All language subtitles for How the Universe Works (2010) - S01E03 - Galaxies (1080p BluRay x265 Garshasp)

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Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:02,703 --> 00:00:06,037 Narrator: We live in a galaxy called the Milky Way, 2 00:00:06,040 --> 00:00:10,375 an empire with hundreds of billions of stars. 3 00:00:10,377 --> 00:00:13,540 Dr. Krauss: How did we get here, and what's our future? 4 00:00:13,547 --> 00:00:16,175 In every way, those questions involve galaxies. 5 00:00:16,183 --> 00:00:20,518 Narrator: There are 200 billion galaxies in the known universe, 6 00:00:20,521 --> 00:00:24,253 each one unique, enormous, and dynamic. 7 00:00:24,258 --> 00:00:26,056 Dr. Kaku: Galaxies are violent. 8 00:00:26,060 --> 00:00:28,324 They were born in a violent history. 9 00:00:28,329 --> 00:00:30,423 They will die a violent death. 10 00:00:30,431 --> 00:00:33,230 Narrator: Where do galaxies come from? 11 00:00:33,234 --> 00:00:37,330 How do they work? What is their future? 12 00:00:37,338 --> 00:00:39,670 And how will they die? 13 00:00:54,154 --> 00:00:59,422 This is our galaxy, the Milky Way. 14 00:00:59,426 --> 00:01:04,227 It's around 12 billion years old. 15 00:01:04,231 --> 00:01:07,064 The galaxy itself is a huge disk 16 00:01:07,067 --> 00:01:11,470 with giant spiral arms and a bulge in the middle. 17 00:01:13,507 --> 00:01:18,968 It's just one of a huge number of galaxies in the universe. 18 00:01:18,979 --> 00:01:21,175 Galaxies are, first and foremost, 19 00:01:21,181 --> 00:01:22,876 large collections of stars. 20 00:01:22,883 --> 00:01:26,513 The average galaxy may contain 100 billion stars. 21 00:01:28,756 --> 00:01:31,225 They're really stellar nurseries, 22 00:01:31,225 --> 00:01:34,923 the place where stars are born and where they also die. 23 00:01:37,831 --> 00:01:40,630 Narrator: The stars in a galaxy are born 24 00:01:40,634 --> 00:01:45,367 in clouds of dust and gas called nebulas. 25 00:01:45,372 --> 00:01:49,536 These are the pillars of creation in the Eagle nebula, 26 00:01:49,543 --> 00:01:54,105 a star nursery deep in the Milky Way. 27 00:01:58,218 --> 00:02:02,155 Our galaxy contains many billions of stars, 28 00:02:02,156 --> 00:02:04,147 and around many of them 29 00:02:04,158 --> 00:02:09,494 are systems of planets and moons. 30 00:02:09,496 --> 00:02:13,990 But for a long time, we didn't know much about galaxies. 31 00:02:14,001 --> 00:02:15,901 Just a century ago, 32 00:02:15,903 --> 00:02:20,397 we thought that the Milky Way was all there was. 33 00:02:20,407 --> 00:02:24,537 Scientists called it our island universe. 34 00:02:24,545 --> 00:02:28,379 For them, no other galaxies existed. 35 00:02:28,382 --> 00:02:34,378 Then, in 1924, astronomer Edwin Hubble changed all that. 36 00:02:34,388 --> 00:02:36,823 Hubble was observing the universe 37 00:02:36,824 --> 00:02:39,316 with the most advanced telescope at the time, 38 00:02:39,326 --> 00:02:44,059 the 100-inch Hooker on Mount Wilson near Los Angeles. 39 00:02:45,699 --> 00:02:47,997 Deep in the night sky, 40 00:02:48,002 --> 00:02:53,202 he saw fuzzy blobs of light that were far, far away. 41 00:02:53,207 --> 00:02:57,667 He realized they weren't individual stars at all. 42 00:02:57,678 --> 00:03:00,477 They were whole cities of stars -- 43 00:03:00,481 --> 00:03:06,409 galaxies way beyond the Milky Way. 44 00:03:06,420 --> 00:03:09,355 Astronomers had an existential shock. 45 00:03:09,356 --> 00:03:11,450 In one year, 46 00:03:11,458 --> 00:03:15,554 we went from the universe being the Milky Way galaxy 47 00:03:15,562 --> 00:03:19,430 to a universe of billions of galaxies. 48 00:03:23,137 --> 00:03:26,505 Narrator: Hubble had made one of the greatest discoveries 49 00:03:26,507 --> 00:03:28,271 in the history of astronomy -- 50 00:03:28,275 --> 00:03:29,606 the universe contains 51 00:03:29,610 --> 00:03:33,774 not just one but a great number of galaxies. 52 00:03:35,649 --> 00:03:38,050 This is the Whirlpool galaxy. 53 00:03:38,052 --> 00:03:40,851 It has two giant spiral arms 54 00:03:40,854 --> 00:03:44,791 and contains around 160 million stars. 55 00:03:48,028 --> 00:03:53,489 And Galaxy M87, a giant elliptical galaxy -- 56 00:03:53,500 --> 00:03:56,800 it's one of the oldest in the universe, 57 00:03:56,804 --> 00:03:59,603 and the stars glow gold. 58 00:04:06,180 --> 00:04:08,979 And this is the Sombrero galaxy. 59 00:04:08,982 --> 00:04:11,349 It has a huge, glowing core 60 00:04:11,351 --> 00:04:15,049 with a ring of gas and dust all around it. 61 00:04:18,258 --> 00:04:21,159 Dr. Kaku: Galaxies are gorgeous. 62 00:04:21,161 --> 00:04:23,061 They represent, in some sense, 63 00:04:23,063 --> 00:04:25,589 the basic unit of the universe itself. 64 00:04:25,599 --> 00:04:29,092 They're like gigantic pinwheels twirling in outer space. 65 00:04:29,103 --> 00:04:32,733 It's like fireworks created by Mother Nature. 66 00:04:36,276 --> 00:04:40,873 Narrator: Galaxies are big -- really, really big. 67 00:04:40,881 --> 00:04:43,816 On Earth, we measure distance in miles. 68 00:04:43,817 --> 00:04:48,948 In space, astronomers use light-years... 69 00:04:48,956 --> 00:04:52,620 The distance light travels in a year. 70 00:04:54,795 --> 00:04:59,528 That's just under 6 trillion miles. 71 00:04:59,533 --> 00:05:00,898 Dr. Krauss: Here we are, 72 00:05:00,901 --> 00:05:03,734 25,000 light-years away from the center of our galaxy, 73 00:05:03,737 --> 00:05:07,469 and our galaxy is over 100,000 light-years across. 74 00:05:07,474 --> 00:05:09,772 But even that, as large as it is, 75 00:05:09,777 --> 00:05:12,906 is kind of a speck in the cosmic-distance scale. 76 00:05:12,913 --> 00:05:16,406 Narrator: Our Milky Way galaxy may seem big to us, 77 00:05:16,416 --> 00:05:18,851 but compared to some others out there... 78 00:05:20,554 --> 00:05:24,286 ...it's actually pretty small. 79 00:05:24,291 --> 00:05:27,420 Andromeda, our nearest galactic neighbor, 80 00:05:27,427 --> 00:05:30,158 is over 200,000 light-years across -- 81 00:05:30,164 --> 00:05:33,623 twice the size of the Milky Way. 82 00:05:33,634 --> 00:05:36,592 M87 is the largest elliptical galaxy 83 00:05:36,603 --> 00:05:41,006 in our own cosmic backyard, and much bigger than Andromeda. 84 00:05:43,544 --> 00:05:49,142 But M87 is tiny compared to this giant. 85 00:05:49,149 --> 00:05:52,175 6 million light-years across, 86 00:05:52,186 --> 00:05:58,023 IC 1011 is the biggest galaxy ever found. 87 00:05:58,025 --> 00:06:03,395 It's 60 times larger than our Milky Way. 88 00:06:03,397 --> 00:06:08,335 We know galaxies are big and they're everywhere, 89 00:06:08,335 --> 00:06:09,496 but why is that? 90 00:06:09,503 --> 00:06:12,131 Dr. Strauss: One of the very big questions 91 00:06:12,139 --> 00:06:15,404 we have in astrophysics is where galaxies come from. 92 00:06:15,409 --> 00:06:18,435 We really don't have a complete understanding of that. 93 00:06:21,682 --> 00:06:24,640 The universe started in what we call a Big Bang, 94 00:06:24,651 --> 00:06:27,211 an extremely hot and extremely dense phase 95 00:06:27,221 --> 00:06:30,020 about 13.7 billion years ago. 96 00:06:30,023 --> 00:06:32,788 We know that nothing like a galaxy could have existed 97 00:06:32,793 --> 00:06:34,090 at that time. 98 00:06:34,094 --> 00:06:37,029 So galaxies must have been born, they must have formed, 99 00:06:37,030 --> 00:06:38,862 out of that very early universe. 100 00:06:38,866 --> 00:06:42,928 Narrator: It takes gravity to make stars 101 00:06:42,936 --> 00:06:47,305 and even more gravity to pull stars together into galaxies. 102 00:06:47,307 --> 00:06:49,105 The first stars formed 103 00:06:49,109 --> 00:06:52,511 just 200 million years after the Big Bang. 104 00:06:52,512 --> 00:06:55,447 Then gravity pulled them together, 105 00:06:55,449 --> 00:06:57,645 building the first galaxies. 106 00:06:59,920 --> 00:07:04,153 The Hubble Space Telescope has allowed us to peer back in time 107 00:07:04,157 --> 00:07:06,285 to almost the dawn of time... 108 00:07:08,095 --> 00:07:12,191 ...the period when galaxies have just begun to form. 109 00:07:12,199 --> 00:07:15,658 Narrator: The Hubble sees lots of galaxies. 110 00:07:15,669 --> 00:07:19,105 But the light we see today from those galaxies 111 00:07:19,106 --> 00:07:24,704 left there thousands, millions, even billions of years ago. 112 00:07:24,711 --> 00:07:27,544 It's taken all that time to reach us, 113 00:07:27,547 --> 00:07:29,948 so what we see today 114 00:07:29,950 --> 00:07:34,319 is the ancient history of those galaxies. 115 00:07:34,321 --> 00:07:36,187 When we look at the Hubble Deep Field, 116 00:07:36,189 --> 00:07:37,657 what we see are little smudges. 117 00:07:37,658 --> 00:07:40,093 They don't look much like the galaxies we see today. 118 00:07:40,093 --> 00:07:42,926 They're just little smudges of light 119 00:07:42,930 --> 00:07:44,591 that we can barely discern. 120 00:07:44,598 --> 00:07:48,159 Those smudges of light contain millions or billions of stars 121 00:07:48,168 --> 00:07:50,637 that have just begun to merge together. 122 00:07:50,637 --> 00:07:53,334 Narrator: These faint smudges 123 00:07:53,340 --> 00:07:56,332 are the earliest galaxies of all. 124 00:07:56,343 --> 00:07:58,038 They were formed 125 00:07:58,045 --> 00:08:03,814 around one billion years after the beginning of the universe. 126 00:08:03,817 --> 00:08:07,082 But that's as far back as Hubble can see. 127 00:08:07,087 --> 00:08:09,522 If we want to go even further back in time, 128 00:08:09,523 --> 00:08:12,458 we need a different kind of telescope -- 129 00:08:12,459 --> 00:08:15,190 one too big to launch into space. 130 00:08:20,867 --> 00:08:26,237 Well, now we have one, in the high desert of northern Chile. 131 00:08:26,239 --> 00:08:32,337 This is ACT, the Atacama Cosmology Telescope. 132 00:08:32,346 --> 00:08:34,713 At 17,000 feet, 133 00:08:34,715 --> 00:08:39,346 it's the highest ground-based telescope in the world. 134 00:08:42,956 --> 00:08:45,357 Dr. Staggs: I really like working 135 00:08:45,359 --> 00:08:47,794 in the extreme environment of ACT. 136 00:08:47,794 --> 00:08:52,789 It's very, very cold often, and the wind blows violently. 137 00:08:52,799 --> 00:08:55,928 But the good thing about it from our point of view 138 00:08:55,936 --> 00:08:59,372 is that the sky is very, very clear almost all the time. 139 00:09:01,208 --> 00:09:03,199 Narrator: Clear skies are important 140 00:09:03,210 --> 00:09:07,943 for ACT's precise mirrors to focus on the earliest galaxies. 141 00:09:10,183 --> 00:09:13,983 With ACT, we're able to zoom in with unprecedented detail 142 00:09:13,987 --> 00:09:16,354 on parts of the sky. 143 00:09:16,356 --> 00:09:20,327 We can also study the progress of growth of structures, 144 00:09:20,327 --> 00:09:22,261 where structures are things like galaxies 145 00:09:22,262 --> 00:09:23,423 and clusters of galaxies, 146 00:09:23,430 --> 00:09:27,628 with a very fine-scale detail. 147 00:09:27,634 --> 00:09:31,195 Narrator: ACT doesn't detect visible light. 148 00:09:31,204 --> 00:09:34,071 It detects cosmic microwaves from the time 149 00:09:34,074 --> 00:09:37,601 the universe was just a few hundred thousand years old. 150 00:09:39,246 --> 00:09:42,739 The telescope not only detects early galaxies -- 151 00:09:42,749 --> 00:09:46,310 it actually sees how they grew. 152 00:09:46,319 --> 00:09:48,083 We're able to track the progress 153 00:09:48,088 --> 00:09:51,183 of the formations of galaxies and clusters of galaxies. 154 00:09:51,191 --> 00:09:55,856 We see the footprints of all the galaxies that have grown 155 00:09:55,862 --> 00:09:57,796 in the time between when the universe was 156 00:09:57,798 --> 00:09:59,732 a few hundred thousand years old till now. 157 00:10:01,568 --> 00:10:04,594 Narrator: ACT has helped astronomers understand 158 00:10:04,604 --> 00:10:06,368 how galaxies have evolved 159 00:10:06,373 --> 00:10:10,003 since almost the beginning of time itself. 160 00:10:10,010 --> 00:10:11,500 [indistinct conversation] 161 00:10:11,511 --> 00:10:13,843 Dr. Strauss: And we can start answering the question, 162 00:10:13,847 --> 00:10:16,976 what did galaxies look like when they were young? 163 00:10:16,983 --> 00:10:19,953 How did they compare with modern-day galaxies? 164 00:10:19,953 --> 00:10:21,250 How have they grown? 165 00:10:24,091 --> 00:10:27,117 Narrator: Astronomers are seeing how galaxies evolve 166 00:10:27,127 --> 00:10:29,824 from groups of stars 167 00:10:29,830 --> 00:10:32,458 into the patchwork of systems we see today. 168 00:10:32,466 --> 00:10:35,629 Our current understanding is that stars form clusters 169 00:10:35,635 --> 00:10:37,194 that build into galaxies 170 00:10:37,204 --> 00:10:39,673 that build into clusters of galaxies 171 00:10:39,673 --> 00:10:41,505 that build into superclusters of galaxies, 172 00:10:41,508 --> 00:10:43,977 the largest structures we observe in the universe today. 173 00:10:43,977 --> 00:10:47,538 Narrator: Early galaxies were a mess -- 174 00:10:47,547 --> 00:10:51,711 lumpy bunches of stars, gas, and dust. 175 00:10:51,718 --> 00:10:55,655 Buttoday galaxies look neat and orderly. 176 00:10:55,655 --> 00:10:59,125 So, how do messy galaxies transform 177 00:10:59,126 --> 00:11:02,084 into beautiful spirals and pinwheels? 178 00:11:02,095 --> 00:11:04,587 The answer is gravity. 179 00:11:04,598 --> 00:11:08,762 Gravity shapes galaxies and controls their future. 180 00:11:14,141 --> 00:11:16,803 There is an unimaginably powerful 181 00:11:16,810 --> 00:11:20,212 and incredibly destructive source of gravity 182 00:11:20,213 --> 00:11:22,910 at the heart of most galaxies. 183 00:11:25,886 --> 00:11:29,550 And there's one buried deep at the center 184 00:11:29,556 --> 00:11:32,082 of our own Milky Way. 185 00:11:38,231 --> 00:11:42,065 Narrator: Galaxies have existed for over 12 billion years. 186 00:11:44,171 --> 00:11:47,300 We know these vast empires of stars 187 00:11:47,307 --> 00:11:49,332 come in all shapes and sizes, 188 00:11:49,342 --> 00:11:54,212 from swirling spirals to huge balls of stars. 189 00:11:54,214 --> 00:11:58,583 But there's still a lot about galaxies we don't know. 190 00:11:58,585 --> 00:12:01,179 How did galaxies come to have the shapes they do? 191 00:12:01,188 --> 00:12:03,748 Was a spiral galaxy always a spiral galaxy? 192 00:12:03,757 --> 00:12:05,816 The answer is almost certainly no. 193 00:12:07,794 --> 00:12:11,355 Narrator: Very young galaxies are messy and chaotic, 194 00:12:11,364 --> 00:12:15,961 a jumble of stars, gas, and dust. 195 00:12:15,969 --> 00:12:18,597 Then, over billions of years, 196 00:12:18,605 --> 00:12:22,667 they evolve into neat, organized structures, 197 00:12:22,676 --> 00:12:26,408 like the Whirlpool galaxy... 198 00:12:26,413 --> 00:12:30,782 Or our own Milky Way. 199 00:12:30,784 --> 00:12:35,153 Our Milky Way began not as a single baby galaxy, but many. 200 00:12:35,155 --> 00:12:36,850 What is now our Milky Way 201 00:12:36,856 --> 00:12:40,258 was once comprised of lots of small structures, 202 00:12:40,260 --> 00:12:44,629 irregularly shaped objects that began to merge. 203 00:12:44,631 --> 00:12:47,896 Narrator: The thing that pulls the small structures together 204 00:12:47,901 --> 00:12:49,391 is gravity. 205 00:12:49,402 --> 00:12:53,339 Gradually, it pulls stars inward. 206 00:12:53,340 --> 00:12:56,742 They begin spinning faster and faster 207 00:12:56,743 --> 00:13:00,373 and flatten into a disk. 208 00:13:00,380 --> 00:13:02,940 Stars and gas are swept 209 00:13:02,949 --> 00:13:06,977 into huge spiral arms. 210 00:13:06,987 --> 00:13:11,185 This process was repeated billions and billions of times 211 00:13:11,191 --> 00:13:14,320 across the universe. 212 00:13:16,963 --> 00:13:19,864 Each of these galaxies looks different, 213 00:13:19,866 --> 00:13:22,767 but they do have one thing in common -- 214 00:13:22,769 --> 00:13:26,899 they all seem to orbit something at their center. 215 00:13:29,476 --> 00:13:31,808 For years, scientists wondered 216 00:13:31,811 --> 00:13:36,442 what could be powerful enough to change how a galaxy behaves. 217 00:13:36,449 --> 00:13:40,477 They found out -- a black hole. 218 00:13:40,487 --> 00:13:43,821 And not just any kind of black hole -- 219 00:13:43,823 --> 00:13:46,986 a supermassive black hole. 220 00:13:49,362 --> 00:13:52,195 The first clue that supermassive black holes existed 221 00:13:52,198 --> 00:13:54,428 was that at the heart of some galaxies, 222 00:13:54,434 --> 00:13:56,425 there was an immense amount of energy 223 00:13:56,436 --> 00:13:57,961 emanating out from the center. 224 00:13:57,971 --> 00:14:01,601 What we're seeing is the black holes in these galaxies 225 00:14:01,608 --> 00:14:04,270 feasting on the material around them, 226 00:14:04,277 --> 00:14:08,111 so it's like having a huge Thanksgiving dinner. 227 00:14:08,114 --> 00:14:11,607 Narrator: The meal is gas and stars, 228 00:14:11,618 --> 00:14:16,249 and it's being eaten by the supermassive black hole. 229 00:14:16,256 --> 00:14:20,693 When black holes eat, they sometimes eat too fast 230 00:14:20,694 --> 00:14:23,527 and spit their dinner back out into space 231 00:14:23,530 --> 00:14:26,625 in beams of pure energy. 232 00:14:29,502 --> 00:14:31,766 It's called a quasar. 233 00:14:35,975 --> 00:14:39,878 When scientists see a quasar blasting from a galaxy, 234 00:14:39,879 --> 00:14:42,849 they know it has a supermassive black hole. 235 00:14:46,953 --> 00:14:52,016 But what about our galaxy? There's no quasar here. 236 00:14:53,827 --> 00:14:58,628 Does that mean there's no supermassive black hole? 237 00:14:58,631 --> 00:15:00,827 Andrea Ghez and her team 238 00:15:00,834 --> 00:15:05,328 have spent the last 15 years trying to find out. 239 00:15:05,338 --> 00:15:07,102 Dr. Ghez: So, the key to discovering 240 00:15:07,107 --> 00:15:10,907 a supermassive black hole at the center of our Milky Way 241 00:15:10,910 --> 00:15:12,878 is to watch how the stars move. 242 00:15:12,879 --> 00:15:15,439 The stars move because of the gravity, 243 00:15:15,448 --> 00:15:18,076 just like the planets orbiting the Sun. 244 00:15:18,084 --> 00:15:22,055 Narrator: But the stars closest to the center of the galaxy 245 00:15:22,055 --> 00:15:24,012 are hidden by clouds of dust. 246 00:15:24,023 --> 00:15:28,358 So Ghez used the giant Keck telescope in Hawaii 247 00:15:28,361 --> 00:15:31,262 to look through the clouds. 248 00:15:31,264 --> 00:15:36,259 What she saw was a strange and brutal place. 249 00:15:36,269 --> 00:15:38,397 Dr. Ghez: Everything is more extreme 250 00:15:38,405 --> 00:15:39,930 at the center of our galaxy. 251 00:15:39,939 --> 00:15:41,407 Things move really fast. 252 00:15:41,408 --> 00:15:45,538 Stars are gonna be whizzing by one another. 253 00:15:45,545 --> 00:15:47,377 It's windy. It's violent. 254 00:15:47,380 --> 00:15:49,940 It's unlike anyplace else in our galaxy. 255 00:15:52,952 --> 00:15:56,183 Narrator: Ghez and her team began to take pictures 256 00:15:56,189 --> 00:16:01,093 of a few stars orbiting near the center. 257 00:16:01,094 --> 00:16:03,563 Dr. Ghez: The task has been to make a movie 258 00:16:03,563 --> 00:16:05,053 of the stars at the center, 259 00:16:05,064 --> 00:16:06,498 and so you have to be patient, 260 00:16:06,499 --> 00:16:09,196 because you take a picture, and then you take another one, 261 00:16:09,202 --> 00:16:10,135 and you see it move. 262 00:16:12,172 --> 00:16:14,766 Narrator: The pictures of the orbiting stars 263 00:16:14,774 --> 00:16:16,674 revealed something amazing. 264 00:16:18,578 --> 00:16:23,675 They were moving at several million miles an hour. 265 00:16:23,683 --> 00:16:26,277 Dr. Ghez: When we had the second picture 266 00:16:26,286 --> 00:16:29,381 was the most exciting point in this experiment, 267 00:16:29,389 --> 00:16:34,384 because it was clear to us that these stars were moving so fast 268 00:16:34,394 --> 00:16:37,694 that the supermassive-black-hole hypothesis had to be right. 269 00:16:40,033 --> 00:16:42,263 Narrator: And it was right. 270 00:16:42,268 --> 00:16:45,363 Ghez and her team tracked the movement of the stars 271 00:16:45,371 --> 00:16:47,772 and pinpointed what they were orbiting. 272 00:16:49,809 --> 00:16:52,437 There's only one thing powerful enough 273 00:16:52,445 --> 00:16:55,073 to sling big stars around like that -- 274 00:16:55,081 --> 00:16:57,243 a supermassive black hole. 275 00:16:57,250 --> 00:17:00,083 Dr. Ghez: It's the gravity of the supermassive black hole 276 00:17:00,086 --> 00:17:02,214 that makes these stars orbit, 277 00:17:02,222 --> 00:17:04,623 so the curvature was the definitive proof 278 00:17:04,624 --> 00:17:07,821 of a supermassive black hole at the center of our galaxy. 279 00:17:07,827 --> 00:17:12,162 Narrator: The black hole at the center of the Milky Way 280 00:17:12,165 --> 00:17:17,296 is gigantic -- 15 million miles across. 281 00:17:17,303 --> 00:17:20,739 So, is Earth in any danger? 282 00:17:20,740 --> 00:17:22,708 We are in absolutely no danger 283 00:17:22,709 --> 00:17:25,974 of being sucked into our supermassive black hole. 284 00:17:25,979 --> 00:17:27,572 It's simply too far away. 285 00:17:31,317 --> 00:17:35,345 Narrator: In fact, the Earth is 25,000 light-years away 286 00:17:35,355 --> 00:17:39,690 from the supermassive black hole at the center of the Milky Way. 287 00:17:39,692 --> 00:17:43,322 That's many trillions of miles. 288 00:17:43,329 --> 00:17:46,663 The Earth is safe -- for now. 289 00:17:54,007 --> 00:17:56,203 Supermassive black holes may be 290 00:17:56,209 --> 00:17:59,076 the source of huge amounts of gravity, 291 00:17:59,078 --> 00:18:03,413 but they don't have enough power to hold galaxies together. 292 00:18:03,416 --> 00:18:06,351 In fact, according to the laws of physics, 293 00:18:06,352 --> 00:18:08,320 galaxies should fly apart. 294 00:18:10,890 --> 00:18:12,449 So why don't they? 295 00:18:12,458 --> 00:18:15,450 Because there's something out there 296 00:18:15,461 --> 00:18:19,898 even more powerful than a supermassive black hole. 297 00:18:19,899 --> 00:18:24,803 It can't be seen, and it's virtually impossible to detect. 298 00:18:24,804 --> 00:18:29,674 It's called dark matter, and it's everywhere. 299 00:18:34,581 --> 00:18:35,810 Narrator: Astronomers have figured out 300 00:18:35,815 --> 00:18:39,149 that supermassive black holes live at the heart of galaxies 301 00:18:39,152 --> 00:18:44,090 and pull stars at incredible speeds. 302 00:18:44,090 --> 00:18:45,182 But they're not strong enough 303 00:18:45,191 --> 00:18:50,152 to hold all the stars in a gigantic galaxy together. 304 00:18:50,163 --> 00:18:54,259 So, what does hold them together? 305 00:18:54,267 --> 00:18:55,530 It was a mystery 306 00:18:55,535 --> 00:18:58,732 until a maverick scientist came up with the idea 307 00:18:58,738 --> 00:19:03,608 that something unknown was at work. 308 00:19:03,610 --> 00:19:07,740 Back in the 1930s, Swiss astronomer Fritz Zwicky 309 00:19:07,747 --> 00:19:13,652 wondered why galaxies stayed together in groups. 310 00:19:13,653 --> 00:19:17,021 By his calculations, they didn't generate enough gravity, 311 00:19:17,023 --> 00:19:21,290 so they should fly away from each other. 312 00:19:21,294 --> 00:19:24,787 And so he said, "Well, I know that they haven't flown apart. 313 00:19:24,797 --> 00:19:27,789 I see them all gathered together in this nice collection. 314 00:19:27,800 --> 00:19:31,566 Therefore, something must be holding them in place." 315 00:19:31,571 --> 00:19:34,871 But our own gravity was just not strong enough. 316 00:19:34,874 --> 00:19:36,342 And so he concluded 317 00:19:36,342 --> 00:19:38,834 that it must be something which nobody had detected before, 318 00:19:38,845 --> 00:19:39,903 nobody had thought about, 319 00:19:39,912 --> 00:19:42,040 and he gave it this name, dark matter. 320 00:19:42,048 --> 00:19:44,983 And this is really a stroke of genius. 321 00:19:47,553 --> 00:19:51,114 Fritz Zwicky was decades ahead of his time, 322 00:19:51,124 --> 00:19:55,186 and that's why he grated on the astronomical community. 323 00:19:55,194 --> 00:19:57,390 But, you know, he was right. 324 00:20:01,067 --> 00:20:03,627 Narrator: if what Zwicky called dark matter 325 00:20:03,636 --> 00:20:05,536 held galaxies together in groups, 326 00:20:05,538 --> 00:20:10,339 perhaps it also holds individual galaxies together. 327 00:20:10,343 --> 00:20:15,008 To find out, scientists built virtual galaxies in computers 328 00:20:15,014 --> 00:20:18,314 with virtual stars and virtual gravity. 329 00:20:18,317 --> 00:20:20,445 We did a simulation 330 00:20:20,453 --> 00:20:26,222 where we put a lot of particles in orbit in a flat disk, 331 00:20:26,225 --> 00:20:28,922 which was just like the picture of our galaxy. 332 00:20:28,928 --> 00:20:32,626 And we expected to find that we get a perfectly good galaxy, 333 00:20:32,632 --> 00:20:36,159 and we were looking to see if it had a spiral or whatnot. 334 00:20:36,169 --> 00:20:39,298 But we found it always came apart. 335 00:20:39,305 --> 00:20:41,933 Narrator: There just wasn't enough gravity in the galaxy 336 00:20:41,941 --> 00:20:43,409 to hold it together. 337 00:20:43,409 --> 00:20:47,141 So Ostriker then added extra gravity, 338 00:20:47,146 --> 00:20:49,581 from virtual dark matter. 339 00:20:49,582 --> 00:20:51,277 It seemed like a natural thing to try. 340 00:20:51,284 --> 00:20:52,945 And it solved the problem. It fixed it. 341 00:20:54,687 --> 00:20:59,523 Narrator: Gravity from dark matter held the galaxy together. 342 00:20:59,525 --> 00:21:01,289 Dr. Benson: Dark matter acts 343 00:21:01,294 --> 00:21:04,025 as a sort of protective scaffolding for galaxies 344 00:21:04,030 --> 00:21:06,795 that really holds them up and holds them in place 345 00:21:06,799 --> 00:21:08,995 and prevents them from falling apart. 346 00:21:09,001 --> 00:21:11,971 Narrator: Now scientists are discovering 347 00:21:11,971 --> 00:21:15,874 that dark matter doesn't just hold galaxies together -- 348 00:21:15,875 --> 00:21:19,140 it might have sparked them into life. 349 00:21:19,145 --> 00:21:22,171 Dr. Kaku: We think that dark matter was created 350 00:21:22,181 --> 00:21:23,512 out of the Big Bang, 351 00:21:23,516 --> 00:21:25,780 and dark matter began to clump, 352 00:21:25,785 --> 00:21:28,516 and these clumpings of dark matter 353 00:21:28,521 --> 00:21:32,617 eventually became the nuclei, the seeds, for our galaxy. 354 00:21:32,625 --> 00:21:35,458 Narrator: But scientists still have no idea 355 00:21:35,461 --> 00:21:38,158 what dark matter actually is. 356 00:21:38,164 --> 00:21:41,065 Dark matter is weird because we don't understand it at all. 357 00:21:41,067 --> 00:21:43,126 It's clearly not made of the same stuff 358 00:21:43,136 --> 00:21:44,501 that you and I are made of. 359 00:21:44,504 --> 00:21:47,235 You can't push against it. You can't feel it. 360 00:21:47,240 --> 00:21:49,140 Yet it's probably all around us. 361 00:21:49,142 --> 00:21:51,304 It's a ghostlike material 362 00:21:51,310 --> 00:21:55,975 that will pass right through you as if you didn't exist at all. 363 00:21:59,118 --> 00:22:01,985 Narrator: We might not know much about dark matter, 364 00:22:01,988 --> 00:22:06,858 but the universe is full of it. 365 00:22:06,859 --> 00:22:09,624 So, the dark matter, weight-for-weight, 366 00:22:09,629 --> 00:22:13,054 makes up at least six times as much of the universe 367 00:22:13,065 --> 00:22:16,228 as does normal matter, the stuff that we're all made from. 368 00:22:16,235 --> 00:22:17,737 And without it, 369 00:22:17,737 --> 00:22:21,105 the universe just wouldn't work the way that it seems to work. 370 00:22:21,107 --> 00:22:22,905 Narrator: But the universe does work, 371 00:22:22,909 --> 00:22:28,040 so maybe dark matter is real. 372 00:22:28,047 --> 00:22:29,412 Strange stuff, 373 00:22:29,415 --> 00:22:33,648 and recently, it's been detected in deep space -- 374 00:22:33,653 --> 00:22:38,591 not directly but by observing what it does to light. 375 00:22:38,591 --> 00:22:44,291 It bends it in a process called gravitational lensing. 376 00:22:44,297 --> 00:22:47,631 Gravitational lensing really allows us to test 377 00:22:47,633 --> 00:22:49,624 the presence of dark matter. 378 00:22:49,635 --> 00:22:51,831 And the way that works is that, 379 00:22:51,838 --> 00:22:54,273 as a beam of light from some distant galaxy 380 00:22:54,273 --> 00:22:55,604 is traveling towards us, 381 00:22:55,608 --> 00:22:58,339 if it passes by a large collection of dark matter, 382 00:22:58,344 --> 00:23:01,109 its path will be deflected around that dark matter 383 00:23:01,113 --> 00:23:02,478 by the gravitational pull. 384 00:23:04,917 --> 00:23:07,443 Narrator: When the Hubble telescope looks 385 00:23:07,453 --> 00:23:08,852 deep into the universe, 386 00:23:08,855 --> 00:23:12,519 some galaxies do seem distorted and stretched. 387 00:23:14,527 --> 00:23:18,794 That's caused by the dark matter, which warps the image. 388 00:23:18,798 --> 00:23:22,826 It's sort of like looking through a goldfish bowl. 389 00:23:22,835 --> 00:23:25,429 Dr. Benson: By probing the shapes of those galaxies 390 00:23:25,438 --> 00:23:26,997 and the degree of distortion, 391 00:23:27,006 --> 00:23:29,304 we can really measure very accurately 392 00:23:29,308 --> 00:23:31,606 the amount of dark matter that's there. 393 00:23:34,380 --> 00:23:35,939 Narrator: It's clear now 394 00:23:35,948 --> 00:23:38,883 that dark matter is a vital ingredient of the universe. 395 00:23:41,020 --> 00:23:43,887 It's been working since the dawn of time 396 00:23:43,890 --> 00:23:48,350 and affects everything everywhere. 397 00:23:48,361 --> 00:23:51,353 It triggers the birth of galaxies 398 00:23:51,364 --> 00:23:55,358 and keeps them from falling apart. 399 00:23:55,368 --> 00:23:58,463 We can't see it or detect it, 400 00:23:58,471 --> 00:24:04,433 but, nevertheless, dark matter is the master of the universe. 401 00:24:10,950 --> 00:24:13,612 Narrator: Galaxies look isolated. 402 00:24:13,619 --> 00:24:16,919 It's true -- they are trillions of miles apart. 403 00:24:16,923 --> 00:24:20,860 But, actually, they live in groups called clusters. 404 00:24:23,029 --> 00:24:26,863 And these clusters of galaxies are linked together 405 00:24:26,866 --> 00:24:31,303 in superclusters, containing tens of thousands of galaxies. 406 00:24:31,304 --> 00:24:35,070 So, where does our Milky Way galaxy fit in? 407 00:24:35,074 --> 00:24:37,736 Dr. Kaku: If you take a look at the big picture, 408 00:24:37,743 --> 00:24:39,677 you realize that our galaxy 409 00:24:39,679 --> 00:24:43,138 is part of a local group of galaxies, perhaps 30, 410 00:24:43,149 --> 00:24:45,641 and our galaxy and Andromeda 411 00:24:45,651 --> 00:24:49,713 are the two biggest galaxies in this local group. 412 00:24:49,722 --> 00:24:52,316 But if you look even farther out, 413 00:24:52,325 --> 00:24:57,593 we are part of the Virgo supercluster of galaxies. 414 00:24:57,596 --> 00:24:59,530 Narrator: Scientists are now mapping 415 00:24:59,532 --> 00:25:01,489 the overall structure of the universe 416 00:25:01,500 --> 00:25:05,903 and the position of clusters and superclusters of galaxies. 417 00:25:07,707 --> 00:25:10,108 [thunder crashes] 418 00:25:10,109 --> 00:25:14,239 This is Apache Point Observatory in New Mexico, 419 00:25:14,246 --> 00:25:18,342 home to the Sloan Digital Sky Survey, or SDSS. 420 00:25:20,820 --> 00:25:24,188 It's a small telescope with a big price tag, 421 00:25:24,190 --> 00:25:26,215 and it has a unique mission. 422 00:25:35,701 --> 00:25:40,867 SDSS is building the first 3-D map of the night sky, 423 00:25:40,873 --> 00:25:44,366 a process that's identifying the exact positions 424 00:25:44,377 --> 00:25:48,837 of tens of millions of galaxies. 425 00:25:50,449 --> 00:25:54,511 To do it, SDSS goes galaxy hunting 426 00:25:54,520 --> 00:25:59,617 way out into space, far beyond our Milky Way. 427 00:25:59,625 --> 00:26:03,721 It pinpoints the positions of galaxies, 428 00:26:03,729 --> 00:26:07,996 and this information is copied onto aluminum disks. 429 00:26:08,000 --> 00:26:12,198 Long: These aluminum disks are about 30 inches across, 430 00:26:12,204 --> 00:26:14,764 and they have 640 holes each, 431 00:26:14,774 --> 00:26:17,141 and these holes correspond 432 00:26:17,143 --> 00:26:20,044 to the objects of interest in the sky. 433 00:26:20,046 --> 00:26:22,538 Narrator: Each object is a galaxy. 434 00:26:22,548 --> 00:26:25,347 Light from the galaxy is channeled through a hole 435 00:26:25,351 --> 00:26:28,013 and down a fiberoptic cable. 436 00:26:28,020 --> 00:26:31,581 This method records data on distance and position 437 00:26:31,590 --> 00:26:35,356 from thousands of galaxies and plots their location in 3-D. 438 00:26:35,361 --> 00:26:38,092 Long: It's telling us about their shape. 439 00:26:38,097 --> 00:26:40,532 It's telling us about their makeup. 440 00:26:40,533 --> 00:26:43,366 It's telling us how they're distributed. 441 00:26:43,369 --> 00:26:45,633 And all of this is very important 442 00:26:45,638 --> 00:26:48,403 to astronomy and understanding our universe. 443 00:26:50,509 --> 00:26:53,171 Narrator: And this is what they're creating -- 444 00:26:53,179 --> 00:26:56,342 the biggest 3-D map ever. 445 00:26:59,785 --> 00:27:03,915 The map is showing us things we've never seen before. 446 00:27:03,923 --> 00:27:09,487 It shows galaxies in clusters and superclusters... 447 00:27:09,495 --> 00:27:11,156 But pull back even more, 448 00:27:11,163 --> 00:27:14,599 and we see that these superclusters are connected 449 00:27:14,600 --> 00:27:19,060 into structures called filaments. 450 00:27:19,071 --> 00:27:21,369 SDSS has found one 451 00:27:21,373 --> 00:27:25,970 that's 1.4 billion light-years across. 452 00:27:29,081 --> 00:27:31,573 It's called the Great Sloan Wall, 453 00:27:31,584 --> 00:27:34,246 and it's the largest single structure 454 00:27:34,253 --> 00:27:37,951 ever discovered in the history of science. 455 00:27:40,192 --> 00:27:45,187 Long: You get a sense that you are in something quite vast. 456 00:27:45,197 --> 00:27:47,564 You can see the clusters and filaments 457 00:27:47,566 --> 00:27:49,227 as the data would scroll by. 458 00:27:49,235 --> 00:27:52,296 And, you know, each one of these little, fuzzy spots 459 00:27:52,304 --> 00:27:55,296 were actually galaxies -- not stars but galaxies -- 460 00:27:55,307 --> 00:27:57,935 and so you're seeing whole clusters of these things. 461 00:27:57,943 --> 00:28:02,210 Narrator: SDSS is showing galactic geography 462 00:28:02,214 --> 00:28:03,909 on a vast scale. 463 00:28:03,916 --> 00:28:07,511 Scientists have taken it even further. 464 00:28:08,521 --> 00:28:13,391 They've built the whole universe in a supercomputer. 465 00:28:13,392 --> 00:28:16,828 Here you can't see individual galaxies. 466 00:28:16,829 --> 00:28:19,992 You can't even see galaxy clusters. 467 00:28:19,999 --> 00:28:24,232 What you can see are superclusters, 468 00:28:24,236 --> 00:28:29,902 linked together on filaments in a vast cosmic web. 469 00:28:29,909 --> 00:28:31,866 Dr. Krauss: As one begins to come back 470 00:28:31,877 --> 00:28:33,811 from the whole scale of the universe, 471 00:28:33,812 --> 00:28:36,213 one begins to reveal a filamentary pattern, 472 00:28:36,215 --> 00:28:40,311 a cosmic web containing galaxies 473 00:28:40,319 --> 00:28:43,380 and clusters of galaxies that light up the universe 474 00:28:43,389 --> 00:28:45,255 where there are as many galaxies in that direction 475 00:28:45,257 --> 00:28:47,453 as that direction as that direction as that direction. 476 00:28:47,459 --> 00:28:49,928 And, in fact, on larger scales, 477 00:28:49,929 --> 00:28:53,354 the universe kind of looks like a sponge. 478 00:28:53,365 --> 00:28:56,232 Narrator: Each of the filaments is home 479 00:28:56,235 --> 00:28:58,397 to millions of galaxy clusters, 480 00:28:58,404 --> 00:29:02,272 all bound together by dark matter. 481 00:29:02,274 --> 00:29:04,709 In this computer simulation, 482 00:29:04,710 --> 00:29:08,442 the dark matter glows along the filaments. 483 00:29:08,447 --> 00:29:12,350 Dark matter affects where in the universe galaxies will form. 484 00:29:12,351 --> 00:29:13,512 When we look at galaxies, 485 00:29:13,519 --> 00:29:15,385 they're not sprinkled around at random. 486 00:29:15,387 --> 00:29:17,412 They actually tend to form in little groups, 487 00:29:17,423 --> 00:29:19,755 and that's really reflecting 488 00:29:19,758 --> 00:29:23,524 the large-scale distribution of dark matter. 489 00:29:23,529 --> 00:29:26,430 Narrator: Dark matter is the glue 490 00:29:26,432 --> 00:29:31,063 holding together the whole superstructure of the universe. 491 00:29:31,070 --> 00:29:34,802 It binds galaxies in clusters 492 00:29:34,807 --> 00:29:38,801 and clusters in superclusters. 493 00:29:38,811 --> 00:29:44,272 All these are locked together in a web of filaments. 494 00:29:44,283 --> 00:29:45,751 Without dark matter, 495 00:29:45,751 --> 00:29:48,345 the whole structure of the universe 496 00:29:48,354 --> 00:29:51,415 would simply fall apart. 497 00:29:51,423 --> 00:29:55,087 This is the big picture of our universe. 498 00:29:57,263 --> 00:30:00,665 It's a giant cosmic web. 499 00:30:00,666 --> 00:30:04,660 And hidden deep in one of these filaments is the Milky Way. 500 00:30:04,670 --> 00:30:08,436 It's been around for nearly 12 billion years. 501 00:30:12,211 --> 00:30:14,270 But in the future, 502 00:30:14,280 --> 00:30:19,980 it's going to be destroyed in a gigantic cosmic collision. 503 00:30:29,128 --> 00:30:33,531 Narrator: Galaxies are vast kingdoms of stars. 504 00:30:33,532 --> 00:30:36,331 Some are giant balls, 505 00:30:36,335 --> 00:30:39,236 and others, complex spirals. 506 00:30:39,238 --> 00:30:42,799 The thing is, they never stop changing. 507 00:30:42,808 --> 00:30:45,573 While it may seem, when we look out at our galaxy, 508 00:30:45,577 --> 00:30:49,741 that our galaxy is static and been here forever, it's not. 509 00:30:49,748 --> 00:30:51,910 Our galaxy is a dynamic place. 510 00:30:51,917 --> 00:30:55,547 Its very nature has been changing over cosmic time. 511 00:30:57,923 --> 00:31:02,326 Narrator: Galaxies not only change -- they move, as well. 512 00:31:05,197 --> 00:31:07,757 And sometimes they run into each other. 513 00:31:07,766 --> 00:31:12,533 And when they do, it's eat or be eaten. 514 00:31:15,574 --> 00:31:20,239 There's a zoo of galaxies that you can find out there, 515 00:31:20,245 --> 00:31:23,237 and this entire zoo can interact or collide 516 00:31:23,248 --> 00:31:26,047 with any of the other members of the zoo. 517 00:31:28,120 --> 00:31:32,648 Narrator: This is NGC 2207. 518 00:31:32,658 --> 00:31:37,255 It looks like an enormous double-spiral galaxy, 519 00:31:37,262 --> 00:31:42,701 but it's actually two galaxies colliding. 520 00:31:42,701 --> 00:31:45,830 The collision will last millions of years, 521 00:31:45,838 --> 00:31:50,002 and eventually the two galaxies will become one. 522 00:31:54,079 --> 00:31:57,379 Collisions like this happen all over the universe. 523 00:31:57,383 --> 00:32:02,344 Our own Milky Way is no exception. 524 00:32:02,354 --> 00:32:06,052 The Milky Way is, in fact, a cannibal, 525 00:32:06,058 --> 00:32:08,789 and it exists in its present form 526 00:32:08,794 --> 00:32:11,786 by having cannibalized small galaxies 527 00:32:11,797 --> 00:32:13,765 that it literally ate up. 528 00:32:13,766 --> 00:32:16,360 And today we can see small streams of stars 529 00:32:16,368 --> 00:32:19,167 that are left over from the most recent mergers 530 00:32:19,171 --> 00:32:21,469 that have formed the Milky Way galaxy. 531 00:32:24,276 --> 00:32:28,179 Narrator: But that's nothing compared to what's coming up. 532 00:32:28,180 --> 00:32:33,812 We are on a collision course with the galaxy Andromeda. 533 00:32:33,819 --> 00:32:37,949 And for the Milky Way, that's bad news. 534 00:32:40,559 --> 00:32:44,223 Our Milky Way galaxy is approaching Andromeda 535 00:32:44,229 --> 00:32:47,893 at the rate of about a quarter of a million miles per hour, 536 00:32:47,900 --> 00:32:51,268 which means that in 5 billion to 6 billion years, 537 00:32:51,270 --> 00:32:54,262 it's all over for the Milky Way galaxy. 538 00:32:54,273 --> 00:32:58,938 You would see the entire Andromeda galaxy 539 00:32:58,944 --> 00:33:03,347 speeding towards us, really barreling straight into us. 540 00:33:03,348 --> 00:33:05,442 As the two galaxies interact, 541 00:33:05,451 --> 00:33:08,512 they both become more and more disturbed 542 00:33:08,520 --> 00:33:10,750 and closer and closer together. 543 00:33:10,756 --> 00:33:13,589 And the whole process starts to snowball. 544 00:33:13,592 --> 00:33:16,584 The two galaxies will enter a death dance. 545 00:33:16,595 --> 00:33:20,589 Narrator: This is a simulation of the future collision, 546 00:33:20,599 --> 00:33:22,966 sped up millions of times. 547 00:33:27,372 --> 00:33:29,773 As the galaxies crash together, 548 00:33:29,775 --> 00:33:34,269 clouds of gas and dust are thrown out in all directions. 549 00:33:42,387 --> 00:33:44,913 Gravity from the merging galaxies 550 00:33:44,923 --> 00:33:50,453 rips stars from their orbits and shoots them deep into space. 551 00:33:50,462 --> 00:33:52,897 Dr. Kaku: As we approach doomsday 552 00:33:52,898 --> 00:33:56,334 for the Milky Way galaxy, it would be spectacular. 553 00:33:56,335 --> 00:33:58,394 We would have a front-row seat 554 00:33:58,403 --> 00:34:01,065 on the destruction of our own galaxy. 555 00:34:04,176 --> 00:34:08,204 And eventually, the two galaxies will go right through each other 556 00:34:08,213 --> 00:34:11,444 and then come back and then coalesce. 557 00:34:11,450 --> 00:34:16,115 Narrator: It's strange, but the stars themselves won't collide. 558 00:34:16,121 --> 00:34:19,955 They're still too far apart. 559 00:34:19,958 --> 00:34:21,392 All of the stars are basically 560 00:34:21,393 --> 00:34:23,259 just gonna pass right by each other. 561 00:34:23,262 --> 00:34:26,163 The probability of one individual star 562 00:34:26,164 --> 00:34:29,828 hitting another individual star are basically zero. 563 00:34:33,305 --> 00:34:36,764 Narrator: However, the gas and dust between the stars 564 00:34:36,775 --> 00:34:38,277 will start to heat up. 565 00:34:38,277 --> 00:34:40,507 Eventually, it ignites, 566 00:34:40,512 --> 00:34:44,813 and the clashing galaxies will glow white-hot. 567 00:34:46,885 --> 00:34:51,721 So, at a certain point, the sky could be on fire. 568 00:34:55,661 --> 00:35:00,223 The Milky Way and Andromeda as we know it will cease to exist, 569 00:35:00,232 --> 00:35:02,963 and Milkomeda will be born, 570 00:35:02,968 --> 00:35:06,802 and it will look like a whole new galaxy. 571 00:35:18,350 --> 00:35:21,149 Narrator: This new galaxy, Milkomeda, 572 00:35:21,153 --> 00:35:23,884 will become a huge, elliptical galaxy 573 00:35:23,889 --> 00:35:26,358 without any arms or spiral shape. 574 00:35:28,293 --> 00:35:31,627 There's no escaping what's going to happen. 575 00:35:31,630 --> 00:35:35,362 The question is, what's it mean for planet Earth? 576 00:35:35,367 --> 00:35:37,995 We may either be thrown out into outer space 577 00:35:38,003 --> 00:35:43,874 when the arms of the Milky Way galaxy are ripped apart, 578 00:35:43,875 --> 00:35:48,574 or we could wind up in the stomach of this new galaxy. 579 00:35:48,580 --> 00:35:53,677 Narrator: Stars and planets will be pushed all over the place, 580 00:35:53,685 --> 00:35:58,714 so this may well be the end of planet Earth. 581 00:36:05,464 --> 00:36:10,197 Galaxies all over the universe will continue to collide. 582 00:36:13,071 --> 00:36:16,097 But this age of galactic cannibalism 583 00:36:16,108 --> 00:36:19,840 will eventually pass... 584 00:36:19,845 --> 00:36:23,179 Because there is an even more destructive force 585 00:36:23,181 --> 00:36:24,410 in the universe, 586 00:36:24,416 --> 00:36:26,748 a force that nothing can stop. 587 00:36:30,822 --> 00:36:35,123 It will ultimately push galaxies away from each other, 588 00:36:35,127 --> 00:36:39,894 stretching everything, until the universe... 589 00:36:39,898 --> 00:36:42,390 Rips itself apart. 590 00:36:48,640 --> 00:36:49,698 Narrator: Galaxies are home 591 00:36:49,708 --> 00:36:54,874 to stars, solar systems, planets, and moons. 592 00:36:54,880 --> 00:37:00,011 Everything that's important happens in galaxies. 593 00:37:00,018 --> 00:37:03,283 Dr. Krauss: Galaxies are the lifeblood of the universe. 594 00:37:03,288 --> 00:37:06,053 We arose because we live in a galaxy, 595 00:37:06,058 --> 00:37:07,355 and everything we can see 596 00:37:07,359 --> 00:37:09,885 and everything that matters to us in the universe 597 00:37:09,895 --> 00:37:11,090 happens within galaxies. 598 00:37:12,898 --> 00:37:14,889 Narrator: But the truth is, 599 00:37:14,900 --> 00:37:19,633 galaxies are delicate structures held together by dark matter. 600 00:37:19,638 --> 00:37:22,266 Now scientists have found another force 601 00:37:22,274 --> 00:37:23,935 at work in the universe. 602 00:37:23,942 --> 00:37:27,207 It's called dark energy. 603 00:37:27,212 --> 00:37:30,773 Dark energy has the opposite effect of dark matter. 604 00:37:30,782 --> 00:37:34,844 Instead of binding galaxies together, it pushes them apart. 605 00:37:34,853 --> 00:37:36,878 Dr. Krauss: The dark energy, 606 00:37:36,888 --> 00:37:39,949 which we've only discovered in the last decade, 607 00:37:39,958 --> 00:37:42,222 which is the dominant stuff in the universe, 608 00:37:42,227 --> 00:37:43,422 is far more mysterious. 609 00:37:43,428 --> 00:37:45,795 We don't have the slightest idea why it's there. 610 00:37:50,168 --> 00:37:53,263 Dr. Benson: What it's made from, we don't really know. 611 00:37:53,271 --> 00:37:55,899 We know it's there, but we don't really know 612 00:37:55,907 --> 00:37:57,409 what it is or what it's doing. 613 00:37:57,409 --> 00:37:59,776 Dark energy is really weird. 614 00:37:59,778 --> 00:38:03,339 It's as if space has little springs in it 615 00:38:03,348 --> 00:38:07,649 which are causing things to repel each other 616 00:38:07,652 --> 00:38:09,677 and push them apart. 617 00:38:09,688 --> 00:38:11,622 Narrator: Far in the future, 618 00:38:11,623 --> 00:38:14,251 scientists think that dark energy will win 619 00:38:14,259 --> 00:38:17,991 the cosmic battle with dark matter. 620 00:38:17,996 --> 00:38:21,057 And that victory will start to drive galaxies apart. 621 00:38:21,066 --> 00:38:24,001 Dr. Krauss: Dark energy's gonna kill galaxies off. 622 00:38:24,002 --> 00:38:27,267 It's gonna do that by causing all the galaxies to recede 623 00:38:27,272 --> 00:38:30,572 further and further away from us until they're invisible, 624 00:38:30,575 --> 00:38:32,009 until they're moving away from us 625 00:38:32,010 --> 00:38:33,273 faster than the speed of light. 626 00:38:33,278 --> 00:38:35,372 So, the rest of the universe will literally disappear 627 00:38:35,380 --> 00:38:36,711 before our very eyes. 628 00:38:36,715 --> 00:38:40,083 Not today, not tomorrow, but in perhaps a trillion years, 629 00:38:40,085 --> 00:38:42,952 the rest of the universe will have disappeared. 630 00:38:42,954 --> 00:38:47,790 Narrator: Galaxies will become lonely outposts in deep space. 631 00:38:51,730 --> 00:38:56,463 But that's not going to happen for a very, very long time. 632 00:38:56,468 --> 00:38:59,961 For now, the universe is thriving 633 00:38:59,971 --> 00:39:02,963 and galaxies are creating the right conditions 634 00:39:02,974 --> 00:39:05,102 for life to exist. 635 00:39:05,110 --> 00:39:07,579 Without galaxies, I wouldn't be here. 636 00:39:07,579 --> 00:39:08,978 You wouldn't be here. 637 00:39:08,980 --> 00:39:11,381 Perhaps life itself wouldn't be here. 638 00:39:13,418 --> 00:39:15,113 Narrator: We're lucky. 639 00:39:15,120 --> 00:39:17,020 Life has only evolved on Earth 640 00:39:17,022 --> 00:39:19,582 because our tiny solar system was born 641 00:39:19,591 --> 00:39:21,559 in the right part of the galaxy. 642 00:39:24,529 --> 00:39:27,055 If we were any closer to the center, 643 00:39:27,065 --> 00:39:30,228 well, we wouldn't be here. 644 00:39:32,270 --> 00:39:34,534 Dr. Kaku: At the center of a galaxy, 645 00:39:34,539 --> 00:39:36,303 life can be extremely violent. 646 00:39:36,308 --> 00:39:39,107 And, in fact, if our solar system were closer 647 00:39:39,110 --> 00:39:40,805 to the center of our galaxy, 648 00:39:40,812 --> 00:39:44,214 it would be so radioactive that we couldn't exist at all. 649 00:39:44,216 --> 00:39:49,518 Narrator: Too far away from the center would be just as bad. 650 00:39:53,291 --> 00:39:57,091 Out there, there aren't as many stars. 651 00:39:57,095 --> 00:40:00,258 We might not exist at all. 652 00:40:00,265 --> 00:40:04,600 So, in some sense, we are in the Goldilocks Zone of the galaxy -- 653 00:40:04,603 --> 00:40:08,631 not too close, not too far, but just right. 654 00:40:08,640 --> 00:40:10,665 Narrator: Scientists believe 655 00:40:10,675 --> 00:40:13,042 that this galactic Goldilocks Zone 656 00:40:13,044 --> 00:40:17,140 might contain millions of stars, 657 00:40:17,148 --> 00:40:21,745 so there may be other solar systems that can support life 658 00:40:21,753 --> 00:40:24,085 right here in our own galaxy. 659 00:40:24,089 --> 00:40:26,854 And if our galaxy has a habitable zone, 660 00:40:26,858 --> 00:40:28,952 then other galaxies could, too. 661 00:40:28,960 --> 00:40:31,429 Dr. Ghez: The universe is immense, 662 00:40:31,429 --> 00:40:35,127 and the amazing thing is that we're always discovering more. 663 00:40:35,133 --> 00:40:38,831 Every time we think we know the answer to one problem, 664 00:40:38,837 --> 00:40:42,102 we find it's embedded in a much bigger problem. 665 00:40:42,107 --> 00:40:43,506 And that's exciting. 666 00:40:46,111 --> 00:40:48,842 Narrator: There are endless questions to ask 667 00:40:48,847 --> 00:40:50,941 and mysteries to solve... 668 00:40:50,949 --> 00:40:54,010 In our own galaxy, the Milky Way, 669 00:40:54,019 --> 00:40:57,045 and in galaxies all across the universe. 670 00:40:57,055 --> 00:40:58,853 10 years ago, who would have thought 671 00:40:58,857 --> 00:41:00,450 that we would be able to identify 672 00:41:00,458 --> 00:41:01,857 the black hole at the center? 673 00:41:01,860 --> 00:41:04,056 Who would have thought 10 years ago 674 00:41:04,062 --> 00:41:05,826 that the astronomical community 675 00:41:05,830 --> 00:41:08,527 would believe in dark matter and dark energy? 676 00:41:08,533 --> 00:41:10,160 Narrator: More and more, 677 00:41:10,168 --> 00:41:14,264 scientific research is focusing on galaxies. 678 00:41:14,272 --> 00:41:18,334 They hold the key to how the universe works. 679 00:41:18,343 --> 00:41:20,835 We should be amazed to live at this time, here, 680 00:41:20,845 --> 00:41:23,371 at a random time in the history of the universe, 681 00:41:23,381 --> 00:41:26,817 on a random planet, at the outskirts of a random galaxy, 682 00:41:26,818 --> 00:41:29,685 where we can ask questions and understand things 683 00:41:29,688 --> 00:41:33,215 from the beginning of the universe to the end. 684 00:41:33,224 --> 00:41:36,717 We should celebrate our brief moment in the sun. 685 00:41:39,331 --> 00:41:42,699 Narrator: Galaxies are born... 686 00:41:42,701 --> 00:41:46,126 They evolve... 687 00:41:46,137 --> 00:41:49,767 They collide... 688 00:41:49,774 --> 00:41:53,039 And they die. 689 00:41:53,044 --> 00:41:58,847 Galaxies are the superstars of the scientific world. 690 00:41:58,850 --> 00:42:04,812 And even the scientists who study them have their favorites. 691 00:42:04,823 --> 00:42:07,656 The Whirlpool galaxy, or M51. 692 00:42:11,629 --> 00:42:13,927 I kind of like the Sombrero galaxy, 693 00:42:13,932 --> 00:42:16,401 if I had to put one on a wall. 694 00:42:16,401 --> 00:42:17,527 [laughs] 695 00:42:17,535 --> 00:42:20,869 Dr. Krauss: The Sombrero galaxy, ring galaxies -- 696 00:42:20,872 --> 00:42:22,772 they're just beautiful to look at. 697 00:42:25,877 --> 00:42:29,142 My favorite galaxy is the Milky Way galaxy. 698 00:42:29,147 --> 00:42:31,980 It's my true home. 699 00:42:41,126 --> 00:42:43,720 Narrator: We're lucky that the Milky Way 700 00:42:43,728 --> 00:42:46,595 provides the right conditions for us to live. 701 00:42:46,598 --> 00:42:51,968 Our destiny is linked to our galaxy and to all galaxies. 702 00:42:55,840 --> 00:42:58,639 They made us, they shape us, 703 00:42:58,643 --> 00:43:02,238 and our future is in their hands. 56710

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