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#CarlSagan covers a wide range of scientific subjects, including the origin of life and a perspective of our place in the universe.
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00:00:00Hello, my name is Anne Drian.
00:00:11When Carl Sagan, Steven Soder, and I wrote the Cosmos television series in the late 1970s,
00:00:17a lot of things were different.
00:00:19Back then, the United States and the Soviet Union held the whole planet
00:00:22in a perpetual hostage crisis called the Cold War.
00:00:26The wealth and scientific ingenuity of our civilization was being squandered
00:00:31on a runaway arms race that employed more than half the world's scientists
00:00:35and infested the Earth with 50,000 nuclear weapons.
00:00:41So much has happened since then.
00:00:43The Cold War is history, and science has made great strides.
00:00:48We've completed the spacecraft reconnaissance of the solar system,
00:00:52the preliminary mapping of the visible universe that surrounds us,
00:00:56and we've charted the universe within, the human genome.
00:01:01When Cosmos was first broadcast, there was no World Wide Web.
00:01:05It was a different world.
00:01:07What a tribute to Carl Sagan,
00:01:09a scientist who took many a punch for daring to speculate
00:01:13that even after twenty of the most eventful years in the history of science,
00:01:18Cosmos requires few revisions and indeed is rich in prophecy.
00:01:24Cosmos is both a history of the scientific enterprise
00:01:28and an attempt to convey the soaring spiritual high of its central revelation,
00:01:34our oneness with the universe.
00:01:37Now, please, enjoy Cosmos, the proud saga of how,
00:01:41through the searching of 40,000 generations of our ancestors,
00:01:46we have come to discover our coordinates in space and in time,
00:01:51and how, through the awesomely powerful method of science,
00:01:56we have been able to reconstruct the sweep of cosmic evolution
00:02:00and to find our own part in its great story.
00:02:05.
00:06:38Drawn by the music of cosmic harmonies, it can take us anywhere in space and time.
00:06:44Perfect as a snowflake, organic as a dandelion seed, it will carry us to worlds of dreams and worlds of facts.
00:06:56Come with me.
00:07:08Before us is the cosmos on the grandest scale we know.
00:07:18We are far from the shores of Earth, in the uncharted reaches of the cosmic ocean.
00:07:25Strewn like sea froth on the waves of space are innumerable faint tendrils of light,
00:07:31some of them containing hundreds of billions of suns.
00:07:38These are the galaxies, drifting endlessly in the great cosmic dark.
00:07:47In our ship of the imagination, we are halfway to the edge of the known universe.
00:07:53In this, the first of our cosmic voyages, we begin to explore the universe revealed by science.
00:08:10Our course will eventually carry us to a far-off and exotic world.
00:08:23But from the depths of space, we cannot detect even the cluster of galaxies in which our Milky Way is embedded,
00:08:30much less the sun or the Earth.
00:08:32We are in the realm of the galaxies, 8 billion light-years from home.
00:08:54No matter where we travel, the patterns of nature are the same as in the form of this spiral galaxy.
00:09:07The same laws of physics apply everywhere, throughout the cosmos.
00:09:15But we have just begun to understand these laws.
00:09:24The universe is rich in mystery.
00:09:27Near the center of a cluster of galaxies, there's sometimes a rogue, elliptical galaxy made of a trillion suns,
00:09:41which devours its neighbors.
00:09:44Perhaps this cyclone of stars is what astronomers on Earth call a quasar.
00:09:49Our ordinary measures of distance fail us here in the realm of the galaxies.
00:10:12We need a much larger unit, the light-year.
00:10:15It measures how far light travels in a year, nearly 10 trillion kilometers.
00:10:21It measures not time, but enormous distances.
00:10:24In the Hercules cluster, the individual galaxies are about 300,000 light-years apart.
00:10:46So light takes about 300,000 years to go from one galaxy to another.
00:10:54Like stars and planets and people, galaxies are born, live, and die.
00:11:05They may all experience a tumultuous adolescence.
00:11:09During their first hundred million years, their cores may explode.
00:11:13Seen in radio light, great jets of energy pour out and echo across the cosmos.
00:11:19Worlds near the core, or along the jets, would be incinerated.
00:11:26I wonder how many planets and how many civilizations might be destroyed.
00:11:31In the Pegasus cluster, there's a ring galaxy, the wreckage left from the collision of two galaxies,
00:11:47a splash in the cosmic pond.
00:11:51Individual galaxies may explode and collide, and their constituent stars may blow up as well.
00:11:58In this supernova explosion, a single star outshines the rest of its galaxy.
00:12:05We are approaching what astronomers on Earth call the local group.
00:12:16Three million light-years across, it contains some 20 galaxies.
00:12:22It's a sparse and rather typical chain of islands in the immense cosmic ocean.
00:12:28We are now only two million light-years from home.
00:12:35On the maps of space, this galaxy is called M31, the great galaxy in Andromeda.
00:12:41It's a vast storm of stars and gas and dust.
00:12:45As we pass over it, we see one of its small satellite galaxies.
00:12:49Clusters of galaxies and the stars of individual galaxies are all held together by gravity.
00:13:02Surrounding M31 are hundreds of globular star clusters.
00:13:08We're approaching one of them.
00:13:11Each cluster orbits the massive center of the galaxy.
00:13:15Some contain up to a million separate stars.
00:13:18Every globular cluster is like a swarm of bees bound by gravity.
00:13:25Every bee, a sun.
00:13:30From the Pegasus cluster, our voyage has taken us 200 million light-years
00:13:34to the local group, dominated by two great spiral galaxies.
00:13:42Beyond M31 is another very similar galaxy.
00:13:46Its spiral arms slowly turning once every quarter billion years.
00:13:57This is our own Milky Way, seen from the outside.
00:14:03This is the home galaxy of the human species.
00:14:14In the obscure backwaters of the Carina Cygnus spiral arm,
00:14:27we humans have evolved to consciousness and some measure of understanding.
00:14:33Concentrated in its brilliant core and strewn along its spiral arms are 400 billion suns.
00:14:52It takes light 100,000 years to travel from one end of the galaxy to the other.
00:15:02Within this galaxy are stars and worlds,
00:15:06and it may be an enormous diversity of living things
00:15:11and intelligent beings and space-faring civilizations.
00:15:24Scattered among the stars of Milky Way are supernova remnants,
00:15:29each one the remains of a colossal stellar explosion.
00:15:32These filaments of glowing gas are the outer layers of a star which has recently destroyed itself.
00:15:39The gas is unraveling, returning star stuff back into space.
00:15:45And at its heart are the remains of the original star,
00:15:53a dense, shrunken, stellar fragment called a pulsar,
00:15:58a natural lighthouse, blinking and hissing,
00:16:02a sun that spins twice each second.
00:16:04Pulsars keep such perfect time that the first one discovered
00:16:14was thought to be a sign of extraterrestrial intelligence,
00:16:18perhaps a navigational beacon for great ships
00:16:21that travel across the light years and between the stars.
00:16:25There may be such intelligences and such starships,
00:16:33but pulsars are not their signature.
00:16:47Instead, they are the doleful reminders
00:16:50that nothing lasts forever,
00:16:52that stars also die.
00:16:57We continue to plummet,
00:16:59falling thousands of light years
00:17:01towards the plane of the galaxy.
00:17:06This is the Milky Way,
00:17:09our galaxy seen edge on,
00:17:11billions of nuclear furnaces
00:17:13converting matter into starlight.
00:17:16Some stars are flimsy as a soap bubble.
00:17:25Others are a hundred trillion times denser than lead.
00:17:29The hottest stars are destined to die young.
00:17:33But red giants are mostly elderly.
00:17:37Such stars are unlikely to have inhabited planets.
00:17:40But yellow dwarf stars,
00:17:45like the sun,
00:17:46are middle-aged,
00:17:48and they are far more common.
00:17:51These stars may have planetary systems,
00:17:54and on such planets,
00:17:55for the first time in our cosmic voyage,
00:17:58we encounter rare forms of matter,
00:18:01ice and rock,
00:18:03air and liquid water.
00:18:04Close to this yellow star
00:18:12is a small, warm, cloudy world
00:18:15with continents and oceans.
00:18:18These conditions
00:18:18permit an even more precious form of matter
00:18:22to arise,
00:18:23life.
00:18:23But this is not the Earth.
00:18:34Intelligent beings have evolved
00:18:36and reworked this planetary surface
00:18:38in a massive engineering enterprise.
00:18:42In the Milky Way galaxy,
00:18:43there may be many worlds
00:18:45on which matter has grown to consciousness.
00:18:47I wonder,
00:18:57are they very different from us?
00:18:59What do they look like?
00:19:01What are their politics,
00:19:02technology, music, religion?
00:19:05Or do they have patterns of culture
00:19:07we can't begin to imagine?
00:19:10Are they also a danger to themselves?
00:19:17Among the many glowing clouds
00:19:23of interstellar gas
00:19:24is one called
00:19:26the Orion Nebula,
00:19:28only 1,500 light years from Earth.
00:19:36These three bright stars
00:19:38are seen by Earthlings
00:19:40as the belt
00:19:41in the familiar constellation
00:19:43of Orion the Hunter.
00:19:47The nebula appears from Earth
00:19:53as a patch of light,
00:19:55the middle star
00:19:57in Orion's sword.
00:20:07But it is not a star.
00:20:10It is another thing entirely,
00:20:13a cloud that veils
00:20:15one of nature's secret places.
00:20:17This is a stellar nursery,
00:20:29a place where stars are born.
00:20:32They condense by gravity
00:20:33from gas and dust
00:20:35until their temperatures
00:20:36become so high
00:20:37that they begin to shine.
00:20:40Such clouds mark the births of stars
00:20:43as others bear witness
00:20:44to their deaths.
00:20:52And after stars condense
00:20:54in the hidden interiors
00:20:55of interstellar clouds,
00:20:56what happens to them?
00:20:58The Pleiades
00:20:59are a loose cluster
00:21:01of young stars
00:21:02only 50 million years old.
00:21:04These fledgling stars
00:21:06are just being let out
00:21:08into the galaxy,
00:21:10still surrounded
00:21:11by wisps of nebulosity,
00:21:13the gas and dust
00:21:14from which they formed.
00:21:16The Pleiades
00:21:17and Life
00:21:18and Life
00:21:19and Life
00:21:19and Life
00:21:23are just running
00:21:29thoose
00:21:42There are clouds that hang like inkblots between the stars.
00:21:56They are made of fine rocky dust, organic matter, and ice.
00:22:03Inside, a few stars begin to turn on.
00:22:07Nearby worlds of ice evaporate and form long comet-like tails, driven back by the stellar winds.
00:22:20Black clouds, light-years across, drift between the stars.
00:22:26They're filled with organic molecules.
00:22:29The building blocks of life are everywhere. They're easily made.
00:22:34On how many worlds have such complex molecules assembled themselves into patterns we would call alive?
00:22:43Most stars belong to systems of two or three or many suns bound together by gravity.
00:22:56Each system is isolated from its neighbors by the light-years.
00:23:00We are approaching a single, ordinary yellow dwarf star, surrounded by a system of nine planets, dozens of moons, thousands of asteroids, and billions of comets, the family of the Sun.
00:23:16Only four light hours from Earth is the planet Neptune and its giant satellite, Triton.
00:23:25Even in the outskirts of our own solar system, we humans have barely begun our explorations.
00:23:35Only a century ago, we were ignorant even of the existence of the planet Pluto.
00:23:44Its moon, Charon, remained undiscovered until 1978.
00:23:49The rings of Uranus were first detected in 1977.
00:23:59There are new worlds to chart even this close to home.
00:24:07Saturn is a giant gas world.
00:24:10If it has a solid surface, it must lie far below the clouds we see.
00:24:16Saturn's majestic rings are made of trillions of orbiting snowballs.
00:24:29We are now only 80 light minutes from home.
00:24:33A mere one and a half billion kilometers.
00:24:36The largest planet in our solar system is Jupiter.
00:24:54On its dark side, superbolts of lightning illuminate the clouds, as first revealed by the Voyager spacecraft in 1979.
00:25:03Inside the orbit of Jupiter are countless shattered and broken worldlets, the asteroids.
00:25:22These reefs and shoals mark the border of the realm of giant planets.
00:25:29We are now entering the shallows of the solar system.
00:25:33Here there are worlds with thin atmospheres and solid surfaces, Earth-like planets, with landscapes crying out for careful exploration.
00:25:45This world is Mars.
00:25:48In 1976, after a year's voyage, two robot explorers from Earth landed on this alien shore.
00:26:00On Mars, there is a volcano as wide as Arizona and almost three times the height of Mount Everest.
00:26:09We've named it Mount Olympus.
00:26:12This is a world of wonders.
00:26:19Mars is a planet with ancient river valleys and violent sandstorms driven by winds at half the speed of sand.
00:26:28There is a giant rift in its surface, 5,000 kilometers long.
00:26:41It's called Valles Marineris, the valley of the Mariner spacecraft that came to explore Mars from a nearby world.
00:26:51In this, our first cosmic voyage, we have just begun the reconnaissance of Mars and all those other planets and stars and galaxies.
00:27:20In voyages to come, we will explore them more fully.
00:27:32But now, we travel the few remaining light minutes to a blue and cloudy world, third from the sun.
00:27:41The end of our long journey is the world where we began.
00:27:45Our travels allow us to see the Earth anew as if we came from somewhere else.
00:27:57There are a hundred billion galaxies and a billion trillion stars.
00:28:02Why should this modest planet be the only inhabited world?
00:28:07To me, it seems far more likely that the cosmos is brimming over with life and intelligence.
00:28:14But so far, every living thing, every conscious being, every civilization we know anything about, lived there, on Earth.
00:28:28And so far, every living thing is the only thing that we need.
00:28:32Beneath these clouds, the drama of the human species has been unfolding.
00:28:40We have at last come home.
00:28:42come home.
00:28:53Welcome to the planet Earth, a place with blue nitrogen skies, oceans of liquid water,
00:29:01cool forests, soft meadows, a world positively rippling with life.
00:29:07In the cosmic perspective, it is for the moment unique.
00:29:12The only world in which we know with certainty that the matter of the cosmos has become alive
00:29:17and aware.
00:29:18There must be many such worlds scattered through space, but our search for them begins here,
00:29:24with the accumulated wisdom of the men and women of our species, acquired at great cost
00:29:30over a million years.
00:29:50There was once a time when our little planet seemed immense, when it was the only world
00:29:57we could explore.
00:29:58Its two size was first worked out in a simple and ingenious way, by a man who lived here
00:30:04in Egypt in the third century BC.
00:30:11in the third century BC.
00:30:18This tower may have been a communications tower, part of a network running along the North African
00:30:25coast, by which signal bonfires were used to communicate messages of state.
00:30:30It also may have been used as a lighthouse, a navigational beacon for sailing ships out there in the Mediterranean Sea.
00:30:45It is about 50 kilometers west of what was once one of the great cities of the world, Alexandria.
00:31:04In Alexandria, at that time, there lived a man named Eratosthenes.
00:31:12One of his envious contemporaries called him Beta, the second letter of the Greek alphabet,
00:31:17because, he said, Eratosthenes was second best in the world in everything.
00:31:21But it seems clear that, in many fields, Eratosthenes was Alpha.
00:31:27He was an astronomer, historian, geographer, philosopher, poet, theater critic, and mathematician.
00:31:35He was also the chief librarian of the great library of Alexandria.
00:31:39And, one day, while reading a papyrus book in the library, he came upon a curious account.
00:31:51Far to the south, he read, at the frontier outpost of Syene, something notable could be seen on the longest day of the year.
00:32:09On June 21st, the shadows of a temple column, or a vertical stick, would grow shorter as noon approached.
00:32:21And, as the hours crept towards midday, the sun's rays would slither down the sides of a deep well,
00:32:28which, on other days, would remain in shadow.
00:32:34And then, precisely at noon, columns would cast no shadows,
00:32:43and the sun would shine directly down into the water of the well.
00:32:48At that moment, the sun was exactly overhead.
00:32:58It was an observation that someone else might easily have ignored.
00:33:08Sticks, shadows, reflections in wells, the position of the sun.
00:33:14Simple, everyday matters of what possible importance might they be.
00:33:19But, Eratosthenes was a scientist.
00:33:22And, his contemplation of these homely matters changed the world.
00:33:26In a way, made the world.
00:33:28Because, Eratosthenes had the presence of mind to experiment,
00:33:33to actually ask whether, back here, near Alexandria,
00:33:37a stick cast a shadow, near noon on June 21st.
00:33:43And, it turns out, sticks do.
00:33:46An overly skeptical person might have said that the report from Syene was in error.
00:33:53But, it's an absolutely straightforward observation.
00:33:56Why would anyone lie on such a trivial matter?
00:34:00Eratosthenes asked himself how it could be that, at the same moment,
00:34:05a stick in Syene would cast no shadow,
00:34:08and a stick in Alexandria, 800 kilometers to the north,
00:34:12would cast a very definite shadow.
00:34:17Here's a map of ancient Egypt.
00:34:21I've inserted two sticks, or obelisks,
00:34:25one up here in Alexandria, and one down here in Syene.
00:34:30Now, if at a certain moment, each stick casts no shadow, no shadow at all,
00:34:36that's perfectly easy to understand, provided the Earth is flat.
00:34:41If the shadow at Syene is at a certain length,
00:34:44and the shadow at Alexandria is the same length,
00:34:47that also makes sense, on a flat Earth.
00:34:50But, how could it be, Eratosthenes asked,
00:34:53that at the same instant, there was no shadow at Syene,
00:34:58and a very substantial shadow at Alexandria?
00:35:03The only answer was that the surface of the Earth is curved.
00:35:09Not only that, but the greater the curvature,
00:35:13the bigger the difference in the lengths of the shadows.
00:35:16The Sun is so far away that its rays are parallel when they reach the Earth.
00:35:21Sticks at different angles to the Sun's rays will cast shadows at different lengths.
00:35:26Could be observed difference in these shadow lengths.
00:35:29The distance between Alexandria and Syene had to be about seven degrees along the surface of the Earth.
00:35:36By that I mean, if you imagine these sticks extending all the way down to the center of the Earth,
00:35:43they would there intersect at an angle of about seven degrees.
00:35:46Well, seven degrees is something like a fiftieth of the full circumference of the Earth, 360 degrees.
00:35:53Eratosthenes knew the distance between Alexandria and Syene.
00:35:58He knew it was eight hundred kilometers.
00:36:00Why?
00:36:01Because he hired a man to pace out the entire distance so that he could perform the calculation I'm talking about.
00:36:08Now, eight hundred kilometers times fifty is forty thousand kilometers.
00:36:14So that must be the circumference of the Earth.
00:36:16That's how far it is to go once around the Earth.
00:36:19That's the right answer.
00:36:21Eratosthenes' only tools were sticks, eyes, feet and brains.
00:36:28Plus a zest for experiment.
00:36:31With those tools, he correctly deduced the circumference of the Earth to high precision with an error of only a few percent.
00:36:42That's pretty good figuring for 2200 years ago.
00:36:48Then, as now, the Mediterranean was teeming with ships, merchantmen, fishing vessels, naval flotillas.
00:37:05But there were also courageous voyages into the unknown.
00:37:09400 years before Eratosthenes, Africa was circumnavigated by a Phoenician fleet in the employ of the Egyptian pharaoh Necho.
00:37:21They set sail, probably in boats as frail and open as these, out from the Red Sea, down the east coast of Africa, up into the Atlantic, and then back through the Mediterranean.
00:37:34That epic journey took three years, about as long as it takes Voyager to journey from Earth to Saturn.
00:37:43After Eratosthenes, some may have attempted to circumnavigate the Earth.
00:37:49But until the time of Magellan, no one succeeded.
00:37:52What tales of adventure and daring must earlier have been told as sailors and navigators, practical men of the world, gambled their lives on the mathematics of a scientist from ancient Alexandria?
00:38:11Today, Alexandria shows few traces of its ancient glory, of the days when Eratosthenes walked its broad avenues.
00:38:23Over the centuries, waves of conquerors converted its palaces and temples into castles and churches, then into minarets and mosques.
00:38:34The city was chosen to be the capital of his empire by Alexander the Great on a winter's afternoon in 331 BC.
00:38:43A century later, it had become the greatest city of the world.
00:38:47Each successive civilization has left its mark.
00:38:51But what now remains of the marble city of Alexander's dream?
00:39:03Alexandria is still a thriving marketplace, still a crossroads for the peoples of the Near East.
00:39:16It was radiant with self-confidence, certain of its power.
00:39:27Can you recapture a vanished epoch from a few broken statues and scraps of ancient manuscripts?
00:39:33In Alexandria, there was an immense library and an associated research institute, and in them worked the finest minds in the ancient world.
00:39:52Of that legendary library, all that survives is this dank and forgotten cellar.
00:40:21It's in the library annex, the Serapeum, which was once a temple, but was later re-consecrated to knowledge.
00:40:30These few moldering shelves, probably once in a basement storage room, are its only physical remains.
00:40:40But this place was once the brain and glory of the greatest city on the planet Earth.
00:40:49If I could travel back into time, this is the place I would visit.
00:41:03The library of Alexandria at its height 2,000 years ago.
00:41:14Here, in an important sense, began the intellectual adventure which has led us into space.
00:41:20All the knowledge in the ancient world was once within these marble walls.
00:41:33In the great hall, there may have been a mural of Alexander with the crook and flail and ceremonial headdress of the pharaohs of ancient Egypt.
00:41:47This library was a citadel of human consciousness, a beacon on our journey to the stars.
00:42:02It was the first true research institute in the history of the world.
00:42:07And what did they study?
00:42:09They studied everything.
00:42:11The entire cosmos.
00:42:13Cosmos is a Greek word for the order of the universe.
00:42:18In a way, it's the opposite of chaos.
00:42:21It implies a deep interconnectedness of all things.
00:42:27The intricate and subtle way that the universe is put together.
00:42:33Genius flourished here.
00:42:37In addition to Eratosthenes, there was the astronomer Hipparchus who mapped the constellations and established the brightness of the stars.
00:42:46And there was Euclid who brilliantly systematized geometry, who told his king, who was struggling with some difficult problem in mathematics, that there was no royal road to geometry.
00:43:03There was Dionysius of Thrace, the man who defined the parts of speech, nouns, verbs, and so on, who did for language in a way what Euclid did for geometry.
00:43:13There was Herophilus, a physiologist who identified the brain rather than the heart as the seat of intelligence.
00:43:22There was Archimedes, the greatest mechanical genius until the time of Leonardo da Vinci.
00:43:26And there was the astronomer Ptolemy who compiled much of what today is the pseudo-science of astrology.
00:43:34His Earth-centered universe held sway for 1500 years, showing that intellectual brilliance is no guarantee against being dead wrong.
00:43:44And among these great men, there was also a great woman. Her name was Hypatia. She was a mathematician and an astronomer, the last light of the library, whose martyrdom is bound up with the destruction of this place seven centuries after it was founded.
00:44:05Look at this place. The Greek kings of Egypt, who succeeded Alexander, regarded advances in science, literature, and medicine,
00:44:12as among the treasures of the empire. For centuries they generously supported research and scholarship.
00:44:19An enlightenment shared by few heads of state, then or now.
00:44:29Off this great hall were ten large research libraries.
00:44:32The Greek kings of Egypt, who succeeded Alexander, regarded advances in science, literature, and medicine,
00:44:36as among the treasures of the empire. For centuries they generously supported research and scholarship.
00:44:42An enlightenment shared by few heads of state, then or now.
00:44:47Off this great hall were ten large research laboratories. There were fountains and colonnades, botanical gardens,
00:45:04and even a zoo with animals from India and sub-Saharan Africa. There were dissecting rooms and an astronomical observatory.
00:45:13But the treasure of the library, consecrated to the god Serapis, built in the city of Alexander, was its collection of books.
00:45:26The organizers of the library combed all the cultures and languages of the world for books.
00:45:32They sent agents abroad to buy up libraries. Commercial ships docking in Alexandria harbor were searched by the police.
00:45:40Not for contraband, but for books. The scrolls were borrowed, copied, and returned to their owners.
00:45:47Until studied, these scrolls were collected in great stacks called books from the ships.
00:45:54Accurate numbers are difficult to come by, but it seems that the library contained at its peak nearly one million scrolls.
00:46:03The papyrus reed grows in Egypt. It's the origin of our word for paper.
00:46:22And each of those million volumes which once existed in this library were handwritten on papyrus manuscript scrolls.
00:46:33What happened to all those books?
00:46:35Well, the classical civilization that created them disintegrated.
00:46:38The library itself was destroyed. Only a small fraction of the works survived.
00:46:44And as for the rest, we are left only with pathetic, scattered fragments.
00:46:50But how tantalizing those remaining bits and pieces are.
00:46:55For example, we know that there once existed here a book by the astronomer Aristarchus of Samos.
00:47:03Who apparently argued that the Earth was one of the planets, that like the other planets, it orbits the sun, and that the stars are enormously far away.
00:47:16All absolutely correct.
00:47:18But we had to wait nearly 2,000 years for these facts to be rediscovered.
00:47:24The astronomy stacks of the Alexandria Library.
00:47:35Yparcos, Ptolemos. Here we are.
00:47:43Aristarchus.
00:47:45This is the book.
00:47:48How I'd love to be able to read this book.
00:47:51to know how Aristarchus figured it out.
00:47:55But it's gone, utterly and forever.
00:47:59If we multiply our sense of loss for this work of Aristarchus by 100,000,
00:48:05we begin to appreciate the grandeur of the achievement of classical civilization
00:48:10and the tragedy of its destruction.
00:48:43From the creation of the world to the Great Flood,
00:48:47a period that he took to be 432,000 years,
00:48:51or about 100 times longer than the Old Testament chronology.
00:48:55What wonders were in the books of Barossus?
00:48:59But why have I brought you across 2,000 years to the Library of Alexandria?
00:49:06Because this was when and where we humans first collected seriously and systematically
00:49:14the knowledge of the world.
00:49:16This is the Earth as Eratosthenes knew it.
00:49:20It's a tiny, spherical world afloat in an immense space and time.
00:49:27We were, at long last, beginning to find our true bearings in the cosmos.
00:49:32The scientists of antiquity took the first and most important steps in that direction
00:49:39before their civilization fell apart.
00:49:42But after the Dark Ages, it was by and large the rediscovery of the works of these scholars,
00:49:48done here, that made the Renaissance possible and thereby powerfully influenced our own culture.
00:49:54When, in the 15th century, Europe was at last ready to awaken from its long sleep,
00:50:02it picked up some of the tools, the books, and the concepts,
00:50:06laid down here more than 1,000 years before.
00:50:10By 1600, the long-forgotten ideas of Aristarchus had been rediscovered.
00:50:22Johannes Kepler constructed elaborate models to understand the motion and arrangement of the planets,
00:50:29the clockwork of the heavens.
00:50:35And at night, he dreamt of traveling to the moon.
00:50:40His principal scientific tools were the mathematics of the Alexandrian library
00:50:55and an unswerving respect for the facts, however disquieting they might be.
00:51:05His story and the story of the scientists who came after him
00:51:08are also part of our voyage.
00:51:13Seventy years later,
00:51:15the sun-centered universe of Aristarchus and Copernicus
00:51:18was widely accepted in the Europe of the Enlightenment.
00:51:22The idea arose that the planets were worlds
00:51:26governed by laws of nature
00:51:27and scientific speculation turned to the motions of the stars.
00:51:31The clockwork in the heavens was imitated by the watchmakers of Earth.
00:51:37Precise timekeeping permitted great sailing ship voyages
00:51:41of exploration and discovery,
00:51:43which bound up the Earth.
00:51:45This was a time when free inquiry was valued once again.
00:51:59250 years later, the Earth was all explored.
00:52:03New adventurers now looked to the planets and the stars.
00:52:06The galaxies were recognized as great aggregates of stars,
00:52:11island universes,
00:52:13millions of light-years away.
00:52:16In the 1920s, astronomers had begun to measure
00:52:19the speeds of distant galaxies.
00:52:21They found that the galaxies were flying away from one another.
00:52:37To the astonishment of everyone,
00:52:39the entire universe was expanding.
00:52:41We had begun to plumb the true depths of time and space.
00:52:55The long collective enterprise of science
00:52:58has revealed a universe some 15 billion years old,
00:53:03the time since the explosive birth of the cosmos,
00:53:06the Big Bang.
00:53:11The cosmic calendar compresses the local history of the universe
00:53:17into a single year.
00:53:20If the universe began on January 1st,
00:53:22it was not until May that the Milky Way formed.
00:53:26Other planetary systems may have appeared in June, July, and August,
00:53:32but our sun on Earth, not until mid-September.
00:53:36Life arose soon after.
00:53:37Everything humans have ever done
00:53:40occurred in that bright speck
00:53:43at the lower right of the cosmic calendar.
00:53:48The Big Bang is at upper left
00:53:51in the first second of January 1st.
00:53:54Fifteen billion years later
00:53:56is our present time,
00:53:58the last second of December 31st.
00:54:01Every month is one and a quarter billion years long.
00:54:10Each day represents 40 million years.
00:54:13Each second stands for some 500 years of our history,
00:54:17the blinking of an eye
00:54:18in the drama of cosmic time.
00:54:21At this scale,
00:54:28the cosmic calendar is the size of a football field,
00:54:31but all of human history
00:54:32would occupy an area
00:54:34the size of my hand.
00:54:36We're just beginning to trace
00:54:38the long and tortuous path
00:54:40which began with the primeval fireball
00:54:42and led to the condensation of matter.
00:54:46Gas, dust, stars, galaxies,
00:54:48and at least in our little nook of the universe,
00:54:51planets and life,
00:54:53intelligence and inquisitive men and women.
00:54:56We've emerged so recently
00:54:57that the familiar events of our recorded history
00:55:00occupy only the last seconds
00:55:02of the last minute of December 31st.
00:55:05Some critical events for the human species,
00:55:07however, began much earlier,
00:55:09minutes earlier.
00:55:10So we change our scale
00:55:13from months to minutes.
00:55:15Down here,
00:55:17the first humans made their debut
00:55:18around 10.30 p.m.
00:55:21on December 31st.
00:55:25And with the passing of every cosmic minute,
00:55:28each minute 30,000 years long,
00:55:30we began the arduous journey
00:55:31towards understanding where we live
00:55:33and who we are.
00:55:391146.
00:55:40Only 14 minutes ago,
00:55:43humans have tamed fire.
00:55:4711.59.20,
00:55:49the evening of the last day of the cosmic year,
00:55:52the 11th hour,
00:55:53the 59th minute,
00:55:54the 20th second,
00:55:56the domestication of plants and animals begins.
00:55:59An application of the human talent
00:56:01for making tools.
00:56:0611.59.35,
00:56:15settled agricultural communities
00:56:18evolve into the first cities.
00:56:20We humans appear on the cosmic calendar
00:56:25so recently
00:56:26that our recorded history occupies
00:56:28only the last few seconds
00:56:30of the last minute
00:56:32of December 31st.
00:56:34In the vast ocean of time,
00:56:37which this calendar represents,
00:56:39all our memories
00:56:40are confined
00:56:42to this small square.
00:56:47Every person we've ever heard of
00:56:50lived somewhere in there.
00:56:53All those kings and battles,
00:56:55migrations and inventions,
00:56:57wars and loves,
00:56:58everything in the history books
00:57:00happens here
00:57:02in the last 10 seconds
00:57:04of the cosmic calendar.
00:57:11We on Earth
00:57:13have just awakened
00:57:14to the great oceans
00:57:16of space and time
00:57:17from which we have emerged.
00:57:20We are the legacy
00:57:22of 15 billion years
00:57:24of cosmic evolution.
00:57:26We have a choice.
00:57:28We can enhance life
00:57:30and come to know
00:57:31the universe that made us
00:57:32or we can squander
00:57:34our 15 billion year heritage
00:57:35in meaningless self-destruction.
00:57:40What happens
00:57:41in the first second
00:57:42of the next cosmic year
00:57:43depends on what we do
00:57:45here and now
00:57:46with our intelligence
00:57:48and our knowledge
00:57:50of the cosmos.
00:57:51We have a choice.
00:57:51We have a choice.
00:58:21We have a choice.
00:58:22We have a choice.
00:58:23We have a choice.
00:58:24We have a choice.
00:58:25We have a choice.
00:58:26We have a choice.
00:58:27We have a choice.
00:58:28We have a choice.
00:58:29We have a choice.
00:58:30We have a choice.
00:58:31We have a choice.
00:58:32We have a choice.
00:58:33We have a choice.
00:58:34We have a choice.
00:58:35We have a choice.
00:58:36We have a choice.
00:58:37We have a choice.
00:58:38We have a choice.
00:58:39We have a choice.
00:58:40We have a choice.
00:58:41We have a choice.
00:58:42We have a choice.
00:58:43We have a choice.
00:58:44We have a choice.
00:58:45We have a choice.
00:58:46We have a choice.
00:58:47We have a choice.
00:58:48We have a choice.
00:58:49We have a choice.