WEBVTT 00:01.233 --> 00:05.033 This is the third update lecture for Frontiers 00:05.033 --> 00:07.573 and Controversies in Astrophysics. 00:07.567 --> 00:11.127 We're doing this little series of update lectures to bring the 00:11.133 --> 00:14.373 material up to date from when the lectures were first 00:14.367 --> 00:16.867 recorded in 2007. 00:16.867 --> 00:20.097 This particular lecture will have to do with cosmology; 00:20.100 --> 00:23.230 that's the third and final segment of the course. 00:23.233 --> 00:27.903 Cosmology is the study of the universe as a whole - the 00:27.900 --> 00:32.430 origin, evolution, and structure of the universe considered as 00:32.433 --> 00:34.003 a single object. 00:34.000 --> 00:37.630 And, over the past five years, something quite remarkable has 00:37.633 --> 00:40.203 happened in the study of cosmology, 00:40.200 --> 00:44.530 and that remarkable thing is that nothing fundamental has 00:44.533 --> 00:47.973 changed about the way we think about the universe. 00:47.967 --> 00:49.497 Now, why is that remarkable? 00:49.500 --> 00:53.200 That's remarkable because in the previous 10 years - in the 10 00:53.200 --> 00:58.270 years leading up to 2007, there had been a drastic change in 00:58.267 --> 01:00.627 what we think the universe consists of. 01:00.633 --> 01:05.403 And we had come up with this model of the universe in which 01:05.400 --> 01:09.870 over 95% of the constituents of the universe were things we 01:09.867 --> 01:11.497 didn't understand at all. 01:11.500 --> 01:15.130 We gave them names and labels - dark matter, 01:15.133 --> 01:19.933 dark energy - but we actually don't understand any of that. 01:19.933 --> 01:23.133 But, it turned out that we had good reason to believe that over 01:23.133 --> 01:28.033 95% of the material in the universe came in these forms, 01:28.033 --> 01:31.533 and that the ordinary material with which we're familiar - 01:31.533 --> 01:37.433 atoms, radiation, and so forth - was actually less than 5% of the 01:37.433 --> 01:39.273 stuff in the universe. 01:39.267 --> 01:42.067 Really, kind of a bizarre situation. 01:42.067 --> 01:47.327 Over the past five years, a vast amount of new data has come in; 01:47.333 --> 01:51.103 new models and new computer simulations of the universe have 01:51.100 --> 01:54.600 been performed and the consequence of all this stuff is 01:54.600 --> 01:59.170 that this very strange vision of the universe has been confirmed 01:59.167 --> 02:03.497 repeatedly, over and over again, by all of the information we 02:03.500 --> 02:05.600 have at our disposal. 02:05.600 --> 02:09.470 And so, people are really starting to believe that this 02:09.467 --> 02:10.627 might turn out to be true. 02:10.633 --> 02:16.633 The basic information that we have is kind of summed up 02:16.633 --> 02:18.003 in this graph. 02:18.000 --> 02:19.900 I showed a version of this, I think, 02:19.900 --> 02:22.730 at the end of the lecture series. 02:22.733 --> 02:26.503 And what this is is it plots the amount of dark energy in 02:26.500 --> 02:29.500 the universe vs. the amount of dark matter 02:29.500 --> 02:30.630 in the universe; 02:30.633 --> 02:34.833 and each one of these different colors is a different way of 02:34.833 --> 02:38.003 constraining the dark matter and the dark energy. 02:38.000 --> 02:40.700 So, in the course, we spent most of our time worrying about 02:40.700 --> 02:44.970 supernovae, and the supernovae are, 02:44.967 --> 02:48.627 it turns out, are - demonstrate that the universe is expanding 02:48.633 --> 02:50.503 faster and faster and faster. 02:50.500 --> 02:54.900 So, there must be some universal repulsive force in the universe 02:54.900 --> 02:57.770 that's pushing it apart at an ever-increasing rate. 02:57.767 --> 02:59.597 This is what we call dark energy. 02:59.600 --> 03:03.700 And the discovery that the supernova evidence showed that 03:03.700 --> 03:06.700 the universe was expanding faster as time went on, 03:06.700 --> 03:11.000 rather than slower, that was what was discovered in 1998, 03:11.000 --> 03:15.130 and it began this change in our view of what the 03:15.133 --> 03:16.273 universe consisted of. 03:16.267 --> 03:21.527 And for this to be true, there has to be more dark energy in 03:21.533 --> 03:22.833 the universe than there is dark matter, 03:22.833 --> 03:25.303 and so, that's this region of the plot. 03:25.300 --> 03:27.630 And you can figure out how much more as well. 03:27.633 --> 03:33.773 If the dark matter there is .4 in whatever units these are, 03:33.767 --> 03:37.727 then the amount of dark energy has to be something like .8, 03:37.733 --> 03:41.103 and so you have a diagonal in this direction. 03:41.100 --> 03:45.370 The orange stuff here is from observations of the cosmic 03:45.367 --> 03:48.967 microwave background, and in particular, 03:48.967 --> 03:53.697 of the fluctuations; the non-uniformity of the cosmic 03:53.700 --> 03:54.800 microwave background. 03:54.800 --> 03:58.200 I'll come back and talk about that a little more later on. 03:58.200 --> 04:03.570 And, what you can derive from those is the total amount of 04:03.567 --> 04:06.267 dark matter and dark energy in the universe, 04:06.267 --> 04:11.127 so this number has to add up, plus this number has to add up 04:11.133 --> 04:12.833 to something that's more or less the same. 04:12.833 --> 04:14.903 And so, if there's less dark matter, 04:14.900 --> 04:16.970 there has to be more dark energy. 04:16.967 --> 04:20.097 That's why this one goes in this direction. 04:20.100 --> 04:24.170 And then, the green has to do with the clustering in the 04:24.167 --> 04:28.197 universe - how, the fact that galaxies are not uniformly 04:28.200 --> 04:31.300 spread across the universe, but they're clustered into clusters 04:31.300 --> 04:34.170 of galaxies and even bigger structures, 04:34.167 --> 04:37.197 whereas there are other parts of the universe that are voids. 04:37.200 --> 04:40.070 And how much clustering there is, 04:40.067 --> 04:41.627 which is something we can measure, 04:41.633 --> 04:44.933 has to do, basically, with how much dark matter there is. 04:44.933 --> 04:48.473 Doesn't depend so much on how - it depends a little on dark 04:48.467 --> 04:51.127 energy, but not so much, and that's why that's kind of 04:51.133 --> 04:54.573 vertical, because it picks out a particular value of 04:54.567 --> 04:56.097 the dark matter. 04:56.100 --> 04:58.430 And so, the remarkable thing turns out to be that there are 04:58.433 --> 05:03.103 these three ways of measuring how much dark matter and energy 05:03.100 --> 05:07.270 there is, each one of which defines a line in this graph. 05:07.267 --> 05:10.697 Now, if you have two lines in a two-dimensional graph, 05:10.700 --> 05:13.570 they'll cross somewhere unless they're perfectly parallel. 05:13.567 --> 05:16.327 They'll cross somewhere, and that's not a big surprise. 05:16.333 --> 05:20.273 But if there's a third line, it doesn't have to cross where the 05:20.267 --> 05:22.167 other two do, in fact, in general it won't. 05:22.167 --> 05:24.467 So you could have two lines that cross here, 05:24.467 --> 05:26.427 the third line could be over here somewhere, 05:26.433 --> 05:29.173 and it would cross each of those other lines somewhere, 05:29.167 --> 05:31.527 but not necessarily at the same point. 05:31.533 --> 05:34.903 So, the fact that we have these three fundamentally different 05:34.900 --> 05:38.270 ways of measuring things, and they all agree, 05:38.267 --> 05:43.027 is basically the basis for why we believe this is true. 05:43.033 --> 05:46.733 And, what has happened - this particular plot is from 2010, 05:46.733 --> 05:49.233 with some of the latest observations included. 05:49.233 --> 05:52.603 Each one of these methods is being worked on all the time, 05:52.600 --> 05:56.770 and the range that is allowed is getting narrower and 05:56.767 --> 05:58.367 narrower and narrower. 05:58.367 --> 06:02.227 And as that is being done, they still cross each other. 06:02.233 --> 06:05.603 And so, it is now the case that the only region of this plot 06:05.600 --> 06:10.030 that is allowed by all three of these methods is this little 06:10.033 --> 06:11.473 region in here. 06:11.467 --> 06:16.367 And that gives us the parameters of what has come to be called 06:16.367 --> 06:19.697 the "concordance cosmology." Cosmology, 06:19.700 --> 06:23.470 which includes all evidence that we have to date. 06:23.467 --> 06:27.627 Let me make one passing remark about this plot - in the 06:27.633 --> 06:31.573 previous plot, this stripe here was labeled "clusters of 06:31.567 --> 06:35.567 galaxies." Nowadays, we have a new fancier name for it - this 06:35.567 --> 06:37.597 is one of the things that happened in the past five years. 06:37.600 --> 06:40.770 We call it "Baryon Acoustic Oscillations; 06:40.767 --> 06:43.297 that means the clustering of galaxies. 06:43.300 --> 06:46.770 Baryons are ordinary matter, that's what galaxy consists of. 06:46.767 --> 06:50.127 Acoustic oscillations are why they cluster, 06:50.133 --> 06:53.673 and I'll come back to that in a little bit later, 06:53.667 --> 06:57.227 but I just wanted to point out that there's this excellent new 06:57.233 --> 07:02.473 jargon term, which we use for that part of the plot. 07:02.467 --> 07:05.327 So, here is the concordance cosmology, 07:05.333 --> 07:08.003 it's also called lambda CDM. 07:08.000 --> 07:10.530 Lambda is the symbol we give for the dark energy; 07:10.533 --> 07:13.303 CDM stands for cold dark matter, and so, 07:13.300 --> 07:16.530 this is a universe which is dominated by dark energy 07:16.533 --> 07:17.833 and dark matter. 07:17.833 --> 07:21.873 And, the amount of dark energy - that's the lambda here, 07:21.867 --> 07:24.667 is .73 out of the total. 07:24.667 --> 07:27.927 The amount of dark matter is .23, 07:27.933 --> 07:30.733 and that leaves for ordinary material. 07:30.733 --> 07:35.533 The B is for Baryons, there; for ordinary material, 4%. 07:35.533 --> 07:39.603 And this is - these are what we believe to be the constituents 07:39.600 --> 07:42.570 of the universe. 07:42.567 --> 07:44.867 There's also a couple other things we know - the Hubble 07:44.867 --> 07:49.167 constant is how fast the universe is expanding right now. 07:49.167 --> 07:52.427 This is given in units of kilometers per second, 07:52.433 --> 07:53.833 per megaparsec (km/s/Mpc). 07:53.833 --> 07:56.773 What that means is if you look at something a megaparsec away, 07:56.767 --> 08:00.367 it's moving away from us at 72 km/s. 08:00.367 --> 08:04.027 If you look at something 10 megaparsecs away, 08:04.033 --> 08:08.033 it's receding from us at 720 km/s, 08:08.033 --> 08:12.233 so this is expressed in km/s/Mpc. 08:12.233 --> 08:16.333 For two generations, people argued about whether this number 08:16.333 --> 08:18.203 was 50 or 100. 08:18.200 --> 08:20.230 And so, of course, the answer is 75, 08:20.233 --> 08:22.373 more or less. 08:22.367 --> 08:24.467 And, if you put all of this stuff together, 08:24.467 --> 08:27.667 you can calculate, with considerable precision, 08:27.667 --> 08:30.127 what the age of the universe must be. 08:30.133 --> 08:33.173 How long it has been since the Big Bang occurred. 08:33.167 --> 08:36.567 And the answer to that is 13.7 billion years. 08:36.567 --> 08:39.567 The G stands for giga, which means billion, 08:39.567 --> 08:42.197 so astronomers like to talk about gigayears. 08:42.200 --> 08:46.330 And so, the universe, if you believe in these numbers here, 08:46.333 --> 08:47.873 is 13.7 gigayears old. 08:47.867 --> 08:51.127 And it's really quite remarkable we have that to several 08:51.133 --> 08:53.003 decimal places now. 08:53.000 --> 08:55.770 And that's the really extraordinary thing about the 08:55.767 --> 08:59.167 concordance cosmology is that these numbers have been around, 08:59.167 --> 09:04.397 people have been exploring them now in a large number of ways 09:04.400 --> 09:08.300 for some number of years, and it keeps coming out to 09:08.300 --> 09:09.570 the same answer. 09:09.567 --> 09:13.967 So much so, as I said, people have started to believe it, 09:13.967 --> 09:16.227 and you can tell that people have started to believe it 09:16.233 --> 09:18.533 because they gave a Nobel Prize for it. 09:18.533 --> 09:23.503 And the 2011 Nobel Prize in physics was awarded to people 09:23.500 --> 09:26.000 who made this discovery about the supernovae, 09:26.000 --> 09:30.270 and thus, essentially discovered the existence of dark energy. 09:30.267 --> 09:32.497 And so, Saul Perlmutter, and Brian Schmidt, 09:32.500 --> 09:35.700 and Adam Riess were given the Nobel Prize - these were the 09:35.700 --> 09:39.930 leaders of the two teams competing with each other 09:39.933 --> 09:42.873 who made the same discovery at the same time. 09:42.867 --> 09:45.797 There was some issue about who should be awarded the prize for 09:45.800 --> 09:49.170 this, it was clear that the discovery was prize-worthy. 09:49.167 --> 09:52.267 Perlmutter was the clear leader of one of these groups, 09:52.267 --> 09:57.727 but the other group didn't have a clear leadership structure in 09:57.733 --> 09:58.873 quite the same way. 09:58.867 --> 10:02.797 There was a lot of independent actors working together. 10:02.800 --> 10:06.900 Schmidt and Reiss were the principal authors of the key 10:06.900 --> 10:10.630 papers, and indeed, did much of the work and leadership; 10:10.633 --> 10:14.733 but they were both, you know, graduate students and post-docs 10:14.733 --> 10:18.103 of a particular guy at Harvard named Bob Kirschner, 10:18.100 --> 10:20.000 who didn't get the award. 10:20.000 --> 10:22.770 And there were, you know, 40 other people who might have - 10:22.767 --> 10:26.697 who have contributed very strongly to that. 10:26.700 --> 10:29.600 And, this I think points up a problem that we're having in 10:29.600 --> 10:33.900 science these days: it's getting harder and harder to associate a 10:33.900 --> 10:37.170 particular scientific advance with a particular person. 10:37.167 --> 10:41.167 And the whole concept of the Nobel Prize - among other 10:41.167 --> 10:43.297 prizes, but the Nobel, of course, 10:43.300 --> 10:45.770 is the most famous - is that people, 10:45.767 --> 10:48.567 individual people make discoveries. 10:48.567 --> 10:52.467 And back when there was Einstein and Planck and Bohr and all 10:52.467 --> 10:54.027 these fabulous people a century ago, 10:54.033 --> 10:55.003 that was kind of true. 10:55.000 --> 10:58.130 Now people work in these big teams because the projects are 10:58.133 --> 11:01.733 too big for any one person. 11:01.733 --> 11:04.703 And so, the whole concept of giving prizes to people has 11:04.700 --> 11:06.100 become a little problematic. 11:06.100 --> 11:09.270 The Nobel Prize in particular has a rule - you can only give 11:09.267 --> 11:11.227 it to three people at once. 11:11.233 --> 11:16.603 And so they picked Saul, who was the head of one of the groups, 11:16.600 --> 11:18.030 and that was fine. 11:18.033 --> 11:20.603 And, you could have picked a whole bunch of people 11:20.600 --> 11:21.870 on this side. 11:21.867 --> 11:24.897 And indeed, there was another prize that was given for this, 11:24.900 --> 11:27.130 the Catholic prize, where they gave it to the whole group. 11:27.133 --> 11:31.633 So, everybody got 1/65 of a prize or something like that. 11:31.633 --> 11:33.403 And so, there's a problem, I think, 11:33.400 --> 11:35.830 these days in assigning credit. 11:35.833 --> 11:40.403 Be that as it may, this discovery clearly worthy of a 11:40.400 --> 11:43.430 Nobel Prize; it revolutionized our understanding 11:43.433 --> 11:44.433 of the universe. 11:44.433 --> 11:47.503 And of course, they don't like to give prizes to things before 11:47.500 --> 11:49.870 people really believe that it's true. 11:49.867 --> 11:52.267 And so, the fact that they finally got around to giving the 11:52.267 --> 11:55.997 Nobel Prize for the discovery of dark energy means that the 11:56.000 --> 12:01.730 physics community has decided that dark energy really exists. 12:01.733 --> 12:03.533 So, where do we go from here? 12:03.533 --> 12:08.173 Now that we have the basic parameters of the universe, 12:08.167 --> 12:09.767 what do you do next? 12:09.767 --> 12:12.597 And one of the things that's being done is the study of 12:12.600 --> 12:16.200 cosmic structures - structures in the galaxy, 12:16.200 --> 12:18.930 in the universe; and how they evolve, 12:18.933 --> 12:21.533 where they came from; and how they're likely to evolve 12:21.533 --> 12:22.833 in the future. 12:22.833 --> 12:27.073 So, if you look as far back as you can in time - back, 12:27.067 --> 12:29.197 you know, as you looked at something further and further 12:29.200 --> 12:33.330 away, you're looking back in time because the speed of light, 12:33.333 --> 12:36.933 as you have to account for the length of time the light has 12:36.933 --> 12:38.233 been travelling towards you. 12:38.233 --> 12:40.603 The furthest back you can look is the cosmic microwave 12:40.600 --> 12:47.100 background; that's emanating from material shortly after 12:47.100 --> 12:47.970 the Big Bang. 12:47.967 --> 12:52.267 And the waves of light that have been emitted from that, 12:52.267 --> 12:56.127 have been redshifted, have increased their wavelength by a 12:56.133 --> 12:59.733 factor of 1000 between when they were emitted and now. 12:59.733 --> 13:04.003 One way to think about that is, that's the amount the universe 13:04.000 --> 13:06.930 has expanded since that light was emitted. 13:06.933 --> 13:10.903 So, this light was emitted when the universe was 1000 times 13:10.900 --> 13:15.330 smaller than it is today, and this is a famous picture from 13:15.333 --> 13:19.273 the Kobe satellite from the 1990's when they discovered that 13:19.267 --> 13:21.597 it's not quite uniform. 13:21.600 --> 13:24.270 It's very close to uniform across the sky. 13:24.267 --> 13:26.897 And this is color-coded for high-density and low-density 13:26.900 --> 13:31.070 regions, and the variations between the high-density and the 13:31.067 --> 13:34.667 low-density region are about a part in 100,000. 13:34.667 --> 13:38.397 So, not big variations, but this was a very sensitive instrument 13:38.400 --> 13:40.170 that could see it. 13:40.167 --> 13:44.667 If you look in the nearby, present-day universe, 13:44.667 --> 13:46.327 you can also see structure. 13:46.333 --> 13:49.903 This is the distribution of galaxies in a particular survey 13:49.900 --> 13:53.430 - the two-degree field survey done by people in Australia - 13:53.433 --> 13:56.633 and you can see, there's some regions where there are lots and 13:56.633 --> 13:59.403 lots of galaxies; there are some regions where there are very few 13:59.400 --> 14:03.030 galaxies - voids, we call them - and these are 14:03.033 --> 14:05.873 structures as well. 14:05.867 --> 14:09.167 In this case, you're looking at galaxies with a redshift of 14:09.167 --> 14:11.497 between zero and one. 14:11.500 --> 14:13.270 Basically, the way to interpret this map is, 14:13.267 --> 14:16.567 we sit here and we're looking in one direction there, 14:16.567 --> 14:19.597 and one direction that way; you can't see up and down because 14:19.600 --> 14:24.570 our own galaxy gets in the way. 14:24.567 --> 14:27.897 But, the amplitude of the variations is very much bigger. 14:27.900 --> 14:33.600 If you compare the density of the material in this room as 14:33.600 --> 14:37.000 compared to the density of material in the intergalactic 14:37.000 --> 14:40.970 void, there's 10 to the 29 times greater density 14:40.967 --> 14:42.127 of material here. 14:42.133 --> 14:45.603 And in fact, it can be a difference of effectively 14:45.600 --> 14:47.900 infinity, if you look at black holes. 14:47.900 --> 14:53.500 But there's, instead of one part in 10 to the 5, 14:53.500 --> 14:57.630 we now have 29 orders of magnitude difference in density. 14:57.633 --> 15:02.003 And so, the clumping is much more now than it was back then. 15:02.000 --> 15:06.700 Nevertheless, the hypothesis is that these tiny ripples in the 15:06.700 --> 15:11.500 cosmic microwave background have been amplified over the history 15:11.500 --> 15:15.870 of the universe to create these enormous differences in density 15:15.867 --> 15:18.697 that we see today, and that they're basically 15:18.700 --> 15:20.100 the same thing. 15:20.100 --> 15:24.570 It's just that over time, they get bigger and bigger because if 15:24.567 --> 15:28.267 you have an over dense region, it has extra gravity to pull 15:28.267 --> 15:32.067 stuff in; and the under dense region doesn't have as much 15:32.067 --> 15:34.367 gravity, and the stuff streams away. 15:34.367 --> 15:40.297 So, over time, small density perturbations will be amplified. 15:40.300 --> 15:43.830 But, there's an interesting problem in that there's a region 15:43.833 --> 15:47.633 in time between the cosmic microwave background and the 15:47.633 --> 15:52.103 galaxies we see today, which you don't see any radiation from. 15:52.100 --> 15:55.700 This is what's referred to sometimes as the "Dark Ages, 15:55.700 --> 15:57.600 so, at a redshift of a thousand, 15:57.600 --> 16:00.570 you can see the cosmic microwave background - that's the moment 16:00.567 --> 16:02.897 where the universe goes from being opaque 16:02.900 --> 16:04.430 to being transparent. 16:04.433 --> 16:09.133 The reason it does that is it's become cool enough for hydrogen 16:09.133 --> 16:13.003 - for electrons and protons to combine to make atomic hydrogen. 16:13.000 --> 16:15.670 Atomic hydrogen is much more transparent 16:15.667 --> 16:18.027 than ionized hydrogen. 16:18.033 --> 16:21.603 And so, when it's hot, you can't see through it; 16:21.600 --> 16:27.600 and when it cools down and the atomic hydrogen can be created, 16:27.600 --> 16:30.330 all of a sudden, the universe is transparent, 16:30.333 --> 16:34.833 and you see this sort of hot, opaque wall on the other side. 16:34.833 --> 16:36.673 But then, it's transparent. 16:36.667 --> 16:37.767 Nothing happens. 16:37.767 --> 16:41.527 No radiation is emitted until much, 16:41.533 --> 16:46.103 much later when the density contrast has become sufficiently 16:46.100 --> 16:50.470 great, that stars and galaxies actually begin to form. 16:50.467 --> 16:53.227 And, between the cosmic microwave background and the 16:53.233 --> 16:58.003 first stars and galaxies, there's this long period of time 16:58.000 --> 17:01.570 where you have no information, because no photons were emitted. 17:01.567 --> 17:05.767 And so, if you want to test the hypothesis that the stars and 17:05.767 --> 17:09.897 galaxies evolved from these tiny little fluctuations that you 17:09.900 --> 17:12.170 observe in the cosmic microwave background, 17:12.167 --> 17:14.467 there's a problem, from an observational point of view, 17:14.467 --> 17:18.697 because you can't see any - you can't see this process going on 17:18.700 --> 17:22.630 until stars actually begin to form, 17:22.633 --> 17:25.533 and begin to shine. 17:25.533 --> 17:28.473 So, the approach has been to model this 17:28.467 --> 17:30.397 with computer simulations. 17:30.400 --> 17:36.470 So, what you do is you start out with the observed structure of 17:36.467 --> 17:40.097 the cosmic microwave background - the size and the shape of 17:40.100 --> 17:42.570 those tiny irregularities. 17:42.567 --> 17:45.967 And then, two things - and then you do a computer model which 17:45.967 --> 17:47.797 includes two different effects. 17:47.800 --> 17:50.570 One is the fact that the universe is expanding, 17:50.567 --> 17:53.227 and now that we have the concordance cosmology 17:53.233 --> 17:57.303 lambda CDM - we know how fast it's expanding, 17:57.300 --> 18:00.570 and how much dark energy is pushing it out, 18:00.567 --> 18:03.297 how much dark matter is pulling it in. 18:03.300 --> 18:06.130 And then, you also add to that the Law of Gravity - Newton's 18:06.133 --> 18:09.733 Law of Gravity - which, as I mentioned before has this effect 18:09.733 --> 18:12.033 that the dense regions pull stuff in, 18:12.033 --> 18:15.773 and the low-density regions lose their material to the 18:15.767 --> 18:17.227 high-density regions. 18:17.233 --> 18:21.733 And with those two effects, you simply calculate the clumping of 18:21.733 --> 18:24.473 the matter, and how much the matter clumps as 18:24.467 --> 18:26.427 the universe expands. 18:26.433 --> 18:29.103 And, you keep this going from when the cosmic microwave 18:29.100 --> 18:31.230 background happened to the present day, 18:31.233 --> 18:33.903 and you say, "all right, if I run this little computer 18:33.900 --> 18:39.100 program, and I end up with a certain amount of clumping, 18:39.100 --> 18:43.670 I can then compare those clumps to the clumping of the galaxies 18:43.667 --> 18:46.497 that we see today, and see whether it works" - whether the 18:46.500 --> 18:50.130 clumps are the right size and shape and density contrast. 18:50.133 --> 18:53.803 And, it turns out that this works really well for lambda 18:53.800 --> 18:58.800 cold dark matter universes, but not for other possible values of 18:58.800 --> 19:00.270 the cosmic parameters. 19:00.267 --> 19:03.897 This is the Baryon Acoustic Oscillation calculation that I 19:03.900 --> 19:05.730 was discussing before, and that's what gives you 19:05.733 --> 19:07.233 the green stripe. 19:07.233 --> 19:11.033 That's the range of cosmic parameters that makes the 19:11.033 --> 19:14.303 clumping work out. 19:14.300 --> 19:16.930 So, let me just show you an example of one of 19:16.933 --> 19:18.133 these computer simulations. 19:18.133 --> 19:20.733 These are kind of cool to watch. 19:20.733 --> 19:24.673 Let's see here... 19:24.667 --> 19:28.027 So, this is a bunch of material, 19:28.033 --> 19:32.003 and it starts out in a fairly uniform state, 19:32.000 --> 19:35.770 and, as time goes on, you can see it clumps more and more and 19:35.767 --> 19:37.527 more into these structures. 19:37.533 --> 19:42.803 You can see these long structures surrounding voids 19:42.800 --> 19:44.170 where there's no material at all; 19:44.167 --> 19:46.397 there's kind of one in the center of the box. 19:46.400 --> 19:52.000 And - I'll show it again - and what's being kept track of, 19:52.000 --> 19:54.000 in the upper left hand corner here, 19:54.000 --> 19:56.930 this quantity Z, that's the redshift. 19:56.933 --> 20:02.573 This particular simulation only goes from a redshift of 15 to 20:02.567 --> 20:05.467 the current day, but the principle is the same. 20:05.467 --> 20:08.867 And so - I'll show it to you again - and as you'll see, 20:08.867 --> 20:12.967 it starts out very uniform and it clumps more and more. 20:12.967 --> 20:16.667 What this isn't showing is that is should get bigger; 20:16.667 --> 20:18.227 the universe is expanding. 20:18.233 --> 20:22.303 So really, it should start 13 times smaller than it ends, 20:22.300 --> 20:24.200 but then you can't see what's going on. 20:24.200 --> 20:29.070 And so, what they do is they're changing the scale as it goes 20:29.067 --> 20:31.297 along to keep the box the same size. 20:31.300 --> 20:34.830 So, you have to imagine in your head that this box is increasing 20:34.833 --> 20:36.803 in size along with the redshift. 20:36.800 --> 20:40.400 So, let's at it again, and here's the uniform start at a 20:40.400 --> 20:45.400 redshift of about 10, and as it comes closer and closer to the 20:45.400 --> 20:49.800 present time - present time is redshift zero - you can see that 20:49.800 --> 20:52.770 the clumping gets more and more and more significant. 20:52.767 --> 20:58.027 And this is a particular range of initial perturbations and a 20:58.033 --> 21:03.403 particular cosmology; and people are amusing themselves by doing 21:03.400 --> 21:07.230 this kind of calculation over and over again on the current 21:07.233 --> 21:09.233 day super computers. 21:14.300 --> 21:18.570 So, the idea is, as I said, you start with the observed 21:18.567 --> 21:20.667 structures, you apply the expansion of the universe and 21:20.667 --> 21:23.127 the law of gravity, you see how things clump, 21:23.133 --> 21:27.403 and you compare that to what you observe. 21:27.400 --> 21:30.170 There's a little bit of a problem in interpreting these 21:30.167 --> 21:34.567 computer simulations; you have to be careful what is plotted in 21:34.567 --> 21:36.327 that computer simulation is cold, 21:36.333 --> 21:40.933 dark matter, which is the material - the most of the 21:40.933 --> 21:42.373 matter in the universe. 21:42.367 --> 21:46.667 And, the reason you plot that is because dark matter interacts 21:46.667 --> 21:50.767 only by gravity; but of course, we don't see dark matter. 21:50.767 --> 21:54.027 By definition, you don't see dark matter - it's dark. 21:54.033 --> 21:55.873 And so, what do you see? 21:55.867 --> 21:58.597 You see glowing gas; that's what we observe. 21:58.600 --> 22:02.800 Stars, nebulae, things of this nature - those are all Baryons, 22:02.800 --> 22:06.200 that's this little extra stuff that rides along with the 22:06.200 --> 22:07.400 cold dark matter. 22:07.400 --> 22:12.070 At least it rides along for a while because gas doesn't only 22:12.067 --> 22:13.697 interact through gravity. 22:13.700 --> 22:16.470 There's also radiation, pushes the gas around, 22:16.467 --> 22:20.527 pressure of various kinds, streams of gas can run into 22:20.533 --> 22:23.733 each other and have shockwaves. 22:23.733 --> 22:27.833 And after a while, the gas is not necessarily in the same 22:27.833 --> 22:29.803 place as the dark matter is. 22:29.800 --> 22:33.170 And so, the difference between where the gas is and where the 22:33.167 --> 22:36.867 dark matter is is referred to as the bias in the observations. 22:36.867 --> 22:40.997 And the distribution of the gas is actually much harder to model 22:41.000 --> 22:43.800 by computer simulations, because you have to include these other 22:43.800 --> 22:47.730 effects, than is the distribution of the dark matter. 22:47.733 --> 22:51.333 And so, this is sometimes referred to as "gastrophysics;" 22:51.333 --> 22:54.803 trying to figure out where the gas is is actually much harder 22:54.800 --> 22:57.830 than trying to figure out where the dark matter is, 22:57.833 --> 23:01.903 even though gas is something we understand and dark matter is 23:01.900 --> 23:04.100 something we don't know what it is. 23:04.100 --> 23:07.830 The only thing we know about it is, it doesn't interact. 23:07.833 --> 23:11.433 So, one of the big research efforts going on now is to 23:11.433 --> 23:16.673 include calculations of the bias in these computer simulations, 23:16.667 --> 23:20.567 so that you can actually compare the computer simulations to the 23:20.567 --> 23:25.197 galaxies and the distribution of galaxies that we see. 23:25.200 --> 23:28.030 There's also new observations being planned. 23:28.033 --> 23:31.303 The idea is to look at the radiating matter, 23:31.300 --> 23:34.870 further and further away at higher and higher redshifts. 23:34.867 --> 23:38.767 We can now observe galaxies and quasars and other things up to 23:38.767 --> 23:41.027 redshifts of seven and eight. 23:41.033 --> 23:44.273 This is much further away than we've been able to do before. 23:44.267 --> 23:46.467 And as you can see in that simulation, 23:46.467 --> 23:49.997 you expect the clustering to change over that time. 23:50.000 --> 23:53.200 So now, we don't just look at how things are clustered now, 23:53.200 --> 23:55.400 we look at how it changes with time. 23:55.400 --> 23:57.900 But you need better observations to do this; 23:57.900 --> 24:00.730 these objects are very distant, they're therefore faint. 24:00.733 --> 24:02.873 You need the biggest, most powerful telescopes 24:02.867 --> 24:04.597 to observe them. 24:04.600 --> 24:06.770 They're also redshifted, and therefore, 24:06.767 --> 24:09.997 their radiation is not an optical light where stars emit 24:10.000 --> 24:13.730 radiation, but in the infrared instead. 24:13.733 --> 24:17.803 And infrared observations get to be difficult from the ground. 24:17.800 --> 24:20.370 That's because the Earth glows in the infrared; 24:20.367 --> 24:23.127 that's how night-vision goggles work. 24:23.133 --> 24:26.103 You can see human beings glow in the dark, 24:26.100 --> 24:29.570 telescopes glow in the dark, buildings glow in the dark, 24:29.567 --> 24:31.167 astronomers glow in the dark, and so, 24:31.167 --> 24:34.327 making a good infrared observations from the ground is 24:34.333 --> 24:36.573 actually tricky to do. 24:36.567 --> 24:39.897 And so, they are planning new space telescopes in order to 24:39.900 --> 24:42.870 carry out these observations of distant, 24:42.867 --> 24:46.367 faint, redshifted objects. 24:46.367 --> 24:50.027 So, the most prominent of these telescopes being planned is 24:50.033 --> 24:52.333 something called the "James Webb Space Telescope" (JWST). 24:52.333 --> 24:56.873 James Webb was the administrator of NASA in the early 60's, 24:56.867 --> 24:58.427 when we went to the moon. 24:58.433 --> 25:02.233 And you'll notice that the new space telescopes are named not 25:02.233 --> 25:05.133 after scientists like the Hubble space telescope was, 25:05.133 --> 25:07.433 but after NASA administrators. 25:07.433 --> 25:09.803 You know, whatever it takes to get the thing built. 25:09.800 --> 25:13.970 So, the JWST is a large space telescope; 25:13.967 --> 25:17.227 it's much bigger than the Hubble space telescope, 25:17.233 --> 25:19.903 more powerful that the Hubble space telescope, 25:19.900 --> 25:23.800 and optimized for infrared observations so that it can 25:23.800 --> 25:28.230 observe the most distant galaxies and stars, 25:28.233 --> 25:30.773 right after galaxies and stars began to form. 25:30.767 --> 25:34.167 And, they're going to stick it, not in near Earth orbit - 25:34.167 --> 25:37.067 as I say, Earth glows in the infrared - but, 25:37.067 --> 25:40.867 a fair distance away at what's called the L2 point, 25:40.867 --> 25:44.027 which is a gravitational equilibrium point in a kind of 25:44.033 --> 25:47.203 triangle with the Earth and the Sun and the moon. 25:47.200 --> 25:51.770 And, it has this - here's the segments of the telescope itself 25:51.767 --> 25:54.897 - takes the light from distant stars and focuses it on 25:54.900 --> 25:56.300 something out here. 25:56.300 --> 26:00.600 And, this is a big heat shield, and it points toward the sun 26:00.600 --> 26:04.530 because you don't want the heat from the Sun 26:04.533 --> 26:05.533 interfering with it. 26:05.533 --> 26:07.933 And so it kind of always keeps its backside toward the Sun. 26:07.933 --> 26:12.103 And, this is going to be the next great space telescope; 26:12.100 --> 26:16.170 more powerful - in particular for these cosmological 26:16.167 --> 26:18.567 observations - much more powerful than the Hubble space 26:18.567 --> 26:19.697 telescope has been. 26:19.700 --> 26:22.330 There's one big mistake in this image. 26:22.333 --> 26:25.573 This, again, is a piece of NASA propaganda, 26:25.567 --> 26:30.627 2013, that might have been true in 2007, 26:30.633 --> 26:34.833 but I think 2018 might be more accurate now. 26:34.833 --> 26:37.303 There have been a lot of cost overruns and delays with this 26:37.300 --> 26:40.000 mission, which have turned out to be a problem. 26:40.000 --> 26:42.270 Given the economic problems we've been having for the past 26:42.267 --> 26:45.167 five years, the fact that this is a multi-billion dollar 26:45.167 --> 26:48.497 project that keeps being more costly and more delayed. 26:48.500 --> 26:50.800 And the consequence is that we haven't started 26:50.800 --> 26:52.170 any new projects. 26:52.167 --> 26:55.027 And so, it's actually getting to be a kind of an issue, 26:55.033 --> 26:58.103 as the current generation of space telescopes get older; 26:58.100 --> 27:02.300 this is the only replacement that's really on track to be 27:02.300 --> 27:05.600 launched any time this decade. 27:05.600 --> 27:07.530 But, that doesn't stop people of thinking of new, 27:07.533 --> 27:09.103 clever things to do. 27:09.100 --> 27:12.900 Here's another planned infrared space telescope called the Wide 27:12.900 --> 27:16.400 Field Infrared space telescope, or WFIRST. 27:16.400 --> 27:20.930 The key to this and the reason it's different from the JWST is 27:20.933 --> 27:23.433 the wide field. 27:23.433 --> 27:28.633 JWST will only look at a small, tiny piece of the sky at once. 27:28.633 --> 27:31.873 It will look really powerfully and distantly at this. 27:31.867 --> 27:36.397 This is not as big a telescope as the JWST, 27:36.400 --> 27:39.100 but it looks at much more of the sky at once. 27:39.100 --> 27:41.300 And so, this thing will do two projects; 27:41.300 --> 27:45.130 it will not only do the cosmology project and thus be a 27:45.133 --> 27:48.273 successor to JWST and the ground-based, 27:48.267 --> 27:52.067 and HST and the ground-based infrared telescopes; 27:52.067 --> 27:55.997 it will also be a successor to the Kepler mission that is 27:56.000 --> 28:00.900 exploring exoplanets because it has a wide field of view. 28:00.900 --> 28:05.100 And, the other thing is, you'll be able to see more light from 28:05.100 --> 28:09.230 the planet in the infrared than you could in optical light; 28:09.233 --> 28:13.933 and so this is planned to be both an exoplanet mission and 28:13.933 --> 28:15.433 a cosmology mission. 28:15.433 --> 28:18.033 It was ranked the number one project by a 28:18.033 --> 28:19.473 group of scientists. 28:19.467 --> 28:22.197 Every 10 years, the astronomers get together to try and 28:22.200 --> 28:25.800 prioritize all their projects so they can present a united front 28:25.800 --> 28:28.830 to Congress when they want many billions of dollars; 28:28.833 --> 28:31.873 and this exercise took place in 2010. 28:31.867 --> 28:34.467 It happens, as I say, every decade, 28:34.467 --> 28:37.567 and this was the number one ranked space mission that came 28:37.567 --> 28:39.897 out of that project, but it still doesn't have a launch date 28:39.900 --> 28:43.870 because we're not far enough along in JWST to really commit 28:43.867 --> 28:46.797 ourselves to the next project. 28:46.800 --> 28:49.200 There's another approach that's possible, 28:49.200 --> 28:52.770 in which you don't even try and look at stars. 28:52.767 --> 28:56.127 It turns out, you can look at cold hydrogen gas because 28:56.133 --> 28:59.303 hydrogen gas emits radio waves at a wavelength 28:59.300 --> 29:00.770 of 21 centimeters. 29:00.767 --> 29:04.267 And even before stars and galaxies formed, 29:04.267 --> 29:07.527 you should still be able to see this hydrogen gas and the 29:07.533 --> 29:11.473 further away it is, the more redshifted it has become, 29:11.467 --> 29:14.797 and so you could, in principle, go back to redshifts of 20 or 29:14.800 --> 29:18.330 more looking at just the hydrogen gas. 29:18.333 --> 29:21.573 To do this requires arrays of radio telescope, 29:21.567 --> 29:25.567 and they have to be sensitive to very long wavelengths, 29:25.567 --> 29:28.197 because it's 21 centimeter radiation, 29:28.200 --> 29:30.100 but redshifted by a factor of 20, 29:30.100 --> 29:32.900 so that's now about at 400 centimeters, 29:32.900 --> 29:35.570 four-meter wavelengths. 29:35.567 --> 29:37.527 Four-meter wavelengths and so forth. 29:37.533 --> 29:40.033 That is to say, very low frequencies. 29:40.033 --> 29:46.573 And, there are a couple of ground-based radio telescope 29:46.567 --> 29:47.927 arrays being planned. 29:47.933 --> 29:51.033 LOFAR is the low-frequency array, 29:51.033 --> 29:54.733 WMA is an array in Australia, and eventually, 29:54.733 --> 30:00.803 something called SKA that stands for the Square Kilometer Array. 30:00.800 --> 30:06.900 A square kilometer, solidly covered by radio telescopes 30:06.900 --> 30:09.730 that's going to be built partly in South Africa, 30:09.733 --> 30:12.003 and partly in Australia. 30:12.000 --> 30:15.600 You need to build these things in the desert because - 30:15.600 --> 30:18.930 cell phones, very bad for radial astronomy. 30:18.933 --> 30:22.533 And so, the middle of the uninhabited Australian desert 30:22.533 --> 30:24.603 turns out to be the only place in the world you can 30:24.600 --> 30:26.600 really do this. 30:27.867 --> 30:30.367 So, the current state of cosmology is 30:30.367 --> 30:31.567 basically the following. 30:31.567 --> 30:36.027 One of the great triumphs of 21st century science, 30:36.033 --> 30:40.033 and really realized in the first decade of the 21st century, 30:40.033 --> 30:43.733 has been that we really now do understand the dynamics of the 30:43.733 --> 30:47.633 universe - what its age is, what its constituents are, 30:47.633 --> 30:52.573 how fast it's expanding, how will it expand in the future, 30:52.567 --> 30:53.967 and so forth. 30:53.967 --> 30:56.427 This is really a remarkable triumph; 30:56.433 --> 30:58.233 you wouldn't have thought that cosmology would be a 30:58.233 --> 30:59.503 science at all. 30:59.500 --> 31:02.000 It's only one object and we're in the middle of it, 31:02.000 --> 31:04.000 how can you figure stuff out? 31:04.000 --> 31:08.400 But we can, and so, we have this concordance cosmology, 31:08.400 --> 31:12.370 which really seems to be true, but we don't understand the 31:12.367 --> 31:15.567 details of the things the universe contains. 31:15.567 --> 31:17.267 We don't know what the dark matter is, 31:17.267 --> 31:19.197 we don't know what the dark energy is, 31:19.200 --> 31:23.130 we haven't mapped the clumping of the gas during the dark ages, 31:23.133 --> 31:26.103 and we don't understand the gastrophysics of the radiating 31:26.100 --> 31:29.300 objects - the stars and galaxies themselves. 31:29.300 --> 31:33.600 So, there's plenty of work to be done in the 21st century, 31:33.600 --> 31:38.000 but it will all be based on this basic picture of cosmology 31:38.000 --> 31:41.200 that's been developed since 1998. 31:41.200 --> 31:43.830 Thank you.