it's slowed down these two black holes in the last moments of their life are orbiting each other at 200 times a second so they're 30 times the mass of the Sun orbiting each other 200 times a second okay that alone is amazing in any case you can see what happens as they move around this is slowed down this is the last two-tenths of a second in the life of these of these two black holes you'll see them as they coalesce here's obviously they're distorting space around them as they coalesce at the moment they they they collide you'll see the gravitational wave signals he spaced jitter so look for that there it is shake okay that was that that was the effect that later on 1.3 billion years later was seen here now this is an amazing thing because in that too so we have a 36 solar mass black hole colliding with a 29 solar mass black hole so what size of the black hole they form this is an advanced audience you should be able to do this out 36 solar mass black hole plus 29 you would we would think it would be 65 I'm not gonna pick in anybody but it's actually wrong it's a 62 solar mass black hole that means 3 times the mass of the Sun 3 times the mass of the Sun is converted to gravitational waves in two-tenths of a second now to put that in perspective the Sun burns a hundred billion hydrogen bombs every every second over its 10 billion year lifetime will convert less than 1% the mass of the Sun into energy still enough to power our civilization and everything else so for 10 billion years a hundred billion hydrogen bombs every second 1% of the mass of the Sun in two-tenths of a second this collision converted three times the mass of the Sun into energy that means during that 2/10 of a second more energy was emitted in that system than is emitted by all the stars in the visible universe and more energy is emitted into gravitational waves in two-tenths of a second then is emitted into light by all the stars during that same time in the visible universe it's an amazing it's amazing to think of that of the violence of that event but at the same time it was completely invisible and it would have been invisible if we hadn't developed the technology to look for it and we now have opened a new window on the universe this is a new form of astronomy will be these the new new astronomy of the 21st and 22nd century we're living at a time that in that sense that's akin to the time in Galileo first turned his telescope and saw the moons of Jupiter opening in a window of visible astronomy and we've heard about various people who have used that in many important ways and in understanding universe this will reveal mysteries and aspects of the universe that are otherwise hidden and it is amazing but in fact it's not the kind of gravitational waves I want to focus on it's one kind of discovery is is remarkable and it will win a Nobel Prize this October I expect but there's another source of gravitational waves that's more interesting it and those come from literally the beginning of time and we have another kind of detector to look for them too this is this is one of the detectors this is at the South Pole this is the bicep detector at the South Pole it looks at the cosmic microwave background radiation which I told you comes from the time when the universe was three hundred thousand years old but in fact there's an imprint there's a signal we think is imprinted in that radiation that comes from a much earlier time a time when the universe was a millionth of a billionth of a billionth of a billionth of a second old a millionth of a billionth of a billionth of a billionth of a sec if we can see that signal we will observe what the universe was like when it was a millionth of a billionth of a billionth of a billionth of a second which is a time I think that's shorter than any of those times that I was otherwise been considered at this meeting probably okay now this detector in order to do this we have to use sophisticated technology because the the imprint and the microwave background is very small so in fact we the South Pole is not cold enough we have to send liquid helium down there which we do only in the summer it I was amazed when I first learned this about 20 years ago maybe you know this but we can't send aircraft down to the South Pole in the wintertime we can go to the moon well that was fakes but we can we can know and we can go to the deep ocean we can go but we can't go to the South Pole so we send it in the summertime that's why this particular picture that I'm going to show you is one of my favorites it's a picture taken from the bicep telescope it's a sunset and the South Pole now sunset and the South Pole happens once a year so but because we can't send aircraft down there if you're taking this picture you're there for the winter which is why was taken by a graduate student okay so what what signal are we looking for well now I want to do I want to I I don't want to make this just a qualit quality of talk so I want to talk a little bit of physics and and and and introduce you to a little bit of quantum field theory of the which is the theory we need to describe the early universe we the current idea is that in the early history of the universe when it was a millionth of a billionth of a billionth of a billionth of a second old the younger universe underwent a rapid expansion increasing in size in volume by a factor of at least 10 to the 90th in a millionth of a billionth of a billionth of a billionth of a second due to the fact that was an energy stored in space if you put energy in empty space its gravitational repulsive and it caused the universe to expand very fast and that energy eventually was released that's that's just the theory called inflation and I'll talk a little bit about it later why we think it happened but it produced if the wonderful thing about this theory is it explains the two questions that I gave you earlier why does the universe look the same in all directions and why are there small lumps where did they come from who created them certainly not God physics okay now the first answer is quite easy to the first question why is the universe the same in all directions if the universe expanded by a huge amount in a short time then regions which would otherwise now when we look at the universe we think that this is the first time they're causally connected but if it early times the universe was much smaller than we would have otherwise thought those regions were in causal contact and but for inflation happened they could thermalize and the universe could become the same in temperature so there was enough look it was enough time for the temperature become uniform so inflation would in some sense predict why the universe is the same it would predict the universe looks the same in all directions because what would happen then is the universe would expand out very very fast and get frozen in that situation until that energy was released and we come and we cause a hot Big Bang but that Big Bang would be uniform so one of the first predictions of inflation is the universe should be uniform in all directions great but it goes beyond that it predicts small lumps and it's amazing that those small lumps are due to quantum mechanics at the forefront of physics today is is in some sense quantum engineering is trying to look for macroscopic manifestations of quantum mechanics be it by quantum computing or quantum teleportation and and so these are using quantum mechanics over macroscopic scales is kind of one of the four fronts of the technical aspects of physics but in fact we're all manifestations of this as I look out at the lumps in this room we're all macroscopic quantum mechanics because inflation says that those lumps that later created the galaxies and and and clusters and eventually stars and planets and people came by quantum mechanics and I want to explain to you how that happens so we have this period inflation we think happened when the universe was very early at 10 to the minus 35 seconds and it underwent this rapid period of expansion and as they say that's why it explains things because the standard model the universe would have been the saw at this time the universe would have been the size of a soccer ball but if inflation happened before that time the universe would be the size of an atom and there would have been enough time for for for things to thermalize over what is now our observable universe but a rapid expansion of an entire universe is a far more cataclysmic event than the collision of two black holes moving the mass of our entire universe rapidly expanding it will produce gravitational waves and I want to show you how but first I want to so so I want to tell you this miracle of how quantum mechanical fluctuations became us and it's it's sort of it's a little technical but not too technical so inflation happens because there's a phase transition in the early universe when water is supercooled and turns to ice that's a phase transition okay it's a metastable state water below 32 degrees on the roads in the winter time getting stirred up by cars remains water until the evening when the cars don't go by and suddenly it freezes forming black ice and and and you and you have accidents that we can a phase transition in physics can be thought of as by some something called an order parameter some some parameter gets stuck in some metastable state and eventually goes down to the minimum of potential and that produces a phase transition okay now in physics we think there's a field we can't imagine fields quantum fields that get stuck in some metastable state and when they get stuck in some metastable state they store energy and that energy density is as I say will cause the universe to expand exponentially because if you store energy and empty space it's gravitationally repulsive not attractive so in the so-some field in the early history of the universe as it was cooling down got stuck and if it's stiff it remains stuck we'd still be expanding exponentially and there'd be nothing left in the universe and the universe expansion would be so fast that nothing would have happened eventually in some region the transition happened and that energy that was stored in empty space gets turned in after that field goes to its new minimum gets turned in the energy of radiation and matter and you have a hot Big Bang so this is a transition that's the end of inflation turning all of that energy of empty space to the energy of everything we see now what can cause that transition well this is a quantum field theory and in quantum mechanics always has fluctuations so that field is not still it's fluctuating due to quantum mechanics and it turns out that the scale of those fluctuations is turn is determined by the energy stored in the field it's the only dimensional parameter around in the problem so the scale of fluctuate all fluctuations have to have a scale determined by the only dimensional parameter in the problem which is the energy stored in the field and so we can say that this field the expectation value of the fluctuations this field is proportional to that parameter it's called the Hubble constant it's related to the energy density stored in that field that's simple okay now if you have a perfectly flat potential the only thing that's going to cause that field to move is quantum fluctuations okay if however you have a potential that's strong that has a strong curvature there a big slope then in addition to the quantum fluctuations there'll be a classical rolling down of the field now what causes the density fluctuations we see in the universe today what happens is that due to quantum fluctuations one region in the universe leaves inflation before another region and when and when things are inflating the energy density is constant it doesn't change once you've left inflation and you produce matter and radiation then the internet sees the energy density changes as the universe expands the energy of nothing doesn't change the energy of something gets diluted as the universe expands so the region that Li inflation a little bit before another region we'll have a little bit smaller energy density today because that radiation will have redshifted it'll have it'll have gotten smaller now if there were quantum fluctuations and nothing else then if they occur very randomly then well then see fluctuations would be huge because one region would leave inflation a lot longer than another lot earlier than another region if if there's a huge slope to this potential then all regions of the universe are leaving inflation at the same time and some regions will leave a little bit earlier than other regions so if you work that out the density fluctuations we see in the universe today will depend upon two things the slope of that potential and the energy density in the potential if the slope were zero the density fluctuations would essentially be infinite because one region would leave inflation infinitely before another region essentially if the slope is very large then the density fluctuations are very small because all regions leave inflation at the same time this is a prediction of inflation it will produce a uniform basically a Gaussian distribution of density fluctuations independent of frequency independent of wavelength and and depending upon only these two parameters and so it will produce a scale the independent spectrum of fluctuations and that's precisely what we see in the Cosmic Microwave Background today a scale independent spectrum of fluctuation so so what that really means is that quantum mechanical fluctuations produce everything we see we are a manifestation of macroscopic quantum mechanics and that's remarkable now it you might say since that observes with the observations we make we know inflation happened we can't say that because inflation is an idea not a theory and it can depend upon the details of how this happens and it turns out that after you change those details you could agree with the predictions of almost anything we see so a theory that can't be falsified is not a theory necessarily and so we there's strong circumstantial evidence we think the simplest theory of inflation I should say produces exactly what we see with fancy versions inflation you computed other things since what we see is consistent with the simplest version of inflation it gives us great confidence that inflation happened but there's a way to look for an unambiguous signal of inflation something I've been interested in for 30 years and that is inflation doesn't just produce these density fluctuations it produces gravitational waves and it produces them by the same kind of mechanism if gravity is a quantum theory then there must be fluctuations in space and time as well as fluctuations in quantum fields and it turns out that if you look at gravitational waves they come in to holistic just to like electromagnetic waves but H olicity State looks just like one of these scalar fields in an expanding universe so the magnitude of fluctuations in the metric should be the same as the magnitude of the fluctuation and other scalar fields up to constants gravitational constants and then it turns out that that this is the strain parameter telling you how much what the relative change in lengths are Delta length over length how big a gravitational wave produces as a change in length it's proportional to this parameter and as scaled of independent inflation should produce a scale independent spectrum of gravitational waves in the universe whose magnitude depends upon the energy density stored during inflation that's an unambiguous in prediction of inflation independent of any of the details of don't worry about that that's just technical details but it's a generic prediction of inflation and it doesn't depend on the shape of the potential or anything else so if we could measure gravitational waves for inflation that would be an unambiguous test that inflation happened and the intensity of the gravitational waves will depend upon the energy density stored during inflation the scale of inflation okay so this is this is a complicated picture from a scientific American article I wrote a few years ago on this and as it's hard to understand but I spent 10 hours with the artist so you have to suffer through it this is a brief history of time this is looking at the universe the first picture I showed you the universe today we go back in time we get to the time where the Cosmic Microwave Background was produced when the universe was three hundred thousand years old and then we go all the way back to the earliest moments of the Big Bang when inflation happened now inflation produces we predict gravitational waves of all frequencies with the same intensity what will that produce in the universe today so there are quantum fluctuations they produce gravitational waves but of course let's take a gravitational wave with a frequency of one Hertz okay that wave does not start to vibrate until the universe is one second old so it you don't get those vibrations but once the wave starts to vibrate in redshifts as the universe expands it gets stretched and its intensity goes down so what you have let's say when the universe is one second old you have this one second period gravitational wave starting to vibrate but it gets it gets damped out as the universe expands then you'll have gravitational waves of period one year when the universe is one year old they'll start to vibrate but then they'll get damped out when you let's say a thousand years there'll be gravitational waves it'll don't map out but there will be gravitational waves a period three hundred thousand years they will just begin to vibrate when this Cosmic Microwave Background is formed and what will they produce they'll produce a polarization in that background because if I think of what hot what produces the background what produces the microwave background is say this is an electron at that moment when the universe becomes neutral it's about to be captured by hydrogen it scatters radiation and it scatters radiation uniformly the radiation if the uniform radiation is uniform it scatters out radiation to us and then it gets captured and that's and that's the creation of the microwave background the last electrons that are that are that are scattering radiation just before the universe becomes transparent but if a gravitational wave the size of the visible universe comes by then the universe will shrink in one direction and stretch in the other direction at least from the frame reference frame of that electron and that means that electron will see more intense radiation in this direction than that direction and that will produce a polarization signal if you think about it if you haven't a lot of you if you work it out if you have an electron and you have more intense radiation in one direction and another and you work out the scattering you'll find out that in the perpendicular direction the radiation will be polarized and it turns out you can work out the kinds of polarization that happened and we and we label one kind --mode polarization another kind be mode to reflect the same kind of things we talked about as as as divergence and and and curl in electromagnetism but it turns out gravitational waves produce a very specific type of polarization in the microwave background because their quadrupole waves that's all you need to know so we can look for this kind of polarization in the microwave background as potentially a signal of gravitational waves of period three hundred thousand years that were generated at the beginning of time it's not easy here's what take a small region in in that picture I showed you earlier the hot spots and the cold spots there there are going to be random polarizations of the radiation so this is what the universe would look like what the signal would look like if there are no gravitational waves and this is a signal with gravitational waves it looks exactly the same it's a signal that's one part in a million it's damn hard to look for nevertheless experiments like bicep we're designed to look for it and bicep did a simulation of what they might see looking at a small region in the microwave background looking for these kind of snake-like patterns of polarization this is what they said they might see if you have gravitational ways from inflation in February 2014 they published this data it was exactly what we predicted exactly these these are exactly the amplitude and the Nate the shape of gravitational waves that you would imagine would in polarization produced by gravitational waves from the beginning of time the we claimed or they claimed we observed gravitational waves from a time when the universe was a millionth of a billionth of a billionth of a billionth second old if this were true this would be a direct measurement of what the universe looked like of the physics of the universe at the beginning of time now I say if it were true and the reason you're probably not aware of it is because this probably isn't true it may not be true and the problem is this this is another way of plotting the effect the the what gravitational waves from the beginning of time would do to the microwave background this is a multiple expansion this is looking for the intensity of polarization as a function of angle on the sky and and this is the prediction of inflation that's all you need to know that's the prediction of inflation this is the data they took look pretty good now what are all these curves these are noise backgrounds there are other backgrounds that will produce polarization there's polarization in our galaxy radiation that's coming from our galaxy is polarized and also dust in our galaxy if the dust particles are polarized electromagnetic polarized their dipoles then they'll scatter radiation and produce also polarized radiation so this was the estimate of the dust in our galaxy and it certainly didn't seem to get in the way the signal so this was this was from the bicep detector at the same time the Planck detector the satellite was up there and that was also designed to look for polarization clearly this would be a Nobel Prize and the Planck people were very upset that they got scooped by the bicep people but they were very happy because the bicep looked at a small region in the sky but Planck looks over the entire sky in many different frequencies and they could measure and they within two months produced a figure that said okay this is this part here is this this is the prediction for inflation and this is what they said could be due to dust in our galaxy turns on our galaxy is much dustier than we thought and they said Goss dust could produce a signal of the same intensity polarized dust in our galaxy could produce a signal of the same intensity as was seen there now it doesn't have the curvature that you see here but you know this could be just an accident of the eye and they were very happy because they said maybe these people are wrong now I this is really a very important part of science one of the reasons I love science because these people hated these people and these people hated these people so what did they do they didn't cut each other's heads off they said let's do a joint analysis and find out what the right answer is because they didn't care who and ultimately who was right they cared what was right and and they did a joint analysis now the two experiments look at different regions so you couldn't do things exactly but it turned out when you do a joint analysis things are different so let me just show you what this was the original result that came from bicep it was some number that is zero if there's no polarization and it's nonzero if there's polarization due to inflation and the number was very large was point two and you could see that with high confidence they claimed to observer gravitational waves in the beginning of time this and I'll go back for a second so you can see it this was the new analysis well likelihood this is a likelihood plot and so the likelihood is still maximum at some nonzero value of this quantity R but it's not zero at zero and this is why this is physics and not medicine because what you can work out is that there's a 92% likelihood that that the signal is non zero but 92% is not good enough if you're gonna make a great discovery in in in my field of particle physics you need five Sigma 99.99999 5% okay and so if you read the paper that came out in February of 2015 it says the final result is expressed as a likelihood curve yields an upper limit of our of 0.2 at 95% confidence it peaks at 0.5 but disfavor of 0 only by a factor of 2 point 5 this is expected by chance 8 percent of the time so an 8 percent of the universe's we live in this you'll see a signal like this just due to noise and so while while the meet I mean - if you follow this the media said oh the signal is wrong it's not clearly wrong there may they may have seen something but they haven't seen something at the level of confidence where you can claim a discovery and we are building new polarization detectors of them of the South Pole that are more sensitive and so we may know the answer in the next year or two it may be that we can't get an answer because while we were lucky enough to be able to extract the galaxy from the temperature fluctuations it could just simply be that the galaxy is so dusty we can't extract the signal from the beginning of time for that we may not be able to do it but we're on the threshold where we may be able to do that and some part of this signal baby right and I just want to end this talk with some of the implications of what if that signal is true what it tells us it's kind of remarkable I was gonna do one it's actually a 1 I will tell you but I was gonna show you the math but I decided not to one of the interesting things is that that I talked about quantum fluctuations in space and time we don't have a quantum theory of gravity and the point and some people have argued maybe gravity isn't a quantum theory do we have no evidence that gravity is a quantum theory it turns out if you could measure these fluctuations we'd be able to prove that gravity is a quantum theory and it's a paper we wrote off years ago so it'd be remarkable the first thing we'd be able to say is that gravity is a quantum theory and we need to find what that quantum theory is we still don't know but it would tell us that gravity is that space and time themselves are quantum mechanical they fluctuate quantum mechanically which would be remarkable if you're interested in time at some very small time scale the Planck time becomes a stochastic quantum mechanical parameter but the other thing is is is thinking about what happened here if inflation happened because of some phase transition when phase transitions happen in particle physics the nature of forces change that's what we mean we know a phase transition happened at least one in the early history of the universe because we know that there are two forces that are very different now electromagnetism and the weak force which actually unified into a single theory we now call the electroweak theory and when the universe was a millionth of a millionth of a second old those two forces began to diverge because of a phase transition related to a field we call the Higgs field which we discovered by looking for the particles associated with that field called Higgs particles and CERN in 2012 discovered those particles so we know that phase transition happen but if inflation happened it happened due to a phase transition much earlier why would we expect to face transition to happen well it turns out these are the three non-gravitational forces in nature the the strong force the weak force and the electromagnetic force on scales we measure they're very very different the strong force which holds together quarks in protons is very much stronger than the weak force which which is responsible for nuclear reactions and electromagnetism the electromagnetic force but it turns out due to quantum mechanics we can show that as you explore those forces on nature on smaller and smaller scales the magnitude of those forces changes and since by the Heisenberg uncertainty principle exploring things on smaller scales means using more energy to do it if we think about it as we explore systems with more and more energy though the magnitude of those forces changes and it was known in the 1970s doesn't take a rocket scientist to realize that what the the the elect the weak and electromagnetic forces get stronger on smaller scales but the strong force gets weaker and maybe they unify together at a certain scale and that was that and that scale we called the grand unified scale if they were unified it was a scale 15 orders of magnitude higher in energy than the magnet than the energy of a proton or 15 orders of magnitude smaller and scale than the size of a proton well it turns out that that hope didn't work out we can now measure these things exactly if the only forces in nature and the only particles in nature are the ones we measure it doesn't work but it was soon realized that if in fact there was a new symmetry of nature which we looked in particle physics look think of as being useful for other reasons if that new symmetry came into play and new particles in nature came in to operate at a scale around the scale where the Higgs particle exists then the way those forces would change would be different and lo and behold they would unify in a single point at the scale this represents a phase transition because before that all the forces in nature had be unified afterwards they would diverge this phase transition could be associated with the scale of inflation that's why we think inflation may have happened and the amazing thing is that if we measure gravitational waves from inflation we will be able to probe the physics of this scale well actually now sixteen orders of magnitude higher in energy than the scale of the proton thirteen orders of magnitude higher in energy then we can explore at the Large Hadron Collider we will never be able to create accelerators that can probe this energy directly to create such an accelerator would require a radius of the earth-moon distance that's not going to happen given the economics of the world today not gonna happen anyway now we we do build other devices to look for things that could happen to that scale because interesting enough to go back if the three forces of nature unify at that scale then it produces another interesting phenomenon diamonds are not forever protons will decay all the matter in the universe will decay happily for those of you who have diamonds the lifetime of a proton we can calculate and it's about 10 to the 33 years which is twenty three orders of magnitude longer than the current age of the universe so you don't have to worry how could we measure such a phenomenon if every proton lives ten to thirty three years well it's quantum mechanics so it's ballistic if we could get 10 to the 33 protons in a room one of them would decay each year so he built a large detector this is the largest detector you put what do you get 2 into the 33 protons 50,000 tons of water and in the kameoka mine in Japan there's an amazing machine where where we in a working mind 50,000 tons of water with the laboratory cleanliness of a cleanroom put together with 11,000 photo tubes waiting for a proton to decay we haven't seen one decay yet in the last 20 years of course remember what happened with the gravitational wave detector if this machine goes offline for one second and that's the second when it's a case then you have to wait again for another 10 or 20 years so in fact we haven't seen anything it doesn't indicate anything yet if we measure inflation if we measure gravitational waves from inflation we will know the scale of inflation we'll be able to predict how this could occur and help us build new detectors in the future alternatively there is near here the most complicated machine humans have ever built the Large Hadron Collider at CERN if you go to Geneva near here if you take the tjv you could see Geneva and if you go out at the airport you'll see beautiful farmland but underneath the farmland is a 26 kilometer long tunnel with amazing detectors no I guess I didn't present detectors I was going to with amazing detectors inside of them and the point is that the Large Hadron Collider detected the Higgs but maybe it will detect supersymmetric particles in fact many of us thought it would detect supersymmetric particles before it detected the Higgs it didn't but it's still running and it's going to run for 20 years if it detects a supersymmetric particles it will give us independent information about the possible existence of grand unification so measuring gravitational waves for inflation will not only give us a picture of what the universe was like when it was a millionth of a billionth of a billionth of a billion second old and by the way I would argue that is the greatest single development in the history of physics those of you who work on time frequency measurements know I think that if you can improve the precision accuracy of your experiments by a factor of two that's a big deal by an order of magnitude be amazing right now the earliest we can see into that universe is when it was three hundred thousand years old if we measure gravitational waves from inflation that will improve our measurement accuracy by a factor of 10 to the 49th we will go back to measure from 300,000 years to a millionth of a billionth of a billionth of a billionth of a second never in the history of science have we taken a leap like that it would be the most important leap in the history of physics but there's the last thing I want to mention and that is kind of remarkable if inflation happens it generically produces more than one universe we now mean something different by universe than we used to mean used to when I was a student or maybe before when I was a student when I was younger the university used to mean everything whatever that was now we have a much more precise measurement of the definition of universe the universe is that region of space with which we could have once had causal contact or one day we'll have causal contact namely it's that region of space that could even over in an infinite amount of time communicate with one another ok that's a reasonable definition of universe because anything outside of that cannot impact physically on anything inside of that now inflation causes the early in space to expand exponentially and what happens is because of quantum fluctuations some region leaves inflation here it's like a seed forming in a snowflake forming a phase transition happens here and we get a hot Big Bang but the rest of space is still expanding exponentially and then later on some rather region may leave inflation and some other region but there but the space between those regions is expanding exponentially and inflation in in fact in general is eternal space is generally most of space is still expanding exponentially we live in a region where a hot Big Bang happened and if that's the case then we live in a multiverse not a universe we live in a space in which there are many different universes and interestingly when you leave inflation the physics that results after inflation can depend upon how you leave inflation just like if you have ice crystals on a window pane in the morning they could point in many different directions randomly depending upon how the phase transition happens when you leave inflation the laws of physics after after inflation ends the forces can be different and that means in each universe the laws of physics can be different this is sort of a artist's rendering of what you would expect this is sort of inflation the regions of space happening expanding in between them there's some universes forming and in some universes the laws of physics are such that galaxies form in other universes the laws of physics are such that no galaxies form and if that's the case we may understand why the parameters of the universe are the way they are and it's kind of just it's a disappointing result if it's true it means that the universe is the way it is because there are astronomers here to measure it not because it was designed for astronomers but it's kind of cosmic natural selection we would be amazed to find ourselves living in a universe in which we couldn't live that would be worth a book but no one be around to read it so this is that I wrote about this years ago and then and people have we've been speculating that maybe many aspects of our universe are so-called anthropic maybe certain parameters of our universe are just an accident now this is speculative and it almost sounds religious and people have argued well it's not physics it's metaphysics that's true but the important thing is if we can measure gravitational waves from inflation we will be able to check the model of inflation we'll be able to probe the physics that produced our universe and we'll be able to discover empirically if that model produces an eternally expanding universe elsewhere so even though we won't be able to measure these other universes directly we will have a model that describes the three forces of nature that other than gravity that may make 51 predictions and the 50 second prediction is that there's a multiverse we can check all the other 51 predictions and and if we they agree with observations we pretty well are confident that the fifty second prediction is correct it's the same as 1905 when we first predicted the existence of atoms when Einstein did his his calculations PhD Cathy says calculations no one thought we'd measure atoms no one imagined we'd ever see atoms we all knew they existed if we can measure gravitational waves from the beginning of time we will not only learn about the beginning of our universe but the beginning of many universes and I find that remarkable we are living in a remarkable time going back to the original picture this is the universe we see it is amazing to be living at a time where not only that we can see this image but we're on the threshold potentially of going back and observing the universe at it's very beginning the beginning of time it's exciting time thank you very much so we'll take time for a few questions it's hard to see you guys if there are any handle like to point out that here in this community every time somebody makes one over F noise measurement he does in fact perform a macroscopic quantum interference process he actually and we have and we have been doing that the community since 1925 since people learned to amplify signals and it is present for instance in a quartz crystal when the elementary act of dissipation happens and one phonon is lost from the main resonator mode then two copies are formed actually an infinity of copies are formed the one that's the crystal and the other one is everything is that obtained with bremsstrahlung associating the loss of that phone on and these two interfere and they give the observed one whereas people here in the room have demonstrated for first time I'm talking about the professors at franche-comté University I'm talking about for instance Fabrice Stahl I'm talking about Sabir professors from parties eight of them in a collaboration of five years have proven this standing on the shoulders Fred walls from NISD thanks very much I didn't really hear a question there but I'll take it as a comment but but um usually comments are longer than questions but but it look that's this the work that's being done in in many areas here and elsewhere on measuring macroscopic quantum mechanics is remarkable and as our precision increases we'll be able to do even more interesting measurements and so in normal sense was I arguing that this was the first example of the measurement of macroscopic quantum mechanics I was arguing that it may be surprising to people that the universe itself isn't is it and in fact everything we see in the universe is an explicit example of macroscopic quantum mechanics and so to the extent that we can measure in the laboratory we have greater confidence that our application to the universe works are there any other questions oh okay James compar oh so I've wondered about this for a long time the people talk about quantizing gravity and so that's quantizing the metric but the metric comes from the field equations and so the metric is defined by mass energy density all right because maybe that's maybe that's where I'm getting confused but so couldn't it be that the feet that the metric is classical but it takes on quantum appearance because it's being generated by quantum mechanical matter okay Einstein's equations equate the metric not really the metric but but something related to the metric curvature tensor to the energy momentum tensor matter okay and and what you're talking about is something called semi classical gravity where you have classical gravity which interacts with quantum material and and and we actually could do calculations in in that domain very well and we predict for examples that black hole radiates black holes radiate Hawking's prediction the black holes radiate its gravity is a classical phenomenon and and and interacts it with quantum matter but empty space devoid of matter and radiation in general relativity the metric the metric of flat space if gravity itself is quantized will fluctuate even in the absence of matter and radiation if the metric itself the metric is a quantum mechanical parameter it will fluctuate and so that is quantum gravity the problem is that when we try and turn general relativity into quantum theory we take pure gravity no matter no radiation just pure gravity they need a metric they we get infinities we can't do it we don't know how what the results are and that's the quantum theory we'd like to figure out and we develop string theory and other candidates we don't have we don't know what the answer is but the metric itself if if gravity is a quantum theory the metric itself will fluctuate independent of the presence of matter and radiation and what is exciting to me is that and I could have shown you in two slides but we've shown that the that if the metric does not fluctuate independent matter radiation then you will not generate gravitational waves during inflation and that's what I find very exciting because and and the reason well maybe I'll end with this but it's kind of interesting you probably heard a Freeman Dyson you know who if he is Freeman is a contrarian and lovely contrarian sometimes and he is he's written a beautiful paper that shows there's no way we can measure that grab on earth that gravity is a quantum theory to do that you'd have to measure individual gravitons if gravity is a quantum theory then then gravitational waves are composed of particles like electromagnetic waves are composed of photons gravitons but if you bend you could built look for a graviton detector by making a very sensitive version of LIGO sensitive to a single graviton just like you can detect individual photons he's shown that if you built a detector like that on earth it would collapse to form a black hole before you could make the observation you can never do it so he's argued maybe maybe gravity is a qualm theory and what I find very exciting is the universe as a graviton detector the universe allows us to do what you can't do causally and I find that remarkable I mean I actually came up with this when I was listening to Freeman talk about how impossible it was to measure it on earth so the if we can measure gravitational waves from inflation we will have a graviton detector and we'll know that gravity is a quantum theory and so that would be a very from my mind it very important because empirically we don't know we all think gravity's a quantum theory at least most of us do but we don't know for sure maybe that's a good way to ender I think so we're running a little bit late so let's thank Lawrence Krauss again please let's start the next sessions ten minutes late I think we have the flexibility to do that so thanks everybody and thank you again to Professor Cass [Applause]
