Original subtitles

Space.

It seems like it must go on forever.

But does it?

Out there in the farthest depths of the Universe,

might there be someplace

where something turns into absolutely nothing?

Scientists are probing the far-flung reaches of the cosmos,

trying to detect that outer limit,

to find the shape of space.

Now surprising evidence suggests

that not only is there a place where the Universe ends,

but that there might be something lurking beyond it --

something unimaginably alien.

Space, time, life itself.

The secrets of the cosmos lie through the wormhole.

♪ Through the Wormhole 02x02 ♪ Is There an Edge to the Universe? Original Air Date on June 15, 2011

== sync, corrected by elderman ==

Once in a while, a really big idea comes along --

one that completely changes our concept of who we are.

In 1543, Nicolas Copernicus proved that the Earth

was not at the center of the cosmos.

In the 1920s, Edwin Hubble saw

that all the galaxies in the Universe

were rushing away from one another,

sparking the idea

that the Universe had not been here forever

but was created in one explosive moment --

the Big Bang.

Now another monumental change is upon us.

We've long imagined the Universe to be infinite in size,

but many cosmologists now think the Universe...

is finite.

Some believe they even know its shape.

If we do discover an edge to the Universe,

we'll have to grapple

with another very challenging and unsettling question.

What lies beyond the edge?

Every day on my way home from school,

I used to pass a long wall.

It was at least twice my height.

I had no change of seeing over it,

but I could hear strange sounds coming from behind it.

My mind ran wild

imagining what might be back there.

Wild animals? Outlaws?

Or some fearsome monster?

I would press my ear up against it

to try and decipher what it could be.

I never did find out, but I never stopped wondering.

Neil Cornish is a cosmologist

who lives and works in the big sky country of Montana.

The only walls out here

are fences to keep his horses from roaming off.

Neil is the latest in a long line of thinkers

to contemplate the size of the Universe.

The first we know of was a Greek philosopher king

called Architus.

The Greek philosopher Architus

offered an argument for why the Universe must be infinite.

He said, "if I was to go out to the edge of the Universe

"and then extend my staff to here,

"that would now be the edge of the Universe.

"And then, if I was to extend my staff to here,

"that would now be the new edge of the Universe.

"And if I was to extend my staff out to here,

"that would now be the edge of the Universe.

So the Universe must be infinite."

Freeman: Architus's mental game set the tone

for over 2,000 years of scientific dogma --

our Universe must be infinitely large

and has existed forever.

But that dogma is now being challenged.

So, one problem with an infinite universe

that's not just infinite in space

but also infinite in time -- has no beginning --

you have an infinite number of stars.

So the sky would be just completely covered in white,

bright, bright -- so bright that it would fry you.

So, when we look out at night, that's not what we see.

We see a star here or there

and then, essentially, darkness all around.

So this tells us something.

It tells us we don't live in an infinite Universe

that's infinitely old.

Freeman: It was our dark sky

that inspired a revolutionary idea about the cosmos --

that it cannot have been here forever.

The Big Bang --

a moment where all the space and matter we can see

burst into existence,

expanding out from a single point.

But the Big Bang creates a problem

for astronomers searching for the edge of the Universe.

Because it takes light time

to travel across the vastness of space,

astronomers were always looking back in time,

and, eventually, they run out of time.

Cornish: So, when we look out at the stars at night,

we're seeing those stars as they were years ago.

The nearby stars, maybe a few years ago.

Looking out across the galaxy, thousands of years ago.

And going back and back,

we see galaxies back billions of years ago.

And then, beyond that, where we see no more galaxies.

13 billion years ago

is the next thing that we've managed to image,

and it is the after-glow of the Big Bang.

Freeman: It's called the cosmic microwave background,

and it's a picture of the way the Universe looked

about 400,000 years after the Big Bang.

Cornish: The Universe is filled with this hot gas, this hot plasma.

Light really can't go anywhere.

So we can't see any further back,

just as we can't see into the Sun.

Freeman: The cosmic microwave background

is a barrier that blocks our vision.

Behind it, there could be an edge.

Or perhaps the Universe does extend on forever.

But no matter how powerful our telescopes become,

that domain will never be visible.

But there might be another way to discover

if the Universe has an edge.

Janna Levin is a theoretician

who uses complex numerical simulations

to solve some of science's most challenging problems.

[ Groans ]

It might surprise you that a game as old as "Asteroids"

can teach us something about the Universe,

but there's a rule in the game

to make a world out of the game that makes sense,

where, if you exit the top, you re-enter the bottom,

or if you exit the left, you re-enter from the right.

And that rule makes this world

in which you're playing the game,

this space in which you're playing the game,

a finite space.

And that's kind of like

the rules we're imagining for the Universe.

Freeman: If our Universe is finite,

scientists believe its edges must also be linked,

that the entire cosmos

must act like a giant game of "Asteroids."

If we could bend this space,

we would see that it looks like something more intuitive.

Like, for example, if I were to take this menu

and apply that rule from the "Asteroid" game.

You know, I exit the top, I enter the bottom.

That's exactly the same as taking the menu

and rolling it up and gluing the sides together.

It gives the same effect.

And if I could bend this rather too stiff menu,

I would try to bend it

so that the two edges came together and were glued.

And then I'd be making something kind of like,

you know, a bagel -- a classic, New York bagel.

And the bagel is glued together not just like a cylinder

but also around the other side.

Freeman: Even though the surface of this bagel is clearly finite,

no one living in this space would ever run into an edge,

so it feels boundless and infinite.

When we live inside the Universe,

we can't step outside of it.

There's no other dimension to look down from,

onto our 3-dimensional Universe, so it's harder to visualize.

But we can use the rules

like the rules that are used in the "Asteroids" game.

And then we add one more rule

for three rules for three dimensions.

Go out the back face, come in the front.

Freeman: If we do live in a cosmic asteroid cube,

there is a way we could discover the edges --

not by flying a spaceship across them,

but by standing still

and watching light as it wraps around the Universe.

If the Universe were the size of a room

and you stood in the middle of it holding up a lantern,

light beaming out from your back

would zip out one wall

and re-enter the room from the other side

so you'd see an image of your back

on the wall in front of you.

Looking out to the right,

you'd see light coming from your left side.

The room would appear to be covered in mirrors.

Whichever wall you looked at, you'd see an image of yourself.

When we look at the night sky,

we don't see this hall of mirrors.

But space is so vast,

light could take billions of years

to loop around the Universe.

Space and time on this epic scale

mean that mirror images would look nothing like one another.

So, imagine this corral is our Universe.

There will be repeats of this corral ad infinitum,

giving an illusion that we live in an infinite space.

But if this corral were just 30 light-years across,

when I look out there,

I wouldn't see myself as I am now.

I'd see myself as a 10-year-old boy

'cause I'd be looking 30 years back in time.

Freeman: Our Milky Way is around 13 billion years old.

It's been around almost as long as the Universe itself.

Could a distant image of the Milky Way

be hidden somewhere in the night sky,

disguised the way it looked 5 or 10 billion years ago?

If it is, how would we even recognize this youthful twin?

This scientist believes the cosmos is a hall of mirrors,

that the Universe is finite,

and that he knows its size and shape.

Imagine if the entire Universe

was just the size of this room

and that space wrapped around itself

so each wall was the passageway to the wall opposite.

Looking around, I would see myself fractured,

as if by a crystal, into multiple copies,

and each version would be slipped backward in time.

Backward in time.

Backward in time.

Is our Universe a hall of mirrors?

[ Indistinct conversations ]

Astronomers have looked

for repeating patterns of galaxies for years,

looking for evidence that the Universe has an edge.

But they've never found any.

Jean-Pierre Luminet is a senior scientist

at the Paris Observatory.

He's been fascinated with the shape of space

ever since he was a child.

I was always interested in shapes created by nature.

And while it's a nice idea

to imagine a typical snail with a spiral, for instance --

and you know there are spiral galaxies, for instance --

the question is,

why is this shape gonna be also in the sky?

Freeman: Jean-Pierre's passion

to discover the shape of the cosmos

grew from the groundbreaking work

of the great Albert Einstein.

His theory of relativity

showed that space is a flexible fabric

whose shape is deformed by matter and energy.

Einstein imagined the Universe as a flat sheet,

stretching out to infinity.

But there's no reason it can't also be finite

and curled up on itself.

[ Piano playing ]

Jean-Pierre realized he might be able to tell the difference

between a finite and infinite Universe

by thinking of the cosmos as a giant musical instrument.

The cosmic microwave background image

shows us the Universe the way it was 13.7 billion years ago --

a hot liquid vibrating with aftershocks of the Big Bang,

like water rippling in a bathtub.

So in some way,

the Universe vibrated like a piano or like a drum.

So, for instance, this is equivalent for the Big Bang.

[ Discordant notes play ]

It's a complicated mixture of many harmonics, okay?

And now we have the fundamental harmonics,

which gives the pitch.

And after, the other harmonics are like this.

[ Harmonious notes play ]

And so on, okay?

So, the full sound that we can listen to

is a mixture of all these harmonics.

Freeman: But the number of harmonics you can hear

depends on the size of the piano.

The size of any musical instrument is finite.

And a string, for instance, cannot vibrate on wavelengths

larger than the size of the string.

So, maybe, if we observe that the Universe

didn't vibrate on very long wavelengths,

maybe the explanation is that space has a finite size.

Freeman: When Jean-Pierre analyzed the ripples

in the cosmic microwave background,

he found that the longest wavelength ripples

were, indeed, missing.

We are surprised because there was missing wavelengths,

missing fluctuation, missing low tones --

you know, like low notes.

Low like this, okay?

They are missing from the cosmic squall.

Freeman: Jean-Pierre's passion for music

gave him a profound cosmic insight --

that the Universe appears to be finite.

But what shape could it be?

Jean-Pierre spends months

carefully testing different shapes for his finite Universe,

trying to make it fit the vibrations

of the cosmic microwave background

as closely as possible,

until, finally, he finds the perfect fit...

...A 12-sided dodecahedron...

A soccer ball.

Here in my hands here are two different kinds of dodechahedra.

The first one is just an ordinary dodechahedron,

namely 12 pentagonal faces

arranged in a symmetrical manner.

This is a figure known since antiquity.

You see that the Pentagons are flat, okay?

Here, you have a different styling of the sphere.

You see that the Pentagons are curved, okay?

So this is called the circle dodecahedron.

Freeman: If Jean-Pierre is right, the shape of the Universe

is a lot more complex than a six-sided "Asteroids" game cube.

The Universe has 12 sides,

and leaving one face leads you

to a matching Pentagon on the opposite side,

but with a twist.

This edge is exactly the same as the opposite edge.

So, as soon as you get to this point,

you re-enter your space on the opposite side,

and, in addition, you have to turn by 36 degrees.

Freeman: If the Universe were a dodecahedron

only slightly bigger than Earth,

light would zip around it in minutes,

and you would see twisted copies of Earth

in a dozen different directions in the sky.

But if the edges of Jean-Pierre's dodecahedron

are billions of light-years apart,

the distant and faint reflections on them

could have escaped the notice of the most careful astronomers.

And if the edges lie further

than 13.7 billion light-years from Earth,

we would never be able to see them

because our view would be blocked

by the hot soup of the cosmic microwave background.

As soon as Jean-Pierre announced his results,

Neil Cornish begins looking for signs

of his colossal soccer ball.

He's a key scientist

on a NASA spacecraft called WMAP,

which spent five years photographing

the cosmic microwave background in unprecedented detail.

So, here's a possible model of the Universe

based on a dodecahedron.

Inside, we have a balloon

representing the visible Universe,

how far we can see.

And if it was like this,

where the balloon is much smaller than the space,

there would be no signs that we're living in a finite Universe.

[ Air hissing ]

But if the visible Universe was so large

that it actually touched onto the edges of the dodecahedron,

then light would actually be able to travel,

wrap right around the Universe.

So now we would have these matching circles

on the microwave sky

where these two spheres intersect to form a circle.

A circle here matching the circle down here.

Now, we have looked

at the microwave background data from the WMAP satellite,

and we haven't seen this pattern of matching circles.

Freeman: But Jean-Pierre Luminet

is not ready to give up his soccer-ball Universe.

His ideas have triggered a scientific battle

that spans continents and years of meticulous work.

At stake is nothing less than the truth about where we live,

where we came from,

and whether our Universe is alone.

Einstein said,

"only two things are infinite -- the Universe and human folly."

But he admitted he couldn't be sure about the Universe.

In fact, we are now faced with tantalizing hints

that our Universe may not stretch on forever,

that there is a point out there

where the Universe as we know it does not exist.

It's an almost frightening thought.

But before we try to grasp

just what might lay beyond that final boundary,

we need proof.

Glenn Starkman is a Canadian physicist

at Case Western University in Cleveland.

He's taken data analysis to new heights

in search of that proof.

Call him an information junky.

The joke about Canadians is that you go to an airport

and you put up a sign --

"free sex to the right"

and "free information on sex to the left" --

and the Canadians are all the ones that go to the left.

I hope I'm not that boring.

Freeman: Glenn had been poring

over cosmic microwave background data from the WMAP probe

for most of the past seven years.

Along with Neil Cornish,

he's been trying to test Jean-Pierre Luminet's prediction

that the shape of space is like a 12-sided soccer ball.

I would have been really happy to find the pattern of circles

that the dodecahedron told us would be there

if the dodecahedron was small,

and we looked for and we didn't find.

Freeman: But all of their tests assumed

that the edges of the soccer-ball Universe

are closer than the microwave background that blocks our view.

Now Glenn believes he's found a way

to detect the edge of the Universe,

even if it lurks beyond the area we can see.

What you have to understand

is what is this actual pattern of hot and cold spots

that we're seeing on the sphere.

And what it really is is sound waves

that were traveling through the Universe when it was very young.

So you can imagine it like stretching the top of a drum.

At the same time that as it was stretching,

it was actually making the drum vibrate a little.

Freeman: Different-shaped Universes, like different-shaped drums,

should leave different patterns of vibrations

on the early Universe.

So, what we're gonna do is we're gonna look at

some different-shaped and different-sized drums,

and what we have over here is a spectrum analyzer.

And Tom has set things up so that when we make some sound,

we're going to get some traces on this computer screen.

So let's start with our nice, round, little drum.

[ Drum beats ]

Now let's go with our heart-shaped drum.

It certainly sounded a little bit different.

[ Drum beats ]

Finally, we have a star-shaped drum.

[ Drum beating ]

When we superimpose the patterns of those three small drums,

we'll see that they're not quite exactly the same.

They have different patterns

and so we can tell the difference

between one small drum and another.

In the same way, what we're planning to do

is use a spectrum analyzer

to look at the different sounds that the Universe made

and to tell what the shape of the Universe is.

Freeman: Glenn's analysis involves such complex mathematics

that he imagines it will take years to find the answer.

I will be incredibly excited

if we turn out to find Jean-Pierre's dodechahedra.

It will be like discovering that the Earth is round

rather than flat.

Freeman: But this scientist is not waiting for data

to answer this monumental question.

Andy Albrecht, a theoretical physicist at U.C. Davis,

is sure the Universe is finite.

He even thinks he can calculate its size.

Andy studies the very first moments after the Big Bang,

when space was nothing more

than a seething, chaotic ball of energy.

Suddenly, a process called inflation takes hold.

It balloons up the Universe at an incredible rate,

doubling its size 100,000 times.

A fraction of a second later,

all space and matter is smoothly spread out.

Most scientists believe

inflation is still happening today.

The going way of thinking about inflation

is that it gives us a truly infinite Universe.

The inflation itself never ends.

The more I thought about what that infiniti might really mean,

the more I realized it probably didn't make sense.

Freeman: So, Andy began working on a new theory of inflation,

without infinities.

It's dizzying mathematics,

dealing with the laws of physics

before the Universe as we know it existed.

But at its core, it all boils down to bubbles.

A random process starts the formation

of the bubble that is our Universe.

I will be the random process and blow the bubble.

Freeman: The traditional view of inflation

imagines this bubble inflates forever.

But Andy now takes the lessons he learned in kindergarten

as a serious insight.

A bubble can only grow so big before it pops.

Andy believes inflation must stop

when space gets to a certain maximum size,

and his pioneering theory predicts that size.

The Universe is actually just about 20% bigger

than what we see around us today.

When I first started trying out those ideas,

it was really difficult to go all the way from infinity

to such a small thing, just a little bit larger --

just 20% larger than what we see around us today.

I actually felt claustrophobic.

Freeman: But if Andy's new theory is right

and inflation does not go on forever,

our Universe could look something like this --

a large bubble surrounded by a cluster of smaller ones.

Most cosmologists think inflation

is the best explanation for the even spread of galaxies

across our visible Universe.

But far out in space,

there may be regions where inflation never took place.

Find those, and you could be the first

to find evidence of the edge of the Universe.

The eternal dance of light in the night sky --

it has fascinated humankind for thousands of years,

given birth to Gods, myths,

and, finally, to science.

But now there are hints of strange movements

in the heavens.

If they can be verified,

they'll be the first hard evidence

that there is an edge to the Universe.

Sasha Kashlinsky is a NASA astronomer.

He claims to have detected

a pattern of movement in the heavens so bizarre

that it could revolutionize our theory of the Universe,

just as the Big Bang once did.

We're here at Glendale Golf Course

near NASA's Goddard Space Flight Center.

And we came here to simulate the Big Bang.

So let me try and do that.

As you see, the balls,

they just move away from the mutual center.

Freeman: This even spreading-out of galaxies

from a central explosive beginning

is what astronomers see when they look at the night sky.

But Sasha wanted to check more precisely

how fast and in what direction galaxies are moving

to see if there might be any subtle deviations.

He used an effect that can only be seen

when clusters of galaxies are colliding.

The gases around them get heated to millions of degrees.

When light from the cosmic microwave background

passes through that hot gas,

it gets subtly altered.

How much it changes depends on exactly how fast

the gas and the galaxies it surrounds are moving.

But the change is tiny

and almost completely buried in background noise.

For each individual cluster, this is a very tiny amount,

and it gets drowned by the noise.

But if you have many clusters, you can beat down the noise,

but it's exceedingly difficult.

Freeman: Sasha methodically worked his way

through a catalog of galaxy clusters

from an orbiting X-ray telescope,

checked their precise position using ground telescopes,

and then carefully lined them up

with the cosmic microwave background.

Oh, we were quite shocked

when we saw these results at first.

In fact, so much that we didn't know what to do with it.

We kept checking and checking.

We sat on the data for a year-plus,

just checking everything,

because it just didn't make sense to us.

Freeman: What Sasha's data showed was almost unbelievable.

All the galaxy clusters,

no matter where they were in the sky,

were all veering off to one side of the Universe.

It was as if they were being pulled

towards a mysterious attractor beyond the visible edge.

He called it "dark flow."

We called it "dark flow" because

the observed distribution of matter in the Universe

cannot account for this motion.

Freeman: But if nothing Sasha could see

was pulling the galaxies to one side,

what could be responsible for the effect?

The answer could be the edge of the Universe.

Kashlinsky: If you live in this part of the world,

then, at first, you would imagine that the entire world

is as flat as what you see locally.

But if you were to look sufficiently far away,

you may discover that the world

is very different from what you see locally.

Freeman: Cosmologists, ever since Einstein,

have thought of the Universe being like a flat putting green

that extends on forever.

But dark flow could be hinting that our Universe

is a finite space...

Surrounded by stranger terrain.

So, this was Big Bang on a flat surface.

So, now let's go to a different part of the world.

The balls did, indeed, disperse,

but, in addition, they also have another velocity,

which is associated with the tilt of this surface.

They move collectively and systematically

from the higher ground to the lower ground.

Freeman: Sasha's discovery of a collective, systematic movement

of galaxies to one side of the cosmos

has shaken the field of cosmology.

Some scientists refuse to believe it.

But for this woman, dark flow was entirely expected,

and her ideas about the Universe

are even more mind-bending than Sasha's.

She believes she's found evidence

that another Universe is reaching out and touching ours.

Scientists have discovered a mysterious dark flow of galaxies

all veering off to one side of our Universe.

It could be a sign that way out beyond that furthest star

lurks a portion of the cosmos

vastly different than the Universe we know.

But there's an even more shocking possibility.

Dark flow could be evidence

of another Universe reaching out to us.

That's what theoretical physicist

Laura Mersini-Houghton thinks.

The seed of this idea was planted many years ago

when she realized she had a problem with the Universe --

a pretty big problem.

According to her calculations,

the Universe should not exist.

The chances to start the Universe

with the high-energy Big Bang

are one in 10 with another 10 zeros behind it

and another 123 zeros behind it.

So, pretty much, zero.

So whenever in science we end up with an answer

that "this seems very unlikely.

This event is not generic,"

then it usually indicates

that we have blundered in something very basic.

Freeman: But Laura had an idea of how to stop the Big Bang

from being such an unlikely event.

You might call it a gambler's hunch.

If you're playing a slot machine

where the odds of hitting the jackpot

are 1 million to one,

you could play all day and never strike it rich.

But if all 6 billion people on Earth

each played their own slot machine,

someone somewhere is going to get rich

about once every few seconds.

Laura realized that one branch of theoretical physics

offered a way to turn the Big Bang into a sure bet.

It was string theory.

This view of reality suggests

that alongside the normal three dimensions of space,

there are another seven hidden dimensions

wrapped up so tightly, we cannot see them.

Mersini-Houghton: You start wrapping up

those extra dimensions, the extra seven dimensions.

There are so many ways of doing that process.

String theorists ended up

with not just one 3-dimensional world,

but with many, many possible 3-dimensional worlds.

Freeman: In fact, string theorists realized

there were 10 to the power of 500 possible ways

to arrange these dimensions.

That's a one with 500 zeros behind it,

a number countless times bigger

than the odds against our Big Bang.

The only way we can ask the question

about the origins of the Universe

is if we have a multiverse structure

from which our Universe is born,

a landscape of many possible places in this multiverse

where the Universe can start from.

Freeman: If each of these balls of wrapped-up dimensions

is an energy site where a Universe could start,

then the odds of a Big Bang happening in one of them

is no longer an enormous long shot.

In fact, the odds are good enough

that Laura's willing to bet this landscape

should contain many Big Bangs and many Universes.

You can think of this multiverse landscape

as the biggest hotel you can imagine,

a hotel with 10 to the power of 500 rooms,

each one waiting for a guest to check in.

Mersini-Houghton: Every room would represent

an energy site of that landscape.

There is an infinite number of people

that can try to check in into these hotel rooms.

I try to go into a room,

and I discover that energy site is taken.

Someone else is there.

Once a Universe is born in that energy site,

first, that energy site

cannot be shared with another Universe.

So I try to go to the next room.

Until I find an empty room.

That room is really boiling hot, so it contains a lot of energy.

Once I am in the room, I cannot get out of it anymore.

The door is locked. That's how the Universe is born.

Freeman: But if our Universe is like a hotel room,

shouldn't we be able to detect the presence of guests

in the room next door?

That earth-shattering evidence

could look as subtle as this small blue patch.

In 2007, data from the WMAP spacecraft

confirmed the presence of a strange, cold spot

in the cosmic microwave background.

If I have an empty region of space,

that would show as a cold temperature region.

In the case of the cold spot,

the only way such a part of the sky

could just be completely, entirely empty,

that kind of bizarre behavior of the Universe

can occur only if there is some other force at work.

Laura believes the cold spot

is evidence of another Universe right next to ours,

its enormous mass pulling on matter at the edge of our world.

Mersini-Houghton: If there are some very massive objects in the next room --

in other words, in the neighboring Universe --

then I should be able to feel that gravitational pull,

although I cannot directly see it.

Freeman: But for a theory as radical

as the existence of another Universe,

the cold spot alone is not enough.

Laura needs more evidence.

And help is at hand.

Two scientists are about to join forces

in a remarkable endeavor

to find the size and shape of our Universe

and the Universe next door.

Is the Universe infinite?

Or does it have an edge?

Or is our Universe just one member

of a cosmic family of Universes,

spread across a strange and uncharted landscape?

Just a few years ago,

even asking these questions was unthinkable.

Now we're close to finding the answer.

Sasha Kashlinsky is convinced

that some mysterious attractor at the edge of our Universe

is pulling on galaxies,

forcing them to move with what he calls "dark flow."

His work is still controversial,

and to convince the skeptics, he needs more data.

We hope, in a few years,

to have a catalog of up to 2,000 galaxy clusters in total.

And with the new data, we hope that we'll be able

to measure the flow to much larger scales.

Freeman: But Sasha now has a powerful ally.

1,000 miles away, in Toronto,

Laura Mersini-Houghton was defining her own calculations

about the edge of the Universe

when she got a phone call from her mother.

Mersini-Houghton: And she says to me, "Did you see the news

"about something called dark flow or another?

There was a NASA person there."

And I said, "No, I haven't."

So I went straight into my computer

and found out that a team at NASA led by Sasha Kashlinsky

had reported they had seen the dark flow

of structure in the Universe.

That was exactly in perfect agreement

with the prediction we had made two years ago.

But what made it spookier was that even the numbers,

the speed at which those galaxies were moving

and the direction into which they were moving

were in absolute perfect agreement astronomically

with our predictions.

Freeman: Now Laura and Sasha are both contemplating

just how this exotic landscape outside our Universe

might behave.

Mersini-Houghton: I can think of this board as the landscape,

the energy sites onto which

these wave pockets of the Universe

will eventually settle.

Now, I have to send the wave pockets

through that landscape, through that board

in order to populate it.

Freeman: Think of this marble

as the pulse of energy that triggered our Big Bang.

Soon, another pulse of energy comes along.

It falls into a different dip,

and a neighboring Universe is born.

That Universe is not a place we can ever go.

Its arrangement of dimensions

will be completely different from ours.

But there is one way we can sense its presence.

If the two Universes are close enough together,

their gravitational attraction will pull anything with mass

towards their respective edges.

That's why we see the cold spot

and that's why there's a dark flow of galaxies

moving across the cosmos.

This other Universe is pulling on ours.

Until about three, four years ago,

we knew nothing of the multiverse.

However, things are changing dramatically

in the last few years.

Technology is helping us find signatures

of the existence of the multiverse.

Freeman: But across the world of cosmology,

the reactions to these scientists' controversial work

is mixed.

If any one of them is right,

the implications would be enormous.

Why do we even care about the size and shape of the Universe?

That part of the story is critical

for our attempts to understand how it all came into being,

why it is the way it is,

and why we see what we see around us.

All these questions have very different answers

if we're looking at the infinite story

or the finite story.

We'd be able to say, "Look, here is the Universe.

This is its shape. And that's where we live."

And that's a revolution in physics --

going outside our Universe,

at least with the power of our imagination.

But then that's what makes human beings special.

Freeman: Every now and again,

our perception of the Universe and our place in it

undergoes a revolution.

We used to think the Earth was the center of all creation.

For the past century,

we've learned to accept that we live

in a nondescript region of a backwater galaxy

in a Universe that is unimaginably vast.

Now it's time for another change of perspective.

Our Universe itself, once assumed to be infinite,

might have to shrink down and take its rightful place

as a humble member of a truly giant multiverse,

a multiverse filled with Universes

beyond our wildest imaginations.

== sync, corrected by elderman ==