1 00:00:50,600 --> 00:00:52,932 The sky calls to us. 2 00:00:53,303 --> 00:00:55,396 If we do not destroy ourselves... 3 00:00:55,605 --> 00:00:58,631 ...we will one day venture to the stars. 4 00:00:59,542 --> 00:01:03,000 There was a time when the stars seemed an impenetrable mystery. 5 00:01:03,213 --> 00:01:06,546 Today, we have begun to understand them. 6 00:01:06,750 --> 00:01:11,687 In our personal lives also, we journey from ignorance to knowledge. 7 00:01:11,921 --> 00:01:16,358 Our individual growth reflects the advancement of the species. 8 00:01:16,860 --> 00:01:18,794 The exploration of the cosmos is... 9 00:01:18,995 --> 00:01:22,021 ...a voyage of self-discovery. 10 00:01:32,542 --> 00:01:35,477 When I was a child, I lived here... 11 00:01:35,678 --> 00:01:39,978 ...in the Bensonhurst section of Brooklyn in the city of New York. 12 00:01:40,183 --> 00:01:43,243 I knew my immediate neighborhood intimately... 13 00:01:43,453 --> 00:01:47,719 ...every candy store, front stoop... 14 00:01:47,924 --> 00:01:50,188 ...back yard, empty lot... 15 00:01:50,393 --> 00:01:53,487 ...and wall for playing Chinese handball. 16 00:01:59,102 --> 00:02:01,229 It was my whole world. 17 00:02:20,323 --> 00:02:22,450 But more than a few blocks away... 18 00:02:22,659 --> 00:02:27,358 ...north of the raucous traffic and elevated railway on 86th Street... 19 00:02:27,564 --> 00:02:31,227 ...was an unknown territory off-limits to my wanderings. 20 00:02:32,168 --> 00:02:34,932 It could have been Mars for all I knew. 21 00:02:39,042 --> 00:02:41,875 Even with an early bedtime in the winter... 22 00:02:42,145 --> 00:02:45,137 ...you could occasionally see the stars. 23 00:02:45,648 --> 00:02:48,947 I would look up at them and wonder what they were. 24 00:02:49,252 --> 00:02:52,016 I'd ask other kids and adults... 25 00:02:52,589 --> 00:02:54,181 ...and they would answer: 26 00:02:54,390 --> 00:02:56,449 "They're lights in the sky, kid." 27 00:02:56,659 --> 00:03:00,618 Well, I could tell they were lights in the sky, but what were they? 28 00:03:00,830 --> 00:03:04,266 There had to be some deeper answer. 29 00:03:09,672 --> 00:03:13,164 I remember I was issued my first library card. 30 00:03:13,376 --> 00:03:17,938 It was some library on 85th Street. Anyway, it was in alien territory. 31 00:03:18,414 --> 00:03:22,111 And I asked the librarian for a book on stars. 32 00:03:22,552 --> 00:03:23,985 She gave me... 33 00:03:24,420 --> 00:03:27,355 ...a picture book with portraits of men and women... 34 00:03:27,557 --> 00:03:31,186 ...with names like Veronica Lake and Alan Ladd. 35 00:03:31,728 --> 00:03:35,129 I explained that wasn't what I wanted at all. 36 00:03:35,732 --> 00:03:39,168 And for some reason, then obscure to me, she smiled... 37 00:03:39,369 --> 00:03:42,532 ...and got me another book, the right kind of book. 38 00:03:42,839 --> 00:03:45,137 I was so excited to know the answer... 39 00:03:45,341 --> 00:03:48,401 ...I opened the book breathlessly, right there in the library... 40 00:03:48,611 --> 00:03:51,444 ...and the book said something astonishing... 41 00:03:51,648 --> 00:03:54,139 ...a very big thought. 42 00:03:54,851 --> 00:03:58,184 Stars, it said, were suns... 43 00:03:58,388 --> 00:04:00,151 ...but very far away. 44 00:04:00,356 --> 00:04:04,292 The sun was a star, but close-up. 45 00:04:11,968 --> 00:04:15,699 How, I wondered, could anybody know such things for sure? 46 00:04:15,905 --> 00:04:19,432 How did they figure it out? Where did they even begin? 47 00:04:28,985 --> 00:04:31,954 I was ignorant of the idea of angular size. 48 00:04:32,155 --> 00:04:36,148 I didn't know about the inverse square law of the propagation of light. 49 00:04:36,359 --> 00:04:40,159 I didn't have any chance of calculating the distance to the stars. 50 00:04:40,363 --> 00:04:43,457 But I could tell that if the stars were suns... 51 00:04:43,666 --> 00:04:46,134 ...they had to be awfully far away. 52 00:04:46,336 --> 00:04:50,568 Further away than 86th Street, further away than Manhattan... 53 00:04:50,773 --> 00:04:54,140 ...further away, probably, than New Jersey. 54 00:04:54,344 --> 00:04:58,041 The universe had become much grander... 55 00:04:58,248 --> 00:05:00,614 ...than I had ever guessed. 56 00:05:03,553 --> 00:05:06,215 And then I read another astonishing fact. 57 00:05:06,422 --> 00:05:09,721 The Earth, which includes Brooklyn... 58 00:05:09,926 --> 00:05:11,223 ...was a planet. 59 00:05:11,427 --> 00:05:13,486 It went around the sun. 60 00:05:13,696 --> 00:05:15,288 There were other planets. 61 00:05:15,498 --> 00:05:17,762 They also went around the sun... 62 00:05:17,967 --> 00:05:21,266 ...some closer to the sun, some further from the sun. 63 00:05:21,504 --> 00:05:26,032 But planets didn't shine by their own light the way the sun does. 64 00:05:26,776 --> 00:05:30,735 No, planets simply reflected the little bit of light... 65 00:05:30,947 --> 00:05:34,542 ...that shines on them from the sun back to us. 66 00:05:34,751 --> 00:05:37,015 If you were a great distance from the sun... 67 00:05:37,220 --> 00:05:40,951 ...you wouldn't be able to see the Earth or the other planets at all. 68 00:05:41,190 --> 00:05:43,886 Well, then, it stood to reason, I thought... 69 00:05:44,093 --> 00:05:47,722 ...that those other stars ought to have their own planets... 70 00:05:47,930 --> 00:05:50,194 ...and some of those planets ought to have life. 71 00:05:50,833 --> 00:05:52,061 Why not? 72 00:05:52,268 --> 00:05:56,671 And that life ought to be pretty different from life as we know it... 73 00:05:56,873 --> 00:05:58,864 ...life here in Brooklyn. 74 00:05:59,075 --> 00:06:02,203 Ganymede. Look at this amazing Ganymede stuff. 75 00:06:02,412 --> 00:06:03,470 Wait, wait, wait. 76 00:06:03,680 --> 00:06:06,080 As a child, it was my immense good fortune... 77 00:06:06,282 --> 00:06:10,309 ...to have parents and a few teachers who encouraged my curiosity. 78 00:06:10,520 --> 00:06:12,852 This was my 6th-grade classroom. 79 00:06:13,056 --> 00:06:16,025 I came back here one day to remember what it was like. 80 00:06:16,225 --> 00:06:18,955 I brought some of the pictures of other worlds... 81 00:06:19,162 --> 00:06:21,790 ...that were radioed back by the Voyager spacecraft... 82 00:06:21,998 --> 00:06:24,125 ...of Jupiter and its moons. 83 00:06:24,334 --> 00:06:25,892 This is Calisto which is... 84 00:06:29,639 --> 00:06:31,573 What is a Calisto? I want a Calisto. 85 00:06:31,774 --> 00:06:33,071 Now you got it. What is it? 86 00:06:33,276 --> 00:06:36,768 It's the outermost big moon of Jupiter. 87 00:06:37,847 --> 00:06:40,281 Who is this guy? Europa. 88 00:06:41,684 --> 00:06:43,311 Another Europa. 89 00:06:43,686 --> 00:06:46,746 A black-and-white picture of a ring of Jupiter. 90 00:06:47,156 --> 00:06:50,182 There you go. That's a prize for honesty. 91 00:06:50,827 --> 00:06:52,317 You didn't get a second. 92 00:06:52,528 --> 00:06:54,018 Which one would you like? 93 00:07:06,209 --> 00:07:09,269 Every one of us begins life with an open mind... 94 00:07:09,479 --> 00:07:13,415 ...a driving curiosity, a sense of wonder. 95 00:07:14,517 --> 00:07:17,850 I thought it might be fun if we now had some questions. 96 00:07:18,054 --> 00:07:21,956 Why is the Earth round? Why isn't it square or any other shape? 97 00:07:22,658 --> 00:07:24,250 That's a good question. 98 00:07:24,460 --> 00:07:28,897 That's a question I've asked myself. The answer has to do with gravity. 99 00:07:29,399 --> 00:07:31,230 The Earth has a strong gravity. 100 00:07:31,434 --> 00:07:33,994 If you were to make a mountain very high... 101 00:07:34,203 --> 00:07:37,104 ...higher than Everest, the biggest mountain on Earth... 102 00:07:37,306 --> 00:07:39,638 ...it would be crushed by its own weight. 103 00:07:39,842 --> 00:07:42,504 Gravity pulls everything towards the center. 104 00:07:42,712 --> 00:07:45,977 So any really big bump on the Earth is crushed. 105 00:07:46,182 --> 00:07:49,811 But if you had a small object, a tiny world... 106 00:07:50,019 --> 00:07:51,680 ...the gravity is very low... 107 00:07:51,888 --> 00:07:55,051 ...and then it can be very different from a sphere. 108 00:07:55,258 --> 00:07:59,661 I think I have here a world that isn't a sphere. 109 00:08:00,029 --> 00:08:01,087 Here. 110 00:08:02,298 --> 00:08:03,629 Look at this one. 111 00:08:04,834 --> 00:08:06,324 See? It's lumpy. 112 00:08:08,104 --> 00:08:09,298 It's a lumpy world. 113 00:08:10,373 --> 00:08:11,738 It looks like a potato. 114 00:08:12,475 --> 00:08:15,638 There's a large potato orbiting the planet Mars. 115 00:08:15,845 --> 00:08:18,075 This is one of the moons of Mars. 116 00:08:18,281 --> 00:08:20,511 That's a perfect example. 117 00:08:20,716 --> 00:08:24,709 You can have big departures from a sphere if your gravity is low. 118 00:08:24,921 --> 00:08:26,821 Now the question in the front. 119 00:08:27,023 --> 00:08:30,254 Is the sun considered part of the Milky Way galaxy? 120 00:08:30,460 --> 00:08:33,588 Sure, you're considered part of the Milky Way galaxy. 121 00:08:34,030 --> 00:08:38,330 Everything except other galaxies is part of the Milky Way galaxy. 122 00:08:38,534 --> 00:08:40,092 The sun is one star. 123 00:08:40,303 --> 00:08:45,240 There is a few hundred billion stars in the Milky Way. 124 00:08:45,541 --> 00:08:48,271 Around each star, maybe, is a whole bunch of planets. 125 00:08:49,145 --> 00:08:52,376 And on one of those planets is life... 126 00:08:52,582 --> 00:08:56,450 ...and one of the life forms on that planet is you. 127 00:08:56,652 --> 00:08:59,018 You're a part of the Milky Way galaxy too. 128 00:09:09,499 --> 00:09:14,436 Sometimes I think, how lucky we are to live in this time... 129 00:09:14,637 --> 00:09:18,300 ...the first moment in human history when we are, in fact... 130 00:09:18,508 --> 00:09:20,100 ...visiting other worlds... 131 00:09:20,309 --> 00:09:24,541 ...and engaging in a deep reconnaissance of the cosmos. 132 00:09:24,914 --> 00:09:27,542 But if we had been born in a much earlier age... 133 00:09:27,750 --> 00:09:30,844 ...no matter how great our dedication, we couldn't have understood... 134 00:09:31,053 --> 00:09:33,317 ...what the stars and planets are. 135 00:09:42,865 --> 00:09:47,359 We would not have known that there were other suns and other worlds. 136 00:09:50,706 --> 00:09:54,665 This is one of the great secrets wrested from nature... 137 00:09:54,877 --> 00:09:59,337 ...through a million years of patient observation and courageous thinking. 138 00:10:02,818 --> 00:10:06,618 Human beings have always asked questions about the stars. 139 00:10:06,822 --> 00:10:09,882 It's as natural as breathing. 140 00:10:10,126 --> 00:10:13,960 But imagine a time before science had found out the answers. 141 00:10:14,163 --> 00:10:16,757 Imagine what it was like, say... 142 00:10:16,966 --> 00:10:20,493 ...hundreds of thousands of years ago... 143 00:10:20,703 --> 00:10:24,298 ...soon after the discovery of fire. 144 00:10:24,507 --> 00:10:28,102 We were just as smart and just as curious then... 145 00:10:28,311 --> 00:10:29,972 ...as we are now. 146 00:10:30,179 --> 00:10:32,044 Sometimes it seems to me that... 147 00:10:32,248 --> 00:10:35,274 ...there were people then who thought like this: 148 00:10:37,653 --> 00:10:41,214 We are wandering hunter folk. 149 00:10:41,424 --> 00:10:43,085 Fire keeps us warm. 150 00:10:43,292 --> 00:10:46,523 Its light makes holes in the darkness. 151 00:10:46,729 --> 00:10:48,993 It keeps hungry animals away. 152 00:10:49,432 --> 00:10:52,924 In the darkness, we can see each other and talk. 153 00:10:54,103 --> 00:10:56,094 We take care of the flame. 154 00:10:56,305 --> 00:10:59,297 The flame takes care of us. 155 00:11:00,209 --> 00:11:02,507 The stars are not near to us. 156 00:11:02,712 --> 00:11:06,409 When we climb a hill or a tree, they are no closer. 157 00:11:06,616 --> 00:11:10,552 They flicker with a strange, cold, white... 158 00:11:11,354 --> 00:11:12,412 ...faraway light. 159 00:11:13,356 --> 00:11:17,656 Many of them, all over the sky, but only at night. 160 00:11:18,027 --> 00:11:20,120 I wonder what they are. 161 00:11:20,930 --> 00:11:24,457 One night I thought the stars are flames. 162 00:11:24,667 --> 00:11:27,864 They give a little light at night as fire does. 163 00:11:28,070 --> 00:11:30,129 Maybe the stars are campfires... 164 00:11:30,339 --> 00:11:33,502 ...which other wanderers light at night. 165 00:11:34,210 --> 00:11:37,543 The stars give a much smaller light than campfires... 166 00:11:37,747 --> 00:11:40,545 ...so they must be very far away. 167 00:11:41,117 --> 00:11:43,779 I wonder if our campfires... 168 00:11:43,986 --> 00:11:46,750 ...look like stars to the people in the sky. 169 00:11:47,156 --> 00:11:51,650 But why don't those campfires and the wanderers who made them... 170 00:11:51,861 --> 00:11:53,692 ...fall down at our feet? 171 00:11:53,896 --> 00:11:58,094 Why don't strange tribes drop from the sky? 172 00:11:59,902 --> 00:12:04,669 Those beings in the sky must have great powers. 173 00:12:11,681 --> 00:12:14,309 I don't suppose that every hunter-gatherer... 174 00:12:14,517 --> 00:12:17,247 ...had such thoughts about the stars. 175 00:12:17,453 --> 00:12:20,889 But we know from contemporary hunter-gatherer communities... 176 00:12:21,090 --> 00:12:24,821 ...that very imaginative ideas arise. 177 00:12:25,261 --> 00:12:27,786 The Kung Bushmen... 178 00:12:27,997 --> 00:12:31,057 ...of the Kalahari Desert in the Republic of Botswana... 179 00:12:31,267 --> 00:12:33,997 ...have an explanation of the Milky Way. 180 00:12:34,203 --> 00:12:37,172 At their latitude, it's often overhead. 181 00:12:37,373 --> 00:12:41,400 They call it the "backbone of night." 182 00:12:41,610 --> 00:12:44,238 They believe it holds the sky up. 183 00:12:44,447 --> 00:12:46,779 They believe that if not for the Milky Way... 184 00:12:46,982 --> 00:12:50,611 ...pieces of sky would come crashing down at our feet. 185 00:12:50,820 --> 00:12:54,449 So the Milky Way, in their view, has some practical value. 186 00:12:54,657 --> 00:12:57,182 The backbone of night. 187 00:13:00,029 --> 00:13:02,725 Later on, metaphors about... 188 00:13:02,998 --> 00:13:05,489 ...campfires or backbones... 189 00:13:05,701 --> 00:13:09,000 ...or holes through which the flame could be seen... 190 00:13:09,205 --> 00:13:13,574 ...were replaced in most human communities by another idea. 191 00:13:14,043 --> 00:13:18,912 The powerful beings in the sky were promoted to gods. 192 00:13:19,548 --> 00:13:22,642 They were given names and relatives... 193 00:13:22,852 --> 00:13:24,786 ...and special responsibilities... 194 00:13:24,987 --> 00:13:28,354 ...for the cosmic services they were expected to perform. 195 00:13:28,557 --> 00:13:32,425 There was a god for every human concern. 196 00:13:32,628 --> 00:13:33,686 Gods ran nature. 197 00:13:33,896 --> 00:13:38,333 Nothing happened without the direct intervention of some god. 198 00:13:38,634 --> 00:13:42,092 If the gods were happy, there was plenty of food... 199 00:13:42,304 --> 00:13:43,862 ...and humans were happy. 200 00:13:45,674 --> 00:13:48,438 But if something displeased the gods... 201 00:13:48,644 --> 00:13:52,944 ...and it didn't take much, the consequences were awesome: 202 00:13:53,149 --> 00:13:56,380 Droughts, floods, storms, wars... 203 00:13:56,585 --> 00:14:00,214 ...earthquakes, volcanic eruptions, epidemics. 204 00:14:01,123 --> 00:14:04,149 The gods had to be propitiated. 205 00:14:04,360 --> 00:14:07,022 And a vast industry of priests arose... 206 00:14:07,229 --> 00:14:09,754 ...to make the gods less angry. 207 00:14:10,366 --> 00:14:13,426 But because the gods were capricious... 208 00:14:13,636 --> 00:14:16,127 ...you couldn't be sure what they would do. 209 00:14:16,338 --> 00:14:18,772 Nature was a mystery. 210 00:14:19,041 --> 00:14:21,566 It was hard to understand the world. 211 00:14:24,613 --> 00:14:27,776 Our ancestors groped in darkness... 212 00:14:27,983 --> 00:14:30,281 ...to make sense of their surroundings. 213 00:14:30,486 --> 00:14:31,976 Powerless before nature... 214 00:14:32,655 --> 00:14:35,215 ...they invented rituals and myths... 215 00:14:35,424 --> 00:14:37,984 ...some desperate and cruel... 216 00:14:38,194 --> 00:14:41,857 ...others imaginative and benign. 217 00:14:42,198 --> 00:14:44,428 The ancient Greeks explained... 218 00:14:44,633 --> 00:14:48,091 ...that diffuse band of brightness in the night sky... 219 00:14:48,304 --> 00:14:50,966 ...as the milk of the goddess Hera... 220 00:14:51,173 --> 00:14:54,142 ...squirted from her breast across the heavens. 221 00:14:54,343 --> 00:14:57,779 We still call it the Milky Way. 222 00:15:04,286 --> 00:15:07,278 In gratitude for the many gifts of the gods... 223 00:15:07,489 --> 00:15:11,619 ...our ancestors created works of surpassing beauty. 224 00:15:14,563 --> 00:15:17,054 This is all that remains... 225 00:15:17,266 --> 00:15:20,667 ...of the ancient temple of Hera, queen of heaven: 226 00:15:21,036 --> 00:15:25,905 A single marble column standing in a vast field of ruins... 227 00:15:26,609 --> 00:15:28,600 ...on the Greek island of Samos. 228 00:15:28,811 --> 00:15:30,779 It was one of the wonders of the world... 229 00:15:31,247 --> 00:15:35,707 ...built by people with an extraordinary eye for clarity... 230 00:15:35,918 --> 00:15:37,476 ...and symmetry. 231 00:15:44,860 --> 00:15:47,192 Those who thronged to that temple... 232 00:15:47,396 --> 00:15:49,990 ...were also the architects of a bridge... 233 00:15:50,199 --> 00:15:52,997 ...from their world to ours. 234 00:15:55,604 --> 00:16:00,098 We were moving once again in our voyage of self-discovery... 235 00:16:00,376 --> 00:16:03,004 ...on our journey to the stars. 236 00:16:07,950 --> 00:16:11,647 Here, 25 centuries ago... 237 00:16:12,288 --> 00:16:15,655 ...on the island of Samos and in the other Greek colonies... 238 00:16:15,858 --> 00:16:18,418 ...which had grown up in the busy Aegean Sea... 239 00:16:18,627 --> 00:16:21,221 ...there was a glorious awakening. 240 00:16:21,430 --> 00:16:24,991 Suddenly, people believed that everything was made of atoms... 241 00:16:25,200 --> 00:16:29,466 ...that human beings and other animals had evolved from simpler forms... 242 00:16:29,672 --> 00:16:34,302 ...that diseases were not caused by demons or the gods... 243 00:16:34,510 --> 00:16:38,810 ...that the Earth was only a planet going around a sun... 244 00:16:39,014 --> 00:16:41,380 ...which was very far away. 245 00:16:44,954 --> 00:16:49,050 This revolution made cosmos out of chaos. 246 00:16:49,458 --> 00:16:52,791 Here, in the sixth century B.C., a new idea developed... 247 00:16:52,995 --> 00:16:55,657 ...one of the great ideas of the human species. 248 00:16:55,864 --> 00:16:59,925 It was argued that the universe was knowable. 249 00:17:00,235 --> 00:17:02,897 Why? Because it was ordered. 250 00:17:03,105 --> 00:17:05,665 Because there are regularities in nature... 251 00:17:05,874 --> 00:17:08,707 ...which permitted secrets to be uncovered. 252 00:17:10,946 --> 00:17:14,347 Nature was not entirely unpredictable. 253 00:17:14,550 --> 00:17:18,281 There were rules which even she had to obey. 254 00:17:20,823 --> 00:17:25,487 This ordered and admirable character of the universe... 255 00:17:25,694 --> 00:17:27,685 ...was called cosmos. 256 00:17:28,864 --> 00:17:31,594 And it was set in stark contradiction... 257 00:17:31,800 --> 00:17:34,030 ...to the idea of chaos. 258 00:17:34,903 --> 00:17:39,169 This was the first conflict of which we know... 259 00:17:39,608 --> 00:17:41,838 ...between science and mysticism... 260 00:17:42,644 --> 00:17:45,374 ...between nature and the gods. 261 00:17:51,186 --> 00:17:53,154 But why here? 262 00:17:53,756 --> 00:17:58,193 Why in these remote islands and inlets of the eastern Mediterranean? 263 00:17:58,394 --> 00:18:00,692 Why not in the great cities of... 264 00:18:00,896 --> 00:18:05,560 ...India or Egypt, Babylon, China, Mesoamerica? 265 00:18:08,237 --> 00:18:11,536 Because they were all at the center of old empires. 266 00:18:14,109 --> 00:18:17,636 They were set in their ways, hostile to new ideas. 267 00:18:17,846 --> 00:18:19,609 But here in lonia... 268 00:18:19,815 --> 00:18:23,717 ...were a multitude of newly colonized islands and city-states. 269 00:18:23,919 --> 00:18:28,253 Isolation, even if incomplete, promotes diversity. 270 00:18:28,457 --> 00:18:32,621 No single concentration of power could enforce conformity. 271 00:18:32,828 --> 00:18:35,763 Free inquiry became possible. 272 00:18:36,665 --> 00:18:39,998 They were beyond the frontiers of the empires. 273 00:18:40,202 --> 00:18:43,694 The merchants and tourists and sailors of Africa... 274 00:18:43,906 --> 00:18:46,966 ...Asia and Europe met in the harbors of lonia... 275 00:18:47,843 --> 00:18:51,643 ...to exchange goods and stories and ideas. 276 00:18:51,847 --> 00:18:55,112 There was a vigorous and heady interaction... 277 00:18:55,317 --> 00:19:00,118 ...of many traditions, prejudices, languages and gods. 278 00:19:09,965 --> 00:19:13,366 These people were ready to experiment. 279 00:19:13,936 --> 00:19:17,030 Once you are open to questioning rituals... 280 00:19:17,239 --> 00:19:19,207 ...and time-honored practices... 281 00:19:19,408 --> 00:19:23,811 ...you find that one question leads to another. 282 00:19:33,522 --> 00:19:36,650 What do you do when you're faced with several different gods... 283 00:19:36,859 --> 00:19:39,259 ...each claiming the same territory? 284 00:19:39,461 --> 00:19:42,021 The Babylonian Marduk and the Greek Zeus... 285 00:19:42,231 --> 00:19:45,689 ...were each considered king of the gods... 286 00:19:45,901 --> 00:19:47,835 ...master of the sky. 287 00:19:48,303 --> 00:19:51,670 You might decide, since they otherwise had different attributes... 288 00:19:51,874 --> 00:19:54,638 ...that one of them was merely invented by the priests. 289 00:19:54,843 --> 00:19:57,505 But if one, why not both? 290 00:20:03,285 --> 00:20:06,311 And so it was here that the great idea arose: 291 00:20:06,522 --> 00:20:08,547 The realization that there might be a way... 292 00:20:08,757 --> 00:20:11,351 ...to know the world without the god hypothesis. 293 00:20:11,560 --> 00:20:16,327 That there be principles, forces, laws of nature... 294 00:20:16,532 --> 00:20:20,024 ...through which the world might be understood without attributing... 295 00:20:20,235 --> 00:20:24,296 ...the fall of every sparrow to the direct intervention of Zeus. 296 00:20:24,706 --> 00:20:27,903 This is the place where science was born. 297 00:20:28,277 --> 00:20:30,108 That's why we're here. 298 00:20:31,647 --> 00:20:36,584 This Greek revolution happened between 600 and 400 B.C. 299 00:20:37,252 --> 00:20:40,415 It was accomplished by the same practical and productive people... 300 00:20:40,622 --> 00:20:42,453 ...who made the society function. 301 00:20:42,658 --> 00:20:45,752 Political power was in the hands of the merchants... 302 00:20:45,961 --> 00:20:49,192 ...who promoted the technology on which their prosperity depended. 303 00:20:49,598 --> 00:20:51,759 The earliest pioneers of science were... 304 00:20:51,967 --> 00:20:55,130 ...merchants and artisans and their children. 305 00:21:01,310 --> 00:21:04,711 The first lonian scientist was named Thales. 306 00:21:05,180 --> 00:21:07,944 He was born over there in the city of Miletus... 307 00:21:08,150 --> 00:21:10,448 ...across this narrow strait. 308 00:21:10,652 --> 00:21:12,415 He had traveled in Egypt... 309 00:21:12,621 --> 00:21:15,454 ...and was conversant with the knowledge of Babylon. 310 00:21:15,891 --> 00:21:20,385 Like the Babylonians, he believed that the world had once all been water. 311 00:21:21,029 --> 00:21:23,122 To explain the dry land... 312 00:21:23,332 --> 00:21:26,495 ...the Babylonians added that their god, Marduk... 313 00:21:26,702 --> 00:21:30,297 ...had placed a mat on the face of the waters... 314 00:21:30,505 --> 00:21:32,803 ...and piled dirt on top of it. 315 00:21:34,309 --> 00:21:36,004 Thales had a similar view... 316 00:21:36,211 --> 00:21:39,112 ...but he left Marduk out. 317 00:21:39,915 --> 00:21:43,214 Yes, the world had once been mostly water... 318 00:21:43,719 --> 00:21:48,247 ...but it was a natural process which explained the dry land. 319 00:21:48,457 --> 00:21:52,689 Thales thought it was similar to the silting up he had observed... 320 00:21:52,894 --> 00:21:55,385 ...at the delta of the river Nile. 321 00:21:56,632 --> 00:22:00,295 Whether Thales' conclusions were right or wrong... 322 00:22:00,502 --> 00:22:03,960 ...is not nearly as important as his approach. 323 00:22:04,172 --> 00:22:07,699 The world was not made by the gods... 324 00:22:07,909 --> 00:22:11,072 ...but instead was the result of material forces... 325 00:22:11,280 --> 00:22:13,180 ...interacting in nature. 326 00:22:13,782 --> 00:22:17,616 Thales brought back from Babylon and Egypt... 327 00:22:17,819 --> 00:22:21,050 ...the seeds of new sciences: 328 00:22:21,290 --> 00:22:23,690 Astronomy and geometry... 329 00:22:23,892 --> 00:22:26,690 ...sciences which would sprout and grow... 330 00:22:26,895 --> 00:22:29,921 ...in the fertile soil of lonia. 331 00:22:31,500 --> 00:22:35,402 Anaximander of Miletus, over there... 332 00:22:35,837 --> 00:22:38,101 ...was a friend and colleague of Thales... 333 00:22:38,307 --> 00:22:40,468 ...one of the first people that we know of... 334 00:22:40,676 --> 00:22:42,906 ...to have actually done an experiment. 335 00:22:43,111 --> 00:22:47,639 By examining the moving shadow cast by a vertical stick... 336 00:22:47,849 --> 00:22:52,377 ...he determined accurately the lengths of the year and seasons. 337 00:22:52,587 --> 00:22:55,818 For ages, men had used sticks... 338 00:22:56,024 --> 00:22:58,083 ...to club and spear each other. 339 00:22:58,293 --> 00:23:01,820 Anaximander used a stick to measure time. 340 00:23:06,301 --> 00:23:10,897 In 540 B.C., or thereabouts, on this island of Samos... 341 00:23:11,106 --> 00:23:15,634 ...there came to power a tyrant named Polycrates. 342 00:23:15,911 --> 00:23:17,936 He seems to have started as a caterer... 343 00:23:18,146 --> 00:23:21,047 ...and then went on to international piracy. 344 00:23:21,383 --> 00:23:25,911 His loot was unloaded on this very breakwater. 345 00:23:34,496 --> 00:23:38,557 But he oppressed his own people, he made war on his neighbors. 346 00:23:38,767 --> 00:23:40,894 He quite rightly feared invasion. 347 00:23:41,103 --> 00:23:46,006 So Polycrates surrounded his capital city with an impressive wall... 348 00:23:46,208 --> 00:23:49,143 ...whose remains stand till this day. 349 00:23:58,553 --> 00:24:02,512 To carry water from a distant spring through the fortifications... 350 00:24:02,724 --> 00:24:05,522 ...he ordered this great tunnel built. 351 00:24:05,727 --> 00:24:09,219 A kilometer long, it pierces a mountain. 352 00:24:09,498 --> 00:24:11,830 Two cuttings were dug from either side... 353 00:24:12,033 --> 00:24:14,297 ...which met almost perfectly in the middle. 354 00:24:14,503 --> 00:24:17,734 The project took some 15 years to complete. 355 00:24:18,673 --> 00:24:22,234 It is a token of the civil engineering of its day... 356 00:24:22,444 --> 00:24:26,278 ...and an indication of the extraordinary practical capability... 357 00:24:26,481 --> 00:24:27,379 ...of the lonians. 358 00:24:30,685 --> 00:24:32,983 The enduring legacy of the lonians... 359 00:24:33,188 --> 00:24:35,622 ...is the tools and techniques they developed... 360 00:24:35,824 --> 00:24:39,089 ...which remain the basis of modern technology. 361 00:24:43,265 --> 00:24:46,496 This was the time of Theodorus... 362 00:24:46,701 --> 00:24:49,431 ...the master engineer of the age... 363 00:24:49,638 --> 00:24:53,631 ...a man who is credited with the invention of... 364 00:24:53,842 --> 00:24:57,801 ...the key, the ruler, the carpenter's square... 365 00:24:58,013 --> 00:25:00,880 ...the level, the lathe, bronze casting. 366 00:25:01,383 --> 00:25:04,352 Why are there no monuments to this man? 367 00:25:05,353 --> 00:25:08,845 Those who dreamt and speculated... 368 00:25:09,057 --> 00:25:11,457 ...and deduced about the laws of nature... 369 00:25:11,660 --> 00:25:14,128 ...talked to the engineers and the technologists. 370 00:25:14,329 --> 00:25:16,354 They were often the same people. 371 00:25:16,731 --> 00:25:20,690 The practical and the theoretical were one. 372 00:25:27,542 --> 00:25:31,205 This new hybrid of abstract thought... 373 00:25:31,413 --> 00:25:34,814 ...and everyday experience blossomed into science. 374 00:25:36,184 --> 00:25:40,314 When these practical men turned their attention to the natural world... 375 00:25:40,522 --> 00:25:42,649 ...they began to uncover hidden wonders... 376 00:25:43,625 --> 00:25:46,185 ...and breathtaking possibilities. 377 00:25:46,828 --> 00:25:50,286 Anaximander studied the profusion of living things... 378 00:25:50,499 --> 00:25:53,024 ...and saw their interrelationships. 379 00:25:53,235 --> 00:25:57,365 He concluded that life had originated in water and mud... 380 00:25:57,839 --> 00:26:00,569 ...and then colonized the dry land. 381 00:26:01,409 --> 00:26:03,240 "Human beings," he said... 382 00:26:03,445 --> 00:26:06,346 "...must have evolved from simpler forms." 383 00:26:06,848 --> 00:26:11,785 This insight had to wait 24 centuries until its truth was demonstrated... 384 00:26:12,387 --> 00:26:14,150 ...by Charles Darwin. 385 00:26:22,764 --> 00:26:26,962 Nothing was excluded from the investigations of the first scientists. 386 00:26:27,168 --> 00:26:31,468 Even the air became the subject of close examination... 387 00:26:31,673 --> 00:26:35,666 ...by a Greek from Sicily named Empedocles. 388 00:26:37,312 --> 00:26:39,872 He made an astonishing discovery... 389 00:26:40,081 --> 00:26:44,518 ...with a household implement that people had used for centuries. 390 00:26:44,853 --> 00:26:48,016 This is the so-called water thief. 391 00:26:48,223 --> 00:26:52,421 It's a brazen sphere with a neck and a hole at the top... 392 00:26:52,627 --> 00:26:55,187 ...and a set of little holes at the bottom. 393 00:26:55,397 --> 00:26:57,058 It was used as a kitchen ladle. 394 00:26:57,599 --> 00:27:01,296 You fill it by immersing it in water. 395 00:27:03,805 --> 00:27:06,103 If, after it's been in there a little bit... 396 00:27:06,308 --> 00:27:09,471 ...you pull it out with the neck uncovered... 397 00:27:10,745 --> 00:27:14,545 ...then the water trickles out the little holes making a small shower. 398 00:27:15,684 --> 00:27:19,313 Instead, if you pull it out with the neck covered... 399 00:27:20,088 --> 00:27:21,715 ...the water is retained. 400 00:27:33,535 --> 00:27:35,628 Now try to fill it... 401 00:27:35,870 --> 00:27:39,328 ...with the neck covered with my thumb. 402 00:27:43,445 --> 00:27:44,571 Nothing happens. 403 00:27:45,447 --> 00:27:46,573 Why not? 404 00:27:47,148 --> 00:27:48,945 There's something in the way. 405 00:27:49,150 --> 00:27:54,087 Some material is blocking the access of the water into the sphere. 406 00:27:54,422 --> 00:27:56,617 I can't see any such material. 407 00:27:57,492 --> 00:27:59,119 What could it be? 408 00:27:59,861 --> 00:28:02,352 Empedocles identified it... 409 00:28:02,564 --> 00:28:03,963 ...as air. 410 00:28:04,599 --> 00:28:06,362 What else could it be? 411 00:28:06,735 --> 00:28:09,863 A thing you can't see can exert pressure... 412 00:28:10,071 --> 00:28:13,871 ...can frustrate my wish to fill this vessel with water... 413 00:28:14,075 --> 00:28:18,341 ...if I were dumb enough to leave my thumb on the neck. 414 00:28:19,180 --> 00:28:22,843 Empedocles had discovered... 415 00:28:24,185 --> 00:28:25,675 ...the invisible. 416 00:28:26,287 --> 00:28:29,279 Air, he thought, must be matter... 417 00:28:29,491 --> 00:28:32,858 ...in a form so finely divided... 418 00:28:33,728 --> 00:28:35,093 ...that it couldn't be seen. 419 00:28:36,564 --> 00:28:40,967 This hint, this whiff of the existence of atoms... 420 00:28:41,169 --> 00:28:45,538 ...was carried much further by a contemporary named Democritus. 421 00:28:46,007 --> 00:28:50,273 Of all the ancient scientists, it is he who speaks most clearly to us... 422 00:28:50,478 --> 00:28:52,002 ...across the centuries. 423 00:28:52,213 --> 00:28:55,444 The few surviving fragments of his scientific writings... 424 00:28:55,650 --> 00:28:59,279 ...reveal a mind of the highest logical and intuitive powers. 425 00:28:59,487 --> 00:29:04,288 He believed that a large number of other worlds wander through space... 426 00:29:04,492 --> 00:29:06,790 ...that worlds are born and die... 427 00:29:06,995 --> 00:29:08,986 ...that some are rich and living creatures... 428 00:29:09,197 --> 00:29:12,428 ...and others are dry and barren. 429 00:29:13,802 --> 00:29:16,635 He was the first to understand that the Milky Way... 430 00:29:16,838 --> 00:29:20,433 ...is an aggregate of the light of innumerable faint stars. 431 00:29:20,642 --> 00:29:24,510 Beyond campfires in the sky, beyond the milk of Hera... 432 00:29:24,713 --> 00:29:29,650 ...beyond the backbone of night, the mind of Democritus soared. 433 00:29:34,923 --> 00:29:38,154 He saw deep connections between the heavens and the Earth. 434 00:29:38,760 --> 00:29:41,695 "Man," he said, "is a microcosm... 435 00:29:42,130 --> 00:29:43,722 ...a little cosmos." 436 00:30:07,555 --> 00:30:11,491 Democritus came from the lonian town of Abdera... 437 00:30:11,693 --> 00:30:13,991 ...on the northern Aegean shore. 438 00:30:17,332 --> 00:30:21,666 In those days, Abdera was the butt of jokes. 439 00:30:22,570 --> 00:30:24,663 If, around the year 400 B.C... 440 00:30:24,873 --> 00:30:27,341 ...in the equivalent of a restaurant like this... 441 00:30:27,909 --> 00:30:30,537 ...you told a story about someone from Abdera... 442 00:30:30,745 --> 00:30:32,679 ...you were guaranteed a laugh. 443 00:30:35,550 --> 00:30:37,518 It was, in a way... 444 00:30:37,719 --> 00:30:40,119 ...the Brooklyn of its time. 445 00:30:42,624 --> 00:30:46,822 For Democritus, all of life was to be enjoyed and understood. 446 00:30:47,028 --> 00:30:49,326 For him, understanding and enjoyment... 447 00:30:49,531 --> 00:30:51,829 ...were pretty much the same thing. 448 00:30:52,033 --> 00:30:56,663 He said, "A life without festivity is a long road without an inn." 449 00:30:56,871 --> 00:31:00,568 Democritus may have come from Abdera, but he was no dummy. 450 00:31:04,379 --> 00:31:07,371 Democritus understood that the complex forms... 451 00:31:07,582 --> 00:31:10,983 ...changes and motions of the material world... 452 00:31:11,186 --> 00:31:15,748 ...all derived from the interaction of very simple moving parts. 453 00:31:15,957 --> 00:31:18,653 He called these parts atoms. 454 00:31:23,631 --> 00:31:27,328 All material objects are collections of atoms... 455 00:31:27,869 --> 00:31:29,302 ...intricately assembled... 456 00:31:29,504 --> 00:31:30,801 ...even we. 457 00:31:31,039 --> 00:31:33,303 When I cut this apple... 458 00:31:33,575 --> 00:31:35,600 ...the knife must be passing through... 459 00:31:35,877 --> 00:31:39,369 ...empty spaces between the atoms, Democritus argued. 460 00:31:39,581 --> 00:31:43,017 If there were no such empty spaces, no void... 461 00:31:43,218 --> 00:31:47,780 ...then the knife would encounter some impenetrable atom... 462 00:31:47,989 --> 00:31:49,923 ...and the apple wouldn't be cut. 463 00:31:50,124 --> 00:31:53,218 Let's compare the cross sections of the two pieces. 464 00:31:53,428 --> 00:31:56,022 Are the exposed areas exactly equal? 465 00:31:56,231 --> 00:31:58,961 No, said Democritus, the curvature of the apple... 466 00:31:59,167 --> 00:32:03,968 ...forces this slice to be slightly shorter than the rest of the apple. 467 00:32:04,372 --> 00:32:07,739 If they were equally tall, then we'd have... 468 00:32:07,942 --> 00:32:10,001 ...a cylinder and not an apple. 469 00:32:10,245 --> 00:32:12,372 No matter how sharp the knife... 470 00:32:12,580 --> 00:32:15,447 ...these two pieces have unequal cross sections. 471 00:32:15,650 --> 00:32:17,015 But why? 472 00:32:17,218 --> 00:32:20,244 Because on the scale of the very small... 473 00:32:20,455 --> 00:32:23,720 ...matter exhibits some irreducible roughness... 474 00:32:23,925 --> 00:32:27,656 ...and this fine scale of roughness Democritus of Abdera identified... 475 00:32:27,929 --> 00:32:29,863 ...with the world of the atoms. 476 00:32:30,064 --> 00:32:32,225 His arguments are not those we use today. 477 00:32:32,433 --> 00:32:36,733 But they're elegant and subtle and derived from everyday experience. 478 00:32:36,938 --> 00:32:40,374 And his conclusions were fundamentally right. 479 00:32:45,647 --> 00:32:48,741 Democritus believed that nothing happens at random... 480 00:32:48,950 --> 00:32:52,215 ...that everything has a material cause. 481 00:32:53,554 --> 00:32:57,490 He said, "I would rather understand one cause... 482 00:32:57,692 --> 00:32:59,956 ...than be king of Persia." 483 00:33:00,161 --> 00:33:03,392 He believed that poverty in a democracy was far better... 484 00:33:03,598 --> 00:33:05,225 ...than wealth in a tyranny. 485 00:33:05,433 --> 00:33:08,925 He believed that the prevailing religions of his time were evil... 486 00:33:09,137 --> 00:33:13,164 ...and that neither souls nor immortal gods existed. 487 00:33:13,775 --> 00:33:18,712 There is no evidence that Democritus was persecuted for his beliefs. 488 00:33:19,280 --> 00:33:22,272 But then again, he came from Abdera. 489 00:33:24,552 --> 00:33:25,883 However, in his time... 490 00:33:26,087 --> 00:33:29,523 ...the brief tradition of tolerance for unconventional views... 491 00:33:29,724 --> 00:33:31,692 ...was beginning to erode. 492 00:33:32,193 --> 00:33:34,718 For instance, the prevailing belief was... 493 00:33:34,929 --> 00:33:37,693 ...that the moon and the sun were gods. 494 00:33:38,333 --> 00:33:42,099 Another contemporary of Democritus, named Anaxagoras, taught... 495 00:33:42,303 --> 00:33:46,069 ...that the moon was a place made of ordinary matter... 496 00:33:46,274 --> 00:33:50,506 ...and that the sun was a red-hot stone far away in the sky. 497 00:33:50,745 --> 00:33:53,839 For this, Anaxagoras was condemned... 498 00:33:54,048 --> 00:33:57,643 ...convicted and imprisoned for impiety... 499 00:33:57,852 --> 00:33:59,615 ...a religious crime. 500 00:33:59,821 --> 00:34:03,416 People began to be persecuted for their ideas. 501 00:34:03,725 --> 00:34:06,387 A portrait of Democritus is now... 502 00:34:06,594 --> 00:34:09,290 ...on the Greek 100-drachma note. 503 00:34:10,164 --> 00:34:12,325 But his ideas were suppressed... 504 00:34:12,533 --> 00:34:14,728 ...and his influence on history made minor. 505 00:34:14,936 --> 00:34:17,632 The mystics were beginning to win. 506 00:34:24,445 --> 00:34:27,039 You see, lonia was also the home... 507 00:34:27,248 --> 00:34:30,081 ...of another quite different intellectual tradition. 508 00:34:30,284 --> 00:34:32,912 Its founder was Pythagoras... 509 00:34:33,121 --> 00:34:36,522 ...who lived here on Samos in the 6th century B.C. 510 00:34:37,725 --> 00:34:40,023 According to local legend... 511 00:34:40,228 --> 00:34:43,789 ...this cave was once his abode. 512 00:34:44,132 --> 00:34:46,657 Maybe that was once his living room. 513 00:34:46,868 --> 00:34:48,836 Many centuries later... 514 00:34:49,103 --> 00:34:52,869 ...this small Greek Orthodox shrine was erected on his front porch. 515 00:34:53,074 --> 00:34:58,011 There's a continuity of tradition from Pythagoras to Christianity. 516 00:34:58,246 --> 00:35:01,909 Pythagoras was the first person in the history of the world... 517 00:35:02,116 --> 00:35:05,244 ...to decide that the Earth was a sphere. 518 00:35:05,486 --> 00:35:09,684 Perhaps he argued by analogy with the moon or the sun... 519 00:35:09,891 --> 00:35:12,917 ...maybe he noticed the curved shadow of the Earth on the moon... 520 00:35:13,127 --> 00:35:14,719 ...during a lunar eclipse. 521 00:35:14,929 --> 00:35:17,727 Or maybe he recognized that when ships leave Samos... 522 00:35:17,932 --> 00:35:20,366 ...their masts disappear last. 523 00:35:25,640 --> 00:35:29,132 Pythagoras believed that a mathematical harmony... 524 00:35:29,343 --> 00:35:31,208 ...underlies all of nature. 525 00:35:31,412 --> 00:35:33,676 The modern tradition of mathematical argument... 526 00:35:33,881 --> 00:35:37,248 ...essential in all of science owes much to him. 527 00:35:37,452 --> 00:35:41,218 And the notion that the heavenly bodies move to a kind of... 528 00:35:41,422 --> 00:35:43,652 ...music of the spheres... 529 00:35:43,958 --> 00:35:46,483 ...was also derived from Pythagoras. 530 00:35:47,095 --> 00:35:49,962 It was he who first used the word cosmos... 531 00:35:50,164 --> 00:35:52,997 ...to mean a well-ordered and harmonious universe... 532 00:35:53,201 --> 00:35:56,693 ...a world amenable to human understanding. 533 00:36:01,075 --> 00:36:04,511 For this great idea, we are indebted to Pythagoras. 534 00:36:04,712 --> 00:36:09,240 But there were deep ironies and contradictions in his thoughts. 535 00:36:09,717 --> 00:36:11,617 Many of the lonians believed... 536 00:36:11,819 --> 00:36:16,313 ...that the underlying harmony and unity of the universe was accessible... 537 00:36:16,524 --> 00:36:19,220 ...through observation and experiment... 538 00:36:19,427 --> 00:36:21,895 ...the method which dominates science today. 539 00:36:22,163 --> 00:36:24,927 However, Pythagoras had a very different method. 540 00:36:25,133 --> 00:36:30,070 He believed that the laws of nature can be deduced by pure thought. 541 00:36:30,471 --> 00:36:33,531 He and his followers were not basically experimentalists... 542 00:36:33,741 --> 00:36:35,538 ...they were mathematicians... 543 00:36:35,743 --> 00:36:38,610 ...and they were thoroughgoing mystics. 544 00:36:39,514 --> 00:36:43,450 They were fascinated by these five regular solids... 545 00:36:43,651 --> 00:36:46,950 ...bodies whose faces are all polygons: 546 00:36:47,155 --> 00:36:49,783 Triangles or squares... 547 00:36:49,991 --> 00:36:51,390 ...or pentagons. 548 00:36:51,592 --> 00:36:54,356 There can be an infinite number of polygons... 549 00:36:54,562 --> 00:36:57,588 ...but only five regular solids. 550 00:37:00,168 --> 00:37:05,105 Four of the solids were associated with earth, fire, air and water. 551 00:37:05,773 --> 00:37:09,368 The cube, for example, represented earth. 552 00:37:09,577 --> 00:37:13,673 These four elements, they thought, make up terrestrial matter. 553 00:37:15,049 --> 00:37:16,846 So the fifth solid... 554 00:37:17,051 --> 00:37:20,282 ...they mystically associated with the cosmos. 555 00:37:20,488 --> 00:37:23,389 Perhaps it was the substance of the heavens. 556 00:37:23,591 --> 00:37:26,151 This fifth solid was called... 557 00:37:26,360 --> 00:37:28,828 ...the dodecahedron. 558 00:37:29,197 --> 00:37:32,689 Its faces are pentagons, 12 of them. 559 00:37:33,301 --> 00:37:35,030 Knowledge of the dodecahedron... 560 00:37:35,236 --> 00:37:38,501 ...was considered too dangerous for the public. 561 00:37:40,741 --> 00:37:45,201 Ordinary people were to be kept ignorant of the dodecahedron. 562 00:37:45,446 --> 00:37:48,279 In love with whole numbers, the Pythagoreans believed... 563 00:37:48,482 --> 00:37:50,643 ...that all things could be derived from them... 564 00:37:50,851 --> 00:37:52,842 ...certainly all other numbers. 565 00:37:53,054 --> 00:37:56,080 So a crisis in doctrine occurred when they discovered... 566 00:37:56,290 --> 00:37:58,724 ...that the square root of two was irrational. 567 00:37:58,926 --> 00:38:02,054 The square root of two could not be represented as the ratio... 568 00:38:02,263 --> 00:38:04,959 ...of two whole numbers no matter how big they were. 569 00:38:05,333 --> 00:38:08,029 Irrational originally meant only that... 570 00:38:08,236 --> 00:38:11,205 ...that you can't express a number as a ratio. 571 00:38:11,405 --> 00:38:14,602 But for the Pythagoreans, it came to mean something else... 572 00:38:14,809 --> 00:38:16,709 ...something threatening... 573 00:38:16,911 --> 00:38:21,007 ...a hint that their world-view might not make sense... 574 00:38:21,215 --> 00:38:24,048 ...the other meaning of irrational. 575 00:38:24,952 --> 00:38:29,616 Instead of wanting everyone to share and know of their discoveries... 576 00:38:29,824 --> 00:38:33,021 ...the Pythagoreans suppressed the square root of two... 577 00:38:33,227 --> 00:38:34,888 ...and the dodecahedron. 578 00:38:35,096 --> 00:38:37,587 The outside world was not to know. 579 00:38:43,504 --> 00:38:45,768 The Pythagoreans had discovered... 580 00:38:45,973 --> 00:38:48,601 ...in the mathematical underpinnings of nature... 581 00:38:48,809 --> 00:38:51,437 ...one of the two most powerful scientific tools. 582 00:38:51,646 --> 00:38:54,740 The other, of course, is experiment. 583 00:38:55,049 --> 00:38:57,609 But instead of using their insight to advance... 584 00:38:57,818 --> 00:39:00,480 ...the collective voyage of human discovery... 585 00:39:00,688 --> 00:39:05,250 ...they made of it little more than the hocus-pocus of a mystery cult. 586 00:39:05,459 --> 00:39:08,553 Science and mathematics were to be removed from the hands... 587 00:39:08,763 --> 00:39:10,390 ...of merchants and artisans. 588 00:39:11,332 --> 00:39:14,267 This tendency found its most effective advocate... 589 00:39:14,468 --> 00:39:17,835 ...in a follower of Pythagoras named Plato. 590 00:39:18,105 --> 00:39:22,804 He preferred the perfection of these mathematical abstractions... 591 00:39:23,010 --> 00:39:26,138 ...to the imperfections of everyday life. 592 00:39:26,347 --> 00:39:30,681 He believed that ideas were far more real than the natural world. 593 00:39:30,885 --> 00:39:33,513 He advised the astronomers not to waste their time... 594 00:39:33,721 --> 00:39:35,450 ...observing stars and planets. 595 00:39:35,656 --> 00:39:39,217 It was better, he believed, just to think about them. 596 00:39:40,061 --> 00:39:43,656 Plato expressed hostility to observation and experiment. 597 00:39:43,864 --> 00:39:46,298 He taught contempt for the real world... 598 00:39:46,500 --> 00:39:50,493 ...and disdain for the practical application of scientific knowledge. 599 00:39:52,173 --> 00:39:55,904 Plato's followers succeeded in extinguishing the light... 600 00:39:56,110 --> 00:39:57,941 ...of science and experiment... 601 00:39:58,145 --> 00:40:02,445 ...that had been kindled by Democritus and the other lonians. 602 00:40:05,286 --> 00:40:08,687 Plato's unease with the world as revealed by our senses... 603 00:40:08,889 --> 00:40:13,622 ...was to dominate and stifle Western philosophy. 604 00:40:16,063 --> 00:40:17,860 Even as late as 1600... 605 00:40:18,065 --> 00:40:21,432 ...Johannes Kepler was still struggling to interpret... 606 00:40:21,635 --> 00:40:23,728 ...the structure of the cosmos in terms of... 607 00:40:23,938 --> 00:40:28,375 ...Pythagorean solids and Platonic perfection. 608 00:40:28,576 --> 00:40:32,512 Ironically, it was Kepler who helped re-establish the old lonian method... 609 00:40:32,713 --> 00:40:35,147 ...of testing ideas against observations. 610 00:40:35,683 --> 00:40:38,516 But why had science lost its way in the first place? 611 00:40:38,719 --> 00:40:41,654 What appeal did Pythagoras' and Plato's teachings... 612 00:40:41,856 --> 00:40:43,721 ...have for their contemporaries? 613 00:40:43,924 --> 00:40:45,551 They provided, I believe... 614 00:40:45,760 --> 00:40:48,695 ...an intellectually respectable justification... 615 00:40:48,896 --> 00:40:51,763 ...for a corrupt social order. 616 00:40:55,336 --> 00:40:58,533 The mercantile tradition which had led to lonian science... 617 00:40:58,739 --> 00:41:01,003 ...also led to a slave economy. 618 00:41:01,876 --> 00:41:03,867 You could get richer... 619 00:41:04,078 --> 00:41:06,638 ...if you owned a lot of slaves. 620 00:41:07,014 --> 00:41:10,006 Athens, in the time of Plato and Aristotle... 621 00:41:10,217 --> 00:41:12,981 ...had a vast slave population. 622 00:41:13,187 --> 00:41:17,089 All of that brave Athenian talk about democracy... 623 00:41:17,291 --> 00:41:20,192 ...applied only to a privileged few. 624 00:41:20,795 --> 00:41:25,129 Plato and Aristotle were comfortable in a slave society. 625 00:41:25,332 --> 00:41:28,426 They offered justifications for oppression. 626 00:41:29,069 --> 00:41:31,037 They served tyrants. 627 00:41:31,238 --> 00:41:34,401 They taught the alienation of the body from the mind... 628 00:41:34,608 --> 00:41:38,635 ...a natural enough idea, I suppose, in a slave society. 629 00:41:38,846 --> 00:41:41,371 They separated thought from matter. 630 00:41:41,582 --> 00:41:43,948 They divorced the Earth from the heavens. 631 00:41:44,151 --> 00:41:48,019 Divisions which were to dominate Western thinking... 632 00:41:48,222 --> 00:41:50,315 ...for more than 20 centuries. 633 00:41:50,524 --> 00:41:52,958 The Pythagoreans had won. 634 00:41:59,133 --> 00:42:02,159 In the recognition by Pythagoras and Plato... 635 00:42:02,369 --> 00:42:04,337 ...that the cosmos is knowable... 636 00:42:04,538 --> 00:42:07,632 ...that there is a mathematical underpinning to nature... 637 00:42:07,842 --> 00:42:10,936 ...they greatly advanced the cause of science. 638 00:42:11,545 --> 00:42:15,606 But in the suppression of disquieting facts... 639 00:42:15,816 --> 00:42:20,515 ...the sense that science should be kept for a small elite... 640 00:42:20,721 --> 00:42:24,782 ...the distaste for experiment, the embrace of mysticism... 641 00:42:25,426 --> 00:42:28,759 ...the easy acceptance of slave societies... 642 00:42:28,963 --> 00:42:32,831 ...their influence has significantly set back... 643 00:42:33,033 --> 00:42:34,660 ...the human endeavor. 644 00:42:36,036 --> 00:42:40,973 The books of the lonian scientists are entirely lost. 645 00:42:41,876 --> 00:42:46,609 Their views were suppressed, ridiculed and forgotten... 646 00:42:47,381 --> 00:42:50,043 ...by the Platonists and by the Christians... 647 00:42:50,251 --> 00:42:53,743 ...who adopted much of the philosophy of Plato. 648 00:42:54,522 --> 00:42:59,255 Finally, after a long, mystical sleep... 649 00:42:59,527 --> 00:43:04,123 ...in which the tools of scientific inquiry lay moldering... 650 00:43:04,331 --> 00:43:07,129 ...the lonian approach was rediscovered. 651 00:43:12,106 --> 00:43:14,802 The Western world reawakened. 652 00:43:15,009 --> 00:43:18,467 Experiment and open inquiry... 653 00:43:18,679 --> 00:43:22,080 ...slowly became respectable once again. 654 00:43:22,783 --> 00:43:26,844 Forgotten books and fragments were read once more. 655 00:43:27,221 --> 00:43:31,282 Leonardo and Copernicus and Columbus... 656 00:43:31,492 --> 00:43:34,655 ...were inspired by the lonian tradition. 657 00:43:46,907 --> 00:43:50,707 The Pythagoreans and their successors... 658 00:43:50,911 --> 00:43:53,903 ...held the peculiar notion that... 659 00:43:54,114 --> 00:43:56,378 ...the Earth was tainted... 660 00:43:56,584 --> 00:43:59,018 ...somehow nasty... 661 00:43:59,219 --> 00:44:03,849 ...while the heavens were pristine and divine. 662 00:44:04,525 --> 00:44:07,255 So the fundamental idea that the Earth is a planet... 663 00:44:07,461 --> 00:44:10,191 ...that we're citizens of the universe... 664 00:44:10,397 --> 00:44:13,127 ...was rejected and forgotten. 665 00:44:16,537 --> 00:44:20,337 This idea was first argued by Aristarchus... 666 00:44:20,541 --> 00:44:24,500 ...born here on Samos, three centuries after Pythagoras. 667 00:44:24,712 --> 00:44:27,545 He held that the Earth moves around the sun. 668 00:44:27,748 --> 00:44:30,979 He correctly located our place in the solar system. 669 00:44:31,185 --> 00:44:35,053 For his trouble, he was accused of heresy. 670 00:44:36,824 --> 00:44:41,158 From the size of the Earth's shadow on the moon during a lunar eclipse... 671 00:44:41,362 --> 00:44:45,560 ...he deduced that the sun had to be much, much larger... 672 00:44:45,766 --> 00:44:48,860 ...than the Earth, and also very far away. 673 00:44:49,269 --> 00:44:51,863 From this he may have argued that it was absurd... 674 00:44:52,072 --> 00:44:55,098 ...for so large an object as the sun to be going around... 675 00:44:55,309 --> 00:44:58,403 ...so small an object as the Earth. 676 00:44:58,612 --> 00:45:03,481 So he put the sun rather than the Earth at the center of the solar system. 677 00:45:03,684 --> 00:45:07,211 And he had the Earth and the other planets going around the sun. 678 00:45:07,421 --> 00:45:10,788 He also had the Earth rotating on its axis once a day. 679 00:45:10,991 --> 00:45:15,155 These are ideas that we ordinarily associate with the name Copernicus. 680 00:45:15,362 --> 00:45:18,854 But Copernicus seems to have gotten some hint of these ideas... 681 00:45:19,066 --> 00:45:21,694 ...by reading about Aristarchus. 682 00:45:22,169 --> 00:45:24,899 In fact, in the manuscript of Copernicus' book... 683 00:45:25,105 --> 00:45:28,541 ...he referred to Aristarchus, but in the final version... 684 00:45:28,742 --> 00:45:31,438 ...he suppressed the citation. 685 00:45:32,146 --> 00:45:35,013 Resistance to Aristarchus, a kind of... 686 00:45:35,649 --> 00:45:38,140 ...geocentrism in everyday life, is with us still. 687 00:45:38,352 --> 00:45:41,287 We still talk about a sun rising... 688 00:45:41,488 --> 00:45:43,956 ...and the sun setting. 689 00:45:44,658 --> 00:45:47,252 It's 2200 years since Aristarchus... 690 00:45:47,461 --> 00:45:52,330 ...and the language still pretends that the Earth does not turn... 691 00:45:53,167 --> 00:45:57,194 ...that the sun is not at the center of the solar system. 692 00:46:00,307 --> 00:46:04,073 Aristarchus understood the basic scheme of the solar system... 693 00:46:04,278 --> 00:46:06,041 ...but not its scale. 694 00:46:08,649 --> 00:46:12,312 He knew that the planets move in concentric orbits about the sun... 695 00:46:12,519 --> 00:46:15,750 ...and he probably knew their order out to Saturn. 696 00:46:17,291 --> 00:46:19,521 But he was much too modest in his estimates... 697 00:46:19,727 --> 00:46:22,218 ...of how far apart the planets are. 698 00:46:22,563 --> 00:46:25,930 In order to calculate the true scale of the solar system... 699 00:46:26,133 --> 00:46:27,760 ...you need a telescope. 700 00:46:28,168 --> 00:46:31,660 It wasn't until the 17th century that astronomers were able to get... 701 00:46:31,872 --> 00:46:35,569 ...even a rough estimate of the distance to the sun. 702 00:46:37,578 --> 00:46:40,069 And once you knew the distance to the sun... 703 00:46:40,280 --> 00:46:41,838 ...what about the stars? 704 00:46:42,049 --> 00:46:44,483 How far away are they? 705 00:46:48,388 --> 00:46:51,880 There is a way to measure the distance to the stars... 706 00:46:52,092 --> 00:46:54,822 ...and the lonians were fully capable of discovering it. 707 00:46:55,028 --> 00:46:58,828 Aristarchus had toyed with the daring idea... 708 00:46:59,032 --> 00:47:01,762 ...that the stars were distant suns. 709 00:47:01,969 --> 00:47:04,437 Now, if a star were as near as the sun... 710 00:47:04,638 --> 00:47:07,869 ...it should appear as big and as bright as the sun. 711 00:47:08,075 --> 00:47:11,841 Everyone knows that the farther away an object is, the smaller it seems. 712 00:47:12,045 --> 00:47:15,503 This inverse proportionality between apparent size and distance... 713 00:47:15,716 --> 00:47:19,413 ...is the basis of perspective in art and photography. 714 00:47:19,620 --> 00:47:22,316 So the further away we are from the sun... 715 00:47:22,523 --> 00:47:25,424 ...the smaller and dimmer it appears. 716 00:47:25,626 --> 00:47:28,823 How far from the sun would we have to be for it to appear... 717 00:47:29,029 --> 00:47:31,293 ...as small and dim as a star? 718 00:47:31,498 --> 00:47:34,467 Or equivalently, how small a piece of sun... 719 00:47:34,668 --> 00:47:36,898 ...would be as bright as a star? 720 00:47:37,271 --> 00:47:41,765 An experiment to answer this question was performed in 17th-century Holland... 721 00:47:41,975 --> 00:47:46,810 ...by Christiaan Huygens and is very much in the lonian tradition. 722 00:47:47,014 --> 00:47:51,951 Huygens drilled a number of holes in a brass plate... 723 00:47:52,386 --> 00:47:54,786 ...and held the plate up to the sun. 724 00:47:54,988 --> 00:47:59,789 He asked himself, which hole seemed as bright... 725 00:47:59,993 --> 00:48:04,259 ...as he remembered the star Sirius to have been the previous evening. 726 00:48:04,464 --> 00:48:07,490 Well, the hole that matched was effectively... 727 00:48:07,701 --> 00:48:12,434 ...1 l28,000th the apparent size of the sun. 728 00:48:12,706 --> 00:48:16,767 So Sirius, he reasoned, must be 28,000 times... 729 00:48:16,977 --> 00:48:21,277 ...further away than the sun, or about half a light-year away. 730 00:48:21,882 --> 00:48:24,646 It's hard to remember just how bright a star is... 731 00:48:24,852 --> 00:48:28,686 ...hours after you've looked at it, but Huygens remembered very well. 732 00:48:28,889 --> 00:48:32,916 If he had known that Sirius was intrinsically brighter than the sun... 733 00:48:33,126 --> 00:48:35,526 ...he would've gotten the answer exactly right. 734 00:48:35,729 --> 00:48:39,790 Sirius is 8.8 light-years away from us. 735 00:48:40,767 --> 00:48:43,634 Between Aristarchus and Huygens... 736 00:48:43,837 --> 00:48:47,068 ...people had answered that question which had so excited me... 737 00:48:47,274 --> 00:48:49,139 ...as a young boy growing up in Brooklyn: 738 00:48:49,343 --> 00:48:51,709 The question, "What are the stars?" 739 00:48:55,148 --> 00:49:00,085 And the answer is that the stars are mighty suns, light-years away... 740 00:49:00,287 --> 00:49:02,687 ...in the depths of interstellar space. 741 00:49:08,495 --> 00:49:12,829 And around those suns, are there other planets? 742 00:49:13,901 --> 00:49:15,869 And on those other worlds... 743 00:49:16,069 --> 00:49:19,038 ...are there beings who wonder as we do? 744 00:49:23,410 --> 00:49:25,810 Here is a light bulb... 745 00:49:26,013 --> 00:49:28,573 ...which is supposed to represent a nearby star. 746 00:49:28,782 --> 00:49:32,240 Next to it, and very hard to see because of the bright light... 747 00:49:32,452 --> 00:49:33,817 ...is a planet. 748 00:49:34,021 --> 00:49:37,548 We'll need a volunteer. Who would like to come up, please? 749 00:49:38,225 --> 00:49:40,819 Ordinarily, it's hard to see the planet... 750 00:49:41,028 --> 00:49:44,987 ...because it's so close that the star washes out the planet. 751 00:49:45,198 --> 00:49:49,635 But if we're able to put something in front of the star... 752 00:49:49,836 --> 00:49:53,363 ...to make an artificial eclipse, then we might be able to see the planet. 753 00:49:53,573 --> 00:49:57,839 I'm gonna stand over here. Imagine that I'm a telescope... 754 00:49:58,045 --> 00:49:59,478 ...somewhere near the Earth. 755 00:49:59,680 --> 00:50:03,582 And, Tab, if you'd slowly move the disc across. 756 00:50:03,784 --> 00:50:05,775 Good. A little faster would be nice. 757 00:50:05,986 --> 00:50:08,614 Now you're just beginning to cover over the star. 758 00:50:08,822 --> 00:50:11,848 I really can't see the planet at all. Keep going. 759 00:50:12,059 --> 00:50:13,526 Now, right there... 760 00:50:13,727 --> 00:50:16,093 ...I can't see the star at all... 761 00:50:16,296 --> 00:50:20,198 ...and I see the planet lit by the light of the star. 762 00:50:20,400 --> 00:50:23,733 Now, that is a method for looking for planets... 763 00:50:23,937 --> 00:50:25,768 ...around nearby stars. 764 00:50:25,973 --> 00:50:30,910 And that method uses a spacecraft to hold the disc... 765 00:50:31,445 --> 00:50:33,913 ...and scan the sky for another telescope... 766 00:50:34,114 --> 00:50:36,844 ...to see if there are any planets. 767 00:50:37,050 --> 00:50:41,384 Tab, you accomplished your mission to look for planets around other stars. 768 00:50:41,588 --> 00:50:44,751 Thank you for being our interplanetary spacecraft. 769 00:50:44,958 --> 00:50:47,552 So this is one way. 770 00:50:47,761 --> 00:50:51,162 And there are spaceships that will be able to do this... 771 00:50:51,365 --> 00:50:53,128 ...in the next 10 years or so. 772 00:50:53,333 --> 00:50:54,800 And there's another way. 773 00:50:55,002 --> 00:50:57,527 This has already been tried from the Earth. 774 00:50:57,738 --> 00:51:01,834 Imagine that there's a nearby star that you can see. 775 00:51:02,042 --> 00:51:06,035 It's bright and it has a dark companion, a planet... 776 00:51:06,246 --> 00:51:09,647 ...shining only by reflected light near it, so dim you can't see it. 777 00:51:09,850 --> 00:51:14,617 But imagine that this planet and its star... 778 00:51:14,821 --> 00:51:16,686 ...are going around each other. 779 00:51:17,824 --> 00:51:19,155 Like that: 780 00:51:19,359 --> 00:51:21,953 You can see the star, you can't see the planet. 781 00:51:22,162 --> 00:51:24,528 So now I'm gonna need two volunteers. 782 00:51:26,733 --> 00:51:27,757 You two. 783 00:51:29,102 --> 00:51:31,969 Just to save time because they're in the front row. 784 00:51:32,172 --> 00:51:35,198 I need one of you to turn the star and the planet... 785 00:51:35,409 --> 00:51:39,368 ...and another person to pull the star and planet along. 786 00:51:39,579 --> 00:51:41,046 And what you will see... 787 00:51:41,248 --> 00:51:44,581 ...is that the star you can make out... 788 00:51:44,785 --> 00:51:47,413 ...will be moving in a funny, wiggly pattern... 789 00:51:47,621 --> 00:51:49,748 ...which will be the clue, the evidence... 790 00:51:49,956 --> 00:51:52,220 ...for the existence of the dark planet. 791 00:51:52,426 --> 00:51:55,623 Okay, let's have a spin. Good. And a pull. 792 00:51:55,829 --> 00:51:57,490 And you see this funny motion... 793 00:51:57,697 --> 00:52:02,361 ...that the star makes because of the planet. Thank you. 794 00:52:02,569 --> 00:52:05,766 That's another way of finding out the existence of a planet... 795 00:52:05,972 --> 00:52:08,873 ...that you couldn't see directly. 796 00:52:09,076 --> 00:52:12,204 Well, both of these methods are being used. 797 00:52:12,512 --> 00:52:17,176 And by the time that you people are... 798 00:52:17,384 --> 00:52:19,181 ...as old as I am... 799 00:52:19,386 --> 00:52:22,753 ...we should know, for all the nearest stars... 800 00:52:22,956 --> 00:52:25,390 ...if they have planets going around them. 801 00:52:25,592 --> 00:52:29,961 We might know dozens or even hundreds of other planetary systems... 802 00:52:30,163 --> 00:52:33,462 ...and see if they're like our own or very different... 803 00:52:33,667 --> 00:52:37,262 ...or no other planets going around other stars at all. 804 00:52:37,471 --> 00:52:39,735 That will happen in your lifetime. 805 00:52:39,940 --> 00:52:44,604 It'll be the first time in the world's history that anybody found out... 806 00:52:45,345 --> 00:52:48,075 ...if there are planets around the other stars. 807 00:52:48,281 --> 00:52:53,218 Now, the nearby stars, the ones you can see with the naked eye... 808 00:52:53,520 --> 00:52:55,784 ...those are all in the solar neighborhood. 809 00:52:55,989 --> 00:52:58,480 That's what astronomers call it: The neighborhood. 810 00:52:58,692 --> 00:53:03,288 But it's a very tiny place in the Milky Way galaxy. 811 00:53:04,231 --> 00:53:06,358 The Milky Way is that band of light... 812 00:53:06,566 --> 00:53:09,660 ...that you see across the sky on a clear night. 813 00:53:09,870 --> 00:53:12,998 I can't tell if there are any more clear nights in Brooklyn. 814 00:53:13,206 --> 00:53:16,869 You must've seen the Milky Way, a faint band of light at night. 815 00:53:17,077 --> 00:53:21,707 Well, that's just 100 billion stars... 816 00:53:21,915 --> 00:53:23,849 ...all seen together... 817 00:53:24,050 --> 00:53:26,644 ...edge on, as in this picture. 818 00:53:26,853 --> 00:53:30,186 If you could get out of the Milky Way and look down on it... 819 00:53:30,390 --> 00:53:32,290 ...it would look like that picture. 820 00:53:32,492 --> 00:53:34,653 If we did look down on the Milky Way... 821 00:53:34,861 --> 00:53:37,557 ...where would the sun and nearby stars be? 822 00:53:37,764 --> 00:53:40,927 Would it be in the center where things look important... 823 00:53:41,134 --> 00:53:42,601 ...or at least well-lit? 824 00:53:43,336 --> 00:53:46,669 No. We would be way out here... 825 00:53:46,873 --> 00:53:50,866 ...in the suburbs, in the countryside of the galaxy. 826 00:53:51,077 --> 00:53:52,738 We're not in any important place. 827 00:53:52,946 --> 00:53:56,712 All the stars you could see would be in a little place like that. 828 00:53:56,917 --> 00:54:00,114 And the Milky Way would be this band of light... 829 00:54:00,320 --> 00:54:02,880 ...100 billion stars all together. 830 00:54:03,356 --> 00:54:06,291 The fact that we live in the outskirts of the galaxy... 831 00:54:06,493 --> 00:54:09,985 ...was discovered a long time ago... 832 00:54:10,197 --> 00:54:12,757 ...towards the end of the First World War... 833 00:54:12,966 --> 00:54:15,264 ...by a man named Harlow Shapley... 834 00:54:15,468 --> 00:54:19,700 ...who was mapping the position of these clusters of stars. 835 00:54:19,906 --> 00:54:22,397 See, every one of these is a bunch... 836 00:54:22,609 --> 00:54:25,077 ...of maybe 10,000 stars all together. 837 00:54:25,278 --> 00:54:27,269 It's called a globular cluster. 838 00:54:27,480 --> 00:54:30,779 And you can see that they are centered around the middle... 839 00:54:30,984 --> 00:54:32,815 ...the center of the galaxy. 840 00:54:33,086 --> 00:54:36,852 People used to think that the sun was at the center of the galaxy... 841 00:54:37,057 --> 00:54:41,289 ...something important about our position. That turns out to be wrong. 842 00:54:41,628 --> 00:54:43,858 We live in the outskirts... 843 00:54:44,064 --> 00:54:46,498 ...the globular clusters are centered around... 844 00:54:47,000 --> 00:54:50,663 ...the marvelous middle of the Milky Way galaxy. 845 00:54:50,870 --> 00:54:54,704 And then it turned out that this isn't the only galaxy. 846 00:54:54,908 --> 00:54:57,342 We live in this one... 847 00:54:57,944 --> 00:54:59,707 ...but there are many others. 848 00:55:00,080 --> 00:55:03,072 And as this picture reminds us... 849 00:55:03,783 --> 00:55:06,217 ...there are many different kinds of galaxies... 850 00:55:06,419 --> 00:55:08,819 ...of which ours might be just this one. 851 00:55:09,022 --> 00:55:13,584 There are, in fact, 100 billion other galaxies... 852 00:55:13,793 --> 00:55:18,730 ...each of which contains something like 100 billion stars. 853 00:55:19,466 --> 00:55:24,403 Think of how many stars and planets and kinds of life there may be... 854 00:55:25,205 --> 00:55:29,369 ...in this vast and awesome universe. 855 00:55:32,178 --> 00:55:34,339 As long as there have been humans... 856 00:55:34,547 --> 00:55:37,948 ...we have searched for our place in the cosmos. 857 00:55:38,151 --> 00:55:40,949 Where are we? Who are we? 858 00:55:43,056 --> 00:55:47,356 We find that we live on an insignificant planet... 859 00:55:47,560 --> 00:55:49,528 ...of a humdrum star... 860 00:55:49,729 --> 00:55:52,892 ...lost in a galaxy tucked away in some... 861 00:55:53,099 --> 00:55:56,296 ...forgotten corner of a universe in which there are... 862 00:55:56,503 --> 00:55:59,768 ...far more galaxies than people. 863 00:56:03,009 --> 00:56:06,775 We make our world significant by the courage of our questions... 864 00:56:07,213 --> 00:56:09,841 ...and by the depth of our answers. 865 00:56:11,418 --> 00:56:14,512 We embarked on our journey to the stars... 866 00:56:15,121 --> 00:56:17,715 ...with a question first framed... 867 00:56:17,924 --> 00:56:20,449 ...in the childhood of our species... 868 00:56:20,894 --> 00:56:25,160 ...and in each generation asked anew... 869 00:56:25,432 --> 00:56:27,593 ...with undiminished wonder: 870 00:56:27,967 --> 00:56:30,128 "What are the stars?" 871 00:56:48,221 --> 00:56:51,088 Exploration is in our nature. 872 00:56:51,691 --> 00:56:53,989 We began as wanderers... 873 00:56:54,294 --> 00:56:57,161 ...and we are wanderers still. 874 00:57:08,441 --> 00:57:11,137 We have lingered long enough... 875 00:57:11,344 --> 00:57:14,142 ...on the shores of the cosmic ocean. 876 00:57:14,381 --> 00:57:16,178 We are ready at last... 877 00:57:16,383 --> 00:57:19,614 ...to set sail for the stars.