Good morning, everybody.
400 years ago, Galileo pointed his telescope at the sky, and ever since then, we’ve built bigger and more powerful telescopes to look at the sky in increasingly more detail. And though we’ve learned a lot, there are some problems that we still can’t answer.
Today I’m going to describe to you the things we still don’t understand about the universe and how we, in Australia, are going to take a new approach to try and answer them. I’m going to start by putting the entire history of the universe on one slide.
So, here it is. Pretty amazing that we can do this. The Big Bang at the top and us, 13.7 billion years later, at the bottom. So we know the universe began in this huge explosion, a Βig Βang. We know that for a long period after that not much happened. The universe was dark. Gas was floating around in that darkness. We call that period the Dark Ages. Then after about a billion years or so, these clouds of gas collapsed under gravity and formed stars and galaxies. “Let there be light,” as someone once said; the stars turned on. You might call this the Cosmic Renaissance.
We now have stars and galaxies and for billions of years; they have evolved, collided, aged, and eventually giving birth to the Sun, the solar system, and us. And we now look at the sky and try to understand it. And while we know a lot about the beginning, we actually know quite a lot about the Big Bang, except the minor detail of why it happened in the first place – and we know a lot about the universe now, but there’s that big gap in between the Dark Ages and the Cosmic Renaissance. We don’t know how we got from the Big Bang to us.
So, we have a problem: we don’t understand how the universe has evolved. There’s a second problem. The universe is changing, and it’s changing quite quickly. In December 2004, a little star, about 50,000 light-years away, gave off a sudden flash. For a quarter of a second, this star was brighter than the Milky Way by a factor of a 1,000. This intense radiation hurdled across space and crashed into the Earth’s atmosphere, lighting up the ionosphere and knocking out satellites all over the world.
Now, luckily we happened to see that when it happened. A quarter of a second it was on, and then it was gone. But it turns out, there are explosions like this happening all over the sky every day. We don’t understand what they are and what they’re telling us. And unless we’re looking at the right place at the right time, we normally miss them. The universe is dynamic. Not only do we not understand it, but we’re not even seeing the whole story.
And there’s a third problem, a very minor problem that we don’t actually know what the universe is made of. Now, the stuff we think about when we look at the sky –galaxies, stars, planets, trees, people– they’re all made of atoms. We think we understand atoms. But atoms are only 5 percent of the universe. There is a lot of other stuff out there. Stuff that we can’t see and we don’t understand. About 23 percent of the universe is something we have no idea what it is, so we just call it dark matter.
But if that’s not bad enough, 72 percent of the universe is filled with something even less understandable, some sort of mysterious anti-gravity force called dark energy. So, 95 percent of the universe is completely mysterious. Or as my colleague Bob Kirschner likes to say, “The universe is like Los Angeles. It’s only 5 percent substance and 95 percent energy.”
So, the universe evolves, and we don’t understand that. The universe changes; we don’t understand that. The universe is dark, and we don’t understand that either. We haven’t really done much in the last 400 years. So, why don’t we understand these problems? We’ve got these amazing telescopes.
What is the problem? The problem is that the answers to these questions are not buried in individual objects that we can study in great detail. Here is a typical picture from the Hubble Space Telescope, the most powerful telescope ever built. You’ve seen breathtaking images of incredibly distant stars. But the answers to these questions are not in individual objects, but they’re written on the whole sky. They have subtle imprints that you need to look at the whole sky at once to get the answers for.
To show you the contrast between the Hubble Space Telescope and the whole sky, here it is what Hubble sees, and let’s just see how much of the sky we see every time we take a picture with Hubble. There’s a nice galaxy. There are some stars. But we’re still going, we’re still going, and this is about a quarter of the sky. So, you can see Hubble is only telling you a tiny, tiny part of the story. You need to take this new approach of all-sky astronomy if you really want to see what’s going on.
So, why don’t we do that? Why don’t we just point Hubble all over the whole sky? Well, there are three problems. There are three reasons why we can’t do this all-sky astronomy just yet. The first is that our telescopes simply can’t see that much of the sky at once. So, as I said, the Hubble Space Telescope, best telescope ever built –billions of dollars; let’s ask it to take a picture of the Moon. That’s a bit embarrassing. You don’t ask something as amazing as Hubble to take a picture of the Moon. Surely that’s way beneath its capabilities.