1 00:00:43,110 --> 00:00:45,442 SAGAN: The sky calls to us. 2 00:00:45,813 --> 00:00:47,906 If we do not destroy ourselves... 3 00:00:48,116 --> 00:00:51,143 ...we will one day venture to the stars. 4 00:00:52,054 --> 00:00:55,512 There was a time when the stars seemed an impenetrable mystery. 5 00:00:55,724 --> 00:00:59,058 Today, we have begun to understand them. 6 00:00:59,262 --> 00:01:04,200 In our personal lives also, we journey from ignorance to knowledge. 7 00:01:04,435 --> 00:01:08,873 Our individual growth reflects the advancement of the species. 8 00:01:09,374 --> 00:01:11,309 The exploration of the cosmos is... 9 00:01:11,511 --> 00:01:14,537 ...a voyage of self-discovery. 10 00:01:25,059 --> 00:01:27,995 When I was a child, I lived here... 11 00:01:28,197 --> 00:01:32,498 ...in the Bensonhurst section of Brooklyn in the city of New York. 12 00:01:32,702 --> 00:01:35,762 I knew my immediate neighborhood intimately... 13 00:01:35,972 --> 00:01:40,239 ...every candy store, front stoop... 14 00:01:40,444 --> 00:01:42,709 ...back yard, empty lot... 15 00:01:42,915 --> 00:01:46,009 ...and wall for playing Chinese handball. 16 00:01:51,625 --> 00:01:53,752 It was my whole world. 17 00:02:12,850 --> 00:02:14,977 But more than a few blocks away... 18 00:02:15,186 --> 00:02:19,886 ...north of the raucous traffic and elevated railway on 86th Street... 19 00:02:20,092 --> 00:02:23,756 ...was an unknown territory off-limits to my wanderings. 20 00:02:24,698 --> 00:02:27,463 It could have been Mars for all I knew. 21 00:02:31,572 --> 00:02:34,406 Even with an early bed time in the winter... 22 00:02:34,676 --> 00:02:37,669 ...you could occasionally see the stars. 23 00:02:38,181 --> 00:02:41,480 I would look up at them and wonder what they were. 24 00:02:41,785 --> 00:02:44,549 I'd ask other kids and adults... 25 00:02:45,122 --> 00:02:46,714 ...and they would answer: 26 00:02:46,925 --> 00:02:48,984 "They're lights in the sky, kid." 27 00:02:49,194 --> 00:02:53,154 Well, I could tell they were lights in the sky, but what were they? 28 00:02:53,366 --> 00:02:56,802 There had to be some deeper answer. 29 00:03:02,210 --> 00:03:05,702 I remember I was issued my first library card. 30 00:03:05,913 --> 00:03:10,476 It was some library on 85th Street. Anyway, it was in alien territory. 31 00:03:10,953 --> 00:03:14,651 And I asked the librarian for a book on stars. 32 00:03:15,091 --> 00:03:16,524 She gave me... 33 00:03:16,960 --> 00:03:19,896 ...a picture book with portraits of men and women... 34 00:03:20,097 --> 00:03:23,727 ...with names like Veronica Lake and Alan Ladd. 35 00:03:24,269 --> 00:03:27,671 I explained that wasn't what I wanted at all. 36 00:03:28,274 --> 00:03:31,710 And for some reason, then obscure to me, she smiled... 37 00:03:31,911 --> 00:03:35,075 ...and got me another book, the right kind of book. 38 00:03:35,382 --> 00:03:37,681 I was so excited to know the answer... 39 00:03:37,886 --> 00:03:40,946 ...I opened the book breathlessly, right there in the library... 40 00:03:41,156 --> 00:03:43,990 ...and the book said something astonishing... 41 00:03:44,193 --> 00:03:46,684 ...a very big thought. 42 00:03:47,397 --> 00:03:50,730 Stars, it said, were suns... 43 00:03:50,934 --> 00:03:52,698 ...but very far away. 44 00:03:52,904 --> 00:03:56,840 The sun was a star, but close-up. 45 00:04:04,517 --> 00:04:08,249 How, I wondered, could anybody know such things forsure? 46 00:04:08,456 --> 00:04:11,983 How did they figure it out? Where did they even begin? 47 00:04:21,537 --> 00:04:24,507 I was ignorant of the idea of angular size. 48 00:04:24,708 --> 00:04:28,702 I didn't know about the inverse square law of the propagation of light. 49 00:04:28,913 --> 00:04:32,713 I didn't have any chance of calculating the distance to the stars. 50 00:04:32,918 --> 00:04:36,012 But I could tell that if the stars were suns... 51 00:04:36,222 --> 00:04:38,691 ...they had to be awfully far away. 52 00:04:38,892 --> 00:04:43,125 Further away than 86th Street, further away than Manhattan... 53 00:04:43,331 --> 00:04:46,698 ...further away, probably, than New Jersey. 54 00:04:46,901 --> 00:04:50,599 The universe had become much grander... 55 00:04:50,806 --> 00:04:53,173 ...than I had ever guessed. 56 00:04:56,112 --> 00:04:58,775 And then I read another astonishing fact. 57 00:04:58,983 --> 00:05:02,282 The Earth, which includes Brooklyn... 58 00:05:02,486 --> 00:05:03,784 ...was a planet. 59 00:05:03,989 --> 00:05:06,048 It went around the sun. 60 00:05:06,258 --> 00:05:07,850 There were other planets. 61 00:05:08,059 --> 00:05:10,324 They also went around the sun... 62 00:05:10,530 --> 00:05:13,830 ...some closer to the sun, some further from the sun. 63 00:05:14,067 --> 00:05:18,596 But planets didn't shine by their own light the way the sun does. 64 00:05:19,340 --> 00:05:23,300 No, planets simply reflected the little bit of light... 65 00:05:23,512 --> 00:05:27,107 ...that shines on them from the sun back to us. 66 00:05:27,316 --> 00:05:29,581 If you were a great distance from the sun... 67 00:05:29,786 --> 00:05:33,518 ...you wouldn't be able to see the Earth or the other planets at all. 68 00:05:33,758 --> 00:05:36,454 Well, then, it stood to reason, I thought... 69 00:05:36,661 --> 00:05:40,291 ...that those other stars ought to have their own planets... 70 00:05:40,499 --> 00:05:42,763 ...and some of those planets ought to have life. 71 00:05:43,403 --> 00:05:44,631 Why not? 72 00:05:44,838 --> 00:05:49,242 And that life ought to be pretty different from life as we know it... 73 00:05:49,443 --> 00:05:51,434 ...life here in Brooklyn. 74 00:05:51,645 --> 00:05:54,774 Ganymede. Look at this amazing Ganymede stuff. 75 00:05:54,983 --> 00:05:56,041 Wait, wait, wait. 76 00:05:56,251 --> 00:05:58,652 As a child, it was my immense good fortune... 77 00:05:58,855 --> 00:06:02,882 ...to have parents and a few teachers who encouraged my curiosity. 78 00:06:03,092 --> 00:06:05,425 This was my 6th-grade classroom. 79 00:06:05,629 --> 00:06:08,598 I came back here one day to remember what it was like. 80 00:06:08,800 --> 00:06:11,530 I brought some of the pictures of other worlds... 81 00:06:11,736 --> 00:06:14,365 ...that were radioed back by the Voyager spacecraft... 82 00:06:14,573 --> 00:06:16,700 ...of Jupiter and its moons. 83 00:06:16,909 --> 00:06:18,467 This is Calisto which is... 84 00:06:18,677 --> 00:06:19,838 (SAGAN LAUGHS) 85 00:06:22,215 --> 00:06:24,150 What is a Calisto? I want a Calisto. 86 00:06:24,352 --> 00:06:25,649 Now you got it. What is it? 87 00:06:25,853 --> 00:06:29,346 It's the outermost big moon of Jupiter. 88 00:06:30,425 --> 00:06:32,859 Who is this guy? Europa. 89 00:06:34,264 --> 00:06:35,891 Another Europa. 90 00:06:36,266 --> 00:06:39,327 A black-and-white picture of a ring of Jupiter. 91 00:06:39,737 --> 00:06:42,763 There you go. That's a prize for honesty. 92 00:06:43,407 --> 00:06:44,898 You didn't get a second. 93 00:06:45,110 --> 00:06:46,600 Which one would you like? 94 00:06:58,792 --> 00:07:01,853 Every one of us begins life with an open mind... 95 00:07:02,063 --> 00:07:06,000 ...a driving curiosity, a sense of wonder. 96 00:07:07,102 --> 00:07:10,436 I thought it might be fun if we now had some questions. 97 00:07:10,640 --> 00:07:14,543 Why is the Earth round? Why isn't it square or any other shape? 98 00:07:15,246 --> 00:07:16,838 That's a good question. 99 00:07:17,048 --> 00:07:21,486 That's a question I've asked myself. The answer has to do with gravity. 100 00:07:21,987 --> 00:07:23,818 The Earth has a strong gravity. 101 00:07:24,022 --> 00:07:26,583 If you were to make a mountain very high... 102 00:07:26,793 --> 00:07:29,695 ...higher than Everest, the biggest mountain on Earth... 103 00:07:29,897 --> 00:07:32,229 ...it would be crushed by its own weight. 104 00:07:32,433 --> 00:07:35,096 Gravity pulls everything towards the center. 105 00:07:35,303 --> 00:07:38,568 So any really big bump on the Earth is crushed. 106 00:07:38,773 --> 00:07:42,403 But if you had a small object, a tiny world... 107 00:07:42,612 --> 00:07:44,273 ...the gravity is very low... 108 00:07:44,480 --> 00:07:47,644 ...and then it can be very different from a sphere. 109 00:07:47,851 --> 00:07:52,255 I think I have here a world that isn't a sphere. 110 00:07:52,624 --> 00:07:53,682 Here. 111 00:07:54,893 --> 00:07:56,224 Look at this one. 112 00:07:57,429 --> 00:07:58,919 See? It's lumpy. 113 00:08:00,700 --> 00:08:01,894 It's a lumpy world. 114 00:08:02,969 --> 00:08:04,334 It looks like a potato. 115 00:08:05,072 --> 00:08:08,235 There's a large potato orbiting the planet Mars. 116 00:08:08,442 --> 00:08:10,673 This is one of the moons of Mars. 117 00:08:10,879 --> 00:08:13,109 That's a perfect example. 118 00:08:13,315 --> 00:08:17,309 You can have big departures from a sphere if your gravity is low. 119 00:08:17,520 --> 00:08:19,420 Now the question in the front. 120 00:08:19,622 --> 00:08:22,854 Is the sun considered part of the Milky Way galaxy? 121 00:08:23,060 --> 00:08:26,189 Sure, you're considered part of the Milky Way galaxy. 122 00:08:26,631 --> 00:08:30,932 Everything except other galaxies is part of the Milky Way galaxy. 123 00:08:31,137 --> 00:08:32,695 The sun is one star. 124 00:08:32,905 --> 00:08:37,843 There is a few hundred billion stars in the Milky Way. 125 00:08:38,145 --> 00:08:40,876 Around each star, maybe, is a whole bunch of planets. 126 00:08:41,749 --> 00:08:44,980 And on one of those planets is life... 127 00:08:45,187 --> 00:08:49,055 ...and one of the life forms on that planet is you. 128 00:08:49,258 --> 00:08:51,625 You're a part of the Milky Way galaxy too. 129 00:09:02,107 --> 00:09:07,045 Sometimes I think, how lucky we are to live in this time... 130 00:09:07,246 --> 00:09:10,910 ...the first moment in human history when we are, in fact... 131 00:09:11,118 --> 00:09:12,710 ...visiting other worlds... 132 00:09:12,920 --> 00:09:17,153 ...and engaging in a deep reconnaissance of the cosmos. 133 00:09:17,525 --> 00:09:20,153 But if we had been born in a much earlier age... 134 00:09:20,361 --> 00:09:23,456 ...no matter how great our dedication, we couldn't have understood... 135 00:09:23,666 --> 00:09:25,931 ...what the stars and planets are. 136 00:09:35,480 --> 00:09:39,975 We would not have known that there were other suns and other worlds. 137 00:09:43,323 --> 00:09:47,283 This is one of the great secrets wrested from nature... 138 00:09:47,495 --> 00:09:51,956 ...through a million years of patient observation and courageous thinking. 139 00:09:55,437 --> 00:09:59,238 Human beings have always asked questions about the stars. 140 00:09:59,442 --> 00:10:02,503 It's as natural as breathing. 141 00:10:02,746 --> 00:10:06,581 But imagine a time before science had found out the answers. 142 00:10:06,785 --> 00:10:09,379 Imagine what it was like, say... 143 00:10:09,587 --> 00:10:13,115 ...hundreds of thousands of years ago... 144 00:10:13,325 --> 00:10:16,921 ...soon after the discovery of fire. 145 00:10:17,130 --> 00:10:20,725 We were just as smart and just as curious then... 146 00:10:20,934 --> 00:10:22,596 ...as we are now. 147 00:10:22,804 --> 00:10:24,669 Sometimes it seems to me that... 148 00:10:24,872 --> 00:10:27,899 ...there were people then who thought like this: 149 00:10:30,279 --> 00:10:33,841 We are wandering hunter folk. 150 00:10:34,050 --> 00:10:35,711 Fire keeps us warm. 151 00:10:35,919 --> 00:10:39,151 Its light makes holes in the darkness. 152 00:10:39,356 --> 00:10:41,621 It keeps hungry animals away. 153 00:10:42,060 --> 00:10:45,552 In the darkness, we can see each other and talk. 154 00:10:46,732 --> 00:10:48,723 We take care of the flame. 155 00:10:48,935 --> 00:10:51,928 The flame takes care of us. 156 00:10:52,840 --> 00:10:55,138 The stars are not near to us. 157 00:10:55,342 --> 00:10:59,040 When we climb a hill or a tree, they are no closer. 158 00:10:59,247 --> 00:11:03,184 They flicker with a strange, cold, white... 159 00:11:03,986 --> 00:11:05,044 ...far away light. 160 00:11:05,988 --> 00:11:10,289 Many of them, all over the sky, but only at night. 161 00:11:10,660 --> 00:11:12,754 I wonder what they are. 162 00:11:13,564 --> 00:11:17,092 One night I thought the stars are flames. 163 00:11:17,302 --> 00:11:20,499 They give a little light at night as fire does. 164 00:11:20,706 --> 00:11:22,766 Maybe the stars are campfires... 165 00:11:22,976 --> 00:11:26,139 ...which other wanderers light at night. 166 00:11:26,847 --> 00:11:30,180 The stars give a much smaller light than campfires... 167 00:11:30,384 --> 00:11:33,183 ...so they must be very far away. 168 00:11:33,755 --> 00:11:36,417 I wonder if our campfires... 169 00:11:36,625 --> 00:11:39,390 ...look like stars to the people in the sky. 170 00:11:39,795 --> 00:11:44,290 But why don't those campfires and the wanderers who made them... 171 00:11:44,501 --> 00:11:46,332 ...fall down at our feet? 172 00:11:46,536 --> 00:11:50,735 Why don't strange tribes drop from the sky? 173 00:11:52,544 --> 00:11:57,312 Those beings in the sky must have great powers. 174 00:12:04,325 --> 00:12:06,953 I don't suppose that every hunter-gatherer... 175 00:12:07,162 --> 00:12:09,892 ...had such thoughts about the stars. 176 00:12:10,098 --> 00:12:13,535 But we know from contemporary hunter-gatherer communities... 177 00:12:13,736 --> 00:12:17,468 ...that very imaginative ideas arise. 178 00:12:17,908 --> 00:12:20,433 The Kung Bushmen... 179 00:12:20,644 --> 00:12:23,705 ...of the Kalahari Desert in the Republic of Botswana... 180 00:12:23,915 --> 00:12:26,645 ...have an explanation of the Milky Way. 181 00:12:26,851 --> 00:12:29,821 At their latitude, it's often overhead. 182 00:12:30,022 --> 00:12:34,050 They call it the "backbone of night." 183 00:12:34,261 --> 00:12:36,889 They believe it holds the sky up. 184 00:12:37,097 --> 00:12:39,430 They believe that if not for the Milky Way... 185 00:12:39,634 --> 00:12:43,264 ...pieces of sky would come crashing down at our feet. 186 00:12:43,472 --> 00:12:47,101 So the Milky Way, in their view, has some practical value. 187 00:12:47,309 --> 00:12:49,835 The backbone of night. 188 00:12:52,683 --> 00:12:55,379 Later on, metaphors about... 189 00:12:55,653 --> 00:12:58,145 ...campfires or backbones... 190 00:12:58,357 --> 00:13:01,656 ...or holes through which the flame could be seen... 191 00:13:01,860 --> 00:13:06,230 ...were replaced in most human communities by another idea. 192 00:13:06,699 --> 00:13:11,569 The powerful beings in the sky were promoted to gods. 193 00:13:12,206 --> 00:13:15,301 They were given names and relatives... 194 00:13:15,510 --> 00:13:17,444 ...and special responsibilities... 195 00:13:17,646 --> 00:13:21,013 ...for the cosmic services they were expected to perform. 196 00:13:21,217 --> 00:13:25,086 There was a god for every human concern. 197 00:13:25,288 --> 00:13:26,346 Gods ran nature. 198 00:13:26,556 --> 00:13:30,994 Nothing happened without the direct intervention of some god. 199 00:13:31,295 --> 00:13:34,754 If the gods were happy, there was plenty of food... 200 00:13:34,967 --> 00:13:36,525 ...and humans were happy. 201 00:13:38,338 --> 00:13:41,102 But if something displeased the gods... 202 00:13:41,307 --> 00:13:45,608 ...and it didn't take much, the consequences were awesome: 203 00:13:45,813 --> 00:13:49,045 Droughts, floods, storms, wars... 204 00:13:49,251 --> 00:13:52,880 ...earthquakes, volcanic eruptions, epidemics. 205 00:13:53,790 --> 00:13:56,816 The gods had to be propitiated. 206 00:13:57,026 --> 00:13:59,689 And a vast industry of priests arose... 207 00:13:59,897 --> 00:14:02,422 ...to make the gods less angry. 208 00:14:03,033 --> 00:14:06,094 But because the gods were capricious... 209 00:14:06,304 --> 00:14:08,796 ...you couldn't be sure what they would do. 210 00:14:09,008 --> 00:14:11,442 Nature was a mystery. 211 00:14:11,710 --> 00:14:14,236 It was hard to understand the world. 212 00:14:17,284 --> 00:14:20,448 Our ancestors groped in darkness... 213 00:14:20,655 --> 00:14:22,953 ...to make sense of their surroundings. 214 00:14:23,157 --> 00:14:24,648 Powerless before nature... 215 00:14:25,327 --> 00:14:27,887 ...they invented rituals and myths... 216 00:14:28,097 --> 00:14:30,658 ...some desperate and cruel... 217 00:14:30,867 --> 00:14:34,531 ...others imaginative and benign. 218 00:14:34,872 --> 00:14:37,102 The ancient Greeks explained... 219 00:14:37,308 --> 00:14:40,767 ...that diffuse band of brightness in the night sky... 220 00:14:40,979 --> 00:14:43,642 ...as the milk of the goddess Hera... 221 00:14:43,850 --> 00:14:46,819 ...squirted from her breast across the heavens. 222 00:14:47,019 --> 00:14:50,456 We still call it the Milky Way. 223 00:14:56,965 --> 00:14:59,958 In gratitude for the many gifts of the gods... 224 00:15:00,169 --> 00:15:04,300 ...our ancestors created works of surpassing beauty. 225 00:15:07,244 --> 00:15:09,736 This is all that remains... 226 00:15:09,947 --> 00:15:13,348 ...of the ancient temple of Hera, queen of heaven: 227 00:15:13,719 --> 00:15:18,588 A single marble column standing in a vast field of ruins... 228 00:15:19,292 --> 00:15:21,283 ...on the Greek island of Samos. 229 00:15:21,494 --> 00:15:23,462 It was one of the wonders of the world... 230 00:15:23,931 --> 00:15:28,391 ...built by people with an extraordinary eye for clarity... 231 00:15:28,602 --> 00:15:30,161 ...and symmetry. 232 00:15:37,547 --> 00:15:39,880 Those who thronged to that temple... 233 00:15:40,083 --> 00:15:42,677 ...were also the architects of a bridge... 234 00:15:42,886 --> 00:15:45,685 ...from their world to ours. 235 00:15:48,293 --> 00:15:52,788 We were moving once again in our voyage of self-discovery... 236 00:15:53,065 --> 00:15:55,694 ...on our journey to the stars. 237 00:16:00,641 --> 00:16:04,339 Here, 25 centuries ago... 238 00:16:04,980 --> 00:16:08,347 ...on the island of Samos and in the other Greek colonies... 239 00:16:08,550 --> 00:16:11,111 ...which had grown up in the busy Aegean Sea... 240 00:16:11,321 --> 00:16:13,915 ...there was a glorious awakening. 241 00:16:14,123 --> 00:16:17,685 Suddenly, people believed that everything was made of atoms... 242 00:16:17,895 --> 00:16:22,162 ...that human beings and other animals had evolved from simpler forms... 243 00:16:22,367 --> 00:16:26,998 ...that diseases were not caused by demons or the gods... 244 00:16:27,206 --> 00:16:31,507 ...that the Earth was only a planet going around a sun... 245 00:16:31,712 --> 00:16:34,078 ...which was very far away. 246 00:16:37,652 --> 00:16:41,749 This revolution made cosmos out of chaos. 247 00:16:42,157 --> 00:16:45,491 Here, in the sixth century B.C., a new idea developed... 248 00:16:45,695 --> 00:16:48,357 ...one of the great ideas of the human species. 249 00:16:48,565 --> 00:16:52,627 It was argued that the universe was knowable. 250 00:16:52,937 --> 00:16:55,600 Why? Because it was ordered. 251 00:16:55,807 --> 00:16:58,367 Because there are regularities in nature... 252 00:16:58,577 --> 00:17:01,411 ...which permitted secrets to be uncovered. 253 00:17:03,650 --> 00:17:07,052 Nature was not entirely unpredictable. 254 00:17:07,254 --> 00:17:10,986 There were rules which even she had to obey. 255 00:17:13,528 --> 00:17:18,193 This ordered and admirable character of the universe... 256 00:17:18,401 --> 00:17:20,393 ...was called cosmos. 257 00:17:21,571 --> 00:17:24,301 And it was set in stark contradiction... 258 00:17:24,508 --> 00:17:26,739 ...to the idea of chaos. 259 00:17:27,612 --> 00:17:31,879 This was the first conflict of which we know... 260 00:17:32,318 --> 00:17:34,548 ...between science and mysticism... 261 00:17:35,355 --> 00:17:38,085 ...between nature and the gods. 262 00:17:43,898 --> 00:17:45,867 But why here? 263 00:17:46,468 --> 00:17:50,906 Why in these remote islands and inlets of the eastern Mediterranean? 264 00:17:51,107 --> 00:17:53,405 Why not in the great cities of... 265 00:17:53,609 --> 00:17:58,274 ...India or Egypt, Babylon, China, Mesoamerica? 266 00:18:00,952 --> 00:18:04,251 Because they were all at the center of old empires. 267 00:18:06,826 --> 00:18:10,354 They were set in their ways, hostile to new ideas. 268 00:18:10,564 --> 00:18:12,327 But here in Ionia... 269 00:18:12,532 --> 00:18:16,435 ...were a multitude of newly colonized islands and city-states. 270 00:18:16,637 --> 00:18:20,972 Isolation, even if incomplete, promotes diversity. 271 00:18:21,176 --> 00:18:25,340 No single concentration of power could enforce conformity. 272 00:18:25,548 --> 00:18:28,483 Free inquiry became possible. 273 00:18:29,386 --> 00:18:32,720 They were beyond the frontiers of the empires. 274 00:18:32,923 --> 00:18:36,416 The merchants and tourists and sailors of Africa... 275 00:18:36,628 --> 00:18:39,688 ...Asia and Europe met in the harbors of Ionia... 276 00:18:40,565 --> 00:18:44,366 ...to exchange goods and stories and ideas. 277 00:18:44,570 --> 00:18:47,836 There was a vigorous and heady interaction... 278 00:18:48,041 --> 00:18:52,843 ...of many traditions, prejudices, languages and gods. 279 00:19:02,692 --> 00:19:06,094 These people were ready to experiment. 280 00:19:06,664 --> 00:19:09,758 Once you are open to questioning rituals... 281 00:19:09,967 --> 00:19:11,936 ...and time-honored practices... 282 00:19:12,137 --> 00:19:16,541 ...you find that one question leads to another. 283 00:19:26,254 --> 00:19:29,382 What do you do when you're faced with several different gods... 284 00:19:29,591 --> 00:19:31,992 ...each claiming the same territory? 285 00:19:32,195 --> 00:19:34,755 The Babylonian Marduk and the Greek Zeus... 286 00:19:34,964 --> 00:19:38,423 ...were each considered king of the gods... 287 00:19:38,635 --> 00:19:40,569 ...master of the sky. 288 00:19:41,038 --> 00:19:44,406 You might decide, since they otherwise had different attributes... 289 00:19:44,609 --> 00:19:47,374 ...that one of them was merely invented by the priests. 290 00:19:47,580 --> 00:19:50,242 But if one, why not both? 291 00:19:56,022 --> 00:19:59,049 And so it was here that the great idea arose: 292 00:19:59,260 --> 00:20:01,285 The realization that there might be a way... 293 00:20:01,497 --> 00:20:04,091 ...to know the world without the god hypothesis. 294 00:20:04,299 --> 00:20:09,067 That there be principles, forces, laws of nature... 295 00:20:09,272 --> 00:20:12,765 ...through which the world might be understood without attributing... 296 00:20:12,977 --> 00:20:17,039 ...the fall of every sparrow to the direct intervention of Zeus. 297 00:20:17,449 --> 00:20:20,646 This is the place where science was born. 298 00:20:21,019 --> 00:20:22,851 That's why we're here. 299 00:20:24,390 --> 00:20:29,328 This Greek revolution happened between 600 and 400 B.C. 300 00:20:29,997 --> 00:20:33,161 It was accomplished by the same practical and productive people... 301 00:20:33,368 --> 00:20:35,199 ...who made the society function. 302 00:20:35,403 --> 00:20:38,498 Political power was in the hands of the merchants... 303 00:20:38,707 --> 00:20:41,939 ...who promoted the technology on which their prosperity depended. 304 00:20:42,345 --> 00:20:44,506 The earliest pioneers of science were... 305 00:20:44,714 --> 00:20:47,878 ...merchants and artisans and their children. 306 00:20:54,059 --> 00:20:57,461 The first Ionian scientist was named Thales. 307 00:20:57,931 --> 00:21:00,695 He was born over there in the city of Miletus... 308 00:21:00,900 --> 00:21:03,199 ...across this narrow strait. 309 00:21:03,404 --> 00:21:05,167 He had traveled in Egypt... 310 00:21:05,372 --> 00:21:08,206 ...and was conversant with the knowledge of Babylon. 311 00:21:08,643 --> 00:21:13,138 Like the Babylonians, he believed that the world had once all been water. 312 00:21:13,783 --> 00:21:15,876 To explain the dry land... 313 00:21:16,085 --> 00:21:19,249 ...the Babylonians added that their god, Marduk... 314 00:21:19,456 --> 00:21:23,052 ...had placed a mat on the face of the waters... 315 00:21:23,261 --> 00:21:25,559 ...and piled dirt on top of it. 316 00:21:27,065 --> 00:21:28,761 Thales had a similar view... 317 00:21:28,968 --> 00:21:31,869 ...but he left Marduk out. 318 00:21:32,672 --> 00:21:35,971 Yes, the world had once been mostly water... 319 00:21:36,476 --> 00:21:41,005 ...but it was a natural process which explained the dry land. 320 00:21:41,215 --> 00:21:45,448 Thales thought it was similar to the silting up he had observed... 321 00:21:45,654 --> 00:21:48,146 ...at the delta of the river Nile. 322 00:21:49,392 --> 00:21:53,056 Whether Thales' conclusions were right or wrong... 323 00:21:53,263 --> 00:21:56,721 ...is not nearly as important as his approach. 324 00:21:56,934 --> 00:22:00,462 The world was not made by the gods... 325 00:22:00,672 --> 00:22:03,836 ...but instead was the result of material forces... 326 00:22:04,043 --> 00:22:05,943 ...interacting in nature. 327 00:22:06,545 --> 00:22:10,380 Thales brought back from Babylon and Egypt... 328 00:22:10,584 --> 00:22:13,816 ...the seeds of new sciences: 329 00:22:14,055 --> 00:22:16,455 Astronomy and geometry... 330 00:22:16,658 --> 00:22:19,457 ...sciences which would sprout and grow... 331 00:22:19,662 --> 00:22:22,689 ...in the fertile soil of Ionia. 332 00:22:24,267 --> 00:22:28,170 Anaximander of Miletus, over there... 333 00:22:28,606 --> 00:22:30,870 ...was a friend and colleague of Thales... 334 00:22:31,075 --> 00:22:33,237 ...one of the first people that we know of... 335 00:22:33,445 --> 00:22:35,675 ...to have actually done an experiment. 336 00:22:35,881 --> 00:22:40,410 By examining the moving shadow cast by a vertical stick... 337 00:22:40,620 --> 00:22:45,149 ...he determined accurately the lengths of the year and seasons. 338 00:22:45,359 --> 00:22:48,591 For ages, men had used sticks... 339 00:22:48,797 --> 00:22:50,856 ...to club and spear each other. 340 00:22:51,066 --> 00:22:54,594 Anaximander used a stick to measure time. 341 00:22:59,076 --> 00:23:03,673 In 540 B.C., or thereabouts, on this island of Samos... 342 00:23:03,881 --> 00:23:08,410 ...there came to power a tyrant named Polycrates. 343 00:23:08,687 --> 00:23:10,712 He seems to have started as a caterer... 344 00:23:10,923 --> 00:23:13,825 ...and then went on to international piracy. 345 00:23:14,160 --> 00:23:18,689 His loot was unloaded on this very breakwater. 346 00:23:18,899 --> 00:23:21,390 (DRUM BEATS) 347 00:23:27,275 --> 00:23:31,337 But he oppressed his own people, he made war on his neighbors. 348 00:23:31,547 --> 00:23:33,675 He quite rightly feared invasion. 349 00:23:33,884 --> 00:23:38,788 So Polycrates surrounded his capital city with an impressive wall... 350 00:23:38,990 --> 00:23:41,925 ...whose remains stand till this day. 351 00:23:51,338 --> 00:23:55,298 To carry water from a distant spring through the fortifications... 352 00:23:55,510 --> 00:23:58,308 ...he ordered this great tunnel built. 353 00:23:58,513 --> 00:24:02,006 A kilometer long, it pierces a mountain. 354 00:24:02,284 --> 00:24:04,617 Two cuttings were dug from either side... 355 00:24:04,821 --> 00:24:07,085 ...which met almost perfectly in the middle. 356 00:24:07,290 --> 00:24:10,522 The project took some 15 years to complete. 357 00:24:11,462 --> 00:24:15,024 It is a token of the civil engineering of its day... 358 00:24:15,233 --> 00:24:19,068 ...and an indication of the extraordinary practical capability... 359 00:24:19,272 --> 00:24:20,170 ...of the Ionians. 360 00:24:23,476 --> 00:24:25,775 The enduring legacy of the Ionians... 361 00:24:25,979 --> 00:24:28,413 ...is the tools and techniques they developed... 362 00:24:28,615 --> 00:24:31,881 ...which remain the basis of modern technology. 363 00:24:36,058 --> 00:24:39,290 This was the time of Theodorus... 364 00:24:39,496 --> 00:24:42,226 ...the master engineer of the age... 365 00:24:42,432 --> 00:24:46,426 ...a man who is credited with the invention of... 366 00:24:46,637 --> 00:24:50,597 ...the key, the ruler, the carpenter's square... 367 00:24:50,809 --> 00:24:53,676 ...the level, the lathe, bronze casting. 368 00:24:54,180 --> 00:24:57,149 Why are there no monuments to this man? 369 00:24:58,151 --> 00:25:01,644 Those who dreamt and speculated... 370 00:25:01,856 --> 00:25:04,257 ...and deduced about the laws of nature... 371 00:25:04,459 --> 00:25:06,927 ...talked to the engineers and the technologists. 372 00:25:07,128 --> 00:25:09,153 They were often the same people. 373 00:25:09,532 --> 00:25:13,491 The practical and the theoretical were one. 374 00:25:14,538 --> 00:25:19,476 (DRUM BEATS) 375 00:25:20,345 --> 00:25:24,008 This new hybrid of abstract thought... 376 00:25:24,215 --> 00:25:27,617 ...and everyday experience blossomed into science. 377 00:25:28,988 --> 00:25:33,119 When these practical men turned their attention to the natural world... 378 00:25:33,326 --> 00:25:35,454 ...they began to uncover hidden wonders... 379 00:25:36,430 --> 00:25:38,990 ...and breathtaking possibilities. 380 00:25:39,635 --> 00:25:43,093 Anaximander studied the profusion of living things... 381 00:25:43,305 --> 00:25:45,831 ...and saw theirinterrelationships. 382 00:25:46,042 --> 00:25:50,173 He concluded that life had originated in water and mud... 383 00:25:50,648 --> 00:25:53,378 ...and then colonized the dry land. 384 00:25:54,218 --> 00:25:56,050 "Human beings," he said... 385 00:25:56,254 --> 00:25:59,155 "...must have evolved from simpler forms." 386 00:25:59,658 --> 00:26:04,596 This insight had to wait 24 centuries until its truth was demonstrated... 387 00:26:05,198 --> 00:26:06,961 ...by Charles Darwin. 388 00:26:15,577 --> 00:26:19,775 Nothing was excluded from the investigations of the first scientists. 389 00:26:19,983 --> 00:26:24,283 Even the airbecame the subject of close examination... 390 00:26:24,487 --> 00:26:28,481 ...by a Greek from Sicily named Empedocles. 391 00:26:30,128 --> 00:26:32,688 He made an astonishing discovery... 392 00:26:32,898 --> 00:26:37,336 ...with a household implement that people had used for centuries. 393 00:26:37,670 --> 00:26:40,834 This is the so-called water thief. 394 00:26:41,041 --> 00:26:45,240 It's a brazen sphere with a neck and a hole at the top... 395 00:26:45,447 --> 00:26:48,007 ...and a set of little holes at the bottom. 396 00:26:48,216 --> 00:26:49,877 It was used as a kitchen ladle. 397 00:26:50,419 --> 00:26:54,116 You fill it by immersing it in water. 398 00:26:56,626 --> 00:26:58,924 If, after it's been in there a little bit... 399 00:26:59,129 --> 00:27:02,293 ...you pull it out with the neck uncovered... 400 00:27:03,568 --> 00:27:07,369 ...then the water trickles out the little holes making a small shower. 401 00:27:08,507 --> 00:27:12,137 Instead, if you pull it out with the neck covered... 402 00:27:12,912 --> 00:27:14,539 ...the water is retained. 403 00:27:26,362 --> 00:27:28,455 Now try to fill it... 404 00:27:28,698 --> 00:27:32,157 ...with the neck covered with my thumb. 405 00:27:36,274 --> 00:27:37,400 Nothing happens. 406 00:27:38,276 --> 00:27:39,402 Why not? 407 00:27:39,978 --> 00:27:41,776 There's something in the way. 408 00:27:41,981 --> 00:27:46,919 Some material is blocking the access of the water into the sphere. 409 00:27:47,254 --> 00:27:49,449 I can't see any such material. 410 00:27:50,323 --> 00:27:51,951 What could it be? 411 00:27:52,693 --> 00:27:55,184 Empedocles identified it... 412 00:27:55,396 --> 00:27:56,796 ...as air. 413 00:27:57,433 --> 00:27:59,196 What else could it be? 414 00:27:59,568 --> 00:28:02,697 A thing you can't see can exert pressure... 415 00:28:02,906 --> 00:28:06,707 ...can frustrate my wish to fill this vessel with water... 416 00:28:06,911 --> 00:28:11,178 ...if I were dumb enough to leave my thumb on the neck. 417 00:28:12,017 --> 00:28:15,680 Empedocles had discovered... 418 00:28:17,023 --> 00:28:18,513 ...the invisible. 419 00:28:19,125 --> 00:28:22,118 Air, he thought, must be matter... 420 00:28:22,329 --> 00:28:25,696 ...in a form so finely divided... 421 00:28:26,568 --> 00:28:27,933 ...that it couldn't be seen. 422 00:28:29,404 --> 00:28:33,808 This hint, this whiff of the existence of atoms... 423 00:28:34,009 --> 00:28:38,379 ...was carried much further by a contemporary named Democritus. 424 00:28:38,849 --> 00:28:43,116 Of all the ancient scientists, it is he who speaks most clearly to us... 425 00:28:43,321 --> 00:28:44,845 ...across the centuries. 426 00:28:45,056 --> 00:28:48,288 The few surviving fragments of his scientific writings... 427 00:28:48,494 --> 00:28:52,124 ...reveal a mind of the highest logical and intuitive powers. 428 00:28:52,332 --> 00:28:57,134 He believed that a large number of other worlds wander through space... 429 00:28:57,338 --> 00:28:59,636 ...that worlds are born and die... 430 00:28:59,840 --> 00:29:01,832 ...that some are rich and living creatures... 431 00:29:02,043 --> 00:29:05,274 ...and others are dry and barren. 432 00:29:06,649 --> 00:29:09,482 He was the first to understand that the Milky Way... 433 00:29:09,685 --> 00:29:13,281 ...is an aggregate of the light of innumerable faint stars. 434 00:29:13,490 --> 00:29:17,359 Beyond campfires in the sky, beyond the milk of Hera... 435 00:29:17,562 --> 00:29:22,500 ...beyond the backbone of night, the mind of Democritus soared. 436 00:29:27,774 --> 00:29:31,005 He saw deep connections between the heavens and the Earth. 437 00:29:31,611 --> 00:29:34,547 "Man," he said, "is a microcosm... 438 00:29:34,982 --> 00:29:36,574 ...a little cosmos." 439 00:30:00,413 --> 00:30:04,350 Democritus came from the Ionian town of Abdera... 440 00:30:04,551 --> 00:30:06,849 ...on the northern Aegean shore. 441 00:30:10,191 --> 00:30:14,526 In those days, Abdera was the butt of jokes. 442 00:30:15,431 --> 00:30:17,525 If, around the year 400 B.C... 443 00:30:17,734 --> 00:30:20,202 ...in the equivalent of a restaurant like this... 444 00:30:20,770 --> 00:30:23,399 ...you told a story about someone from Abdera... 445 00:30:23,608 --> 00:30:25,542 ...you were guaranteed a laugh. 446 00:30:28,413 --> 00:30:30,381 It was, in a way... 447 00:30:30,582 --> 00:30:32,983 ...the Brooklyn of its time. 448 00:30:35,488 --> 00:30:39,687 For Democritus, all of life was to be enjoyed and understood. 449 00:30:39,893 --> 00:30:42,191 For him, understanding and enjoyment... 450 00:30:42,397 --> 00:30:44,695 ...were pretty much the same thing. 451 00:30:44,899 --> 00:30:49,530 He said, "A life without festivity is a long road without an inn." 452 00:30:49,739 --> 00:30:53,437 Democritus may have come from Abdera, but he was no dummy. 453 00:30:57,247 --> 00:31:00,240 Democritus understood that the complex forms... 454 00:31:00,451 --> 00:31:03,853 ...changes and motions of the material world... 455 00:31:04,056 --> 00:31:08,619 ...all derived from the interaction of very simple moving parts. 456 00:31:08,828 --> 00:31:11,524 He called these parts atoms. 457 00:31:16,504 --> 00:31:20,202 All material objects are collections of atoms... 458 00:31:20,742 --> 00:31:22,175 ...intricately assembled... 459 00:31:22,377 --> 00:31:23,675 ...even we. 460 00:31:23,913 --> 00:31:26,177 When I cut this apple... 461 00:31:26,449 --> 00:31:28,475 ...the knife must be passing through... 462 00:31:28,752 --> 00:31:32,244 ...empty spaces between the atoms, Democritus argued. 463 00:31:32,456 --> 00:31:35,893 If there were no such empty spaces, no void... 464 00:31:36,094 --> 00:31:40,657 ...then the knife would encounter some impenetrable atom... 465 00:31:40,866 --> 00:31:42,800 ...and the apple wouldn't be cut. 466 00:31:43,003 --> 00:31:46,097 Let's compare the cross sections of the two pieces. 467 00:31:46,306 --> 00:31:48,901 Are the exposed areas exactly equal? 468 00:31:49,110 --> 00:31:51,840 No, said Democritus, the curvature of the apple... 469 00:31:52,046 --> 00:31:56,848 ...forces this slice to be slightly shorter than the rest of the apple. 470 00:31:57,252 --> 00:32:00,620 If they were equally tall, then we'd have... 471 00:32:00,824 --> 00:32:02,883 ...a cylinder and not an apple. 472 00:32:03,127 --> 00:32:05,254 No matter how sharp the knife... 473 00:32:05,463 --> 00:32:08,331 ...these two pieces have unequal cross sections. 474 00:32:08,533 --> 00:32:09,898 But why? 475 00:32:10,102 --> 00:32:13,128 Because on the scale of the very small... 476 00:32:13,339 --> 00:32:16,604 ...matter exhibits some irreducible roughness... 477 00:32:16,809 --> 00:32:20,541 ...and this fine scale of roughness Democritus of Abdera identified... 478 00:32:20,814 --> 00:32:22,748 ...with the world of the atoms. 479 00:32:22,950 --> 00:32:25,112 His arguments are not those we use today. 480 00:32:25,320 --> 00:32:29,621 But they're elegant and subtle and derived from everyday experience. 481 00:32:29,825 --> 00:32:33,261 And his conclusions were fundamentally right. 482 00:32:38,536 --> 00:32:41,630 Democritus believed that nothing happens at random... 483 00:32:41,839 --> 00:32:45,105 ...that everything has a material cause. 484 00:32:46,445 --> 00:32:50,382 He said, "I would rather understand one cause... 485 00:32:50,583 --> 00:32:52,847 ...than be king of Persia." 486 00:32:53,052 --> 00:32:56,284 He believed that poverty in a democracy was far better... 487 00:32:56,490 --> 00:32:58,117 ...than wealth in a tyranny. 488 00:32:58,325 --> 00:33:01,818 He believed that the prevailing religions of his time were evil... 489 00:33:02,030 --> 00:33:06,058 ...and that neither souls nor immortal gods existed. 490 00:33:06,669 --> 00:33:11,607 There is no evidence that Democritus was persecuted for his beliefs. 491 00:33:12,176 --> 00:33:15,169 But then again, he came from Abdera. 492 00:33:17,449 --> 00:33:18,781 However, in his time... 493 00:33:18,984 --> 00:33:22,420 ...the brief tradition of tolerance for unconventional views... 494 00:33:22,621 --> 00:33:24,590 ...was beginning to erode. 495 00:33:25,091 --> 00:33:27,616 For instance, the prevailing belief was... 496 00:33:27,828 --> 00:33:30,593 ...that the moon and the sun were gods. 497 00:33:31,232 --> 00:33:34,999 Another contemporary of Democritus, named Anaxagoras, taught... 498 00:33:35,204 --> 00:33:38,971 ...that the moon was a place made of ordinary matter... 499 00:33:39,175 --> 00:33:43,407 ...and that the sun was a red-hot stone far away in the sky. 500 00:33:43,646 --> 00:33:46,741 For this, Anaxagoras was condemned... 501 00:33:46,951 --> 00:33:50,547 ...convicted and imprisoned for impiety... 502 00:33:50,755 --> 00:33:52,518 ...a religious crime. 503 00:33:52,724 --> 00:33:56,320 People began to be persecuted for their ideas. 504 00:33:56,629 --> 00:33:59,292 A portrait of Democritus is now... 505 00:33:59,500 --> 00:34:02,196 ...on the Greek 100-drachma note. 506 00:34:03,070 --> 00:34:05,232 But his ideas were suppressed... 507 00:34:05,440 --> 00:34:07,635 ...and his influence on history made minor. 508 00:34:07,842 --> 00:34:10,539 The mystics were beginning to win. 509 00:34:10,746 --> 00:34:14,877 (DRUM BEATS) 510 00:34:17,354 --> 00:34:19,949 You see, Ionia was also the home... 511 00:34:20,157 --> 00:34:22,990 ...of another quite different intellectual tradition. 512 00:34:23,194 --> 00:34:25,823 Its founder was Pythagoras... 513 00:34:26,031 --> 00:34:29,433 ...who lived here on Samos in the 6th century B.C. 514 00:34:30,637 --> 00:34:32,935 According to local legend... 515 00:34:33,139 --> 00:34:36,701 ...this cave was once his abode. 516 00:34:37,044 --> 00:34:39,570 Maybe that was once his living room. 517 00:34:39,781 --> 00:34:41,749 Many centuries later... 518 00:34:42,017 --> 00:34:45,784 ...this small Greek Orthodox shrine was erected on his front porch. 519 00:34:45,988 --> 00:34:50,926 There's a continuity of tradition from Pythagoras to Christianity. 520 00:34:51,161 --> 00:34:54,825 Pythagoras was the first person in the history of the world... 521 00:34:55,033 --> 00:34:58,161 ...to decide that the Earth was a sphere. 522 00:34:58,403 --> 00:35:02,602 Perhaps he argued by analogy with the moon or the sun... 523 00:35:02,808 --> 00:35:05,835 ...maybe he noticed the curved shadow of the Earth on the moon... 524 00:35:06,046 --> 00:35:07,638 ...during a lunar eclipse. 525 00:35:07,847 --> 00:35:10,646 Or maybe he recognized that when ships leave Samos... 526 00:35:10,851 --> 00:35:13,285 ...their masts disappear last. 527 00:35:18,560 --> 00:35:22,053 Pythagoras believed that a mathematical harmony... 528 00:35:22,265 --> 00:35:24,130 ...underlies all of nature. 529 00:35:24,334 --> 00:35:26,599 The modern tradition of mathematical argument... 530 00:35:26,804 --> 00:35:30,172 ...essential in all of science owes much to him. 531 00:35:30,375 --> 00:35:34,141 And the notion that the heavenly bodies move to a kind of... 532 00:35:34,346 --> 00:35:36,577 ...music of the spheres... 533 00:35:36,882 --> 00:35:39,407 ...was also derived from Pythagoras. 534 00:35:40,019 --> 00:35:42,887 It was he who first used the word cosmos... 535 00:35:43,090 --> 00:35:45,924 ...to mean a well-ordered and harmonious universe... 536 00:35:46,127 --> 00:35:49,619 ...a world amenable to human understanding. 537 00:35:54,003 --> 00:35:57,440 For this great idea, we are indebted to Pythagoras. 538 00:35:57,641 --> 00:36:02,170 But there were deep ironies and contradictions in his thoughts. 539 00:36:02,647 --> 00:36:04,547 Many of the Ionians believed... 540 00:36:04,749 --> 00:36:09,244 ...that the underlying harmony and unity of the universe was accessible... 541 00:36:09,454 --> 00:36:12,151 ...through observation and experiment... 542 00:36:12,358 --> 00:36:14,826 ...the method which dominates science today. 543 00:36:15,094 --> 00:36:17,859 However, Pythagoras had a very different method. 544 00:36:18,065 --> 00:36:23,003 He believed that the laws of nature can be deduced by pure thought. 545 00:36:23,405 --> 00:36:26,466 He and his followers were not basically experimentalists... 546 00:36:26,676 --> 00:36:28,473 ...they were mathematicians... 547 00:36:28,678 --> 00:36:31,546 ...and they were thoroughgoing mystics. 548 00:36:32,449 --> 00:36:36,386 They were fascinated by these five regular solids... 549 00:36:36,587 --> 00:36:39,886 ...bodies whose faces are all polygons: 550 00:36:40,091 --> 00:36:42,720 Triangles or squares... 551 00:36:42,928 --> 00:36:44,327 ...or pentagons. 552 00:36:44,530 --> 00:36:47,295 There can be an infinite number of polygons... 553 00:36:47,500 --> 00:36:50,526 ...but only five regular solids. 554 00:36:53,107 --> 00:36:58,045 Four of the solids were associated with earth, fire, air and water. 555 00:36:58,714 --> 00:37:02,310 The cube, for example, represented earth. 556 00:37:02,518 --> 00:37:06,615 These four elements, they thought, make up terrestrial matter. 557 00:37:07,991 --> 00:37:09,788 So the fifth solid... 558 00:37:09,993 --> 00:37:13,225 ...they mystically associated with the cosmos. 559 00:37:13,431 --> 00:37:16,333 Perhaps it was the substance of the heavens. 560 00:37:16,535 --> 00:37:19,095 This fifth solid was called... 561 00:37:19,305 --> 00:37:21,774 ...the dodecahedron. 562 00:37:22,142 --> 00:37:25,634 Its faces are pentagons, 12 of them. 563 00:37:26,247 --> 00:37:27,976 Knowledge of the dodecahedron... 564 00:37:28,182 --> 00:37:31,448 ...was considered too dangerous for the public. 565 00:37:33,689 --> 00:37:38,150 Ordinary people were to be kept ignorant of the dodecahedron. 566 00:37:38,394 --> 00:37:41,228 In love with whole numbers, the Pythagoreans believed... 567 00:37:41,432 --> 00:37:43,593 ...that all things could be derived from them... 568 00:37:43,801 --> 00:37:45,792 ...certainly all other numbers. 569 00:37:46,003 --> 00:37:49,030 So a crisis in doctrine occurred when they discovered... 570 00:37:49,241 --> 00:37:51,676 ...that the square root of two was irrational. 571 00:37:51,878 --> 00:37:55,006 The square root of two could not be represented as the ratio... 572 00:37:55,214 --> 00:37:57,911 ...of two whole numbers no matter how big they were. 573 00:37:58,285 --> 00:38:00,981 Irrational originally meant only that... 574 00:38:01,188 --> 00:38:04,158 ...that you can't express a number as a ratio. 575 00:38:04,359 --> 00:38:07,557 But for the Pythagoreans, it came to mean something else... 576 00:38:07,763 --> 00:38:09,663 ...something threatening... 577 00:38:09,865 --> 00:38:13,962 ...a hint that their world-view might not make sense... 578 00:38:14,171 --> 00:38:17,005 ...the other meaning of irrational. 579 00:38:17,909 --> 00:38:22,574 Instead of wanting everyone to share and know of their discoveries... 580 00:38:22,781 --> 00:38:25,978 ...the Pythagoreans suppressed the square root of two... 581 00:38:26,185 --> 00:38:27,847 ...and the dodecahedron. 582 00:38:28,054 --> 00:38:30,545 The outside world was not to know. 583 00:38:36,463 --> 00:38:38,728 The Pythagoreans had discovered... 584 00:38:38,934 --> 00:38:41,562 ...in the mathematical underpinnings of nature... 585 00:38:41,770 --> 00:38:44,399 ...one of the two most powerful scientific tools. 586 00:38:44,607 --> 00:38:47,702 The other, of course, is experiment. 587 00:38:48,011 --> 00:38:50,571 But instead of using their insight to advance... 588 00:38:50,781 --> 00:38:53,444 ...the collective voyage of human discovery... 589 00:38:53,651 --> 00:38:58,214 ...they made of it little more than the hocus-pocus of a mystery cult. 590 00:38:58,424 --> 00:39:01,518 Science and mathematics were to be removed from the hands... 591 00:39:01,727 --> 00:39:03,355 ...of merchants and artisans. 592 00:39:04,297 --> 00:39:07,233 This tendency found its most effective advocate... 593 00:39:07,435 --> 00:39:10,802 ...in a follower of Pythagoras named Plato. 594 00:39:11,072 --> 00:39:15,772 He preferred the perfection of these mathematical abstractions... 595 00:39:15,978 --> 00:39:19,107 ...to the imperfections of everyday life. 596 00:39:19,315 --> 00:39:23,650 He believed that ideas were far more real than the natural world. 597 00:39:23,854 --> 00:39:26,482 He advised the astronomers not to waste their time... 598 00:39:26,690 --> 00:39:28,420 ...observing stars and planets. 599 00:39:28,627 --> 00:39:32,188 It was better, he believed, just to think about them. 600 00:39:33,032 --> 00:39:36,627 Plato expressed hostility to observation and experiment. 601 00:39:36,836 --> 00:39:39,271 He taught contempt for the real world... 602 00:39:39,473 --> 00:39:43,467 ...and disdain for the practical application of scientific knowledge. 603 00:39:45,146 --> 00:39:48,878 Plato's followers succeeded in extinguishing the light... 604 00:39:49,084 --> 00:39:50,915 ...of science and experiment... 605 00:39:51,120 --> 00:39:55,421 ...that had been kindled by Democritus and the other Ionians. 606 00:39:58,262 --> 00:40:01,663 Plato's unease with the world as revealed by our senses... 607 00:40:01,866 --> 00:40:06,600 ...was to dominate and stifle Western philosophy. 608 00:40:09,042 --> 00:40:10,839 Even as late as 1600... 609 00:40:11,044 --> 00:40:14,412 ...Johannes Kepler was still struggling to interpret... 610 00:40:14,615 --> 00:40:16,708 ...the structure of the cosmos in terms of... 611 00:40:16,917 --> 00:40:21,355 ...Pythagorean solids and Platonic perfection. 612 00:40:21,556 --> 00:40:25,493 Ironically, it was Kepler who helped re-establish the old Ionian method... 613 00:40:25,695 --> 00:40:28,130 ...of testing ideas against observations. 614 00:40:28,665 --> 00:40:31,498 But why had science lost its way in the first place? 615 00:40:31,702 --> 00:40:34,638 What appeal did Pythagoras' and Plato's teachings... 616 00:40:34,839 --> 00:40:36,704 ...have for their contemporaries? 617 00:40:36,908 --> 00:40:38,536 They provided, I believe... 618 00:40:38,744 --> 00:40:41,679 ...an intellectually respectable justification... 619 00:40:41,880 --> 00:40:44,748 ...for a corrupt social order. 620 00:40:48,322 --> 00:40:51,519 The mercantile tradition which had led to Ionian science... 621 00:40:51,726 --> 00:40:53,991 ...also led to a slave economy. 622 00:40:54,863 --> 00:40:56,854 You could get richer... 623 00:40:57,065 --> 00:40:59,626 ...if you owned a lot of slaves. 624 00:41:00,003 --> 00:41:02,995 Athens, in the time of Plato and Aristotle... 625 00:41:03,207 --> 00:41:05,971 ...had a vast slave population. 626 00:41:06,176 --> 00:41:10,079 All of that brave Athenian talk about democracy... 627 00:41:10,281 --> 00:41:13,183 ...applied only to a privileged few. 628 00:41:13,786 --> 00:41:18,120 Plato and Aristotle were comfortable in a slave society. 629 00:41:18,325 --> 00:41:21,419 They offered justifications for oppression. 630 00:41:22,062 --> 00:41:24,031 They served tyrants. 631 00:41:24,232 --> 00:41:27,395 They taught the alienation of the body from the mind... 632 00:41:27,602 --> 00:41:31,630 ...a natural enough idea, I suppose, in a slave society. 633 00:41:31,840 --> 00:41:34,366 They separated thought from matter. 634 00:41:34,577 --> 00:41:36,943 They divorced the Earth from the heavens. 635 00:41:37,147 --> 00:41:41,016 Divisions which were to dominate Western thinking... 636 00:41:41,218 --> 00:41:43,311 ...for more than 20 centuries. 637 00:41:43,522 --> 00:41:45,956 The Pythagoreans had won. 638 00:41:52,131 --> 00:41:55,158 In the recognition by Pythagoras and Plato... 639 00:41:55,369 --> 00:41:57,337 ...that the cosmos is knowable... 640 00:41:57,538 --> 00:42:00,633 ...that there is a mathematical underpinning to nature... 641 00:42:00,842 --> 00:42:03,937 ...they greatly advanced the cause of science. 642 00:42:04,547 --> 00:42:08,608 But in the suppression of disquieting facts... 643 00:42:08,819 --> 00:42:13,518 ...the sense that science should be kept for a small elite... 644 00:42:13,723 --> 00:42:17,785 ...the distaste for experiment, the embrace of mysticism... 645 00:42:18,429 --> 00:42:21,763 ...the easy acceptance of slave societies... 646 00:42:21,967 --> 00:42:25,836 ...their influence has significantly set back... 647 00:42:26,039 --> 00:42:27,666 ...the human endeavor. 648 00:42:29,043 --> 00:42:33,981 The books of the Ionian scientists are entirely lost. 649 00:42:34,883 --> 00:42:39,617 Their views were suppressed, ridiculed and forgotten... 650 00:42:40,389 --> 00:42:43,051 ...by the Platonists and by the Christians... 651 00:42:43,259 --> 00:42:46,752 ...who adopted much of the philosophy of Plato. 652 00:42:47,531 --> 00:42:52,265 Finally, after a long, mystical sleep... 653 00:42:52,537 --> 00:42:57,134 ...in which the tools of scientific inquiry lay moldering... 654 00:42:57,343 --> 00:43:00,142 ...the Ionian approach was rediscovered. 655 00:43:05,119 --> 00:43:07,815 The Western world reawakened. 656 00:43:08,022 --> 00:43:11,481 Experiment and open inquiry... 657 00:43:11,693 --> 00:43:15,095 ...slowly became respectable once again. 658 00:43:15,798 --> 00:43:19,860 Forgotten books and fragments were read once more. 659 00:43:20,237 --> 00:43:24,298 Leonardo and Copernicus and Columbus... 660 00:43:24,509 --> 00:43:27,672 ...were inspired by the Ionian tradition. 661 00:43:39,928 --> 00:43:43,728 The Pythagoreans and their successors... 662 00:43:43,932 --> 00:43:46,925 ...held the peculiar notion that... 663 00:43:47,136 --> 00:43:49,400 ...the Earth was tainted... 664 00:43:49,605 --> 00:43:52,040 ...somehow nasty... 665 00:43:52,242 --> 00:43:56,873 ...while the heavens were pristine and divine. 666 00:43:57,548 --> 00:44:00,279 So the fundamental idea that the Earth is a planet... 667 00:44:00,485 --> 00:44:03,215 ...that we're citizens of the universe... 668 00:44:03,422 --> 00:44:06,153 ...was rejected and forgotten. 669 00:44:09,562 --> 00:44:13,363 This idea was first argued by Aristarchus... 670 00:44:13,567 --> 00:44:17,527 ...born here on Samos, three centuries after Pythagoras. 671 00:44:17,739 --> 00:44:20,573 He held that the Earth moves around the sun. 672 00:44:20,776 --> 00:44:24,007 He correctly located our place in the solar system. 673 00:44:24,213 --> 00:44:28,082 For his trouble, he was accused of heresy. 674 00:44:29,853 --> 00:44:34,188 From the size of the Earth's shadow on the moon during a lunar eclipse... 675 00:44:34,392 --> 00:44:38,591 ...he deduced that the sun had to be much, much larger... 676 00:44:38,797 --> 00:44:41,892 ...than the Earth, and also very far away. 677 00:44:42,302 --> 00:44:44,896 From this he may have argued that it was absurd... 678 00:44:45,105 --> 00:44:48,132 ...for so large an object as the sun to be going around... 679 00:44:48,342 --> 00:44:51,437 ...so small an object as the Earth. 680 00:44:51,647 --> 00:44:56,517 So he put the sun rather than the Earth at the center of the solar system. 681 00:44:56,719 --> 00:45:00,246 And he had the Earth and the other planets going around the sun. 682 00:45:00,457 --> 00:45:03,824 He also had the Earth rotating on its axis once a day. 683 00:45:04,028 --> 00:45:08,193 These are ideas that we ordinarily associate with the name Copernicus. 684 00:45:08,400 --> 00:45:11,893 But Copernicus seems to have gotten some hint of these ideas... 685 00:45:12,104 --> 00:45:14,732 ...by reading about Aristarchus. 686 00:45:15,207 --> 00:45:17,938 In fact, in the manuscript of Copernicus' book... 687 00:45:18,145 --> 00:45:21,582 ...he referred to Aristarchus, but in the final version... 688 00:45:21,783 --> 00:45:24,479 ...he suppressed the citation. 689 00:45:25,186 --> 00:45:28,054 Resistance to Aristarchus, a kind of... 690 00:45:28,691 --> 00:45:31,183 ...geocentrism in everyday life, is with us still. 691 00:45:31,394 --> 00:45:34,329 We still talk about a sun rising... 692 00:45:34,531 --> 00:45:37,000 ...and the sun setting. 693 00:45:37,702 --> 00:45:40,296 It's 2200 years since Aristarchus... 694 00:45:40,504 --> 00:45:45,374 ...and the language still pretends that the Earth does not turn... 695 00:45:46,212 --> 00:45:50,239 ...that the sun is not at the center of the solar system. 696 00:45:53,354 --> 00:45:57,121 Aristarchus understood the basic scheme of the solar system... 697 00:45:57,325 --> 00:45:59,088 ...but not its scale. 698 00:46:01,697 --> 00:46:05,360 He knew that the planets move in concentric orbits about the sun... 699 00:46:05,568 --> 00:46:08,800 ...and he probably knew their order out to Saturn. 700 00:46:10,340 --> 00:46:12,571 But he was much too modest in his estimates... 701 00:46:12,777 --> 00:46:15,268 ...of how far apart the planets are. 702 00:46:15,613 --> 00:46:18,981 In order to calculate the true scale of the solar system... 703 00:46:19,184 --> 00:46:20,811 ...you need a telescope. 704 00:46:21,221 --> 00:46:24,713 It wasn't until the 17th century that astronomers were able to get... 705 00:46:24,924 --> 00:46:28,622 ...even a rough estimate of the distance to the sun. 706 00:46:30,631 --> 00:46:33,123 And once you knew the distance to the sun... 707 00:46:33,335 --> 00:46:34,893 ...what about the stars? 708 00:46:35,103 --> 00:46:37,538 How far away are they? 709 00:46:41,445 --> 00:46:44,937 There is a way to measure the distance to the stars... 710 00:46:45,149 --> 00:46:47,880 ...and the Ionians were fully capable of discovering it. 711 00:46:48,086 --> 00:46:51,887 Aristarchus had toyed with the daring idea... 712 00:46:52,091 --> 00:46:54,821 ...that the stars were distant suns. 713 00:46:55,027 --> 00:46:57,496 Now, if a star were as near as the sun... 714 00:46:57,697 --> 00:47:00,928 ...it should appear as big and as bright as the sun. 715 00:47:01,134 --> 00:47:04,901 Everyone knows that the farther away an object is, the smaller it seems. 716 00:47:05,106 --> 00:47:08,565 This inverse proportionality between apparent size and distance... 717 00:47:08,777 --> 00:47:12,475 ...is the basis of perspective in art and photography. 718 00:47:12,682 --> 00:47:15,378 So the further away we are from the sun... 719 00:47:15,585 --> 00:47:18,487 ...the smaller and dimmer it appears. 720 00:47:18,689 --> 00:47:21,887 How far from the sun would we have to be for it to appear... 721 00:47:22,093 --> 00:47:24,357 ...as small and dim as a star? 722 00:47:24,563 --> 00:47:27,533 Or equivalently, how small a piece of sun... 723 00:47:27,733 --> 00:47:29,963 ...would be as bright as a star? 724 00:47:30,336 --> 00:47:34,831 An experiment to answer this question was performed in 17th-century Holland... 725 00:47:35,042 --> 00:47:39,878 ...by Christiaan Huygens and is very much in the Ionian tradition. 726 00:47:40,081 --> 00:47:45,019 Huygens drilled a number of holes in a brass plate... 727 00:47:45,454 --> 00:47:47,855 ...and held the plate up to the sun. 728 00:47:48,058 --> 00:47:52,860 He asked himself, which hole seemed as bright... 729 00:47:53,064 --> 00:47:57,331 ...as he remembered the star Sirius to have been the previous evening. 730 00:47:57,536 --> 00:48:00,562 Well, the hole that matched was effectively... 731 00:48:00,772 --> 00:48:05,506 ...1/28,000th the apparent size of the sun. 732 00:48:05,778 --> 00:48:09,840 So Sirius, he reasoned, must be 28,000 times... 733 00:48:10,050 --> 00:48:14,351 ...further away than the sun, or about half a light-year away. 734 00:48:14,956 --> 00:48:17,721 It's hard to remember just how bright a star is... 735 00:48:17,927 --> 00:48:21,761 ...hours after you've looked at it, but Huygens remembered very well. 736 00:48:21,964 --> 00:48:25,992 If he had known that Sirius was intrinsically brighter than the sun... 737 00:48:26,203 --> 00:48:28,604 ...he would've gotten the answer exactly right. 738 00:48:28,806 --> 00:48:32,868 Sirius is 8.8 light-years away from us. 739 00:48:33,846 --> 00:48:36,713 Between Aristarchus and Huygens... 740 00:48:36,916 --> 00:48:40,148 ...people had answered that question which had so excited me... 741 00:48:40,353 --> 00:48:42,218 ...as a young boy growing up in Brooklyn: 742 00:48:42,423 --> 00:48:44,789 The question, "What are the stars?" 743 00:48:48,230 --> 00:48:53,168 And the answer is that the stars are mighty suns, light-years away... 744 00:48:53,369 --> 00:48:55,769 ...in the depths of interstellar space. 745 00:49:01,579 --> 00:49:05,914 And around those suns, are there other planets? 746 00:49:06,985 --> 00:49:08,954 And on those other worlds... 747 00:49:09,155 --> 00:49:12,124 ...are there beings who wonder as we do? 748 00:49:16,496 --> 00:49:18,897 Here is a light bulb... 749 00:49:19,100 --> 00:49:21,660 ...which is supposed to represent a nearby star. 750 00:49:21,869 --> 00:49:25,328 Next to it, and very hard to see because of the bright light... 751 00:49:25,541 --> 00:49:26,906 ...is a planet. 752 00:49:27,109 --> 00:49:30,637 We'll need a volunteer. Who would like to come up, please? 753 00:49:31,314 --> 00:49:33,909 Ordinarily, it's hard to see the planet... 754 00:49:34,118 --> 00:49:38,078 ...because it's so close that the star washes out the planet. 755 00:49:38,290 --> 00:49:42,727 But if we're able to put something in front of the star... 756 00:49:42,929 --> 00:49:46,456 ...to make an artificial eclipse, then we might be able to see the planet. 757 00:49:46,666 --> 00:49:50,933 I'm gonna stand over here. Imagine that I'm a telescope... 758 00:49:51,138 --> 00:49:52,571 ...somewhere near the Earth. 759 00:49:52,773 --> 00:49:56,676 And, Tab, if you'd slowly move the disc across. 760 00:49:56,878 --> 00:49:58,870 Good. A little faster would be nice. 761 00:49:59,081 --> 00:50:01,709 Now you're just beginning to cover over the star. 762 00:50:01,917 --> 00:50:04,944 I really can't see the planet at all. Keep going. 763 00:50:05,155 --> 00:50:06,622 Now, right there... 764 00:50:06,823 --> 00:50:09,190 ...I can't see the star at all... 765 00:50:09,394 --> 00:50:13,297 ...and I see the planet lit by the light of the star. 766 00:50:13,499 --> 00:50:16,832 Now, that is a method for looking for planets... 767 00:50:17,036 --> 00:50:18,868 ...around nearby stars. 768 00:50:19,072 --> 00:50:24,010 And that method uses a spacecraft to hold the disc... 769 00:50:24,545 --> 00:50:27,013 ...and scan the sky for another telescope... 770 00:50:27,214 --> 00:50:29,945 ...to see if there are any planets. 771 00:50:30,152 --> 00:50:34,487 Tab, you accomplished your mission to look for planets around other stars. 772 00:50:34,691 --> 00:50:37,854 Thank you for being our interplanetary spacecraft. 773 00:50:38,061 --> 00:50:40,656 So this is one way. 774 00:50:40,864 --> 00:50:44,266 And there are spaceships that will be able to do this... 775 00:50:44,469 --> 00:50:46,232 ...in the next 10 years or so. 776 00:50:46,438 --> 00:50:47,905 And there's another way. 777 00:50:48,106 --> 00:50:50,632 This has already been tried from the Earth. 778 00:50:50,843 --> 00:50:54,940 Imagine that there's a nearby star that you can see. 779 00:50:55,148 --> 00:50:59,142 It's bright and it has a dark companion, a planet... 780 00:50:59,353 --> 00:51:02,754 ...shining only by reflected light near it, so dim you can't see it. 781 00:51:02,957 --> 00:51:07,725 But imagine that this planet and its star... 782 00:51:07,930 --> 00:51:09,796 ...are going around each other. 783 00:51:10,934 --> 00:51:12,265 Like that: 784 00:51:12,469 --> 00:51:15,064 You can see the star, you can't see the planet. 785 00:51:15,272 --> 00:51:17,638 So now I'm gonna need two volunteers. 786 00:51:19,845 --> 00:51:20,869 You two. 787 00:51:22,214 --> 00:51:25,082 Just to save time because they're in the front row. 788 00:51:25,284 --> 00:51:28,310 I need one of you to turn the star and the planet... 789 00:51:28,521 --> 00:51:32,481 ...and another person to pull the star and planet along. 790 00:51:32,693 --> 00:51:34,161 And what you will see... 791 00:51:34,362 --> 00:51:37,695 ...is that the star you can make out... 792 00:51:37,899 --> 00:51:40,528 ...will be moving in a funny, wiggly pattern... 793 00:51:40,736 --> 00:51:42,863 ...which will be the clue, the evidence... 794 00:51:43,072 --> 00:51:45,337 ...for the existence of the dark planet. 795 00:51:45,542 --> 00:51:48,739 Okay, let's have a spin. Good. And a pull. 796 00:51:48,945 --> 00:51:50,607 And you see this funny motion... 797 00:51:50,815 --> 00:51:55,480 ...that the star makes because of the planet. Thank you. 798 00:51:55,687 --> 00:51:58,884 That's another way of finding out the existence of a planet... 799 00:51:59,091 --> 00:52:01,993 ...that you couldn't see directly. 800 00:52:02,195 --> 00:52:05,324 Well, both of these methods are being used. 801 00:52:05,633 --> 00:52:10,298 And by the time that you people are... 802 00:52:10,505 --> 00:52:12,302 ...as old as I am... 803 00:52:12,507 --> 00:52:15,875 ...we should know, for all the nearest stars... 804 00:52:16,078 --> 00:52:18,512 ...if they have planets going around them. 805 00:52:18,714 --> 00:52:23,084 We might know dozens or even hundreds of other planetary systems... 806 00:52:23,287 --> 00:52:26,587 ...and see if they're like our own or very different... 807 00:52:26,791 --> 00:52:30,387 ...or no other planets going around other stars at all. 808 00:52:30,596 --> 00:52:32,860 That will happen in your lifetime. 809 00:52:33,065 --> 00:52:37,730 It'll be the first time in the world's history that anybody found out... 810 00:52:38,471 --> 00:52:41,202 ...if there are planets around the other stars. 811 00:52:41,409 --> 00:52:46,347 Now, the nearby stars, the ones you can see with the naked eye... 812 00:52:46,648 --> 00:52:48,912 ...those are all in the solar neighborhood. 813 00:52:49,117 --> 00:52:51,609 That's what astronomers call it: The neighborhood. 814 00:52:51,821 --> 00:52:56,418 But it's a very tiny place in the Milky Way galaxy. 815 00:52:57,361 --> 00:52:59,488 The Milky Way is that band of light... 816 00:52:59,697 --> 00:53:02,792 ...that you see across the sky on a clear night. 817 00:53:03,001 --> 00:53:06,130 I can't tell if there are any more clear nights in Brooklyn. 818 00:53:06,339 --> 00:53:10,003 You must've seen the Milky Way, a faint band of light at night. 819 00:53:10,210 --> 00:53:14,840 Well, that's just 100 billion stars... 820 00:53:15,049 --> 00:53:16,983 ...all seen together... 821 00:53:17,185 --> 00:53:19,779 ...edge on, as in this picture. 822 00:53:19,989 --> 00:53:23,322 If you could get out of the Milky Way and look down on it... 823 00:53:23,525 --> 00:53:25,426 ...it would look like that picture. 824 00:53:25,629 --> 00:53:27,790 If we did look down on the Milky Way... 825 00:53:27,998 --> 00:53:30,695 ...where would the sun and nearby stars be? 826 00:53:30,902 --> 00:53:34,065 Would it be in the center where things look important... 827 00:53:34,272 --> 00:53:35,740 ...or at least well-lit? 828 00:53:36,475 --> 00:53:39,808 No. We would be way out here... 829 00:53:40,012 --> 00:53:44,006 ...in the suburbs, in the countryside of the galaxy. 830 00:53:44,217 --> 00:53:45,879 We're not in any important place. 831 00:53:46,086 --> 00:53:49,852 All the stars you could see would be in a little place like that. 832 00:53:50,057 --> 00:53:53,255 And the Milky Way would be this band of light... 833 00:53:53,461 --> 00:53:56,022 ...100 billion stars all together. 834 00:53:56,499 --> 00:53:59,434 The fact that we live in the outskirts of the galaxy... 835 00:53:59,635 --> 00:54:03,128 ...was discovered a long time ago... 836 00:54:03,340 --> 00:54:05,901 ...towards the end of the First World War... 837 00:54:06,110 --> 00:54:08,408 ...by a man named Harlow Shapley... 838 00:54:08,613 --> 00:54:12,846 ...who was mapping the position of these clusters of stars. 839 00:54:13,052 --> 00:54:15,544 See, every one of these is a bunch... 840 00:54:15,755 --> 00:54:18,223 ...of maybe 10,000 stars all together. 841 00:54:18,425 --> 00:54:20,416 It's called a globular cluster. 842 00:54:20,628 --> 00:54:23,927 And you can see that they are centered around the middle... 843 00:54:24,131 --> 00:54:25,963 ...the center of the galaxy. 844 00:54:26,234 --> 00:54:30,000 People used to think that the sun was at the center of the galaxy... 845 00:54:30,205 --> 00:54:34,438 ...something important about our position. That turns out to be wrong. 846 00:54:34,777 --> 00:54:37,008 We live in the outskirts... 847 00:54:37,214 --> 00:54:39,648 ...the globular clusters are centered around... 848 00:54:40,150 --> 00:54:43,814 ...the marvelous middle of the Milky Way galaxy. 849 00:54:44,022 --> 00:54:47,857 And then it turned out that this isn't the only galaxy. 850 00:54:48,060 --> 00:54:50,494 We live in this one... 851 00:54:51,098 --> 00:54:52,861 ...but there are many others. 852 00:54:53,233 --> 00:54:56,226 And as this picture reminds us... 853 00:54:56,938 --> 00:54:59,372 ...there are many different kinds of galaxies... 854 00:54:59,574 --> 00:55:01,975 ...of which ours might be just this one. 855 00:55:02,177 --> 00:55:06,740 There are, in fact, 100 billion other galaxies... 856 00:55:06,950 --> 00:55:11,888 ...each of which contains something like 100 billion stars. 857 00:55:12,623 --> 00:55:17,561 Think of how many stars and planets and kinds of life there may be... 858 00:55:18,363 --> 00:55:22,528 ...in this vast and awesome universe. 859 00:55:25,338 --> 00:55:27,500 As long as there have been humans... 860 00:55:27,708 --> 00:55:31,109 ...we have searched for our place in the cosmos. 861 00:55:31,312 --> 00:55:34,110 Where are we? Who are we? 862 00:55:36,218 --> 00:55:40,518 We find that we live on an insignificant planet... 863 00:55:40,723 --> 00:55:42,692 ...of a humdrum star... 864 00:55:42,893 --> 00:55:46,056 ...lost in a galaxy tucked away in some... 865 00:55:46,263 --> 00:55:49,461 ...forgotten corner of a universe in which there are... 866 00:55:49,667 --> 00:55:52,933 ...farmore galaxies than people. 867 00:55:56,175 --> 00:55:59,942 We make our world significant by the courage of our questions... 868 00:56:00,380 --> 00:56:03,009 ...and by the depth of our answers. 869 00:56:04,585 --> 00:56:07,680 We embarked on our journey to the stars... 870 00:56:08,290 --> 00:56:10,884 ...with a question first framed... 871 00:56:11,093 --> 00:56:13,619 ...in the childhood of our species... 872 00:56:14,063 --> 00:56:18,330 ...and in each generation asked anew... 873 00:56:18,602 --> 00:56:20,763 ...with undiminished wonder: 874 00:56:21,138 --> 00:56:23,300 "What are the stars?" 875 00:56:41,395 --> 00:56:44,263 Exploration is in our nature. 876 00:56:44,867 --> 00:56:47,166 We began as wanderers... 877 00:56:47,470 --> 00:56:50,337 ...and we are wanderers still. 878 00:57:01,620 --> 00:57:04,317 We have lingered long enough... 879 00:57:04,524 --> 00:57:07,323 ...on the shores of the cosmic ocean. 880 00:57:07,561 --> 00:57:09,358 We are ready at last... 881 00:57:09,563 --> 00:57:12,795 ...to set sail for the stars.