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00:00:00Hello. My name is Stephen Hawking. Physicist, cosmologist, and something of a dreamer.
00:00:15Although I cannot move, and I have to speak through a computer, in my mind, I am free.
00:00:25Free to tour the universe, and tell the ultimate story.
00:00:33The story of everything there ever was.
00:00:40From the moment the cosmos began, to the creation of our world and everything in it,
00:00:50and beyond, to the far, far future, and the end of the universe itself.
00:00:58A journey through all of space, and all of time.
00:01:06Check it out.
00:01:26I spend a lot of time thinking about the universe, but I never get bored.
00:01:32After all, it's a pretty extraordinary place.
00:01:37This is the cosmos, at a very large scale.
00:01:42Each tiny point of light is an entire galaxy.
00:01:47Each a cluster of as many as 400 billion individual stars.
00:01:54This view of the universe is only possible due to the latest supercomputers.
00:02:02I find it indescribably beautiful.
00:02:06Uncountable billions of galaxies, forming a vast web stretching away in all directions.
00:02:13What's more, I never get over the fact that within this massive universe lies one perfectly ordinary spiral galaxy.
00:02:25Inside that galaxy exists a commonplace yellow star.
00:02:35Orbited by eight planets.
00:02:45On one of those planets lives a species that has only just worked out what a remarkable place the universe is.
00:02:52We've discovered more about the cosmos in the last century than in all previous human history.
00:03:14Finally, we are solving the basic mysteries that have perplexed our ancestors for at least 200,000 years.
00:03:27What I like above all is that the facts themselves are both breathtakingly elegant and surprising.
00:03:42We're living just as it dawns on us that the earth and everything around us was made by the stars.
00:03:52Boiling furnaces of hydrogen gas, like our sun, made even the atoms in your eyelashes.
00:03:59We've worked out that the universe is almost unimaginably ancient.
00:04:06About 14 billion years old.
00:04:09And that it will continue to exist for at least twice that long.
00:04:13But without a doubt, the most remarkable fact of all is that the entire enormous universe, all the innumerable galaxies, even time and space, and the forces of nature themselves, simply materialized out of nothing.
00:04:40So now is a good time to be alive, I think.
00:04:47We may only be an advanced breed of monkey, living on a small planet, but we are able to contemplate the universe as a whole, which makes us very special.
00:04:59My goal has always been simple, to work out how the universe works, and why it exists at all.
00:05:08Luckily there are clues everywhere, and the most important one is right above our heads.
00:05:18Join them and console.
00:05:19In the world where we are.
00:05:20Examine any patch of the night sky, even one as small as the head of a pin, and this is what you'll find.
00:05:34galaxies. It's less than a millionth of what we can see of the cosmos from our little planet.
00:05:41But even this tiny sample is enough to find the clue, the key to the past, the present,
00:05:50and perhaps the future too. The clue is that seen from Earth, all these distant galaxies
00:05:58are slightly red in colour. They appear almost as if we were looking through rose-tinted glasses.
00:06:09It's this very redness that reveals how the universe was born.
00:06:14And to show you why, I need a straight road and a noisy car.
00:06:29Listen to the sound as it passes by.
00:06:35As the car approaches, the pitch of its engine rises.
00:06:42As it goes away, the pitch of its engine falls.
00:06:50This phenomenon is called a Doppler shift.
00:06:53And the exact same thing happens with light.
00:06:59If our eyes were more sensitive to colour, we could see that the car is actually very slightly blue as it approaches.
00:07:10And very slightly red as it goes away.
00:07:13The same rules apply in space.
00:07:23All distant galaxies are slightly red in colour.
00:07:29So by the exact same piece of basic physics, they must all be moving away too.
00:07:34In fact, the whole universe is expanding.
00:07:39In all directions.
00:07:42Getting bigger and bigger.
00:07:45Like a balloon inflating.
00:07:47I admit this sounds strange.
00:07:51But to cosmologists, it's like winning the lottery.
00:07:54Because to work out where the universe came from, all we need to do is to stop time and make it run in reverse.
00:08:06Rewind far enough, and everything gets closer together.
00:08:14A lot closer together.
00:08:17All the galaxies.
00:08:19In fact, every single thing.
00:08:21Converges to a single point.
00:08:24The start of everything.
00:08:2713.7 billion years ago.
00:08:29So it's quite simple, really.
00:08:43Follow the clues.
00:08:45And we can deduce that a very long time ago, the universe simply burst into existence.
00:08:52An event called the Big Bang.
00:08:59But I'm afraid we have to stop a moment.
00:09:07Before we get carried away by fire and noise.
00:09:11At the very beginning, the Big Bang actually happened in total darkness.
00:09:18Because light didn't exist yet.
00:09:22To see it, we'd have needed some kind of cosmic night vision.
00:09:29But even this, a view from the outside, is impossible.
00:09:36Again, it sounds strange.
00:09:39But space didn't exist then either.
00:09:43So there was no outside.
00:09:46The only place there was, was inside.
00:09:50This early universe was a very strange thing indeed.
00:10:01There's still much I'd dearly love to know about it.
00:10:04But standard concepts of time or space don't really apply.
00:10:10It was just a very tiny, ultra-hot fog of energy.
00:10:15Then it expanded.
00:10:16With a tremendous flash of radiation.
00:10:29From smaller than an atom, to about the size of an orange, in less than a trillionth of a second.
00:10:36Almost no time at all.
00:10:44The universe simply inflated into existence.
00:10:49Unfolding.
00:10:51Unfurling.
00:10:53Getting bigger and cooler with every passing moment.
00:10:56Within 100 seconds, it was as big as our solar system.
00:11:08Trillions of miles across.
00:11:14While this was happening, the pure energy of the cosmos began to cool and create matter.
00:11:20In the form of countless trillions of subatomic particles.
00:11:28The first stuff there ever was.
00:11:34Half these particles were made of matter.
00:11:37The same kind of stuff which makes us.
00:11:40The rest were made of the opposite of matter.
00:11:43Stuff called anti-matter.
00:11:45When the two meet, they destroy each other in a flash of energy.
00:12:03It seems as if building a universe is a pretty wasteful process.
00:12:07Fortunately, there was just a bit more matter than anti-matter.
00:12:17Just one in a billion particles of stuff survived.
00:12:28Which was lucky for us.
00:12:30Because that residue is what our present-day universe is made of.
00:12:35You could say that we are made of the smoke of the Big Bang.
00:12:45By the time the cosmos was 10 minutes old, it was already thousands of light years in diameter.
00:12:55After that, everything spread out and cooled for about 330,000 years.
00:13:00When finally the fog cleared, and the universe became visible.
00:13:06So that's how everything got going.
00:13:08Which I think is a pretty fantastic story.
00:13:09And probably much stranger than anything our ancestors came up with by way of an explanation.
00:13:13But the next thing that happened.
00:13:14Well, that's pretty spectacular too.
00:13:15But the next thing that happened.
00:13:16Well, that's pretty spectacular too.
00:13:20Good morning.
00:13:27I was so mad at the end.
00:13:28You were at the end of the day.
00:13:30How did you get out of the world?
00:13:32I was on the day.
00:13:33On the day.
00:13:34But I was so mad, I was so mad.
00:13:36Well, that's pretty spectacular, too.
00:13:53This is the universe seen in extreme fast forward.
00:13:58All 14 billion years in less than a minute.
00:14:02It shows how the universe changed from a cloud of gas into a place filled with perhaps a hundred billion galaxies swirling in a vast chaotic dance.
00:14:20What I love to get people thinking about is that all this had to be built atom by atom.
00:14:27Celestial engineering on a spectacular scale.
00:14:34So what drove this cosmic clockwork?
00:14:38I'd say it was the force of gravity.
00:14:42The idea of gravity was worked out by Sir Isaac Newton, who had the same job as me here at Cambridge University back in the 17th century.
00:14:59It supposedly dawned on him when an apple fell on his head.
00:15:06The apple helped him realize that all objects attract each other, and the greater the mass, the stronger the pool.
00:15:24The apples are attracted to the earth, and although you can't see it, the earth moves very slightly up, towards the apples.
00:15:37All things come together through the power of gravity.
00:15:43All things come together through the power of gravity.
00:15:50Gravity was created in the Big Bang, and has been at work ever since.
00:15:55It's what keeps you, me, and apples, stuck to the earth.
00:16:06In the early universe, gravity had a much bigger role to play.
00:16:18Right after the Big Bang, the universe was just gas, almost perfectly spread out throughout space.
00:16:33Over the next 200 million years, gravity began to pull the gas back together, to produce the very first structures from which everything else would grow.
00:16:53But even this very nearly didn't happen.
00:16:56If it weren't for another stroke of cosmic luck, there would be no you, no me, no stars or planets, or anything at all.
00:17:16We know this, because in 1982 a group of scientists, including myself, spent three solid weeks working it out.
00:17:26Although the calculations were hard, demonstrating what we discovered is easy.
00:17:33First, I need a nice flat floor, like this one, for example.
00:17:38This is the dining room in my college.
00:17:42I'm going to fill the place with lots and lots of ball bearings.
00:17:56These balls represent the matter of the early universe.
00:18:15A thin gas spread out evenly across the vast cosmos.
00:18:18Here's where luck comes in.
00:18:31If they're all the same distance apart, gravity pulls each ball the same amount in all directions.
00:18:38They stay perfectly aligned, and precisely nothing happens.
00:18:47Fortunately, one of the basic rules of the universe is that nothing's perfect.
00:18:54Perfection simply doesn't exist.
00:18:57The early universe had a tiny unevenness that can be simulated by removing just five ball bearings.
00:19:11It may not look like much has changed, but to gravity, those missing balls create a giant opportunity.
00:19:29Gravity now pulls more strongly on one side of some of the bearings.
00:19:41The tiny irregularities in the sea of ball bearings have given gravity something to sink its teeth into.
00:19:48And this is exactly what happened back where we left the young universe.
00:19:59Parts of the sea of early gas were ever so slightly thinner than others.
00:20:05The less dense areas were like the gaps between the ball bearings.
00:20:09The denser parts of the sea of gas, where gravity was having its way, clumped together.
00:20:20And it was in these areas that all the stars and galaxies would form.
00:20:30The cosmos had taken its first step towards the beautiful place it is today.
00:20:36All thanks to irregularity, imperfections, a lack of order.
00:20:47So next time someone complains that you have made a mistake,
00:20:51tell them that may be a good thing.
00:20:54Because without imperfection, neither you, nor I would exist.
00:20:58Thirteen point five billion years ago, the universe was mostly hydrogen gas.
00:21:16With gravity doing what gravity does, which is to slowly pull it into vast clouds.
00:21:21Hydrogen is the simplest of gases, but it has a very special property.
00:21:29It's a tremendous source of power.
00:21:33Heat hydrogen to around ten million degrees,
00:21:39and it begins to produce the energy that makes the stars shine.
00:21:43And supplies the universe with warmth and light.
00:21:48To see how this works, let's imagine we could make a small star here on Earth.
00:21:56First, we need plenty of hydrogen gas.
00:22:00About a sports stadium full would be perfect.
00:22:03Next, we need to imagine squishing this hydrogen together.
00:22:08Just as gravity does in space.
00:22:20As the hydrogen compacts, the atoms of gas start bouncing off each other.
00:22:26And the temperature begins to rise.
00:22:29By the time it's compressed down to the size of a soccer ball,
00:22:37the hydrogen reaches the critical ten million degrees,
00:22:43and a process called nuclear fusion begins.
00:22:48The hydrogen starts to fuse together, making a new, heavier material.
00:22:58Helium.
00:23:02With every step of this tiny bump and grind,
00:23:06some matter gets converted into pure energy.
00:23:09energy.
00:23:19We have created a miniature star.
00:23:21A miniature star.
00:23:34Of course, if this was a real experiment,
00:23:37you wouldn't want to go anywhere near it.
00:23:39The energy given off even from a star this small would be devastating.
00:24:02Back in the early universe,
00:24:03the same process happened for the first time on a much, much bigger scale.
00:24:13Gravity compressed the hydrogen gas clouds over millions of years,
00:24:18until deep in the center,
00:24:20the hydrogen became hot enough for fusion to occur.
00:24:33The first star burst into life,
00:24:40pouring its energy into the vast universe.
00:24:46A product of the laws of nature and the raw materials left over from the Big Bang.
00:24:52It was almost a thousand times bigger than our own sun,
00:24:58and burnt a deep blue.
00:25:00What's more, this star soon had company.
00:25:06The stars were turning on.
00:25:13The same process still happens in our sun,
00:25:15which is where we get the energy we need to live.
00:25:18But there was still a long way to go to get from this to where we are today.
00:25:36You can't build a world like ours from simple gases such as hydrogen and helium.
00:25:55You need all sorts of other elements.
00:25:56You need elements like oxygen and carbon and iron and many more.
00:26:03But we got lucky yet again.
00:26:07Because the very same process that causes the stars to shine,
00:26:11also just happens to make materials like oxygen and carbon and iron.
00:26:16stars, simply by accident, are giant factories.
00:26:33To see a star in action, let's imagine I could split one in half.
00:26:38Just as in the soccer ball star, the hydrogen atoms are fusing together, creating helium,
00:26:53which produces the star's energy.
00:26:55But helium is slightly heavier than hydrogen, so it sinks to the center of the star.
00:27:05And now the helium atoms take center stage.
00:27:10As they fuse together, they produce even more energy,
00:27:14and form yet another new element.
00:27:18Carbon.
00:27:22A vital building block of every living thing.
00:27:29The process repeats itself over and over,
00:27:32and the star becomes layered like an onion.
00:27:35A really big onion.
00:27:39The closer to the center, the heavier the elements,
00:27:42like neon, oxygen, and last of all,
00:27:47iron.
00:27:49Now things change.
00:27:51Iron doesn't produce energy when it fuses,
00:27:55so the fire begins to go out.
00:27:59More and more iron builds up in the star's core
00:28:03until almost all the remaining fuel runs out.
00:28:06Now gravity takes over, and squashes the star in on itself.
00:28:17As its core gets more and more compressed,
00:28:21its temperature soars,
00:28:23until it's over 100 times hotter than the core of our own sun.
00:28:27Finally, the star collapses, and explodes.
00:28:38and explodes.
00:28:57This is a supernova.
00:28:58The death of a star, and the birth of something new.
00:29:11In these brief microseconds, a massive shockwave passes through the star.
00:29:18The blast is so powerful that it forces some of the iron to fuse into even heavier elements.
00:29:24And that's how heavy elements, such as gold, or platinum, or lead, are made.
00:29:33Forged in the heart of an exploding star.
00:29:37So if you have a gold ring, make sure you appreciate it.
00:29:42The metal was made in a blinding flash of light, billions of years ago.
00:29:50The finale of the process that produced the elements all around us today.
00:29:55It never ceases to amaze me that our bodies are constructed of the stuff of the stars.
00:30:08And that our hearts beat because of the energy given off as those materials are made.
00:30:13But as magical as a star is, there are even more fascinating and powerful things in our enormous cosmos.
00:30:21Around 300 million years after the Big Bang, the early stars began to form galaxies.
00:30:35Which slowly took on a bewildering variety of shapes and sizes.
00:30:53Our galaxy, the Milky Way, is thought to be one of the oldest, having started to assemble itself some 13 billion years ago.
00:31:05It's roughly 6,000 billion miles in diameter, and contains something like 200 billion individual stars.
00:31:17Nobody's quite sure exactly how many, since they can't all be seen from Earth, and anyway, it would take a long time to count them.
00:31:31Because all these stars were built by gravity, you could say gravity's the hero of the universe.
00:31:38After all, it turned a meaningless soup of gas into something of beauty and power.
00:31:44But like all interesting heroes, gravity has its dark side.
00:31:57Right in the center of our galaxy lies an example of what happens when gravity rules unchallenged.
00:32:11A black hole.
00:32:14When I was in my twenties, I did some of the basic mathematics of black holes.
00:32:25But few people shared my fascination.
00:32:29These days, they are a popular subject.
00:32:35Physicists all over the world are studying black hole behavior.
00:32:39We now know that black holes are not only fascinating in their own right, but that they play a fundamental role in the formation of galaxies.
00:32:51They also give us a glimpse of how the universe may end.
00:32:55A black hole forms when a large star, one say twenty times the mass of our sun, comes to the end of its life.
00:33:07Such a star looks nothing like our sun, because it's become unstable, convulsing violently as its death throes begin.
00:33:20Finally, it runs out of fuel and begins to shrink, getting denser and denser, hotter and hotter.
00:33:33But with a star this massive, there is no force in the universe capable of stopping the collapse.
00:33:43The core is so heavy that it just keeps on falling in on itself.
00:33:48Gravity is running wild.
00:33:52In just fifteen seconds or so, the unstoppable force crushes the star from millions of miles in diameter to as little as twelve miles in diameter.
00:34:07All the mass that was in the star is still there, but its own weight keeps forcing it down smaller and smaller still.
00:34:24The temperature of the core soars to a hundred billion degrees.
00:34:28The outer layers are blasted away in a massive supernova.
00:34:47But deep in the center, the core falls down what we call a gravitational well.
00:34:55It crushes itself into a single point.
00:35:00A black hole is born.
00:35:03Nothing nearby can escape its pull.
00:35:06Not even light.
00:35:11It's hard to imagine just how dense a black hole can be.
00:35:16But I'll try and put it into perspective using something familiar.
00:35:21The Earth.
00:35:25Imagine, piece by piece, I could compress our planet and crush it until gravity took over.
00:35:35And it became a black hole.
00:35:39How small would it have to be to vanish down its own gravitational well?
00:35:45From eight thousand miles in diameter, I'd have to crush it to the size of a pea.
00:36:03In my years studying black holes, one of my most unexpected discoveries was that a black hole cannot be perfectly black.
00:36:16For much the same reason as the early universe could not have been perfectly spread out.
00:36:26There is no such thing as perfection.
00:36:28Black holes must give off radiation.
00:36:34The smaller the black hole, the greater the radiation.
00:36:39An even tinier black hole with only the mass of a mountain range would actually shine.
00:36:45Out in space, most black holes are much larger.
00:36:59The smaller ones have around four times the mass of our sun and are 15 miles in diameter.
00:37:05Some are much larger, containing the mass of thousands of suns.
00:37:13And then there are the really big ones.
00:37:17Supermassive black holes that exist at the centers of galaxies like our own.
00:37:24This black hole is thought to have the mass of four million suns.
00:37:36And a diameter of 11 million miles.
00:37:41Black holes like these are the heavy hubs around which many galaxies, including the Milky Way, rotate.
00:37:49A kind of stabilizer that gives them form and shape.
00:37:57So eight billion years after the Big Bang, after a long and remarkable run of good luck,
00:38:05we have stars and we have galaxies, slowly rotating around giant black holes.
00:38:11Now the scene is set for something close to our hearts.
00:38:16The formation of our sun, the Earth, and ultimately, us.
00:38:23Our solar system, the place we call home,
00:38:38lies about 26,000 light-years from the center of our galaxy, the Milky Way.
00:38:47Or around two-thirds the way out.
00:38:50The story of how these huge planets came to be orbiting an average yellow star is six billion years long.
00:38:59And since we don't have that much time, I'll speed it up a bit.
00:39:02It starts with a bang.
00:39:13Long ago, an ancient star exploded, littering space with swirling clouds of the materials it had made while it lived,
00:39:22and the heavier metals it created as it died.
00:39:27We know this because we can see similar fields of dust out in space today.
00:39:34They are called nebulae.
00:39:37And they are very beautiful.
00:39:39Every nebula is different.
00:39:43And in our case, the clouds contained nitrogen, and oxygen, and iron, and silica, and all the other stuff needed to build a world like ours.
00:39:55Then the tireless force of gravity started to pull it all back together.
00:39:59And the heavy engineering that produces planets began.
00:40:13Vast spirals of dust began to fall.
00:40:16And at the center of one of these, a rocky planet called Earth started to take shape.
00:40:26Built of stardust and assembled by gravity.
00:40:30Fast forward 100 million years, and it had grown into a giant ball, sweeping up billions of tons of celestial debris.
00:40:51This is where the Earth came from.
00:40:54And therefore, how you and I began.
00:40:56But our planet would have remained a large, sterile ball of rock and metals and minerals forever,
00:41:10were it not for one more event, one more expression of the forces of nature.
00:41:2093 million miles away, at the heart of the giant nebula,
00:41:24the pressure and temperature of a ball of hydrogen gas had become so great that the atoms were beginning to fuse.
00:41:33A new star, our sun, was coming to life.
00:41:38As the sun ignited, it gave off a huge blast of solar wind.
00:41:54A radioactive gust of energy.
00:41:56This blew all the remaining dust and gas that was left over from the nebula, out to the edge of the solar system.
00:42:06Which is why everything is nice and orderly today.
00:42:09In the outer reaches of the solar system, we have the huge gas planets, Jupiter, Saturn, Uranus, and Neptune.
00:42:24Further in are the denser, rockier planets.
00:42:28Mercury.
00:42:30Venus.
00:42:32Mars.
00:42:34And of course, the Earth.
00:42:37Lucky for us, the sun is 865,000 miles in diameter, or just the right size to burn consistently for a very long time.
00:42:488 billion years.
00:42:52Long enough to allow the next development to take place.
00:42:57Life.
00:43:07Life is one of the strangest phenomena known.
00:43:10In my opinion, it shows that the universe is capable of almost anything.
00:43:19Yet, it amazes me that we can know so much about how the universe began many billions of years ago.
00:43:27But we have yet to discover how life itself began.
00:43:31The most likely explanation is probably that we are an accident.
00:43:44Just by chance, some molecules bumped into each other at random, until finally one formed that could copy itself.
00:43:54Then began the slow process of evolution that led to all the extraordinary diversity of life on Earth.
00:44:04Life seems to be simply what matter does, given the right conditions and enough time.
00:44:12I think that life is probably quite common throughout the universe, but that's another tale altogether.
00:44:19As life developed, it changed the planet on which it was born, altering the very fabric of the Earth.
00:44:30After four and a half billion years, the human race arrived on the scene.
00:44:46But one thing often troubles people when they hear this story.
00:44:54Outward such an astounding chain of events, which resulted in us, being an accident.
00:45:02Perhaps science has revealed there is some higher authority at work, setting the laws of nature so that our universe and we can exist.
00:45:14On the face of it, life does seem to be too unlikely to be just a coincidence.
00:45:31Think about it.
00:45:32The Earth lies at exactly the right distance from the Sun to allow liquid water to exist on its surface.
00:45:42And the Sun just happens to be the right size to burn for billions of years, long enough for life to have evolved.
00:45:48The Solar System is littered with all the elements needed for life.
00:45:57These elements themselves are only possible because of older stars that have burnt up.
00:46:02These older stars only existed because of a tiny unevenness in the early primordial gas.
00:46:14That was itself produced by a one in a billion imbalance in the sea of particles that came from the Big Bang.
00:46:21So is there a grand designer?
00:46:33Who lined up all this good fortune?
00:46:36In my opinion, not necessarily.
00:46:41Look at it this way.
00:46:43What if there were other universes?
00:46:46Ones not as lucky as ours.
00:46:48Each of these universes could have come from its own Big Bang.
00:46:53With different laws of physics and different conditions.
00:46:59In some, gravity might not exist.
00:47:02And there could be no life.
00:47:05In others, hydrogen might not fuse.
00:47:08So there would be no stars.
00:47:11And again, no life.
00:47:12No life.
00:47:13And for any number of reasons, universes could have come and gone without producing anything at all.
00:47:20So perhaps we should not be too surprised to find ourselves in a perfect universe.
00:47:30Orbiting a perfect sun on a perfect planet.
00:47:33Because such perfect places are the only ones where life like us can exist.
00:47:49We are one of the many products of the universe.
00:47:51The result of an ancient and elegant mechanism.
00:47:56But even this remarkable discovery is only just the beginning of what physics can tell us.
00:48:03We can find out what humankind will face in the distant future.
00:48:08And ultimately, we might discover the fate of the universe itself.
00:48:22One reason I love cosmology is that it tells us not only where the vast web of galaxies in our universe came from.
00:48:42But also what lies in store for both the universe and for us.
00:48:46I think it's pretty exciting to be among the first human beings able to look forward for hundreds and even billions of years.
00:48:58Maybe as far as the end of time itself.
00:49:05What I see is not only the future of the cosmos we inhabit.
00:49:10But also the enormous challenges our species will face.
00:49:13After all, we are puny organisms compared to the mighty universe that made us.
00:49:21Even the earth that gave us life will not always be the blue sanctuary it is today.
00:49:28The continents of our planet are drifting.
00:49:39Fast forward 75 million years and they will be clustered towards the South Pole.
00:49:46No one knows if the earth will still be habitable then, but the sad truth is that we may not last long enough to find out.
00:49:56As we gaze into the future, it turns out that the universe is a pretty dangerous place.
00:50:04Just look at our neighborhood. It's littered with billions of asteroids. Ancient remnants left over from the process that built the solar system.
00:50:18The possibility of one of these wiping us out isn't just the stuff of Hollywood disaster movies.
00:50:28The threat from asteroids is real.
00:50:31We've even given some of them names.
00:50:38This one is called Apophis.
00:50:42After a mythical Egyptian demon.
00:50:45A god of darkness and destruction.
00:50:48Apophis.
00:50:53Discovered in 2004, Apophis is the size of a 100-story skyscraper.
00:51:00It weighs about 20 million tons.
00:51:04Speeding through space at 28,000 miles an hour, ten times as fast as a bullet.
00:51:20It carries almost as much energy as all the world's nuclear weapons.
00:51:25Combined.
00:51:27And we know roughly where it's headed.
00:51:35The precise path is not yet fully known.
00:51:42But on April the 13th, 2029, this huge rock is likely to pass within 23,000 miles of the planet's surface.
00:51:52Close enough to pass beneath satellites in orbit around the Earth and give us all the scare.
00:52:05Luckily, there's very little chance that Apophis will actually hit us.
00:52:11But the problem for humanity is that in space, there's always a bigger rock.
00:52:17There are thousands of really large asteroids out here.
00:52:36Some are over 10 miles long.
00:52:39The size of Manhattan.
00:52:41An asteroid this size hits the Earth every 100 million years or so.
00:52:47The last one struck the Earth 65 million years ago, and probably was responsible for wiping out the dinosaurs.
00:53:11We don't know when the next asteroid will strike, but if it was big enough, it could sterilize our planet.
00:53:25That would be the end of the five billion year long story of life on Earth.
00:53:33But even if we avoid such a natural catastrophe, we could all too easily end up destroying ourselves.
00:53:42In the last 10,000 years, humans have come to dominate the planet.
00:53:58We're so successful that it's tempting to think we are evolution's grand prize.
00:54:04But I believe intelligence is probably overrated.
00:54:10It's not necessarily a good thing for a species' survival.
00:54:15Bacteria have managed without it for over three billion years.
00:54:22Intelligence, at least in our case, leads to technology.
00:54:26And there are many ways technology could wipe us out.
00:54:33The most obvious, of course, the threat from nuclear weapons.
00:54:39Even if the risk of a nuclear war happening in one year is minuscule, say only one in a million,
00:54:46if we run those odds over 100,000 years, the chance of catastrophe falls to one in ten.
00:54:54If we run those odds over 100,000 years, we can't.
00:54:57If we run those odds over 100,000 years, we can't.
00:55:01Personally, I worry that even this might be over-optimistic.
00:55:07Although we are clever enough to have designed such weapons,
00:55:13I'm not sure we are clever enough not to use them.
00:55:16As time marches relentlessly into the future,
00:55:21the universe has other surprises in store.
00:55:28There are some powerful things out there.
00:55:33Some of which could destroy the Earth without any help from us.
00:55:37As the universe continues to dance to its ancient rhythm, stars will come and go in a relentless cycle.
00:55:55And because there are hundreds of billions of stars, there's always one dying in a supernova somewhere.
00:56:02In our galaxy, for instance, a star dies every 50 years or so,
00:56:09which is but the briefest of moments to the universe.
00:56:14It's just about conceivable that a supernova could damage the Earth,
00:56:19if you consider the likelihood over a long enough timescale.
00:56:25One kind of supernova, discovered entirely by accident, is thought to be particularly dangerous.
00:56:33In 1967, when the Cold War was at its height,
00:56:44US military satellites picked up a massive burst of something called gamma radiation.
00:56:49Gamma radiation is the most dangerous type of radiation known.
00:57:02It's also the tell-tale sign of an atomic weapon.
00:57:05Were the gamma rays detected evidence of a new and powerful Soviet bomb?
00:57:20Thankfully, the answer was no.
00:57:23After careful analysis of the data, they discovered that the sudden bursts of gamma rays were actually coming from space.
00:57:37Not even the Russians had that kind of technology.
00:57:42Decades later, we still don't have proof of what causes the bursts of radiation.
00:57:50But there's a well-respected theory that they are produced by a special kind of supernova,
00:57:57called a gamma ray burster.
00:58:00What's more, there might be one quite nearby.
00:58:11Hidden within this massive spiral plume of plasma, 8,000 light-years from Earth,
00:58:17is a star called WR-104.
00:58:24Deep inside the star itself is a bright sphere,
00:58:27throwing off a shell of hot gas as it nears its end.
00:58:42If this star is what we think it is, then as it dies,
00:58:46it will produce two tightly focused beams of radiation,
00:58:50one from each pole.
00:58:51The star destroys itself as it produces these beams,
00:59:04which contain more energy than our sun will produce in its entire life.
00:59:09The brightest known phenomenon in the entire universe.
00:59:24No one is sure if WR-104 will do this, or if the beam would strike the Earth.
00:59:27But if so, we could be bathed in high-intensity radiation,
00:59:43with some devastating consequences.
00:59:48The beam would cause spectacular auroras, stripping the ozone from the atmosphere,
01:00:00allowing deadly radiation from the sun to strike the Earth.
01:00:07It may sound like science fiction,
01:00:10but this could be the second time skies like these have been seen on our world.
01:00:15450 million years ago, over half of all living creatures were wiped out in a great extinction.
01:00:27One explanation is that a gamma ray burster irradiated the planet so badly
01:00:33that Earth's ecosystem virtually collapsed.
01:00:37I don't want to worry anyone,
01:00:39but I think it's definitely a good idea for the human race to venture far beyond the Earth.
01:00:50We would be wise to keep our eggs in as many baskets as possible.
01:00:56Thankfully, that process has already begun.
01:00:59In my opinion, the launch of Apollo 11 is probably the most important moment in human history.
01:01:15It was a turning point for the universe too.
01:01:35Life, in the form of us, escaped its home planet.
01:01:39and stepped on another surface.
01:01:44The astronauts' footprints stand preserved to this day.
01:02:03A testament to the beginning of what I think could be the next chapter in the story of the cosmos.
01:02:14The spread of life to other parts of the universe.
01:02:17As the universe gets older, we will have to get wiser.
01:02:34I think we'll have to go much further than the moon.
01:02:39At the very least, to Mars.
01:02:41The red planet is likely to play an important part in our evolution.
01:02:52And maybe even in the story of the cosmos.
01:02:57It's the second and possibly the most important stepping stone on humanity's journey to the stars.
01:03:03Robot missions to Mars have revealed a spectacularly beautiful, yet dangerous and desolate place.
01:03:26I imagine that being a human pioneer here would be an exciting business.
01:03:30For a start, it's cold.
01:03:48It's 50 million miles further from the sun than the earth.
01:03:52And so it receives half as much warmth.
01:03:55And the temperatures fluctuate wildly.
01:03:58From 80 degrees to minus 200 in a matter of minutes.
01:04:10If the cold doesn't get you, the low gravity will.
01:04:15Mars is just half the size of the earth and has just 38% of its gravity.
01:04:21Over time, explorers' bones would weaken and their muscles would waste away.
01:04:30Spend long enough on Mars and you could find yourself too weak to safely return to Earth.
01:04:36The low gravity also means Mars struggles to hold on to an atmosphere.
01:04:48Here, there's nothing more than a thin wisp of carbon dioxide at just one hundredth the pressure of our air.
01:04:55Mars is also bathed in harmful radiation from the sun.
01:05:09Even though it's further away, unlike Earth, it has no magnetic field and no ozone layer to protect it.
01:05:16Early explorers would have to be careful to minimize their exposure.
01:05:27Perhaps they'd even have to live underground.
01:05:29But one day, I think it will be possible to drastically alter conditions on Mars.
01:05:46Perhaps using space-borne mirrors to supply warmth and power.
01:05:50With perfectly foreseeable technology, much more could become possible.
01:06:02If we could erect giant domes made of glass and plastic to block out the radiation,
01:06:08inside them we could enrich the atmosphere.
01:06:10500 years from now, which really is a very short time indeed,
01:06:20I think Mars will have its own language, its own currency, its own cuisine.
01:06:26Although I'll bet you, you'll still be able to get a hamburger somewhere.
01:06:30But it's clear that as the universe continues to age,
01:06:39even advances like these will not be enough to guarantee humanity's existence for a very long time.
01:06:45Look further into the future, and ultimately our solar system will follow the same path as countless billions of solar systems before it,
01:07:06and cease to exist.
01:07:07Right now, the Sun is in the middle of its life cycle.
01:07:16During this phase, it is getting gradually hotter and brighter all the time,
01:07:22by about 6% every billion years.
01:07:28In about 5 billion years, the Sun's temperature will have grown to nearly 200 billion degrees.
01:07:35At this point, the Earth will be an unrecognizable ball of molten rock,
01:07:47all life having long since perished.
01:07:52This is our planet's unavoidable destiny.
01:07:56But that's not all the Sun has in store.
01:07:58As it runs out of fuel, the Sun will start to expand, turning into what's called a red giant.
01:08:10It will change from being the object that gave us life to the one that annihilates it.
01:08:15In about 7 billion years, the Sun will be 200 times bigger.
01:08:24About 200 million miles across.
01:08:28So vast, it will obliterate the inner planets one after the other.
01:08:34Mercury, Venus, and most probably the lifeless Earth.
01:08:39But as the Universe continues to evolve at its own relentless pace,
01:08:53new opportunities will present themselves to us, if we are able to preserve the life that the cosmos made.
01:09:11This is Gliese 581D.
01:09:24It's a large, rocky Earth-like planet, the nearest known.
01:09:29It's just possible that this world, or one like it, could in the future become home to the human race.
01:09:39A second sanctuary against the unforgiving blackness of space.
01:09:50Discovered in 2007, it's seven times bigger than Earth.
01:09:54It orbits a star smaller and redder than our own.
01:10:00But it lies at just the right distance from its Sun to allow water to exist on the surface.
01:10:09But even if this is the perfect home away from home, there is a fundamental problem we will have to overcome.
01:10:16Gliese is a very, very long way away.
01:10:29More than 20 light years from Earth.
01:10:34That's 120 trillion miles.
01:10:38To get some idea of this extraordinary distance and the challenge it presents,
01:10:45I'm going to imagine that we could hitch a ride on the fastest man-made object in existence.
01:10:52Voyager 1 was launched in 1977.
01:11:05Now over 30 years old, it's traveled more than 13 billion miles.
01:11:10Its mission so far has taken it to Jupiter and Saturn.
01:11:23By using their gravity to boost its speed, the little spacecraft has entered the record books.
01:11:29It might not look fast, but Voyager is racing through space at 11 miles a second.
01:11:43On Earth, 11 miles a second looks like this.
01:11:46It's 39,000 miles an hour.
01:12:02At this speed, we could circle the globe one and a half times in an hour.
01:12:10So how long would it take a spaceship traveling at Voyager's speed
01:12:13to get to the nearest Earth-like planet, Gliese?
01:12:21The answer reveals the true scale of the cosmos.
01:12:27For even traveling at 11 miles a second,
01:12:31the journey to Gliese would still take over 350,000 years.
01:12:43I think we have a chance to become a lasting part of the ever-changing universe,
01:12:48and to discover what other wonders it might hold.
01:12:52But to do this,
01:12:54we will have to develop new technology on an enormous scale.
01:12:59And that's going to take some serious engineering.
01:13:02There are many in the field of cosmology who believe, as I do,
01:13:19that finding ways to travel great distances will be essential to keeping humankind alive in an aging universe.
01:13:27If we could build a machine capable of traveling to other solar systems,
01:13:34we'd open up a fascinating possibility.
01:13:37The survival of the human race for billions of years.
01:13:41Present day engineers have begun thinking about the principles of building such a ship.
01:13:58This is what it might look like.
01:14:01It could use atomic energy, or perhaps more exotic fuels such as antimatter, supplying it with enormous amounts of power.
01:14:18Yet I think the main challenges won't be technical.
01:14:22The first will be financial.
01:14:24The cost of constructing an interstellar spacecraft would be huge.
01:14:33And for the society that made it, there would be little payback.
01:14:37They would never see it again.
01:14:40So constructing such a machine will either be the greatest act of generosity in history,
01:14:59or it will have to be funded by the travelers themselves.
01:15:03And that raises the second problem.
01:15:11Even if it could travel mind-numbingly fast, say a thousand times faster than Voyager,
01:15:1811,000 miles a second,
01:15:21a journey to the nearest star system would still take...
01:15:2973 years.
01:15:42Such a long trip means that at least one whole generation of humans
01:15:46would have to live their entire lives in space.
01:15:51And we couldn't exactly say they had volunteered for the mission.
01:16:00The ethics of sending a human cargo on such a voyage would have to be carefully considered.
01:16:06Unless we could extend human lifespans to long enough to make such massive journeys.
01:16:21And that, I think, is what we will ultimately end up doing.
01:16:25The process has already begun, as I know from personal experience.
01:16:38My muscles no longer function, although my eyes and my brain are still working pretty well.
01:16:45But technology helps me to move and communicate.
01:16:49In the future, technology will do much more than that for all of us.
01:16:59Within the next thousand years,
01:17:01we will see unprecedented changes in our physical capabilities.
01:17:10Genetic engineering will give us longer lifespans and greater intelligence.
01:17:14Modifying our genes could give us skin that protects us from radiation.
01:17:24The ability to breathe poisonous atmospheres.
01:17:29Resistance to infection.
01:17:36We may even develop sophisticated artificial life forms using synthetic DNA.
01:17:41Custom designed for the challenges of space travel.
01:17:48These advances would allow us to survive long journeys and inhospitable worlds.
01:17:58I imagine a time when our descendants spread to planets orbiting other stars all over our galaxy.
01:18:04And perhaps, further still.
01:18:07Carrying their biological cargo to solar systems we have yet to discover.
01:18:13Ships like this one could be designed to split up and spread out.
01:18:18Ships like this one could be designed to split up and spread out.
01:18:35A true diaspora of life that would have started with us.
01:18:40Always be the place that would be designed with us.
01:18:41149-850-280-680-1080.
01:18:42With us.
01:18:43149-850-170-280-280-1080.
01:18:44149-2020-950.
01:18:49159-1280-680-Z The least change it up with us.
01:18:53A true race for Earth!
01:18:59149-2280-170-170.
01:19:00As we journey across interstellar space, I'm sure that we will unlock nature's deepest secrets.
01:19:20My great hope is that we will discover how the universe will end and solve the ultimate
01:19:31mystery, why the universe ever existed at all.
01:19:49I once gave a lecture in Japan, where I was asked not to mention the end of the universe
01:19:54in case it affected the Japanese stock market.
01:19:58Well, I don't know if or when the universe will end, but for those of you who are nervous
01:20:05about your investments, I think it's a bit early to sell.
01:20:15At 13.7 billion years old, our universe is still in its youth.
01:20:27The earliest date we cosmologists think it could end is 30 billion years from now.
01:20:34There's still plenty of action to come.
01:20:43Even long after our sun has died, new stars will be born, some of which will have new
01:20:49planets around them, made of the same atoms that make you and me.
01:20:56We will end up as part of some future alien ecosystem, although that's probably a bit of a long shot.
01:21:06What's true is that we are only the temporary custodians of the particles which we are made
01:21:11of.
01:21:12They will go on to lead a future existence in the enormous universe that made them.
01:21:23Certainly gravity will continue its tireless, incessant work.
01:21:28It will go on shaping the vast strings of galaxies as it has ever since the Big Bang.
01:21:37Using supercomputers, we can simulate how gravity, even now, causes galaxies to be attracted to
01:21:43one another, resulting in vast, slow collisions.
01:21:57Our galaxy will merge with its nearest neighbor, the Andromeda galaxy, in around 3 billion years.
01:22:06A slow motion collision that will take place over 2 billion years.
01:22:26The same process is happening all over the cosmos.
01:22:31Entire clusters of galaxies are constantly colliding and reforming.
01:22:37Giant collisions as trillions of stars pull on one another.
01:22:42Their vast masses causing them to spin and dance.
01:22:53Gravity is driving the cosmic clockwork as it has done ever since the Big Bang.
01:23:03This is what the universe looks like when we are released from time on a human scale.
01:23:18But will this cosmic whirlpool go on forever?
01:23:22As an endless maelstrom of mass and energy, space and time?
01:23:29What an extraordinary question to even be able to ask.
01:23:38I think the solution lies back where we began.
01:23:50The first time the big bang you have released of the big bang.
01:23:51You know?
01:23:52What is happening?
01:23:53It's ancient.
01:23:54It's ancient.
01:23:55It's ancient.
01:23:56The world is old.
01:23:57It's ancient.
01:23:58The universe is ancient.
01:23:59It's ancient metal.
01:24:00It's ancient.
01:24:01It's ancient.
01:24:02It's ancient.
01:24:03It's ancient.
01:24:04It's ancient.
01:24:05When we can answer that and fully understand the Big Bang, we will also learn the fate
01:24:17of the universe.
01:24:19The key to it all is something called dark energy, a mysterious form of energy that pushes
01:24:27space itself apart, even as gravity is making matter clump together.
01:24:36It seems as if dark energy supplied the kick that inflated the universe, although we're
01:24:42not quite sure how.
01:24:46What is certain is that the fate of the universe depends on how this dark energy behaves.
01:24:53If the dark energy slowly weakens, then gravity could get the upper hand, and in 20 billion
01:25:01years or so, the universe would go into reverse and drive everything back to whence it came.
01:25:10In a strange reversal of the Big Bang, space itself would contract.
01:25:18This theory is known as the Big Crunch.
01:25:24In the end, if the theory is right, in 30 billion years from now, all the matter of the universe
01:25:31would be swallowed by a single black hole.
01:25:42The entire universe would exist as one tiny point, much as it was at the instant of the
01:25:49Big Bang.
01:25:53But although that's a neat ending, I think that it's more likely that dark energy will
01:26:02drive the expansion of the universe forever, and that ultimately everything will just keep
01:26:08spreading out until the universe is cold and dark.
01:26:14Everything will become so far apart that even gravity will be defeated.
01:26:20I think a big chill is what we've got in store, not a big crunch.
01:26:28So will this be the end of us and life as we know it?
01:26:33Or will we have figured out how to navigate to a new universe before then?
01:26:38I think we'll only know when we truly understand why the universe exists at all.
01:26:47Perhaps then, when we finally unravel the whole cosmic puzzle, we will become masters.
01:26:55Just of our universe, but the universe next door.
01:27:02It's nothing in danger.
01:27:10I think we'll come back.