1 00:00:03,044 --> 00:00:06,839 For thousands of years, we have looked at the night sky... 2 00:00:06,881 --> 00:00:09,299 and believed that the illuminated stuff... 3 00:00:09,342 --> 00:00:12,219 was all that made up our universe. 4 00:00:15,390 --> 00:00:19,351 Scientists now realize it's not what shines in the light... 5 00:00:19,394 --> 00:00:21,270 but what hides in the dark... 6 00:00:21,312 --> 00:00:24,481 that holds the true secrets of our sky. 7 00:00:25,650 --> 00:00:27,776 There is a mysterious dark matter... 8 00:00:27,819 --> 00:00:30,821 that binds stars and galaxies together... 9 00:00:30,864 --> 00:00:35,409 and strange particles like WIMPS, axions, and MACHOs... 10 00:00:35,452 --> 00:00:36,785 might be to blame. 11 00:00:37,954 --> 00:00:40,914 And there is a dark, repulsive energy... 12 00:00:40,957 --> 00:00:44,209 that is creating space in the universe... 13 00:00:44,252 --> 00:00:47,629 but driving the galaxies further and further apart... 14 00:00:47,672 --> 00:00:49,048 to a dismal fate. 15 00:00:51,092 --> 00:00:54,219 Combined, dark matter and dark energy... 16 00:00:54,262 --> 00:00:58,348 make up ninety-six percent of the universe... 17 00:00:58,391 --> 00:01:00,309 and uncovering their secrets... 18 00:01:00,351 --> 00:01:03,187 is like making the one-in-a-million shot. 19 00:01:03,229 --> 00:01:07,066 If uncovered, the ultimate fate of the universe... 20 00:01:07,108 --> 00:01:08,192 might be revealed. 21 00:01:09,569 --> 00:01:12,780 Will it crash and burn in a horrific collision... 22 00:01:12,822 --> 00:01:15,741 of gravitational forces... 23 00:01:15,784 --> 00:01:20,079 or will dark energy tear the universe apart? 24 00:01:20,121 --> 00:01:24,124 The betting is the universe will die in ice. 25 00:01:24,167 --> 00:01:27,920 Understanding these two quantities, dark matter and dark energy... 26 00:01:27,962 --> 00:01:30,923 is really fundamental to understanding the universe. 27 00:01:30,965 --> 00:01:34,051 This is a trip to the dark side of the universe. 28 00:01:36,805 --> 00:01:41,016 This is the hunt for "Dark Matter and Dark Energy. " 29 00:01:55,281 --> 00:02:00,452 Dark matter is unlike anything we have ever encountered on Earth. 30 00:02:00,495 --> 00:02:02,663 Billions of these strange particles... 31 00:02:02,705 --> 00:02:06,792 pass through everything they encounter each second. 32 00:02:06,835 --> 00:02:08,961 They are so massive in weight... 33 00:02:09,003 --> 00:02:12,631 they have the power to influence the galaxies- 34 00:02:12,674 --> 00:02:15,759 how they form and how fast they spin. 35 00:02:20,181 --> 00:02:23,642 Dark matter's invisible presence is everywhere... 36 00:02:23,685 --> 00:02:25,978 or so it seems. 37 00:02:26,020 --> 00:02:31,150 Science has not directly proven dark matter particles exist. 38 00:02:31,192 --> 00:02:34,486 There are many suspects, but no answers... 39 00:02:34,529 --> 00:02:38,365 and observing something you can't see isn't easy. 40 00:02:40,201 --> 00:02:42,828 It doesn't emit light, and it doesn't absorb light. 41 00:02:42,871 --> 00:02:44,913 It doesn't interact with light at all. 42 00:02:46,624 --> 00:02:48,250 Not only does it not shine... 43 00:02:48,293 --> 00:02:50,627 you can't easily see it in obscuration. 44 00:02:51,713 --> 00:02:55,340 But the evidence is there. Science knows it. 45 00:02:55,383 --> 00:02:57,551 Every textbook on the planet Earth... 46 00:02:57,594 --> 00:02:59,636 says that the universe is made out of atoms... 47 00:02:59,679 --> 00:03:01,638 and some subatomic particles. 48 00:03:01,681 --> 00:03:05,934 Well, all those textbooks are wrong. 49 00:03:05,977 --> 00:03:09,396 And they are going underground to prove it. 50 00:03:09,439 --> 00:03:12,024 When they hear about this invisible matter... 51 00:03:12,066 --> 00:03:15,152 called dark matter, they say, "Bah, humbug. 52 00:03:15,195 --> 00:03:18,030 "Show me proof that dark matter exists. " 53 00:03:21,034 --> 00:03:26,747 Soudan, Minnesota, 200 miles from any major city lights... 54 00:03:26,789 --> 00:03:29,666 a perfect place for hunting dark matter... 55 00:03:29,709 --> 00:03:32,169 but not for obvious reasons. 56 00:03:32,212 --> 00:03:35,130 So you'd think we'd want to look up in the sky for dark matter. 57 00:03:35,173 --> 00:03:37,382 That's where dark matter is coming from, after all. 58 00:03:37,425 --> 00:03:39,009 But instead, we're going to don our helmets... 59 00:03:39,052 --> 00:03:40,928 and we're going to walk down into this mine. 60 00:03:45,516 --> 00:03:51,605 2,431 feet underground is the Soudan National Laboratory... 61 00:03:51,648 --> 00:03:56,902 an abandoned iron mine reconfigured into a research facility. 62 00:03:56,945 --> 00:03:59,863 This is just one lab of many around the world... 63 00:03:59,906 --> 00:04:04,743 going underground to shield experiments from cosmic rays. 64 00:04:06,120 --> 00:04:09,748 Each are racing to detect dark matter- 65 00:04:09,791 --> 00:04:13,627 an invisible particle that has only been indirectly observed... 66 00:04:13,670 --> 00:04:15,337 but never captured. 67 00:04:17,382 --> 00:04:20,592 We've been at this for, now, a decade... 68 00:04:20,635 --> 00:04:22,928 and we have yet to see a dark matter particle. 69 00:04:25,098 --> 00:04:28,976 The hunt for dark matter started almost a century ago. 70 00:04:29,018 --> 00:04:33,563 Astronomers finally had the tools to see deep into the night sky... 71 00:04:33,606 --> 00:04:35,899 and the questions began. 72 00:04:35,942 --> 00:04:37,818 So it wasn't until the 1920s... 73 00:04:37,860 --> 00:04:40,487 that the technology developed well enough... 74 00:04:40,530 --> 00:04:43,031 so that we could take the little fuzzy patches... 75 00:04:43,074 --> 00:04:45,158 that people had noticed in their telescopes... 76 00:04:45,201 --> 00:04:47,995 and resolve them and figure out what they are. 77 00:04:48,037 --> 00:04:50,956 Then, Edwin Hubble shocked the world... 78 00:04:50,999 --> 00:04:55,210 and declared the universe was bigger than just the Milky Way. 79 00:04:55,253 --> 00:04:57,963 People realized that some of these little fuzzy patches... 80 00:04:58,006 --> 00:05:01,675 are separate galaxies, just like our Milky Way galaxy. 81 00:05:04,679 --> 00:05:07,597 As astronomers discovered new galaxies... 82 00:05:07,640 --> 00:05:10,517 Cal Tech professor Fritz Zwicky looked up... 83 00:05:10,560 --> 00:05:13,145 to the neighboring Coma Cluster of galaxies... 84 00:05:13,187 --> 00:05:15,397 and observed something strange. 85 00:05:17,692 --> 00:05:19,776 When he measured what the motions were... 86 00:05:19,819 --> 00:05:22,195 in the Coma Cluster of galaxies... 87 00:05:22,238 --> 00:05:26,116 he got an estimate for how much mass there was in that cluster. 88 00:05:26,159 --> 00:05:28,535 Then he compared it to how much mass... 89 00:05:28,578 --> 00:05:30,996 you could actually see by looking at the galaxies. 90 00:05:32,457 --> 00:05:34,458 Something didn't add up. 91 00:05:34,500 --> 00:05:37,836 The galaxies were moving too fast within the cluster... 92 00:05:37,879 --> 00:05:40,881 for the amount of illuminated stuff he could see. 93 00:05:42,550 --> 00:05:44,009 By his calculations... 94 00:05:44,052 --> 00:05:47,846 there should have been 160 times more illuminated mass... 95 00:05:47,889 --> 00:05:51,224 to account for the random speeds of galaxies in the cluster. 96 00:05:51,893 --> 00:05:54,603 Something else was affecting their motions... 97 00:05:54,645 --> 00:05:55,979 but what was it? 98 00:05:57,982 --> 00:05:59,441 He analyzed their motions... 99 00:05:59,484 --> 00:06:02,652 and concluded that the cluster could not be stable... 100 00:06:02,695 --> 00:06:05,113 unless there was a large amount of dark matter present. 101 00:06:05,156 --> 00:06:08,033 In 1933, he was one of the first people... 102 00:06:08,076 --> 00:06:10,160 to really grasp the significance... 103 00:06:10,203 --> 00:06:11,536 of the presence of dark matter. 104 00:06:11,579 --> 00:06:13,038 He called it "missing matter. " 105 00:06:14,707 --> 00:06:19,711 Dark matter, an invisible mass that was gravitationally attractive... 106 00:06:19,754 --> 00:06:21,713 and was able to affect the speeds... 107 00:06:21,756 --> 00:06:25,092 of entire galaxies in a cluster. 108 00:06:25,134 --> 00:06:26,635 Revolutionary thinking? 109 00:06:26,677 --> 00:06:30,847 Yes, but the discovery was largely ignored. 110 00:06:33,810 --> 00:06:36,395 I think that people took Zwicky seriously... 111 00:06:36,437 --> 00:06:38,021 but they didn't jump to any conclusions. 112 00:06:38,064 --> 00:06:39,898 This was a time when the universe... 113 00:06:39,941 --> 00:06:41,441 was just beginning to be explored. 114 00:06:41,484 --> 00:06:43,568 It was the 1920s when we first realized... 115 00:06:43,611 --> 00:06:45,695 there were galaxies outside our own. 116 00:06:45,738 --> 00:06:49,282 What we didn't know back then was whether it was simply galaxies... 117 00:06:49,325 --> 00:06:51,952 or stars or gas or dust that we couldn't see... 118 00:06:51,994 --> 00:06:53,662 or whether it was something truly different. 119 00:06:55,706 --> 00:06:58,917 Zwicky's observations were based on measuring the mass... 120 00:06:58,960 --> 00:07:01,753 in the stars and galaxies. 121 00:07:01,796 --> 00:07:04,589 But how do you weigh stuff in space? 122 00:07:06,676 --> 00:07:08,718 You can't go and put the Sun on a scale. 123 00:07:08,761 --> 00:07:09,761 It's a little bit hard. 124 00:07:09,804 --> 00:07:11,596 But what you can do is you can measure... 125 00:07:11,639 --> 00:07:14,724 how fast the planets are moving around the Sun. 126 00:07:14,767 --> 00:07:16,518 And the more stuff there is in the Sun... 127 00:07:16,561 --> 00:07:18,061 the faster those planets have to move... 128 00:07:18,104 --> 00:07:19,771 to stay in their orbits. 129 00:07:20,815 --> 00:07:23,358 Newton and Einstein both said... 130 00:07:23,401 --> 00:07:26,945 the more mass or stuff you have in an object... 131 00:07:26,988 --> 00:07:29,823 the more gravitational pull it will have. 132 00:07:30,825 --> 00:07:33,910 And the further an object is from the center... 133 00:07:33,953 --> 00:07:36,496 the slower it should travel in orbit... 134 00:07:36,539 --> 00:07:39,499 because the gravitational pull is weaker. 135 00:07:40,877 --> 00:07:43,628 According to Einstein's general theory of relativity... 136 00:07:43,671 --> 00:07:46,339 or even according to Newtonian gravity... 137 00:07:46,382 --> 00:07:49,384 all of the galaxies are pulling on each other. 138 00:07:50,970 --> 00:07:55,182 It's like the Sun's influence on our solar system. 139 00:07:55,224 --> 00:07:58,977 The mass of the Sun pulls Mercury faster than Pluto... 140 00:07:59,020 --> 00:08:02,689 because Mercury is positioned closer to the Sun. 141 00:08:02,732 --> 00:08:04,691 Likewise for a galaxy, you would expect... 142 00:08:04,734 --> 00:08:06,651 as you got further and further away... 143 00:08:06,694 --> 00:08:08,570 things are moving more and more slowly... 144 00:08:08,613 --> 00:08:10,155 to stay in their orbits. 145 00:08:10,198 --> 00:08:12,782 But Zwicky didn't observe that. 146 00:08:12,825 --> 00:08:17,245 Neither did a young scientist named Vera Rubin fifty years later. 147 00:08:17,288 --> 00:08:19,372 She was observing the rotational curves... 148 00:08:19,415 --> 00:08:22,334 of galaxies similar to the Milky Way. 149 00:08:24,378 --> 00:08:28,465 Like Zwicky, her observations also seemed strange. 150 00:08:30,259 --> 00:08:32,260 What Vera Rubin actually measured was... 151 00:08:32,303 --> 00:08:34,179 as you got further and further away... 152 00:08:34,222 --> 00:08:37,974 the velocity of the orbiting gas and dust remained constant. 153 00:08:39,060 --> 00:08:42,562 What Rubin observed was as if a city were a galaxy... 154 00:08:42,605 --> 00:08:46,525 and every car on the road was a planet or star. 155 00:08:46,567 --> 00:08:48,735 And despite the amount of traffic... 156 00:08:48,778 --> 00:08:52,280 every car traveled around the city at the same speed. 157 00:08:54,033 --> 00:08:57,077 This same, consistent rotational speed... 158 00:08:57,119 --> 00:09:00,330 despite the amount of stuff, or traffic... 159 00:09:00,373 --> 00:09:02,707 was exactly what Rubin observed. 160 00:09:05,253 --> 00:09:07,754 The outer parts of the galaxy were rotating fast enough... 161 00:09:07,797 --> 00:09:09,548 that there must be a lot more mass. 162 00:09:09,590 --> 00:09:11,383 Otherwise, the galaxy would have flown apart. 163 00:09:11,425 --> 00:09:13,718 The only way to resolve this paradox... 164 00:09:13,761 --> 00:09:16,555 of galaxies which spin ten times too fast... 165 00:09:16,597 --> 00:09:19,808 is to assume that there is a halo... 166 00:09:19,850 --> 00:09:23,562 a halo of invisible matter surrounding the galaxy... 167 00:09:23,604 --> 00:09:25,105 keeping the galaxy whole. 168 00:09:26,649 --> 00:09:29,693 Dark matter was present in the galaxies... 169 00:09:29,735 --> 00:09:34,030 and it had enough mass to keep the rotation speed constant. 170 00:09:35,449 --> 00:09:37,242 Imagine that I am the dark matter. 171 00:09:37,285 --> 00:09:39,578 This ball is a star orbiting me... 172 00:09:39,620 --> 00:09:42,914 because my gravitational force is keeping it in place. 173 00:09:42,957 --> 00:09:44,624 But even if you couldn't see me... 174 00:09:44,667 --> 00:09:46,418 you would know there must be something here. 175 00:09:46,460 --> 00:09:49,170 Otherwise, the star would just zoom off in a straight line. 176 00:09:49,213 --> 00:09:51,131 There must be something causing that gravity... 177 00:09:51,173 --> 00:09:53,466 and that's how we know that there must be dark matter. 178 00:09:54,719 --> 00:09:58,722 Rubin estimated that there was ten times more dark matter... 179 00:09:58,764 --> 00:10:00,974 than ordinary illuminated stuff. 180 00:10:03,060 --> 00:10:06,104 Since then, we've analyzed hundreds of galaxies... 181 00:10:06,147 --> 00:10:08,106 and they all have the same pattern. 182 00:10:08,149 --> 00:10:10,567 They all rotate too fast for their own good... 183 00:10:10,610 --> 00:10:13,320 and they need dark matter to hold them together. 184 00:10:13,362 --> 00:10:15,822 This time, science paid attention... 185 00:10:15,865 --> 00:10:19,534 and started to wonder: What is dark matter? 186 00:10:19,577 --> 00:10:22,912 How do you find something that is invisible in space? 187 00:10:24,915 --> 00:10:27,417 They needed to see just where dark matter... 188 00:10:27,460 --> 00:10:29,919 was hiding out in the universe. 189 00:10:29,962 --> 00:10:31,963 And even if they couldn't see it... 190 00:10:32,006 --> 00:10:35,842 science realized that dark matter exposed itself... 191 00:10:35,885 --> 00:10:38,219 by bending light that passes through it. 192 00:10:39,347 --> 00:10:44,184 It's called gravitational lensing, and it's a virtual spotlight... 193 00:10:44,226 --> 00:10:48,063 that uncovers any invisible stuff in the universe. 194 00:10:48,105 --> 00:10:51,816 What it does do is it does what all matter does... 195 00:10:51,859 --> 00:10:54,402 in that it can deflect the light ray. 196 00:10:54,445 --> 00:10:59,908 So a light ray can be deflected in its path by dark matter. 197 00:10:59,950 --> 00:11:02,494 By tracing the battered light's path... 198 00:11:02,536 --> 00:11:05,789 gravitational lensing detected dark matter... 199 00:11:05,831 --> 00:11:09,501 concentrated in the halos of galaxies. 200 00:11:09,543 --> 00:11:12,504 Gravitational lensing proved to be infallible... 201 00:11:12,546 --> 00:11:15,882 and dark matter's presence was suddenly revealed. 202 00:11:17,677 --> 00:11:19,594 This technique of gravitational lensing... 203 00:11:19,637 --> 00:11:22,806 is the most precise because we can actually pinpoint... 204 00:11:22,848 --> 00:11:25,475 not just how much dark matter there is... 205 00:11:25,518 --> 00:11:29,521 but how it's distributed in its position on the sky. 206 00:11:29,563 --> 00:11:32,399 And that's because we can measure the distortion... 207 00:11:32,441 --> 00:11:35,318 of the light rays passing through the dark matter. 208 00:11:35,361 --> 00:11:38,029 How do you know that your glasses are there? 209 00:11:38,072 --> 00:11:39,322 Because it bends light. 210 00:11:39,365 --> 00:11:40,699 In the same way... 211 00:11:40,741 --> 00:11:43,660 by looking at Hubble space pictures of the universe... 212 00:11:43,703 --> 00:11:46,037 and looking at the distortion of light... 213 00:11:46,080 --> 00:11:47,706 as it goes through galaxies... 214 00:11:47,748 --> 00:11:50,083 we actually have maps of dark matter. 215 00:11:51,711 --> 00:11:54,713 Most of the mass of a galaxy is from the dark matter. 216 00:11:54,755 --> 00:11:56,840 The ordinary matter accumulates... 217 00:11:56,882 --> 00:11:59,175 in the gravitational field of the dark matter. 218 00:12:00,845 --> 00:12:03,221 But once dark matter came on the scene... 219 00:12:03,264 --> 00:12:07,308 scientists wondered if it was a new, undetected particle... 220 00:12:07,351 --> 00:12:10,019 orjust invisible ordinary matter. 221 00:12:11,105 --> 00:12:12,981 When people found dark matter... 222 00:12:13,023 --> 00:12:15,358 everybody wanted to know, well, what is it, you know? 223 00:12:15,401 --> 00:12:17,360 And, of course, the first answer is... 224 00:12:17,403 --> 00:12:19,404 it's just the stuff that makes up you and me... 225 00:12:19,447 --> 00:12:20,488 but it's not shining. 226 00:12:21,699 --> 00:12:24,075 Scientists started to investigate objects... 227 00:12:24,118 --> 00:12:27,912 in the universe that didn't emit light. 228 00:12:27,955 --> 00:12:29,789 Black holes were considered. 229 00:12:29,832 --> 00:12:33,418 They don't emit light, can draw matter to themselves... 230 00:12:33,461 --> 00:12:36,880 and are detected with gravitational lensing. 231 00:12:36,922 --> 00:12:38,423 It could take a form of black holes... 232 00:12:38,466 --> 00:12:41,843 or MACHOs, massive compact halo objects... 233 00:12:41,886 --> 00:12:44,763 which are basically dark, small stars... 234 00:12:44,805 --> 00:12:46,222 that don't give off a lot of light. 235 00:12:46,265 --> 00:12:49,976 MACHOs hide out in the halo of the Milky Way... 236 00:12:50,019 --> 00:12:53,229 and are detected by gravitational lensing. 237 00:12:53,272 --> 00:12:54,439 But there weren't enough... 238 00:12:54,482 --> 00:12:57,484 to account for the amount of dark matter needed. 239 00:12:59,820 --> 00:13:03,406 Failed stars like brown dwarfs were also suspected. 240 00:13:04,617 --> 00:13:08,203 They are massive enough to make up dark matter's presence. 241 00:13:08,996 --> 00:13:12,290 Whatever dark matter is, there is way more of it... 242 00:13:12,333 --> 00:13:15,418 than the ordinary matter of stars and planets... 243 00:13:15,461 --> 00:13:17,086 ten times more. 244 00:13:19,215 --> 00:13:20,882 All the stuff that you can construct... 245 00:13:20,925 --> 00:13:24,677 from ordinary atoms, protons, and neutrons and electrons... 246 00:13:24,720 --> 00:13:27,305 cannot possibly be enough... 247 00:13:27,348 --> 00:13:29,098 to account for the total amount of matter... 248 00:13:29,141 --> 00:13:30,934 that you see in galaxies and clusters. 249 00:13:32,228 --> 00:13:35,480 Scientists continued to present new suspects... 250 00:13:35,523 --> 00:13:38,066 as the search continued for dark matter. 251 00:13:38,901 --> 00:13:41,277 Previously discovered exotic particles... 252 00:13:41,320 --> 00:13:43,863 like neutrinos, were reconsidered. 253 00:13:45,241 --> 00:13:48,743 Like dark matter, neutrinos are passing through the Earth... 254 00:13:48,786 --> 00:13:51,246 millions of particles at a time... 255 00:13:51,288 --> 00:13:52,455 but they are too light... 256 00:13:52,498 --> 00:13:55,625 to account for dark matter's effect on gravity... 257 00:13:55,668 --> 00:14:00,505 and scientists can recreate neutrinos in particle colliders. 258 00:14:00,548 --> 00:14:02,549 They also come from the Sun. 259 00:14:04,635 --> 00:14:07,929 Axions is also another possible dark matter candidate. 260 00:14:07,972 --> 00:14:11,933 They were invented to explain a particular glitch... 261 00:14:11,976 --> 00:14:14,435 in one of the particle physics theories. 262 00:14:14,478 --> 00:14:16,437 They would be extremely light... 263 00:14:16,480 --> 00:14:18,982 so you search for them in a completely different way... 264 00:14:19,024 --> 00:14:21,192 than what we're doing, but there would be... 265 00:14:21,235 --> 00:14:22,652 They would also be very numerous. 266 00:14:22,695 --> 00:14:25,488 And so they could possibly be the dark matter. 267 00:14:25,531 --> 00:14:27,115 Axions are very light... 268 00:14:27,157 --> 00:14:28,700 and are believed to have been created... 269 00:14:28,742 --> 00:14:32,829 at the moment of the Big Bang, just like dark matter. 270 00:14:32,872 --> 00:14:36,207 But theories suggest that they can change to protons... 271 00:14:36,250 --> 00:14:38,251 while dark matter is stable. 272 00:14:39,378 --> 00:14:41,963 After exhausting all the usual suspects... 273 00:14:42,006 --> 00:14:46,384 many scientists believe dark matter is a new, exotic particle... 274 00:14:46,427 --> 00:14:48,887 unlike anything on Earth... 275 00:14:48,929 --> 00:14:52,765 and billions are passing through us every second. 276 00:14:55,185 --> 00:14:58,021 Up until the discovery of dark matter... 277 00:14:58,063 --> 00:15:00,023 scientists believed the universe... 278 00:15:00,065 --> 00:15:04,027 was made only of protons, neutrons, and electrons... 279 00:15:04,069 --> 00:15:06,863 the stuff everything on Earth is made of. 280 00:15:08,073 --> 00:15:09,908 And we know it has some mass. 281 00:15:09,950 --> 00:15:13,244 And we're left with something that we've not yet detected. 282 00:15:14,288 --> 00:15:16,873 But to be a perfect dark matter candidate... 283 00:15:16,916 --> 00:15:19,751 it must have certain physical properties... 284 00:15:19,793 --> 00:15:22,837 and none of the usual suspects were fitting the crime. 285 00:15:23,797 --> 00:15:27,383 So we know the dark matter is some ponderous substance... 286 00:15:27,426 --> 00:15:29,344 we know that it's not moving too quickly... 287 00:15:29,386 --> 00:15:30,678 and we know that we can't see it. 288 00:15:30,721 --> 00:15:34,223 Dark matter particles are not traveling at the speed of light... 289 00:15:34,266 --> 00:15:37,769 and they don't interact with you and me... 290 00:15:37,811 --> 00:15:40,104 or anything pretty well, and that's why it's been so difficult... 291 00:15:40,147 --> 00:15:42,607 to track down these particles. 292 00:15:42,650 --> 00:15:44,525 And it doesn't interact with ordinary matter... 293 00:15:44,568 --> 00:15:46,235 except through gravity. 294 00:15:46,278 --> 00:15:48,446 If I had some dark matter in my hand... 295 00:15:48,489 --> 00:15:49,614 it would have weight. 296 00:15:49,657 --> 00:15:52,533 But first it would dissolve right through my fingers. 297 00:15:54,828 --> 00:15:57,205 There aren't any candidates for cold dark matter... 298 00:15:57,247 --> 00:15:59,999 within what we call the standard model particle physics. 299 00:16:02,086 --> 00:16:05,004 Like an invisible man passing through walls... 300 00:16:05,047 --> 00:16:09,384 dark matter is passing through Earth billions of particles at a time... 301 00:16:09,426 --> 00:16:11,886 never colliding with ordinary matter. 302 00:16:13,681 --> 00:16:17,016 So the most popular idea for what the dark matter could be... 303 00:16:17,059 --> 00:16:18,184 is something called a WIMP. 304 00:16:19,061 --> 00:16:22,563 WIMPs are weakly interacting massive particles. 305 00:16:22,606 --> 00:16:25,525 They have not been detected, but their characteristics... 306 00:16:25,567 --> 00:16:27,860 match the perfect dark matter candidate. 307 00:16:30,447 --> 00:16:32,573 At the Soudan Laboratory... 308 00:16:32,616 --> 00:16:35,493 the Fermilab team has gone underground... 309 00:16:35,536 --> 00:16:37,912 braving thousands of bats... 310 00:16:37,955 --> 00:16:40,206 to try and capture a WIMP particle. 311 00:16:41,542 --> 00:16:44,460 This is called the cryogenic dark matter search. 312 00:16:44,503 --> 00:16:46,671 CDMS is the acronym for it. 313 00:16:46,714 --> 00:16:52,468 This was an iron ore mine until 1962 when it shut down. 314 00:16:52,511 --> 00:16:54,679 We're half a mile underground. 315 00:16:54,722 --> 00:16:58,766 Fermilab has designed a machine that, at subzero temperatures... 316 00:16:58,809 --> 00:17:02,061 can detect a dark matter particle passing through it... 317 00:17:03,022 --> 00:17:05,273 and its sensor is made of germanium... 318 00:17:05,315 --> 00:17:08,609 a dense metal jam-packed with atoms. 319 00:17:08,652 --> 00:17:11,821 It's a very pure block of germanium. 320 00:17:11,864 --> 00:17:14,490 It's got on the surface of it... 321 00:17:14,533 --> 00:17:17,702 a pattern of tiny little thermometers, basically... 322 00:17:17,745 --> 00:17:20,538 that are able to detect when a particle passes... 323 00:17:20,581 --> 00:17:25,043 through this hockey puck-sized chunk of germanium. 324 00:17:25,085 --> 00:17:27,086 Dark matter is streaming right through us right now... 325 00:17:27,129 --> 00:17:28,421 without doing anything. 326 00:17:29,965 --> 00:17:33,384 Very occasionally, it will bump into the nucleus of an atom. 327 00:17:33,427 --> 00:17:36,262 And that's the signature that we're hoping to see. 328 00:17:37,264 --> 00:17:39,307 To get a clean dark matter hit... 329 00:17:39,349 --> 00:17:42,894 Fermilab needed to filter out junk from space. 330 00:17:43,937 --> 00:17:45,605 We would get so many particles... 331 00:17:45,647 --> 00:17:49,901 that it would be really trying to sift a needle in a haystack. 332 00:17:49,943 --> 00:17:52,904 Fermilab's experiment picks up all matter... 333 00:17:52,946 --> 00:17:54,739 that passes through this detector. 334 00:17:55,491 --> 00:17:56,908 The less junk in the air... 335 00:17:56,950 --> 00:18:00,620 the easier it will be to detect a dark matter particle. 336 00:18:03,373 --> 00:18:05,958 Because dark matter doesn't interact easily... 337 00:18:06,001 --> 00:18:08,753 with regular protons and electrons... 338 00:18:08,796 --> 00:18:11,631 Fermilab has frozen the germanium pucks... 339 00:18:11,673 --> 00:18:13,841 to near subzero temperatures. 340 00:18:14,843 --> 00:18:17,595 If a dark matter particle comes through and hits a nucleus... 341 00:18:17,638 --> 00:18:22,433 it will actually change the temperature of the crystal very slightly... 342 00:18:22,476 --> 00:18:24,143 and so we're looking for that tiny change... 343 00:18:24,186 --> 00:18:26,062 of temperature in the crystal... 344 00:18:26,105 --> 00:18:29,565 to signal that a dark matter particle has passed by. 345 00:18:29,608 --> 00:18:31,400 Sixteen germanium pucks... 346 00:18:31,443 --> 00:18:34,237 sit in a chamber inside a clean room. 347 00:18:35,322 --> 00:18:36,531 So we're suited up... 348 00:18:36,573 --> 00:18:38,783 we're about to go into the experimental room. 349 00:18:38,826 --> 00:18:40,493 It's a Class 10,000 clean room. 350 00:18:40,536 --> 00:18:43,246 That's why we're all suited up so we don't carry in any dust... 351 00:18:43,288 --> 00:18:45,623 because that would cause background for the experiment. 352 00:18:45,666 --> 00:18:46,999 So let's go inside. 353 00:18:50,462 --> 00:18:53,256 So we have scintillation counters... 354 00:18:53,298 --> 00:18:56,467 that are catching any cosmic-ray particles... 355 00:18:56,510 --> 00:18:58,970 that get all the way down underground here. 356 00:18:59,012 --> 00:19:02,306 So right here is what keeps our experiment cold... 357 00:19:02,349 --> 00:19:03,975 a tiny little bit above absolute zero. 358 00:19:04,017 --> 00:19:05,685 This is the dilution refrigerator. 359 00:19:07,020 --> 00:19:08,187 So way inside here... 360 00:19:08,230 --> 00:19:10,231 are the germanium and silicon detectors... 361 00:19:10,274 --> 00:19:14,610 so we're just waiting for a WIMP, a dark matter particle... 362 00:19:14,653 --> 00:19:16,445 to get down to this depth... 363 00:19:16,488 --> 00:19:18,656 and hit one of those germanium and silicon crystals... 364 00:19:18,699 --> 00:19:20,950 that's buried way inside all the shields. 365 00:19:21,702 --> 00:19:25,329 Fermilab has been visiting the mine for nearly two years... 366 00:19:25,372 --> 00:19:27,790 trying to capture dark matter. 367 00:19:29,042 --> 00:19:31,377 This is far harder than it sounds. 368 00:19:31,420 --> 00:19:35,506 Although billions of particles are passing through Earth at one time... 369 00:19:35,549 --> 00:19:37,216 it's a one-in-a-million shot... 370 00:19:37,259 --> 00:19:40,261 dark matter will interact with ordinary matter. 371 00:19:42,347 --> 00:19:45,308 Getting a dark matter particle to hit a germanium atom... 372 00:19:45,350 --> 00:19:47,685 is like an archer trying to hit a bull's eye... 373 00:19:51,982 --> 00:19:54,483 when the target is a mile away. 374 00:19:55,485 --> 00:19:57,361 All these green lights indicate particles... 375 00:19:57,404 --> 00:19:59,697 passing through the germanium and silicon detectors... 376 00:19:59,740 --> 00:20:01,073 that we saw downstairs. 377 00:20:02,075 --> 00:20:04,660 These are almost certainly all background particles. 378 00:20:04,703 --> 00:20:07,038 But maybe it's buried in there someplace as a WIMP... 379 00:20:07,080 --> 00:20:09,248 but we won't know until we analyze the data. 380 00:20:10,083 --> 00:20:12,251 Hunting dark matter is tedious. 381 00:20:12,294 --> 00:20:16,297 Each day, the Fermilab team reports to the underground lab... 382 00:20:16,340 --> 00:20:20,259 analyzes data, and perfects their ping-pong game... 383 00:20:20,302 --> 00:20:24,764 while waiting for the one hit that will prove dark matter exists. 384 00:20:26,850 --> 00:20:30,102 But for all this effort and waiting around... 385 00:20:30,145 --> 00:20:35,316 no dark matter has been detected by Fermilab or by anyone else. 386 00:20:36,068 --> 00:20:37,360 Unfortunately, we've seen... 387 00:20:37,402 --> 00:20:40,696 precisely zero dark matter particles so far. 388 00:20:45,285 --> 00:20:47,370 Any day now, we may have the announcement... 389 00:20:47,412 --> 00:20:50,498 that physicists have captured dark matter in a bottle. 390 00:20:50,540 --> 00:20:53,626 We have a hypothesis. 391 00:20:53,669 --> 00:20:56,921 It certainly seems to explain the universe we live in. 392 00:20:56,964 --> 00:20:58,923 But the plain fact is we haven't yet detected... 393 00:20:58,966 --> 00:21:00,466 this cold dark matter particle. 394 00:21:01,593 --> 00:21:06,055 Finding dark matter will not only give us proof of its existence... 395 00:21:06,098 --> 00:21:09,976 but might also answer the other big questions of space. 396 00:21:12,062 --> 00:21:13,604 Detecting dark matter directly... 397 00:21:13,647 --> 00:21:16,816 will give us a window onto what was going on... 398 00:21:16,858 --> 00:21:19,777 1/10,000th of a second after the Big Bang. 399 00:21:21,738 --> 00:21:25,157 If scientists can discover what dark matter is... 400 00:21:25,200 --> 00:21:29,996 they might also discover how the universe behaved early in its life. 401 00:21:31,206 --> 00:21:34,959 Dark matter is not only a mysterious quantity in the universe... 402 00:21:35,002 --> 00:21:38,296 but also it's fundamental to our, you know... 403 00:21:38,338 --> 00:21:39,463 why we're here, in fact. 404 00:21:39,506 --> 00:21:41,757 It would be difficult to form galaxies... 405 00:21:41,800 --> 00:21:44,218 and, hence, you know, the solar system... 406 00:21:44,261 --> 00:21:45,928 and, hence, life on Earth. 407 00:21:51,059 --> 00:21:53,769 The story of dark matter and dark energy... 408 00:21:53,812 --> 00:21:58,316 can't be told without going back to the beginning of time... 409 00:21:58,358 --> 00:22:03,529 to the moment of the Big Bang when space didn't exist. 410 00:22:03,572 --> 00:22:06,991 There was no center where you can point to. 411 00:22:07,034 --> 00:22:09,160 And that's exactly the analogy for the Big Bang. 412 00:22:09,202 --> 00:22:11,037 There was no direction in the sky... 413 00:22:11,079 --> 00:22:14,040 from which all the galaxies were expanding. 414 00:22:15,375 --> 00:22:19,003 From this moment of nothing to a violent explosion... 415 00:22:19,046 --> 00:22:24,633 space was created, and the universe began to grow from a seed. 416 00:22:25,886 --> 00:22:30,097 Particles formed in a nuclear fusion of gas and energy. 417 00:22:32,642 --> 00:22:35,644 Ordinary matter was reacting with other ordinary matter. 418 00:22:35,687 --> 00:22:38,439 The early universe was in fact a nuclear reactor... 419 00:22:38,482 --> 00:22:39,899 when it was one minute old. 420 00:22:40,942 --> 00:22:46,864 And 380,000 years later, bits of particles began to cluster... 421 00:22:46,907 --> 00:22:51,911 creating the seeds from which stars and galaxies would later form. 422 00:22:51,953 --> 00:22:54,372 Bigger lumps grow to form yet bigger lumps... 423 00:22:54,414 --> 00:22:56,874 and so gravity is a slowly pulling force... 424 00:22:56,917 --> 00:22:58,793 bringing objects together. 425 00:23:01,088 --> 00:23:05,800 What scientists now realize was that at the moment of the Big Bang... 426 00:23:05,842 --> 00:23:07,927 dark matter was created. 427 00:23:09,513 --> 00:23:13,349 And it played a critical role in helping ordinary matter... 428 00:23:13,392 --> 00:23:17,019 clump together to form stars and planets. 429 00:23:19,981 --> 00:23:22,858 Like steel girders used on a building site... 430 00:23:22,901 --> 00:23:26,987 dark matter's slow-moving particles acted like scaffolding... 431 00:23:27,030 --> 00:23:30,282 upon which ordinary matter could attach itself. 432 00:23:32,702 --> 00:23:36,455 We believe that, because it's cold and doesn't interact very much... 433 00:23:36,498 --> 00:23:39,917 that dark matter was pulled together by gravity... 434 00:23:39,960 --> 00:23:41,961 very slowly over time... 435 00:23:42,003 --> 00:23:44,130 and actually formed the seeds... 436 00:23:44,172 --> 00:23:47,508 around which normal matter coalesced into galaxies. 437 00:23:47,551 --> 00:23:50,511 It's like a cosmic web, like a spider's web... 438 00:23:50,554 --> 00:23:52,972 where there are strands of dark matter... 439 00:23:53,014 --> 00:23:58,102 and where these strands intersect, like a scaffolding pattern. 440 00:23:58,145 --> 00:24:00,729 So in a sense, the dark matter is the framework. 441 00:24:00,772 --> 00:24:02,106 It's providing the scaffolding... 442 00:24:02,149 --> 00:24:05,151 for the shining galaxies that we can easily see. 443 00:24:06,653 --> 00:24:08,696 They are really like the Christmas tree lights. 444 00:24:08,738 --> 00:24:10,489 They're not the actual Christmas tree. 445 00:24:10,532 --> 00:24:13,784 They're the things that are visible from very, very far away. 446 00:24:13,827 --> 00:24:17,163 But the reality of the galaxy is a big halo... 447 00:24:17,205 --> 00:24:18,914 most of which you don't see. 448 00:24:18,957 --> 00:24:21,208 You see the shiny bits that are stars and planets... 449 00:24:21,251 --> 00:24:24,128 that have accumulated at the center of that large halo... 450 00:24:24,171 --> 00:24:25,671 which is mostly dark matter. 451 00:24:27,007 --> 00:24:30,134 Scientists have long wondered why galaxies formed... 452 00:24:30,177 --> 00:24:33,179 in seemingly random patterns across space. 453 00:24:34,347 --> 00:24:39,727 Now scientists know it's because of dark matter's gravitational pull. 454 00:24:39,769 --> 00:24:43,481 The universe is not uniform at all, but has voids. 455 00:24:43,523 --> 00:24:46,525 It has clumps, it seems to have bubble-like regions. 456 00:24:47,527 --> 00:24:50,196 Well, we now believe it's due to dark matter. 457 00:24:52,616 --> 00:24:55,576 In the last year, astronomers have been able... 458 00:24:55,619 --> 00:24:58,204 to take their theory one step further... 459 00:24:58,246 --> 00:25:00,831 and create a detailed 3-D map... 460 00:25:00,874 --> 00:25:05,044 of dark matter in the universe, using gravitational lensing. 461 00:25:06,254 --> 00:25:09,256 And Einstein said that gravity affects everything... 462 00:25:09,299 --> 00:25:11,550 just like gravity is caused by everything. 463 00:25:11,593 --> 00:25:15,638 So one of the things that is affected by gravity is light itself. 464 00:25:15,680 --> 00:25:18,641 Because when light goes through dark matter, it bends... 465 00:25:18,683 --> 00:25:21,227 just the way light bends when it goes through glass. 466 00:25:21,895 --> 00:25:26,273 And light doesn't discriminate between ordinary matter and dark. 467 00:25:26,316 --> 00:25:31,070 Both types of matter batter light's path as it travels through galaxies. 468 00:25:33,990 --> 00:25:36,158 Like plotting a course on a map... 469 00:25:36,201 --> 00:25:39,411 astronomers have traced thousands of light sources... 470 00:25:39,454 --> 00:25:41,497 as they pass through dark matter. 471 00:25:42,415 --> 00:25:45,584 It has given science the most accurate picture yet... 472 00:25:45,627 --> 00:25:47,962 of where dark matter hides in space. 473 00:25:51,758 --> 00:25:54,718 We can compare that map of the dark matter... 474 00:25:54,761 --> 00:25:57,304 with where the galaxies are, and, lo and behold... 475 00:25:57,347 --> 00:26:01,225 we find that the dark matter is acting as the skeleton. 476 00:26:01,268 --> 00:26:05,271 It is the backbone around which the visible material is clumping. 477 00:26:07,607 --> 00:26:12,027 By mapping the universe, astronomers can also look back in time... 478 00:26:12,070 --> 00:26:15,739 and predict how much matter was created at the Big Bang. 479 00:26:17,117 --> 00:26:20,411 So if you know how lumpy the universe appears now... 480 00:26:20,453 --> 00:26:22,204 and when it was half its current size... 481 00:26:22,247 --> 00:26:24,873 and when it was half its current size before that... 482 00:26:24,916 --> 00:26:27,710 you can infer the total amount of stuff in the universe. 483 00:26:27,752 --> 00:26:30,921 It gives us another very nice way of matching on... 484 00:26:30,964 --> 00:26:33,048 to what we believe is the total amount of dark matter. 485 00:26:34,259 --> 00:26:36,010 It's estimated dark matter... 486 00:26:36,052 --> 00:26:39,054 makes up twenty-three percent of the universe... 487 00:26:39,097 --> 00:26:42,600 while ordinary matter makes up only four percent. 488 00:26:43,935 --> 00:26:45,978 You need a lot of dark matter... 489 00:26:46,021 --> 00:26:47,563 to account for the total amount of gravity... 490 00:26:47,606 --> 00:26:49,648 that exists in these clusters and galaxies. 491 00:26:51,985 --> 00:26:55,779 But what makes up the final seventy-three percent of the universe? 492 00:26:56,489 --> 00:26:58,782 Scientists were shocked to discover... 493 00:26:58,825 --> 00:27:03,954 a new mysterious dark energy was dominating space. 494 00:27:03,997 --> 00:27:08,334 And its repulsive energy is driving the galaxies apart. 495 00:27:14,924 --> 00:27:16,717 Science always assumed... 496 00:27:16,760 --> 00:27:20,012 that although the universe continues to grow in size... 497 00:27:20,055 --> 00:27:23,057 it would eventually slow in its expansion... 498 00:27:23,099 --> 00:27:25,643 or perhaps even collapse on itself. 499 00:27:25,685 --> 00:27:29,104 Gravity would overcome any momentum it had. 500 00:27:31,191 --> 00:27:34,485 But while measuring the expansion history of the universe... 501 00:27:34,527 --> 00:27:37,112 scientists were shocked to realize... 502 00:27:37,155 --> 00:27:39,615 that the universe wasn't slowing down. 503 00:27:39,658 --> 00:27:40,991 It was speeding up... 504 00:27:41,868 --> 00:27:45,079 and a grim fate awaited any living thing. 505 00:27:45,789 --> 00:27:47,539 The universe will disintegrate... 506 00:27:47,582 --> 00:27:49,625 and temperatures will become so cold... 507 00:27:49,668 --> 00:27:53,170 that any intelligent life will freeze to death. 508 00:27:55,382 --> 00:27:58,509 From the moment the Big Bang created the universe... 509 00:27:58,551 --> 00:28:02,096 space has been expanding and never stopping... 510 00:28:02,138 --> 00:28:05,391 carrying galaxies along for the ride. 511 00:28:05,433 --> 00:28:09,019 The space in between the galaxies is expanding. 512 00:28:09,062 --> 00:28:11,480 The galaxies are not expanding. 513 00:28:11,523 --> 00:28:12,690 The Earth is not expanding. 514 00:28:12,732 --> 00:28:14,358 The solar system is not expanding. 515 00:28:15,318 --> 00:28:17,027 Edwin Hubble first discovered... 516 00:28:17,070 --> 00:28:21,407 galaxies were moving away from the Milky Way in 1929... 517 00:28:21,449 --> 00:28:24,076 by realizing the more distant galaxies... 518 00:28:24,119 --> 00:28:27,413 move faster away from us than the nearby ones. 519 00:28:28,581 --> 00:28:31,333 He realized he could measure their velocities... 520 00:28:31,376 --> 00:28:34,712 by studying their wavelengths through a prism. 521 00:28:34,754 --> 00:28:37,047 It's called measuring the redshift... 522 00:28:37,090 --> 00:28:40,467 and is still used to measure distances in space. 523 00:28:41,386 --> 00:28:43,220 And he found that, in fact... 524 00:28:43,263 --> 00:28:47,474 the greater the distance of a galaxy right now... 525 00:28:47,517 --> 00:28:49,935 the greater the speed with which it's moving away from us. 526 00:28:49,978 --> 00:28:51,729 That is, the greater its redshift. 527 00:28:52,689 --> 00:28:54,022 A few years ago... 528 00:28:54,065 --> 00:28:57,109 astronomers decided to use redshift measurements... 529 00:28:57,152 --> 00:28:59,820 to measure the expansion history of the universe. 530 00:29:02,574 --> 00:29:03,574 But how do you measure... 531 00:29:03,616 --> 00:29:06,952 the entire expansion history of the universe? 532 00:29:06,995 --> 00:29:11,206 How do you travel back twelve billion years in time? 533 00:29:15,170 --> 00:29:18,422 We have the capability of going back in time directly... 534 00:29:18,465 --> 00:29:20,424 to observe the past. 535 00:29:20,467 --> 00:29:23,886 So, much in the same way as a geologist, you know... 536 00:29:23,928 --> 00:29:25,637 looks at layers in the Grand Canyon... 537 00:29:25,680 --> 00:29:28,432 and as he goes down into lower and lower layers... 538 00:29:28,475 --> 00:29:30,476 looking back in history. 539 00:29:30,518 --> 00:29:34,104 If you look at progressively more distant galaxies... 540 00:29:34,147 --> 00:29:35,898 you're looking at them as they were... 541 00:29:35,940 --> 00:29:38,609 at progressively greater times in the past. 542 00:29:39,652 --> 00:29:44,531 To measure expansion history, scientists used Type 1 a supernovas... 543 00:29:44,574 --> 00:29:46,408 as their standard candle. 544 00:29:48,745 --> 00:29:52,956 One example of a standard candle might be a 100-watt light bulb. 545 00:29:52,999 --> 00:29:54,208 You could have a bunch of these things... 546 00:29:54,250 --> 00:29:57,628 sitting around in your room at different distances from you. 547 00:29:57,670 --> 00:30:01,590 Then the more distant ones will appear fainter... 548 00:30:01,633 --> 00:30:04,635 and the more nearby ones will appear brighter. 549 00:30:04,677 --> 00:30:08,639 Type 1 a supernovas are always consistently brilliant... 550 00:30:08,681 --> 00:30:11,016 no matter where they occur in space. 551 00:30:13,895 --> 00:30:17,481 A supernova is the colossal explosion of a star... 552 00:30:17,524 --> 00:30:18,524 at the end of its life. 553 00:30:18,566 --> 00:30:20,609 It just goes kabam. 554 00:30:22,987 --> 00:30:28,325 And it occurs when a dying star, known as a white dwarf... 555 00:30:28,368 --> 00:30:30,994 goes through a nuclear runaway... 556 00:30:31,037 --> 00:30:33,372 and just literally blows itself to smithereens. 557 00:30:34,916 --> 00:30:38,836 We find the Type 1 a supernovae in very distant galaxies... 558 00:30:38,878 --> 00:30:40,337 so they look really faint. 559 00:30:40,380 --> 00:30:43,423 And then we compare them with Type 1 a supernovae... 560 00:30:43,466 --> 00:30:46,760 in nearby galaxies whose distance were- 561 00:30:46,803 --> 00:30:48,929 Distances were measured using Cepheid variables... 562 00:30:48,972 --> 00:30:50,305 or some other technique. 563 00:30:51,891 --> 00:30:54,560 Using these Type 1 a supernovas... 564 00:30:54,602 --> 00:30:57,729 two different teams set out in the 1990s... 565 00:30:57,772 --> 00:31:00,732 to measure the deceleration rate of the universe. 566 00:31:01,818 --> 00:31:04,736 But to capture supernovas as they occur... 567 00:31:04,779 --> 00:31:08,240 astronomers had to put the universe on surveillance. 568 00:31:09,284 --> 00:31:13,120 You can compare this a little bit to perhaps surveying a casino. 569 00:31:14,163 --> 00:31:16,123 So all these cameras are on all the time... 570 00:31:16,165 --> 00:31:19,501 and most of the time, they don't find much of anything interesting. 571 00:31:19,544 --> 00:31:22,212 But, occasionally, they find what they're looking for. 572 00:31:26,301 --> 00:31:28,468 You have to look at lots of galaxies. 573 00:31:28,511 --> 00:31:31,221 So what we did is we took large telescopes... 574 00:31:31,264 --> 00:31:34,391 with cameras that have wide fields of view... 575 00:31:34,434 --> 00:31:37,895 about as wide as, say, the width of the full Moon. 576 00:31:37,937 --> 00:31:44,067 And we took many snapshots of space using this wide-field camera. 577 00:31:44,110 --> 00:31:48,739 And each snapshot contains tens of thousands of galaxies. 578 00:31:50,074 --> 00:31:54,202 And by comparing the apparent brightness of the distant Type 1 a's... 579 00:31:54,245 --> 00:31:59,082 with those of the nearby Type 1 a's in nearby galaxies... 580 00:31:59,125 --> 00:32:02,586 we can get the distance of the distant galaxies... 581 00:32:02,629 --> 00:32:04,963 and, hence, the amount of time... 582 00:32:05,006 --> 00:32:07,799 that we're looking back in the history of the universe. 583 00:32:13,181 --> 00:32:15,474 After the two teams studied the results... 584 00:32:15,516 --> 00:32:18,310 of sixty Type 1 a supernovas... 585 00:32:18,353 --> 00:32:21,813 scientists were shocked at their results. 586 00:32:21,856 --> 00:32:24,441 The universe wasn't slowing down. 587 00:32:24,484 --> 00:32:26,818 Its expansion was speeding up. 588 00:32:28,321 --> 00:32:31,990 We all expected that expansion to be slowing down with time... 589 00:32:32,033 --> 00:32:35,619 because, after all, all of the galaxies are pulling on one another. 590 00:32:35,662 --> 00:32:37,913 We were so confident we were going to measure the rate... 591 00:32:37,956 --> 00:32:40,248 at which the universe was slowing down... 592 00:32:40,291 --> 00:32:42,626 and then we found, of course, a negative answer. 593 00:32:42,669 --> 00:32:44,086 The universe is not slowing down. 594 00:32:44,128 --> 00:32:45,796 It's speeding up... 595 00:32:45,838 --> 00:32:48,173 and this was just a big mystery. 596 00:32:48,216 --> 00:32:50,968 That is really, really weird. 597 00:32:51,010 --> 00:32:54,680 You know, we expected to measure some amount of slowdown... 598 00:32:54,722 --> 00:32:57,182 and instead, it's expanding more quickly. 599 00:32:57,225 --> 00:32:59,351 That's like the wrong sign, right? 600 00:32:59,394 --> 00:33:00,477 We were really afraid... 601 00:33:00,520 --> 00:33:03,355 that we had gotten completely the wrong answer. 602 00:33:04,774 --> 00:33:06,900 We rechecked our measurements. 603 00:33:06,943 --> 00:33:08,276 We checked the analysis. 604 00:33:08,319 --> 00:33:10,654 A bunch of people on each of the two teams... 605 00:33:10,697 --> 00:33:13,824 did the measurements and the analysis independently... 606 00:33:13,866 --> 00:33:16,284 and kept getting the same result. 607 00:33:17,662 --> 00:33:20,914 One of the greatest shocks in the world of cosmology... 608 00:33:20,957 --> 00:33:24,001 just in the last few years has been the realization... 609 00:33:24,043 --> 00:33:26,461 that our universe is accelerating. 610 00:33:26,504 --> 00:33:29,631 This repulsive force driving the universe... 611 00:33:29,674 --> 00:33:33,010 was called dark energy, an invisible energy... 612 00:33:33,052 --> 00:33:36,972 that was nothing anyone expected or understood. 613 00:33:37,015 --> 00:33:42,102 It suggests that over the largest distances in the universe... 614 00:33:42,145 --> 00:33:45,897 there's a repulsive effect that dominates over gravity. 615 00:33:45,940 --> 00:33:49,151 And dark energy was creating space... 616 00:33:49,193 --> 00:33:51,945 taking galaxies along for the ride. 617 00:33:51,988 --> 00:33:54,614 This energy that appears to fill the universe... 618 00:33:54,657 --> 00:33:56,825 and stretch the expansion of the universe... 619 00:33:56,868 --> 00:34:02,706 faster and faster with time is now known as dark energy. 620 00:34:02,749 --> 00:34:05,792 So here I throw the apple, and, initially, it's decelerating. 621 00:34:05,835 --> 00:34:09,296 And then dark energy makes it accelerate away from me. 622 00:34:09,338 --> 00:34:10,756 So you throw the apple... 623 00:34:10,798 --> 00:34:14,259 and it just zooms away faster and faster with time. 624 00:34:14,302 --> 00:34:17,429 Like the apple forever traveling into space... 625 00:34:17,472 --> 00:34:28,565 galaxies are being carried away as more space is created. 626 00:34:28,608 --> 00:34:30,317 So if you could imagine, you know... 627 00:34:30,359 --> 00:34:33,028 a classroom populated by chairs... 628 00:34:33,071 --> 00:34:36,573 and those chairs are slowly getting further apart... 629 00:34:36,616 --> 00:34:39,743 from one another within a classroom... 630 00:34:39,786 --> 00:34:42,746 because if all the chairs are being stretched apart... 631 00:34:42,789 --> 00:34:44,498 like in the expanding universe... 632 00:34:44,540 --> 00:34:46,083 no matter which chair you sit on... 633 00:34:46,125 --> 00:34:48,919 you will find all chairs are moving away from you. 634 00:34:48,961 --> 00:34:51,046 So the chairs are not really expanding. 635 00:34:51,089 --> 00:34:53,507 In fact, the chairs are all the same size, really. 636 00:34:53,549 --> 00:34:56,176 What's happening is that the room is getting bigger... 637 00:34:56,219 --> 00:34:58,261 the sort of the space in between the chairs... 638 00:34:58,304 --> 00:34:59,638 is being stretched apart. 639 00:35:00,640 --> 00:35:04,476 More space is being created in between the galaxies. 640 00:35:04,519 --> 00:35:07,771 So you have individual galaxies remaining a constant size... 641 00:35:07,814 --> 00:35:11,483 in a universe where all of space is getting bigger and bigger. 642 00:35:12,985 --> 00:35:16,488 Dark energy is very different from dark matter. 643 00:35:17,865 --> 00:35:21,868 It doesn't clump up like galaxies do in clusters... 644 00:35:21,911 --> 00:35:24,496 or like stars do in galaxies. 645 00:35:24,539 --> 00:35:26,665 Instead, it appears to be pretty uniform. 646 00:35:26,707 --> 00:35:29,126 And we find the same amount of acceleration... 647 00:35:29,168 --> 00:35:31,294 no matter which direction we look at. 648 00:35:31,337 --> 00:35:32,587 It's probably smooth... 649 00:35:32,630 --> 00:35:35,715 although some people believe there may be structure... 650 00:35:35,758 --> 00:35:38,135 in its distribution and its influence. 651 00:35:38,177 --> 00:35:40,971 Dark energy is the energy of the vacuum... 652 00:35:41,013 --> 00:35:42,222 the energy of nothing. 653 00:35:42,265 --> 00:35:44,516 Even nothingness has energy. 654 00:35:44,559 --> 00:35:48,895 And it's pushing the galaxies apart, creating a runaway universe. 655 00:35:48,938 --> 00:35:52,274 It appears dark energy and dark matter... 656 00:35:52,316 --> 00:35:56,611 have been at war with one another since the beginning of time. 657 00:35:56,654 --> 00:35:59,156 Science believes dark energy was created... 658 00:35:59,198 --> 00:36:03,034 along with dark matter at the moment of the Big Bang. 659 00:36:03,077 --> 00:36:05,620 It has always existed in the universe... 660 00:36:05,663 --> 00:36:09,833 but gravitational forces of dark matter kept it in check... 661 00:36:09,876 --> 00:36:12,169 slowing down the expansion of space... 662 00:36:12,211 --> 00:36:14,880 during the first nine billion years of time. 663 00:36:16,007 --> 00:36:18,633 This changed five billion years ago... 664 00:36:18,676 --> 00:36:20,677 when the universe grew big enough... 665 00:36:20,720 --> 00:36:24,347 so that dark matter was dispersed throughout the universe... 666 00:36:24,390 --> 00:36:28,518 and dark energy wasn't so affected by dark matter's pull. 667 00:36:28,561 --> 00:36:31,771 As a result, the universe began to expand... 668 00:36:31,814 --> 00:36:33,857 at an accelerated rate. 669 00:36:33,900 --> 00:36:39,196 Dark energy is a constant term that was probably very insignificant... 670 00:36:39,238 --> 00:36:42,199 when the universe was hot and dense in the beginning... 671 00:36:42,241 --> 00:36:43,950 and so it doesn't really matter... 672 00:36:43,993 --> 00:36:45,410 whether dark energy is there or not. 673 00:36:45,453 --> 00:36:48,079 It is there, but it's- It just plays no role at all. 674 00:36:48,122 --> 00:36:53,835 And then, as the universe gets cooler and less dense and bigger... 675 00:36:53,878 --> 00:36:56,713 so gravity becomes less important... 676 00:36:56,756 --> 00:36:58,757 and then dark energy takes over. 677 00:36:59,717 --> 00:37:03,553 It's a property of space that we don't yet fully understand. 678 00:37:03,596 --> 00:37:08,058 As the universe expanded, astronomers realized dark energy... 679 00:37:08,100 --> 00:37:09,976 won its struggle with dark matter... 680 00:37:10,019 --> 00:37:13,688 and started the acceleration five billion years ago. 681 00:37:14,899 --> 00:37:17,817 So there came a time, about five billion years ago... 682 00:37:17,860 --> 00:37:20,362 when the dark energy started dominating... 683 00:37:20,404 --> 00:37:23,657 over the attractive matter in the universe. 684 00:37:23,699 --> 00:37:27,202 So, in a sense, if you plot force versus time... 685 00:37:27,245 --> 00:37:29,955 the gravitational attraction is declining with time... 686 00:37:29,997 --> 00:37:32,499 the repulsion is increasing with time... 687 00:37:32,541 --> 00:37:36,419 and about five billion years ago, the two curves crossed... 688 00:37:36,462 --> 00:37:40,215 and that's when the universe started accelerating in its expansion. 689 00:37:42,176 --> 00:37:44,719 Dark energy is fundamental to understand... 690 00:37:44,762 --> 00:37:46,638 because it tells us where the universe is going. 691 00:37:46,681 --> 00:37:47,973 What's the fate of the universe? 692 00:37:48,015 --> 00:37:51,017 Is it going to expand forever and get cold and dark? 693 00:37:51,060 --> 00:37:53,853 Or is there, you know, some end in sight? 694 00:37:54,981 --> 00:37:58,775 Dark energy now drives the expansion of the universe... 695 00:37:58,818 --> 00:38:01,444 and it doesn't seem to be stopping. 696 00:38:01,487 --> 00:38:04,948 The repulsive effect of the dark energy increased... 697 00:38:04,991 --> 00:38:07,993 because the more space there is between galaxies... 698 00:38:08,035 --> 00:38:10,078 the greater is the cumulative effect... 699 00:38:10,121 --> 00:38:11,997 of the dark energy, the repulsive effect. 700 00:38:12,039 --> 00:38:17,085 And individual galaxies seem destined to a lonely existence. 701 00:38:19,046 --> 00:38:23,216 So it looks as if this is the end of everything. 702 00:38:25,886 --> 00:38:28,513 Surprisingly, the theory of dark energy... 703 00:38:28,556 --> 00:38:32,142 was proposed and discarded long ago... 704 00:38:32,184 --> 00:38:34,185 from one of physics' greatest minds. 705 00:38:35,021 --> 00:38:37,022 He called it his biggest blunder. 706 00:38:37,857 --> 00:38:40,483 His name was Einstein, and he might have been... 707 00:38:40,526 --> 00:38:43,737 onto the greatest discovery of the 21 st century... 708 00:38:43,779 --> 00:38:46,906 eighty years before anyone had a clue. 709 00:38:50,911 --> 00:38:52,704 Science now understands... 710 00:38:52,747 --> 00:38:57,042 that dark energy is creating and expanding space. 711 00:38:57,084 --> 00:38:59,169 But in the early 20th century... 712 00:38:59,211 --> 00:39:02,047 astronomers believed the universe was only as big... 713 00:39:02,089 --> 00:39:05,884 as the Milky Way and would never grow in size. 714 00:39:10,306 --> 00:39:13,933 But Einstein had just formed his theory of relativity... 715 00:39:13,976 --> 00:39:17,937 and decided to test it on the static universe. 716 00:39:18,773 --> 00:39:20,857 But as hard as Einstein tried... 717 00:39:20,900 --> 00:39:25,612 he could not balance his equation to equal a static universe. 718 00:39:25,654 --> 00:39:27,864 His calculations showed a universe... 719 00:39:27,907 --> 00:39:30,784 that must either expand or contract. 720 00:39:34,205 --> 00:39:37,248 He realized that if you had a universe that was smooth... 721 00:39:37,291 --> 00:39:39,876 that was uniformly distributed with stuff... 722 00:39:39,919 --> 00:39:41,836 his theory unambiguously predicted... 723 00:39:41,879 --> 00:39:44,756 that it should either be expanding or contracting. 724 00:39:45,633 --> 00:39:49,135 So Einstein proposed a repulsive vacuum energy... 725 00:39:49,178 --> 00:39:52,555 that would hold the universe in balance with attractive gravity. 726 00:39:54,266 --> 00:39:57,060 He called it his cosmological constant... 727 00:39:57,103 --> 00:40:01,481 a constant energy that would hold the universe in balance. 728 00:40:01,524 --> 00:40:03,566 He introduced the cosmological constant... 729 00:40:03,609 --> 00:40:07,195 or dark energy, to hold the universe static. 730 00:40:07,238 --> 00:40:10,407 When Hubble announced space was expanding... 731 00:40:10,449 --> 00:40:14,702 suddenly, Einstein's cosmological constant seemed irrelevant... 732 00:40:14,745 --> 00:40:17,497 and he labeled it his biggest blunder. 733 00:40:17,540 --> 00:40:20,250 Now it turns out that dark energy... 734 00:40:20,292 --> 00:40:25,046 a concept that he threw away back in the 1920s, is, in fact... 735 00:40:25,089 --> 00:40:28,758 the dominant force blowing the universe apart. 736 00:40:28,801 --> 00:40:31,594 Einstein's so-called blunder... 737 00:40:31,637 --> 00:40:33,388 will eventually determine whether or not... 738 00:40:33,431 --> 00:40:36,808 the universe dies in fire or ice. 739 00:40:36,851 --> 00:40:41,146 And the betting is the universe will die in ice. 740 00:40:43,232 --> 00:40:46,359 In trying to survey how the universe behaves... 741 00:40:46,402 --> 00:40:49,779 Einstein had erroneously predicted dark energy... 742 00:40:49,822 --> 00:40:52,824 and what is the total makeup of the universe. 743 00:40:54,160 --> 00:40:56,661 The total amount of stuff in the ordinary matter and dark matter... 744 00:40:56,704 --> 00:41:00,457 is not enough to account for the curvature of space... 745 00:41:00,499 --> 00:41:02,417 that we observe. 746 00:41:02,460 --> 00:41:04,836 Like looking across a horizon on Earth... 747 00:41:04,879 --> 00:41:07,464 the size of the universe is so great... 748 00:41:07,506 --> 00:41:10,467 the curvature of space appears flat. 749 00:41:11,886 --> 00:41:15,972 Add ordinary matter, dark matter, and dark energy together... 750 00:41:16,015 --> 00:41:18,433 that makes a prediction for the curvature of space. 751 00:41:18,476 --> 00:41:20,894 And that prediction comes spot on. 752 00:41:20,936 --> 00:41:22,353 You get the right answer. 753 00:41:23,481 --> 00:41:26,399 Our satellite data now has revealed the fact... 754 00:41:26,442 --> 00:41:30,945 that seventy-three percent of the matter-energy content... 755 00:41:30,988 --> 00:41:32,489 of the universe is dark energy. 756 00:41:32,531 --> 00:41:36,284 Dark energy, which was once Einstein's blunder... 757 00:41:36,327 --> 00:41:40,497 is now known to be the dominant force in the universe. 758 00:41:40,539 --> 00:41:42,540 His blunders are our great discoveries. 759 00:41:44,210 --> 00:41:47,337 Scientists are at the very beginning of understanding... 760 00:41:47,379 --> 00:41:52,008 what effect dark energy will have on the fate of the universe. 761 00:41:52,051 --> 00:41:55,220 Ideally, we'd like to measure... 762 00:41:55,262 --> 00:41:59,224 how dark energy is behaving as the universe ages. 763 00:42:00,351 --> 00:42:01,851 Eventually, when the dark energy... 764 00:42:01,894 --> 00:42:04,854 completely dominates over dark matter... 765 00:42:04,897 --> 00:42:09,317 the universe will enter a stage known as exponential expansion. 766 00:42:09,360 --> 00:42:13,613 For every given unit of time, it'll double in size... 767 00:42:13,656 --> 00:42:19,577 And unless the dark energy changes sign someday... 768 00:42:19,620 --> 00:42:22,705 and becomes gravitationally attractive... 769 00:42:22,748 --> 00:42:26,209 the fate of the universe is to expand forever... 770 00:42:26,252 --> 00:42:28,503 more and more quickly with time. 771 00:42:28,546 --> 00:42:31,214 We don't understand if the vacuum energy is driving... 772 00:42:31,257 --> 00:42:35,635 the acceleration of the universe, why it has the amount it does. 773 00:42:35,678 --> 00:42:37,178 That is one of the deepest puzzles... 774 00:42:37,221 --> 00:42:38,930 remaining in theoretical physics today. 775 00:42:38,973 --> 00:42:40,890 Trillions of years from now... 776 00:42:40,933 --> 00:42:43,059 it's going to be a very lonely place. 777 00:42:43,102 --> 00:42:44,435 We'll look up in the sky... 778 00:42:44,478 --> 00:42:46,896 and the skies will be practically dark. 779 00:42:46,939 --> 00:42:48,982 The oceans will freeze over... 780 00:42:49,024 --> 00:42:53,403 and it looks as if this is the death of all intelligent life. 781 00:42:53,445 --> 00:42:56,739 It looks as if dark energy and the laws of physics... 782 00:42:56,782 --> 00:43:01,452 are a death warrant to all intelligent life in the universe. 783 00:43:02,955 --> 00:43:05,790 In discovering dark matter and dark energy... 784 00:43:05,833 --> 00:43:10,211 science is one step closer to defining the theory of everything: 785 00:43:10,254 --> 00:43:15,675 One equation that will define the entire workings of the universe. 786 00:43:17,094 --> 00:43:19,762 Once we have the theory of everything... 787 00:43:19,805 --> 00:43:22,640 we'll be able to answer some of the deepest questions... 788 00:43:22,683 --> 00:43:26,477 ever since man and women first looked at the heavens. 789 00:43:28,355 --> 00:43:30,607 This could be the crowning achievement... 790 00:43:30,649 --> 00:43:35,361 of 2,000 years of investigation into the laws of nature... 791 00:43:35,404 --> 00:43:37,530 ever since the Greeks asked the question... 792 00:43:37,573 --> 00:43:39,866 "What are things made of?" 793 00:43:41,619 --> 00:43:44,370 For now, dark matter and dark energy... 794 00:43:44,413 --> 00:43:47,665 continue to be the greatest cosmological questions... 795 00:43:47,708 --> 00:43:50,668 of the 21 st century. 796 00:43:50,711 --> 00:43:51,711 It's certainly frustrating. 797 00:43:51,754 --> 00:43:54,964 Yes, I mean, it's humbling, too, to know that... 798 00:43:55,007 --> 00:43:57,467 you know, all that we know about physics... 799 00:43:57,509 --> 00:43:59,135 is restricted to normal matter... 800 00:43:59,178 --> 00:44:02,221 and yet there's all this other dark matter and dark energy... 801 00:44:02,264 --> 00:44:04,432 that we really understand very little about. 802 00:44:05,976 --> 00:44:09,020 It's the beginning of a new era and the mysteries... 803 00:44:09,063 --> 00:44:12,148 of the dark side of the universe. 804 00:44:12,191 --> 00:44:14,984 It's the Wild West as far as particle astrophysics... 805 00:44:15,027 --> 00:44:16,653 which is what we call this field. 806 00:44:16,695 --> 00:44:20,615 It's a property of space that we don't yet fully understand.