WEBVTT 00:00:03.200 --> 00:00:05.400 Hello. My name is Ann Druyan. 00:00:05.400 --> 00:00:07.400 When Carl Sagan, Steven Soter and I... 00:00:07.400 --> 00:00:11.200 ...wrote the Cosmos TV series in the late 1970s... 00:00:11.200 --> 00:00:12.900 ...a lot of things where different. 00:00:12.900 --> 00:00:15.100 Back then, the U.S. and the Soviet Union... 00:00:15.100 --> 00:00:18.300 ...held the hole planet in their perpetual hostage crisis... 00:00:18.300 --> 00:00:20.200 ...called the Cold War. 00:00:20.200 --> 00:00:23.600 The wealth and scientific ingenuity of our civilization... 00:00:23.600 --> 00:00:26.300 ...was being squandered on a runaway arms raise. 00:00:26.300 --> 00:00:29.200 Then employed half the world scientists... 00:00:29.200 --> 00:00:35.100 ...and infested the world with 50.000 nuclear weapons. 00:00:35.100 --> 00:00:37.400 So much has happened since then. 00:00:37.400 --> 00:00:39.000 The Cold War is history... 00:00:39.000 --> 00:00:42.000 ...and science has made great strides. 00:00:42.000 --> 00:00:45.800 We've completed the spacecraft recognizance of the Solar System... 00:00:45.800 --> 00:00:49.800 ...the preliminary mapping of the visible universe that surrounds us... 00:00:49.800 --> 00:00:54.700 ...and we've charted the universe within: the human genome. 00:00:54.700 --> 00:00:58.600 When Cosmos was first broadcast there was no World Wide Web... 00:00:58.600 --> 00:01:00.800 ...it was a different world. 00:01:00.800 --> 00:01:02.900 What a tribute to Carl Sagan... 00:01:02.900 --> 00:01:06.600 ...a scientist who took many a punch for daring to speculate... 00:01:06.600 --> 00:01:11.400 ...that even after 20 of the most eventful years in the history of science... 00:01:11.400 --> 00:01:18.000 ...Cosmos requires few revisions and indeed is rich in prophecy. 00:01:18.000 --> 00:01:22.000 Cosmos is both the history of the scientific enterprise... 00:01:22.000 --> 00:01:26.100 ...and an attempt to convey the spiritual high... 00:01:26.100 --> 00:01:28.400 ...of its central revelation: 00:01:28.400 --> 00:01:31.300 Our oneness with the universe. 00:01:31.300 --> 00:01:35.300 Now, please, enjoy Cosmos, the proud saga of how... 00:01:35.300 --> 00:01:40.000 ...through the searching of 40.000 generations of our ancestors... 00:01:40.000 --> 00:01:42.400 ...we have come to discover our coordinates... 00:01:42.400 --> 00:01:45.300 ...in space and in time. 00:01:45.300 --> 00:01:50.100 And how, through the awesomely powerful method of science... 00:01:50.100 --> 00:01:54.700 ...we have been able to reconstruct the sweep of cosmic evolution... 00:01:54.700 --> 00:03:12.278 ...and defined our own part in its great story. 00:03:12.278 --> 00:03:15.314 SAGAN: The cosmos is all that is... 00:03:15.314 --> 00:03:18.818 ...or ever was or ever will be. 00:03:18.818 --> 00:03:23.889 Our contemplations of the cosmos stir us. 00:03:23.889 --> 00:03:27.793 There is a tingling in the spine, a catch in the voice... 00:03:27.793 --> 00:03:31.464 ...a faint sensation, as if a distant memory... 00:03:31.464 --> 00:03:34.033 ...of falling from a great height. 00:03:34.033 --> 00:03:42.875 We know we are approaching the grandest of mysteries. 00:03:42.875 --> 00:03:45.978 The size and age of the cosmos... 00:03:45.978 --> 00:03:48.647 ...are beyond ordinary human understanding. 00:03:48.647 --> 00:03:53.452 Lost somewhere between immensity and eternity... 00:03:53.452 --> 00:03:56.589 ...is our tiny planetary home, the Earth. 00:03:56.589 --> 00:04:00.025 For the first time, we have the power to decide... 00:04:00.025 --> 00:04:02.828 ...the fate of our planet and ourselves. 00:04:02.828 --> 00:04:04.864 This is a time of great danger. 00:04:04.864 --> 00:04:09.301 But our species is young and curious and brave. 00:04:09.301 --> 00:04:11.203 It shows much promise. 00:04:11.203 --> 00:04:13.539 In the last few millennia, we've made... 00:04:13.539 --> 00:04:16.609 ...the most astonishing and unexpected discoveries... 00:04:16.609 --> 00:04:20.045 ...about the cosmos and our place within it. 00:04:20.045 --> 00:04:23.048 I believe our future depends powerfully on... 00:04:23.048 --> 00:04:25.584 ...how well we understand this cosmos... 00:04:25.584 --> 00:04:28.921 ...in which we float like a mote of dust... 00:04:28.921 --> 00:04:31.457 ...in the morning sky. 00:04:31.457 --> 00:04:35.928 (SEA GULL CHIRPS) 00:04:35.928 --> 00:04:40.866 We're about to begin a journey through the cosmos. 00:04:40.866 --> 00:04:44.069 We'll encounter galaxies and suns and planets... 00:04:44.069 --> 00:04:46.205 ...life and consciousness... 00:04:46.205 --> 00:04:50.442 ...coming into being, evolving and perishing. 00:04:50.442 --> 00:04:54.113 Worlds of ice and stars of diamond. 00:04:54.113 --> 00:04:56.315 Atoms as massive as suns... 00:04:56.315 --> 00:04:59.685 ...and universes smaller than atoms. 00:04:59.685 --> 00:05:02.254 But it's also a story of our own planet... 00:05:02.254 --> 00:05:05.057 ...and the plants and animals that share it with us. 00:05:05.057 --> 00:05:08.327 And it's a story about us: 00:05:08.327 --> 00:05:11.931 How we achieved our present understanding of the cosmos... 00:05:11.931 --> 00:05:15.434 ...how the cosmos has shaped our evolution and our culture... 00:05:15.434 --> 00:05:22.274 ...and what our fate may be. 00:05:22.274 --> 00:05:25.811 We wish to pursue the truth, no matter where it leads. 00:05:25.811 --> 00:05:30.382 But to find the truth, we need imagination and skepticism both. 00:05:30.382 --> 00:05:32.852 We will not be afraid to speculate. 00:05:32.852 --> 00:05:37.489 But we will be careful to distinguish speculation from fact. 00:05:37.489 --> 00:05:42.328 The cosmos is full beyond measure of elegant truths... 00:05:42.328 --> 00:05:44.830 ...of exquisite interrelationships... 00:05:44.830 --> 00:05:49.101 ...of the awesome machinery of nature. 00:05:49.101 --> 00:05:53.873 The surface of the Earth is the shore of the cosmic ocean. 00:05:53.873 --> 00:05:57.443 On this shore, we have learned most of what we know. 00:05:57.443 --> 00:06:00.212 Recently, we've waded a little way out... 00:06:00.212 --> 00:06:04.917 ...maybe ankle-deep, and the water seems inviting. 00:06:04.917 --> 00:06:09.688 Some part of our being knows this is where we came from. 00:06:09.688 --> 00:06:12.491 We long to return. 00:06:12.491 --> 00:06:13.792 And we can. 00:06:13.792 --> 00:06:18.130 Because the cosmos is also within us. We're made of star-stuff. 00:06:18.130 --> 00:06:22.868 We are a way for the cosmos to know itself. 00:06:22.868 --> 00:06:25.871 The journey for each of us begins here. 00:06:25.871 --> 00:06:29.775 We're going to explore the cosmos in a ship of the imagination... 00:06:29.775 --> 00:06:34.213 ...unfettered by ordinary limits on speed and size... 00:06:34.213 --> 00:06:37.149 ...drawn by the music of cosmic harmonies... 00:06:37.149 --> 00:06:40.486 ...it can take us anywhere in space and time. 00:06:40.486 --> 00:06:42.955 Perfect as a snowflake... 00:06:42.955 --> 00:06:46.725 ...organic as a dandelion seed... 00:06:46.725 --> 00:06:48.093 ...it will carry us... 00:06:48.093 --> 00:06:52.932 ...to worlds of dreams and worlds of facts. 00:06:52.932 --> 00:07:05.077 Come with me. 00:07:05.077 --> 00:07:15.387 Before us is the cosmos on the grandest scale we know. 00:07:15.387 --> 00:07:18.023 We are far from the shores of Earth... 00:07:18.023 --> 00:07:21.360 ...in the uncharted reaches of the cosmic ocean. 00:07:21.360 --> 00:07:25.064 Strewn like sea froth on the waves of space... 00:07:25.064 --> 00:07:28.000 ...are innumerable faint tendrils of light. 00:07:28.000 --> 00:07:30.569 Some of them containing hundreds... 00:07:30.569 --> 00:07:33.973 ...of billions of suns. 00:07:33.973 --> 00:07:36.842 These are the galaxies... 00:07:36.842 --> 00:07:43.582 ...drifting endlessly in the great cosmic dark. 00:07:43.582 --> 00:07:45.784 In our ship of the imagination... 00:07:45.784 --> 00:07:59.198 ...we are halfway to the edge of the known universe. 00:07:59.198 --> 00:08:02.901 In this, the first of our cosmic voyages... 00:08:02.901 --> 00:08:14.413 ...we begin to explore the universe revealed by science. 00:08:14.413 --> 00:08:19.518 Our course will eventually carry us to a far-off and exotic world. 00:08:19.518 --> 00:08:22.721 But from the depths of space, we cannot detect even... 00:08:22.721 --> 00:08:26.158 ...the cluster of galaxies in which our Milky Way is embedded... 00:08:26.158 --> 00:08:45.377 ...much less the sun or the Earth. 00:08:45.377 --> 00:08:48.013 We are in the realm of the galaxies... 00:08:48.013 --> 00:08:56.221 ...8 billion light years from home. 00:08:56.221 --> 00:09:01.060 No matter where we travel, the patterns of nature are the same... 00:09:01.060 --> 00:09:06.665 ...as in the form of this spiral galaxy. 00:09:06.665 --> 00:09:09.701 The same laws of physics apply everywhere... 00:09:09.701 --> 00:09:17.076 ...throughout the cosmos. 00:09:17.076 --> 00:09:20.379 But we have just begun to understand these laws. 00:09:20.379 --> 00:09:29.121 The universe is rich in mystery. 00:09:29.121 --> 00:09:31.890 Near the center of a cluster of galaxies... 00:09:31.890 --> 00:09:35.894 ...there's sometimes a rogue, elliptical galaxy... 00:09:35.894 --> 00:09:38.163 ...made of a trillion suns... 00:09:38.163 --> 00:09:40.566 ...which devours its neighbors. 00:09:40.566 --> 00:09:43.001 Perhaps this cyclone of stars... 00:09:43.001 --> 00:10:02.087 ...is what astronomers on Earth call a quasar. 00:10:02.087 --> 00:10:05.691 Our ordinary measures of distance fail us... 00:10:05.691 --> 00:10:08.660 ...here in the realm of the galaxies. 00:10:08.660 --> 00:10:11.463 We need a much larger unit: the light year. 00:10:11.463 --> 00:10:14.233 It measures how far light travels in a year... 00:10:14.233 --> 00:10:17.336 ...nearly 10 trillion kilometers. 00:10:17.336 --> 00:10:35.654 It measures not time, but enormous distances. 00:10:35.654 --> 00:10:37.589 In the Hercules cluster... 00:10:37.589 --> 00:10:42.261 ...the individual galaxies are about 300,000 light years apart. 00:10:42.261 --> 00:10:46.198 So light takes about 300,000 years... 00:10:46.198 --> 00:10:52.704 ...to go from one galaxy to another. 00:10:52.704 --> 00:10:56.475 Like stars and planets and people... 00:10:56.475 --> 00:11:01.146 ...galaxies are born, live and die. 00:11:01.146 --> 00:11:05.350 They may all experience a tumultuous adolescence. 00:11:05.350 --> 00:11:09.688 During their first 100 million years, their cores may explode. 00:11:09.688 --> 00:11:12.824 Seen in radio light, great jets of energy... 00:11:12.824 --> 00:11:17.062 ...pour out and echo across the cosmos. 00:11:17.062 --> 00:11:22.301 Worlds near the core or along the jets would be incinerated. 00:11:22.301 --> 00:11:26.471 I wonder how many planets and how many civilizations... 00:11:26.471 --> 00:11:36.415 ...might be destroyed. 00:11:36.415 --> 00:11:40.452 In the Pegasus cluster, there's a ring galaxy... 00:11:40.452 --> 00:11:43.822 ...the wreckage left from the collision of two galaxies. 00:11:43.822 --> 00:11:47.859 A splash in the cosmic pond. 00:11:47.859 --> 00:11:51.496 Individual galaxies may explode and collide... 00:11:51.496 --> 00:11:55.834 ...and their constituent stars may blow up as well. 00:11:55.834 --> 00:11:58.403 In this supernova explosion... 00:11:58.403 --> 00:12:05.277 ...a single star outshines the rest of its galaxy. 00:12:05.277 --> 00:12:08.947 We are approaching what astronomers on Earth call... 00:12:08.947 --> 00:12:12.951 ...the Local Group. 00:12:12.951 --> 00:12:18.924 Three million light years across, it contains some 20 galaxies. 00:12:18.924 --> 00:12:22.761 It's a sparse and rather typical chain of islands... 00:12:22.761 --> 00:12:26.598 ...in the immense cosmic ocean. 00:12:26.598 --> 00:12:31.803 We are now only 2 million light years from home. 00:12:31.803 --> 00:12:35.440 On the maps of space, this galaxy is called M31... 00:12:35.440 --> 00:12:37.843 ...the great galaxy Andromeda. 00:12:37.843 --> 00:12:41.647 It's a vast storm of stars and gas and dust. 00:12:41.647 --> 00:12:43.148 As we pass over it... 00:12:43.148 --> 00:12:50.656 ...we see one of its small satellite galaxies. 00:12:50.656 --> 00:12:52.491 Clusters of galaxies... 00:12:52.491 --> 00:12:55.260 ...and the stars of individual galaxies... 00:12:55.260 --> 00:12:58.196 ...are all held together by gravity. 00:12:58.196 --> 00:13:00.132 Surrounding M31... 00:13:00.132 --> 00:13:04.870 ...are hundreds of globular star clusters. 00:13:04.870 --> 00:13:07.472 We're approaching one of them. 00:13:07.472 --> 00:13:11.276 Each cluster orbits the massive center of the galaxy. 00:13:11.276 --> 00:13:15.914 Some contain up to a million separate stars. 00:13:15.914 --> 00:13:19.685 Every globular cluster is like a swarm of bees... 00:13:19.685 --> 00:13:21.286 ...bound by gravity... 00:13:21.286 --> 00:13:26.658 ...every bee, a sun. 00:13:26.658 --> 00:13:29.361 From Pegasus, our voyage has taken us... 00:13:29.361 --> 00:13:33.098 ...200 million light years to the Local Group... 00:13:33.098 --> 00:13:38.537 ...dominated by two great spiral galaxies. 00:13:38.537 --> 00:13:42.574 Beyond M31 is another very similar galaxy. 00:13:42.574 --> 00:13:45.210 Its spiral arms slowly turning... 00:13:45.210 --> 00:13:54.286 ...once every quarter billion years. 00:13:54.286 --> 00:13:57.289 This is our own Milky Way... 00:13:57.289 --> 00:14:06.431 ...seen from the outside. 00:14:06.431 --> 00:14:18.577 This is the home galaxy of the human species. 00:14:18.577 --> 00:14:23.782 In the obscure backwaters of the Carina-Cygnus spiral arm... 00:14:23.782 --> 00:14:27.252 ...we humans have evolved to consciousness... 00:14:27.252 --> 00:14:30.088 ...and some measure of understanding. 00:14:30.088 --> 00:14:33.625 This region of the Milky Way galaxy is now usually called the Local Arm... 00:14:33.625 --> 00:14:38.630 ...or the Orion Arm, but the spiral arm nomenclature remains rather fuzzy. 00:14:38.630 --> 00:14:41.566 Concentrated in its brilliant core... 00:14:41.566 --> 00:14:44.503 ...and strewn along its spiral arms... 00:14:44.503 --> 00:14:50.909 ...are 400 billion suns. 00:14:50.909 --> 00:14:53.612 It takes light 100,000 years to travel... 00:14:53.612 --> 00:14:58.617 ...from one end of the galaxy to the other. 00:14:58.617 --> 00:15:02.788 Within this galaxy are stars and worlds... 00:15:02.788 --> 00:15:07.325 ...and, it may be, an enormous diversity of living things... 00:15:07.325 --> 00:15:20.172 ...and intelligent beings and space faring civilizations. 00:15:20.172 --> 00:15:23.175 Scattered among the stars of the Milky Way... 00:15:23.175 --> 00:15:25.343 ...are supernova remnants... 00:15:25.343 --> 00:15:29.881 ...each one the remains of a colossal stellar explosion. 00:15:29.881 --> 00:15:32.117 These filaments of glowing gas... 00:15:32.117 --> 00:15:36.354 ...are the outer layers of a star which has recently destroyed itself. 00:15:36.354 --> 00:15:38.290 The gas is unraveling... 00:15:38.290 --> 00:15:42.060 ...returning star-stuff back into space. 00:15:42.060 --> 00:15:46.031 (PULSAR HISSES) 00:15:46.031 --> 00:15:49.501 And at its heart, are the remains of the original star... 00:15:49.501 --> 00:15:54.372 ...a dense, shrunken stellar fragment called a pulsar. 00:15:54.372 --> 00:15:57.909 A natural lighthouse, blinking and hissing. 00:15:57.909 --> 00:16:07.252 A sun that spins twice each second. 00:16:07.252 --> 00:16:10.822 Pulsars keep such perfect time that the first one discovered... 00:16:10.822 --> 00:16:13.925 ...was thought to be a sign of extraterrestrial intelligence. 00:16:13.925 --> 00:16:16.495 Perhaps a navigational beacon... 00:16:16.495 --> 00:16:19.764 ...for great ships that travel across the light years... 00:16:19.764 --> 00:16:25.437 ...and between the stars. 00:16:25.437 --> 00:16:29.241 There may be such intelligences and such starships... 00:16:29.241 --> 00:16:43.188 ...but pulsars are not their signature. 00:16:43.188 --> 00:16:46.791 Instead, they are the doleful reminders... 00:16:46.791 --> 00:16:48.760 ...that nothing lasts forever... 00:16:48.760 --> 00:16:54.099 ...that stars also die. 00:16:54.099 --> 00:16:58.236 We continue to plummet, falling thousands of light years... 00:16:58.236 --> 00:17:03.108 ...towards the plane of the galaxy. 00:17:03.108 --> 00:17:04.943 This is the Milky Way... 00:17:04.943 --> 00:17:07.612 ...our galaxy seen edge on. 00:17:07.612 --> 00:17:09.915 Billions of nuclear furnaces... 00:17:09.915 --> 00:17:17.889 ...converting matter into starlight. 00:17:17.889 --> 00:17:20.992 Some stars are flimsy as a soap bubble. 00:17:20.992 --> 00:17:25.564 Others are 100 trillion times denser than lead. 00:17:25.564 --> 00:17:29.534 The hottest stars are destined to die young. 00:17:29.534 --> 00:17:33.004 But red giants are mostly elderly. 00:17:33.004 --> 00:17:39.978 Such stars are unlikely to have inhabited planets. 00:17:39.978 --> 00:17:42.881 But yellow dwarf stars, like the sun... 00:17:42.881 --> 00:17:47.452 ...are middle-aged and they are far more common. 00:17:47.452 --> 00:17:50.589 These stars may have planetary systems. 00:17:50.589 --> 00:17:54.392 And on such planets, for the first time on our cosmic voyage... 00:17:54.392 --> 00:17:57.095 ...we encounter rare forms of matter: 00:17:57.095 --> 00:18:06.638 Ice and rock, air and liquid water. 00:18:06.638 --> 00:18:08.506 Close to this yellow star... 00:18:08.506 --> 00:18:11.710 ...is a small, warm, cloudy world... 00:18:11.710 --> 00:18:14.079 ...with continents and oceans. 00:18:14.079 --> 00:18:19.417 These conditions permit an even more precious form of matter to arise: 00:18:19.417 --> 00:18:27.926 Life. 00:18:27.926 --> 00:18:29.995 But this is not the Earth. 00:18:29.995 --> 00:18:34.866 Intelligent beings have evolved and reworked this planetary surface... 00:18:34.866 --> 00:18:37.936 ...in a massive engineering enterprise. 00:18:37.936 --> 00:18:41.373 In the Milky Way galaxy, there may be many worlds... 00:18:41.373 --> 00:18:52.083 ...on which matter has grown to consciousness. 00:18:52.083 --> 00:18:55.620 I wonder, are they very different from us? 00:18:55.620 --> 00:18:57.255 What do they look like? 00:18:57.255 --> 00:19:01.860 What are their politics, technology, music, religion? 00:19:01.860 --> 00:19:06.564 Or do they have patterns of culture we can't begin to imagine? 00:19:06.564 --> 00:19:17.709 Are they also a danger to themselves? 00:19:17.709 --> 00:19:21.446 Among the many glowing clouds of interstellar gas... 00:19:21.446 --> 00:19:24.683 ...is one called the Orion Nebula... 00:19:24.683 --> 00:19:33.224 ...only 1500 light years from Earth. 00:19:33.224 --> 00:19:36.828 These three bright stars are seen by earthlings... 00:19:36.828 --> 00:19:48.039 ...as the belt in the familiar constellation of Orion the hunter. 00:19:48.039 --> 00:19:51.409 The nebula appears from Earth as a patch of light... 00:19:51.409 --> 00:20:03.621 ...the middle star in Orion's sword. 00:20:03.621 --> 00:20:06.291 But it is not a star. 00:20:06.291 --> 00:20:09.427 It is another thing entirely. 00:20:09.427 --> 00:20:23.241 A cloud that veils one of nature's secret places. 00:20:23.241 --> 00:20:28.413 This is a stellar nursery, a place where stars are born. 00:20:28.413 --> 00:20:31.382 They condense by gravity from gas and dust... 00:20:31.382 --> 00:20:36.755 ...until their temperatures become so high that they begin to shine. 00:20:36.755 --> 00:20:39.691 Such clouds mark the births of stars... 00:20:39.691 --> 00:20:48.633 ...as others bear witness to their deaths. 00:20:48.633 --> 00:20:53.071 After stars condense in the hidden interiors of interstellar clouds... 00:20:53.071 --> 00:20:54.773 ...what happens to them? 00:20:54.773 --> 00:20:58.510 The Pleiades are a loose cluster of young stars... 00:20:58.510 --> 00:21:00.779 ...only 50 million years old. 00:21:00.779 --> 00:21:05.950 These fledgling stars are just being let out into the galaxy. 00:21:05.950 --> 00:21:09.354 Still surrounded by wisps of nebulosity... 00:21:09.354 --> 00:21:47.292 ...the gas and dust from which they formed. 00:21:47.292 --> 00:21:50.862 There are clouds that hang like inkblots... 00:21:50.862 --> 00:21:52.697 ...between the stars. 00:21:52.697 --> 00:21:55.700 They are made of fine, rocky dust... 00:21:55.700 --> 00:21:59.804 ...organic matter and ice. 00:21:59.804 --> 00:22:04.008 Inside, a few stars begin to turn on. 00:22:04.008 --> 00:22:06.110 Nearby worlds of ice evaporate... 00:22:06.110 --> 00:22:08.913 ...and form long, comet-like tails... 00:22:08.913 --> 00:22:16.788 ...driven back by the stellar winds. 00:22:16.788 --> 00:22:20.258 Black clouds, light years across... 00:22:20.258 --> 00:22:22.427 ...drift between the stars. 00:22:22.427 --> 00:22:25.563 They're filled with organic molecules. 00:22:25.563 --> 00:22:28.633 The building blocks of life are everywhere. 00:22:28.633 --> 00:22:30.802 They are easily made. 00:22:30.802 --> 00:22:36.007 On how many worlds have such complex molecules assembled themselves... 00:22:36.007 --> 00:22:45.016 ...into patterns we would call alive? 00:22:45.016 --> 00:22:50.088 Most stars belong to systems of two or three or many suns... 00:22:50.088 --> 00:22:52.290 ...bound together by gravity. 00:22:52.290 --> 00:22:55.727 Each system is isolated from its neighbors... 00:22:55.727 --> 00:22:59.597 ...by the light years. 00:22:59.597 --> 00:23:03.601 We are approaching a single, ordinary, yellow dwarf star... 00:23:03.601 --> 00:23:06.504 ...surrounded by a system of nine planets... 00:23:06.504 --> 00:23:11.209 ...dozens of moons, thousands of asteroids and billions of comets: 00:23:11.209 --> 00:23:14.979 The family of the sun. 00:23:14.979 --> 00:23:19.450 Only four light hours from Earth is the planet Neptune... 00:23:19.450 --> 00:23:25.957 ...and its giant satellite, Triton. 00:23:25.957 --> 00:23:29.027 Even in the outskirts of our own solar system... 00:23:29.027 --> 00:23:35.566 ...we humans have barely begun our explorations. 00:23:35.566 --> 00:23:37.168 Only a century ago... 00:23:37.168 --> 00:23:41.239 ...we were ignorant even of the existence of the planet Pluto. 00:23:41.239 --> 00:23:43.574 Its moon, Charon, remained undiscovered until 1978. 00:23:43.574 --> 00:23:48.446 Since the discovery of Kuiper Belt objects in 1992, Pluto has come to be seen... 00:23:48.446 --> 00:23:51.149 ...as the largest member of this population of comets. 00:23:51.149 --> 00:23:51.516 The rings of Uranus were first detected in 1977. 00:23:51.516 --> 00:23:55.820 Many astronomers no longer regard it as a planet. 00:23:55.820 --> 00:24:03.127 There are new worlds to chart even this close to home. 00:24:03.127 --> 00:24:06.664 Saturn is a giant gas world. 00:24:06.664 --> 00:24:08.833 If it has a solid surface... 00:24:08.833 --> 00:24:14.272 ...it must lie far below the clouds we see. 00:24:14.272 --> 00:24:16.407 Saturn's majestic rings... 00:24:16.407 --> 00:24:25.550 ...are made of trillions of orbiting snowballs. 00:24:25.550 --> 00:24:29.787 We are now only 80 light minutes from home. 00:24:29.787 --> 00:24:47.105 A mere 1 1/2 billion kilometers. 00:24:47.105 --> 00:24:51.175 The largest planet in our solar system is Jupiter. 00:24:51.175 --> 00:24:55.713 On its dark side, super bolts of lightning illuminate the clouds... 00:24:55.713 --> 00:25:12.764 ...as first revealed by the Voyager spacecraft in 1979. 00:25:12.764 --> 00:25:14.799 Inside the orbit of Jupiter... 00:25:14.799 --> 00:25:18.603 ...are countless shattered and broken world-lets: 00:25:18.603 --> 00:25:20.405 The asteroids. 00:25:20.405 --> 00:25:22.707 These reefs and shoals... 00:25:22.707 --> 00:25:26.077 ...mark the border of the realm of giant planets. 00:25:26.077 --> 00:25:32.216 We are now entering the shallows of the solar system. 00:25:32.216 --> 00:25:36.754 Here there are worlds with thin atmospheres and solid surfaces: 00:25:36.754 --> 00:25:38.289 Earth-like planets... 00:25:38.289 --> 00:25:42.527 ...with landscapes crying out for careful exploration. 00:25:42.527 --> 00:25:47.999 This world is Mars. 00:25:47.999 --> 00:25:51.702 In 1976, after a year's voyage... 00:25:51.702 --> 00:25:54.405 ...two robot explorers from Earth... 00:25:54.405 --> 00:25:58.876 ...landed on this alien shore. 00:25:58.876 --> 00:26:02.680 On Mars, there is a volcano as wide as Arizona... 00:26:02.680 --> 00:26:05.650 ...and almost three times the height of Mount Everest. 00:26:05.650 --> 00:26:13.491 We've named it Mount Olympus. 00:26:13.491 --> 00:26:18.096 This is a world of wonders. 00:26:18.096 --> 00:26:20.932 Mars is a planet with ancient river valleys... 00:26:20.932 --> 00:26:33.077 ...and violent sandstorms driven by winds at half the speed of sound. 00:26:33.077 --> 00:26:38.116 There is a giant rift in its surface 5000 kilometers long. 00:26:38.116 --> 00:26:41.786 It's called Vallis Marinaris. 00:26:41.786 --> 00:26:44.322 The valley of the Mariner spacecraft... 00:26:44.322 --> 00:27:06.744 ...that came to explore Mars from a nearby world. 00:27:06.744 --> 00:27:10.214 In this, our first cosmic voyage... 00:27:10.214 --> 00:27:13.251 ...we have just begun the reconnaissance of Mars... 00:27:13.251 --> 00:27:16.921 ...and all those other planets and stars and galaxies. 00:27:16.921 --> 00:27:28.733 In voyages to come, we will explore them more fully. 00:27:28.733 --> 00:27:32.603 But now, we travel the few remaining light minutes... 00:27:32.603 --> 00:27:37.742 ...to a blue and cloudy world, third from the sun. 00:27:37.742 --> 00:27:40.011 The end of our long journey... 00:27:40.011 --> 00:27:42.747 ...is the world where we began. 00:27:42.747 --> 00:27:44.782 Our travels allow us... 00:27:44.782 --> 00:27:47.251 ...to see the Earth anew... 00:27:47.251 --> 00:27:52.757 ...as if we came from somewhere else. 00:27:52.757 --> 00:27:55.593 There are a hundred billion galaxies... 00:27:55.593 --> 00:27:58.796 ...and a billion trillion stars. 00:27:58.796 --> 00:28:03.601 Why should this modest planet be the only inhabited world? 00:28:03.601 --> 00:28:08.406 To me, it seems far more likely that the cosmos is brimming over... 00:28:08.406 --> 00:28:10.741 ...with life and intelligence. 00:28:10.741 --> 00:28:13.611 But so far, every living thing... 00:28:13.611 --> 00:28:15.413 ...every conscious being... 00:28:15.413 --> 00:28:18.316 ...every civilization we know anything about... 00:28:18.316 --> 00:28:28.259 ...lived there, on Earth. 00:28:28.259 --> 00:28:30.094 Beneath these clouds... 00:28:30.094 --> 00:28:36.367 ...the drama of the human species has been unfolded. 00:28:36.367 --> 00:28:49.313 We have, at last, come home. 00:28:49.313 --> 00:28:51.849 Welcome to the planet Earth. 00:28:51.849 --> 00:28:54.885 A place with blue nitrogen skies... 00:28:54.885 --> 00:28:56.988 ...oceans of liquid water... 00:28:56.988 --> 00:28:58.522 ...cool forests... 00:28:58.522 --> 00:29:00.124 ...soft meadows. 00:29:00.124 --> 00:29:04.295 A world positively rippling with life. 00:29:04.295 --> 00:29:08.032 In the cosmic perspective, it is, for the moment, unique. 00:29:08.032 --> 00:29:10.868 The only world in which we know with certainty... 00:29:10.868 --> 00:29:15.106 ...that the matter of the cosmos has become alive and aware. 00:29:15.106 --> 00:29:18.142 There must be many such worlds scattered through space... 00:29:18.142 --> 00:29:20.778 ...but our search for them begins here... 00:29:20.778 --> 00:29:24.382 ...with the accumulated wisdom of the men and women of our species... 00:29:24.382 --> 00:29:26.384 ...acquired at great cost... 00:29:26.384 --> 00:30:11.662 ...over a million years. 00:30:11.662 --> 00:30:14.765 There was once a time when our planet seemed immense. 00:30:14.765 --> 00:30:17.468 When it was the only world we could explore. 00:30:17.468 --> 00:30:21.906 Its true size was first worked out in a simple and ingenious way... 00:30:21.906 --> 00:30:32.116 ...by a man who lived here in Egypt, in the third century B.C. 00:30:32.116 --> 00:30:36.587 This tower may have been a communications tower. 00:30:36.587 --> 00:30:40.558 Part of a network running along the North African coast... 00:30:40.558 --> 00:30:45.162 ...by which signal bonfires were used to communicate messages of state. 00:30:45.162 --> 00:30:49.767 It also may have been used as a lighthouse... 00:30:49.767 --> 00:30:53.237 ...a navigational beacon for sailing ships... 00:30:53.237 --> 00:30:55.773 ...out there in the Mediterranean Sea. 00:30:55.773 --> 00:30:58.509 It is about 50 kilometers west... 00:30:58.509 --> 00:31:04.115 ...of what was once one of the great cities of the world, Alexandria. 00:31:04.115 --> 00:31:06.350 In Alexandria, at that time... 00:31:06.350 --> 00:31:09.587 ...there lived a man named Eratosthenes. 00:31:09.587 --> 00:31:14.291 A competitor called him "beta," the second letter of the Greek alphabet... 00:31:14.291 --> 00:31:19.196 ...because, he said, "Eratosthenes was second best in everything." 00:31:19.196 --> 00:31:24.135 But it seems clear, in many fields, Eratosthenes was "alpha." 00:31:24.135 --> 00:31:28.038 He was an astronomer, historian, geographer... 00:31:28.038 --> 00:31:32.109 ...philosopher, poet, theater critic and mathematician. 00:31:32.109 --> 00:31:36.714 He was also the chief librarian of the Great Library of Alexandria. 00:31:36.714 --> 00:31:41.852 And one day while reading a papyrus book in the library... 00:31:41.852 --> 00:31:53.030 ...he came upon a curious account. 00:31:53.030 --> 00:31:55.065 Far to the south, he read... 00:31:55.065 --> 00:31:57.601 ...at the frontier outpost of Syene... 00:31:57.601 --> 00:32:06.076 ...something notable could be seen on the longest day of the year. 00:32:06.076 --> 00:32:07.812 On June 21st... 00:32:07.812 --> 00:32:11.081 ...the shadows of a temple column, or a vertical stick... 00:32:11.081 --> 00:32:19.623 ...would grow shorter as noon approached. 00:32:19.623 --> 00:32:21.459 As the hours crept towards midday... 00:32:21.459 --> 00:32:25.896 ...the sun's rays would slither down the sides of a deep well... 00:32:25.896 --> 00:32:35.339 ...which on other days would remain in shadow. 00:32:35.339 --> 00:32:38.175 And then, precisely at noon... 00:32:38.175 --> 00:32:40.778 ...columns would cast no shadows. 00:32:40.778 --> 00:32:51.455 And the sun would shine directly down into the water of the well. 00:32:51.455 --> 00:32:53.090 At that moment... 00:32:53.090 --> 00:33:00.831 ...the sun was exactly overhead. 00:33:00.831 --> 00:33:05.369 It was an observation that someone else might easily have ignored. 00:33:05.369 --> 00:33:09.440 Sticks, shadows, reflections in wells... 00:33:09.440 --> 00:33:11.375 ...the position of the sun... 00:33:11.375 --> 00:33:13.611 ...simple, everyday matters. 00:33:13.611 --> 00:33:17.047 Of what possible importance might they be? 00:33:17.047 --> 00:33:19.950 But Eratosthenes was a scientist... 00:33:19.950 --> 00:33:23.621 ...and his contemplation of these homely matters changed the world... 00:33:23.621 --> 00:33:26.090 ...in a way, made the world. 00:33:26.090 --> 00:33:30.427 Because Eratosthenes had the presence of mind to experiment... 00:33:30.427 --> 00:33:35.099 ...to actually ask whether back here, near Alexandria... 00:33:35.099 --> 00:33:40.404 ...a stick cast a shadow near noon on June the 21 st. 00:33:40.404 --> 00:33:45.476 And it turns out, sticks do. 00:33:45.476 --> 00:33:48.112 An overly skeptical person might have said... 00:33:48.112 --> 00:33:50.981 ...that the report from Syene was an error. 00:33:50.981 --> 00:33:53.984 But it's an absolutely straightforward observation. 00:33:53.984 --> 00:33:57.354 Why would anyone lie on such a trivial matter? 00:33:57.354 --> 00:34:00.291 Eratosthenes asked himself how it could be... 00:34:00.291 --> 00:34:02.526 ...that at the same moment... 00:34:02.526 --> 00:34:05.396 ...a stick in Syene would cast no shadow... 00:34:05.396 --> 00:34:09.166 ...and a stick in Alexandria, 800 kilometers to the north... 00:34:09.166 --> 00:34:14.805 ...would cast a very definite shadow. 00:34:14.805 --> 00:34:18.909 Here is a map of ancient Egypt. 00:34:18.909 --> 00:34:22.479 I've inserted two sticks, or obelisks. 00:34:22.479 --> 00:34:27.151 One up here in Alexandria and one down here in Syene. 00:34:27.151 --> 00:34:31.188 Now, if at a certain moment each stick casts... 00:34:31.188 --> 00:34:33.958 ...no shadow, no shadow at all... 00:34:33.958 --> 00:34:38.429 ...that's perfectly easy to understand, provided the Earth is flat. 00:34:38.429 --> 00:34:41.832 If the shadow at Syene is at a certain length... 00:34:41.832 --> 00:34:44.468 ...and the shadow at Alexandria is the same length... 00:34:44.468 --> 00:34:47.504 ...that also makes sense on a flat Earth. 00:34:47.504 --> 00:34:50.941 But how could it be, Eratosthenes asked... 00:34:50.941 --> 00:34:55.779 ...that at the same instant there was no shadow at Syene... 00:34:55.779 --> 00:35:01.785 ...and a very substantial shadow at Alexandria? 00:35:01.785 --> 00:35:06.590 The only answer was that the surface of the Earth is curved. 00:35:06.590 --> 00:35:08.125 Not only that... 00:35:08.125 --> 00:35:12.129 ...but the greater the curvature, the bigger the difference... 00:35:12.129 --> 00:35:16.033 ...in the lengths of the shadows. The sun is so far away... 00:35:16.033 --> 00:35:18.669 ...that its rays are parallel when they reach the Earth. 00:35:18.669 --> 00:35:23.140 Sticks at different angles to the sun will cast shadows at different lengths. 00:35:23.140 --> 00:35:26.777 For the observed difference in the shadow lengths... 00:35:26.777 --> 00:35:29.413 ...the distance between Alexandria and Syene... 00:35:29.413 --> 00:35:33.517 ...had to be about seven degrees along the surface of the Earth. 00:35:33.517 --> 00:35:37.621 By that, I mean, if you would imagine these sticks extending... 00:35:37.621 --> 00:35:40.324 ...all the way down to the center of the Earth... 00:35:40.324 --> 00:35:43.627 ...they would there intersect at an angle of seven degrees. 00:35:43.627 --> 00:35:46.997 Well, seven degrees is something like a 50th... 00:35:46.997 --> 00:35:50.768 ...of the full circumference of the Earth, 360 degrees. 00:35:50.768 --> 00:35:55.506 Eratosthenes knew the distance between Alexandria and Syene. 00:35:55.506 --> 00:35:57.675 He knew it was 800 kilometers. 00:35:57.675 --> 00:36:02.479 Why? Because he hired a man to pace out the entire distance... 00:36:02.479 --> 00:36:06.150 ...so that he could perform the calculation I'm talking about. 00:36:06.150 --> 00:36:11.088 Now, 800 kilometers times 50 is 40,000 kilometers. 00:36:11.088 --> 00:36:13.390 That must be the circumference of the Earth. 00:36:13.390 --> 00:36:17.061 That's how far it is to go once around the Earth. 00:36:17.061 --> 00:36:18.729 That's the right answer. 00:36:18.729 --> 00:36:21.265 Eratosthenes' only tools were... 00:36:21.265 --> 00:36:25.669 ...sticks, eyes, feet and brains. 00:36:25.669 --> 00:36:29.406 Plus a zest for experiment. 00:36:29.406 --> 00:36:33.343 With those tools, he correctly deduced the circumference of the Earth... 00:36:33.343 --> 00:36:38.916 ...to high precision with an error of only a few percent. 00:36:38.916 --> 00:36:54.198 That's pretty good figuring for 2200 years ago. 00:36:54.198 --> 00:36:58.135 Then, as now, the Mediterranean was teeming with ships. 00:36:58.135 --> 00:37:02.439 Merchantmen, fishing vessels, naval flotillas. 00:37:02.439 --> 00:37:08.212 But there were also courageous voyages into the unknown. 00:37:08.212 --> 00:37:13.050 400 years before Eratosthenes, Africa was circumnavigated... 00:37:13.050 --> 00:37:16.186 ...by a Phoenician fleet in the employ... 00:37:16.186 --> 00:37:18.455 ...of the Egyptian pharaoh Necho. 00:37:18.455 --> 00:37:19.857 They set sail... 00:37:19.857 --> 00:37:24.595 ...probably in boats as frail and open as these... 00:37:24.595 --> 00:37:27.998 ...out from the Red Sea, down the east coast of Africa... 00:37:27.998 --> 00:37:31.668 ...up into the Atlantic and then back through the Mediterranean. 00:37:31.668 --> 00:37:34.571 That epic journey took three years... 00:37:34.571 --> 00:37:36.907 ...about as long as it takes Voyager... 00:37:36.907 --> 00:37:40.477 ...to journey from Earth to Saturn. 00:37:40.477 --> 00:37:43.313 After Eratosthenes, some may have attempted... 00:37:43.313 --> 00:37:45.883 ...to circumnavigate the Earth. 00:37:45.883 --> 00:37:49.386 But until the time of Magellan, no one succeeded. 00:37:49.386 --> 00:37:52.589 What tales of adventure and daring... 00:37:52.589 --> 00:37:54.925 ...must earlier have been told... 00:37:54.925 --> 00:37:59.463 ...as sailors and navigators, practical men of the world... 00:37:59.463 --> 00:38:02.533 ...gambled their lives on the mathematics... 00:38:02.533 --> 00:38:12.576 ...of a scientist from ancient Alexandria. 00:38:12.576 --> 00:38:16.446 Today, Alexandria shows few traces of its ancient glory... 00:38:16.446 --> 00:38:19.983 ...of the days when Eratosthenes walked its broad avenues. 00:38:19.983 --> 00:38:24.855 Over the centuries, waves of conquerors converted its palaces and temples... 00:38:24.855 --> 00:38:30.961 ...into castles and churches, then into minarets and mosques. 00:38:30.961 --> 00:38:35.566 The city was chosen to be the capital of his empire by Alexander the Great... 00:38:35.566 --> 00:38:40.070 ...on a winter's afternoon in 331 B.C. 00:38:40.070 --> 00:38:43.607 A century later, it had become the greatest city of the world. 00:38:43.607 --> 00:38:53.283 Each successive civilization has left its mark. 00:38:53.283 --> 00:38:59.223 But what now remains of the marvel city of Alexander's dream? 00:38:59.223 --> 00:39:02.326 Alexandria is still a thriving marketplace... 00:39:02.326 --> 00:39:12.069 ...still a crossroads for the peoples of the Near East. 00:39:12.069 --> 00:39:15.439 But once, it was radiant with self-confidence... 00:39:15.439 --> 00:39:24.281 ...certain of its power. 00:39:24.281 --> 00:39:26.583 Can you recapture a vanished epoch... 00:39:26.583 --> 00:39:38.629 ...from a few broken statues and scraps of ancient manuscripts? 00:39:38.629 --> 00:39:42.366 In Alexandria, there was an immense library... 00:39:42.366 --> 00:39:45.202 ...and an associated research institute. 00:39:45.202 --> 00:39:52.976 And in them worked the finest minds in the ancient world. 00:39:52.976 --> 00:39:55.212 (CAN CLUNKS) 00:39:55.212 --> 00:40:09.927 (DOOR SQUEAKS) 00:40:09.927 --> 00:40:12.562 Of that legendary library... 00:40:12.562 --> 00:40:15.332 ...all that survives is this... 00:40:15.332 --> 00:40:18.969 ...dank and forgotten cellar. 00:40:18.969 --> 00:40:23.106 It's in the library annex, the Serapeum... 00:40:23.106 --> 00:40:25.275 ...which was once a temple... 00:40:25.275 --> 00:40:28.612 ...but was later reconsecrated to knowledge. 00:40:28.612 --> 00:40:32.716 These few moldering shelves... 00:40:32.716 --> 00:40:35.352 ...probably once in a basement storage room... 00:40:35.352 --> 00:40:38.422 ...are its only physical remains. 00:40:38.422 --> 00:40:41.491 But this place was once... 00:40:41.491 --> 00:40:44.561 ...the brain and glory... 00:40:44.561 --> 00:40:55.706 ...of the greatest city on the planet Earth. 00:40:55.706 --> 00:40:58.508 If I could travel back into time... 00:40:58.508 --> 00:41:01.945 ...this is the place I would visit. 00:41:01.945 --> 00:41:10.520 The Library of Alexandria at its height, 2000 years ago. 00:41:10.520 --> 00:41:13.156 Here, in an important sense... 00:41:13.156 --> 00:41:24.067 ...began the intellectual adventure which has led us into space. 00:41:24.067 --> 00:41:35.112 All the knowledge in the ancient world was once within these marble walls. 00:41:35.112 --> 00:41:38.782 In the great hall, there may have been a mural of Alexander... 00:41:38.782 --> 00:41:42.219 ...with the crook and flail and ceremonial headdress... 00:41:42.219 --> 00:41:48.458 ...of the pharaohs of ancient Egypt. 00:41:48.458 --> 00:41:52.162 This library was a citadel of human consciousness... 00:41:52.162 --> 00:41:59.603 ...a beacon on our journey to the stars. 00:41:59.603 --> 00:42:04.741 It was the first true research institute in the history of the world. 00:42:04.741 --> 00:42:06.977 And what did they study? 00:42:06.977 --> 00:42:11.114 They studied everything. The entire cosmos. 00:42:11.114 --> 00:42:15.719 "Cosmos" is a Greek word for the order of the universe. 00:42:15.719 --> 00:42:19.056 In a way, it's the opposite of chaos. 00:42:19.056 --> 00:42:24.394 It implies a deep interconnectedness of all things. 00:42:24.394 --> 00:42:30.767 The intricate and subtle way that the universe is put together. 00:42:30.767 --> 00:42:33.670 Genius flourished here. 00:42:33.670 --> 00:42:38.208 In addition to Eratosthenes, there was the astronomer Hipparchus... 00:42:38.208 --> 00:42:40.177 ...who mapped the constellation... 00:42:40.177 --> 00:42:43.880 ...and established the brightness of the stars. 00:42:43.880 --> 00:42:46.149 And there was Euclid... 00:42:46.149 --> 00:42:49.186 ...who brilliantly systematized geometry... 00:42:49.186 --> 00:42:51.755 ...who told his king, who was struggling... 00:42:51.755 --> 00:42:54.591 ...with some difficult problem in mathematics... 00:42:54.591 --> 00:42:59.496 ...that there was no royal road to geometry. 00:42:59.496 --> 00:43:02.399 There was Dionysius of Thrace, the man who defined... 00:43:02.399 --> 00:43:06.069 ...the parts of speech: nouns, verbs and so on... 00:43:06.069 --> 00:43:10.207 ...who did for language, in a way, what Euclid did for geometry. 00:43:10.207 --> 00:43:14.444 There was Herophilus, a physiologist who identified... 00:43:14.444 --> 00:43:18.648 ...the brain rather than the heart as the seat of intelligence. 00:43:18.648 --> 00:43:21.551 There was Archimedes, the greatest mechanical genius... 00:43:21.551 --> 00:43:23.954 ...until the time of Leonardo da Vinci. 00:43:23.954 --> 00:43:28.892 And there was the astronomer Ptolemy, who compiled much of what today is... 00:43:28.892 --> 00:43:31.361 ...the pseudoscience of astrology. 00:43:31.361 --> 00:43:33.897 His Earth-centered universe... 00:43:33.897 --> 00:43:36.766 ...held sway for 1500 years... 00:43:36.766 --> 00:43:40.403 ...showing that intellectual brilliance is no guarantee... 00:43:40.403 --> 00:43:42.973 ...against being dead wrong. 00:43:42.973 --> 00:43:47.177 And among these great men, there was also a great woman. 00:43:47.177 --> 00:43:49.579 Her name was Hypatia. 00:43:49.579 --> 00:43:52.649 She was a mathematician and an astronomer... 00:43:52.649 --> 00:43:54.851 ...the last light of the library... 00:43:54.851 --> 00:43:59.956 ...whose martyrdom is bound up with the destruction of this place... 00:43:59.956 --> 00:44:21.645 ...seven centuries after it was founded. 00:44:21.645 --> 00:44:25.115 Look at this place. 00:44:25.115 --> 00:44:28.218 The Greek kings of Egypt who succeeded Alexander... 00:44:28.218 --> 00:44:31.755 ...regarded advances in science, literature and medicine... 00:44:31.755 --> 00:44:34.224 ...as among the treasures of the empire. 00:44:34.224 --> 00:44:38.895 For centuries, they generously supported research and scholarship. 00:44:38.895 --> 00:44:46.136 An enlightenment shared by few heads of state, then or now. 00:44:46.136 --> 00:44:52.776 (FOUNTAIN GURGLES) 00:44:52.776 --> 00:44:56.947 Off this great hall were 10 large research laboratories. 00:44:56.947 --> 00:45:01.284 There were fountains and colonnades, botanical gardens... 00:45:01.284 --> 00:45:05.855 ...and even a zoo with animals from India and sub-Saharan Africa. 00:45:05.855 --> 00:45:12.562 There were dissecting rooms and an astronomical observatory. 00:45:12.562 --> 00:45:14.598 But the treasure of the library... 00:45:14.598 --> 00:45:18.068 ...consecrated to the god Serapis... 00:45:18.068 --> 00:45:21.071 ...built in the city of Alexander... 00:45:21.071 --> 00:45:23.106 ...was its collection of books. 00:45:23.106 --> 00:45:25.508 The organizers of the library combed... 00:45:25.508 --> 00:45:28.945 ...all the cultures and languages of the world for books. 00:45:28.945 --> 00:45:32.515 They sent agents abroad to buy up libraries. 00:45:32.515 --> 00:45:37.687 Commercial ships docking in Alexandria harbor were searched by the police... 00:45:37.687 --> 00:45:40.323 ...not for contraband, but for books. 00:45:40.323 --> 00:45:44.094 The scrolls were borrowed, copied and returned to their owners. 00:45:44.094 --> 00:45:48.365 Until studied, these scrolls were collected in great stacks... 00:45:48.365 --> 00:45:51.935 ...called, "books from the ships." 00:45:51.935 --> 00:45:54.571 Accurate numbers are difficult to come by... 00:45:54.571 --> 00:45:57.774 ...but it seems that the library contained at its peak... 00:45:57.774 --> 00:46:14.424 ...nearly one million scrolls. 00:46:14.424 --> 00:46:18.061 The papyrus reed grows in Egypt. 00:46:18.061 --> 00:46:20.463 It's the origin of our word for "paper." 00:46:20.463 --> 00:46:24.434 Each of those million volumes which once existed in this library... 00:46:24.434 --> 00:46:29.839 ...were handwritten on papyrus manuscript scrolls. 00:46:29.839 --> 00:46:31.908 What happened to all those books? 00:46:31.908 --> 00:46:35.545 The classical civilization that created them disintegrated. 00:46:35.545 --> 00:46:38.248 The library itself was destroyed. 00:46:38.248 --> 00:46:41.618 Only a small fraction of the works survived. 00:46:41.618 --> 00:46:44.954 And as for the rest, we're left only with pathetic... 00:46:44.954 --> 00:46:47.457 ...scattered fragments. 00:46:47.457 --> 00:46:51.928 But how tantalizing those remaining bits and pieces are. 00:46:51.928 --> 00:46:55.799 For example, we know that there once existed here... 00:46:55.799 --> 00:47:00.337 ...a book by the astronomer Aristarchus of Samos... 00:47:00.337 --> 00:47:04.674 ...who apparently argued that the Earth was one of the planets... 00:47:04.674 --> 00:47:08.378 ...that, like the other planets, it orbits the sun... 00:47:08.378 --> 00:47:13.116 ...and that the stars are enormously far away. 00:47:13.116 --> 00:47:15.785 All absolutely correct. 00:47:15.785 --> 00:47:18.621 But we had to wait nearly 2000 years... 00:47:18.621 --> 00:47:28.865 ...for these facts to be rediscovered. 00:47:28.865 --> 00:47:33.470 The astronomy stacks of the Alexandria Library. 00:47:33.470 --> 00:47:35.739 Hipparchus. 00:47:35.739 --> 00:47:39.743 Ptolomeus. Here we are. 00:47:39.743 --> 00:47:43.646 Aristarchus. 00:47:43.646 --> 00:47:45.315 This is the book. 00:47:45.315 --> 00:47:48.885 How I'd love to be able to read this book... 00:47:48.885 --> 00:47:52.055 ...to know how Aristarchus figured it out. 00:47:52.055 --> 00:47:55.892 But it's gone. Utterly and forever. 00:47:55.892 --> 00:48:00.463 If we multiply our sense of loss for this work of Aristarchus... 00:48:00.463 --> 00:48:02.065 ...by 100,000... 00:48:02.065 --> 00:48:04.734 ...we begin to appreciate the grandeur... 00:48:04.734 --> 00:48:07.804 ...of the achievement of classical civilization... 00:48:07.804 --> 00:48:14.177 ...and the tragedy of its destruction. 00:48:14.177 --> 00:48:18.915 We have far surpassed the science known to the ancient world... 00:48:18.915 --> 00:48:22.752 ...but there are irreparable gaps in our historical knowledge. 00:48:22.752 --> 00:48:26.322 Imagine what mysteries of the past could be solved... 00:48:26.322 --> 00:48:28.958 ...with a borrower's card to this library. 00:48:28.958 --> 00:48:33.396 For example, we know of a three-volume history of the world... 00:48:33.396 --> 00:48:38.101 ...now lost, written by a Babylonian priest named Berossus. 00:48:38.101 --> 00:48:41.938 Volume I dealt with the interval from the creation of the world... 00:48:41.938 --> 00:48:43.306 ...to the Great Flood. 00:48:43.306 --> 00:48:47.577 A period that he took to be 432,000 years... 00:48:47.577 --> 00:48:51.514 ...or about 100 times longer than the Old Testament chronology. 00:48:51.514 --> 00:48:56.519 What wonders were in the books of Berossus! 00:48:56.519 --> 00:49:00.757 But why have I brought you across 2000 years... 00:49:00.757 --> 00:49:03.760 ...to the Library of Alexandria? 00:49:03.760 --> 00:49:07.263 Because this was when and where we humans... 00:49:07.263 --> 00:49:11.568 ...first collected seriously and systematically... 00:49:11.568 --> 00:49:13.803 ...the knowledge of the world. 00:49:13.803 --> 00:49:16.506 This is the Earth as Eratosthenes knew it. 00:49:16.506 --> 00:49:19.976 A tiny, spherical world, afloat... 00:49:19.976 --> 00:49:23.446 ...in an immensity of space and time. 00:49:23.446 --> 00:49:26.349 We were, at long last, beginning to find... 00:49:26.349 --> 00:49:30.053 ...our true bearings in the cosmos. 00:49:30.053 --> 00:49:32.121 The scientists of antiquity... 00:49:32.121 --> 00:49:35.925 ...took the first and most important steps in that direction... 00:49:35.925 --> 00:49:38.995 ...before their civilization fell apart. 00:49:38.995 --> 00:49:42.065 But after the Dark Ages, it was by and large... 00:49:42.065 --> 00:49:46.202 ...the rediscovery of the works of these scholars done here... 00:49:46.202 --> 00:49:48.605 ...that made the Renaissance possible... 00:49:48.605 --> 00:49:51.875 ...and thereby powerfully influenced our own culture. 00:49:51.875 --> 00:49:55.311 When, in the 15th century, Europe was at last ready... 00:49:55.311 --> 00:49:58.314 ...to awaken from its long sleep... 00:49:58.314 --> 00:50:02.785 ...it picked up some of the tools, the books and the concepts... 00:50:02.785 --> 00:50:12.262 ...laid down here more than a thousand years before. 00:50:12.262 --> 00:50:16.366 By 1600, the long-forgotten ideas of Aristarchus... 00:50:16.366 --> 00:50:18.668 ...had been rediscovered. 00:50:18.668 --> 00:50:22.138 Johannes Kepler constructed elaborate models... 00:50:22.138 --> 00:50:25.241 ...to understand the motion and arrangement of the planets... 00:50:25.241 --> 00:50:32.015 ...the clockwork of the heavens. 00:50:32.015 --> 00:50:46.563 And at night, he dreamt of traveling to the moon. 00:50:46.563 --> 00:50:48.965 His principal scientific tools were... 00:50:48.965 --> 00:50:51.968 ...the mathematics of the Alexandrian Library... 00:50:51.968 --> 00:50:54.604 ...and an unswerving respect for the facts... 00:50:54.604 --> 00:51:01.444 ...however disquieting they might be. 00:51:01.444 --> 00:51:05.081 His story, and the story of the scientists who came after him... 00:51:05.081 --> 00:51:09.886 ...are also part of our voyage. 00:51:09.886 --> 00:51:13.056 Seventy years later, the sun-centered universe... 00:51:13.056 --> 00:51:14.857 ...of Aristarchus and Copernicus... 00:51:14.857 --> 00:51:18.928 ...was widely accepted in the Europe of the Enlightenment. 00:51:18.928 --> 00:51:22.565 The idea arose that the planets were worlds... 00:51:22.565 --> 00:51:24.400 ...governed by laws of nature... 00:51:24.400 --> 00:51:28.838 ...and scientific speculation turned to the motions of the stars. 00:51:28.838 --> 00:51:31.674 The clockwork in the heavens was imitated... 00:51:31.674 --> 00:51:34.043 ...by the watchmakers of Earth. 00:51:34.043 --> 00:51:37.747 Precise timekeeping permitted great sailing ship voyages... 00:51:37.747 --> 00:51:40.483 ...of exploration and discovery... 00:51:40.483 --> 00:51:44.487 ...which bound up the Earth. 00:51:44.487 --> 00:51:47.023 This was a time when free inquiry... 00:51:47.023 --> 00:51:49.192 ...was valued once again. 00:51:49.192 --> 00:51:55.898 (SPEAKING IN FOREIGN LANGUAGE) 00:51:55.898 --> 00:51:59.502 250 years later, the Earth was all explored. 00:51:59.502 --> 00:52:03.406 New adventurers now looked to the planets and the stars. 00:52:03.406 --> 00:52:07.276 The galaxies were recognized as great aggregates of stars... 00:52:07.276 --> 00:52:12.115 ...island universes millions of light years away. 00:52:12.115 --> 00:52:15.451 In the 1920s, astronomers had begun to measure... 00:52:15.451 --> 00:52:22.959 ...the speeds of distant galaxies. 00:52:22.959 --> 00:52:24.127 ASTRONOMER 1: What time is it? 00:52:24.127 --> 00:52:26.262 7:15. 00:52:26.262 --> 00:52:28.398 ASTRONOMER 1: Lights off, please. 00:52:28.398 --> 00:52:33.236 They found that the galaxies were flying away from one another. 00:52:33.236 --> 00:52:35.338 To the astonishment of everyone... 00:52:35.338 --> 00:52:44.380 ...the entire universe was expanding. 00:52:44.380 --> 00:52:51.621 We had begun to plumb the true depths of time and space. 00:52:51.621 --> 00:52:54.524 The long, collective enterprise of science... 00:52:54.524 --> 00:52:59.028 ...has revealed a universe some 15 billion years old. 00:52:59.028 --> 00:53:02.231 The time since the explosive birth of the cosmos... 00:53:02.231 --> 00:53:03.466 ...the big bang. 00:53:03.466 --> 00:53:03.833 The current estimates for the age of the universe range from 12 to 15 billion years. 00:53:03.833 --> 00:53:09.972 (THUNDER CRASHES) 00:53:09.972 --> 00:53:14.210 The cosmic calendar compresses the local history of the universe... 00:53:14.210 --> 00:53:16.145 ...into a single year. 00:53:16.145 --> 00:53:18.915 If the universe began on January 1st... 00:53:18.915 --> 00:53:23.052 ...it was not until May that the Milky Way formed. 00:53:23.052 --> 00:53:26.022 Other planetary systems may have appeared... 00:53:26.022 --> 00:53:29.192 ...in June, July and August... 00:53:29.192 --> 00:53:32.128 ...but our sun and Earth, not until mid-September. 00:53:32.128 --> 00:53:35.364 Life arose soon after. 00:53:35.364 --> 00:53:39.635 Everything humans have ever done occurred in that bright speck... 00:53:39.635 --> 00:53:45.341 ...at the lower right of the cosmic calendar. 00:53:45.341 --> 00:53:47.543 The big bang is at upper left... 00:53:47.543 --> 00:53:50.513 ...in the first second of January 1st. 00:53:50.513 --> 00:53:54.417 Fifteen billion years later is our present time... 00:53:54.417 --> 00:54:02.759 ...the last second of December 31st. 00:54:02.759 --> 00:54:06.195 Every month is 1ΕΊ billion years long. 00:54:06.195 --> 00:54:09.298 Each day represents 40 million years. 00:54:09.298 --> 00:54:13.236 Each second stands for some 500 years of our history. 00:54:13.236 --> 00:54:22.845 The blinking of an eye in the drama of cosmic time. 00:54:22.845 --> 00:54:27.517 At this scale, the cosmic calendar is the size of a football field... 00:54:27.517 --> 00:54:30.887 ...but all of human history would occupy an area... 00:54:30.887 --> 00:54:32.722 ...the size of my hand. 00:54:32.722 --> 00:54:36.392 We're just beginning to trace the long and tortuous path... 00:54:36.392 --> 00:54:39.328 ...which began with the primeval fireball... 00:54:39.328 --> 00:54:42.231 ...and led to the condensation of matter: 00:54:42.231 --> 00:54:45.067 Gas, dust, stars, galaxies, and... 00:54:45.067 --> 00:54:47.637 ...at least in our little nook of the universe... 00:54:47.637 --> 00:54:52.141 ...planets, life, intelligence and inquisitive men and women. 00:54:52.141 --> 00:54:53.943 We've emerged so recently... 00:54:53.943 --> 00:54:57.013 ...that the familiar events of our recorded history... 00:54:57.013 --> 00:55:01.450 ...occupy only the last seconds of the last minute of December 31st. 00:55:01.450 --> 00:55:05.288 But some critical events for the human species began much earlier... 00:55:05.288 --> 00:55:08.324 ...minutes earlier. 00:55:08.324 --> 00:55:11.928 So we change our scale from months to minutes. 00:55:11.928 --> 00:55:15.298 Down here, the first humans made their debut... 00:55:15.298 --> 00:55:21.671 ...around 10:30 p.m. on December 31st. 00:55:21.671 --> 00:55:24.207 And with the passing of every cosmic minute... 00:55:24.207 --> 00:55:26.475 ...each minute 30,000 years long... 00:55:26.475 --> 00:55:29.011 ...we began the arduous journey towards understanding... 00:55:29.011 --> 00:55:34.517 ...where we live and who we are. 00:55:34.517 --> 00:55:36.819 11:46... 00:55:36.819 --> 00:55:39.655 ...only 14 minutes ago... 00:55:39.655 --> 00:55:43.359 ...humans have tamed fire. 00:55:43.359 --> 00:55:48.364 11:59:20, the evening of the last day of the cosmic year... 00:55:48.364 --> 00:55:52.401 ...the 11th hour, the 59th minute, the 20th second... 00:55:52.401 --> 00:55:55.471 ...the domestication of plants and animals begins: 00:55:55.471 --> 00:56:01.244 An application of the human talent... 00:56:01.244 --> 00:56:10.186 ...for making tools. 00:56:10.186 --> 00:56:14.891 11:59:35, settled agricultural communities... 00:56:14.891 --> 00:56:18.561 ...evolved into the first cities. 00:56:18.561 --> 00:56:22.865 We humans appear on the comic calendar so recently... 00:56:22.865 --> 00:56:25.468 ...that our recorded history occupies only... 00:56:25.468 --> 00:56:31.140 ...the last few seconds of the last minute of December 31 st. 00:56:31.140 --> 00:56:36.112 In the vast ocean of time which this calendar represents... 00:56:36.112 --> 00:56:41.651 ...all our memories are confined... 00:56:41.651 --> 00:56:44.253 ...to this small square. 00:56:44.253 --> 00:56:49.558 Every person we've ever heard of lived somewhere in there. 00:56:49.558 --> 00:56:54.931 All those kings and battles, migrations and inventions, wars and loves. 00:56:54.931 --> 00:56:56.899 Everything in the history books... 00:56:56.899 --> 00:56:59.702 ...happens here... 00:56:59.702 --> 00:57:08.377 ...in the last 10 seconds of the cosmic calendar. 00:57:08.377 --> 00:57:11.080 We on Earth have just awakened... 00:57:11.080 --> 00:57:14.083 ...to the great oceans of space and time... 00:57:14.083 --> 00:57:17.353 ...from which we have emerged. 00:57:17.353 --> 00:57:19.121 We are the legacy... 00:57:19.121 --> 00:57:23.259 ...of 15 billion years of cosmic evolution. 00:57:23.259 --> 00:57:25.261 We have a choice: 00:57:25.261 --> 00:57:28.965 We can enhance life and come to know the universe that made us... 00:57:28.965 --> 00:57:32.401 ...or we can squander our 15 billion-year heritage... 00:57:32.401 --> 00:57:36.572 ...in meaningless self-destruction. 00:57:36.572 --> 00:57:39.976 What happens in the first second of the next cosmic year... 00:57:39.976 --> 00:57:43.346 ...depends on what we do, here and now... 00:57:43.346 --> 00:57:45.348 ...with our intelligence... 00:57:45.348 --> 99:59:59.999 ...and our knowledge of the cosmos.