1 00:00:43,100 --> 00:00:45,432 SAGAN: The sky calls to us. 2 00:00:45,803 --> 00:00:47,896 If we do not destroy ourselves... 3 00:00:48,105 --> 00:00:51,131 ...we will one day venture to the stars. 4 00:00:52,042 --> 00:00:55,500 There was a time when the stars seemed an impenetrable mystery. 5 00:00:55,713 --> 00:00:59,046 Today, we have begun to understand them. 6 00:00:59,250 --> 00:01:04,187 In our personal lives also, we journey from ignorance to knowledge. 7 00:01:04,421 --> 00:01:08,858 Our individual growth reflects the advancement of the species. 8 00:01:09,360 --> 00:01:11,294 The exploration of the cosmos is... 9 00:01:11,495 --> 00:01:14,521 ...a voyage of self-discovery. 10 00:01:25,042 --> 00:01:27,977 When I was a child, I lived here... 11 00:01:28,178 --> 00:01:32,478 ...in the Bensonhurst section of Brooklyn in the city of New York. 12 00:01:32,683 --> 00:01:35,743 I knew my immediate neighborhood intimately... 13 00:01:35,953 --> 00:01:40,219 ...every candy store, front stoop... 14 00:01:40,424 --> 00:01:42,688 ...back yard, empty lot... 15 00:01:42,893 --> 00:01:45,987 ...and wall for playing Chinese handball. 16 00:01:51,602 --> 00:01:53,729 It was my whole world. 17 00:02:12,823 --> 00:02:14,950 But more than a few blocks away... 18 00:02:15,159 --> 00:02:19,858 ...north of the raucous traffic and elevated railway on 86th Street... 19 00:02:20,064 --> 00:02:23,727 ...was an unknown territory off-limits to my wanderings. 20 00:02:24,668 --> 00:02:27,432 It could have been Mars for all I knew. 21 00:02:31,542 --> 00:02:34,375 Even with an early bedtime in the winter... 22 00:02:34,645 --> 00:02:37,637 ...you could occasionally see the stars. 23 00:02:38,148 --> 00:02:41,447 I would look up at them and wonder what they were. 24 00:02:41,752 --> 00:02:44,516 I'd ask other kids and adults... 25 00:02:45,089 --> 00:02:46,681 ...and they would answer: 26 00:02:46,890 --> 00:02:48,949 "They're lights in the sky, kid." 27 00:02:49,159 --> 00:02:53,118 Well, I could tell they were lights in the sky, but what were they? 28 00:02:53,330 --> 00:02:56,766 There had to be some deeper answer. 29 00:03:02,172 --> 00:03:05,664 I remember I was issued my first library card. 30 00:03:05,876 --> 00:03:10,438 It was some library on 85th Street. Anyway, it was in alien territory. 31 00:03:10,914 --> 00:03:14,611 And I asked the librarian for a book on stars. 32 00:03:15,052 --> 00:03:16,485 She gave me... 33 00:03:16,920 --> 00:03:19,855 ...a picture book with portraits of men and women... 34 00:03:20,057 --> 00:03:23,686 ...with names like Veronica Lake and Alan Ladd. 35 00:03:24,228 --> 00:03:27,629 I explained that wasn't what I wanted at all. 36 00:03:28,232 --> 00:03:31,668 And for some reason, then obscure to me, she smiled... 37 00:03:31,869 --> 00:03:35,032 ...and got me another book, the right kind of book. 38 00:03:35,339 --> 00:03:37,637 I was so excited to know the answer... 39 00:03:37,841 --> 00:03:40,901 ...I opened the book breathlessly, right there in the library... 40 00:03:41,111 --> 00:03:43,944 ...and the book said something astonishing... 41 00:03:44,148 --> 00:03:46,639 ...a very big thought. 42 00:03:47,351 --> 00:03:50,684 Stars, it said, were suns... 43 00:03:50,888 --> 00:03:52,651 ...but very far away. 44 00:03:52,856 --> 00:03:56,792 The sun was a star, but close-up. 45 00:04:04,468 --> 00:04:08,199 How, I wondered, could anybody know such things for sure? 46 00:04:08,405 --> 00:04:11,932 How did they figure it out? Where did they even begin? 47 00:04:21,485 --> 00:04:24,454 I was ignorant of the idea of angular size. 48 00:04:24,655 --> 00:04:28,648 I didn't know about the inverse square law of the propagation of light. 49 00:04:28,859 --> 00:04:32,659 I didn't have any chance of calculating the distance to the stars. 50 00:04:32,863 --> 00:04:35,957 But I could tell that if the stars were suns... 51 00:04:36,166 --> 00:04:38,634 ...they had to be awfully far away. 52 00:04:38,836 --> 00:04:43,068 Further away than 86th Street, further away than Manhattan... 53 00:04:43,273 --> 00:04:46,640 ...further away, probably, than New Jersey. 54 00:04:46,844 --> 00:04:50,541 The universe had become much grander... 55 00:04:50,748 --> 00:04:53,114 ...than I had ever guessed. 56 00:04:56,053 --> 00:04:58,715 And then I read another astonishing fact. 57 00:04:58,922 --> 00:05:02,221 The Earth, which includes Brooklyn... 58 00:05:02,426 --> 00:05:03,723 ...was a planet. 59 00:05:03,927 --> 00:05:05,986 It went around the sun. 60 00:05:06,196 --> 00:05:07,788 There were other planets. 61 00:05:07,998 --> 00:05:10,262 They also went around the sun... 62 00:05:10,467 --> 00:05:13,766 ...some closer to the sun, some further from the sun. 63 00:05:14,004 --> 00:05:18,532 But planets didn't shine by their own light the way the sun does. 64 00:05:19,276 --> 00:05:23,235 No, planets simply reflected the little bit of light... 65 00:05:23,447 --> 00:05:27,042 ...that shines on them from the sun back to us. 66 00:05:27,251 --> 00:05:29,515 If you were a great distance from the sun... 67 00:05:29,720 --> 00:05:33,451 ...you wouldn't be able to see the Earth or the other planets at all. 68 00:05:33,690 --> 00:05:36,386 Well, then, it stood to reason, I thought... 69 00:05:36,593 --> 00:05:40,222 ...that those other stars ought to have their own planets... 70 00:05:40,430 --> 00:05:42,694 ...and some of those planets ought to have life. 71 00:05:43,333 --> 00:05:44,561 Why not? 72 00:05:44,768 --> 00:05:49,171 And that life ought to be pretty different from life as we know it... 73 00:05:49,373 --> 00:05:51,364 ...life here in Brooklyn. 74 00:05:51,575 --> 00:05:54,703 Ganymede. Look at this amazing Ganymede stuff. 75 00:05:54,912 --> 00:05:55,970 Wait, wait, wait. 76 00:05:56,180 --> 00:05:58,580 As a child, it was my immense good fortune... 77 00:05:58,782 --> 00:06:02,809 ...to have parents and a few teachers who encouraged my curiosity. 78 00:06:03,020 --> 00:06:05,352 This was my 6th-grade classroom. 79 00:06:05,556 --> 00:06:08,525 I came back here one day to remember what it was like. 80 00:06:08,725 --> 00:06:11,455 I brought some of the pictures of other worlds... 81 00:06:11,662 --> 00:06:14,290 ...that were radioed back by the Voyager spacecraft... 82 00:06:14,498 --> 00:06:16,625 ...of Jupiter and its moons. 83 00:06:16,834 --> 00:06:18,392 This is Calisto which is... 84 00:06:18,602 --> 00:06:19,762 (SAGAN LAUGHS) 85 00:06:22,139 --> 00:06:24,073 What is a Calisto? I want a Calisto. 86 00:06:24,274 --> 00:06:25,571 Now you got it. What is it? 87 00:06:25,776 --> 00:06:29,268 It's the outermost big moon of Jupiter. 88 00:06:30,347 --> 00:06:32,781 Who is this guy? Europa. 89 00:06:34,184 --> 00:06:35,811 Another Europa. 90 00:06:36,186 --> 00:06:39,246 A black-and-white picture of a ring of Jupiter. 91 00:06:39,656 --> 00:06:42,682 There you go. That's a prize for honesty. 92 00:06:43,327 --> 00:06:44,817 You didn't get a second. 93 00:06:45,028 --> 00:06:46,518 Which one would you like? 94 00:06:58,709 --> 00:07:01,769 Every one of us begins life with an open mind... 95 00:07:01,979 --> 00:07:05,915 ...a driving curiosity, a sense of wonder. 96 00:07:07,017 --> 00:07:10,350 I thought it might be fun if we now had some questions. 97 00:07:10,554 --> 00:07:14,456 Why is the Earth round? Why isn't it square or any other shape? 98 00:07:15,158 --> 00:07:16,750 That's a good question. 99 00:07:16,960 --> 00:07:21,397 That's a question I've asked myself. The answer has to do with gravity. 100 00:07:21,899 --> 00:07:23,730 The Earth has a strong gravity. 101 00:07:23,934 --> 00:07:26,494 If you were to make a mountain very high... 102 00:07:26,703 --> 00:07:29,604 ...higher than Everest, the biggest mountain on Earth... 103 00:07:29,806 --> 00:07:32,138 ...it would be crushed by its own weight. 104 00:07:32,342 --> 00:07:35,004 Gravity pulls everything towards the center. 105 00:07:35,212 --> 00:07:38,477 So any really big bump on the Earth is crushed. 106 00:07:38,682 --> 00:07:42,311 But if you had a small object, a tiny world... 107 00:07:42,519 --> 00:07:44,180 ...the gravity is very low... 108 00:07:44,388 --> 00:07:47,551 ...and then it can be very different from a sphere. 109 00:07:47,758 --> 00:07:52,161 I think I have here a world that isn't a sphere. 110 00:07:52,529 --> 00:07:53,587 Here. 111 00:07:54,798 --> 00:07:56,129 Look at this one. 112 00:07:57,334 --> 00:07:58,824 See? It's lumpy. 113 00:08:00,604 --> 00:08:01,798 It's a lumpy world. 114 00:08:02,873 --> 00:08:04,238 It looks like a potato. 115 00:08:04,975 --> 00:08:08,138 There's a large potato orbiting the planet Mars. 116 00:08:08,345 --> 00:08:10,575 This is one of the moons of Mars. 117 00:08:10,781 --> 00:08:13,011 That's a perfect example. 118 00:08:13,216 --> 00:08:17,209 You can have big departures from a sphere if your gravity is low. 119 00:08:17,421 --> 00:08:19,321 Now the question in the front. 120 00:08:19,523 --> 00:08:22,754 Is the sun considered part of the Milky Way galaxy? 121 00:08:22,960 --> 00:08:26,088 Sure, you're considered part of the Milky Way galaxy. 122 00:08:26,530 --> 00:08:30,830 Everything except other galaxies is part of the Milky Way galaxy. 123 00:08:31,034 --> 00:08:32,592 The sun is one star. 124 00:08:32,803 --> 00:08:37,740 There is a few hundred billion stars in the Milky Way. 125 00:08:38,041 --> 00:08:40,771 Around each star, maybe, is a whole bunch of planets. 126 00:08:41,645 --> 00:08:44,876 And on one of those planets is life... 127 00:08:45,082 --> 00:08:48,950 ...and one of the life forms on that planet is you. 128 00:08:49,152 --> 00:08:51,518 You're a part of the Milky Way galaxy too. 129 00:09:01,999 --> 00:09:06,936 Sometimes I think, how lucky we are to live in this time... 130 00:09:07,137 --> 00:09:10,800 ...the first moment in human history when we are, in fact... 131 00:09:11,008 --> 00:09:12,600 ...visiting other worlds... 132 00:09:12,809 --> 00:09:17,041 ...and engaging in a deep reconnaissance of the cosmos. 133 00:09:17,414 --> 00:09:20,042 But if we had been born in a much earlier age... 134 00:09:20,250 --> 00:09:23,344 ...no matter how great our dedication, we couldn't have understood... 135 00:09:23,553 --> 00:09:25,817 ...what the stars and planets are. 136 00:09:35,365 --> 00:09:39,859 We would not have known that there were other suns and other worlds. 137 00:09:43,206 --> 00:09:47,165 This is one of the great secrets wrested from nature... 138 00:09:47,377 --> 00:09:51,837 ...through a million years of patient observation and courageous thinking. 139 00:09:55,318 --> 00:09:59,118 Human beings have always asked questions about the stars. 140 00:09:59,322 --> 00:10:02,382 It's as natural as breathing. 141 00:10:02,626 --> 00:10:06,460 But imagine a time before science had found out the answers. 142 00:10:06,663 --> 00:10:09,257 Imagine what it was like, say... 143 00:10:09,466 --> 00:10:12,993 ...hundreds of thousands of years ago... 144 00:10:13,203 --> 00:10:16,798 ...soon after the discovery of fire. 145 00:10:17,007 --> 00:10:20,602 We were just as smart and just as curious then... 146 00:10:20,811 --> 00:10:22,472 ...as we are now. 147 00:10:22,679 --> 00:10:24,544 Sometimes it seems to me that... 148 00:10:24,748 --> 00:10:27,774 ...there were people then who thought like this: 149 00:10:30,153 --> 00:10:33,714 We are wandering hunter folk. 150 00:10:33,924 --> 00:10:35,585 Fire keeps us warm. 151 00:10:35,792 --> 00:10:39,023 Its light makes holes in the darkness. 152 00:10:39,229 --> 00:10:41,493 It keeps hungry animals away. 153 00:10:41,932 --> 00:10:45,424 In the darkness, we can see each other and talk. 154 00:10:46,603 --> 00:10:48,594 We take care of the flame. 155 00:10:48,805 --> 00:10:51,797 The flame takes care of us. 156 00:10:52,709 --> 00:10:55,007 The stars are not near to us. 157 00:10:55,212 --> 00:10:58,909 When we climb a hill or a tree, they are no closer. 158 00:10:59,116 --> 00:11:03,052 They flicker with a strange, cold, white... 159 00:11:03,854 --> 00:11:04,912 ...faraway light. 160 00:11:05,856 --> 00:11:10,156 Many of them, all over the sky, but only at night. 161 00:11:10,527 --> 00:11:12,620 I wonder what they are. 162 00:11:13,430 --> 00:11:16,957 One night I thought the stars are flames. 163 00:11:17,167 --> 00:11:20,364 They give a little light at night as fire does. 164 00:11:20,570 --> 00:11:22,629 Maybe the stars are campfires... 165 00:11:22,839 --> 00:11:26,002 ...which other wanderers light at night. 166 00:11:26,710 --> 00:11:30,043 The stars give a much smaller light than campfires... 167 00:11:30,247 --> 00:11:33,045 ...so they must be very far away. 168 00:11:33,617 --> 00:11:36,279 I wonder if our campfires... 169 00:11:36,486 --> 00:11:39,250 ...look like stars to the people in the sky. 170 00:11:39,656 --> 00:11:44,150 But why don't those campfires and the wanderers who made them... 171 00:11:44,361 --> 00:11:46,192 ...fall down at our feet? 172 00:11:46,396 --> 00:11:50,594 Why don't strange tribes drop from the sky? 173 00:11:52,402 --> 00:11:57,169 Those beings in the sky must have great powers. 174 00:12:04,181 --> 00:12:06,809 I don't suppose that every hunter-gatherer... 175 00:12:07,017 --> 00:12:09,747 ...had such thoughts about the stars. 176 00:12:09,953 --> 00:12:13,389 But we know from contemporary hunter-gatherer communities... 177 00:12:13,590 --> 00:12:17,321 ...that very imaginative ideas arise. 178 00:12:17,761 --> 00:12:20,286 The Kung Bushmen... 179 00:12:20,497 --> 00:12:23,557 ...of the Kalahari Desert in the Republic of Botswana... 180 00:12:23,767 --> 00:12:26,497 ...have an explanation of the Milky Way. 181 00:12:26,703 --> 00:12:29,672 At their latitude, it's often overhead. 182 00:12:29,873 --> 00:12:33,900 They call it the "backbone of night." 183 00:12:34,110 --> 00:12:36,738 They believe it holds the sky up. 184 00:12:36,947 --> 00:12:39,279 They believe that if not for the Milky Way... 185 00:12:39,482 --> 00:12:43,111 ...pieces of sky would come crashing down at our feet. 186 00:12:43,320 --> 00:12:46,949 So the Milky Way, in their view, has some practical value. 187 00:12:47,157 --> 00:12:49,682 The backbone of night. 188 00:12:52,529 --> 00:12:55,225 Later on, metaphors about... 189 00:12:55,498 --> 00:12:57,989 ...campfires or backbones... 190 00:12:58,201 --> 00:13:01,500 ...or holes through which the flame could be seen... 191 00:13:01,705 --> 00:13:06,074 ...were replaced in most human communities by another idea. 192 00:13:06,543 --> 00:13:11,412 The powerful beings in the sky were promoted to gods. 193 00:13:12,048 --> 00:13:15,142 They were given names and relatives... 194 00:13:15,352 --> 00:13:17,286 ...and special responsibilities... 195 00:13:17,487 --> 00:13:20,854 ...for the cosmic services they were expected to perform. 196 00:13:21,057 --> 00:13:24,925 There was a god for every human concern. 197 00:13:25,128 --> 00:13:26,186 Gods ran nature. 198 00:13:26,396 --> 00:13:30,833 Nothing happened without the direct intervention of some god. 199 00:13:31,134 --> 00:13:34,592 If the gods were happy, there was plenty of food... 200 00:13:34,804 --> 00:13:36,362 ...and humans were happy. 201 00:13:38,174 --> 00:13:40,938 But if something displeased the gods... 202 00:13:41,144 --> 00:13:45,444 ...and it didn't take much, the consequences were awesome: 203 00:13:45,649 --> 00:13:48,880 Droughts, floods, storms, wars... 204 00:13:49,085 --> 00:13:52,714 ...earthquakes, volcanic eruptions, epidemics. 205 00:13:53,623 --> 00:13:56,649 The gods had to be propitiated. 206 00:13:56,860 --> 00:13:59,522 And a vast industry of priests arose... 207 00:13:59,729 --> 00:14:02,254 ...to make the gods less angry. 208 00:14:02,866 --> 00:14:05,926 But because the gods were capricious... 209 00:14:06,136 --> 00:14:08,627 ...you couldn't be sure what they would do. 210 00:14:08,838 --> 00:14:11,272 Nature was a mystery. 211 00:14:11,541 --> 00:14:14,066 It was hard to understand the world. 212 00:14:17,113 --> 00:14:20,276 Our ancestors groped in darkness... 213 00:14:20,483 --> 00:14:22,781 ...to make sense of their surroundings. 214 00:14:22,986 --> 00:14:24,476 Powerless before nature... 215 00:14:25,155 --> 00:14:27,715 ...they invented rituals and myths... 216 00:14:27,924 --> 00:14:30,484 ...some desperate and cruel... 217 00:14:30,694 --> 00:14:34,357 ...others imaginative and benign. 218 00:14:34,698 --> 00:14:36,928 The ancient Greeks explained... 219 00:14:37,133 --> 00:14:40,591 ...that diffuse band of brightness in the night sky... 220 00:14:40,804 --> 00:14:43,466 ...as the milk of the goddess Hera... 221 00:14:43,673 --> 00:14:46,642 ...squirted from her breast across the heavens. 222 00:14:46,843 --> 00:14:50,279 We still call it the Milky Way. 223 00:14:56,786 --> 00:14:59,778 In gratitude for the many gifts of the gods... 224 00:14:59,989 --> 00:15:04,119 ...our ancestors created works of surpassing beauty. 225 00:15:07,063 --> 00:15:09,554 This is all that remains... 226 00:15:09,766 --> 00:15:13,167 ...of the ancient temple of Hera, queen of heaven: 227 00:15:13,536 --> 00:15:18,405 A single marble column standing in a vast field of ruins... 228 00:15:19,109 --> 00:15:21,100 ...on the Greek island of Samos. 229 00:15:21,311 --> 00:15:23,279 It was one of the wonders of the world... 230 00:15:23,747 --> 00:15:28,207 ...built by people with an extraordinary eye for clarity... 231 00:15:28,418 --> 00:15:29,976 ...and symmetry. 232 00:15:37,360 --> 00:15:39,692 Those who thronged to that temple... 233 00:15:39,896 --> 00:15:42,490 ...were also the architects of a bridge... 234 00:15:42,699 --> 00:15:45,497 ...from their world to ours. 235 00:15:48,104 --> 00:15:52,598 We were moving once again in our voyage of self-discovery... 236 00:15:52,876 --> 00:15:55,504 ...on our journey to the stars. 237 00:16:00,450 --> 00:16:04,147 Here, 25 centuries ago... 238 00:16:04,788 --> 00:16:08,155 ...on the island of Samos and in the other Greek colonies... 239 00:16:08,358 --> 00:16:10,918 ...which had grown up in the busy Aegean Sea... 240 00:16:11,127 --> 00:16:13,721 ...there was a glorious awakening. 241 00:16:13,930 --> 00:16:17,491 Suddenly, people believed that everything was made of atoms... 242 00:16:17,700 --> 00:16:21,966 ...that human beings and other animals had evolved from simpler forms... 243 00:16:22,172 --> 00:16:26,802 ...that diseases were not caused by demons or the gods... 244 00:16:27,010 --> 00:16:31,310 ...that the Earth was only a planet going around a sun... 245 00:16:31,514 --> 00:16:33,880 ...which was very far away. 246 00:16:37,454 --> 00:16:41,550 This revolution made cosmos out of chaos. 247 00:16:41,958 --> 00:16:45,291 Here, in the sixth century B.C., a new idea developed... 248 00:16:45,495 --> 00:16:48,157 ...one of the great ideas of the human species. 249 00:16:48,364 --> 00:16:52,425 It was argued that the universe was knowable. 250 00:16:52,735 --> 00:16:55,397 Why? Because it was ordered. 251 00:16:55,605 --> 00:16:58,165 Because there are regularities in nature... 252 00:16:58,374 --> 00:17:01,207 ...which permitted secrets to be uncovered. 253 00:17:03,446 --> 00:17:06,847 Nature was not entirely unpredictable. 254 00:17:07,050 --> 00:17:10,781 There were rules which even she had to obey. 255 00:17:13,323 --> 00:17:17,987 This ordered and admirable character of the universe... 256 00:17:18,194 --> 00:17:20,185 ...was called cosmos. 257 00:17:21,364 --> 00:17:24,094 And it was set in stark contradiction... 258 00:17:24,300 --> 00:17:26,530 ...to the idea of chaos. 259 00:17:27,403 --> 00:17:31,669 This was the first conflict of which we know... 260 00:17:32,108 --> 00:17:34,338 ...between science and mysticism... 261 00:17:35,144 --> 00:17:37,874 ...between nature and the gods. 262 00:17:43,686 --> 00:17:45,654 But why here? 263 00:17:46,256 --> 00:17:50,693 Why in these remote islands and inlets of the eastern Mediterranean? 264 00:17:50,894 --> 00:17:53,192 Why not in the great cities of... 265 00:17:53,396 --> 00:17:58,060 ...India or Egypt, Babylon, China, Mesoamerica? 266 00:18:00,737 --> 00:18:04,036 Because they were all at the center of old empires. 267 00:18:06,609 --> 00:18:10,136 They were set in their ways, hostile to new ideas. 268 00:18:10,346 --> 00:18:12,109 But here in Ionia... 269 00:18:12,315 --> 00:18:16,217 ...were a multitude of newly colonized islands and city-states. 270 00:18:16,419 --> 00:18:20,753 Isolation, even if incomplete, promotes diversity. 271 00:18:20,957 --> 00:18:25,121 No single concentration of power could enforce conformity. 272 00:18:25,328 --> 00:18:28,263 Free inquiry became possible. 273 00:18:29,165 --> 00:18:32,498 They were beyond the frontiers of the empires. 274 00:18:32,702 --> 00:18:36,194 The merchants and tourists and sailors of Africa... 275 00:18:36,406 --> 00:18:39,466 ...Asia and Europe met in the harbors of Ionia... 276 00:18:40,343 --> 00:18:44,143 ...to exchange goods and stories and ideas. 277 00:18:44,347 --> 00:18:47,612 There was a vigorous and heady interaction... 278 00:18:47,817 --> 00:18:52,618 ...of many traditions, prejudices, languages and gods. 279 00:19:02,465 --> 00:19:05,866 These people were ready to experiment. 280 00:19:06,436 --> 00:19:09,530 Once you are open to questioning rituals... 281 00:19:09,739 --> 00:19:11,707 ...and time-honored practices... 282 00:19:11,908 --> 00:19:16,311 ...you find that one question leads to another. 283 00:19:26,022 --> 00:19:29,150 What do you do when you're faced with several different gods... 284 00:19:29,359 --> 00:19:31,759 ...each claiming the same territory? 285 00:19:31,961 --> 00:19:34,521 The Babylonian Marduk and the Greek Zeus... 286 00:19:34,731 --> 00:19:38,189 ...were each considered king of the gods... 287 00:19:38,401 --> 00:19:40,335 ...master of the sky. 288 00:19:40,803 --> 00:19:44,170 You might decide, since they otherwise had different attributes... 289 00:19:44,374 --> 00:19:47,138 ...that one of them was merely invented by the priests. 290 00:19:47,343 --> 00:19:50,005 But if one, why not both? 291 00:19:55,785 --> 00:19:58,811 And so it was here that the great idea arose: 292 00:19:59,022 --> 00:20:01,047 The realization that there might be a way... 293 00:20:01,257 --> 00:20:03,851 ...to know the world without the god hypothesis. 294 00:20:04,060 --> 00:20:08,827 That there be principles, forces, laws of nature... 295 00:20:09,032 --> 00:20:12,524 ...through which the world might be understood without attributing... 296 00:20:12,735 --> 00:20:16,796 ...the fall of every sparrow to the direct intervention of Zeus. 297 00:20:17,206 --> 00:20:20,403 This is the place where science was born. 298 00:20:20,777 --> 00:20:22,608 That's why we're here. 299 00:20:24,147 --> 00:20:29,084 This Greek revolution happened between 600 and 400 B.C. 300 00:20:29,752 --> 00:20:32,915 It was accomplished by the same practical and productive people... 301 00:20:33,122 --> 00:20:34,953 ...who made the society function. 302 00:20:35,158 --> 00:20:38,252 Political power was in the hands of the merchants... 303 00:20:38,461 --> 00:20:41,692 ...who promoted the technology on which their prosperity depended. 304 00:20:42,098 --> 00:20:44,259 The earliest pioneers of science were... 305 00:20:44,467 --> 00:20:47,630 ...merchants and artisans and their children. 306 00:20:53,810 --> 00:20:57,211 The first Ionian scientist was named Thales. 307 00:20:57,680 --> 00:21:00,444 He was born over there in the city of Miletus... 308 00:21:00,650 --> 00:21:02,948 ...across this narrow strait. 309 00:21:03,152 --> 00:21:04,915 He had traveled in Egypt... 310 00:21:05,121 --> 00:21:07,954 ...and was conversant with the knowledge of Babylon. 311 00:21:08,391 --> 00:21:12,885 Like the Babylonians, he believed that the world had once all been water. 312 00:21:13,529 --> 00:21:15,622 To explain the dry land... 313 00:21:15,832 --> 00:21:18,995 ...the Babylonians added that their god, Marduk... 314 00:21:19,202 --> 00:21:22,797 ...had placed a mat on the face of the waters... 315 00:21:23,005 --> 00:21:25,303 ...and piled dirt on top of it. 316 00:21:26,809 --> 00:21:28,504 Thales had a similar view... 317 00:21:28,711 --> 00:21:31,612 ...but he left Marduk out. 318 00:21:32,415 --> 00:21:35,714 Yes, the world had once been mostly water... 319 00:21:36,219 --> 00:21:40,747 ...but it was a natural process which explained the dry land. 320 00:21:40,957 --> 00:21:45,189 Thales thought it was similar to the silting up he had observed... 321 00:21:45,394 --> 00:21:47,885 ...at the delta of the river Nile. 322 00:21:49,132 --> 00:21:52,795 Whether Thales' conclusions were right or wrong... 323 00:21:53,002 --> 00:21:56,460 ...is not nearly as important as his approach. 324 00:21:56,672 --> 00:22:00,199 The world was not made by the gods... 325 00:22:00,409 --> 00:22:03,572 ...but instead was the result of material forces... 326 00:22:03,780 --> 00:22:05,680 ...interacting in nature. 327 00:22:06,282 --> 00:22:10,116 Thales brought back from Babylon and Egypt... 328 00:22:10,319 --> 00:22:13,550 ...the seeds of new sciences: 329 00:22:13,790 --> 00:22:16,190 Astronomy and geometry... 330 00:22:16,392 --> 00:22:19,190 ...sciences which would sprout and grow... 331 00:22:19,395 --> 00:22:22,421 ...in the fertile soil of Ionia. 332 00:22:24,000 --> 00:22:27,902 Anaximander of Miletus, over there... 333 00:22:28,337 --> 00:22:30,601 ...was a friend and colleague of Thales... 334 00:22:30,807 --> 00:22:32,968 ...one of the first people that we know of... 335 00:22:33,176 --> 00:22:35,406 ...to have actually done an experiment. 336 00:22:35,611 --> 00:22:40,139 By examining the moving shadow cast by a vertical stick... 337 00:22:40,349 --> 00:22:44,877 ...he determined accurately the lengths of the year and seasons. 338 00:22:45,087 --> 00:22:48,318 For ages, men had used sticks... 339 00:22:48,524 --> 00:22:50,583 ...to club and spear each other. 340 00:22:50,793 --> 00:22:54,320 Anaximander used a stick to measure time. 341 00:22:58,801 --> 00:23:03,397 In 540 B.C., or thereabouts, on this island of Samos... 342 00:23:03,606 --> 00:23:08,134 ...there came to power a tyrant named Polycrates. 343 00:23:08,411 --> 00:23:10,436 He seems to have started as a caterer... 344 00:23:10,646 --> 00:23:13,547 ...and then went on to international piracy. 345 00:23:13,883 --> 00:23:18,411 His loot was unloaded on this very breakwater. 346 00:23:18,621 --> 00:23:21,112 (DRUM BEATS) 347 00:23:26,996 --> 00:23:31,057 But he oppressed his own people, he made war on his neighbors. 348 00:23:31,267 --> 00:23:33,394 He quite rightly feared invasion. 349 00:23:33,603 --> 00:23:38,506 So Polycrates surrounded his capital city with an impressive wall... 350 00:23:38,708 --> 00:23:41,643 ...whose remains stand till this day. 351 00:23:51,053 --> 00:23:55,012 To carry water from a distant spring through the fortifications... 352 00:23:55,224 --> 00:23:58,022 ...he ordered this great tunnel built. 353 00:23:58,227 --> 00:24:01,719 A kilometer long, it pierces a mountain. 354 00:24:01,998 --> 00:24:04,330 Two cuttings were dug from either side... 355 00:24:04,533 --> 00:24:06,797 ...which met almost perfectly in the middle. 356 00:24:07,003 --> 00:24:10,234 The project took some 15 years to complete. 357 00:24:11,173 --> 00:24:14,734 It is a token of the civil engineering of its day... 358 00:24:14,944 --> 00:24:18,778 ...and an indication of the extraordinary practical capability... 359 00:24:18,981 --> 00:24:19,879 ...of the Ionians. 360 00:24:23,185 --> 00:24:25,483 The enduring legacy of the Ionians... 361 00:24:25,688 --> 00:24:28,122 ...is the tools and techniques they developed... 362 00:24:28,324 --> 00:24:31,589 ...which remain the basis of modern technology. 363 00:24:35,765 --> 00:24:38,996 This was the time of Theodorus... 364 00:24:39,201 --> 00:24:41,931 ...the master engineer of the age... 365 00:24:42,138 --> 00:24:46,131 ...a man who is credited with the invention of... 366 00:24:46,342 --> 00:24:50,301 ...the key, the ruler, the carpenter's square... 367 00:24:50,513 --> 00:24:53,380 ...the level, the lathe, bronze casting. 368 00:24:53,883 --> 00:24:56,852 Why are there no monuments to this man? 369 00:24:57,853 --> 00:25:01,345 Those who dreamt and speculated... 370 00:25:01,557 --> 00:25:03,957 ...and deduced about the laws of nature... 371 00:25:04,160 --> 00:25:06,628 ...talked to the engineers and the technologists. 372 00:25:06,829 --> 00:25:08,854 They were often the same people. 373 00:25:09,231 --> 00:25:13,190 The practical and the theoretical were one. 374 00:25:14,236 --> 00:25:19,173 (DRUM BEATS) 375 00:25:20,042 --> 00:25:23,705 This new hybrid of abstract thought... 376 00:25:23,913 --> 00:25:27,314 ...and everyday experience blossomed into science. 377 00:25:28,684 --> 00:25:32,814 When these practical men turned their attention to the natural world... 378 00:25:33,022 --> 00:25:35,149 ...they began to uncover hidden wonders... 379 00:25:36,125 --> 00:25:38,685 ...and breathtaking possibilities. 380 00:25:39,328 --> 00:25:42,786 Anaximander studied the profusion of living things... 381 00:25:42,999 --> 00:25:45,524 ...and saw their interrelationships. 382 00:25:45,735 --> 00:25:49,865 He concluded that life had originated in water and mud... 383 00:25:50,339 --> 00:25:53,069 ...and then colonized the dry land. 384 00:25:53,909 --> 00:25:55,740 "Human beings," he said... 385 00:25:55,945 --> 00:25:58,846 "...must have evolved from simpler forms." 386 00:25:59,348 --> 00:26:04,285 This insight had to wait 24 centuries until its truth was demonstrated... 387 00:26:04,887 --> 00:26:06,650 ...by Charles Darwin. 388 00:26:15,264 --> 00:26:19,462 Nothing was excluded from the investigations of the first scientists. 389 00:26:19,668 --> 00:26:23,968 Even the air became the subject of close examination... 390 00:26:24,173 --> 00:26:28,166 ...by a Greek from Sicily named Empedocles. 391 00:26:29,812 --> 00:26:32,372 He made an astonishing discovery... 392 00:26:32,581 --> 00:26:37,018 ...with a household implement that people had used for centuries. 393 00:26:37,353 --> 00:26:40,516 This is the so-called water thief. 394 00:26:40,723 --> 00:26:44,921 It's a brazen sphere with a neck and a hole at the top... 395 00:26:45,127 --> 00:26:47,687 ...and a set of little holes at the bottom. 396 00:26:47,897 --> 00:26:49,558 It was used as a kitchen ladle. 397 00:26:50,099 --> 00:26:53,796 You fill it by immersing it in water. 398 00:26:56,305 --> 00:26:58,603 lf, after it's been in there a little bit... 399 00:26:58,808 --> 00:27:01,971 ...you pull it out with the neck uncovered... 400 00:27:03,245 --> 00:27:07,045 ...then the water trickles out the little holes making a small shower. 401 00:27:08,184 --> 00:27:11,813 Instead, if you pull it out with the neck covered... 402 00:27:12,588 --> 00:27:14,215 ...the water is retained. 403 00:27:26,035 --> 00:27:28,128 Now try to fill it... 404 00:27:28,370 --> 00:27:31,828 ...with the neck covered with my thumb. 405 00:27:35,945 --> 00:27:37,071 Nothing happens. 406 00:27:37,947 --> 00:27:39,073 Why not? 407 00:27:39,648 --> 00:27:41,445 There's something in the way. 408 00:27:41,650 --> 00:27:46,587 Some material is blocking the access of the water into the sphere. 409 00:27:46,922 --> 00:27:49,117 I can't see any such material. 410 00:27:49,992 --> 00:27:51,619 What could it be? 411 00:27:52,361 --> 00:27:54,852 Empedocles identified it... 412 00:27:55,064 --> 00:27:56,463 ...as air. 413 00:27:57,099 --> 00:27:58,862 What else could it be? 414 00:27:59,235 --> 00:28:02,363 A thing you can't see can exert pressure... 415 00:28:02,571 --> 00:28:06,371 ...can frustrate my wish to fill this vessel with water... 416 00:28:06,575 --> 00:28:10,841 ...if I were dumb enough to leave my thumb on the neck. 417 00:28:11,680 --> 00:28:15,343 Empedocles had discovered... 418 00:28:16,685 --> 00:28:18,175 ...the invisible. 419 00:28:18,787 --> 00:28:21,779 Air, he thought, must be matter... 420 00:28:21,991 --> 00:28:25,358 ...in a form so finely divided... 421 00:28:26,228 --> 00:28:27,593 ...that it couldn't be seen. 422 00:28:29,064 --> 00:28:33,467 This hint, this whiff of the existence of atoms... 423 00:28:33,669 --> 00:28:38,038 ...was carried much further by a contemporary named Democritus. 424 00:28:38,507 --> 00:28:42,773 Of all the ancient scientists, it is he who speaks most clearly to us... 425 00:28:42,978 --> 00:28:44,502 ...across the centuries. 426 00:28:44,713 --> 00:28:47,944 The few surviving fragments of his scientific writings... 427 00:28:48,150 --> 00:28:51,779 ...reveal a mind of the highest logical and intuitive powers. 428 00:28:51,987 --> 00:28:56,788 He believed that a large number of other worlds wander through space... 429 00:28:56,992 --> 00:28:59,290 ...that worlds are born and die... 430 00:28:59,495 --> 00:29:01,486 ...that some are rich and living creatures... 431 00:29:01,697 --> 00:29:04,928 ...and others are dry and barren. 432 00:29:06,302 --> 00:29:09,135 He was the first to understand that the Milky Way... 433 00:29:09,338 --> 00:29:12,933 ...is an aggregate of the light of innumerable faint stars. 434 00:29:13,142 --> 00:29:17,010 Beyond campfires in the sky, beyond the milk of Hera... 435 00:29:17,213 --> 00:29:22,150 ...beyond the backbone of night, the mind of Democritus soared. 436 00:29:27,423 --> 00:29:30,654 He saw deep connections between the heavens and the Earth. 437 00:29:31,260 --> 00:29:34,195 "Man," he said, "is a microcosm... 438 00:29:34,630 --> 00:29:36,222 ...a little cosmos." 439 00:30:00,055 --> 00:30:03,991 Democritus came from the Ionian town of Abdera... 440 00:30:04,193 --> 00:30:06,491 ...on the northern Aegean shore. 441 00:30:09,832 --> 00:30:14,166 In those days, Abdera was the butt of jokes. 442 00:30:15,070 --> 00:30:17,163 lf, around the year 400 B.C... 443 00:30:17,373 --> 00:30:19,841 ...in the equivalent of a restaurant like this... 444 00:30:20,409 --> 00:30:23,037 ...you told a story about someone from Abdera... 445 00:30:23,245 --> 00:30:25,179 ...you were guaranteed a laugh. 446 00:30:28,050 --> 00:30:30,018 It was, in a way... 447 00:30:30,219 --> 00:30:32,619 ...the Brooklyn of its time. 448 00:30:35,124 --> 00:30:39,322 For Democritus, all of life was to be enjoyed and understood. 449 00:30:39,528 --> 00:30:41,826 For him, understanding and enjoyment... 450 00:30:42,031 --> 00:30:44,329 ...were pretty much the same thing. 451 00:30:44,533 --> 00:30:49,163 He said, "A life without festivity is a long road without an inn." 452 00:30:49,371 --> 00:30:53,068 Democritus may have come from Abdera, but he was no dummy. 453 00:30:56,879 --> 00:30:59,871 Democritus understood that the complex forms... 454 00:31:00,082 --> 00:31:03,483 ...changes and motions of the material world... 455 00:31:03,686 --> 00:31:08,248 ...all derived from the interaction of very simple moving parts. 456 00:31:08,457 --> 00:31:11,153 He called these parts atoms. 457 00:31:16,131 --> 00:31:19,828 All material objects are collections of atoms... 458 00:31:20,369 --> 00:31:21,802 ...intricately assembled... 459 00:31:22,004 --> 00:31:23,301 ...even we. 460 00:31:23,539 --> 00:31:25,803 When I cut this apple... 461 00:31:26,075 --> 00:31:28,100 ...the knife must be passing through... 462 00:31:28,377 --> 00:31:31,869 ...empty spaces between the atoms, Democritus argued. 463 00:31:32,081 --> 00:31:35,517 If there were no such empty spaces, no void... 464 00:31:35,718 --> 00:31:40,280 ...then the knife would encounter some impenetrable atom... 465 00:31:40,489 --> 00:31:42,423 ...and the apple wouldn't be cut. 466 00:31:42,624 --> 00:31:45,718 Let's compare the cross sections of the two pieces. 467 00:31:45,928 --> 00:31:48,522 Are the exposed areas exactly equal? 468 00:31:48,731 --> 00:31:51,461 No, said Democritus, the curvature of the apple... 469 00:31:51,667 --> 00:31:56,468 ...forces this slice to be slightly shorter than the rest of the apple. 470 00:31:56,872 --> 00:32:00,239 If they were equally tall, then we'd have... 471 00:32:00,442 --> 00:32:02,501 ...a cylinder and not an apple. 472 00:32:02,745 --> 00:32:04,872 No matter how sharp the knife... 473 00:32:05,080 --> 00:32:07,947 ...these two pieces have unequal cross sections. 474 00:32:08,150 --> 00:32:09,515 But why? 475 00:32:09,718 --> 00:32:12,744 Because on the scale of the very small... 476 00:32:12,955 --> 00:32:16,220 ...matter exhibits some irreducible roughness... 477 00:32:16,425 --> 00:32:20,156 ...and this fine scale of roughness Democritus of Abdera identified... 478 00:32:20,429 --> 00:32:22,363 ...with the world of the atoms. 479 00:32:22,564 --> 00:32:24,725 His arguments are not those we use today. 480 00:32:24,933 --> 00:32:29,233 But they're elegant and subtle and derived from everyday experience. 481 00:32:29,438 --> 00:32:32,874 And his conclusions were fundamentally right. 482 00:32:38,147 --> 00:32:41,241 Democritus believed that nothing happens at random... 483 00:32:41,450 --> 00:32:44,715 ...that everything has a material cause. 484 00:32:46,054 --> 00:32:49,990 He said, "I would rather understand one cause... 485 00:32:50,192 --> 00:32:52,456 ...than be king of Persia." 486 00:32:52,661 --> 00:32:55,892 He believed that poverty in a democracy was far better... 487 00:32:56,098 --> 00:32:57,725 ...than wealth in a tyranny. 488 00:32:57,933 --> 00:33:01,425 He believed that the prevailing religions of his time were evil... 489 00:33:01,637 --> 00:33:05,664 ...and that neither souls nor immortal gods existed. 490 00:33:06,275 --> 00:33:11,212 There is no evidence that Democritus was persecuted for his beliefs. 491 00:33:11,780 --> 00:33:14,772 But then again, he came from Abdera. 492 00:33:17,052 --> 00:33:18,383 However, in his time... 493 00:33:18,587 --> 00:33:22,023 ...the brief tradition of tolerance for unconventional views... 494 00:33:22,224 --> 00:33:24,192 ...was beginning to erode. 495 00:33:24,693 --> 00:33:27,218 For instance, the prevailing belief was... 496 00:33:27,429 --> 00:33:30,193 ...that the moon and the sun were gods. 497 00:33:30,833 --> 00:33:34,599 Another contemporary of Democritus, named Anaxagoras, taught... 498 00:33:34,803 --> 00:33:38,569 ...that the moon was a place made of ordinary matter... 499 00:33:38,774 --> 00:33:43,006 ...and that the sun was a red-hot stone far away in the sky. 500 00:33:43,245 --> 00:33:46,339 For this, Anaxagoras was condemned... 501 00:33:46,548 --> 00:33:50,143 ...convicted and imprisoned for impiety... 502 00:33:50,352 --> 00:33:52,115 ...a religious crime. 503 00:33:52,321 --> 00:33:55,916 People began to be persecuted for their ideas. 504 00:33:56,225 --> 00:33:58,887 A portrait of Democritus is now... 505 00:33:59,094 --> 00:34:01,790 ...on the Greek 100-drachma note. 506 00:34:02,664 --> 00:34:04,825 But his ideas were suppressed... 507 00:34:05,033 --> 00:34:07,228 ...and his influence on history made minor. 508 00:34:07,436 --> 00:34:10,132 The mystics were beginning to win. 509 00:34:10,339 --> 00:34:14,469 (DRUM BEATS) 510 00:34:16,945 --> 00:34:19,539 You see, Ionia was also the home... 511 00:34:19,748 --> 00:34:22,581 ...of another quite different intellectual tradition. 512 00:34:22,784 --> 00:34:25,412 Its founder was Pythagoras... 513 00:34:25,621 --> 00:34:29,022 ...who lived here on Samos in the 6th century B.C. 514 00:34:30,225 --> 00:34:32,523 According to local legend... 515 00:34:32,728 --> 00:34:36,289 ...this cave was once his abode. 516 00:34:36,632 --> 00:34:39,157 Maybe that was once his living room. 517 00:34:39,368 --> 00:34:41,336 Many centuries later... 518 00:34:41,603 --> 00:34:45,369 ...this small Greek Orthodox shrine was erected on his front porch. 519 00:34:45,574 --> 00:34:50,511 There's a continuity of tradition from Pythagoras to Christianity. 520 00:34:50,746 --> 00:34:54,409 Pythagoras was the first person in the history of the world... 521 00:34:54,616 --> 00:34:57,744 ...to decide that the Earth was a sphere. 522 00:34:57,986 --> 00:35:02,184 Perhaps he argued by analogy with the moon or the sun... 523 00:35:02,391 --> 00:35:05,417 ...maybe he noticed the curved shadow of the Earth on the moon... 524 00:35:05,627 --> 00:35:07,219 ...during a lunar eclipse. 525 00:35:07,429 --> 00:35:10,227 Or maybe he recognized that when ships leave Samos... 526 00:35:10,432 --> 00:35:12,866 ...their masts disappear last. 527 00:35:18,140 --> 00:35:21,632 Pythagoras believed that a mathematical harmony... 528 00:35:21,843 --> 00:35:23,708 ...underlies all of nature. 529 00:35:23,912 --> 00:35:26,176 The modern tradition of mathematical argument... 530 00:35:26,381 --> 00:35:29,748 ...essential in all of science owes much to him. 531 00:35:29,952 --> 00:35:33,718 And the notion that the heavenly bodies move to a kind of... 532 00:35:33,922 --> 00:35:36,152 ...music of the spheres... 533 00:35:36,458 --> 00:35:38,983 ...was also derived from Pythagoras. 534 00:35:39,595 --> 00:35:42,462 It was he who first used the word cosmos... 535 00:35:42,664 --> 00:35:45,497 ...to mean a well-ordered and harmonious universe... 536 00:35:45,701 --> 00:35:49,193 ...a world amenable to human understanding. 537 00:35:53,575 --> 00:35:57,011 For this great idea, we are indebted to Pythagoras. 538 00:35:57,212 --> 00:36:01,740 But there were deep ironies and contradictions in his thoughts. 539 00:36:02,217 --> 00:36:04,117 Many of the Ionians believed... 540 00:36:04,319 --> 00:36:08,813 ...that the underlying harmony and unity of the universe was accessible... 541 00:36:09,024 --> 00:36:11,720 ...through observation and experiment... 542 00:36:11,927 --> 00:36:14,395 ...the method which dominates science today. 543 00:36:14,663 --> 00:36:17,427 However, Pythagoras had a very different method. 544 00:36:17,633 --> 00:36:22,570 He believed that the laws of nature can be deduced by pure thought. 545 00:36:22,971 --> 00:36:26,031 He and his followers were not basically experimentalists... 546 00:36:26,241 --> 00:36:28,038 ...they were mathematicians... 547 00:36:28,243 --> 00:36:31,110 ...and they were thoroughgoing mystics. 548 00:36:32,014 --> 00:36:35,950 They were fascinated by these five regular solids... 549 00:36:36,151 --> 00:36:39,450 ...bodies whose faces are all polygons: 550 00:36:39,655 --> 00:36:42,283 Triangles or squares... 551 00:36:42,491 --> 00:36:43,890 ...or pentagons. 552 00:36:44,092 --> 00:36:46,856 There can be an infinite number of polygons... 553 00:36:47,062 --> 00:36:50,088 ...but only five regular solids. 554 00:36:52,668 --> 00:36:57,605 Four of the solids were associated with earth, fire, air and water. 555 00:36:58,273 --> 00:37:01,868 The cube, for example, represented earth. 556 00:37:02,077 --> 00:37:06,173 These four elements, they thought, make up terrestrial matter. 557 00:37:07,549 --> 00:37:09,346 So the fifth solid... 558 00:37:09,551 --> 00:37:12,782 ...they mystically associated with the cosmos. 559 00:37:12,988 --> 00:37:15,889 Perhaps it was the substance of the heavens. 560 00:37:16,091 --> 00:37:18,651 This fifth solid was called... 561 00:37:18,860 --> 00:37:21,328 ...the dodecahedron. 562 00:37:21,697 --> 00:37:25,189 Its faces are pentagons, 12 of them. 563 00:37:25,801 --> 00:37:27,530 Knowledge of the dodecahedron... 564 00:37:27,736 --> 00:37:31,001 ...was considered too dangerous for the public. 565 00:37:33,241 --> 00:37:37,701 Ordinary people were to be kept ignorant of the dodecahedron. 566 00:37:37,946 --> 00:37:40,779 In love with whole numbers, the Pythagoreans believed... 567 00:37:40,982 --> 00:37:43,143 ...that all things could be derived from them... 568 00:37:43,351 --> 00:37:45,342 ...certainly all other numbers. 569 00:37:45,554 --> 00:37:48,580 So a crisis in doctrine occurred when they discovered... 570 00:37:48,790 --> 00:37:51,224 ...that the square root of two was irrational. 571 00:37:51,426 --> 00:37:54,554 The square root of two could not be represented as the ratio... 572 00:37:54,763 --> 00:37:57,459 ...of two whole numbers no matter how big they were. 573 00:37:57,833 --> 00:38:00,529 Irrational originally meant only that... 574 00:38:00,736 --> 00:38:03,705 ...that you can't express a number as a ratio. 575 00:38:03,905 --> 00:38:07,102 But for the Pythagoreans, it came to mean something else... 576 00:38:07,309 --> 00:38:09,209 ...something threatening... 577 00:38:09,411 --> 00:38:13,507 ...a hint that their world-view might not make sense... 578 00:38:13,715 --> 00:38:16,548 ...the other meaning of irrational. 579 00:38:17,452 --> 00:38:22,116 Instead of wanting everyone to share and know of their discoveries... 580 00:38:22,324 --> 00:38:25,521 ...the Pythagoreans suppressed the square root of two... 581 00:38:25,727 --> 00:38:27,388 ...and the dodecahedron. 582 00:38:27,596 --> 00:38:30,087 The outside world was not to know. 583 00:38:36,004 --> 00:38:38,268 The Pythagoreans had discovered... 584 00:38:38,473 --> 00:38:41,101 ...in the mathematical underpinnings of nature... 585 00:38:41,309 --> 00:38:43,937 ...one of the two most powerful scientific tools. 586 00:38:44,146 --> 00:38:47,240 The other, of course, is experiment. 587 00:38:47,549 --> 00:38:50,109 But instead of using their insight to advance... 588 00:38:50,318 --> 00:38:52,980 ...the collective voyage of human discovery... 589 00:38:53,188 --> 00:38:57,750 ...they made of it little more than the hocus-pocus of a mystery cult. 590 00:38:57,959 --> 00:39:01,053 Science and mathematics were to be removed from the hands... 591 00:39:01,263 --> 00:39:02,890 ...of merchants and artisans. 592 00:39:03,832 --> 00:39:06,767 This tendency found its most effective advocate... 593 00:39:06,968 --> 00:39:10,335 ...in a follower of Pythagoras named Plato. 594 00:39:10,605 --> 00:39:15,304 He preferred the perfection of these mathematical abstractions... 595 00:39:15,510 --> 00:39:18,638 ...to the imperfections of everyday life. 596 00:39:18,847 --> 00:39:23,181 He believed that ideas were far more real than the natural world. 597 00:39:23,385 --> 00:39:26,013 He advised the astronomers not to waste their time... 598 00:39:26,221 --> 00:39:27,950 ...observing stars and planets. 599 00:39:28,156 --> 00:39:31,717 It was better, he believed, just to think about them. 600 00:39:32,561 --> 00:39:36,156 Plato expressed hostility to observation and experiment. 601 00:39:36,364 --> 00:39:38,798 He taught contempt for the real world... 602 00:39:39,000 --> 00:39:42,993 ...and disdain for the practical application of scientific knowledge. 603 00:39:44,673 --> 00:39:48,404 Plato's followers succeeded in extinguishing the light... 604 00:39:48,610 --> 00:39:50,441 ...of science and experiment... 605 00:39:50,645 --> 00:39:54,945 ...that had been kindled by Democritus and the other Ionians. 606 00:39:57,786 --> 00:40:01,187 Plato's unease with the world as revealed by our senses... 607 00:40:01,389 --> 00:40:06,122 ...was to dominate and stifle Western philosophy. 608 00:40:08,563 --> 00:40:10,360 Even as late as 1600... 609 00:40:10,565 --> 00:40:13,932 ...Johannes Kepler was still struggling to interpret... 610 00:40:14,135 --> 00:40:16,228 ...the structure of the cosmos in terms of... 611 00:40:16,438 --> 00:40:20,875 ...Pythagorean solids and Platonic perfection. 612 00:40:21,076 --> 00:40:25,012 Ironically, it was Kepler who helped re-establish the old Ionian method... 613 00:40:25,213 --> 00:40:27,647 ...of testing ideas against observations. 614 00:40:28,183 --> 00:40:31,016 But why had science lost its way in the first place? 615 00:40:31,219 --> 00:40:34,154 What appeal did Pythagoras' and Plato's teachings... 616 00:40:34,356 --> 00:40:36,221 ...have for their contemporaries? 617 00:40:36,424 --> 00:40:38,051 They provided, I believe... 618 00:40:38,260 --> 00:40:41,195 ...an intellectually respectable justification... 619 00:40:41,396 --> 00:40:44,263 ...for a corrupt social order. 620 00:40:47,836 --> 00:40:51,033 The mercantile tradition which had led to Ionian science... 621 00:40:51,239 --> 00:40:53,503 ...also led to a slave economy. 622 00:40:54,376 --> 00:40:56,367 You could get richer... 623 00:40:56,578 --> 00:40:59,138 ...if you owned a lot of slaves. 624 00:40:59,514 --> 00:41:02,506 Athens, in the time of Plato and Aristotle... 625 00:41:02,717 --> 00:41:05,481 ...had a vast slave population. 626 00:41:05,687 --> 00:41:09,589 All of that brave Athenian talk about democracy... 627 00:41:09,791 --> 00:41:12,692 ...applied only to a privileged few. 628 00:41:13,295 --> 00:41:17,629 Plato and Aristotle were comfortable in a slave society. 629 00:41:17,832 --> 00:41:20,926 They offered justifications for oppression. 630 00:41:21,569 --> 00:41:23,537 They served tyrants. 631 00:41:23,738 --> 00:41:26,901 They taught the alienation of the body from the mind... 632 00:41:27,108 --> 00:41:31,135 ...a natural enough idea, I suppose, in a slave society. 633 00:41:31,346 --> 00:41:33,871 They separated thought from matter. 634 00:41:34,082 --> 00:41:36,448 They divorced the Earth from the heavens. 635 00:41:36,651 --> 00:41:40,519 Divisions which were to dominate Western thinking... 636 00:41:40,722 --> 00:41:42,815 ...for more than 20 centuries. 637 00:41:43,024 --> 00:41:45,458 The Pythagoreans had won. 638 00:41:51,633 --> 00:41:54,659 In the recognition by Pythagoras and Plato... 639 00:41:54,869 --> 00:41:56,837 ...that the cosmos is knowable... 640 00:41:57,038 --> 00:42:00,132 ...that there is a mathematical underpinning to nature... 641 00:42:00,342 --> 00:42:03,436 ...they greatly advanced the cause of science. 642 00:42:04,045 --> 00:42:08,106 But in the suppression of disquieting facts... 643 00:42:08,316 --> 00:42:13,015 ...the sense that science should be kept for a small elite... 644 00:42:13,221 --> 00:42:17,282 ...the distaste for experiment, the embrace of mysticism... 645 00:42:17,926 --> 00:42:21,259 ...the easy acceptance of slave societies... 646 00:42:21,463 --> 00:42:25,331 ...their influence has significantly set back... 647 00:42:25,533 --> 00:42:27,160 ...the human endeavor. 648 00:42:28,536 --> 00:42:33,473 The books of the Ionian scientists are entirely lost. 649 00:42:34,376 --> 00:42:39,109 Their views were suppressed, ridiculed and forgotten... 650 00:42:39,881 --> 00:42:42,543 ...by the Platonists and by the Christians... 651 00:42:42,751 --> 00:42:46,243 ...who adopted much of the philosophy of Plato. 652 00:42:47,022 --> 00:42:51,755 Finally, after a long, mystical sleep... 653 00:42:52,027 --> 00:42:56,623 ...in which the tools of scientific inquiry lay moldering... 654 00:42:56,831 --> 00:42:59,629 ...the Ionian approach was rediscovered. 655 00:43:04,606 --> 00:43:07,302 The Western world reawakened. 656 00:43:07,509 --> 00:43:10,967 Experiment and open inquiry... 657 00:43:11,179 --> 00:43:14,580 ...slowly became respectable once again. 658 00:43:15,283 --> 00:43:19,344 Forgotten books and fragments were read once more. 659 00:43:19,721 --> 00:43:23,782 Leonardo and Copernicus and Columbus... 660 00:43:23,992 --> 00:43:27,155 ...were inspired by the Ionian tradition. 661 00:43:39,407 --> 00:43:43,207 The Pythagoreans and their successors... 662 00:43:43,411 --> 00:43:46,403 ...held the peculiar notion that... 663 00:43:46,614 --> 00:43:48,878 ...the Earth was tainted... 664 00:43:49,084 --> 00:43:51,518 ...somehow nasty... 665 00:43:51,719 --> 00:43:56,349 ...while the heavens were pristine and divine. 666 00:43:57,025 --> 00:43:59,755 So the fundamental idea that the Earth is a planet... 667 00:43:59,961 --> 00:44:02,691 ...that we're citizens of the universe... 668 00:44:02,897 --> 00:44:05,627 ...was rejected and forgotten. 669 00:44:09,037 --> 00:44:12,837 This idea was first argued by Aristarchus... 670 00:44:13,041 --> 00:44:17,000 ...born here on Samos, three centuries after Pythagoras. 671 00:44:17,212 --> 00:44:20,045 He held that the Earth moves around the sun. 672 00:44:20,248 --> 00:44:23,479 He correctly located our place in the solar system. 673 00:44:23,685 --> 00:44:27,553 For his trouble, he was accused of heresy. 674 00:44:29,324 --> 00:44:33,658 From the size of the Earth's shadow on the moon during a lunar eclipse... 675 00:44:33,862 --> 00:44:38,060 ...he deduced that the sun had to be much, much larger... 676 00:44:38,266 --> 00:44:41,360 ...than the Earth, and also very far away. 677 00:44:41,769 --> 00:44:44,363 From this he may have argued that it was absurd... 678 00:44:44,572 --> 00:44:47,598 ...for so large an object as the sun to be going around... 679 00:44:47,809 --> 00:44:50,903 ...so small an object as the Earth. 680 00:44:51,112 --> 00:44:55,981 So he put the sun rather than the Earth at the center of the solar system. 681 00:44:56,184 --> 00:44:59,711 And he had the Earth and the other planets going around the sun. 682 00:44:59,921 --> 00:45:03,288 He also had the Earth rotating on its axis once a day. 683 00:45:03,491 --> 00:45:07,655 These are ideas that we ordinarily associate with the name Copernicus. 684 00:45:07,862 --> 00:45:11,354 But Copernicus seems to have gotten some hint of these ideas... 685 00:45:11,566 --> 00:45:14,194 ...by reading about Aristarchus. 686 00:45:14,669 --> 00:45:17,399 In fact, in the manuscript of Copernicus' book... 687 00:45:17,605 --> 00:45:21,041 ...he referred to Aristarchus, but in the final version... 688 00:45:21,242 --> 00:45:23,938 ...he suppressed the citation. 689 00:45:24,646 --> 00:45:27,513 Resistance to Aristarchus, a kind of... 690 00:45:28,149 --> 00:45:30,640 ...geocentrism in everyday life, is with us still. 691 00:45:30,852 --> 00:45:33,787 We still talk about a sun rising... 692 00:45:33,988 --> 00:45:36,456 ...and the sun setting. 693 00:45:37,158 --> 00:45:39,752 It's 2200 years since Aristarchus... 694 00:45:39,961 --> 00:45:44,830 ...and the language still pretends that the Earth does not turn... 695 00:45:45,667 --> 00:45:49,694 ...that the sun is not at the center of the solar system. 696 00:45:52,807 --> 00:45:56,573 Aristarchus understood the basic scheme of the solar system... 697 00:45:56,778 --> 00:45:58,541 ...but not its scale. 698 00:46:01,149 --> 00:46:04,812 He knew that the planets move in concentric orbits about the sun... 699 00:46:05,019 --> 00:46:08,250 ...and he probably knew their order out to Saturn. 700 00:46:09,791 --> 00:46:12,021 But he was much too modest in his estimates... 701 00:46:12,227 --> 00:46:14,718 ...of how far apart the planets are. 702 00:46:15,063 --> 00:46:18,430 In order to calculate the true scale of the solar system... 703 00:46:18,633 --> 00:46:20,260 ...you need a telescope. 704 00:46:20,668 --> 00:46:24,160 It wasn't until the 17th century that astronomers were able to get... 705 00:46:24,372 --> 00:46:28,069 ...even a rough estimate of the distance to the sun. 706 00:46:30,078 --> 00:46:32,569 And once you knew the distance to the sun... 707 00:46:32,780 --> 00:46:34,338 ...what about the stars? 708 00:46:34,549 --> 00:46:36,983 How far away are they? 709 00:46:40,888 --> 00:46:44,380 There is a way to measure the distance to the stars... 710 00:46:44,592 --> 00:46:47,322 ...and the Ionians were fully capable of discovering it. 711 00:46:47,528 --> 00:46:51,328 Aristarchus had toyed with the daring idea... 712 00:46:51,532 --> 00:46:54,262 ...that the stars were distant suns. 713 00:46:54,469 --> 00:46:56,937 Now, if a star were as near as the sun... 714 00:46:57,138 --> 00:47:00,369 ...it should appear as big and as bright as the sun. 715 00:47:00,575 --> 00:47:04,341 Everyone knows that the farther away an object is, the smaller it seems. 716 00:47:04,545 --> 00:47:08,003 This inverse proportionality between apparent size and distance... 717 00:47:08,216 --> 00:47:11,913 ...is the basis of perspective in art and photography. 718 00:47:12,120 --> 00:47:14,816 So the further away we are from the sun... 719 00:47:15,023 --> 00:47:17,924 ...the smaller and dimmer it appears. 720 00:47:18,126 --> 00:47:21,323 How far from the sun would we have to be for it to appear... 721 00:47:21,529 --> 00:47:23,793 ...as small and dim as a star? 722 00:47:23,998 --> 00:47:26,967 Or equivalently, how small a piece of sun... 723 00:47:27,168 --> 00:47:29,398 ...would be as bright as a star? 724 00:47:29,771 --> 00:47:34,265 An experiment to answer this question was performed in 17th-century Holland... 725 00:47:34,475 --> 00:47:39,310 ...by Christiaan Huygens and is very much in the Ionian tradition. 726 00:47:39,514 --> 00:47:44,451 Huygens drilled a number of holes in a brass plate... 727 00:47:44,886 --> 00:47:47,286 ...and held the plate up to the sun. 728 00:47:47,488 --> 00:47:52,289 He asked himself, which hole seemed as bright... 729 00:47:52,493 --> 00:47:56,759 ...as he remembered the star Sirius to have been the previous evening. 730 00:47:56,964 --> 00:47:59,990 Well, the hole that matched was effectively... 731 00:48:00,201 --> 00:48:04,934 ...1 l28,000th the apparent size of the sun. 732 00:48:05,206 --> 00:48:09,267 So Sirius, he reasoned, must be 28,000 times... 733 00:48:09,477 --> 00:48:13,777 ...further away than the sun, or about half a light-year away. 734 00:48:14,382 --> 00:48:17,146 It's hard to remember just how bright a star is... 735 00:48:17,352 --> 00:48:21,186 ...hours after you've looked at it, but Huygens remembered very well. 736 00:48:21,389 --> 00:48:25,416 If he had known that Sirius was intrinsically brighter than the sun... 737 00:48:25,626 --> 00:48:28,026 ...he would've gotten the answer exactly right. 738 00:48:28,229 --> 00:48:32,290 Sirius is 8.8 light-years away from us. 739 00:48:33,267 --> 00:48:36,134 Between Aristarchus and Huygens... 740 00:48:36,337 --> 00:48:39,568 ...people had answered that question which had so excited me... 741 00:48:39,774 --> 00:48:41,639 ...as a young boy growing up in Brooklyn: 742 00:48:41,843 --> 00:48:44,209 The question, "What are the stars?" 743 00:48:47,648 --> 00:48:52,585 And the answer is that the stars are mighty suns, light-years away... 744 00:48:52,787 --> 00:48:55,187 ...in the depths of interstellar space. 745 00:49:00,995 --> 00:49:05,329 And around those suns, are there other planets? 746 00:49:06,401 --> 00:49:08,369 And on those other worlds... 747 00:49:08,569 --> 00:49:11,538 ...are there beings who wonder as we do? 748 00:49:15,910 --> 00:49:18,310 Here is a light bulb... 749 00:49:18,513 --> 00:49:21,073 ...which is supposed to represent a nearby star. 750 00:49:21,282 --> 00:49:24,740 Next to it, and very hard to see because of the bright light... 751 00:49:24,952 --> 00:49:26,317 ...is a planet. 752 00:49:26,521 --> 00:49:30,048 We'll need a volunteer. Who would like to come up, please? 753 00:49:30,725 --> 00:49:33,319 Ordinarily, it's hard to see the planet... 754 00:49:33,528 --> 00:49:37,487 ...because it's so close that the star washes out the planet. 755 00:49:37,698 --> 00:49:42,135 But if we're able to put something in front of the star... 756 00:49:42,336 --> 00:49:45,863 ...to make an artificial eclipse, then we might be able to see the planet. 757 00:49:46,073 --> 00:49:50,339 I'm gonna stand over here. Imagine that I'm a telescope... 758 00:49:50,545 --> 00:49:51,978 ...somewhere near the Earth. 759 00:49:52,180 --> 00:49:56,082 And, Tab, if you'd slowly move the disc across. 760 00:49:56,284 --> 00:49:58,275 Good. A little faster would be nice. 761 00:49:58,486 --> 00:50:01,114 Now you're just beginning to cover over the star. 762 00:50:01,322 --> 00:50:04,348 I really can't see the planet at all. Keep going. 763 00:50:04,559 --> 00:50:06,026 Now, right there... 764 00:50:06,227 --> 00:50:08,593 ...I can't see the star at all... 765 00:50:08,796 --> 00:50:12,698 ...and I see the planet lit by the light of the star. 766 00:50:12,900 --> 00:50:16,233 Now, that is a method for looking for planets... 767 00:50:16,437 --> 00:50:18,268 ...around nearby stars. 768 00:50:18,473 --> 00:50:23,410 And that method uses a spacecraft to hold the disc... 769 00:50:23,945 --> 00:50:26,413 ...and scan the sky for another telescope... 770 00:50:26,614 --> 00:50:29,344 ...to see if there are any planets. 771 00:50:29,550 --> 00:50:33,884 Tab, you accomplished your mission to look for planets around other stars. 772 00:50:34,088 --> 00:50:37,251 Thank you for being our interplanetary spacecraft. 773 00:50:37,458 --> 00:50:40,052 So this is one way. 774 00:50:40,261 --> 00:50:43,662 And there are spaceships that will be able to do this... 775 00:50:43,865 --> 00:50:45,628 ...in the next 10 years or so. 776 00:50:45,833 --> 00:50:47,300 And there's another way. 777 00:50:47,502 --> 00:50:50,027 This has already been tried from the Earth. 778 00:50:50,238 --> 00:50:54,334 Imagine that there's a nearby star that you can see. 779 00:50:54,542 --> 00:50:58,535 It's bright and it has a dark companion, a planet... 780 00:50:58,746 --> 00:51:02,147 ...shining only by reflected light near it, so dim you can't see it. 781 00:51:02,350 --> 00:51:07,117 But imagine that this planet and its star... 782 00:51:07,321 --> 00:51:09,186 ...are going around each other. 783 00:51:10,324 --> 00:51:11,655 Like that: 784 00:51:11,859 --> 00:51:14,453 You can see the star, you can't see the planet. 785 00:51:14,662 --> 00:51:17,028 So now I'm gonna need two volunteers. 786 00:51:19,233 --> 00:51:20,257 You two. 787 00:51:21,602 --> 00:51:24,469 Just to save time because they're in the front row. 788 00:51:24,672 --> 00:51:27,698 I need one of you to turn the star and the planet... 789 00:51:27,909 --> 00:51:31,868 ...and another person to pull the star and planet along. 790 00:51:32,079 --> 00:51:33,546 And what you will see... 791 00:51:33,748 --> 00:51:37,081 ...is that the star you can make out... 792 00:51:37,285 --> 00:51:39,913 ...will be moving in a funny, wiggly pattern... 793 00:51:40,121 --> 00:51:42,248 ...which will be the clue, the evidence... 794 00:51:42,456 --> 00:51:44,720 ...for the existence of the dark planet. 795 00:51:44,926 --> 00:51:48,123 Okay, let's have a spin. Good. And a pull. 796 00:51:48,329 --> 00:51:49,990 And you see this funny motion... 797 00:51:50,197 --> 00:51:54,861 ...that the star makes because of the planet. Thank you. 798 00:51:55,069 --> 00:51:58,266 That's another way of finding out the existence of a planet... 799 00:51:58,472 --> 00:52:01,373 ...that you couldn't see directly. 800 00:52:01,576 --> 00:52:04,704 Well, both of these methods are being used. 801 00:52:05,012 --> 00:52:09,676 And by the time that you people are... 802 00:52:09,884 --> 00:52:11,681 ...as old as I am... 803 00:52:11,886 --> 00:52:15,253 ...we should know, for all the nearest stars... 804 00:52:15,456 --> 00:52:17,890 ...if they have planets going around them. 805 00:52:18,092 --> 00:52:22,461 We might know dozens or even hundreds of other planetary systems... 806 00:52:22,663 --> 00:52:25,962 ...and see if they're like our own or very different... 807 00:52:26,167 --> 00:52:29,762 ...or no other planets going around other stars at all. 808 00:52:29,971 --> 00:52:32,235 That will happen in your lifetime. 809 00:52:32,440 --> 00:52:37,104 It'll be the first time in the world's history that anybody found out... 810 00:52:37,845 --> 00:52:40,575 ...if there are planets around the other stars. 811 00:52:40,781 --> 00:52:45,718 Now, the nearby stars, the ones you can see with the naked eye... 812 00:52:46,020 --> 00:52:48,284 ...those are all in the solar neighborhood. 813 00:52:48,489 --> 00:52:50,980 That's what astronomers call it: The neighborhood. 814 00:52:51,192 --> 00:52:55,788 But it's a very tiny place in the Milky Way galaxy. 815 00:52:56,731 --> 00:52:58,858 The Milky Way is that band of light... 816 00:52:59,066 --> 00:53:02,160 ...that you see across the sky on a clear night. 817 00:53:02,370 --> 00:53:05,498 I can't tell if there are any more clear nights in Brooklyn. 818 00:53:05,706 --> 00:53:09,369 You must've seen the Milky Way, a faint band of light at night. 819 00:53:09,577 --> 00:53:14,207 Well, that's just 100 billion stars... 820 00:53:14,415 --> 00:53:16,349 ...all seen together... 821 00:53:16,550 --> 00:53:19,144 ...edge on, as in this picture. 822 00:53:19,353 --> 00:53:22,686 If you could get out of the Milky Way and look down on it... 823 00:53:22,890 --> 00:53:24,790 ...it would look like that picture. 824 00:53:24,992 --> 00:53:27,153 If we did look down on the Milky Way... 825 00:53:27,361 --> 00:53:30,057 ...where would the sun and nearby stars be? 826 00:53:30,264 --> 00:53:33,427 Would it be in the center where things look important... 827 00:53:33,634 --> 00:53:35,101 ...or at least well-lit? 828 00:53:35,836 --> 00:53:39,169 No. We would be way out here... 829 00:53:39,373 --> 00:53:43,366 ...in the suburbs, in the countryside of the galaxy. 830 00:53:43,577 --> 00:53:45,238 We're not in any important place. 831 00:53:45,446 --> 00:53:49,212 All the stars you could see would be in a little place like that. 832 00:53:49,417 --> 00:53:52,614 And the Milky Way would be this band of light... 833 00:53:52,820 --> 00:53:55,380 ...100 billion stars all together. 834 00:53:55,856 --> 00:53:58,791 The fact that we live in the outskirts of the galaxy... 835 00:53:58,993 --> 00:54:02,485 ...was discovered a long time ago... 836 00:54:02,697 --> 00:54:05,257 ...towards the end of the First World War... 837 00:54:05,466 --> 00:54:07,764 ...by a man named Harlow Shapley... 838 00:54:07,968 --> 00:54:12,200 ...who was mapping the position of these clusters of stars. 839 00:54:12,406 --> 00:54:14,897 See, every one of these is a bunch... 840 00:54:15,109 --> 00:54:17,577 ...of maybe 10,000 stars all together. 841 00:54:17,778 --> 00:54:19,769 It's called a globular cluster. 842 00:54:19,980 --> 00:54:23,279 And you can see that they are centered around the middle... 843 00:54:23,484 --> 00:54:25,315 ...the center of the galaxy. 844 00:54:25,586 --> 00:54:29,352 People used to think that the sun was at the center of the galaxy... 845 00:54:29,557 --> 00:54:33,789 ...something important about our position. That turns out to be wrong. 846 00:54:34,128 --> 00:54:36,358 We live in the outskirts... 847 00:54:36,564 --> 00:54:38,998 ...the globular clusters are centered around... 848 00:54:39,500 --> 00:54:43,163 ...the marvelous middle of the Milky Way galaxy. 849 00:54:43,370 --> 00:54:47,204 And then it turned out that this isn't the only galaxy. 850 00:54:47,408 --> 00:54:49,842 We live in this one... 851 00:54:50,444 --> 00:54:52,207 ...but there are many others. 852 00:54:52,580 --> 00:54:55,572 And as this picture reminds us... 853 00:54:56,283 --> 00:54:58,717 ...there are many different kinds of galaxies... 854 00:54:58,919 --> 00:55:01,319 ...of which ours might be just this one. 855 00:55:01,522 --> 00:55:06,084 There are, in fact, 100 billion other galaxies... 856 00:55:06,293 --> 00:55:11,230 ...each of which contains something like 100 billion stars. 857 00:55:11,966 --> 00:55:16,903 Think of how many stars and planets and kinds of life there may be... 858 00:55:17,705 --> 00:55:21,869 ...in this vast and awesome universe. 859 00:55:24,678 --> 00:55:26,839 As long as there have been humans... 860 00:55:27,047 --> 00:55:30,448 ...we have searched for our place in the cosmos. 861 00:55:30,651 --> 00:55:33,449 Where are we? Who are we? 862 00:55:35,556 --> 00:55:39,856 We find that we live on an insignificant planet... 863 00:55:40,060 --> 00:55:42,028 ...of a humdrum star... 864 00:55:42,229 --> 00:55:45,392 ...lost in a galaxy tucked away in some... 865 00:55:45,599 --> 00:55:48,796 ...forgotten corner of a universe in which there are... 866 00:55:49,003 --> 00:55:52,268 ...far more galaxies than people. 867 00:55:55,509 --> 00:55:59,275 We make our world significant by the courage of our questions... 868 00:55:59,713 --> 00:56:02,341 ...and by the depth of our answers. 869 00:56:03,918 --> 00:56:07,012 We embarked on our journey to the stars... 870 00:56:07,621 --> 00:56:10,215 ...with a question first framed... 871 00:56:10,424 --> 00:56:12,949 ...in the childhood of our species... 872 00:56:13,394 --> 00:56:17,660 ...and in each generation asked anew... 873 00:56:17,932 --> 00:56:20,093 ...with undiminished wonder: 874 00:56:20,467 --> 00:56:22,628 "What are the stars?" 875 00:56:40,721 --> 00:56:43,588 Exploration is in our nature. 876 00:56:44,191 --> 00:56:46,489 We began as wanderers... 877 00:56:46,794 --> 00:56:49,661 ...and we are wanderers still. 878 00:57:00,941 --> 00:57:03,637 We have lingered long enough... 879 00:57:03,844 --> 00:57:06,642 ...on the shores of the cosmic ocean. 880 00:57:06,881 --> 00:57:08,678 We are ready at last... 881 00:57:08,883 --> 00:57:12,114 ...to set sail for the stars.