Wonders of the Universe
Messengers
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 a hundred billion galaxies, each containing hundreds of billions of stars. In this series, I want to tell that story, because ultimately, we're part of the universe, so its story is our story. 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.
2. 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.
3. This is Karnak Temple in Egypt, built by the ancient pharaohs. This vast complex was erected to honour Amun Ra, god of all gods, god of the sun. This worship reaches its peak during one fleeting moment in the solar calendar, an event so brief it lasts for little more than a minute. This temple is built to align with an astronomical event that happens just once a year - the sunrise at the winter solstice. "Solstice" is Latin for "Sun stands still". Because as the Earth orbits around the sun and the year passes, the point at which the sun rises above the eastern horizon moves, so here in Egypt in summer, the sun rises over in that direction, and then as summer turns to autumn, turns to winter, the sunrise point drifts along, until today on December 21st, at 6:30 am in mid-winter, the sun rises exactly between the pillars of this temple.
4. Just once a year, for over 3,000 years, the sun has risen between the two pillars, and casts its light into the temple. There it is, the light from our star cascading down this magnificent structure. I mean, you can literally feel the history of this place, so it's easy to forget that this is 3,500 years old, so in 1500 BC, the most powerful man on the planet, the Pharaoh of Egypt, would have stood here on December 21st every year, just to greet and experience the light from Amun Ra. This moment that the Egyptians worshipped instinctively we now understand in exquisite detail.
5. As the Earth journeys through the Solar System, it's bathed in the light of the star that sits at its centre. This light has travelled some 150 million kilometres from the surface of the Sun. And at the winter solstice, that light pours into the temple at Karnak. Well, this building is honestly the most magnificent structure I've ever seen. Now, it's not built on the scale of men. It's built on the scale of gods, of one god, Amun Ra, the god of the sun. As the Sun sinks below the horizon and night falls, the whole universe of suns fades into view. We no longer build temples to our Sun, we build machines that allow us to peer deeper into space than ever before, to far distant suns out there in the galaxy, and beyond.
6. On a night like this, there are about 2,500 stars visible to the naked eye. But when we started building telescopes instead of temples, we discovered that there are billions more. 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.
7. 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, young, new 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.
8. 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.
9. 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.
10. 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.
11. This is a Hawker Hunter. It was built in the 1950s. When breaking the sound barrier was at the very limit of our technical abilities. A sound barrier's an incredibly evocative term, you know, it has an almost legendary status in the history of aviation, but there's nothing fundamental about it - it's something that you can overcome with some extremely clever engineering, and in the early days, quite a lot of courage. The reason we don't usually think about sound as having some kind of speed limit, a limit in speed, is because it is incredibly fast compared to the things we're used to in everyday life.
12. But today, we're going to try and break it. I'm going to try and break it --- sat in this marvellous machine. On Earth, the speed of sound, depending on altitude is around 1,200 kilometres per hour, known as Mach 1. This jet isn't designed to fly that fast in normal flight, but there is a way to make it travel faster than sound, and for that, we need to fly high. As the plane flies faster, it begins to catch up with its own sound. The sound waves simply can't get out of the way fast enough, so they begin to pile up at the front of the jet.
13. But to outrun our sound waves, we need to push this jet to its absolute limit. In just seconds, the jet smashes through the sound barrier. This can be heard from the ground as a sonic boom. It was a doddle, actually. Well, you know, having said that, it was inverted full throttle at 42,000 feet, but it's a different definition of "Doddle". So this magnificent piece of engineering is fast enough, if you just push it a little bit, to outrun its own sound, so the sound barrier is negotiable. You can smash your way through it.