1 00:00:16,900 --> 00:00:20,160 Good evening, ladies and gentlemen, and welcome to the 13th RNC electorates. 2 00:00:20,170 --> 00:00:25,030 Tremendous to see so many people here. I don't think we're quite going to need the overflow, but it's getting a bit tight. 3 00:00:25,030 --> 00:00:28,659 People who are late will come in the front. So particular. 4 00:00:28,660 --> 00:00:31,660 Welcome to part school from Newbury I somewhere up there. 5 00:00:31,660 --> 00:00:37,090 I think I saw you. Thank you for coming. It's nice to have you with us. So it was nice to have school groups here. 6 00:00:37,720 --> 00:00:45,820 So it's my great pleasure and privilege tonight to introduce to you the 13th Quincy lecturer, Professor David Spergel. 7 00:00:46,450 --> 00:00:50,919 He's the Charles Young professor at the astronomy department in Princeton, 8 00:00:50,920 --> 00:00:56,110 but also holds a number of other appointments at the Institute of Advanced Study in Princeton. 9 00:00:56,110 --> 00:01:00,399 Two at the Institute for the Physics and Mathematics of the Universe. 10 00:01:00,400 --> 00:01:09,010 I think that's a wonderful name directed by a previous NC lecturer, Hitoshi Moriyama, and he's just taken on the role. 11 00:01:09,010 --> 00:01:14,740 He's the founding director of the Centre for Computational Astrophysics at the Flatiron Institute in New York. 12 00:01:14,950 --> 00:01:19,210 So we certainly wish, David, all the best with that new enterprise, which is very exciting. 13 00:01:19,420 --> 00:01:26,020 He's no stranger to Oxford. He first visited here, I think, as a graduate student working with James Binney for a little bit in 1983. 14 00:01:26,590 --> 00:01:30,610 His work on the cosmic microwave background has made him world famous. 15 00:01:31,000 --> 00:01:39,520 He has made a major contribution to our understanding of the standard cosmological model, 16 00:01:40,100 --> 00:01:44,530 an understanding about the age, the shape and composition of our universe. 17 00:01:44,860 --> 00:01:51,190 He also has held a number of influential posts in the United States leadership posts. 18 00:01:51,520 --> 00:01:59,979 So he is the chairman of the National Academy of Sciences Space Study Board, and he's the co-chairman leading a new mission called W First, 19 00:01:59,980 --> 00:02:07,270 which may maybe or maybe not [INAUDIBLE] say something about he has a string of honours, far too many for me to mention all of them. 20 00:02:07,270 --> 00:02:13,060 But most recently he was awarded the Dannie Heineman Prize of the American Astronomical Society. 21 00:02:13,390 --> 00:02:21,790 He he was a member of the W Map team that won the group a prize for their work on the cosmic microwave background that that satellite did. 22 00:02:22,360 --> 00:02:26,919 He won the Shaw Prize in 2010. He was made a member of the National Academy of Sciences. 23 00:02:26,920 --> 00:02:34,690 In 2008, he was a MacArthur Fellow and also won the Yes, Helen B won a prize. 24 00:02:34,690 --> 00:02:37,780 So he's a man of enormous distinction. 25 00:02:38,110 --> 00:02:44,410 He has published a lot of papers, 280 papers and supervised 25 research students. 26 00:02:44,740 --> 00:02:54,459 So it is my great pleasure to introduce David Spergel to give the 13th Tinsley Lecture a simple but strange universe. 27 00:02:54,460 --> 00:03:05,180 David. Thanks. 28 00:03:05,190 --> 00:03:07,110 It's a pleasure to be back in Oxford. 29 00:03:07,950 --> 00:03:19,180 And in many ways, the theme of this lecture is the remarkable progress we've made since I was a graduate student here in 83. 30 00:03:19,230 --> 00:03:25,110 In understanding our universe, understanding its structure and origin and properties. 31 00:03:25,110 --> 00:03:28,560 And the bottom line of the talk is really the title. 32 00:03:29,770 --> 00:03:34,240 Our universe is remarkably simple. And remarkably strange. 33 00:03:35,650 --> 00:03:40,930 Much simpler than I thought it would have been back in 1983 when I was a student here. 34 00:03:42,010 --> 00:03:45,560 But also much stranger. And what do I mean by that? 35 00:03:46,520 --> 00:03:54,290 We can take a simple model, one that I'll talk about through word torque, which we call the Lambda CBR model. 36 00:03:55,430 --> 00:04:02,270 That model has really five basic parameters the age of the universe, the density of atoms, 37 00:04:02,600 --> 00:04:07,760 the density of matter, how lumpy the universe is, and how that lumpiness varies with scale. 38 00:04:08,360 --> 00:04:11,480 So with those five numbers I could fit. 39 00:04:12,790 --> 00:04:19,600 Hundreds of millions of pieces of data I can fit are measurements of the microwave background, which will be the theme of much of my talk. 40 00:04:20,260 --> 00:04:26,649 I will sit observations of a large scale structure from things like the Sloan Digital Sky Survey, Supernova measurements. 41 00:04:26,650 --> 00:04:27,820 Many of the observations, 42 00:04:28,180 --> 00:04:38,200 the expansion of the universe from the Hubble telescope all the ways we have of measuring the universe are all fit by these same basic five numbers. 43 00:04:39,100 --> 00:04:42,930 So as a scientist, that in some ways can't be simpler. 44 00:04:42,940 --> 00:04:47,090 I know all the properties of millions of galaxies determined by five numbers. 45 00:04:47,110 --> 00:04:51,810 It's a remarkably simple universe. It's also really strange. 46 00:04:52,790 --> 00:04:59,630 Adam's. The stuff that makes up us in this model makes up only 5% of the universe. 47 00:05:01,250 --> 00:05:08,750 There's six times as much stuff in the form of what we call it, five times as much stuff and what we call a dark matter. 48 00:05:09,620 --> 00:05:17,449 We don't know what the dark matter is. It's stuff that clusters gravitationally on small scales and cluster. 49 00:05:17,450 --> 00:05:22,370 It feels the effects of gravity. It could be some new subatomic particle. 50 00:05:22,370 --> 00:05:25,160 That's our current best guess, but we truly don't know. 51 00:05:27,030 --> 00:05:33,420 And even more strangely, there seems to be energy associated with empty space, something we call dark energy. 52 00:05:34,350 --> 00:05:41,310 You know, our best guess on what that is is something we call vacuum energy. 53 00:05:41,700 --> 00:05:46,110 Energy associated with empty space. But we don't know what makes it. 54 00:05:46,200 --> 00:05:49,829 And something I'll touch on in my talk. 55 00:05:49,830 --> 00:05:54,420 But really what I think is driving a lot of what we're planning to do in cosmology 56 00:05:54,660 --> 00:05:59,160 in the next several years or ten years is understanding what the dark matter is, 57 00:05:59,160 --> 00:06:06,210 understanding the nature of the dark energy, the origin of cosmic acceleration, and. 58 00:06:07,950 --> 00:06:09,740 You know, understanding the universe, 59 00:06:09,830 --> 00:06:16,920 the origin of the universe's early acceleration that gave rise to the structure we see understanding what we call inflation. 60 00:06:19,290 --> 00:06:22,560 As an American, a couple of days after the election. 61 00:06:23,040 --> 00:06:28,650 I can't resist talking about one idea for cosmic acceleration. 62 00:06:29,160 --> 00:06:35,880 It's an idea called the big riff. So the idea that the universe is not just accelerating as it is now, 63 00:06:36,150 --> 00:06:45,959 but this acceleration will go faster and faster with time and eventually run away and tear up the universe completely. 64 00:06:45,960 --> 00:06:50,810 Tear apart every atom. This possibility is consistent with the data. 65 00:06:51,590 --> 00:06:59,270 And in fact, if you look at some of the data, we have even favours it slightly over our standard model. 66 00:07:00,230 --> 00:07:06,830 So I was interviewed by New Scientist five days ago, and I don't know if they'll go with this quote, but I think they may. 67 00:07:07,190 --> 00:07:12,320 They asked me what I thought the big rep. I said I viewed it as something like the Trump presidency. 68 00:07:12,680 --> 00:07:15,740 Terrifying to contemplate, but I didn't think very likely. 69 00:07:22,800 --> 00:07:28,260 So in order to get into the story, 70 00:07:29,220 --> 00:07:38,100 I want to begin by introducing first special relativity and then general relativity and then use that to construct our basic model. 71 00:07:39,290 --> 00:07:46,130 One of the key things to think about when we're thinking about astronomical observations is light travels at a finite speed. 72 00:07:47,060 --> 00:07:53,330 It takes light about a trillionth of a second to get from the front row to me. 73 00:07:53,840 --> 00:08:00,440 So people in the front row see me as I was a 10th of a second ago in the second row, two trillions and so on. 74 00:08:01,280 --> 00:08:07,790 I don't change that much on that time scale. So you don't see something very different from the back as we do with the front. 75 00:08:08,510 --> 00:08:12,230 So you see, as you look out in space, you look back in time. 76 00:08:13,350 --> 00:08:19,140 When we look at a nearby store, we see it as it was five or ten years ago. 77 00:08:19,620 --> 00:08:23,310 The further out you go in space, the further back you look in time. 78 00:08:24,030 --> 00:08:27,360 We see the Andromeda Galaxy as it was a million years ago. 79 00:08:28,050 --> 00:08:35,010 And if we if there's life on the Andromeda Galaxy that has a telescope looking at us, 80 00:08:35,550 --> 00:08:39,600 it sees the Earth as it was a million years ago because it takes light time travel. 81 00:08:41,270 --> 00:08:44,809 So the further out we go in space, the further back we go in time. 82 00:08:44,810 --> 00:08:53,540 We now have observations with the Hubble telescope that look out for what are 13 billion years, see galaxies as they were 13 billion years ago. 83 00:08:54,290 --> 00:08:59,599 And as we look out at the microwave background, the leftover heat from the Big Bang, 84 00:08:59,600 --> 00:09:05,690 one of the themes of this lecture, we'll see the universe as it was 13.7 billion years ago. 85 00:09:06,710 --> 00:09:11,360 So for us, the key idea of special relativity is light travels at a finite speed. 86 00:09:12,200 --> 00:09:15,320 All right, everyone mastered special relativity. Good. 87 00:09:15,980 --> 00:09:22,220 All right. Now we're going to move on to general relativity. General relativity. 88 00:09:23,210 --> 00:09:32,330 As one of my early mentors, Johnny Wheeler taught consists of two ideas that matter tell space how to curve. 89 00:09:33,170 --> 00:09:37,280 And the curvature of space tells matter and light how to move. 90 00:09:38,300 --> 00:09:50,360 So the picture to have is shown here. This is the sun curving space around it and light from a distance start beamed or even a nearby 91 00:09:50,360 --> 00:09:56,990 star lines up behind the sun being deflected as light from the star moves around from the sun. 92 00:09:58,010 --> 00:10:01,280 So as you can see, if you are an observer on earth, 93 00:10:02,000 --> 00:10:09,500 instead of seeing the star or having the star blocked by the sun, you'll see the star at a different position. 94 00:10:10,560 --> 00:10:17,250 And this was the shift in position was one of the great predictions of general relativity 95 00:10:18,090 --> 00:10:24,360 and one that was tested by Eddington and others in the Great Eclipse expedition. 96 00:10:25,330 --> 00:10:35,600 And. I recently learned with the 100th anniversary of Einstein's theory, a more complete story of what almost happened. 97 00:10:36,980 --> 00:10:40,910 So Einstein's first version of the theory was not complete. 98 00:10:41,660 --> 00:10:45,980 And in his first version, his first calculation of the defection of starlight. 99 00:10:46,730 --> 00:10:50,120 His answer he got was off the right answer by a factor to. 100 00:10:51,360 --> 00:10:59,430 He only later completed the theory in late 1915 and came up with the full answer. 101 00:11:00,690 --> 00:11:07,710 There was an earlier eclipse expedition hat which would have tested his earlier wrong answer. 102 00:11:08,580 --> 00:11:14,550 It got cloudy. So what could have happened is Einstein made one prediction. 103 00:11:15,180 --> 00:11:23,490 The observations were off by a factor of two. And when he came up with the new theory that matched that, we wouldn't have taken it so seriously. 104 00:11:24,550 --> 00:11:30,850 But fortunately it was cloudy. His results were published with the correct number. 105 00:11:31,360 --> 00:11:36,370 And in 1919, here in the pages, this is the New York Times. 106 00:11:37,750 --> 00:11:43,330 Lt's all askew with the heavens. Men of science in those days, mostly men. 107 00:11:43,600 --> 00:11:48,250 Now we hope more men and women of science, more or less a dog lover. 108 00:11:48,260 --> 00:11:51,460 The results of the and Einstein's theory triumphed. 109 00:11:52,210 --> 00:11:59,320 And I like the stars. Not where they seemed or were calculated to be, but nobody need worry. 110 00:12:00,700 --> 00:12:03,820 And in fact, it's true that they weren't where they seemed. 111 00:12:04,420 --> 00:12:10,000 But the important thing is where they were, where Einstein calculated them to be, that this effect is happening. 112 00:12:11,590 --> 00:12:18,340 And based on this and if I have time at the end of my talk, I'll say a bit about the recent local results. 113 00:12:18,850 --> 00:12:26,290 If all reinforces the idea that general relativity is the valid theory to describe the universe on its larger scales. 114 00:12:27,430 --> 00:12:36,850 And general relativity makes this very surprising prediction that the universe is expanding. 115 00:12:37,420 --> 00:12:41,170 It says that space and time are not absolute. 116 00:12:41,740 --> 00:12:46,750 But we really should only talk about the properties of space and time in relative terms, 117 00:12:46,960 --> 00:12:51,640 in terms of the distance between you and me, the distances between objects. 118 00:12:52,000 --> 00:12:57,550 And if I can tell you about distances, I can tell you about geometry and structure of space. 119 00:12:58,660 --> 00:13:03,460 I flew last night from New York to London. 120 00:13:03,880 --> 00:13:10,880 We flew. Over the pole. If I continue on in the next few days, I will not do this trip. 121 00:13:11,180 --> 00:13:19,880 You can fly New York to London, London to Tokyo, Tokyo to New York just by telling you those distances and travel times. 122 00:13:20,330 --> 00:13:23,660 You can figure out that the earth is not flat, but curved. 123 00:13:25,080 --> 00:13:30,000 And that's basically what we do with general relativity in cosmology. 124 00:13:30,450 --> 00:13:36,150 By measuring distances to objects and travel time, we infer the structure of space. 125 00:13:37,590 --> 00:13:47,520 When we talk about the universe expanding. It's not that it's expanding into something, but rather the distances between objects are growing. 126 00:13:48,210 --> 00:13:52,590 The distances between us and a distant galaxy keeps growing. 127 00:13:52,590 --> 00:13:59,370 With time, the whole universe is stretching. So you should have this picture of the universe getting ever bigger. 128 00:14:00,640 --> 00:14:02,110 As expansion goes forward. 129 00:14:04,240 --> 00:14:11,200 The answer I like to give to the question of what the universe is expanding into is to say the universe is expanding into the future. 130 00:14:12,100 --> 00:14:19,330 That I think of the universe as a sphere. I suppressed one dimension and it's a balloon that's being blown ever bigger. 131 00:14:20,170 --> 00:14:24,880 And as just born bigger, the distance between dots on that balloon get larger and larger. 132 00:14:26,380 --> 00:14:34,000 Now let's run that picture backwards. Our universe today is two dimensional version is on a surface of a big balloon. 133 00:14:34,780 --> 00:14:38,500 So we go back in time. The universe gets denser and denser. 134 00:14:39,190 --> 00:14:45,790 Eventually we reach the initial singularity, the star of the Big Bang, where the balloon collapses to a point. 135 00:14:46,540 --> 00:14:51,009 Now you notice there's no particular place of the sphere. 136 00:14:51,010 --> 00:14:52,510 That's the centre of the explosion. 137 00:14:53,410 --> 00:15:04,540 The Big Bang happens everywhere and the universe is expanding from that point in time, 13.8 billion years ago to the universe we see today. 138 00:15:05,760 --> 00:15:12,860 I think this is conceptually the hardest thing for us to think through, because it's most different from our ordinary notion of space and time. 139 00:15:16,540 --> 00:15:28,119 One of the surprises of the last 20 years in this was we had evidence of this before the supernova observations in the late middle 1990s, 140 00:15:28,120 --> 00:15:32,320 but was really strengthened in the definitive observations came from those. 141 00:15:32,860 --> 00:15:38,260 We see that the acceleration of the expansion of the universe was behaving in a very strange way. 142 00:15:39,570 --> 00:15:46,200 What I was taught we expected to happen was gravity should slow things down. 143 00:15:47,040 --> 00:15:51,960 If I toss didn't want to move, my room came up in the air. 144 00:15:52,380 --> 00:16:00,420 Gravity makes it come down. It slows it. Even if I was incredibly strong and able to toss the so fast it would go into orbit. 145 00:16:00,990 --> 00:16:08,170 Gravity still has the same effect of slowing its departure, and we thought that's what gravity would do to the expansion of the universe. 146 00:16:08,580 --> 00:16:12,510 The universe would be expanding, but gravity would slow its expansion. 147 00:16:12,930 --> 00:16:20,040 So the expansion rate of the universe, the size at which the rate at which that balloon is blowing up, would decelerate. 148 00:16:20,220 --> 00:16:28,590 It would slow. And the strange discovery is that our universe is accelerating, that its expansion rates growing with time. 149 00:16:30,080 --> 00:16:35,090 All right. Now let's go to our basic picture. That we have of the universe's history. 150 00:16:35,540 --> 00:16:43,400 We talked about the universe expanding with time, being denser in the past, in addition to being denser in the past. 151 00:16:43,640 --> 00:16:49,790 It was much hotter in the past. The universe is filled with what we call the microwave background radiation. 152 00:16:50,330 --> 00:17:00,920 This is the leftover heat from the big bang. For those of you older members of the audience who remember watching television when it didn't 153 00:17:00,920 --> 00:17:07,280 come through a cable but came from an antenna and you switched your television between stations, 154 00:17:07,850 --> 00:17:12,740 about 2% of the static that you saw was the microwave background. 155 00:17:13,650 --> 00:17:20,520 So those of you old enough to remember some static on your television, you've seen the microwave background with your eyes. 156 00:17:21,950 --> 00:17:28,820 And that's left overheats everywhere. Today, it's a temperature of about three degrees above absolute zero. 157 00:17:29,720 --> 00:17:35,430 But as you go back in time, it gets hotter and hotter. When the universe was half its present size. 158 00:17:35,450 --> 00:17:44,450 So the distances between galaxies down by a factor to the temperature was six degrees, a thousandth of present size, 3000 degrees. 159 00:17:44,930 --> 00:17:48,860 And the further back we go in time, the hotter and hotter the universe gets. 160 00:17:50,340 --> 00:17:59,100 Much of what we'll talk about today involves observations of what the universe looked like 13.7 billion years ago when 161 00:17:59,100 --> 00:18:05,880 it was roughly a thousand its present size and the temperature of the microwave background was about 3000 degrees. 162 00:18:06,510 --> 00:18:18,210 The reason we're observing that time is before that time the universe was ionised, and after that time, electrons and protons combined become neutral. 163 00:18:19,530 --> 00:18:29,390 So we'll turn to the microwave background. The microwave background was first detected by Penzias and Wilson in the sixties, in the 1990s. 164 00:18:30,210 --> 00:18:41,550 A star of the nineties, the Kobe experiment. First, not only so, the microwave background was remarkably uniform and thermal on its largest scales, 165 00:18:41,760 --> 00:18:50,280 but was able to pick up tiny fluctuations at a part one part in 100,000 in the microwave background temperature. 166 00:18:51,000 --> 00:18:54,030 And they won the Nobel Prize for this first discovery. 167 00:18:54,510 --> 00:19:04,950 And this gives us a picture of what I think of as the universe baby picture what the universe looked like when it was only 380,000 years old. 168 00:19:06,920 --> 00:19:16,700 Much of my own work in the past 20 years has involved working with data first from the Wilkinson microwave anisotropy probe, 169 00:19:17,030 --> 00:19:22,230 a mission that NASA launched to make a more precise version of the microwave background. 170 00:19:22,250 --> 00:19:31,790 This is an experiment that we named after our colleague Dave Wilkinson, who helped start the experiment, passed away with cancer. 171 00:19:32,390 --> 00:19:37,670 Soon after, we got the data. This experiment was launched deep out into space. 172 00:19:38,150 --> 00:19:43,760 You want to get away from the Earth's radiation, get away into a benign as environment as possible, 173 00:19:44,360 --> 00:19:50,570 out to four times the distance of the moon, to what's orbit around what's called the second Lagrange point. 174 00:19:50,990 --> 00:19:56,870 This is a point that is so far from the earth that instead of orbiting the Earth, 175 00:19:57,140 --> 00:20:05,750 the satellite follows the Earth as it moves around the sun, always staying with the Earth, the moon in the sun behind it. 176 00:20:06,470 --> 00:20:14,480 This is a really optimal place to put a telescope if you want to look out in space so that this is where the Planck satellite is. 177 00:20:14,810 --> 00:20:17,990 This is where the James Webb Space Telescope is going to go. 178 00:20:18,380 --> 00:20:21,950 It's a nice place to live if you a telescope. 179 00:20:23,640 --> 00:20:28,230 And the goal was to look out this time at which the universe was first ionised. 180 00:20:29,340 --> 00:20:35,280 Our first show, we actually observe in terms of what we see in the sky and then talk about what this means. 181 00:20:35,880 --> 00:20:43,230 So we observe the sky at different frequencies. This is observations, and we're showing the whole sky around us as an ellipse. 182 00:20:43,560 --> 00:20:48,360 You can see this is just like taking a globe and projecting it onto the sky. 183 00:20:48,600 --> 00:20:52,760 So you're seeing at the top of the picture is the North Galactic Pole. 184 00:20:52,770 --> 00:20:57,930 The bottom of the pictures, the South Galactic Pole and those bright red region is our galaxy. 185 00:20:58,470 --> 00:21:02,370 And the striking thing you see in this picture is the bright red stuff. 186 00:21:03,430 --> 00:21:06,550 That's our galaxy. That's not stuff coming from the universe. 187 00:21:07,120 --> 00:21:14,470 Lots of interesting things about our own galaxy that one can learn from this data, but that's not the focus of this talk. 188 00:21:14,680 --> 00:21:21,430 We're going to look at the stuff either above and below this bright red region and that stuff coming from outside our galaxy, 189 00:21:21,430 --> 00:21:32,200 from the microwave background. As we go up in frequency, the galactic emission from relativistic electrons, synchrotron emission orbs gets dimmer. 190 00:21:32,500 --> 00:21:37,569 It's easier to see the cosmological signal that's been travelling to us for 13.7 191 00:21:37,570 --> 00:21:44,510 billion years and eventually we can combine this and get a very clean map of the sky. 192 00:21:45,070 --> 00:21:55,420 And until the Planck's measurements in 2013, which I'll talk about next, this represented our best map of the sky. 193 00:21:56,260 --> 00:21:58,540 One of the features I like to show in this, 194 00:21:59,080 --> 00:22:09,220 and I think this is important for people looking at data to be careful about patterns is the letters H which appear in the map. 195 00:22:10,360 --> 00:22:16,270 And I actually first saw this in the map back in. 196 00:22:17,890 --> 00:22:26,800 23 after we released the data and I went to a talk at a conference where we showed our results and there was a talk by Stephen Hawking. 197 00:22:27,730 --> 00:22:33,310 And I was sitting next to my colleague Lyman Page, who designed a lot of the experiment. 198 00:22:33,730 --> 00:22:38,020 And Lyman pointed out, I said, Hey, students put in some of the data as a joke. 199 00:22:39,220 --> 00:22:44,720 And we looked. Our data. And it was there. 200 00:22:46,220 --> 00:22:49,680 Now. This can have a number of meanings. 201 00:22:52,020 --> 00:22:56,249 This is in the Michael Scott I used to say, because this is back at 23, 202 00:22:56,250 --> 00:23:01,890 that these were actually Saddam Hussein's initials and bad on the wife was God. 203 00:23:02,520 --> 00:23:10,940 And then I sometimes argued when the Planck data would come out and we could see things with higher precision, 204 00:23:10,980 --> 00:23:20,340 we'd see the two missing letters about the cosmological message that was left when this universe was made. 205 00:23:20,670 --> 00:23:26,700 But I think more likely, this tells us something actually about evolution. 206 00:23:27,960 --> 00:23:31,290 We evolved to find patterns and data. 207 00:23:32,600 --> 00:23:37,640 And we find patterns and data, whether they're there or not. 208 00:23:38,120 --> 00:23:48,680 We're selected for finding patterns. And the analogy I think of is you see some rustling in the grass and it looks a little bit like a tiger. 209 00:23:49,130 --> 00:23:53,870 Do you jump or not? There were some humans who are very calm. 210 00:23:55,130 --> 00:23:58,820 They see it and they say, you know, nine times out of ten, that's not a tiger. 211 00:23:59,090 --> 00:24:07,500 They wouldn't run. Our ancestors there did jumping once they ran every time. 212 00:24:09,300 --> 00:24:16,090 And the one time in tennis was a tiger. They didn't get. That's why they're our ancestors. 213 00:24:16,990 --> 00:24:22,180 So we kind of selected for for erring on the side of seeing patterns when they're not there. 214 00:24:23,320 --> 00:24:26,560 That's, I think, important to keep in mind when we look at any data. 215 00:24:27,010 --> 00:24:30,750 That's why we do statistics, because we have to be careful for that. 216 00:24:32,640 --> 00:24:34,890 All right. So how do we do statistics on this data? 217 00:24:35,580 --> 00:24:42,210 What we like to do is measure the lumpiness as a function of scale, measure the temperature on different scales. 218 00:24:42,510 --> 00:24:51,959 Basically, what we do to go back to this picture is we throw down circles and we measure how lumpy the universe is. 219 00:24:51,960 --> 00:24:56,640 What's the average fluctuation as a function of the area of that circle? 220 00:24:58,190 --> 00:25:02,280 And. Measured as a function of scale, angular scale. 221 00:25:03,860 --> 00:25:08,930 For the physicists in the audience, we're taking spherical harmonics and looking at a power spectrum. 222 00:25:09,200 --> 00:25:15,740 And this is a power spectrum. For the non physicists, it's how what are the temperature fluctuations versus angle? 223 00:25:17,240 --> 00:25:25,700 And what you see here and this is the data of as of about five years ago will show some more recent things going forward is. 224 00:25:27,080 --> 00:25:35,140 Our data. And our best foot model. And you see that the model does a beautiful job of fitting the data. 225 00:25:35,530 --> 00:25:38,050 It captures the statistical properties of what we see. 226 00:25:39,490 --> 00:25:48,460 Not only can we compare that to our observations of the microwave sky, we could take that model fit it to. 227 00:25:49,610 --> 00:25:53,960 The microwave data ran a simulation of large scale structure. 228 00:25:54,590 --> 00:26:05,090 Look how clustering forms and compare the pattern of galaxies that are predicted to what's seen in surveys like the Sloan Digital Sky Survey. 229 00:26:05,630 --> 00:26:10,370 See what the model predicts for the universe today. And actually to skip forward. 230 00:26:10,370 --> 00:26:15,560 This is one way of looking at the data, again, the lumpiness versus scale. 231 00:26:16,220 --> 00:26:22,610 This is a plot from Rene Lozzi. This is from her Ph.D. thesis work at Oxford, this plot. 232 00:26:23,330 --> 00:26:27,950 And this shows the fluctuations versus mass scale. 233 00:26:28,730 --> 00:26:34,100 The read points in this plot come from the microwave background observations I've talked about. 234 00:26:34,820 --> 00:26:41,420 They measure how lumpy the universe was. What, 13.7 billion years ago? 235 00:26:41,960 --> 00:26:46,040 The blue points are coming from the Sloan Digital Sky Survey. 236 00:26:46,550 --> 00:26:54,050 They're measuring how lumpy the universe is today, the the blue or the cyan points right here in the middle. 237 00:26:55,540 --> 00:26:56,950 Read points that beautifully. 238 00:26:57,780 --> 00:27:08,820 Our ideas about our model does a beautiful job about protecting the data over a factor of 10 to 13 in scale and ten to the eight in time. 239 00:27:09,690 --> 00:27:11,820 That's remarkable for a model with five numbers. 240 00:27:15,820 --> 00:27:21,340 Once you have a model like this that fits the data, you want to ask what happens when the data improves? 241 00:27:22,380 --> 00:27:29,010 We now that we've based one way to think about this is you basically can fix the parameters with just the W map data. 242 00:27:30,590 --> 00:27:34,909 Measured things with data like the Sloan survey. Future surveys, 243 00:27:34,910 --> 00:27:40,069 which we'll talk about later like the large lr sas t get higher precision 244 00:27:40,070 --> 00:27:44,060 measurement for Planck and ask us the data improves as the models still work. 245 00:27:45,020 --> 00:27:52,669 The Planck satellite was a European space agency led mission that mapped the sky and high 246 00:27:52,670 --> 00:27:58,580 resolution and higher sensitivity of the W map so the next generation and studying this. 247 00:27:59,600 --> 00:28:05,350 And. It reached with higher precision, remarkably similar conclusions. 248 00:28:05,360 --> 00:28:09,439 And this shows first just a comparison of the two datasets. 249 00:28:09,440 --> 00:28:14,060 These are the two maps of the sky, and reassuringly they see the same thing. 250 00:28:17,140 --> 00:28:28,090 We can compare this more quantitatively by measuring the lumpiness versus scale, the power spectrum of the different experiments. 251 00:28:28,090 --> 00:28:35,379 And you can see here first in black that cross what you get from cross correlating the W map and 252 00:28:35,380 --> 00:28:42,820 Planck data and in read the order correlations of the Planck data and they agree incredibly well. 253 00:28:43,660 --> 00:28:49,450 And you can see the Planck data is higher precision so that the red lines is 254 00:28:49,450 --> 00:28:56,739 certainly consistent with the black data at the scales at which the noise is low. 255 00:28:56,740 --> 00:29:00,730 In both experiments, they agree almost identically. Point by point. 256 00:29:02,310 --> 00:29:10,590 And at the smaller scales here. Well, they they agree overall but Planck has high precision. 257 00:29:12,810 --> 00:29:17,070 We can also check our data by comparing the Planck measurements with ground based measurements. 258 00:29:17,070 --> 00:29:20,760 So from the ground we can zoom in on small patches of high resolution. 259 00:29:21,790 --> 00:29:26,110 And this shows two sets of maps, one made by the Planck experiment, 260 00:29:26,680 --> 00:29:31,870 one made by an experiment that we're part of at Princeton called the Atacama Cosmology Telescope. 261 00:29:32,500 --> 00:29:36,430 And they have consistent results on these scales. 262 00:29:38,200 --> 00:29:41,830 Here's another way of seeing the state of play. 263 00:29:42,670 --> 00:29:51,370 This is that same model that we picked to the W map data I showed the W map data sort of cuts off around here. 264 00:29:52,630 --> 00:29:57,100 We could take ground based data that's shown in the red and the green. 265 00:29:58,220 --> 00:30:02,640 And. Compare it to the model. It fits beautifully. 266 00:30:03,120 --> 00:30:10,319 The Planck data fits beautifully. We have a very consistent story where the different experiments basically see the same 267 00:30:10,320 --> 00:30:14,670 thing with the more recent experiments achieving higher precision and resolution. 268 00:30:18,010 --> 00:30:26,170 But we can look at this basic pattern of those sound waves and a bunch of different ways and test things in a bunch of different ways we could. 269 00:30:26,410 --> 00:30:30,880 You've seen the pattern in temperature, the two points below. 270 00:30:31,630 --> 00:30:38,110 So what we get when we measure the temperature and polarisation data and the polarisation and polarisation data. 271 00:30:38,590 --> 00:30:42,819 So here we fit our best model to the Planck data. It's done by the Planck team. 272 00:30:42,820 --> 00:30:48,280 We now see some showing here and you can see that red curve. 273 00:30:49,400 --> 00:30:55,160 Which was not fit to the temperature of polarisation data. The red curve is completely independent of the data. 274 00:30:56,060 --> 00:31:00,080 It's a fit from other data and the blue points. 275 00:31:00,080 --> 00:31:04,850 The data. It's just remarkable how successful the model is. 276 00:31:05,390 --> 00:31:09,470 So the two lower parts are based on large scale structure observations. 277 00:31:10,720 --> 00:31:19,090 These same sound waves that will show a different representation of the data shortly that generates structure in the microwave sky. 278 00:31:19,330 --> 00:31:24,460 The sound waves in the early universe also produced a structure in the distribution of galaxies. 279 00:31:25,690 --> 00:31:31,440 And the plot above comes from work from the Sloan Digital Sky Survey. 280 00:31:31,480 --> 00:31:35,050 Some recent measurements and. 281 00:31:37,360 --> 00:31:43,600 This is structural in the galaxies. We see the same sound wave that we see in the early universe. 282 00:31:44,020 --> 00:31:48,829 We can see in the microwave sky. It all, it'll galaxy distribution. 283 00:31:48,830 --> 00:31:59,280 It's all consistent. And it's a wonderful confirmation of this basic model that goes back to work by Sonja Films, although dovish in the 1970s. 284 00:31:59,490 --> 00:32:05,729 And here's a quote from some named Enzo Darvish saying that a detailed investigation of the spectrum 285 00:32:05,730 --> 00:32:10,440 of fluctuations may in principle lead to an understanding of the initial density perturbations. 286 00:32:10,860 --> 00:32:18,000 Since the distinctive periodic dependence of the spectral density of perturbations on wavelength is peculiar to ET about it perturbations. 287 00:32:19,020 --> 00:32:25,600 We see just what they predicted. I actually like to show the data in this way. 288 00:32:26,500 --> 00:32:29,950 This is taking the temperature data taken. 289 00:32:30,980 --> 00:32:37,350 On the left on this side, cold spots on this side of the map, hot spots. 290 00:32:37,350 --> 00:32:40,880 So I go to the map. You saw I take every cold spot. 291 00:32:41,210 --> 00:32:45,440 I plot the data around a cold spot. I stack up. 292 00:32:46,680 --> 00:32:49,710 Hundreds of thousands, 100,000 cold spots in the map. 293 00:32:50,190 --> 00:32:58,230 I stack up 100,000 hotspots. You could see around every cold spot is a hot red. 294 00:32:59,800 --> 00:33:06,040 Around every hot spot is a cauldron. The bottom plot is. 295 00:33:07,160 --> 00:33:10,340 The data itself. The top part was the theory. 296 00:33:11,480 --> 00:33:17,600 There's other plots for the pattern and polarisation. What we're seeing here are sound waves in the early universe. 297 00:33:18,170 --> 00:33:27,320 What's going on physically is we start out with the regions that have more dark matter, more electrons, more protons, more pressure. 298 00:33:28,360 --> 00:33:34,870 If you have higher pressure? Well, if you create a region of high pressure, it produces a sound with. 299 00:33:35,940 --> 00:33:43,249 That sound way propagates up. So that's the Soundwave propagating out in the electrons and protons and photons. 300 00:33:43,250 --> 00:33:47,090 They're all coupled. The dark matter is not coupled. 301 00:33:47,600 --> 00:33:52,370 It doesn't interact with things. So the dark matter stays in one place. 302 00:33:52,820 --> 00:33:54,140 The sound wave moves out. 303 00:33:54,710 --> 00:34:05,270 Where you have excess dark matter, there's more gravity that produces a cold spot where you have excess variance of photons that produces a hotspot. 304 00:34:05,900 --> 00:34:10,490 The model predicts there should be dark hot spots, hot rings around every dark. 305 00:34:10,490 --> 00:34:20,450 That's dark spot. That's exactly what we said. And all those ripples we saw are just different math ways of representing this pattern we see. 306 00:34:21,470 --> 00:34:25,100 In the sky. So we're seeing just what the model predicts. 307 00:34:25,910 --> 00:34:30,920 And I've mentioned already we see this in the pattern of galaxy distributions in the Sloan survey. 308 00:34:31,670 --> 00:34:39,690 And here's another representation of it. We actually make a lot of use of these ripples. 309 00:34:40,140 --> 00:34:47,820 So now that we've got these sound waves where we can use the first the map and now the Planck data to measure the size of these rings. 310 00:34:48,830 --> 00:34:53,000 That's now a cosmic ruler that we call baryon acoustic oscillations. 311 00:34:53,600 --> 00:34:59,059 And I can use that ruler to measure the distance to different objects. 312 00:34:59,060 --> 00:35:02,450 So I take galaxies in a survey like the Sloan survey. 313 00:35:03,790 --> 00:35:07,870 And I can measure the distance to them as a function of redshift. 314 00:35:08,620 --> 00:35:18,070 And this plot shows the scale of this ring in excess galaxy count that we see as a function of redshift. 315 00:35:18,580 --> 00:35:23,740 And it compares it to our theoretical model, this five parameter model that I talk about. 316 00:35:24,630 --> 00:35:31,160 And you can see the model does a beautiful job of fitting the data. So we really have this consistent cosmology. 317 00:35:31,160 --> 00:35:39,130 And this was true back in 2003 when we had the W map data initially came out, 318 00:35:39,140 --> 00:35:44,210 but over the last 13 years, the data has improved enormously and the pieces all still fit. 319 00:35:46,380 --> 00:35:50,990 So. Are we done? I don't think so. 320 00:35:52,180 --> 00:35:56,890 I would argue that in a sense we've only just begun because we have this model. 321 00:35:57,430 --> 00:36:03,060 And this model requires a lot of new physics that requires dark matter. 322 00:36:03,070 --> 00:36:06,639 We don't know what it is, requires dark energy. We don't know what it is. 323 00:36:06,640 --> 00:36:13,240 Another side piece of open physics is we don't know why there's more math bearing on why there are more protons and antiprotons. 324 00:36:13,570 --> 00:36:18,520 We don't know why the universe doesn't have equal amounts of ordinary matter and anti-matter. 325 00:36:19,510 --> 00:36:25,770 The capacity of Genesis. Nor do we really understand what generates the fluctuations. 326 00:36:25,770 --> 00:36:32,950 We have this idea called inflation that I'll say it a little bit about. But we're really not sure where that comes from. 327 00:36:32,960 --> 00:36:42,650 We'd like to answer these questions. And for me, as a cosmologist, I think what will be driving the field over the next 20 years or so, 328 00:36:43,100 --> 00:36:46,759 looking ahead, is answering these questions What is the dark matter? 329 00:36:46,760 --> 00:36:53,240 What is the dark energy? What is the physics of inflation? And that will drive both theory and experiment. 330 00:36:54,810 --> 00:36:56,250 So a little bit about inflation. 331 00:36:57,330 --> 00:37:06,270 In our standard cosmology, in this expanding universe model, what we would expect is that the size of the universe grows with time. 332 00:37:06,270 --> 00:37:09,330 And this is a plot the size of the universe versus time. 333 00:37:10,820 --> 00:37:16,520 The key idea in the inflationary universe model is that very early in the universe's 334 00:37:16,520 --> 00:37:21,890 history it underwent a period of very rapid expansion that we call inflation, 335 00:37:22,250 --> 00:37:31,040 and this period of accelerated expansion would produce both fluctuations in density and fluctuations that we call gravitational waves. 336 00:37:32,080 --> 00:37:37,150 And what's. You know, and so inflation makes these key predictions. 337 00:37:38,220 --> 00:37:42,120 We want to test these predictions. And again, the microwave background data is very useful. 338 00:37:42,600 --> 00:37:49,230 It lets us show, as we saw already, that the fluctuations are full of these 80 biotic fluctuations, their sound waves. 339 00:37:49,950 --> 00:37:58,270 We can also look at the statistics of the fluctuations, and this shows the distribution of the number of hot and cold spots versus scale. 340 00:37:58,800 --> 00:38:04,260 And they make nice Gaussians. They're nice bell curves that really perfect all curves. 341 00:38:04,800 --> 00:38:10,620 The number equal number of hot and cold spots and their statistical properties are exactly fit by Gaussian. 342 00:38:11,190 --> 00:38:15,600 So that's just a beautiful confirmation of the predictions that the fluctuations are Gaussian. 343 00:38:16,110 --> 00:38:23,640 They're close to scale, invariant. The amplitude is the same on all scales and the fluctuations that we call super horizon. 344 00:38:24,210 --> 00:38:28,080 I could look at two points in the sky that are widely separate. 345 00:38:28,080 --> 00:38:31,530 In fact, so widely separated that in our. 346 00:38:32,820 --> 00:38:36,390 Standard picture where we didn't have this early inflating stage. 347 00:38:36,780 --> 00:38:40,080 Those two points in the sky have never had the chance to communicate. 348 00:38:41,240 --> 00:38:45,500 So if they've never had a chance to communicate, how do they know to have correlated fluctuations? 349 00:38:46,390 --> 00:38:51,730 Well, either they were imprinted someone, you know, they are put in sort of my hand. 350 00:38:52,880 --> 00:39:01,760 At the Big Bang or we're there somehow from a pre big bang phase or they were generated during this period of exponential expansion. 351 00:39:02,240 --> 00:39:04,760 So that, you know, a very important prediction. 352 00:39:05,970 --> 00:39:13,290 So if we look at what are the key predictions of the model, the key predictions that the universe's geometry is flat, 353 00:39:13,830 --> 00:39:19,680 that the super horizon fluctuations are 80, about if the Gaussian are close to scale invariant. 354 00:39:20,350 --> 00:39:27,280 I missed one on my list of. Inflation confirms our observations. 355 00:39:27,280 --> 00:39:36,510 Confirm those first five predictions. What we are left with is a sixth prediction that there should be a background of gravitational waves. 356 00:39:37,760 --> 00:39:44,340 And. I realised when I walked into this room that I think I was in this room. 357 00:39:46,500 --> 00:39:54,270 I guess this was just about look at the date three years ago when this newspaper came out. 358 00:39:55,210 --> 00:40:02,470 And I don't want to talk about Putin's invasion of Crimea, but rather the claim that space time ripples were seen. 359 00:40:03,580 --> 00:40:06,880 There was a group called the Bicep Collaboration. 360 00:40:08,330 --> 00:40:16,550 Led by John Kovac from Harvard that claimed that they had seen gravitational waves in the early universe. 361 00:40:17,510 --> 00:40:20,570 And we were at an acting workshop in Oxford. 362 00:40:21,380 --> 00:40:25,820 We were watching all this, the press conference remotely. 363 00:40:26,690 --> 00:40:31,010 The Internet crashed. We were able to finally download the paper. 364 00:40:31,700 --> 00:40:35,470 We put the paper up and we were very confused for reasons you'll see. 365 00:40:36,520 --> 00:40:41,440 So what was going on here? These were observations of patterns of polarised light. 366 00:40:42,220 --> 00:40:46,150 And what light is an electromagnetic wave? 367 00:40:46,750 --> 00:40:51,380 Electromagnetic waves come with different polarisations. 368 00:40:51,400 --> 00:40:55,780 The electric field could point this way or the electric field could point this way. 369 00:40:56,900 --> 00:41:00,350 Scattered light tends to be polarised when. 370 00:41:01,350 --> 00:41:04,860 No other pocket. It's sunny. Out I go. The beach. 371 00:41:05,820 --> 00:41:08,970 I bring with me and one of my pockets. 372 00:41:09,420 --> 00:41:12,480 Sunglasses. I don't. But you know what they look like. 373 00:41:12,720 --> 00:41:21,600 Some of the reason I do that is polarised light, scatters off the water and tends to scatter one polarisation. 374 00:41:22,410 --> 00:41:28,080 So if I have sunglasses that block a polarisation, I can see more easily on a sun. 375 00:41:31,740 --> 00:41:37,290 The microwave background scatters off of electrons and it produces a polarisation pattern. 376 00:41:38,050 --> 00:41:46,300 And the pattern we see in polarisation could be divided into two types what we call an old pattern, the one on the top. 377 00:41:46,660 --> 00:41:52,150 Those are symmetric. Under narrow reflection. You can take this picture reflected in the mirror. 378 00:41:52,510 --> 00:41:59,780 The emos look the same. You look at the bottom part of the picture, the beam holds, the beam loads. 379 00:41:59,960 --> 00:42:03,770 You shine them, put them in the mirror. They look different. 380 00:42:05,090 --> 00:42:08,690 Variations in density produce only emotes. 381 00:42:09,910 --> 00:42:14,830 Gravitational waves produced both emotes and emotes. 382 00:42:15,670 --> 00:42:19,240 And this is why cosmologists were so eager to check them out. 383 00:42:19,810 --> 00:42:22,960 I'm still over eager to protect emotes because. 384 00:42:24,790 --> 00:42:30,800 They would be the signal gravitational waves. So why would we be excited to see gravitational waves? 385 00:42:30,830 --> 00:42:33,860 Well, it's a glimpse into the universe's first few seconds. 386 00:42:34,490 --> 00:42:39,140 It's testing this idea of inflation. It would open up a new world of cosmology. 387 00:42:39,830 --> 00:42:46,970 So when this map came out showing this playing female pattern and here's the data that they published. 388 00:42:48,030 --> 00:42:55,980 That we were all excited about when I was sitting here in Oxford. This red curve is what we expected without gravitational waves. 389 00:42:57,060 --> 00:43:09,540 The points are their data and the curve is a pattern is a fit through the data that says that there's a gravitational wave signal that's pretty good. 390 00:43:10,710 --> 00:43:16,860 Looks like they Antarctic gravitational waves. The people involved were already claiming the Nobel Prize. 391 00:43:17,460 --> 00:43:26,050 There was a lot of excitement. There's like over a thousand papers people got named most influential. 392 00:43:27,410 --> 00:43:31,040 My experience in this was a bit like the small child. 393 00:43:33,150 --> 00:43:39,270 In the story of the Emperor's New Clothes. Having worked in the microwave background for many years, 394 00:43:39,570 --> 00:43:46,740 I knew that dust was polarised and felt they had not shown that there was any yet, that their signal was not due to dust. 395 00:43:47,520 --> 00:43:52,559 So I went around and started to worry about this. 396 00:43:52,560 --> 00:43:57,060 And since the leader of the experiment was one of my senior thesis students long ago, 397 00:43:57,720 --> 00:44:03,120 I wrote to him a seven page note and said, Here's the concerns I have with the data. 398 00:44:03,630 --> 00:44:08,000 Have you address them? For the students and the audience. 399 00:44:08,660 --> 00:44:17,630 If your advisor from 20 years ago writes you a 27 page note about this thing that you're pushing for the Nobel Prize, 400 00:44:18,560 --> 00:44:23,300 you should read it and answer it. At least say a polite note. 401 00:44:23,540 --> 00:44:27,640 Thank you for your note. That's that's a good social suggestion for the high school. 402 00:44:27,800 --> 00:44:34,820 There are some students here. When your teacher brought you here, writes you a note in 20 years that says, aren't you worried about this? 403 00:44:35,760 --> 00:44:38,700 Answer. So we went. 404 00:44:39,880 --> 00:44:47,080 And checked and said, all right, let's take the data and try to see what the dust model and these were our fits with the dust model. 405 00:44:47,830 --> 00:44:54,730 And you can see our colours in the blue and their curves and the red all go through the data. 406 00:44:56,000 --> 00:45:02,180 And then we went and looked at the plant data they used for analysis and they did something. 407 00:45:03,400 --> 00:45:09,580 That I would call slightly aggressive with the data. The Planck team had not yet released their data. 408 00:45:10,950 --> 00:45:20,280 They had talked about the data in a conference and there was a conference proceeding where they had a PDF from the talk on the web. 409 00:45:21,310 --> 00:45:24,610 They downloaded the PDF and they scanned it. 410 00:45:25,540 --> 00:45:29,050 They use the scanned PDF for their analysis. 411 00:45:30,010 --> 00:45:33,910 The problem was they didn't read the slide. 412 00:45:35,440 --> 00:45:38,560 The slide says not C.I. B subtracted. 413 00:45:39,620 --> 00:45:47,510 It's a technical thing, but it's a nice little bit of algebra. The C D is the cosmic infrared background, so it's the stuff from galaxies. 414 00:45:48,860 --> 00:45:55,430 The polarisation they measured in the map that they used for the correction was the polarisation of the galaxy, 415 00:45:55,880 --> 00:45:59,630 plus the polarisation of those of all these distant galaxies. 416 00:45:59,630 --> 00:46:07,130 Our galaxy. Distant galaxies. Divided by the intensity of our galaxy and the intensity of distant galaxies. 417 00:46:08,070 --> 00:46:14,490 The PCI term is zero. If you these two terms are about the same. 418 00:46:15,240 --> 00:46:20,220 If you ignore one, you get the wrong answer. They assumed one was zero. 419 00:46:21,710 --> 00:46:30,770 So you go back you correct for there the term for what you were told on the slide was there and it all goes away. 420 00:46:31,570 --> 00:46:32,830 And that was our conclusion. 421 00:46:33,400 --> 00:46:41,350 And now that the Planck data is published, the Planck team has done its own analysis and concluded that all that excitement was for nought, 422 00:46:42,190 --> 00:46:50,980 that it all just turned out to be polarised dust. And we can now at least turn this around and say. 423 00:46:52,750 --> 00:46:57,970 Now that we know that's mostly dust, we can constrain the amount of gravitational waves. 424 00:46:58,570 --> 00:47:04,180 And based on that, we could actually focus in on the type of inflation that we think is going on. 425 00:47:07,060 --> 00:47:13,570 Where do we go from here? The next steps is to make better measurements of the microwave sky. 426 00:47:14,110 --> 00:47:21,670 And rather than do it at a single frequency, we want to do this at multiple frequencies so that we can handle dust. 427 00:47:22,270 --> 00:47:29,979 The project that we in Princeton are part of, and Amelia Calabrese, who's here in the audience, 428 00:47:29,980 --> 00:47:41,200 is this is part of our team is something called Advanced Act, where we're going to use five frequencies so we can get a handle on the foregrounds. 429 00:47:42,070 --> 00:47:49,840 We're actually now looking at this is how well we hope to do with measuring the gravitational wave signal. 430 00:47:50,500 --> 00:47:56,840 We also want to measure the effects of lensing on space distortions in space between here. 431 00:47:57,160 --> 00:48:02,470 Here in the distant universe. The gravitational lensing. That's sort of a guaranteed part of our signal. 432 00:48:02,770 --> 00:48:11,889 Typically eager to be able to combine this with upcoming experiments like Elsa's teeth to improve, to look at this piece. 433 00:48:11,890 --> 00:48:18,580 But we're hoping to get them a more complete picture and maybe make a definitive detection of gravitational waves if they're there, 434 00:48:18,580 --> 00:48:25,510 because we have lots of frequencies. We recently announced that we're going to go beyond that experiment. 435 00:48:26,200 --> 00:48:33,669 We've got $45 million from a combination of the Simons Foundation and the 436 00:48:33,670 --> 00:48:38,830 universities that are partners to build a new telescope set of telescopes in Chile. 437 00:48:39,490 --> 00:48:42,280 We just had a big meeting for the brought together. 438 00:48:42,760 --> 00:48:50,770 The two teams involved are now combined into one team to measure the microwave background score with increased precision. 439 00:48:51,550 --> 00:48:59,140 I want to advertise this because we're hoping that there'll be a British participation team where there's a group of 440 00:48:59,440 --> 00:49:06,670 British scientists here and at other universities that we're hoping will join in this international collaboration. 441 00:49:08,380 --> 00:49:14,590 This is in the same site as the ORMEAU Radio Telescope, 442 00:49:14,860 --> 00:49:21,520 and it's basically looking at the same region of the sky as another very important upcoming experiment. 443 00:49:22,180 --> 00:49:25,180 The closest to the Live Synoptic Survey Telescope. 444 00:49:25,570 --> 00:49:29,979 This is a telescope that's going to survey much of the sky. 445 00:49:29,980 --> 00:49:33,070 About two thirds of the sky get very deep images. 446 00:49:33,910 --> 00:49:40,120 It'll do many things. But in cosmology, one of the things we're most interested in is it will trace the large scale distribution 447 00:49:40,120 --> 00:49:46,659 of matter that we can use to test some of these theories on talking about and our test, 448 00:49:46,660 --> 00:49:52,410 our ideas about dark energy and dark matter. And my final. 449 00:49:53,340 --> 00:49:58,980 5 minutes. I want to say a little bit more about gravitational waves because. 450 00:50:00,390 --> 00:50:06,330 I just spent 15 minutes telling you, 10 minutes telling you I don't believe gravitational wave detections. 451 00:50:07,170 --> 00:50:11,970 Well, I didn't believe the claimed detection of gravitational waves in the early universe. 452 00:50:12,900 --> 00:50:19,170 But there's another gravitational wave detection that took place in the last year that I think is remarkably compelling. 453 00:50:20,170 --> 00:50:23,409 On. It tells us mostly about black holes. 454 00:50:23,410 --> 00:50:28,630 But I think as a result, this also ties into this general theme of this lecture, 455 00:50:28,930 --> 00:50:33,370 which is that general relativity seems to be valid on a remarkable range of scales, 456 00:50:34,150 --> 00:50:42,520 and it reinforces the underlying principles that we use for a cosmological analysis. 457 00:50:43,360 --> 00:50:52,930 So it logo is designed to observe is gravitational waves produced from the collision of black holes or black holes and neutron stars? 458 00:50:53,770 --> 00:51:02,320 It's a truly remarkable experiment in that the gravitational waves they're looking for has the effect of shifting to mirrors. 459 00:51:02,830 --> 00:51:11,530 In these experiments in Louisiana and Washington by less than the radius of a neutron. 460 00:51:12,440 --> 00:51:19,160 So you're measuring distances to a changes, some distances to a part and ten to the 21. 461 00:51:20,630 --> 00:51:23,990 And it was a tremendous technical triumph to build this. 462 00:51:25,230 --> 00:51:33,900 It's also, I think, putting on my policy hat, a tremendous triumph for the government agencies involved actually to stick with it. 463 00:51:34,820 --> 00:51:40,070 So they built this experiment. It had sensitivity of a part and ten to the 20. 464 00:51:40,460 --> 00:51:45,380 They spent about $100 million on this. It worked as planned. 465 00:51:45,980 --> 00:51:53,880 They saw nothing. The scientists said, let's spend more money to improve our sensitivity. 466 00:51:54,300 --> 00:52:00,510 This is opening up a new window. The National Science Foundation to its. 467 00:52:01,640 --> 00:52:05,390 Stepped up. Did it made the investment. 468 00:52:06,840 --> 00:52:10,230 Improved sensitivity by another order of magnitude. 469 00:52:10,920 --> 00:52:18,900 And now we're starting to see black hole collisions. And these sound waves are tiny displacements in the mirrors. 470 00:52:19,710 --> 00:52:27,420 And what you see on one side are observations made in Washington, the other in the made in the detector, Louisiana. 471 00:52:27,960 --> 00:52:34,380 And you can see the two experiments saw the same ripples, the same displaced, same sound waves. 472 00:52:35,420 --> 00:52:47,000 At the same time. And the curse underlying them is our theoretical curves based on solutions of general relativity that. 473 00:52:49,340 --> 00:52:56,760 You say that we're seeing the collision of two black holes. And the theory fits the data beautifully. 474 00:52:58,090 --> 00:53:01,990 So this is important. They've detected the first collision of two black holes. 475 00:53:02,890 --> 00:53:09,070 They've tested General to be one of its most important predictions, dramatic predictions, the existence of gravitational waves, 476 00:53:09,490 --> 00:53:15,280 something that actually Einstein predicted, then thought wasn't there, then came back and deciphered. 477 00:53:15,280 --> 00:53:20,200 Yes, it really is. They hard to work through, opened a new area of the universe. 478 00:53:20,710 --> 00:53:24,430 I think it represents the fact that instead of just seeing the universe, 479 00:53:24,430 --> 00:53:29,020 which is what we've done up to now through photons for the first time, we're hearing the universe. 480 00:53:29,440 --> 00:53:36,340 And what we're hearing is it's playing Einsteins to. So let me conclude. 481 00:53:38,710 --> 00:53:42,610 The. We are lucky to live in exciting times. 482 00:53:43,000 --> 00:53:49,700 Cosmologists. We have discovered that we live in a universe that is both remarkably simple, 483 00:53:49,910 --> 00:53:54,980 remarkably strange, simple model with only a handful of parameters fit all of our data. 484 00:53:57,740 --> 00:54:01,400 But it's a model that gives us big open questions. 485 00:54:02,440 --> 00:54:05,710 Dark. What's dark matter? What's dark energy? Was the universe accelerating? 486 00:54:07,670 --> 00:54:12,889 What's exciting looking ahead to the next 20 years is that we can and not only can 487 00:54:12,890 --> 00:54:19,040 we envision we are undertaking a series of experiments and satellites that will. 488 00:54:20,040 --> 00:54:23,160 Test a lot of these ideas, the data will continue to improve. 489 00:54:24,050 --> 00:54:29,870 Particularly, you know, things like the large synoptic survey telescope that will map galaxy positions. 490 00:54:30,970 --> 00:54:37,570 These upcoming microwave background experiments, I think will give us new insights into the nature of dark energy and dark matter, 491 00:54:38,140 --> 00:54:42,400 and perhaps we can even understand the origin of the universe. So let me stop there. 492 00:54:42,670 --> 00:54:43,000 Thank you.