Original subtitles

Did our universe have a beginning?

Why is there a universe like this one?

If time began at the big bang, then was there a time before time?

Why are there rivers and flows and filaments of galaxies?

Is there an end of the universe? Is our universe eternal?

I'm on tour in Australia,

talking to audiences and scientists about two fundamental questions -

how did the universe begin...

Like in the big bang, it feels audacious.

...and how will it end?

Life on earth will become very problematic.

In the last decade,

we've been able to probe these ideas in unprecedented detail.

So, this IS the oldest light in the universe.

This is the story of our scientific quest

to understand the origin of the universe.

Of all the questions in science,

the question of the origin of the universe

is one that I think needs no motivation.

Every human culture has its own creation story,

and science is no different.

For the best part of 100 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.

If this were a lesser program,

we would start it in a deep voice going,

"There was a time... with no time."

"There was a place... not in space."

"THAT is the time before time"

"and place without space"

"that we call the big bang."

That's not what we're doing, though.

I 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.

It's surely something that must occur to everybody at some point -

why do we exist?

When I think of a scientist,

I think of an adult who still has the soul of curiosity of a child.

So I think it's very natural to ask, how did it all get here?

Indigenous 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.

It's the story of 'arang' - the emu.

The emu sacrificed his wings

and was given an eternal place in the southern skies.

Forever you will be seen running across the night sky

and marked as 'dyurra' - the stars.

I've always liked creation stories.

I like reading about them from across the world.

Why do we do it?

Why do we build telescopes to look back to the edge of time?

Why do we measure the expansion rate of the universe

and build theories to explain it?

But the answer is because that's what we've always done.

And the evidence for that is

that every culture you study across the world has a creation story.

And the most wonderful thing

about living in the 21st century, with modern science,

is that we also have a creation story.

You've probably heard it described as 'the big bang'.

But what is the big bang?

And what do we know about the origin of the universe?

With observations and mathematical theorising,

we have a good sense that about 13.8 billion years ago,

the universe was incredibly dense and it was incredibly hot.

Hot! Give me some heat! Give me some density!

Give me some violations of the laws of particle physics.

It underwent a rapid swelling that's called the big bang.

So, what's the big bang?

And the answer is I don't know what the big bang is.

I just know what came after the big bang,

where we have a universe that's expanding very quickly,

it's really hot.

These things, we do know.

It's the things that come after that we understand.

You can trace everything back and you get to a point

where the universe had to have been hot and small and dense

and something happened that made that expand, right?

And so that's this idea that became known as 'the hot big bang'.

I'm liking the big bang.

That just feels right. It feels audacious.

It's common to think of the big bang as the start of time itself.

The moment when everything came from nothing.

But there are cosmologists who think there may be more to it -

that the thing we used to call 'the big bang'

was an event in a pre-existing universe

and not the beginning at all.

But how can we be so confident?

How can we even dare to speak of things

that happened almost 14 billion years ago?

In 1927, the astronomer Edwin Hubble noticed

that the light from distant galaxies is stretched.

That means that space is expanding - our universe is expanding.

So, you run time backwards in your mind's eye,

that means that in the past,

the distances between the galaxies was smaller,

and you can imagine a time when the distances were so small

that everything is effectively on top of each other.

That implies that our universe had a beginning,

there was a day without a yesterday,

and that is what we call the big bang.

More than 30 years after Hubble made his observations,

cosmologists remained divided

about whether the big bang theory was correct.

More evidence was needed.

And it came in the 1960s,

with the discovery of a mysterious faint signal.

We call it the cosmic microwave background radiation.

It's seen as a faint glow, coming literally from everywhere in the sky,

but not being emitted from any particular star, galaxy or object.

So, this is the oldest light in the universe.

There are photons that have travelled 13.8 billion years from over there

and 13.8 billion years from over there,

and they're carrying information about the beginning of time.

One of the many remarkable things about the cosmic microwave background

is the story of its discovery,

because it was found entirely by accident.

We had this result. We couldn't find any explanation for it.

We couldn't make it go away. What were we going to do with this thing?

So, where did the cosmic microwave background come from?

And why do we consider it such strong evidence for the big bang theory?

So, the picture is this - the universe is expanding and cooling.

In the first few minutes, it's extremely hot,

and then the universe is filled by what's called a plasma -

so, it's too hot for atoms to form.

380,000 years after the big bang, it's cool enough for atoms to form,

the universe becomes almost instantly transparent,

so light can travel in straight lines,

and it will continue to travel in straight lines

for the rest of the expansion history of the universe

and it can enter our telescopes here on Earth 13.8 billion years later.

The cosmic microwave background is considered such strong evidence

in large part because

the big bang theory predicted that it should exist.

It was first observed in the mid-1960s,

and it's only then, really, just before I was born,

that the idea that the universe began at a hot, dense origin

really took hold.

It's an almost overwhelming piece of evidence,

because you're seeing the afterglow of that earliest of times.

We can take pictures of that light in great detail now.

We don't see it as a hum.

We can photograph, essentially, the universe as it was,

the whole sky looking out into the universe,

and see it as it was when that first light was released.

This remarkable baby photograph of the universe

confirmed that we had the basics right.

But its great detail presented fresh challenges.

As we often find with science,

when you answer one set of questions, new ones arise.

This idea that the universe had a beginning in the big bang

is in some ways unsatisfactory.

It raises a series of childlike questions.

Like, if the universe had a beginning,

then what happened before the beginning?

What caused it?

If time emerged at the big bang, then was there a time before time?

How can the universe appear spontaneously out of nothing at all?

Was there a before?

Well, that is a philosophical question,

unless you can come up with a theory

that predicts something that you can test against observation.

The clues which point the way to a theory

of what came before the big bang

can be found in problems with the big bang theory itself.

There are two problems with the standard big bang model.

They're called the horizon problem and the flatness problem.

You can picture the horizon problem as follows.

If you look at the universe as far as the eye can see in that direction,

which is to say the cosmic microwave background,

then it's the same temperature to one part in 100,000

as the universe as far as the eye can see in that direction,

which is the cosmic microwave background.

But those two points on the sky are separated today

by 90 billion light-years.

That means if you've got a universe that's been expanding sedately

and is only 13.8 billion years old,

those two points could never have been in contact with each other.

Which means there's no explanation

for how they could be so precisely the same.

And then there's the flatness problem.

When you look at our universe, it appears to be completely flat.

Which seems very strange,

because it could have been curved like the surface of a sphere

or curved like the surface of a saddle.

A solution can be found in a theory known as inflation,

which suggests that there was a time in the history of the universe

when the universe wasn't just expanding sedately as it is today -

it was expanding incredibly fast.

By "fast", I mean that it was doubling in size

every 10 to the -37 seconds.

That's one ten-million-million- million-million-million-millionths

of a second.

Why does that solve the horizon and flatness problems?

Well, first of all, it suggests the universe has to be extremely big -

way bigger than the piece we can see today.

And that means that it's always gonna look flat.

Think about an analogy with the surface of the Earth.

This little piece of the Earth here looks flat,

even though we know the Earth's curved.

Why? Because it's very small compared to the size of the Earth.

So it is, according to the theory of inflation, for our universe.

It also solves our horizon problem,

because it says that that piece of the sky,

which is so far away from that piece,

were once in contact with each other.

They could jiggle around and get to the same temperature,

but then they were ripped apart.

It'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'.

So, what is our current theory?

This theory called inflation

that says there was something going on before,

I suppose that thing we used to call 'the big bang', or is that...

Yeah, yeah, 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.

Yeah.

Yeah, the reason we know that something happened before

is we can look at that primordial fireball state.

Like, we 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.

The, 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. Yeah.

And 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,

it'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.

So inflation leads to a massive universe.

Galaxies way beyond the horizon, way beyond the part that we can see,

possibly infinite in extent.

And that's one of the things inflation does.

So, it tell us that the universe should be significantly bigger

than the patch we can see.

Uh, 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.

Did you understand it all? I wouldn't say I understood it ALL.

Excellent. Very good show. Yes.

Did you understand it all? No.

I'm so confused!

After entertaining the people of Canberra,

I've made my way to Tidbinbilla, just outside the capital.

It'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.

I 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.

So, 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,

with its tiny transmitter - about 16 watts of power,

and THAT dish is the way that we talk to Voyager.

AND - in the background is a famous dish.

It's called Honeysuckle, and that dish is the Apollo dish.

So, 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" -

and that dish through the trees is that dish.

Farewell, Aquarius, and we thank you.

OK, IOS in a minute or a minute and a half.

It's exciting.

- And welcome home. - Thank you.

Well, it's all very well saying that the universe underwent

a period of rapid expansion sometime before the big bang,

but we need some kind of mechanism that might cause that to happen.

And we have one - off the shelf, if you like -

from particle physics.

It's a thing called a scalar field.

You could picture it as a sort of still ocean filling space,

and we call it the inflaton field.

The 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.

If you have an energy

that is uniformly spread out through a region of space,

it can yield a new kind of gravity - repulsive gravity.

Gravity that doesn't pull things together but pushes things apart.

So, they presuppose that this kind of... fuel, if you would,

called 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.

The 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.

Now, you can think of the inflaton field

as a sort of a still ocean filling space,

but quantum theory tells us there's no such thing as a still ocean -

every ocean has ripples in it.

Now, what do those ripples correspond to?

They mean that the inflaton field

is a little bit bigger in some regions than others.

So that means that at the end of inflation

and 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.

So, 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.

Now, imagine what happens as this universe expands and cools.

Those denser regions get denser,

and eventually, they collapse to form the galaxies, the stars.

The fluctuations in the early universe

led to the structures that we see today -

including, of course, us.

Without those seeds, without that structure, we wouldn't exist.

Although 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.

But a more speculative addition to the theory exists,

and it opens the doors to an intriguing possibility -

ours may not be the only universe.

If the theory of inflation is correct,

then you could ask the question,

how long was inflation going on for before the big bang?

And the answer is we don't know.

We have a minimum time, which is quite short, actually -

about 10 to the -35 seconds or so -

but it could have been much longer than that.

And so you ask the question,

could it have been going on for an indefinite period of time?

Could you push the origin of the universe

back and back and back into the infinite past,

so we have an eternal universe?

The answer is we don't know. There's theoretical speculation either way.

But imagine if the universe IS in fact eternal.

There may not have BEEN a beginning.

So, this picture of inflation,

I suppose there are two ways of looking at it.

There's one that this universe is all there is

and it inflates and then slows down and... there we are,

but there are other possibilities, aren't there?

Yeah, for sure.

And the other possibilities suggest

that we're one of a grand collection of universes -

we're part of a multiverse.

And again, it's not an idea that comes out of wild theorising,

it comes right from the math.

You 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,

but the math shows that it's such an efficient process

that you can virtually never fully use up the fuel

that generated our expansion,

so our big bang happens, but there's still some fuel left over.

What does it do? It can generate ANOTHER big bang.

So you get this wonderful process

of big bang after big bang after big bang,

yielding universe after universe after universe.

And that's just this natural outcome

of trying to explain the big bang in OUR universe.

You're naturally led to the possibility

that it simply is not a one-time event.

Well, here is Earth,

and we would think it's special,

because we happen to be pretty close to it,

then you realise, "Oh, it's one of eight planets."

"But our sun..."

"No, no, it's one of 100 billion other suns."

"The galaxy...!"

"No, it's one of 100 billion galaxies."

"The universe!"

Well, is it just gonna stop there and we have only one universe?

The trend line tells us,

why shouldn't there be multiple universes?

If you look out onto this universe, the one in which we live,

and you ask the question, could it have been any different?

What would it have looked like if gravity was a bit stronger?

Or there was a little more dark energy?

Or the force of electromagnetism was a little bit weaker?

Very quickly, you get to a universe which would not permit life to exist.

So it's a legitimate question to ask - are we lucky?

But in theories that allow you to have multiple universes,

such as the inflationary multiverse,

then it CAN be the case

that the different bubble-universes have different laws of physics

and 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.

So that then means that we're not lucky at all,

our existence is inevitable,

because every possible universe with every possible combination

of physical constants and dark energy and masses of the particles -

every one exists.

And not only that, but every one of those is being created

essentially an infinite number of times

and will go on being created into the indefinite future.

And THAT is the inflationary multiverse.

So it says our existence is inevitable.

"How does that make you feel?"

We may never know if our existence is inevitable.

We may never have a complete theory of the origin of the universe.

But it is remarkable that we've made so much progress.

The big bang as we see it

was created in a very special way.

The present understanding is that inflation can do that.

So... that's what I would hang my hat on right now.

But I wouldn't be surprised

if there are changes in the future in our understanding.

One day, some smart person will come along and solve it for you.

That's the beautiful thing of how science works.

The set of questions we're asking now

get us to a new vista, a new place to stand,

and on a new place to stand,

there are other questions we haven't even dreamt of yet

that I'm sure will be more important

than whatever we think we're answering today.

I think cosmology is the most remarkable of the sciences.

I mean, not only are we able to look up into the sky

and collect the light from the most distant galaxies,

and even - in the form of the cosmic microwave background -

from close to the origin of the universe itself,

but we're able to decode the messages that it contains

and build plausible theories of the origin of the universe.

You know, I think our situation was beautifully summed up

by the Belgian priest and mathematician Georges Lemaitre,

one of the fathers of the big bang theory.

He said, "Standing on a well-cooled cinder,"

"we see the slow fading of the suns"

"and try to recall the vanished brilliance"

"of the origin of the worlds."

Is there an end of the universe? Is our universe eternal?

The universe literally tears itself apart.

Will there be stars and galaxies?

What is the fate of the universe? How will it all end?

Captions by Ericsson Access Services

Copyright Australian Broadcasting Corporation