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00:00Did our universe have a beginning?
00:24Why is there a universe like this one?
00:26If time began at the Big Bang, then was there a time before time?
00:36Why are there rivers and flows and filaments of galaxies?
00:42Is there an end of the universe?
00:43Is our universe eternal?
00:47I'm on tour in Australia, talking to audiences and scientists about two fundamental questions.
00:54How did the universe begin?
00:56Like in the Big Bang, it feels audacious.
00:58And how will it end?
01:01Life on Earth will become very problematic.
01:04In the last decade, we've been able to probe these ideas in unprecedented detail.
01:09So this is the oldest light in the universe.
01:13This is the story of our scientific quest to understand the origin of the universe.
01:18Of all the questions of the universe, we've been able to probe these ideas in the universe, we've been able to probe these ideas in the universe.
01:48Questions in science, the question of the origin of the universe is one that I think needs no motivation.
01:55Every human culture has its own creation story and science is no different.
02:00The best part of a hundred years, we've had the theory that the universe began in the Big Bang, but in the last decade or so, new precision measurements of the cosmos coupled with theoretical developments have given us an unprecedented and detailed picture of the origin of the universe.
02:19If this were a lesser program, we would start it in a deep voice going, there was a time with no time.
02:38There was a place not in space.
02:45That is the time before time and place without space that we call the Big Bang.
02:57That is not what we are doing though.
02:58I think if you ask the question, why do you want to know the origins of the universe, I suppose the answer has to be curiosity.
03:07It is surely something that must occur to everybody at some point.
03:11Why do we exist?
03:12When I think of a scientist, I think of an adult who still has the soul of curiosity of a child.
03:26So, I think it is very natural to ask, how did it all get here?
03:33Indigenous Australians have been observing the stars for more than 40,000 years and, like many ancient cultures, have a number of creation stories based on the night sky.
03:45It is the story of Arang, the emu.
03:49The emu sacrificed his wings and was given an eternal place in the southern skies.
03:54Wherever you will be seen, running across the night sky and marked as Jura, the stars.
04:08I have always liked creation stories.
04:10I like reading about them from across the world.
04:13Why do we do it?
04:15Why do we build telescopes to look back to the edge of time?
04:19Why do we measure the expansion rate of the universe and build theories to explain it?
04:24Well, the answer is because that's what we've always done.
04:28And the evidence for that is that every culture you study across the world has a creation story.
04:35And the most wonderful thing about living in the 21st century with modern science is that we also have a creation story.
04:47You've probably heard it described as the Big Bang.
04:50The Big Bang.
04:51But what is the Big Bang?
04:53And what do we know about the origin of the universe?
04:59With observations and mathematical theorizing, we have a good sense that about 13.8 billion years ago, the universe was incredibly dense and it was incredibly hot.
05:10Hot, give me some heat, give me some density, give me some violations of the laws of particle physics.
05:17It underwent a rapid swelling that's called the Big Bang.
05:21So what's the Big Bang?
05:23And the answer is, I don't know what the Big Bang is.
05:25I just know what came after the Big Bang.
05:27Where we have a universe that's expanding very quickly.
05:30It's really hot.
05:32These things we do know.
05:33It's the things that come after that we understand.
05:38You can trace everything back and you get to a point where the universe had to have been hot and small and dense.
05:43And something happened that made that expand.
05:47And so that's this idea that became known as the Hot Big Bang.
05:52I'm liking the Big Bang.
05:53That just feels right.
05:54It feels audacious.
05:59It's common to think of the Big Bang as the start of time itself.
06:06The moment when everything came from nothing.
06:11But there are cosmologists who think there may be more to it.
06:14That the thing we used to call the Big Bang was an event in a pre-existing universe.
06:21And not the beginning at all.
06:29But how can we be so confident?
06:30How can we even dare to speak of things that happened almost 14 billion years ago?
06:36In 1927, the astronomer Edwin Hubble noticed that the light from distant galaxies is stretched.
06:48That means that space is expanding.
06:51Our universe is expanding.
06:53So you run time backwards in your mind's eye.
06:57That means that in the past, the distances between the galaxies were smaller.
07:01And you can imagine a time when the distances were so small that everything is effectively on top of each other.
07:09That implies that our universe had a beginning.
07:13There was a day without a yesterday.
07:16And that is what we call the Big Bang.
07:19More than 30 years after Hubble made his observations,
07:23cosmologists remained divided about whether the Big Bang theory was correct.
07:27More evidence was needed.
07:30And it came in the 1960s with the discovery of a mysterious faint signal.
07:36We call it the Cosmic Microwave Background Radiation.
07:42It's seen as a faint glow, coming literally from everywhere in the sky,
07:48and not being emitted from any particular star, galaxy or object.
07:53So this is the oldest light in the universe.
07:59There are photons that have travelled 13.8 billion years from over there,
08:05and 13.8 billion years from over there.
08:09And they're carrying information about the beginning of time.
08:13One of the many remarkable things about the Cosmic Microwave Background
08:16is the story of its discovery, because it was found entirely by accident.
08:23We had this result. We couldn't find any explanation for it.
08:27We couldn't make it go away. What were we going to do with this thing?
08:30So where did the Cosmic Microwave Background come from?
08:37And why do we consider it such strong evidence for the Big Bang theory?
08:42So the picture is this. The universe is expanding and cooling.
08:47In the first few minutes, it's extremely hot.
08:50And then the universe is filled by what's called a plasma.
08:52So it's too hot for atoms to form.
08:56380,000 years after the Big Bang, it's cool enough for atoms to form,
09:00the universe becomes almost instantly transparent.
09:04So light can travel in straight lines,
09:06and it will continue to travel in straight lines
09:09for the rest of the expansion history of the universe,
09:12and it can enter our telescopes here on Earth 13.8 billion years later.
09:17The Cosmic Microwave Background is considered such strong evidence,
09:22in large part because the Big Bang theory predicted that it should exist.
09:27It was first observed in the mid-1960s,
09:30and it's only then really, just before I was born,
09:33that the idea that the universe began at a hot, dense origin really took hold.
09:40It's an almost overwhelming piece of evidence
09:42because you're seeing the afterglow of that earliest of times.
09:47We can take pictures of that light in great detail now.
09:50We just don't see it as a hum.
09:52We can photograph, essentially, the universe as it was.
09:55The whole sky looking out into the universe,
09:58and see it as it was when that first light was released.
10:04This remarkable baby photograph of the universe
10:07confirmed that we had the basics right.
10:09But it's great detail presented fresh challenges.
10:14As we often find with science,
10:16when you answer one set of questions, new ones arise.
10:24This idea that the universe had a beginning in the Big Bang
10:28is in some ways unsatisfactory.
10:30It raises a series of child-like questions.
10:34Like, if the universe had a beginning,
10:36then what happened before the beginning?
10:38What caused it?
10:40If time emerged at the Big Bang,
10:43then was there a time before time?
10:45How can the universe appear spontaneously at nothing at all?
10:55Was there a before?
10:57Well, that is a philosophical question,
10:59unless you can come up with a theory that predicts something
11:02that you can test against observation?
11:10The clues which point the way to a theory of what came before the Big Bang
11:14can be found in problems with the Big Bang theory itself.
11:19Now, there are two problems with the standard Big Bang model.
11:22What they call the horizon problem and the flatness problem.
11:27You can picture the horizon problem as follows.
11:31If you look at the universe, as far as the eye can see,
11:35in that direction, which is to say, the cosmic microwave background,
11:39then it's the same temperature,
11:42to one part in 100,000 as the universe,
11:46as far as the eye can see, in that direction,
11:48which is the cosmic microwave background.
11:51But those two points on the sky are separated today by 90 billion light years.
11:59That means if you've got a universe that's been expanding sedately
12:04and is only 13.8 billion years old,
12:07those two points could never have been in contact with each other.
12:10Which means there's no explanation for how they could be so precisely the same.
12:19And then there's the flatness problem.
12:22When you look at our universe, it appears to be completely flat,
12:27which seems very strange because it could have been curved
12:31like the surface of a sphere or curved like the surface of a saddle.
12:35A solution can be found in a theory known as inflation,
12:41which suggests that there was a time in the history of the universe
12:45when the universe wasn't just expanding sedately as it is today.
12:49It was expanding incredibly fast.
12:54By fast, I mean that it was doubling in size every 10 to the minus 37 seconds.
13:00That's 1, 10 million, million, million, million, million, millions of a second.
13:12Why does that solve the horizon and flatness problems?
13:16Well, first of all, it suggests the universe has to be extremely big,
13:21way bigger than the piece we can see today.
13:24And that means that it's always going to look flat.
13:26Think about an analogy with the surface of the Earth.
13:30This little piece of the Earth here looks flat, even though we know the Earth's curved.
13:37Why? Because it's very small compared to the size of the Earth.
13:42So it is, according to the theory of inflation, for our universe.
13:46It also solves our horizon problem because it says that that piece of the sky,
13:51which is so far away from that piece, were once in contact with each other.
13:57They could jiggle around and get to the same temperature, but then they were ripped apart.
14:01It's mind-boggling, but it's important to say that if we are right about inflation, then this violent, rapid expansion must have occurred before the thing we used to call the Big Bang.
14:20So, what is our current theory? This theory called inflation, that says there was something going on before.
14:29I suppose that thing we used to call the Big Bang, or is that...?
14:33Yeah, the Hot Big Bang. I make that distinction by saying Hot Big Bang versus Big Bang, because Hot Big Bang does imply sort of the universe is in a fireball kind of state.
14:42Yeah.
14:43I mean, the reason we know that something happened before is we can look at that primordial fireball state.
14:51We can actually see it, because we can see the cosmic microwave background, which is the sort of afterglow of that time when the whole universe was hot and dense.
15:00The sort of important point there is that it was expanding so fast that things that were connected to each other before, close enough together to communicate, to come into equilibrium, to be the same temperature, rapidly come out of contact.
15:10Yeah.
15:11And so that's why now when we look at the sky and we see that two different parts of the universe that should never have been in contact with each other are the same temperature.
15:20It's because you can dial back the expansion and find that they were never in contact, but then there's this extra secret time at the beginning where they did communicate and then they just were sort of pulled apart so quickly that, you know, we can only infer that that happened by the fact that they must have been in contact at some point.
15:38So inflation leads to a massive universe, galaxies way beyond the horizon, way beyond the part that we can see, possibly infinite in extent.
15:48And that's one of the things inflation does. So it tells us that the universe should be significantly bigger than the patch we can see.
15:56Ah, look, I'll probably just stop and have a look at the stars on the way home. It was, yeah, it was really mind expanding stuff.
16:10Did you understand it all?
16:11I wouldn't say I'm stood at all.
16:13Excellent. Very good show, yes.
16:14Did you understand it all?
16:15No.
16:16I'm so confused.
16:21After entertaining the people of Canberra, I've made my way to Tidvin Villa, just outside the capital.
16:27It's home to one of the most important deep space tracking stations on Earth. And it's a must see for an astronomy geek like me.
16:36I always find these places exciting if you're a space geek. And you look out here, that big dish you can see is the only dish in the world that can talk to Voyager 2.
16:47So that iconic spacecraft, I've followed that since 1977, since I was nine years old. We're still in contact with it now, beyond the edge of the solar system.
16:57It's a tiny transmitter, about 16 watts of power. And that dish is the way that we talk to Voyager.
17:04And in the background is a famous dish. It's called honeysuckle. That dish is the Apollo dish.
17:12So when you hear Apollo 11 on the moon, and you hear the last words of NASA as Apollo 13 came back into the atmosphere, the last contact as it re-entered, and the last words you hear is lost contact at honeysuckle.
17:25And that dish through the trees is that dish.
17:27Farewell, Aquarius. We thank you.
17:32OK, LOS in a minute or a minute and a half.
17:37It's exciting.
17:38And welcome home.
17:51It's all very well said that the universe underwent a period of rapid expansion sometime before the Big Bang.
17:57But we need some kind of mechanism that might cause that to happen.
18:02And we have one off the shelf, if you like, from particle physics.
18:07It's a thing called a scalar field.
18:10You could picture it as a sort of still ocean filling space.
18:16We call it the inflaton field.
18:21The thing about that type of field is we know it had to go away at some point, or else the universe would still be exponentially expanding.
18:28If you have an energy that is uniformly spread out through a region of space, it can yield a new kind of gravity.
18:35Repulsive gravity.
18:37Gravity doesn't pull things together, but pushes things apart.
18:40So they presuppose that this kind of fuel, if you wouldn't call it the inflaton field, but it's like a fuel that generates this repulsive gravity, is what drove the universe to start expanding in the first place.
18:53The idea that inflation is driven by the inflaton field leads to one of the most remarkable predictions in the history of cosmology, which is supported by observation.
19:08Now, you can think of the inflaton field as a sort of a still ocean filling space.
19:15But quantum theory tells us there's no such thing as a still ocean.
19:20Every ocean has ripples in it.
19:23Now, what do those ripples correspond to?
19:27They mean that the inflaton field is a little bit bigger in some regions than others.
19:34So that means that at the end of inflation, at the start of the Big Bang, some bits of the universe will have expanded a little bit more than others, and they will be a little less dense than the others.
19:46So at the Big Bang, you get a very natural prediction that some regions of the universe are slightly denser than other regions of the universe.
19:59Now imagine what happens as this universe expands and cools.
20:04Those denser regions get denser, and eventually they collapse to form the galaxies, stars, the fluctuations in the early universe led to the structures that we see today, including, of course, us.
20:18Without those seeds, without that structure, we wouldn't exist.
20:32Although inflationary cosmology does have its critics, this idea that the universe underwent a violent expansion before the hot Big Bang is now accepted by many cosmologists.
20:45But a more speculative addition to the theory exists, and it opens the doors to an intriguing possibility.
20:52Ours may not be the only universe.
20:57If the theory of inflation is correct, then you could ask the question, how long was inflation going on for before the Big Bang?
21:06And the answer is, we don't know.
21:08We have a minimum time, which is quite short actually, 10 to the minus 35 seconds or so.
21:15But it could have been much longer than that.
21:17And so you ask the question, could it have been going on for an indefinite period of time?
21:22Could you push the origin of the universe back and back and back into the infinite past?
21:28So we have an eternal universe.
21:31The answer is, we don't know.
21:32There's theoretical speculation either way.
21:36But imagine if the universe is, in fact, eternal.
21:40There may not have been a beginning.
21:42So this picture of inflation, those are two ways of looking at it.
21:54There's one that this universe is all there is and it inflates and then slows down and there we are.
22:00But there are other possibilities, aren't there?
22:03Yeah, for sure.
22:04And the other possibilities suggest that we're one of a grand collection of universes.
22:10We're part of a multiverse.
22:11And again, that's not an idea that comes out of wild theorizing.
22:14It comes right from the math.
22:16You see, when you try to explain how the universe, say our universe got started, and you have this repulsive gravity coming from the inflaton field, it causes space to expand.
22:28But the math shows that it's such an efficient process that you can virtually never fully use up the fuel that generated our expansion.
22:37So our Big Bang happens, but there's still some fuel left over.
22:40What does it do?
22:41It can generate another Big Bang.
22:43So you get this wonderful process of Big Bang after Big Bang after Big Bang yielding universe after universe after universe.
22:51And that's just this natural outcome of trying to explain the Big Bang in our universe.
22:57You naturally led to the possibility that it simply is not a one-time event.
23:06Well, here's Earth, and we would think it's special because we happen to be pretty close to it.
23:11Then you realize, oh, it's one of eight planets.
23:14But our sun, oh, no, it's one of a hundred billion other suns.
23:19The galaxy, no, it's one of a hundred billion galaxies.
23:23The universe, well, is it just going to stop there and we have only one universe?
23:29The trend line tells us why shouldn't there be multiple universes.
23:33If you look out onto this universe, the one in which we live, and you ask the question, could it have been any different?
23:48What would it have looked like if gravity was a bit stronger, or there's a little more dark energy, or the force of electromagnetism was a little bit weaker?
23:57Very quickly, you get to a universe which would not permit life to exist.
24:03So it's a legitimate question to ask, are we lucky?
24:07But in theories that allow you to have multiple universes, such as the inflationary multiverse,
24:14then it can be the case that the different bubble universes have different laws of physics.
24:20And it can be the case that the mechanism that produces those universes provides a very natural way of exploring the landscape of the laws of physics.
24:31So that then means that we're not lucky at all.
24:34Our existence is inevitable because every possible universe, with every possible combination of physical contents and dark energy and masses of the particles,
24:43every one exists.
24:45And not only that, but every one of those is being created essentially an infinite number of times,
24:52and will go on being created into the indefinite future.
24:55And that is the inflationary multiverse.
24:58So it says our existence is inevitable.
25:03How does that make you feel?
25:11We may never know if our existence is inevitable.
25:14We may never have a complete theory of the origin of the universe.
25:19But it is remarkable that we've made so much progress.
25:27Big Bang, as we see it, was created in a very special way.
25:31The present understanding is that inflation can do that.
25:35So that's what I would hang my hat on right now.
25:38But I wouldn't be surprised if there are changes in the future in our understanding.
25:44One day, some smart person will come along and solve it for you.
25:48That's the beautiful thing of how science works.
25:51The set of questions we're asking now get us to a new vista, a new place to stand.
25:57And on a new place to stand, there are other questions we haven't even dreamt of yet,
26:01that I'm sure will be more important than whatever we think we're answering today.
26:07I think cosmology is the most remarkable of the sciences.
26:10I mean, not only are we able to look up into the sky and collect the light from the most distant galaxies,
26:18and even in the form of the cosmic microwave background from close to the origin of the universe itself,
26:24but we're able to decode the messages that it contains and build plausible theories of the origin of the universe.
26:33Yeah, I think our situation was beautifully summed up by the Belgian priest and mathematician Georges Lemaître,
26:40one of the fathers of the Big Bang Theory.
26:43He said, standing on a well-cooled cinder, we see the slow fading of the suns,
26:49and try to recall the vanished brilliance of the origin of the worlds.
26:55Is there an end of the universe? Is our universe eternal?
27:14The universe literally tears itself apart.
27:18Will there be stars and galaxies?
27:22What is the fate of the universe? How will it all end?
27:27How will it all end?
27:37What is the fate of the universe? How will it all end?
27:42If you have fallen off by the world and you're still dead, it's then moyenn
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