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Wonders of the Universe Messengers
It's a story that we wouldn't be able to tell, were it not for the one thing that connects us vividly to our vast cosmos. Light. Light reveals the wonders of the universe in all their glory - stars that shine with the light of a thousand suns, and vast swirling galaxies. But light is also a messenger from a long-forgotten era, and contained in the light from these faraway places is the story of our universe's origin and evolution. Through light we can stare back across the entire history of the universe and discover how it all began, and ultimately see how light breathed life into us. Every star we see in the night sky is a sun that sits within our own galaxy, the Milky Way. As we step away, our sun gradually fades to become just one dot in a sea of stars. We now know that we're about halfway out from the centre of this beautiful cosmic structure, but even though these worlds are many millions of kilometres away, we know them intimately by their light. These waves of light are messengers from across the cosmos, and through them, we've discovered the wonders of our galaxy. This is the Lagoon Nebula. From a distance, this cloud of dust and gas appears beautiful and serene. But this is a furnace where new stars are forged. The Lagoon Nebula sits about 5,000 light years from Earth, but it can still be seen with the naked eye, because it's 100 light years across, and brightly lit by the hot, new, young star that sits at its centre, a giant called Herschel 36. This newly born star is over 20 times more massive than our sun, and burns much hotter, which makes the light that pours from its surface blue. And there are even bigger stars in our galaxy. 7,500 light years from Earth is a star that dwarfs even Herschel 36. Its name is Eta Carinae. This monster star is over 100 times more massive than our sun, and burns about four million times brighter, making it one of the most luminous stars in the Milky Way. All we know about these incredible worlds has been brought to us on wave after wave of light. Our galaxy is a symphony in light. The Milky Way is home to 200 billion stars, but our galaxy is just the beginning. For each of these stars, there are a billion more in the universe beyond. Across the unimaginable reaches of space, light has allowed us to journey to the most distant galaxies, to see the births and deaths of stars. No matter how far we follow the light, no matter how many billions of miles we cross, the nature of light itself allows us to go on a much richer journey, because to look up, and to look out, is to look back in time. Those ancient beams of light are messengers from the distant past, and they carry with them a story, the story of the origin of the universe. In order to read this story, to see how light can transport us to the past, we must first understand one of its fundamental properties - its speed. Everything in our universe has a speed limit, even intangible phenomena like waves of sound and light. These speed limits are very real physical barriers, and they have profound consequences for our understanding of the universe. Today, I'm going to try and break one of those barriers. At that time, on Earth, there were no humans. Homo habilis, our distant ancestors, were roaming the plains of Africa, and as those light rays travelled through the vastness of space, our species evolved, and thousands and thousands and thousands of generations of humans lived and died, and then 2.5 million years after their journey began, these messengers from the depths of space and from way back in our past, arrived here on Earth, and I just captured them and took that picture. Light's finite speed opens a window onto the past and shows us Andromeda as it looked when our early ancestors walked the Earth 2.5 million years ago. But by peering further than the naked eye will allow, we can journey to a time way before human history, so far back, that we can read the entire history of the universe. In the last 20 years, powerful space telescopes have carried us ever deeper into space, and we have become virtual time travellers. This is Centaurus A, one of our nearest neighbouring galaxies, only ten million light years away. That means that the light began its journey from these old red, and young white and blue stars, only ten million years ago. And stepping out a little further, just 14 million light years, there's this beautiful barred spiral galaxy, and again you can see just lanes and lanes of bright young blue stars, and this blue light has taken 14 million years to journey across the universe to my eye. This is NGC 520, and it's the product of a cosmic collision, but this galaxy is 100 million light years away. That means that the light began its journey from this galaxy to my eye when the dinosaurs roamed the Earth. I think it's a beautiful thought that by capturing this faint light and rebuilding these spectacular images, we are in a very real sense connected to these galaxies, no matter how far away they are across the universe, connected by the light that's journeyed billions of years to reach us. But these spectacular galaxies are not the end of our journey into the past. In 2004, we peered further back in time than ever before, and captured the light from the most distant galaxies in the universe. The image is called the Hubble Ultra Deep Field. It's a picture taken by the Hubble Space Telescope over a period of eleven days and it focused its camera on the tiniest piece of sky just below the constellation of Orion. Now, it's a piece of sky that you'd cover if you took your thumb, held in front of your face and then moved it 20 times further away. But the Hubble captured the faintest lights from the most distant regions of the universe, and it took this photograph. Now, almost every point of light in that image is not a star, but a galaxy of over a hundred billion stars. The most distant galaxies in that image are over 13 billion light years away. That means that the faint light from those galaxies began its journey to Earth 13 billion years ago. That's over three times the age of the Earth. Hubble allows us to peer back almost to the beginning of time itself, and out here in deep space, it reveals a clue to how our universe began. When the space telescope stared across the cosmos, it saw galaxies glow in all different colours. But when it peered to the very edge of the visible universe, it captured these images and saw that every galaxy glowed red. Written in the red light from these distant worlds is the story of our universe's origin and evolution. To reveal it, we must explore one of the most beautiful qualities of light. For centuries, people thought that light just illuminated our world, allowed us to see, and nothing more than that. But we've since learnt that there is a vast amount of information and detail contained within every beam of light. And that information is written in colour. To reveal how colour can unlock the secrets of our universe's creation, I've come to one of the most spectacular natural wonders on Earth. This is Victoria Falls in Zambia. This waterfall stretches for almost two kilometres, making it the largest curtain of falling water in the world. But I'm not here to marvel at the scale of this wonder - I've come to see a much more delicate feature that appears above the water. These magnificent rainbows are a permanent feature in the skies above Victoria Falls. Now, rainbows are a beautiful phenomenon, but I think that they're even more beautiful when you understand how they're made, because they are a visual representation of the fact that light is made up of...well, all the colours of the rainbow. Rays of light from the sun bend as they enter the water droplets, the light beams then reflect off the back of the droplets, and are bent for a second time, as they leave. This bending and reflecting splits the light and the colours hidden inside the white sunlight are revealed. But colour can tell us much more, because understanding the reddening of the galaxies has given us a profound insight into the nature of the universe. What we see as different colours are actually different wavelengths of light.


  BBC Wonders of the Universe Messengers to understand how light holds the key to the story of the universe
 
Centaurus A, one of our nearest neighbouring galaxies
Centaurus A, one of our nearest neighbouring galaxies 		  These waves of light are messengers from across the cosmos, and through them, we've discovered the wonders of our galaxy
These waves of light are messengers from across the cosmos, and through them, we've discovered the wonders of our galaxy 		  200 million years after the Big Bang, the first stars in the cosmos burst into life
200 million years after the Big Bang, the first stars in the cosmos burst into life 		  Darkness was banished and the cosmos began to fill with light
Darkness was banished and the cosmos began to fill with light
 
So blue light has a relatively short wavelength, and then you go through green and yellow, all the way to the red end of the spectrum, which has a very large wavelength. Starlight is made up of countless different wavelengths, all the colours of the rainbow. When light is emitted by a distant star or galaxy, its wavelength doesn't have to stay fixed, it can be squashed or stretched, and when light's stretched, its wavelength increases and it moves to the red end of the spectrum. So the interpretation of the fact that the most distant galaxies appear red is that the space in between them and us has stretched during the time it's taken the light to journey over that vast distance. That means that our entire universe is expanding. Now, just think about what an expanding universe implies, because if the galaxies are all rushing away from each other, that means that if you rewind time, then they must have been closer together in the past, and actually, if you just keep rewinding, then you find that at some point in the past, all the galaxies we can see in the sky were quite literally on top of each other. The universe was squashed down to a point. That implies that the universe may have had a beginning, and that is the Big Bang Theory. Well, that's probably many people's picture of the Big Bang, you know, this vast explosion that flung matter out into the void, but that's completely wrong. As we understand it at the moment, all of space was created at that moment. So the Big Bang didn't just happen somewhere out over there in the universe, it happened everywhere at the same time. It happened here.
So this space here was at the Big Bang. So when we look at the distant galaxies and we see that they're flying away from us, that's not because they were flung out in some massive explosion at the beginning of time. It's because space itself is stretching, and it's been stretching since the Big Bang. The universe we see today is a network of galaxies spanning almost a hundred billion light years. But remarkably, the blueprint for this astonishing structure is written into the very first light released into the universe. Even more remarkably, it's a blueprint that we can read today. This first light is no longer visible, but it's there. The reason we can't see this ancient light is because, as the universe expanded, the light waves were stretched and transformed into radio waves and microwaves. This first light is called the Cosmic Microwave Background, or CMB. The CMB fills every part of the universe. Every second, light from the beginning of time is raining down on the surface of the Earth in a ceaseless torrent. If my eyes could only see it, then the sky would be ablaze with this primordial light, both day and night. These waves have been travelling towards us for over 13 billion years. They are messengers, carrying information about the origin of our universe. In 2001, a satellite called W Map took a photograph of our entire sky to capture this ancient light. The image reveals that the blueprint of the entire universe was created moments after the Big Bang. Well, this is one of the most important images of the sky ever taken in the history of science. It doesn't have the beauty of a spiral galaxy or a nebula but to a scientist, to a cosmologist, it is the most beautiful picture ever taken, because it contains a vast amount of information about the very earliest history of our universe. When the CMB was first detected, it appeared that the universe was exactly the same in all directions. But W Map shows us that the early universe was far from uniform. Some areas were denser than others, and it's these ripples that seeded all the structure in the cosmos. The explanation for those ripples in the CMB is absolutely mind blowing, because it's thought that they originated in the first billion-billionths of a second after the universe began, when the whole observable universe was billions of times smaller than a grain of sand and little fluctuations called quantum fluctuations made little bits of the universe a bit denser. Those dense regions then got denser and denser as the universe continued to expand and they seeded the formation of the first stars and the first galaxies in the universe. The early universe was a hot, almost uniform, sea of matter and radiation. As the universe expanded, the slightly denser regions became increasingly dense. Atoms clumped together to form the first structures. Over time these structures grew so massive that they collapsed under their own gravity. Hydrogen fused, releasing enormous amounts of energy. Darkness was banished and the cosmos began to fill with light. Planets formed and fell into orbit around the stars and these young solar systems orbited the galaxies. And the only reason why any of this exists is because of those tiny density fluctuations that appeared when the observable universe was smaller than a grain of sand. Without them there would be no planets or stars and no galaxies. For billions of years, generations of stars lived and died. And then, nine billion years after it all began, in an unremarkable piece of space in the Orion spur of the Persius arm of a galaxy called the Milky Way, a star was born that we call the Sun, that illuminated our embryonic solar system with light. So the light from the star that bathes the Earth has its ultimate origin in the tiny ripples that appeared in the first moments of our universe's life. By capturing the light from the skies, we've been able to tell the story of the universe's origins and evolution, and it's worth reflecting on what a remarkable thing that is. You know, little beings like me scurrying around on the surface of a rock on the edge of one of the galaxies have been able to understand the very origin and evolution of the universe. But there's one more twist to this story, because that ability to use light, to capture it, and use it to understand our world, may have played a key role in the emergence of complex life on Earth.