#CarlSagan covers a wide range of scientific subjects, including the origin of life and a #perspective of our place in the universe...
A 13-part #documentary #series that covers a wide range of #scientific #subjects, including the #origin of #life and a #perspective of our place in the universe narrated by famous American #Scientist – #Carl #Sagan.
A 13-part #documentary #series that covers a wide range of #scientific #subjects, including the #origin of #life and a #perspective of our place in the universe narrated by famous American #Scientist – #Carl #Sagan.
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LearningTranscript
00:00:00To be continued...
00:00:30There is one experience that every human shares of every language and culture.
00:01:00The experience of birth.
00:01:03Our recollections of birth are hazy at best.
00:01:07They have the feel and aura not so much of memories as of mystical transfigurations.
00:01:15It would be astonishing if this profound early experience did not influence our myths and religions, our philosophy and our science.
00:01:25The birth of a child evokes the mystery of other origins, the beginnings and ends of worlds, infinity and eternity.
00:01:38How did the universe arise?
00:01:43What was around before that?
00:01:47Might there have been no beginning?
00:01:50Could the universe be infinitely old?
00:01:54Are there boundaries to the cosmos?
00:01:58The current scientific story of the origin of the universe begins with an explosion which made space itself expand.
00:02:06About 15 billion years ago, all the matter and energy that today make up the observable universe were concentrated into a space smaller than the head of a pin.
00:02:17The cosmos blew apart in one inconceivably colossal explosion, the Big Bang.
00:02:23And the stuff of the universe together with the fabric of space itself began expanding in all directions as they do today.
00:02:31We can visualize this process with a three-dimensional grid attached to the expanding fabric of space.
00:02:38The early cosmos was everywhere white-hot, but as time passed the radiation expanded and cooled and in ordinary visible light space became dark as it is today.
00:02:51But then little pockets of gas began to grow, tendrils of gossamer clouds formed, colonies of great lumbering, slowly spinning things, steadily brightening, each a kind of beast composed of a hundred billion shining points.
00:03:10The largest recognizable structures in the universe had formed.
00:03:19We see them today, we ourselves inhabit some lost corner of one.
00:03:23We call them the galaxies.
00:03:26We inhabit a universe of galaxies.
00:03:28There are unstructured blobs, the irregular galaxies, globular or elliptical galaxies, and the graceful blue arms of spiral galaxies.
00:03:39We've been investigating the galaxies, their origins, evolution and motions for less than a century.
00:03:47These studies extend our understanding to the farthest reaches of the universe.
00:03:52Our ship of the imagination carries us to that ultimate frontier.
00:03:59We view the cosmos on the grandest of scales.
00:04:04The majesty of the galaxies is revealed by science.
00:04:09There are many different ways in which stars are arrayed into galaxies.
00:04:13When, by chance, the face of a spiral galaxy is turned towards us, we see the spiral arms made luminous by billions of stars.
00:04:26When, in other cases, the edge of a galaxy is towards us, we see the central lanes of gas and dust from which the stars are forming.
00:04:39In barred spirals, a river of star stuff extends through the galactic center, connecting opposite spiral arms.
00:04:49Elliptical galaxies come in giant and dwarf sizes.
00:04:56There are many mysterious galaxies, places where something has gone terribly wrong, where there are explosions and collisions and streamers of gas and stars, bridges between the galaxies.
00:05:11The galaxies look rigid and unmoving, but we see them only for a single frame of the cosmic movie.
00:05:19Their parts are dissipating and reforming on a timescale of hundreds of millions of years.
00:05:25A galaxy is a fluid made of billions of suns all bound together by gravity.
00:05:32These giant galactic forms exist throughout the universe and may be a common source of wonderment and instruction for billions of species of intelligent life.
00:05:49Their evolution is governed everywhere by the same laws of physics.
00:05:58We need a computer to illustrate the collective motion of so many stars, each under the gravitational influence of all the others.
00:06:10A billion years is here, compressed into a few seconds.
00:06:18In some cases, spiral arms form all by themselves.
00:06:33In other cases, the close gravitational encounter of two galaxies will draw out spiral arms.
00:06:47But when two nearby galaxies collide, like a bullet through a swarm of bees, the stars hardly collide at all.
00:06:56But the shapes of the galaxies can be severely distorted.
00:07:00A direct collision of two galaxies can last a hundred million years and spill the constituent stars careening through intergalactic space.
00:07:15When a dense, compact galaxy runs into a larger one face-on, it can produce one of the loveliest of the rare irregulars, a ring galaxy.
00:07:28Thousands of light years across, a ring galaxy is set against the velvet of intergalactic space.
00:07:47It's a temporary configuration of disrupted stars, a splash in the cosmic pond.
00:08:00Galaxies sometimes blow themselves up.
00:08:07The quasars, probably billions of light years away, may be the colossal explosions of young galaxies.
00:08:15But we're not sure.
00:08:17Quasars are a mystery still.
00:08:20The galaxies reveal a universal order and beauty, but also violence on a scale never before imagined.
00:08:34The universe seems neither benign nor hostile.
00:08:38Merely indifferent to the concerns of such creatures as we.
00:08:43Quasars may be monster versions of rapidly rotating pulsars.
00:08:51Or due to multiple collisions of millions of stars densely packed in the galactic core.
00:08:57Or a chain reaction of supernova explosions in such a core.
00:09:04Some astronomers think a quasar is caused by millions of stars falling into an immense black hole in the core of a galaxy.
00:09:12Something like a black hole, something very massive, very dense and very small,
00:09:19is ticking and purring away in the cores of nearby galaxies.
00:09:25Even a well-behaved galaxy like the Milky Way has its stirrings and its dances.
00:09:42The stars of the Milky Way move with systematic grace.
00:09:48The sun takes 250 million years to go once around the core.
00:09:55The outer provinces of the galaxy revolve more slowly than the inner regions.
00:10:00As a result, gas and dust pile up in spiral patterns.
00:10:04These places of greater density are where young, hot, bright stars form.
00:10:09The stars which outline the spiral arms.
00:10:12These hot stars shine for only 10 million years or so and then blow up.
00:10:19But as the stars which outline a spiral arm burn out,
00:10:24new young stars are formed from the debris just behind them.
00:10:27And the spiral pattern persists.
00:10:30The sun marked here with a circle has been in and out of spiral arms often in the 20 times it has gone around the Milky Way.
00:10:40In this epoch, we live at the edge of a spiral arm.
00:10:50We've looked at internal galactic motion on a small scale across a million light years or less.
00:10:57But the motion of the galaxies themselves across billions of light years is different.
00:11:03That motion is a relic of the Big Bang.
00:11:08The key to cosmology, the study of the entire universe, turns out to be a commonplace of nature.
00:11:14An experience of everyday life.
00:11:22Imagine a moving object sending out waves.
00:11:25It could be light waves.
00:11:28It could be sound waves.
00:11:30It could be any kind of wave.
00:11:33When that moving object passes us, we sense a change in pitch.
00:11:42That's called the Doppler effect.
00:11:45If you're the engineer in the cab, then the pitch of your locomotive whistle always sounds the same to you.
00:11:54That's because you're moving along with the source of the sound.
00:11:59But if you're standing alongside the track when the train passes, you hear that familiar shift in pitch, the Doppler shift.
00:12:08The reason this happens is easy to understand once you visualize the waves.
00:12:18A stationary train sends out sound waves in perfect circles like the ripples on a pond.
00:12:24Let's start the train again.
00:12:31Now, the waves spreading out ahead of it get squashed together.
00:12:37And those spreading out behind it get stretched apart.
00:12:40The compressed waves have a higher frequency or pitch than the stretched out waves.
00:12:45The same thing is true for light waves.
00:12:49Color is to light, precisely what pitch is to sound.
00:12:53Compressed light waves are made bluer, they're blue shifted.
00:12:56Stretched out light waves are made redder, they're red shifted.
00:13:03At the speed of a train, you can sense the change of pitch for sound, but not for light.
00:13:08The train is traveling about a million times too slow for that.
00:13:12It turns out that the Doppler effect for light waves is the key to the cosmos.
00:13:25The evidence for this was gathered unexpectedly by a former mule team driver who never went beyond the eighth grade.
00:13:34During the second decade of this century, the world's largest telescope was being assembled on Mount Wilson,
00:13:39overlooking what were then the clear skies of Los Angeles.
00:13:44Large pieces of the telescope had to be hauled to the top of the mountain, a job for mule teams.
00:13:54One of the drivers was a young man named Milton Hummison, the ne'er-do-well son of a California banker.
00:14:00But he was bright and naturally curious about the equipment he had carted up Mount Wilson.
00:14:07And after the telescope was completed in 1917, he managed to stay on here as janitor and electrician.
00:14:13One evening, so the story goes, the observatory's night assistant was ill and Hummison was asked to fill in.
00:14:29Hummison was a gambling man, celebrated for his skill at poker and at the pool table.
00:14:34But his touch with the telescope was admired even more.
00:14:39He discovered he had a natural talent for using astronomical instruments.
00:14:43He became the virtuoso of the 100-inch telescope.
00:14:48In this instrument, the light from distant galaxies is focused on a glass photographic plate
00:14:54by a great encased mirror 100 inches across.
00:14:57By the late 1920s, Hummison was making observations himself.
00:15:03Mr. Nolson?
00:15:13Hummison, by now, had his own night assistant to help him with the observations.
00:15:20Afternoon, Mr. Nolson.
00:15:22Afternoon, Mr. Hummison.
00:15:24We'll start at six.
00:15:26I'll be making a spectrogram at the gas-of-rain focus.
00:15:29Yes, sir.
00:15:31The telescope must be able to point with high accuracy
00:15:34to a designated region of the sky and to keep on pointing there.
00:15:40A machine weighing about 75 tons as massive as a locomotive
00:15:44must move with a precision greater than that of the finest pocket watch.
00:15:47Everything must be checked thoroughly.
00:15:59The electrical power system must work flawlessly.
00:16:03Hours before observations are to begin, the dome is opened to allow the temperature inside and outside to be equalized.
00:16:18Hummison prepared the sensitive photographic emulsions sheathed in their metal holders
00:16:31to capture with the giant telescope the faint light from remote galaxies.
00:16:36This was part of a systematic program which Hummison and his mentor, the astronomer Edwin Hubble, were pursuing to measure the Doppler shift of light from the most distant galaxies then known.
00:16:51But the most distant galaxies are very faint.
00:16:58That's why, even with the largest telescope in the world, it was necessary to take very long time exposures,
00:17:05often lasting the whole night, and sometimes requiring several successive nights.
00:17:09Hummison would give the night assistant the celestial coordinates of the target galaxy.
00:17:26Through the long, cold night, he would have to make fine adjustments
00:17:30so the telescope would precisely track the target galaxy.
00:17:33The galaxy itself was much too faint to see through the great telescope, although it could be recorded photographically with a long time exposure.
00:17:42So the telescope would be pointed at a nearby bright star, and then offset to a featureless patch of sky,
00:17:51from which, over the long night, the light from the unseen galaxy would slowly accumulate.
00:17:56The telescope focused the faint white light from the galaxy into the spectrometer, where it was spread out into its rainbow of constituent colors.
00:18:06The spectrum would be recorded on the little glass plates.
00:18:10All right, would you clap in the drive and slew to the focus star, please?
00:18:14Are you clear? I'm going to slew to the east.
00:18:18Yes, I think I'm clear. Just take it easy.
00:18:22Take it easy.
00:18:43All right, I have it.
00:18:45Now let's go to MGC 7619. I'm clear.
00:18:54Going to do a ten-hour exposure.
00:19:00What time is it?
00:19:01Uh, 7.15.
00:19:03All right, lights out, please.
00:19:10Dark slide is open.
00:19:15A large telescope views only a tiny patch of sky.
00:19:28As the Earth turns, a guide star or a galaxy would drift out of the telescope's field of view in only a few minutes.
00:19:35Hummison had to stay awake, tracking the galaxy, while elaborate machinery moved the telescope slowly in the opposite direction, to compensate for the Earth's rotation.
00:19:46The telescope is a kind of clock.
00:19:48How's the door?
00:19:49You're clear.
00:19:50This work was difficult, routine, tedious, but although they didn't yet know it, Hubble and Hummison were meticulously accumulating the evidence for the Big Bang.
00:20:01They had found that the more distant the galaxy, the more its spectrum of colors was shifted to the red.
00:20:14All right, clear the telescope. I'm coming down now.
00:20:30If this redshift were due to the Doppler effect, the distant galaxies must be running away from us.
00:20:39At the end of his vigil, Hummison would retrieve the tiny galactic spectrum and carefully carry it down to be developed.
00:20:47Thank you, Mr. Nelson. I'm going to the dark room now.
00:21:01Good day.
00:21:02Good day, sir.
00:21:08Hummison found a redshift in almost every galaxy he examined, like the Doppler shift in the sound of a receding locomotive.
00:21:16And the farther away from us they were, the faster they were receding.
00:21:26Tied to the fabric of space, the outward rushing galaxies were tracing the expansion of the universe itself.
00:21:34An awesome conclusion had been captured on these tiny glass slides.
00:21:40Hummison and Hubble had discovered the Big Bang.
00:21:46At top and bottom are calibration lines that Hummison had earlier photographed.
00:21:54In the middle is the spectrum of a relatively nearby galaxy.
00:21:58Every element has a characteristic spectral fingerprint, a set of frequencies where light is absorbed.
00:22:04Prominent here are two dark lines and the violet due to calcium in the atmospheres of the hundreds of billions of stars that constitute this galaxy.
00:22:15Nearby galaxies showed very little Doppler shift.
00:22:18But when he recorded the spectrum of a fainter and more distant galaxy, he found the same telltale pair of lines, but shifted farther right toward the red.
00:22:28And when he examined a remote galaxy four billion light years away, he found that the lines were red shifted even more.
00:22:36This galaxy must be receding at 200 million kilometers an hour.
00:22:40The painstaking observations of Milton Hummison, astronomer and former mule team driver, established the expansion of the universe.
00:22:53In discussing the large scale structure of the cosmos, astronomers sometimes say that space is curved.
00:23:07Or that the universe is finite but unbounded.
00:23:14Whatever are they talking about?
00:23:17Let's imagine that we are perfectly flat. I mean absolutely flat.
00:23:22And that we live, appropriately enough, in a flat land.
00:23:26A land designed and named by Edwin Abbott, a Shakespearean scholar who lived in Victorian England.
00:23:34Everybody in flat land is, of course, exceptionally flat.
00:23:39We have squares, circles, triangles, and we all scurry about, and we can go into our houses and do our flat business.
00:23:49Now, we have width and length, but no height at all.
00:23:57Now, these little cut-outs have some little height, but let's ignore that.
00:24:01Let's imagine that these are absolutely flat.
00:24:04That being the case, we know, us flat-landers, about left-right, and we know about forward-back, but we have never heard of up-down.
00:24:14Let us imagine that into flat land, hovering above it, comes a strange three-dimensional creature which, oddly enough, looks like an apple.
00:24:26And the three-dimensional creature sees an attractive, congenial-looking square, watches it enter its house, and decides, in a gesture of inter-dimensional amity, to say hello.
00:24:41Hello, says the three-dimensional creature. How are you? I am a visitor from the third dimension.
00:24:49Well, the poor square looks around his closed house, sees no one there, and, what's more, has witnessed a greeting coming from his insides, a voice from within.
00:25:02He surely is getting a little worried about his sanity.
00:25:08The three-dimensional creature is unhappy about being considered a psychological aberration, and so he descends to actually enter flat-land.
00:25:20Now, a three-dimensional creature exists in flat-land only partially, only a plane, a cross-section through him, can be seen.
00:25:29So, when the three-dimensional creature first reaches flat-land, it's only the points of contact which can be seen.
00:25:36And we'll represent that by stamping the apple in this ink pad, and placing that image in flat-land.
00:25:45And as the apple were to descend through, slither by, flat-land, we would progressively see higher and higher slices, which we can represent by cutting the apple.
00:26:01So, the square, as time goes on, sees a set of objects mysteriously appear from nowhere, and inside a closed room, and change their shape dramatically.
00:26:19His only conclusion could be that he's gone bonkers.
00:26:23Well, the apple might be a little annoyed at this conclusion, and so, not such a friendly gesture from dimension to dimension.
00:26:31Makes a contact with the square from below, and sends our flat creature fluttering and spinning above flat-land.
00:26:40At first, the square has no idea what's happening.
00:26:43It's terribly confused.
00:26:44This is utterly outside his experience.
00:26:47But after a while, he comes to realize that he is seeing inside closed rooms in flat-land.
00:26:55He is looking inside his fellow flat creatures.
00:26:59He is seeing flat-land from a perspective no one has ever seen it before, to his knowledge.
00:27:04Getting into another dimension provides, as an incidental benefit, a kind of X-ray vision.
00:27:10Now, our flat creature slowly descends to the surface, and his friends rush up to see him.
00:27:19From their point of view, he has mysteriously appeared from nowhere.
00:27:23He hasn't walked from somewhere else.
00:27:25He's come from some other place.
00:27:27They say, for heaven's sake, what's happened to you?
00:27:30And the poor square has to say, well, I was in some other mystic dimension called up.
00:27:38And they will pat him on his side and comfort him, or else they'll ask, well, show us.
00:27:45Where is that third dimension?
00:27:47Point to it.
00:27:48And the poor square will be unable to comply.
00:27:51But maybe more interesting is the other direction in dimensionality.
00:27:57What about the fourth dimension?
00:28:00Now, to approach that, let's consider a cube.
00:28:04We can imagine a cube in the following way.
00:28:07You take a line segment and move it at right angles to itself in equal length.
00:28:12That makes a square.
00:28:13Move that square in equal length at right angles to itself, and you have a cube.
00:28:18Now, this cube, we understand, casts a shadow.
00:28:27And that shadow we recognize.
00:28:32It's, you know, ordinarily drawn in third-grade classrooms as two squares with their vertices connected.
00:28:40Now, if we look at the shadow of a three-dimensional object in two dimensions, we see that, in this case, not all the lines appear equal.
00:28:49Not all the angles are right angles.
00:28:51The three-dimensional object has not been perfectly represented in its projection in two dimensions, but that's part of the cost of losing a dimension in the projection.
00:29:01Now, let's take this three-dimensional cube and project it, carry it, through a fourth physical dimension.
00:29:11Not that way, not that way, not that way, but at right angles to those three directions.
00:29:18I can't show you what direction that is, but imagine that there is a fourth physical dimension.
00:29:22In that case, we would generate a four-dimensional hypercube, which is also called a tesseract.
00:29:29I cannot show you a tesseract, because I and you are trapped in three dimensions.
00:29:35But what I can show you is the shadow in three dimensions of a four-dimensional hypercube, or tesseract.
00:29:43This is it.
00:29:45And you can see, it's two nested cubes, all the vertices connected by lines.
00:29:52And now, the real tesseract in four dimensions would have all the lines of equal length and all the angles right angles.
00:30:00That's not what we see here, but that's the penalty of projection.
00:30:05So, you see, while we cannot imagine the world of four dimensions, we can certainly think about it perfectly well.
00:30:17Now, imagine a universe just like Flatland, truly two-dimensional, and entirely flat in every direction, but with one exception.
00:30:27Unbeknownst to the inhabitants, their two-dimensional universe is curved into a third physical dimension.
00:30:34Maybe into a sphere, but at any rate, into something entirely outside their experience.
00:30:40Locally, their universe still looks flat enough.
00:30:45But if one of them, much smaller and flatter than me, takes a very long walk along what seems to be a straight line,
00:30:53he would uncover a great mystery.
00:30:56Suppose he marked his starting point here, and set off to explore his universe.
00:31:05He never turns around, and he never reaches an edge.
00:31:08He doesn't know that his apparently flat universe is actually curved into an enormous sphere.
00:31:15He doesn't sense that he's walking around a globe.
00:31:21Why should his face be curved?
00:31:23Because there's so much matter in this universe that it gravitationally warps space, closing it back on itself into a sphere.
00:31:31But our Flatlander doesn't know this.
00:31:33After a long while, you'll find he somehow returns to his starting point.
00:31:38There must be a third dimension.
00:31:41Our Flatlander couldn't imagine a third dimension, but he could sure deduce it.
00:31:48Now, increase all the dimensions in this story by one, and you have something like the situation which many cosmologists think may actually apply to us.
00:31:57We are three-dimensional creatures trapped in three dimensions.
00:32:03We imagine our universe to be flat in three dimensions.
00:32:06But maybe it's curved into a fourth.
00:32:10We can talk about a fourth physical dimension, but we can't experience it.
00:32:15No one can point to the fourth dimension.
00:32:17I mean, there's left-right, and there's forward-back, there's up-down, and there's some other direction simultaneously at right angles to those familiar three dimensions.
00:32:29Now, imagine this universe is expanding.
00:32:34If we blow it up like a four-dimensional balloon, what happens?
00:32:38An astronomer on a given galaxy thinks all the other galaxies are running away from him.
00:32:45The more distant the galaxy, the faster it seems to be moving.
00:32:49This is just what Hummison and Hubble found.
00:32:52On the surface of this curved universe, there is no boundary or center.
00:32:59The universe can be both finite and unbounded.
00:33:08The red shift of the distant galaxies seemed to imply to Hummison's contemporaries that we were at the center of an expanding universe,
00:33:15that our place in space was somehow privileged.
00:33:18But if the universe is expanding, whether or not it's curved into a fourth dimension,
00:33:23observers on every galaxy will see precisely the same thing.
00:33:27All the galaxies rushing away from them as if they had made some dreadful intergalactic social blunder.
00:33:35If there's enough matter to close the universe gravitationally, then it's wrapped in on itself like a sphere.
00:33:41If there isn't enough matter to close the cosmos, then our universe has an open shape extending forever in all directions.
00:33:53This saddle universe is only one of an infinite number of possible kinds of open universes.
00:34:00Unlike such closed universes as the sphere, open universes have in them an infinite amount of space.
00:34:12If our universe is in fact closed off, then nothing can get out, not matter, not light.
00:34:18We would then be living inside a black hole.
00:34:21There is one possible way out though, a hypothetical tunnel or wormhole through the next higher dimension,
00:34:29a place sucking in matter and light.
00:34:34Can we find such a wormhole? Could we survive the trip?
00:34:37We might emerge in some other place in time, perhaps in another universe, or perhaps somewhere else in our own.
00:34:50If you want to know what it's like inside a black hole, look around.
00:34:57But we don't yet know whether the universe is open or closed.
00:35:02More than that, there are a few astronomers who doubt that the red shift of distant galaxies is due to the Doppler effect,
00:35:09who are skeptical about the expanding universe and the Big Bang.
00:35:14Perhaps our descendants will regard our present ignorance with as much sympathy as we feel to the ancients
00:35:22for not knowing whether the Earth went around the sun.
00:35:25If the general picture, however, of a Big Bang followed by an expanding universe is correct, what happened before that?
00:35:34Was the universe devoid of all matter and then the matter suddenly somehow created? How did that happen?
00:35:41In many cultures, the customary answer is that a god or gods created the universe out of nothing.
00:35:51But if we wish to pursue this question courageously, we must, of course, ask the next question.
00:35:58Where did God come from?
00:35:59If we decide that this is an unanswerable question, why not save a step and conclude that the origin of the universe is an unanswerable question?
00:36:09Or, if we say that God always existed, why not save a step and conclude that the universe always existed?
00:36:17There's no need for a creation. It was always here. These are not easy questions.
00:36:23Cosmology brings us face to face with the deepest mysteries, with questions that were once treated only in religion and myth.
00:36:32Who knows for certain? Who shall here declare it? Whence was it born? Whence came creation?
00:36:52The gods are later than this world's formation. Who then can know the origins of the world?
00:37:02None knows whence creation arose, or whether he has or has not made it, he who surveys it from the lofty skies.
00:37:12Only he knows, or perhaps he knows not.
00:37:21These words are 3,500 years old. They're taken from the Rig Veda, a collection of early Sanskrit hymns.
00:37:29The most sophisticated ancient cosmological ideas came from Asia, and particularly from India.
00:37:36Here, there's a tradition of skeptical questioning and unselfconscious humility before the great cosmic mysteries.
00:37:44Amidst the routine of daily life, in say the harvesting and winnowing of grain, people all over the world have wondered, where did the universe come from?
00:37:57Asking this question is a hallmark of our species.
00:38:09There's a natural tendency to understand the origin of the cosmos in familiar biological terms.
00:38:14The mating of cosmic deities, or the hatching of a cosmic egg, or maybe the intonation of some magic phrase.
00:38:23The Big Bang is our modern scientific creation myth.
00:38:35It comes from the same human need to solve the cosmological riddle.
00:38:39Most cultures imagined the world to be only a few hundred human generations old.
00:38:46Hardly anyone guessed that the cosmos might be far older.
00:38:50But the ancient Hindus did.
00:38:52They, like every other society, noted and calibrated the cycles in nature.
00:39:05The rising and setting of the sun and stars.
00:39:09The phases of the moon.
00:39:13The passing of the seasons.
00:39:30All over South India, an age-old ceremony takes place every January.
00:39:35A rejoicing in the generosity of nature in the annual harvesting of the crops.
00:39:40Every January, nature provides the rice to celebrate pangal.
00:39:47Even the draft animals are given the day off and garlanded with flowers.
00:40:03Colorful designs are painted on the ground to attract harmony and good fortune for the coming year.
00:40:10Pangal, a simple porridge.
00:40:38A simple porridge, a mixture of rice and sweet milk,
00:40:42symbolizes the harvest, the return of the seasons.
00:40:58However, this is not merely a harvest festival.
00:41:02It has ties to an elegant and much deeper cosmological tradition.
00:41:08The Pungal Festival is a rejoicing in the fact that there are cycles in nature.
00:41:24But how could such cycles come about unless the gods will them?
00:41:28And if there are cycles in the years of humans,
00:41:31might there not be cycles in the eons of the gods?
00:41:36The Hindu religion is the only one of the world's great faiths
00:41:40dedicated to the idea that the cosmos itself
00:41:44undergoes an immense, indeed an infinite, number of deaths and rebirths.
00:41:50It is the only religion in which the timescales correspond, no doubt by accident, to those of modern scientific cosmology.
00:42:00Its cycles run from our ordinary day and night to a day and night of Brahma, 8.64 billion years long.
00:42:10Longer than the age of the earth or the sun, and about half the time since the Big Bang.
00:42:24And there are much longer timescales still.
00:42:34There is the deep and appealing notion that the universe is but the dream of the god,
00:42:50who, after a hundred Brahma years, dissolves himself into a dreamless sleep and the universe dissolves with him.
00:43:02Until, after another Brahma century, he stirs, recomposes himself and begins again to dream the great cosmic lotus dream.
00:43:14Meanwhile, elsewhere, there are an infinite number of other universes, each with its own god dreaming the cosmic dream.
00:43:32These great ideas are tempered by another, perhaps still greater.
00:43:42It is said that men may not be the dreams of the gods, but rather that the gods are the dreams of men.
00:43:53In India, there are many gods, and each god has many manifestations.
00:44:03These Chola bronzes cast in the 11th century include several different incarnations of the god Shiva, seen here at his wedding.
00:44:14The most elegant and sublime of these bronzes is a representation of the creation of the universe at the beginning of each cosmic cycle,
00:44:24a motif known as the cosmic dance of Shiva.
00:44:29The god has four hands.
00:44:32In the upper right hand is a drum whose sound is the sound of creation.
00:44:40In the upper left hand is a tongue of flame, a reminder that the universe, now newly created,
00:44:48will, billions of years from now, be utterly destroyed.
00:44:53Creation, destruction.
00:44:56The world's most important is the world's most important.
00:45:21These profound and lovely ideas are central to ancient Hindu beliefs as exemplified in this Chola temple at Dallas Suram.
00:45:33They are a kind of premonition of modern astronomical ideas.
00:45:38Without doubt, the universe has been expanding since the Big Bang, but it is by no means clear that it will continue to expand forever.
00:45:46If there is less than a certain amount of matter in the universe, then the mutual gravitation of the receding galaxies will be insufficient to stop the expansion and the universe will run away forever.
00:46:01But if there is more matter than we can see, hidden away in black holes, say, or in hot but invisible gas between the galaxies, then the universe holds together and partakes of a very Indian succession of cycles, expansion followed by contraction, cosmos upon cosmos, universes without end.
00:46:25If we live in such an oscillating universe, then the Big Bang is not the creation of the cosmos, but merely the end of the previous cycle, the destruction of the last incarnation of the cosmos.
00:46:38Neither of these modern cosmologies may be altogether to our liking.
00:46:46In one cosmology, the universe is created somehow from nothing 15 to 20 billion years ago and expands forever.
00:46:56The galaxies mutually receding until the last one disappears over our cosmic horizon.
00:47:03Then, the galactic astronomers are out of business, the stars cool and die, matter itself decays, and the universe becomes a thin, cold haze of elementary particles.
00:47:21In the other, the oscillating universe, the cosmos has no beginning and no end, and we are in the midst of an infinite cycle of cosmic deaths and rebirths,
00:47:32with no information trickling through the cusps of the oscillation.
00:47:37Nothing of the galaxies, stars, planets, lifeforms, civilizations evolved in the previous incarnation of the universe trickles through the cusp,
00:47:49flitters past the Big Bang to be known in our universe.
00:47:53The death of the universe in either cosmology may seem a little depressing, but we may take some solace in the time scales involved.
00:48:10These events will take tens of billions of years or more.
00:48:15Human beings, or our descendants, whoever they might be, can do a great deal of good in tens of billions of years before the cosmos dies.
00:48:26If the universe truly oscillates, if the modern scientific version of the old Hindu cosmology is valid, then still stranger questions arise.
00:48:49Some scientists think that when redshift is followed by blueshift, causality will be inverted, and effects will precede causes.
00:49:06First, the ripples spread out from a point on the water's surface.
00:49:11Then, I throw the stone into the pond.
00:49:18Some scientists wonder, in an oscillating universe, about what happens at the cusps, at the transition from contraction to expansion.
00:49:30Some think that the laws of nature are then randomly reshuffled, that the kinds of physics and chemistry we have in this universe represent only one of an infinite range of possible natural laws.
00:49:45It is easy to see that only a very restricted range of laws of nature are consistent with galaxies and stars, planets, life and intelligence.
00:49:57If the laws of nature are randomly reshuffled at the cusps, then it is only the most extraordinary coincidence that the cosmic slot machine has this time come up with a universe consistent with us.
00:50:13Do we live in a universe which expands forever, or in one where there is a nested set of infinite cycles?
00:50:23There is a way to find out the answer to that question, not by mysticism, but through science.
00:50:29By making an accurate census of the total amount of matter in the universe, or by seeing to the very edge of the cosmos.
00:50:41Radio telescopes are able to detect distant quasars billions of light years away, expanding with the fabric of space.
00:51:00By looking far out into space, we are also looking far back into time, back toward the horizon of the universe, back toward the epoch of the Big Bang.
00:51:16Radio telescopes have even detected the cosmic background radiation.
00:51:22The fires of the Big Bang, cooled and redshifted, faintly echoing down the corridors of time.
00:51:30This is the very large array, a collection of 17 separate radio telescopes, all working collectively in a remote region of New Mexico.
00:51:50Modern radio telescopes are exquisitely sensitive.
00:51:55A distant quasar is so faint that its received radiation by some such telescope amounts to maybe a quadrillionth of a watt.
00:52:08In fact, this is a reasonably stunning piece of information, the total amount of energy ever received by all the radio telescopes on the planet Earth is less than the energy of a single snowflake striking the ground.
00:52:25In detecting the cosmic background radiation, in counting quasars, in searching for intelligent signals from space, radio astronomers are dealing with amounts of energy which are barely there at all.
00:52:44These radio telescopes, rising like giant flowers from the New Mexico desert, are monuments to human ingenuity.
00:52:59The faint radio waves are collected, focused, assembled and amplified, and then converted into pictures of nebulae, galaxies and quasars.
00:53:13If you had eyes that worked in radio light, they'd probably be bigger than wagon wheels.
00:53:18And this is the universe you'd see.
00:53:23An elliptical galaxy, for example, leaving behind it a long wake glowing in radio waves.
00:53:34Radio waves reveal a universe of quasars, interacting galaxies, titanic explosions.
00:53:42Every time we use another kind of light to view the cosmos, we open a new door of perception.
00:53:52As the murmurs from the edge of the cosmos slowly accumulate, our understanding grows.
00:54:01This is an exploration of the ancient and the invisible.
00:54:12A continuing human inquiry into the grand cosmological questions.
00:54:17Another important recent finding was made by X-ray observatories in Earth orbit.
00:54:36Artificial satellites launched to view the sky, not in ordinary visible light, not in radio waves, but in X-ray light.
00:54:46There seems to be an immense cloud of extremely hot hydrogen glowing in X-rays between some galaxies.
00:54:56Now, if this amount of intergalactic matter were typical of all clusters of galaxies, then there may be just enough matter to close the cosmos and to trap us forever in an oscillating universe.
00:55:12If the cosmos is closed, there's a strange, haunting, evocative possibility, one of the most exquisite conjectures in science or religion.
00:55:28It's entirely undemonstrated. It may never be proved, but it's stirring.
00:55:34Our entire universe, to the furthest galaxy, we are told, is no more than a closed electron in a far grander universe we can never see.
00:55:45And that universe is only an elementary particle in another still greater universe, and so on, forever.
00:55:52Also, every electron in our universe, it is claimed, is an entire miniature cosmos containing galaxies and stars and life and electrons.
00:56:04Every one of those electrons contains a still smaller universe, an infinite regression, up and down.
00:56:15Every human generation has asked about the origin and fate of the cosmos.
00:56:21Ours is the first generation with a real chance of finding some of the answers.
00:56:28One way or another, we are poised at the edge of forever.
00:56:34Except for planetary exploration, the study of galaxies and cosmology, what this episode was about, have undergone the greatest advances since cosmos was first broadcast.
00:56:54For one thing, at last we have a good photograph of our own Milky Way galaxy, about 100,000 light years across.
00:57:03Here it is.
00:57:09It was taken by NASA's COBE satellite.
00:57:13We see it edge on, of course, since we're embedded in the plane of the galaxy.
00:57:18But you don't need a spacecraft to see it.
00:57:20If it's a clear night tonight, why not go out and take a look at the Milky Way?
00:57:26There's also new evidence suggesting that the Milky Way is not so much an ordinary spiral galaxy as a barred spiral, like this.
00:57:40Important work has now been done on mapping how the galaxies are scattered through intergalactic space.
00:57:47To the surprise of a lot of scientists, on a scale of hundreds of millions of light years, the galaxies turn out not to be strewn at random or concentrated in clusters of galaxies, but instead strung out along odd, irregular surfaces, like this.
00:58:09Every dot in this computer animation is a galaxy.
00:58:14The computer lets us look at this distribution of galaxies from many points of view, but this is how it looks, from the Earth.
00:58:23There's an odd mannequin shape that is presented by the distribution of galaxies.
00:58:31This work has been done mainly by Margaret Geller with her collaborator John Huckra at Harvard University and the Smithsonian Institution.
00:58:42It's a little like soap bubbles in a bathtub or in dishwashing detergent.
00:58:57The galaxies are on the surfaces of the bubbles.
00:59:01The insides of the bubbles seem to have almost no galaxies in them at all.
00:59:05An average bubble is about a hundred million light years across.
00:59:09And that means that we've mapped still only a very small volume of the accessible universe.
00:59:15The galaxy is nearest to us.
00:59:17But pretty soon, we should be able to extend this search out to enormous distances.
00:59:22Out to distances so far away in space that we're looking back to the time that galaxies and their structures were first forming.
00:59:30And this poses a real problem.
00:59:33Most cosmologists hold that the galaxies arise from a pre-existing lumpiness in the early universe with little lumps growing into galaxies.
00:59:43But the background radiation from the Big Bang that fills all of space has now been carefully measured by that same COBE satellite that took that picture.
00:59:54Now, those radio waves seem almost perfectly uniform across the sky as if the Big Bang weren't lumpy or granular at all.
01:00:04But if the early radiation and matter in the universe weren't lumpy, how could individual galaxies form?
01:00:10How could the bubbles form?
01:00:12Is there a contradiction between the uniformity of the Big Bang radio waves and the bubble structures formed by the galaxies?
01:00:19That's the question.
01:00:20When our survey of the galaxies reaches out to billions of light years, we'll have the answer to this question.
01:00:26Incidentally, maybe you're thinking that the bubbles imply a bubble maker.
01:00:36But then I'd have to ask you, who made the bubble maker?
01:00:40There's another infinite regress lurking here.
01:00:44And to one of the grandest questions, whether there's enough matter in the universe to close it, the only fair answer is that we still don't know.
01:00:52If it is closed, what is the hidden matter that's closing it?
01:00:56Is it faint stars, black holes, massive neutrinos, some exotic kind of dark matter unknown on Earth?
01:01:03We don't know.
01:01:04But there are reasons to think that we'll soon find out the answers.
01:01:10We can't wait to see you, too.
01:01:12But you will see that in the universe of the galaxy's heart is why.
01:01:20If there's no doubt, it's azięki zone to help us.
01:01:23The moon is also from the moon.
01:01:25You will soon find the darkness and the dark inside of the sea.
01:01:29I'm like, if there's nothing more.
01:01:31The moon is also from the moon.
01:01:33If there's no doubt about the moon.
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