Wonders of the Universe

Stardust

1. Why are we here? Where do we come from? These are the most enduring of questions and it's an essential part of human nature to want to find the answers. And we can trace our ancestry back hundreds of thousands of years, to the dawn of humankind, but, in reality, our story extends far further back in time. Our story starts with the beginning of the universe. It began 13.7 billion years ago. And today, it's filled with over 100 billion galaxies, each containing hundreds of billions of stars. In this series, I want to tell that story, because, ultimately, we are part of the universe, so its story is our story.

2. This film is about the stuff that makes us and where it all came from, because understanding our own origins means understanding the lives of stars. And how their catastrophic deaths bring new life to the universe. Because every mountain, every rock on this planet, every living thing, every piece of you and me was forged in the furnaces of space. This is Pashupatinath, in the Nepalese capital city of Kathmandu. And Hindus come here from all over India and Nepal to worship the god Shiva. That is Shiva's temple.

3. Now, Shiva is the god of destruction. In the Hindu faith, everything has to be destroyed, so that new things can be created and that's why pilgrims come here to the banks of the Bagmati River, at the foot of Shiva's temple. The belief in this cycle of creation and destruction lends Pashupatinath an added significance. Many of these pilgrims will have come here at the end of their lives, to die here and be cremated. Hindus believe in reincarnation, an eternal sequence of death and rebirth. Cremation helps free the soul so it's ready for the next life. They also believe that the physical elements of the body are released back to the world so they can be recycled in the next stage of creation.

4. It's an ancient belief that touches on a deeper truth about how the universe works. Every civilisation, every religion across the world, has a creation story. It tells of where we came from, of how we came to be here and of what will happen when we die. Well, I have a different creation story to tell and it's based entirely on physics and cosmology. It can tell us what we're made of and where we came from. In fact, it can tell us what everything in the world is made of and where it came from. It also answers that most basic of human needs to feel part of something much bigger, because to tell this story you have to understand the history of the universe. And it teaches us that the path to enlightenment is not an understanding of our own lives and deaths, but the lives and deaths of the stars.

5. My creation story is the story of how we were made by the universe. It explains how every atom in our bodies was formed, not on Earth, but was created in the depths of space, through the epic lifecycle of the stars. And to understand that story we will journey to the stars in all their stages of life. This is where stars are born, a nebula - a stellar nursery, where new stars burst into life. Those stars will burn for billions of years, until their voracious hunger for fuel forces them to blow up, to become giants.....Hundreds of times the size of our sun. And when they die, stars go out with the biggest bang in the universe. But to understand how we came from the stars, we must begin our journey much closer to home.

6. Well, this is sunrise over Nepal and those are the tallest mountains in the world, the Himalayas. Every one of those peaks is over 6,500 metres. What a spectacular sight. But it's incredible to think that, just a few tens of millions of years ago, those mountains were something very different. The Himalayas haven't always been mountains. We can find clues to their true origin by looking at them more closely. This is Himalayan limestone, the rock out of which much of this magnificent mountain range is made. If you look closely, you can see a kind of chalky granular structure, because limestone is made primarily out of the bodies, the shells, of dead sea creatures coral and polyps and when they die, they are put under immense pressures and squashed and eventually form limestone.

7. So the Himalayas were once living creatures. Much of the rock in the Himalayas was formed at the bottom of an ocean, and then over millions of years, it was raised up, to become these vast peaks. We've even found fossils at the top of Mount Everest. It's a beautiful example of the endless recycling of the earth's resources that has been going on since the dawn of time - and we are part of that system. Every atom in my body was once part of something else, so an ancient tree or a dinosaur or a rock, in fact, definitely, a rock. And the reason that the rocks of the Earth can become living things and then living things will return to the rocks of the Earth is because everything is made of the same basic ingredients.

8. Those ingredients are the chemical elements, the building blocks of everything on Earth. Elements like hydrogen, helium, lithium, beryllium, borum, carbon, nitrogen, oxygen, fluorine, neon, sodium, magnesium... Everything in the world is made up of the same basic sets of chemical elements, just assembled in different ways. So these mountains, the Himalayas, are made of limestone - and that's calcium carbonate. Now, calcium, carbon and oxygen are three of the elements that are vital for life, so calcium in my teeth and bones, oxygen in the air that I breathe and carbon in every organic molecule in my body.

9. Now, you're probably pretty familiar with those elements in their combined forms, but you very rarely see the elements on their own. There's a good reason why many of the elements are not found in their raw forms in nature. They're extremely reactive. This is sodium. As you can see, it's a silvery metal and it's also quite reactive. In fact, it's so reactive that when you drop it into water.....You get a violent, almost explosive, reaction, which is all the more surprising when you think that, when combined with chlorine, this forms sodium chloride.....salt, which is vital for life.

10. Excellent! And that's why I love chemistry almost as much as physics! It's this reactivity that enables the elements to combine with one another to make new substances. Where's it gone? Where the hell's it gone?! That, in turn, has allowed the Earth to develop its endless variety. And that variety includes us. So, to explain where we come from, we must also explain where the elements come from. We now know that the Earth is made of 92 chemical elements and that's pretty amazing, if you think of the complexity that we see around us.

11. We also know that everything beyond Earth, everything we can see in the universe, is made of those same 92 elements. And notice that I didn't say, "We think" that's what they're made of. I said, "We know". That's what they're made of, because we can prove it. The chemistry set we have on Earth extends far beyond the planet. We have set foot on the moon and know that it's rich in helium, silver and water. We have sent robot landers to our neighbouring planets and discovered that Mars is rich in iron, which has combined with oxygen to form its familiar rusty-red colour. And we know that Venus's thick atmosphere is full of sulphur.

12. We've sent spacecraft to the edge of the solar system to discover that Neptune is rich in organic molecules, like methane. But what of the rest of the universe? It seems impossible that we could discover what the stars are made of, because they're so far away. Even the nearest star, Proxima Centauri, is ten thousand times more distant than Neptune, 4.2 light years from Earth. And the nearest galaxy, Andromeda, is another 2.5million light years away. Yet despite these vast distances, these alien worlds are constantly sending us signals, telling us exactly what they're made of.

13. Our only contact with the distant stars is their light, that has journeyed across the universe to reach us, and encoded in that light is the key to understanding what the universe is made of. And it's all down to a particular property of the chemical elements. You see, when you heat the elements, when you burn them, then they give off light and each element gives off its own unique set of colours. So this is strontium and it burns with a beautiful red colour. Sodium is yellow. Potassium is lilac. And copper is blue. Each element has its own characteristic colour. It's this property that tells us what the stars are made of.

14. But it's a little more complicated than simply looking at the colour of the light that each star emits. You can see why, by looking at the light from our nearest star, the sun. This is a spectrum of the light taken from our sun and, at first glance, it looks very familiar. It looks like a stretched-out rainbow, because that's exactly what a rainbow is. It's the spectrum of the light from the sun in the sky. But if you look a bit more closely, then you see that this spectrum is covered in black lines. These are called absorption lines.

15. Each element within our sun not only emits light of a certain colour, it also absorbs light of the same colour. By looking for these black lines in the sun's light, we can simply read off a list of its constituent elements, like a bar code. For example, these two black lines in the yellow bit of the spectrum are sodium. You can see iron. Right down here you can see hydrogen. So, by looking at these lines in precise detail, you can work out exactly what elements are present in the sun and it turns out that that's about 70% hydrogen, 28% helium and 2% the rest.

16. And you can do this, not only for the sun, but for any of the stars you can see in the sky and you can measure exactly what they're made of. So that star there is Polaris, the Pole Star, and you can see that because all the other stars in the night sky appear to rotate around it. Now it's 430 light years away. But we know just by looking at the light that it has about the same heavy element abundance as our sun, but it's got markedly less carbon and a lot more nitrogen.

17. And the same applies for other stars. Vega, the second brightest star in the northern sky, has only about a third of the metal content of our sun. Whereas, other stars are metal-heavy. Sirius, the dog star, contains three times as much iron as the sun. And Proxima Centauri is rich in magnesium. But although the quantities of the elements may vary, wherever we look across space, we only ever find the same 92 elements that we find on Earth. We are made of the same stuff as the stars and the galaxies.

18. But where did all this matter come from? And how did it become the complex universe we see today? In order to understand where we came from, we have to understand events that happened in the first few seconds of the life of the universe. So when the universe began, it was unimaginably hot and dense. We, literally, don't have the scientific language to describe it, but it was, in a very real sense, beautiful. There was no structure, there was certainly no matter. It was exactly the same whichever way you look at it.

19. We can get some idea of how the universe developed from this state of pure symmetry by looking at the behaviour of water in this remarkable landscape. These are the El Tatio geysers, high in the Chilean Andes. As the boiling water bubbles up through the ground to meet the freezing mountain air, water can be found in all three of its natural phases - vapour, liquid and ice. In its hottest state, water is, like the early universe, an undifferentiated cloud. But as it cools, it suddenly behaves very differently. You see, if you look at a cloud of steam, it looks the same from every direction, but as it cools down, as it lands on this plate of freezing cold glass, then it immediately crystallises out. It turns into solid water - ice.

20. As the ice crystals form, the symmetry of the water vapour disappears from view and complex, beautiful structure emerges. In the same way, we think that the universe, as it cooled, went through a series of these events, where structure emerged. One of the most important was about a billionth of a second after the Big Bang. In that moment, an important part of the symmetry of the universe was broken. Known as electroweak symmetry breaking, this was the moment when subatomic particles acquired mass substance  for the first time. Amongst them, were the quarks.

21. As the universe continued to cool, those quarks joined together to form larger, more complex structures, called protons and neutrons. Way before the universe was a minute old, the quarks had been locked away inside the protons and the neutrons and they were the building blocks of all atomic nuclei, the building blocks of the elements. These same protons and neutrons are with us to this day. They form the hearts, the nuclei, of all atoms. Just a few seconds after the beginning of the universe, the fundamental building blocks of everything had been created.