0:00:10 > 0:00:12Why are we here?
0:00:12 > 0:00:14Where do we come from?
0:00:14 > 0:00:17These are the most enduring of questions
0:00:17 > 0:00:22and it's an essential part of human nature to want to find the answers.
0:00:28 > 0:00:33And we can trace our ancestry back hundreds of thousands of years
0:00:33 > 0:00:35to the dawn of humankind,
0:00:35 > 0:00:39but in reality, our story extends far further back in time.
0:00:39 > 0:00:43Our story starts with the beginning of the universe.
0:00:47 > 0:00:51It began 13.7 billion years ago.
0:00:55 > 0:00:59And today, it's filled with over a hundred billion galaxies,
0:00:59 > 0:01:03each containing hundreds of billions of stars.
0:01:08 > 0:01:13In this series, I want to tell that story, because ultimately,
0:01:13 > 0:01:20we're part of the universe, so its story is our story.
0:01:22 > 0:01:25It's a story that we wouldn't be able to tell,
0:01:25 > 0:01:28were it not for the one thing that connects us
0:01:28 > 0:01:30vividly to our vast cosmos.
0:01:30 > 0:01:32Light.
0:01:34 > 0:01:38Light reveals the wonders of the universe in all their glory -
0:01:38 > 0:01:43stars that shine with the light of a thousand suns,
0:01:43 > 0:01:46and vast swirling galaxies.
0:01:46 > 0:01:50But light is also a messenger from a long-forgotten era,
0:01:50 > 0:01:54and contained in the light from these faraway places
0:01:54 > 0:01:58is the story of our universe's origin and evolution.
0:01:58 > 0:02:01Through light we can stare back
0:02:01 > 0:02:05across the entire history of the universe
0:02:05 > 0:02:07and discover how it all began,
0:02:07 > 0:02:12and ultimately see how light breathed life into us.
0:02:47 > 0:02:51This is Karnak Temple in Egypt.
0:02:51 > 0:02:56Built by the ancient pharaohs, this vast complex
0:02:56 > 0:03:03was erected to honour Amun Ra, god of all gods, god of the sun.
0:03:08 > 0:03:11This worship reaches its peak
0:03:11 > 0:03:15during one fleeting moment in the solar calendar,
0:03:15 > 0:03:20an event so brief it lasts for little more than a minute.
0:03:25 > 0:03:29This temple is built to align with an astronomical event
0:03:29 > 0:03:31that happens just once a year -
0:03:31 > 0:03:33the sunrise at the winter solstice.
0:03:33 > 0:03:37"Solstice" is Latin for "sun stands still"
0:03:37 > 0:03:41because as the Earth orbits around the sun and the year passes,
0:03:41 > 0:03:46the point at which the sun rises above the eastern horizon moves,
0:03:46 > 0:03:52so here in Egypt in summer, the sun rises over in that direction,
0:03:52 > 0:03:55and then as summer turns to autumn,
0:03:55 > 0:04:00turns to winter, the sunrise point drifts along, until today
0:04:00 > 0:04:02on December 21st,
0:04:02 > 0:04:04at 6:30am in mid-winter,
0:04:04 > 0:04:10the sun rises exactly between the pillars of this temple.
0:04:51 > 0:04:54Just once a year, for over 3,000 years,
0:04:54 > 0:04:57the sun has risen between the two pillars,
0:04:57 > 0:05:00and casts its light into the temple.
0:05:03 > 0:05:07There it is, the light from our star
0:05:07 > 0:05:09cascading down this magnificent structure.
0:05:12 > 0:05:16I mean, you can literally feel the history of this place,
0:05:16 > 0:05:20so it's easy to forget that this is 3,500 years old,
0:05:20 > 0:05:25so in 1500 BC, the most powerful man on the planet,
0:05:25 > 0:05:27the Pharaoh of Egypt,
0:05:27 > 0:05:32would have stood here on December 21st every year,
0:05:32 > 0:05:37just to greet and experience the light
0:05:37 > 0:05:39from Amun Ra.
0:05:54 > 0:05:58This moment that the Egyptians worshipped instinctively
0:05:58 > 0:06:01we now understand in exquisite detail.
0:06:05 > 0:06:08As the Earth journeys through the Solar System,
0:06:08 > 0:06:13it's bathed in the light of the star that sits at its centre.
0:06:19 > 0:06:23This light has travelled some 150 million kilometres
0:06:23 > 0:06:25from the surface of the sun.
0:06:30 > 0:06:32And at the winter solstice,
0:06:32 > 0:06:35that light pours into the temple at Karnak.
0:06:39 > 0:06:43Well, this building is honestly the most magnificent structure
0:06:43 > 0:06:44I've ever seen.
0:06:44 > 0:06:47Now, it's not built on the scale of men.
0:06:47 > 0:06:51It's built on the scale of gods, of one god,
0:06:51 > 0:06:55Amun Ra, the god of the sun.
0:06:55 > 0:07:01As the sun sinks below the horizon and night falls,
0:07:01 > 0:07:05the whole universe of suns fades into view.
0:07:22 > 0:07:26We no longer build temples to our sun, we build machines
0:07:26 > 0:07:31that allow us to peer deeper into space than ever before,
0:07:31 > 0:07:36to far distant suns out there in the galaxy, and beyond.
0:07:46 > 0:07:50On a night like this, there are about 2,500 stars
0:07:50 > 0:07:52visible to the naked eye,
0:07:52 > 0:07:56but when we started building telescopes instead of temples,
0:07:56 > 0:07:59we discovered that there are billions more.
0:08:06 > 0:08:09Every star we see in the night sky
0:08:09 > 0:08:13is a sun that sits within our own galaxy, the Milky Way.
0:08:14 > 0:08:18As we step away, our sun gradually fades
0:08:18 > 0:08:23to become just one dot in a sea of stars.
0:08:23 > 0:08:27We now know that we're about halfway out from the centre
0:08:27 > 0:08:30of this beautiful cosmic structure,
0:08:30 > 0:08:34but even though these worlds are many millions of kilometres away,
0:08:34 > 0:08:38we know them intimately by their light.
0:08:38 > 0:08:42These waves of light are messengers from across the cosmos,
0:08:42 > 0:08:46and through them, we've discovered the wonders of our galaxy.
0:08:48 > 0:08:50This is the Lagoon Nebula.
0:08:54 > 0:08:55From a distance,
0:08:55 > 0:08:59this cloud of dust and gas appears beautiful and serene.
0:09:05 > 0:09:09But this is a furnace where new stars are forged.
0:09:23 > 0:09:27The Lagoon Nebula sits about 5,000 light years from Earth,
0:09:27 > 0:09:30but it can still be seen with the naked eye,
0:09:30 > 0:09:32because it's 100 light years across,
0:09:32 > 0:09:39and brightly lit by the hot, new, young star that sits at its centre,
0:09:39 > 0:09:43a giant called Herschel 36.
0:09:47 > 0:09:51This newly born star is over 20 times more massive than our sun,
0:09:51 > 0:09:53and burns much hotter,
0:09:53 > 0:09:57which makes the light that pours from its surface blue.
0:10:03 > 0:10:06And there are even bigger stars in our galaxy.
0:10:08 > 0:10:147,500 light years from Earth is a star that dwarfs even Herschel 36.
0:10:20 > 0:10:22Its name is Eta Carinae.
0:10:27 > 0:10:31This monster star is over 100 times more massive than our sun,
0:10:31 > 0:10:36and burns about four million times brighter,
0:10:36 > 0:10:41making it one of the most luminous stars in the Milky Way.
0:10:57 > 0:11:02All we know about these incredible worlds has been brought to us
0:11:02 > 0:11:04on wave after wave of light.
0:11:10 > 0:11:13Our galaxy is a symphony in light.
0:11:19 > 0:11:21The Milky Way is home
0:11:21 > 0:11:24to 200 billion stars,
0:11:24 > 0:11:28but our galaxy is just the beginning.
0:11:28 > 0:11:33For each of these stars, there are a billion more in the universe beyond.
0:11:40 > 0:11:44Across the unimaginable reaches of space, light has allowed us
0:11:44 > 0:11:47to journey to the most distant galaxies,
0:11:47 > 0:11:51to see the births and deaths of stars.
0:11:59 > 0:12:02No matter how far we follow the light,
0:12:02 > 0:12:05no matter how many billions of miles we cross,
0:12:05 > 0:12:10the nature of light itself allows us to go on a much richer journey,
0:12:10 > 0:12:15because to look up, and to look out, is to look back in time.
0:12:15 > 0:12:19Those ancient beams of light are messengers from the distant past,
0:12:19 > 0:12:22and they carry with them a story,
0:12:22 > 0:12:27the story of the origin of the universe.
0:12:28 > 0:12:31In order to read this story,
0:12:31 > 0:12:35to see how light can transport us to the past,
0:12:35 > 0:12:39we must first understand one of its fundamental properties -
0:12:39 > 0:12:41its speed.
0:13:03 > 0:13:07Everything in our universe has a speed limit,
0:13:07 > 0:13:11even intangible phenomena like waves of sound and light.
0:13:12 > 0:13:16These speed limits are very real physical barriers,
0:13:16 > 0:13:19and they have profound consequences
0:13:19 > 0:13:22for our understanding of the universe.
0:13:22 > 0:13:26Today, I'm going to try and break one of those barriers.
0:13:32 > 0:13:34This is a Hawker Hunter.
0:13:34 > 0:13:39It was built in the 1950s, when breaking the sound barrier
0:13:39 > 0:13:42was at the very limit of our technical abilities.
0:13:45 > 0:13:49A sound barrier's an incredibly evocative term, you know,
0:13:49 > 0:13:53it has an almost legendary status in the history of aviation,
0:13:53 > 0:13:56but there's nothing fundamental about it -
0:13:56 > 0:14:00it's something that you can overcome with some extremely clever engineering,
0:14:00 > 0:14:04and in the early days, quite a lot of courage.
0:14:04 > 0:14:07The reason we don't usually think about sound
0:14:07 > 0:14:10as having some kind of speed limit, a limit in speed,
0:14:10 > 0:14:13is because it is incredibly fast compared to the things
0:14:13 > 0:14:15we're used to in everyday life.
0:14:15 > 0:14:18But today, we're going to try and break it.
0:14:18 > 0:14:22I'm going to try and break it, sat in this marvellous machine.
0:14:25 > 0:14:28On Earth, the speed of sound, depending on altitude
0:14:28 > 0:14:33is around 1,200 kilometres per hour, known as Mach I.
0:14:40 > 0:14:44This jet isn't designed to fly that fast in normal flight,
0:14:44 > 0:14:49but there is a way to make it travel faster than sound, and for that,
0:14:49 > 0:14:51we need to fly high.
0:15:41 > 0:15:46As the plane flies faster, it begins to catch up with its own sound.
0:15:46 > 0:15:49The sound waves simply can't get out of the way fast enough,
0:15:49 > 0:15:53so they begin to pile up at the front of the jet.
0:15:53 > 0:15:55But to outrun our sound waves,
0:15:55 > 0:15:58we need to push this jet to its absolute limit.
0:16:23 > 0:16:26In just seconds, the jet smashes through the sound barrier.
0:16:26 > 0:16:31This can be heard from the ground as a sonic boom.
0:16:58 > 0:17:01It was a doddle, actually.
0:17:01 > 0:17:06Well, you know, having said that, it was inverted full throttle
0:17:06 > 0:17:10at 42,000 feet, but it's a different definition of "doddle".
0:17:12 > 0:17:16So this magnificent piece of engineering is fast enough,
0:17:16 > 0:17:18if you just push it a little bit,
0:17:18 > 0:17:23to outrun its own sound, so the sound barrier is negotiable.
0:17:23 > 0:17:26You can smash your way through it.
0:17:26 > 0:17:28But the speed of light, the light barrier,
0:17:28 > 0:17:30that's a very different story.
0:17:45 > 0:17:49Sound has a definite speed that we can measure,
0:17:49 > 0:17:53but for thousands of years, the world's greatest minds
0:17:53 > 0:17:55thought that light was different,
0:17:55 > 0:18:00that it travelled instantaneously from object to eye.
0:18:03 > 0:18:05Then, around 350 years ago,
0:18:05 > 0:18:09the truth about light was revealed through a combination
0:18:09 > 0:18:15of one man's genius and the clockwork orbits of the heavens.
0:18:15 > 0:18:18Ever since Galileo discovered that Jupiter had moons,
0:18:18 > 0:18:22astronomers realised that you could use Jupiter and its moons
0:18:22 > 0:18:24as a very precise clock in the sky.
0:18:24 > 0:18:28So here's the Solar System, there's the sun, there's the Earth,
0:18:28 > 0:18:32here's Jupiter, and here is Jupiter's innermost moon, Io.
0:18:32 > 0:18:38It was known that Io takes precisely 42.5 hours to orbit Jupiter,
0:18:38 > 0:18:45so if, from the Earth, you see Io emerge from behind Jupiter at say,
0:18:45 > 0:18:50midnight on a Tuesday, then you know that it should re-emerge again
0:18:50 > 0:18:52at 6.30 on Thursday afternoon.
0:18:52 > 0:18:57Beautiful. Now one of the men charged with making precise tables
0:18:57 > 0:19:02of exactly when Io should be seen to emerge from behind Jupiter
0:19:02 > 0:19:04was the Danish astronomer Ole Romer,
0:19:04 > 0:19:07but he noticed something surprising.
0:19:07 > 0:19:11See, depending on the time of year,
0:19:11 > 0:19:14Io emerged later than expected,
0:19:14 > 0:19:16or earlier than expected.
0:19:16 > 0:19:19Now, Romer's genius was to realise
0:19:19 > 0:19:23that had nothing to do at all with the orbit of Io around Jupiter.
0:19:23 > 0:19:26It was to do with the orbit of the Earth around the sun.
0:19:26 > 0:19:31See, what Romer noticed was that when the Earth was in a position
0:19:31 > 0:19:35in its orbit so that it was close to Jupiter,
0:19:35 > 0:19:38then Io emerged earlier than it was expected to.
0:19:38 > 0:19:43Then, as the year passed and Earth moved around the sun
0:19:43 > 0:19:45and got further away from Jupiter,
0:19:45 > 0:19:50Roma noticed that Io then emerged later than it was expected to.
0:19:50 > 0:19:54Roma realised that it takes time for light to travel from Jupiter
0:19:54 > 0:19:59to the Earth, so when the Earth is far away from Jupiter,
0:19:59 > 0:20:03it takes longer for the light to travel, and therefore
0:20:03 > 0:20:07you see Io emerge from behind Jupiter later than you'd expect.
0:20:07 > 0:20:09Then, when the distance is small,
0:20:09 > 0:20:15it takes less time for the light to travel and you see Io emerge earlier
0:20:15 > 0:20:17than you might expect.
0:20:17 > 0:20:23So Romer had discovered that light doesn't travel instantaneously.
0:20:23 > 0:20:26It moves through space with a finite speed.
0:20:36 > 0:20:40This remarkable insight led to a measurement of the speed of light.
0:20:44 > 0:20:48We now know that light travels
0:20:48 > 0:20:53at precisely 299,792,458 metres per second.
0:20:53 > 0:20:56That means in the time that it takes for me to click my fingers,
0:20:56 > 0:20:59light has travelled around the Earth seven times,
0:20:59 > 0:21:04or that it travels ten million, million kilometres in one year,
0:21:04 > 0:21:09and that's the yardstick that we use to measure the universe,
0:21:09 > 0:21:15as ten million, million kilometres is approximately one light year.
0:21:20 > 0:21:24The speed of light is the speed limit of the universe
0:21:24 > 0:21:31built into the very fabric of space and time itself.
0:21:31 > 0:21:35But because light travels at a finite speed, a light year
0:21:35 > 0:21:37isn't just a measure of distance,
0:21:37 > 0:21:40it's also a measure of time.
0:21:40 > 0:21:46The further away an object is, the further back in time we see it.
0:21:55 > 0:21:59The distances that light travels on Earth are relatively short,
0:21:59 > 0:22:04so the time it takes light to travel to our eye is imperceptible.
0:22:08 > 0:22:11But when we look out to space,
0:22:11 > 0:22:16over astronomical distances, to the stars, planets and galaxies beyond,
0:22:16 > 0:22:20then light's finite speed has profound consequences.
0:22:35 > 0:22:38This is Tanzania in eastern Africa,
0:22:38 > 0:22:40the cradle of humankind.
0:22:42 > 0:22:46It's here that some of our earliest ancestors walked
0:22:46 > 0:22:482.5 million years ago.
0:22:58 > 0:23:03And our evolutionary journey from the distant past to the present day
0:23:03 > 0:23:07ran in parallel with the journey of the light from the stars.
0:23:10 > 0:23:14The sun is 150 million kilometres away.
0:23:16 > 0:23:19Now, that's very close by cosmic standards,
0:23:19 > 0:23:24but light travels at only 300,000 kilometres per second,
0:23:24 > 0:23:29so that means that we're seeing the sun as it was in the past,
0:23:29 > 0:23:32actually eight minutes in the past.
0:23:48 > 0:23:52But when we look beyond our sun to far more distant stars,
0:23:52 > 0:23:57we reach further back in time across the whole of human evolution.
0:23:58 > 0:24:01And the deeper into space we look,
0:24:01 > 0:24:04the further back in time we see.
0:24:12 > 0:24:17As the sun dips below the horizon and night falls,
0:24:17 > 0:24:21the universe just fades into view...
0:24:23 > 0:24:25..and at first, you see the bright planets.
0:24:25 > 0:24:32I can see Venus over there, and then the stars appear one by one,
0:24:32 > 0:24:35thousands of them shining in the sky.
0:24:40 > 0:24:44And then, as it gets darker and darker, the Milky Way appears,
0:24:44 > 0:24:50a vast swathe of billions and billions of suns as you look out
0:24:50 > 0:24:53towards the centre of our Milky Way galaxy.
0:24:57 > 0:25:01But I think, for me, the most magical thing you can see in the sky
0:25:01 > 0:25:06with the naked eye is just below the constellation of Cassiopeia,
0:25:06 > 0:25:09the W of stars in the sky.
0:25:20 > 0:25:22There.
0:25:25 > 0:25:29Look at that. Actually, I've got to say that's amazing.
0:25:31 > 0:25:36See, that misty patch of light is not a cloud in the sky,
0:25:36 > 0:25:41it's not even gas and dust in our galaxy, that is another galaxy.
0:25:41 > 0:25:46It's the Andromeda galaxy, which is roughly the same size as our own,
0:25:46 > 0:25:50an island of hundreds of billions of stars,
0:25:50 > 0:25:5325 million million million kilometres in that direction.
0:25:57 > 0:26:03Like the Milky Way, Andromeda is a spiral galaxy, two ringed arms
0:26:03 > 0:26:06circling a light-filled centre.
0:26:16 > 0:26:21The core of Andromeda is packed with millions of old red stars.
0:26:21 > 0:26:24Very few new stars are born here.
0:26:30 > 0:26:33In contrast, its spiral arms shine
0:26:33 > 0:26:38with the light from clusters of hot young blue stars.
0:26:43 > 0:26:46The light that pours from this stellar city
0:26:46 > 0:26:51connects us to a remarkable time in the story of human evolution.
0:26:55 > 0:27:01The light that I've just captured in my camera began its journey 2.5 million years ago.
0:27:01 > 0:27:06At that time, on Earth, there were no humans.
0:27:06 > 0:27:08Homo habilis, our distant ancestors,
0:27:08 > 0:27:10were roaming the plains of Africa,
0:27:10 > 0:27:13and as those light rays travelled
0:27:13 > 0:27:18through the vastness of space, our species evolved, and thousands
0:27:18 > 0:27:22and thousands and thousands of generations of humans lived
0:27:22 > 0:27:26and died, and then 2.5 million years
0:27:26 > 0:27:32after their journey began, these messengers from the depths of space
0:27:32 > 0:27:35and from way back in our past,
0:27:35 > 0:27:41arrived here on Earth, and I just captured them and took that picture.
0:27:44 > 0:27:50Light's finite speed opens a window onto the past and shows us Andromeda
0:27:50 > 0:27:54as it looked when our early ancestors walked the Earth
0:27:54 > 0:27:552.5 million years ago.
0:28:00 > 0:28:04But by peering further than the naked eye will allow, we can journey
0:28:04 > 0:28:06to a time way before human history,
0:28:06 > 0:28:10so far back, that we can read
0:28:10 > 0:28:13the entire history of the universe.
0:28:16 > 0:28:20In the last 20 years, powerful space telescopes have carried us
0:28:20 > 0:28:23ever deeper into space,
0:28:23 > 0:28:26and we have become virtual time travellers.
0:28:28 > 0:28:32This is Centaurus A, one of our nearest neighbouring galaxies,
0:28:32 > 0:28:36only ten million light years away.
0:28:36 > 0:28:39That means that the light began its journey
0:28:39 > 0:28:42from these old red, and young white and blue stars,
0:28:42 > 0:28:44only ten million years ago.
0:28:51 > 0:28:54And stepping out a little further,
0:28:54 > 0:29:01just 14 million light years, there's this beautiful barred spiral galaxy,
0:29:01 > 0:29:07and again you can see just lanes and lanes of bright young blue stars,
0:29:07 > 0:29:11and this blue light has taken 14 million years to journey
0:29:11 > 0:29:14across the universe to my eye.
0:29:24 > 0:29:29This is NGC 520, and it's the product of a cosmic collision,
0:29:29 > 0:29:34but this galaxy is 100 million light years away.
0:29:34 > 0:29:38That means that the light began its journey from this galaxy to my eye
0:29:38 > 0:29:40when the dinosaurs roamed the Earth.
0:29:48 > 0:29:51I think it's a beautiful thought
0:29:51 > 0:29:54that by capturing this faint light
0:29:54 > 0:29:59and rebuilding these spectacular images, we are in a very real sense
0:29:59 > 0:30:05connected to these galaxies, no matter how far away they are
0:30:05 > 0:30:08across the universe, connected by the light that's journeyed
0:30:08 > 0:30:11billions of years to reach us.
0:30:20 > 0:30:22But these spectacular galaxies
0:30:22 > 0:30:26are not the end of our journey into the past.
0:30:26 > 0:30:31In 2004, we peered further back in time than ever before,
0:30:31 > 0:30:37and captured the light from the most distant galaxies in the universe.
0:30:38 > 0:30:42The image is called the Hubble Ultra Deep Field.
0:30:44 > 0:30:47It's a picture taken by the Hubble Space Telescope
0:30:47 > 0:30:50over a period of eleven days
0:30:50 > 0:30:54and it focused its camera on the tiniest piece of sky
0:30:54 > 0:30:56just below the constellation of Orion.
0:30:56 > 0:31:01Now, it's a piece of sky that you'd cover if you took your thumb,
0:31:01 > 0:31:07held in front of your face and then moved it 20 times further away.
0:31:09 > 0:31:16But the Hubble captured the faintest lights from the most distant regions of the universe,
0:31:16 > 0:31:18and it took this photograph.
0:31:21 > 0:31:26Now, almost every point of light in that image
0:31:26 > 0:31:32is not a star, but a galaxy of over a hundred billion stars.
0:31:32 > 0:31:35The most distant galaxies in that image
0:31:35 > 0:31:38are over 13 billion light years away.
0:31:38 > 0:31:41That means that the faint light
0:31:41 > 0:31:44from those galaxies began its journey
0:31:44 > 0:31:47to Earth 13 billion years ago.
0:31:47 > 0:31:51That's over three times the age of the Earth.
0:32:01 > 0:32:03Hubble allows us to peer back
0:32:03 > 0:32:06almost to the beginning of time itself,
0:32:06 > 0:32:09and out here in deep space,
0:32:09 > 0:32:13it reveals a clue to how our universe began.
0:32:15 > 0:32:19When the space telescope stared across the cosmos,
0:32:19 > 0:32:22it saw galaxies glow in all different colours.
0:32:27 > 0:32:31But when it peered to the very edge of the visible universe,
0:32:33 > 0:32:35it captured these images...
0:32:37 > 0:32:40..and saw that every galaxy glowed red.
0:32:42 > 0:32:46Written in the red light from these distant worlds
0:32:46 > 0:32:49is the story of our universe's origin and evolution.
0:32:51 > 0:32:52To reveal it,
0:32:52 > 0:32:56we must explore one of the most beautiful qualities of light.
0:33:06 > 0:33:12For centuries, people thought that light just illuminated our world,
0:33:12 > 0:33:15allowed us to see, and nothing more than that.
0:33:15 > 0:33:19But we've since learnt that there is a vast amount
0:33:19 > 0:33:24of information and detail contained within every beam of light.
0:33:26 > 0:33:29And that information is written in colour.
0:33:29 > 0:33:34To reveal how colour can unlock the secrets of our universe's creation,
0:33:34 > 0:33:37I've come to one of the most spectacular
0:33:37 > 0:33:39natural wonders on Earth.
0:33:46 > 0:33:50This is Victoria Falls in Zambia.
0:33:59 > 0:34:02This waterfall stretches for almost two kilometres,
0:34:02 > 0:34:07making it the largest curtain of falling water in the world.
0:34:12 > 0:34:17But I'm not here to marvel at the scale of this wonder -
0:34:17 > 0:34:20I've come to see a much more delicate feature that appears
0:34:20 > 0:34:23above the water.
0:34:24 > 0:34:25These magnificent rainbows
0:34:25 > 0:34:31are a permanent feature in the skies above Victoria Falls.
0:34:31 > 0:34:34Now, rainbows are a beautiful phenomenon,
0:34:34 > 0:34:37but I think that they're even more beautiful
0:34:37 > 0:34:39when you understand how they're made,
0:34:39 > 0:34:41because they are a visual representation of the fact
0:34:41 > 0:34:45that light is made up of...well, all the colours of the rainbow.
0:34:47 > 0:34:52Rays of light from the sun bend as they enter the water droplets,
0:34:52 > 0:34:56the light beams then reflect off the back of the droplets,
0:34:56 > 0:35:00and are bent for a second time, as they leave.
0:35:00 > 0:35:03This bending and reflecting splits the light
0:35:03 > 0:35:09and the colours hidden inside the white sunlight are revealed.
0:35:09 > 0:35:12But colour can tell us much more,
0:35:12 > 0:35:15because understanding the reddening of the galaxies
0:35:15 > 0:35:20has given us a profound insight into the nature of the universe.
0:35:21 > 0:35:23What we see as different colours
0:35:23 > 0:35:26are actually different wavelengths of light.
0:35:26 > 0:35:31So blue light has a relatively short wavelength,
0:35:31 > 0:35:33and then you go through green and yellow,
0:35:33 > 0:35:36all the way to the red end of the spectrum,
0:35:36 > 0:35:38which has a very large wavelength.
0:35:41 > 0:35:44Starlight is made up of countless different wavelengths,
0:35:44 > 0:35:46all the colours of the rainbow.
0:35:51 > 0:35:56When light is emitted by a distant star or galaxy, its wavelength
0:35:56 > 0:36:02doesn't have to stay fixed, it can be squashed or stretched,
0:36:02 > 0:36:05and when light's stretched, its wavelength increases and it moves
0:36:05 > 0:36:08to the red end of the spectrum.
0:36:08 > 0:36:10So the interpretation of the fact
0:36:10 > 0:36:13that the most distant galaxies appear red
0:36:13 > 0:36:17is that the space in between them and us has stretched
0:36:17 > 0:36:23during the time it's taken the light to journey over that vast distance.
0:36:23 > 0:36:28That means that our entire universe is expanding.
0:36:30 > 0:36:34Now, just think about what an expanding universe implies,
0:36:34 > 0:36:38because if the galaxies are all rushing away from each other,
0:36:38 > 0:36:41that means that if you rewind time,
0:36:41 > 0:36:45then they must have been closer together in the past, and actually,
0:36:45 > 0:36:49if you just keep rewinding, then you find that at some point
0:36:49 > 0:36:53in the past, all the galaxies we can see in the sky
0:36:53 > 0:36:56were quite literally on top of each other.
0:36:56 > 0:37:00The universe was squashed down to a point.
0:37:00 > 0:37:05That implies that the universe may have had a beginning,
0:37:05 > 0:37:07and that is the Big Bang Theory.
0:37:43 > 0:37:49Well, that's probably many people's picture of the Big Bang, you know,
0:37:49 > 0:37:54this vast explosion that flung matter out into the void,
0:37:54 > 0:37:56but that's completely wrong.
0:37:56 > 0:37:59As we understand it at the moment,
0:37:59 > 0:38:02all of space was created at that moment.
0:38:04 > 0:38:08So the Big Bang didn't just happen somewhere out over there
0:38:08 > 0:38:11in the universe, it happened everywhere at the same time.
0:38:11 > 0:38:15It happened here. So this space here was at the Big Bang.
0:38:20 > 0:38:22So when we look at the distant galaxies
0:38:22 > 0:38:25and we see that they're flying away from us,
0:38:25 > 0:38:28that's not because they were flung out in some massive
0:38:28 > 0:38:30explosion at the beginning of time.
0:38:37 > 0:38:40It's because space itself is stretching,
0:38:40 > 0:38:44and it's been stretching since the Big Bang.
0:38:49 > 0:38:54The universe we see today is a network of galaxies
0:38:54 > 0:38:57spanning almost a hundred billion light years.
0:38:59 > 0:39:03But remarkably, the blueprint for this astonishing structure
0:39:03 > 0:39:08is written into the very first light released into the universe.
0:39:11 > 0:39:16Even more remarkably, it's a blueprint that we can read today.
0:39:21 > 0:39:25This first light is no longer visible, but it's there.
0:39:25 > 0:39:27You just need to know how to look for it.
0:39:58 > 0:40:03This sea of shifting sand is the Namib Desert,
0:40:03 > 0:40:05the oldest desert in the world,
0:40:05 > 0:40:10and, as the wind blows the sand off the top of the dunes,
0:40:10 > 0:40:13this landscape is constantly changing.
0:40:19 > 0:40:23This world has been sculpted by the sun.
0:40:23 > 0:40:26It drives the winds that shape the dunes,
0:40:26 > 0:40:29and its light paints this place a deep orange.
0:40:33 > 0:40:37But even when the sun disappears completely
0:40:37 > 0:40:41this desert is still awash with light and colour,
0:40:41 > 0:40:42we just can't see it.
0:40:46 > 0:40:48Visible wavelengths of light
0:40:48 > 0:40:52are just a tiny fraction of all the light in the universe.
0:40:54 > 0:40:56Beyond the visible spectrum,
0:40:56 > 0:40:59our world is illuminated by invisible light.
0:41:02 > 0:41:07This sand has been under the full glare of the sun all day
0:41:07 > 0:41:10and I can feel the heat radiating off it.
0:41:10 > 0:41:14Well, heat is nothing more than a form of light,
0:41:14 > 0:41:17although we don't normally call it light.
0:41:17 > 0:41:21It's actually infrared light, and the only difference between
0:41:21 > 0:41:25infrared and visible light is the wavelength.
0:41:25 > 0:41:28Infrared has a longer wavelength than visible light.
0:41:31 > 0:41:33Infrared isn't the end of the story.
0:41:33 > 0:41:36There are even longer wavelengths of light.
0:41:37 > 0:41:41Throughout most of human history we've been blind to these more
0:41:41 > 0:41:43unfamiliar forms of light,
0:41:43 > 0:41:47but to detect them you don't need a billion-pound satellite
0:41:47 > 0:41:50or a telescope built into the side of a mountain,
0:41:50 > 0:41:52you just need
0:41:52 > 0:41:56one of these, a radio, because...
0:41:56 > 0:41:59- STATIC - ..when we tune a radio,
0:41:59 > 0:42:03we're tuning in to a form of light, radio waves.
0:42:03 > 0:42:09MUSIC PLAYS THROUGH STATIC
0:42:09 > 0:42:13But detecting them and understanding them
0:42:13 > 0:42:19provides the key to understanding the origin of the universe.
0:42:19 > 0:42:23And when you detune the radio a bit you can just hear static,
0:42:23 > 0:42:30but about 1% of that static is music to the ears of a physicist,
0:42:30 > 0:42:35because that is stretched light from the Big Bang.
0:42:35 > 0:42:39So that sound is the sound of the first light
0:42:39 > 0:42:44released at the beginning of the universe.
0:42:45 > 0:42:49# Carry him home safely to me... #
0:42:51 > 0:42:55The reason we can't see this ancient light is because,
0:42:55 > 0:42:56as the universe expanded,
0:42:56 > 0:43:01the light waves were stretched and transformed
0:43:01 > 0:43:03into radio waves and microwaves.
0:43:04 > 0:43:09This first light is called the Cosmic Microwave Background, or CMB.
0:43:11 > 0:43:15The CMB fills every part of the universe.
0:43:15 > 0:43:20Every second, light from the beginning of time is
0:43:20 > 0:43:25raining down on the surface of the Earth in a ceaseless torrent.
0:43:26 > 0:43:29If my eyes could only see it,
0:43:29 > 0:43:34then the sky would be ablaze with this primordial light,
0:43:34 > 0:43:36both day and night.
0:43:43 > 0:43:47These waves have been travelling towards us
0:43:47 > 0:43:49for over 13 billion years.
0:43:52 > 0:43:53They are messengers,
0:43:53 > 0:43:58carrying information about the origin of our universe.
0:44:21 > 0:44:27In 2001, a satellite called W Map took a photograph of our entire sky
0:44:27 > 0:44:30to capture this ancient light.
0:44:30 > 0:44:33The image reveals that the blueprint
0:44:33 > 0:44:38of the entire universe was created moments after the Big Bang.
0:44:38 > 0:44:43Well, this is one of the most important images of the sky ever
0:44:43 > 0:44:46taken in the history of science.
0:44:46 > 0:44:50It doesn't have the beauty of a spiral galaxy or a nebula
0:44:50 > 0:44:54but to a scientist, to a cosmologist,
0:44:54 > 0:44:58it is the most beautiful picture ever taken,
0:44:58 > 0:45:02because it contains a vast amount of information
0:45:02 > 0:45:07about the very earliest history of our universe.
0:45:10 > 0:45:12When the CMB was first detected,
0:45:12 > 0:45:17it appeared that the universe was exactly the same in all directions.
0:45:22 > 0:45:26But W Map shows us that the early universe was far from uniform.
0:45:26 > 0:45:29Some areas were denser than others,
0:45:29 > 0:45:34and it's these ripples that seeded all the structure in the cosmos.
0:45:34 > 0:45:39The explanation for those ripples in the CMB
0:45:39 > 0:45:41is absolutely mind blowing,
0:45:41 > 0:45:45because it's thought that they originated in
0:45:45 > 0:45:48the first billion-billion-billion- billionths of a second
0:45:48 > 0:45:50after the universe began,
0:45:50 > 0:45:53when the whole observable universe
0:45:53 > 0:45:57was billions of times smaller than a grain of sand
0:45:57 > 0:46:01and little fluctuations called quantum fluctuations
0:46:01 > 0:46:05made little bits of the universe a bit denser.
0:46:08 > 0:46:11Those dense regions then got denser and denser
0:46:11 > 0:46:14as the universe continued to expand
0:46:14 > 0:46:18and they seeded the formation of the first stars
0:46:18 > 0:46:21and the first galaxies in the universe.
0:46:27 > 0:46:30The early universe was a hot,
0:46:30 > 0:46:33almost uniform, sea of matter and radiation.
0:46:40 > 0:46:42As the universe expanded,
0:46:42 > 0:46:46the slightly denser regions became increasingly dense.
0:46:51 > 0:46:55Atoms clumped together to form the first structures.
0:47:00 > 0:47:03Over time these structures grew so massive
0:47:03 > 0:47:07that they collapsed under their own gravity.
0:47:10 > 0:47:15Hydrogen fused, releasing enormous amounts of energy.
0:47:20 > 0:47:23200 million years after the Big Bang,
0:47:23 > 0:47:26the first stars in the cosmos burst into life.
0:47:46 > 0:47:52Darkness was banished and the cosmos began to fill with light.
0:47:58 > 0:48:02Planets formed and fell into orbit around the stars
0:48:02 > 0:48:07and these young solar systems orbited the galaxies.
0:48:12 > 0:48:16And the only reason why any of this exists
0:48:16 > 0:48:19is because of those tiny density fluctuations
0:48:19 > 0:48:22that appeared when the observable universe
0:48:22 > 0:48:25was smaller than a grain of sand.
0:48:27 > 0:48:33Without them there would be no planets or stars and no galaxies.
0:48:33 > 0:48:37Our universe would look the same in every direction.
0:48:51 > 0:48:56For billions of years, generations of stars lived and died.
0:48:57 > 0:49:01And then, nine billion years after it all began,
0:49:01 > 0:49:05in an unremarkable piece of space in the Orion spur
0:49:05 > 0:49:09of the Persius arm of a galaxy called the Milky Way,
0:49:09 > 0:49:13a star was born that we call the Sun, that illuminated
0:49:13 > 0:49:17our embryonic solar system with light.
0:49:19 > 0:49:22So the light from the star that bathes the Earth
0:49:22 > 0:49:23has its ultimate origin
0:49:23 > 0:49:27in the tiny ripples that appeared in the first moments
0:49:27 > 0:49:29of our universe's life.
0:49:33 > 0:49:36By capturing the light from the skies,
0:49:36 > 0:49:38we've been able to tell the story
0:49:38 > 0:49:41of the universe's origins and evolution,
0:49:41 > 0:49:46and it's worth reflecting on what a remarkable thing that is.
0:49:46 > 0:49:48You know, little beings like me
0:49:48 > 0:49:51scurrying around on the surface of a rock
0:49:51 > 0:49:53on the edge of one of the galaxies
0:49:53 > 0:49:56have been able to understand the very origin
0:49:56 > 0:49:59and evolution of the universe.
0:49:59 > 0:50:02But there's one more twist to this story,
0:50:02 > 0:50:07because that ability to use light, to capture it,
0:50:07 > 0:50:10and use it to understand our world,
0:50:10 > 0:50:15may have played a key role in the emergence of complex life on Earth.
0:50:34 > 0:50:38This is the Yoho National Park in the Rocky Mountains of Canada,
0:50:38 > 0:50:42one of the most spectacular mountain ranges in North America.
0:50:48 > 0:50:53100 years ago, a fossil field was discovered here at the Burgess Shale
0:50:53 > 0:50:58that may reveal how light shaped life on Earth.
0:51:05 > 0:51:09Well, this is one of the most important fossil sites in the world,
0:51:09 > 0:51:13but actually it's one of the most important
0:51:13 > 0:51:15scientific sites of any kind,
0:51:15 > 0:51:20and it's not just because of the number and diversity of animals
0:51:20 > 0:51:24you find fossilised in these rocks, it's because of their age.
0:51:24 > 0:51:29These fossils are over 500 million years old.
0:51:29 > 0:51:33There is virtually no record of complex life
0:51:33 > 0:51:35on Earth before this time.
0:51:35 > 0:51:41It's as if, at one instant in this time we call the Cambrian Era,
0:51:41 > 0:51:49complex multi-cellular life suddenly emerged almost intact on the planet.
0:51:49 > 0:51:52It's called the Evolutionary Big Bang.
0:51:57 > 0:52:02This is one of the beautiful animals you find up here in the fossil beds.
0:52:02 > 0:52:05It's called a trilobite. It's a very complex organism.
0:52:05 > 0:52:08It's got an external skeleton, it's got jointed limbs,
0:52:08 > 0:52:15but, perhaps most remarkably, these, because these are compound eyes.
0:52:15 > 0:52:19They were very sophisticated and this was one of the first predators
0:52:19 > 0:52:22to be able to detect shapes and see movement
0:52:22 > 0:52:24and it could successfully chase its prey.
0:52:26 > 0:52:29These creatures were among the first
0:52:29 > 0:52:32to harness the light that filled the universe.
0:52:32 > 0:52:36Before they emerged, the rise and fall of the Sun
0:52:36 > 0:52:40and the stars in the night sky simply went unnoticed.
0:52:41 > 0:52:45Now, there is a speculative theory that the emergence of the eye
0:52:45 > 0:52:48actually triggered the Cambrian Explosion,
0:52:48 > 0:52:50this evolutionary Big Bang,
0:52:50 > 0:52:53because, once one species got eyes,
0:52:53 > 0:52:57then other species had also to develop eyes
0:52:57 > 0:53:02to either chase them as predators or evade them as prey,
0:53:02 > 0:53:05and that led to an evolutionary arms race.
0:53:05 > 0:53:09More and more complex life forms developed.
0:53:13 > 0:53:17So the evolution of the eye may have played a fundamental role
0:53:17 > 0:53:20in the emergence of complex life on Earth...
0:53:23 > 0:53:26..and could have led to the evolution of our species.
0:53:33 > 0:53:37See, this little thing, although it looks unimpressive,
0:53:37 > 0:53:40may be the most important animal
0:53:40 > 0:53:44that we've ever discovered in our history.
0:53:44 > 0:53:48It's called a Pikaia and it's a little wormlike creature
0:53:48 > 0:53:53but it's thought that this is a core date,
0:53:53 > 0:53:55and that is the branch of life
0:53:55 > 0:54:01that we're in, so it could that this is our earliest known ancestor.
0:54:01 > 0:54:06What's also fascinating is it's also thought that this
0:54:06 > 0:54:08may have been able to detect light,
0:54:08 > 0:54:12it may have had primitive cells that were sensitive to light,
0:54:12 > 0:54:15and allowed it in a very loose sense to see.
0:54:15 > 0:54:22But if that's true then this little guy may be our direct ancestor
0:54:22 > 0:54:27and those little cells may be the things that evolved,
0:54:27 > 0:54:32over hundreds of millions of years, into our eyes.
0:54:37 > 0:54:43Without Pikaia we may never have evolved and developed the ability
0:54:43 > 0:54:46to see how this story unfolded.
0:54:50 > 0:54:55Understanding the universe is like a detective story
0:54:55 > 0:54:59and the evidence has been carried to us across
0:54:59 > 0:55:02vast expanses of space by light.
0:55:05 > 0:55:09We've even been able to capture the light from the beginning of time
0:55:09 > 0:55:13and we've glimpsed in it the seeds of our own origins.
0:55:20 > 0:55:23And we've seen things our ancestors wouldn't believe.
0:55:25 > 0:55:28Stars being born in distant realms.
0:55:30 > 0:55:35Alien worlds created by gravity.
0:55:35 > 0:55:39And spectacular galaxies frozen in time.
0:55:45 > 0:55:49But we're not mere witnesses to these events...
0:55:50 > 0:55:54..because the story of the universe is our story.
0:55:58 > 0:56:01We've learned how the dust of the stars makes
0:56:01 > 0:56:03each and every one of us,
0:56:03 > 0:56:08how a simple universal chemistry set makes everything we see.
0:56:11 > 0:56:13We've explored how the secrets
0:56:13 > 0:56:17of deep time shape the destiny of the universe
0:56:17 > 0:56:21and marvelled at the brief flickering moment
0:56:21 > 0:56:23in which life can exist,
0:56:23 > 0:56:25and we've seen how stardust falls
0:56:25 > 0:56:30to build the grandest structures in the universe.
0:56:30 > 0:56:36We know all this because of messages carried on beams of light.
0:56:36 > 0:56:41And isn't it a wonderful thing that these biological light detectors
0:56:41 > 0:56:44that first emerged half a billion years ago
0:56:44 > 0:56:46in the Cambrian Explosion
0:56:46 > 0:56:50have evolved into those most human of things,
0:56:50 > 0:56:53our green, blue and brown eyes
0:56:53 > 0:56:57that are able to gaze up into the night sky,
0:56:57 > 0:57:03capture the light from distant stars and read the story of the universe.
0:57:34 > 0:57:37Subtitles by Red Bee Media Ltd
0:57:37 > 0:57:39E-mail subtitling@bbc.co.uk