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00:00You
00:30The sky calls to us.
00:53If we do not destroy ourselves, we will one day venture to the stars.
00:58There was a time when the stars seemed an impenetrable mystery.
01:03Today, we have begun to understand them.
01:07In our personal lives also, we journey from ignorance to knowledge.
01:12Our individual growth reflects the advancement of the species.
01:17The exploration of the cosmos is a voyage of self-discovery.
01:28When I was a child, I lived here, in the Bensonhurst section of Brooklyn, in the city of New York.
01:40I knew my immediate neighborhood intimately.
01:43Every candy store, front stoop, backyard, empty lot, and wall for playing Chinese handball.
01:59It was my whole world.
02:20But more than a few blocks away, north of the raucous traffic and elevated railway on 86th Street,
02:28was an unknown territory, off-limits to my wanderings.
02:32It could have been Mars for all I knew.
02:39Even with an early bedtime, in the winter, you could occasionally see the stars.
02:46I would look up at them and wonder what they were.
02:49I'd ask other kids and adults, and they would answer,
02:54There are lights in the sky, kid.
02:57Well, I could tell there were lights in the sky, but what were they?
03:01There had to be some deeper answer.
03:10I remember I was issued my first library card.
03:13I think it was some library over there on 85th Street anyway.
03:16It was in alien territory.
03:18And I asked the librarian for a book on stars.
03:22She gave me a funny kind of picture book with portraits of men and women with names like Veronica Lake and Alan Ladd.
03:31I explained that wasn't what I wanted at all.
03:35And for some reason, then obscure to me, she smiled and got me another book, the right kind of book.
03:42I was so excited to know the answer that I opened the book breathlessly right there in the library.
03:48And the book said something astonishing, a very big thought.
03:54Stars, it said, were suns, but very far away.
04:00The sun was a star, but close up.
04:11How, I wondered, could anybody know such things for sure?
04:15How did they figure it out?
04:17Where did they even begin?
04:29I was ignorant of the idea of angular size.
04:32I didn't know a thing about the inverse square law of the propagation of light.
04:36I didn't have the ghost of a chance of calculating the distance to the stars.
04:40But I could tell that if the stars were suns, they had to be awfully far away, further away than 86th Street, further away than Manhattan, further away probably than New Jersey.
04:54The universe had become much grander than I had ever guessed.
05:03And then I read another astonishing fact.
05:06The Earth, which includes Brooklyn, was a planet.
05:12It went around the sun.
05:14There were other planets.
05:15Planets, they also went around the sun, some closer to the sun, some further from the sun.
05:21But planets didn't shine by their own light the way the sun does.
05:25No, planets simply reflected the little bit of light that shines on them from the sun back to us.
05:34If you were a great distance away from the sun, you wouldn't be able to see the Earth or the other planets at all.
05:40Well then, it stood to reason, I thought, that those other stars ought to have their own planets.
05:48And some of those planets ought to have life.
05:51Why not?
05:52And that life ought to be pretty different from life as we know it.
05:57Life here in Brooklyn.
05:59Ganymede!
06:00Look at this amazing Ganymede stuff!
06:02Wait, wait, wait.
06:03I want to give to people...
06:04As a child, it was my immense good fortune to have parents and a few teachers who encouraged my curiosity.
06:09This was my sixth grade classroom.
06:12I came back here one afternoon to remember what it was like.
06:15I brought some of the breathtaking pictures of other worlds
06:18that had been radioed back by the Voyager spacecraft
06:21in their encounters with Jupiter and its moons.
06:24Okay, this is Callisto, which is...
06:27What is a Callisto?
06:30I want a Callisto.
06:31Now you got it.
06:32What is it?
06:33It's the outermost big moon of Jupiter.
06:36Um, who is this guy?
06:38Europa!
06:39Another Europa.
06:42A black and white picture of a ring of Jupiter.
06:45There you go.
06:47That's a prize for honesty.
06:49I can get a second.
06:50You didn't get a second.
06:51You're right.
06:52Which one would you like?
06:53I can get a second.
06:54Okay.
06:55I can get a second.
06:56No.
06:57How do...
06:58You didn't get a second.
06:59Every one of us begins life with an open mind, a driving curiosity, a sense of wonder.
07:12I thought it might be fun if we now had some questions.
07:18Why is the Earth round?
07:19Why isn't it square or any other shape?
07:21That's a good question.
07:23I like that question.
07:24That's a question I have asked myself.
07:26And the answer has to do with gravity.
07:28The Earth has a strong gravity.
07:31If you were to make a mountain very high, higher than Everest, you know, it's the biggest
07:36mountain on the Earth, it would be crushed by its own weight.
07:40You see, gravity pulls everything towards the center.
07:43So any really big bump on the Earth is crushed.
07:46But if you had a small object, a tiny world, the gravity is very low, and then it can be
07:52very different from a sphere.
07:55I think I have here a world that isn't a sphere.
08:00Here.
08:02Look at this one.
08:05See, it's lumpy.
08:08It's a lumpy world.
08:10Looks like a potato, right?
08:12There's a large potato orbiting the planet Mars.
08:16This is one of the moons of Mars.
08:18And that's a perfect example of it.
08:20You can have big departures from a sphere if your gravity is low.
08:25Now, a question in the front.
08:27Is the Sun considered part of the Milky Way galaxy?
08:30Sure.
08:31You're considered part of the Milky Way galaxy.
08:34Everything except other galaxies is part of the Milky Way galaxy.
08:38The Sun is one star.
08:40There is a few hundred billion stars in the Milky Way.
08:45And around each star, maybe, there's a whole bunch of planets.
08:49And on one of those planets is life.
08:52And one of the life forms on that planet is you.
08:56So, you're a part of the Milky Way galaxy, too?
09:09Sometimes, I think, how lucky we are to live in this time, the first moment in human history when we are, in fact, visiting other worlds and engaging in a deep reconnaissance of the cosmos.
09:24But if we had been born in a much earlier age, no matter how great our dedication, we could not have understood what the stars and planets are.
09:34We would not have known that there were other suns and other worlds.
09:50This is one of the great secrets wrested from nature through a million years of patient observation and courageous thinking.
10:02Human beings have always asked questions about the stars.
10:07It's as natural as breathing.
10:10But imagine a time before science had found out the answers.
10:14Imagine what it was like, say, hundreds of thousands of years ago, soon after the discovery of fire.
10:24We were just as smart and just as curious then as we are now.
10:30Sometimes it seems to me that there were people then who thought like this.
10:37We are wandering hunter folk.
10:41Fire keeps us warm.
10:43Its light makes holes in the darkness.
10:46It keeps hungry animals away.
10:48In the darkness, we can see each other and talk.
10:53We take care of the flame.
10:55The flame takes care of us.
10:58The stars are not near to us.
11:02When we climb a hill or a tree, they are no closer.
11:06They flicker with a strange, cold, white, far away light.
11:12Many of them all over the sky, but only at night.
11:18I wonder what they are.
11:20One night I thought the stars are flames.
11:23They give a little light at night, as fire does.
11:27Maybe the stars are campfires, which other wanderers light at night.
11:34The stars give a much smaller light than campfires, so they must be very far away.
11:41I wonder if our campfires look like stars to the people in the sky.
11:46But why don't those campfires and the wanderers who made them fall down at our feet?
11:53Why don't strange tribes drop from the sky?
11:57Those beings in the sky must have great powers.
12:12I don't suppose that every hunter-gatherer had such thoughts about the stars.
12:17But we know from contemporary hunter-gatherer communities that very imaginative ideas arise.
12:25The Ng Bushmen of the Kalahari Desert in the Republic of Botswana have an explanation of the Milky Way.
12:34At their latitude, it's often overhead.
12:37They call it the backbone of night.
12:41They believe it holds the sky up.
12:44They believe that if not for the Milky Way, pieces of sky would come crashing down at our feet.
12:51So the Milky Way, in their view, has some practical value.
12:55The backbone of night.
13:00Later on, metaphors about campfires or backbones or holes through which the flame could be seen
13:09were replaced in most human communities by another idea.
13:14The powerful beings in the sky were promoted to gods.
13:19They were given names and relatives and special responsibilities for the cosmic services they were expected to perform.
13:28There was a god for every human concern.
13:32Gods ran nature. Nothing happened without the direct intervention of some god.
13:38If the gods were happy, there was plenty of food and humans were happy.
13:45But if something displeased the gods and it didn't take much, the consequences were awesome.
13:53Droughts, floods, storms, wars, earthquakes, volcanic eruptions, epidemics.
14:01The gods had to be propitiated.
14:04And a vast industry of priests arose to make the gods less angry.
14:10But because the gods were capricious, you couldn't be sure what they would do.
14:16Nature was a mystery.
14:18It was hard to understand the world.
14:21Our ancestors groped in darkness to make sense of their surroundings.
14:30Powerless before nature, they invented rituals and myths.
14:35Some desperate and cruel.
14:38Others imaginative and benign.
14:42The ancient Greeks explained that diffuse band of brightness in the night sky as the milk of the goddess Hera squirted from her breast across the heavens.
14:54We still call it the Milky Way.
15:04In gratitude for the many gifts of the gods, our ancestors created works of surpassing beauty.
15:15This is all that remains of the ancient temple of Hera, Queen of Heaven.
15:21A single marble column standing in a vast field of ruins on the Greek island of Samos.
15:29It was one of the wonders of the world, built by people with an extraordinary eye for clarity and symmetry.
15:38Those who thronged that temple were also the architects of a bridge from their world to ours.
15:53We were moving once again in our voyage of self-discovery on our journey to the stars.
16:03Here, 25 centuries ago, on the island of Samos and in the other Greek colonies which had grown up in the busy Aegean Sea, there was a glorious awakening.
16:21Suddenly, there were people who believed that everything was made of atoms, that human beings and other animals had evolved from simpler forms,
16:30that diseases were not caused by demons or the gods, that the earth was only a planet going around a sun which was very far away.
16:45This revolution made cosmos out of chaos.
16:49Here, in the sixth century BC, a new idea developed, one of the great ideas of the human species.
16:55It was argued that the universe was knowable.
17:00Why? Because it was ordered, because there are regularities in nature which permit its secrets to be uncovered.
17:08Nature was not entirely unpredictable.
17:15There were rules which even she had to obey.
17:21This ordered and admirable character of the universe was called Cosmos.
17:29And it was set in stark contradiction to the idea of chaos.
17:34This was the first conflict of which we know between science and mysticism, between nature and the gods.
17:46But why here? Why in these remote islands and inlets of the eastern Mediterranean?
17:58Why not in the great cities of India or Egypt, Babylon, China, Mesoamerica?
18:05Because they were all at the center of old empires.
18:14They were set in their ways, hostile to new ideas.
18:18But here, in Ionia, were a multitude of newly colonized islands and city-states.
18:24Isolation, even if incomplete, promotes diversity.
18:28No single concentration of power could enforce conformity.
18:33Free inquiry became possible.
18:36They were beyond the frontiers of the empires.
18:40The merchants and tourists and sailors of Africa, Asia and Europe met in the harbors of Ionia
18:47to exchange goods and stories and ideas.
18:51There was a vigorous and heavy interaction of many traditions, prejudices, languages and gods.
19:10These people were ready to experiment.
19:14Once you are open to questioning rituals and time-honored practices, you find that one question leads to another.
19:33What do you do when you're faced with several different gods, each claiming the same territory?
19:39The Babylonian Marduk and the Greek Zeus were each considered king of the gods, master of the sky.
19:48You might decide, since they otherwise had rather different attributes, that one of them was merely invented by the priests.
19:55But if one, why not both?
19:58And so it was here that the great idea arose, the realization that there might be a way to know the world without the god hypothesis.
20:11That there might be principles, forces, laws of nature through which the world might be understood without attributing the fall of every sparrow to the direct intervention of Zeus.
20:23This is the place where science was born. That's why we're here.
20:30This great revolution happened between 600 and 400 BC.
20:36It was accomplished by the same practical and productive people who made the society function.
20:41Political power was in the hands of the merchants who promoted the technology on which their prosperity depended.
20:48The earliest pioneers of science were merchants and artisans and their children.
21:01The first Ionian scientist was named Thales.
21:05He was born over there in the city of Miletus across this narrow strait.
21:10He had traveled in Egypt and was conversant with the knowledge of Babylon.
21:15Like the Babylonians, he believed that the world had once all been water.
21:20To explain the dry land, the Babylonians added that their god Marduk had placed a mat on the face of the waters and piled dirt on top of it.
21:34Thales had a similar view, but he left Marduk out.
21:39Yes, the world had once been mostly water, but it was a natural process which explained the dry land.
21:48Thales thought it was similar to the silting up he had observed at the delta of the river Nile.
21:55Whether Thales' conclusions were right or wrong is not nearly as important as his approach.
22:04The world was not made by the gods, but instead was the result of material forces interacting in nature.
22:13Thales brought back from Babylon and Egypt the seeds of new sciences, astronomy and geometry.
22:24Sciences which would sprout and grow in the fertile soil of Ionia.
22:30Anaximander of Miletus, over there, was a friend and colleague of Thales.
22:38One of the first people that we know of to have actually done an experiment.
22:42By examining the moving shadow cast by a vertical stick, he determined accurately the length of the year and the length of the seasons.
22:52For ages, men had used sticks to club and spear each other, and Anaximander used a stick to measure time.
23:01In 540 BC, or thereabouts, on this island of Samos, there came to power a tyrant named Polycrates.
23:15He seems to have started as a caterer and then went on to international piracy.
23:21His loot was unloaded on this very breakwater.
23:26But he oppressed his own people. He made war on his neighbors. He quite rightly feared invasion.
23:41So, Polycrates surrounded his capital city with an impressive wall, whose remains stand till this day.
23:50To carry water from a distant spring through the fortifications, he ordered this great tunnel built.
24:05A kilometer long, it pierces a mountain.
24:09Two cuttings were dug from either side, which met almost perfectly in the middle.
24:14The project took some 15 years to complete.
24:18It is a token of the civil engineering of its day, and an indication of the extraordinary practical capability of the Ionians.
24:31The enduring legacy of the Ionians is the tools and techniques they developed, which remain the basis of modern technology.
24:43This was the time of Theodorus, the master engineer of the age.
24:50A man who is credited with the invention of the key, the ruler, the carpenter's square, the level, the lathe, the bronze casting.
25:01Why are there no monuments to this man?
25:05Those who dreamt and speculated and deduced about the laws of nature talked to the engineers and the technologists.
25:14They were often the same people.
25:16The practical and the theoretical were one.
25:28This new hybrid of abstract thought and everyday experience blossomed into science.
25:36When these practical men turned their attention to the natural world, they began to uncover hidden wonders and breathtaking possibilities.
25:46Anaximander studied the profusion of living things and saw their interrelationships.
25:53He concluded that life had originated in water and mud and then colonized the dry land.
26:01Human beings, he said, must have evolved from simpler forms.
26:06This insight had to wait 24 centuries until its truth was demonstrated by Charles Darwin.
26:13Nothing was excluded from the investigations of these first scientists.
26:27Even the air became the subject of close examination by a Greek from Sicily named Empedocles.
26:37He made an astonishing discovery with a household implement that people had used for centuries.
26:44This is the so-called water thief.
26:48It's a brazen sphere with a neck and a hole at the top and a set of little holes at the bottom.
26:55It was used as a kitchen ladle.
26:57You fill it by immersing it in water.
27:02If, after it's been in there a little bit, you pull it out with the neck uncovered, then the water trickles out the little holes making a small shower.
27:14Instead, if you pull it out with the neck covered, the water is retained.
27:33Now, try to fill it with the neck covered with my thumb.
27:43Nothing happens.
27:45Why not?
27:47There's something in the way.
27:49Some material is blocking the access of the water into the sphere.
27:54I can't see any such material.
27:57What could it be?
27:59Empedocles identified it as air.
28:04What else could it be?
28:06A thing you can't see can exert pressure, can frustrate my wish to fill this vessel with water if I were dumb enough to leave my thumb on the neck.
28:19Empedocles had discovered the invisible.
28:26Air, he thought, must be matter in a form so finely divided that it couldn't be seen.
28:36This hint, this whiff of the existence of atoms was carried much further by a contemporary named Democritus.
28:46Of all the ancient scientists, it is he who speaks most clearly to us across the centuries.
28:52The few surviving fragments of his scientific writings reveal a mind of the highest logical and intuitive powers.
28:59He believed that a large number of other worlds wander through space.
29:04That worlds are born and die.
29:07That some are rich in living creatures.
29:09And others are dry and barren.
29:12He was the first to understand that the Milky Way is an aggregate of the light of innumerable faint stars.
29:20Beyond campfires in the sky.
29:23Beyond the milk of Hera.
29:25Beyond the backbone of night.
29:27The mind of Democritus soared.
29:35He saw deep connections between the heavens and the earth.
29:39Man, he said, is a microcosm.
29:42A little cosmos.
29:57Democritus came from the Ionian town of Abdera on the northern Aegean shore.
30:14In those days, Abdera was the butt of jokes.
30:21If around the year 400 BC, in the equivalent of a little outdoor restaurant like this, you told a story about someone from Abdera, you were guaranteed a laugh.
30:32It was, in a way, the Brooklyn of its time.
30:42For Democritus, all of life was to be enjoyed and understood.
30:47In fact, for him, understanding and enjoyment were pretty much the same thing.
30:51He said, a life without festivity is a long road without an inn.
30:56Democritus may have come from Abdera, but he was no dummy.
31:04Democritus understood that the complex forms, changes, and motions of the material world all derive from the interaction of very simple moving parts.
31:15He called these parts atoms.
31:24All material objects are collections of atoms intricately assembled, even we.
31:31When I cut this apple, the knife must be passing through empty spaces between the atoms, Democritus argued.
31:40If there were no such empty spaces, no void, then the knife would encounter some impenetrable atom, and the apple wouldn't be cut.
31:50Let's compare the cross sections of the two pieces.
31:53Are the exposed areas exactly equal?
31:56No, said Democritus.
31:57The curvature of the apple forces this slice to be slightly shorter than the rest of the apple.
32:04If they were equally tall, then we'd have a cylinder and not an apple.
32:10No matter how sharp the knife, these two pieces have unequal cross sections.
32:15But why?
32:17Because, on the scale of the very small, matter exhibits some irreducible roughness.
32:23And this fine scale of roughness, Democritus of Abdera identified with the world of the atoms.
32:29His arguments are not those we use today, but they're elegant and subtle and derived from everyday experience.
32:37And his conclusions were fundamentally right.
32:41Democritus believed that nothing happens at random, that everything has a material cause.
32:54He said, I would rather understand one cause than be king of Persia.
33:00He believed that poverty in a democracy was far better than wealth in a tyranny.
33:05He believed that the prevailing religions of his time were evil.
33:09And that neither souls nor immortal gods existed.
33:13There is no evidence that Democritus was persecuted for his beliefs.
33:19But then again, he came from Abdera.
33:22However, in his time, the brief tradition of tolerance for unconventional views was beginning to erode.
33:32For instance, the prevailing belief was that the moon and the sun were gods.
33:38Another contemporary of Democritus named Anaxagoras taught that the moon was a place made of ordinary matter
33:45and that the sun was a red-hot stone far away in the sky.
33:51For this, Anaxagoras was condemned, convicted, and imprisoned for impiety, a religious crime.
34:00People began to be persecuted for their ideas.
34:04A portrait of Democritus is now on the Greek hundred drachma note.
34:10But his ideas were suppressed and his influence on history made minor.
34:15The mystics were beginning to win.
34:24You see, Ionia was also the home of another quite different intellectual tradition.
34:30Its founder was Pythagoras, who lived here on Samos in the 6th century BC.
34:36According to local legend, this cave was once his abode.
34:43Maybe that was once his living room.
34:46Many centuries later, this small Greek Orthodox shrine was erected on his front porch.
34:53There's a continuity of tradition from Pythagoras to Christianity.
34:57Pythagoras seems to have been the first person in the history of the world to decide that the earth was a sphere.
35:04Perhaps he argued by analogy with the moon or the sun.
35:09Maybe he noticed the curved shadow of the earth on the moon during a lunar eclipse.
35:14Or maybe he recognized that when ships leave Samos, their masts disappear last.
35:19Pythagoras believed that a mathematical harmony underlies all of nature.
35:31The modern tradition of mathematical argument, essential in all of science, owes much to him.
35:37And the notion that the heavenly bodies move to a kind of music of the spheres was also derived from Pythagoras.
35:47It was he who first used the word cosmos to mean a well-ordered and harmonious universe.
35:53A world amenable to human understanding.
35:56For this great idea, we are indebted to Pythagoras.
36:04But there were deep ironies and contradictions in his thoughts.
36:09Many of the Ionians believed that the underlying harmony and unity of the universe was accessible.
36:16Through observation and experiment, the method which dominates science today.
36:21However, Pythagoras had a very different method.
36:25He believed that the laws of nature could be deduced by pure thought.
36:30He and his followers were not basically experimentalists.
36:33They were mathematicians and they were thorough-going mystics.
36:39They were fascinated by these five regular solids.
36:43Bodies whose faces are all polygons.
36:47Triangles or squares or pentagons.
36:51There can be an infinite number of polygons.
36:54But only five regular solids.
36:57Four of the solids were associated with earth, fire, air and water.
37:05The cube, for example, represented earth.
37:09These four elements, they thought, make up terrestrial matter.
37:14So the fifth solid, they mystically associated with the cosmos.
37:20Perhaps it was the substance of the heavens.
37:23This fifth solid was called the dodecahedron.
37:28Its faces are pentagons, twelve of them.
37:33Knowledge of the dodecahedron was considered too dangerous for the public.
37:40Ordinary people were to be kept ignorant of the dodecahedron.
37:45In love with whole numbers, the Pythagoreans believed that all things could be derived from them.
37:50Certainly all other numbers.
37:52So a crisis in doctrine occurred when they discovered that the square root of two was irrational.
37:58That is, the square root of two could not be represented as the ratio of two whole numbers, no matter how big they were.
38:04Irrational originally meant only that, that you can express a number as a ratio.
38:10But for the Pythagoreans, it came to mean something else, something threatening.
38:17A hint that their world view might not make sense.
38:21The other meaning of irrational.
38:25Instead of wanting everyone to share and know of their discoveries,
38:30the Pythagoreans suppressed the square root of two and the dodecahedron.
38:35The outside world was not to know.
38:42The Pythagoreans had discovered, in the mathematical underpinnings of nature,
38:48one of the two most powerful scientific tools.
38:51The other, of course, is experiment.
38:54But instead of using their insight to advance the collective voyage of human discovery,
39:00they made of it little more than the hocus pocus of a mystery cult.
39:05Science and mathematics were to be removed from the hands of the merchants and the artisans.
39:10This tendency found its most effective advocate in a follower of Pythagoras named Plato.
39:17He preferred the perfection of these mathematical abstractions to the imperfections of everyday life.
39:26He believed that ideas were far more real than the natural world.
39:31He advised the astronomers not to waste their time observing the stars and planets.
39:35It was better, he believed, just to think about them.
39:39Plato expressed hostility to observation and experiment.
39:43He taught contempt for the real world and disdain for the practical application of scientific knowledge.
39:50Plato's followers succeeded in extinguishing the light of science and experiment that had been kindled by Democritus and the other Ionians.
40:05Plato's unease with the world as revealed by our senses was to dominate and stifle Western philosophy.
40:16Even as late as 1600, Johannes Kepler was still struggling to interpret the structure of the cosmos in terms of Pythagorean solids and platonic perfection.
40:28Ironically, it was Kepler who helped re-establish the old Ionian method of testing ideas against observations.
40:35But why had science lost its way in the first place?
40:39What appeal could these teachings of Pythagoras and Plato have had for their contemporaries?
40:44They provided, I believe, an intellectually respectable justification for a corrupt social order.
40:55The mercantile tradition which had led to Ionian science also led to a slave economy.
41:02You could get richer if you owned a lot of slaves.
41:07Athens, in the time of Plato and Aristotle, had a vast slave population.
41:13All of that brave Athenian talk about democracy applied only to a privileged few.
41:20Plato and Aristotle were comfortable in a slave society.
41:25They offered justifications for oppression.
41:28They served tyrants.
41:31They taught the alienation of the body from the mind.
41:34A natural enough idea, I suppose, in a slave society.
41:38They separated thought from matter.
41:41They divorced the earth from the heavens.
41:44Divisions which were to dominate Western thinking for more than 20 centuries.
41:50The Pythagoreans had won.
41:55In the recognition by Pythagoras and Plato that the cosmos is knowable.
42:04That there is a mathematical underpinning to nature.
42:07They greatly advanced the cause of science.
42:10But in the suppression of disquieting facts.
42:15The sense that science should be kept for a small elite.
42:20The distaste for experiment.
42:22The embrace of mysticism.
42:24The easy acceptance of slave societies.
42:28Their influence has significantly set back the human endeavor.
42:34The books of the Ionian scientists are entirely lost.
42:41Their views were suppressed, ridiculed, and forgotten.
42:47By the Platonists and by the Christians who adopted much of the philosophy of Plato.
42:53Finally, after a long mystical sleep in which the tools of scientific inquiry lay moldering.
43:04The Ionian approach was rediscovered.
43:11The Western world reawakened.
43:15Experiment and open inquiry slowly became respectable once again.
43:23Forgotten books and fragments were red once more.
43:27Leonardo and Copernicus and Columbus were inspired by the Ionian tradition.
43:34The Pythagoreans and their successors held the peculiar notion that the earth was tainted.
43:56Somehow nasty.
43:59While the heavens were pristine and divine.
44:04So the fundamental idea that the earth is a planet.
44:07That we are citizens of the universe.
44:10Was rejected and forgotten.
44:16This idea was first argued by Aristarchus.
44:20Born here on Samos three centuries after Pythagoras.
44:24He held that the earth moves around the sun.
44:28He correctly located our place in the solar system.
44:31For his trouble.
44:32He was accused of heresy.
44:37From the size of the earth's shadow on the moon during a lunar eclipse.
44:41He deduced that the sun had to be much much larger than the earth.
44:47And also very far away.
44:49From this he may have argued that it was absurd.
44:52For so large an object as the sun to be going around so small an object as the earth.
44:58So he put the sun rather than the earth at the center of the solar system.
45:03And he had the earth and the other planets going around the sun.
45:07He also had the earth rotating on its axis once a day.
45:10These are ideas that we ordinarily associate with the name Copernicus.
45:14But Copernicus seems to have gotten at least some hint of these ideas by reading about Aristarchus.
45:21In fact.
45:22In the manuscript of Copernicus's book.
45:25He referred to Aristarchus.
45:27But in the final version.
45:29He suppressed the citation.
45:31The other version of the moon.
45:33Resistance to Aristarchus.
45:34A kind of geocentrism in everyday life.
45:37Is with us still.
45:38We still talk about the sun rising.
45:41And the sun setting.
45:43setting. It's 2200 years since Aristarchus and the language still pretends that the earth does not
45:52turn. That the sun is not at the center of the solar system. Aristarchus understood the basic
46:02scheme of the solar system but not its scale. He knew that the planets move in concentric orbits
46:11about the sun and he probably knew their order out to Saturn. But he was much too modest in his
46:19estimates of how far apart the planets are. In order to calculate the true scale of the solar system
46:25you need a telescope. It wasn't until the 17th century that astronomers were able to get
46:31even a rough estimate of the distance to the sun.
46:35And once you knew the distance to the sun, what about the stars? How far away are they?
46:48There is a way to measure the distance to the stars and the Ionians were fully capable of
46:54discovering it. Aristarchus had toyed with the daring idea that the stars were distant suns.
47:01Now if a star were as near as the sun, it should appear as big and as bright as the sun. Everyone
47:08knows that the farther away an object is, the smaller it seems. This inverse proportionality
47:14between apparent size and distance is the basis of perspective in art and photography. So the
47:20further away we are from the sun, the smaller and dimmer it appears. How far from the sun would
47:27we have to be for it to appear as small and dim as a star? Or equivalently, how small a piece of sun
47:34would be as bright as a star? An experiment to answer this question was first performed in 17th century
47:41Holland by Christianus Huygens and is very much in the Ionian tradition. Huygens drilled a number of holes
47:50holes in a brass plate and held the plate up to the sun. He asked himself which hole seemed as bright
48:00as he remembered the bright star Sirius to have been the previous evening. Well, the hole that matched was
48:07effectively one 28,000th the apparent size of the sun. So Sirius, he reasoned, must be 28,000 times further away
48:18than the sun or about half a light year away. It's hard to remember just how bright a star is hours
48:25after you looked at it, but Huygens remembered very well. In fact, if he had known that Sirius was
48:31intrinsically brighter than the sun, he would have gotten the answer exactly right. Sirius is 8.8 light
48:38years away from us. Between Aristarchus and Huygens, people had answered that question which had so
48:46excited me as a young boy growing up in Brooklyn, the question, what are the stars?
48:55And the answer is that the stars are mighty suns light years away in the depths of interstellar space.
49:08And around those suns, are there other planets? And on those other worlds,
49:16are there beings who wonder as we do?
49:23Here is a light bulb, which is supposed to represent a nearby star. And next to it, and very hard to see
49:31because the bright light is a planet. Now we'll need a volunteer who would like to come up with these.
49:38Ordinarily, you would have a hard time seeing the planet because it's so close that the star
49:43washes out the planet. But if we're able to put something in front of the star to make an artificial
49:51eclipse, then we might be able to see the planet. So I'm going to stand over here, imagine that I'm
49:56a telescope somewhere near the Earth. And tab, if you'd slowly move the disk across,
50:04good, a little faster, be nice. But now you're just beginning to cover over the star.
50:09I really can't see the planet at all. Keep going. Good. Now right there, I can't see the star at all.
50:16And I see the planet lit by the light of the star. Now, that is a method for looking
50:23for planets around nearby stars. And that method uses a spacecraft to hold the disk and scan the sky
50:33for another telescope to see if there are any planets. So, Tab, you have successfully accomplished
50:39your mission to look for planets around other stars. Thank you for being our interplanetary spacecraft.
50:45So, this is one way. And there are spaceships that will be able to do this in the next 10 years or so.
50:53And there's another way. This has already been tried from the Earth. Imagine that there's a nearby
51:00star that you can see. It's bright. And it has a dark companion, a planet, shining only by reflected
51:07light near it so dim you can't see it. But imagine that this planet and its star are going around each
51:16other like that. You can see the star. You can't see the planet. So, now I'm going to need two volunteers.
51:24One. You two. Because, just to save some time. Now, I need one of you to turn the star on the planet
51:35and another person to pull the star and planet along. And what you will see is that the star you can
51:44make out will be moving in a funny, wiggly pattern, which will be the clue, the evidence for the existence
51:51of the dark planet. Okay. Let's have a spin. Good. And a pull. And you see this funny motion
51:58that the star makes because of the planet. Thank you very much. So, that's another way of finding out
52:04the existence of a planet that you couldn't see directly. Well, both of these methods are being used.
52:11And by the time that you people are as old as I am, we should know for all the nearest stars whether
52:23they have planets going around them or not. We might know dozens or even hundreds of other
52:29planetary systems and see if they're like our own or very different or no other planets going around
52:36other stars at all. That will happen in your lifetime. And it will be the first time in the history of the
52:41world that anybody found out really if there are planets around the other stars. Now, the nearby stars,
52:51the ones you can see with the naked eye, those are all in what's called the solar neighborhood.
52:56That's really what astronomers call it, the neighborhood. But it's a very tiny place in the Milky Way galaxy.
53:02The Milky Way is that band of light that you see across the sky on a clear night. I can't tell if
53:11there are any more clear nights in Brooklyn, but you must have seen the Milky Way, right?
53:15Think band of light at night. Well, that's just a hundred billion stars all seen together, edge on,
53:25as in this picture. If you could get out of the Milky Way galaxy and look down on it, it would look like
53:31that picture. And if we did look down on the Milky Way galaxy, where would the sun and nearby stars be?
53:38Would it be in the center where things look important or at least well lit? No. We would be
53:45way out here in the suburbs, in the countryside of the galaxy. We're not in any important place. All the
53:53stars you could see would be in a little, little place like that. And the Milky Way would be this band
53:59of light, a hundred billion stars all together. The fact that we live in the outskirts of the galaxy
54:06was discovered a long time ago, towards the end of the First World War, by a man named Harlow Shapley,
54:15who was mapping the position of these clusters of stars. See, every one of these is a bunch of maybe
54:2310,000 stars all together. It's called a globular cluster. And you can see that they are centered
54:30around the middle, the center of the galaxy. People used to think that the sun was at the center of
54:36the galaxy, something important about our position. It turns out to be wrong. We live in the outskirts.
54:44The globular clusters are centered around the marvelous middle of the Milky Way galaxy.
54:50And then it turned out that this isn't the only galaxy. We live in this one, but there are many
54:59others. And as this picture reminds us, there are many different kinds of galaxies, of which ours might
55:07be just this one. There are in fact a hundred billion other galaxies, each of which contains something
55:16like a hundred billion stars. Think of how many stars and planets and kinds of life there may be
55:25in this vast and awesome universe.
55:28As long as there have been humans, we have searched for our place in the cosmos. Where are we? Who are we?
55:43We find that we live on an insignificant planet of a humdrum star lost in a galaxy tucked away in some
55:53forgotten corner of the universe in which there are far more galaxies than people.
56:03We make our world significant by the courage of our questions and by the depth of our answers.
56:09We embarked on our journey to the stars with a question first framed in the childhood of our species
56:19and in each generation asked anew with undiminished wonder, what are the stars?
56:40The stars with the stars with the stars with the stars with the stars with the stars with the stars.
56:48Exploration is in our nature. We began as wanderers and we are wanderers still.
56:57We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail
57:17our stars with the stars with the stars.