Original subtitles

(MYSTERIOUS MUSIC)

- [Narrator] Since the very beginning of time,

man has looked to the night sky and asked the same questions,

where are we?

How far do the stars go?

And are we alone?

Today, these same questions linger

in the minds of every human with an inquisitive nature.

Is our world just a speck in an infinite universe,

surrounded by many other worlds and species?

Or is it possible that we are the only intelligent

life in the universe?

If our universe is truly infinite,

then it is thought that anything that could happen

has happened an infinite number of times.

There will be infinite worlds and infinite

intelligent life forms.

Even infinite copies of ourselves.

But we may also exist in an infinite universe, which

is one of infinitely many universes, each existing in

possibly infinite dimensions.

This series explores the many theories and ideas

as to where we all are in this immense system, which

seem to come from nothing in the Big Bang

13.8 billion years ago.

New understanding says this may not be the full story.

We look at the ideas and theories

from a human perspective, and hear from our best scientific

minds, who spend their lives trying to understand

these monumental concepts.

(EPIC MUSIC)

How do we try and understand what may be simply

beyond human comprehension?

- [Narrator] If our universe is finite,

then it would seem to indicate that

there would be some kind of edge

or boundary to the universe.

(INTRIGUING MUSIC)

If this is the case, what possible shape or reality

would this take?

Is it possible that space could just stop at a certain point?

Is there anything beyond this possible boundary?

- [Speaker 1] Well, we haven't found the edge of space,

so maybe it does go for infinity and we haven't really

found the beginning of space, so maybe

it's been going for infinity.

- [Speaker 2] The idea that the universe

is finite is the biggest problem I

have wrapping my head around.

- [Speaker 3] People thought the universe was simply finite.

You know, you went to the end.

And there's a lot of puzzlement about that

because you're always inclined to wonder,

well, what's beyond the end, if it really is finite?

So that-- that led to a lot of puzzlement,

and that made people think, well, maybe the universe

really is infinite.

- [Speaker 1] If there is an edge to our universe

or our multiverse, I think that means we're held

together by some center.

If there's an edge, to me, there would be a center.

- [Speaker 4] The idea of a boundary is something

that we are all used to.

Everything that we think of your head, this room,

that a car, it has a center and then it has an edge

and everything is inside.

Your brain has a center and an edge.

And then when you say, if it's expanding,

it expands into the surrounding space.

That is the most common thought and the most common

misconception about the universe,

because the universe does not have a center,

therefore it can expand without expanding

into anything around it.

There is no around it.

There is no outside it to expand into.

But you say, it has to have that.

It has to have that because everything I know is like that.

Well, welcome to general relativity.

(ENIGMATIC MUSIC)

- [Narrator] Throughout history,

man has had many ideas as to the extent of the universe,

with an Italian Giordano Bruno being one of the first

to declare that the universe is truly

infinite and that the stars were in fact,

just distant suns.

But what are the alternatives if the universe is bounded?

The most popular theory is that the universe is bounded

by some sort of a sphere.

- [Speaker 3] In the 20th century, with modern cosmology,

people began to pedal back from the idea that the universe was

infinite and think that it was finite,

but nonetheless unbounded.

So just like on the surface of a sphere,

if you kind of walk around on the surface of a sphere

and you stay on the surface, you'll never come to an edge.

You'll never come to a boundary.

But nonetheless, there's a fixed amount of space

on that surface it's finite.

So people thought the universe was like that.

There was a fixed amount of space in it,

a fixed amount of volume in it, but that no matter

how far you traveled, you'd never come to a boundary.

You'd, you know-- you'd just end up in other parts

of this finite space.

- [Speaker 5] The one thing as a physicist,

I can tell you is that the universe,

if it's flat in terms of space time, will go on for infinity.

But what we've measured is that it's pretty flat.

It might have a slight curve, we can't tell.

That means, in just the same way

that the Earth looks pretty flat as I look out around me.

That's because the curvature is enormous

in the sense of the radius of the Earth

is vast on our scales.

And if I can see a slight curve to that, say, a ship going

over the horizon, the base of that ship

disappears from view first, well, I

can see an implication of the curvature of that Earth.

I can't tell the difference between a universe that

goes on forever and one that will

wrap back on itself after some impossibly large

distance traveled.

In the same way that you can walk around the Earth

and you will come back to where you started.

But if I made the Earth a trillion kilometers,

it would really appear to you as if it were infinite.

That curvature of the ground would

be so slight it would take so long

to even notice it was beginning to come back on itself.

To the ability to measure, it would appear the same

as if it were infinite.

- [Narrator] Again, we are up against the limits

of our technology, which leaves an open

question as to the extent of our universe.

- [Speaker 6] We look out as far as we can,

and the universe just stays pretty much the same all over.

We see no sign of an edge or a tailing off.

- [Narrator] Although we cannot be certain,

as we look further into space, it appears

as if the universe is continuing to expand

at an ever-increasing rate.

As it looks to us now, it does seem

to indicate an infinite universe

without an edge or boundary.

- [Speaker 6] You somehow got to contrive

some complicated explanation to make an edge of the universe.

And we have this principle in science, Occam's razor, which

says, on the whole, the simplest explanations

tend to be the right ones.

And the simplest explanation is,

well, when we look at the universe,

it looks the same everywhere.

We don't see any evidence of an edge

or anything slowing down or reducing or anything like that.

So Occam's razor says, well, the simplest explanation is it

just keeps on going as it is.

- [Narrator] This expansion of the universe

is evidence that the universe is getting larger and larger.

But can we rule out some kind of edge or boundary,

as we can only see so far into the universe in what is called

the observable universe?

- [Speaker 7] If we keep on extrapolating what

we've already seen, then the universe gets

bigger and bigger and bigger, and we

keep on multiplying things.

And the older the universe, the bigger

the multiplication factor.

We have already strong evidence of things expanding by at least

30 orders of magnitude.

That's taking something the size of a golf ball

to the size of the current universe.

And we have many reasons to believe

it's even more than that.

Just because we think the universe goes beyond the part

that we can just see, it doesn't suddenly

end just conveniently beyond the 13.8 billion years of it

that we can see.

- [Narrator] Infinity is the concept

of a universe that never ends.

However, what if our universe is in an endless rebirthing

process where one universe dies and another is born

in an infinite cyclic process?

- [Speaker 8] I can imagine the universe as it is now expanding

and expanding and expanding until it gets to the point that

it starts to contract and get smaller again,

and can come down to this infinitesimally small point

and then (IMITATES EPLOSION) explode out again

to create another universe--

(EXPLOSION)

--that may be entirely different to the-- to the one

that we have now.

- [Speaker 7] I think most people,

including myself, find it very easy of understanding

a cyclic universe.

So it turns out through the equations of general relativity

and the simplest form, you could have

a universe that is finite.

This is a universe that was born in a Big Bang,

it rises and slows down, reaches a maximum size,

starts to collapse and then ends.

And so what happens before the Big Bang

and what happens after the Gnab Gib, the Big Bang in reverse,

well, that's someone's imagination.

And you could imagine that maybe it just keeps on going on

and on and on and on and on.

(DRAMATIC MUSIC)

- [Speaker 9] A long time ago, people thought

that the universe was actually something

called a cyclic universe.

So the Big Bang happened, the big-- the universe

would stop growing, gravity would collapse back on itself,

and then the Big Bang would kind of reunite.

So you get this, you know, boom, boom.

So you just get this kind of oscillating almost universe.

Now, we know that's not true right now, that our universe

isn't doing it.

It's actually speeding up.

So it's growing faster and faster and faster.

But some people have hypothesized that the universe

will grow so much it'll rip itself apart in something

called the Big Rip.

(MYSTERIOUS MUSIC)

Now, if you're ripping the entire amount of the universe,

you're ripping all of the energy

and all of the matter of that universe.

And when that happens, you're actually

creating the conditions of a new Big Bang.

So if our universe rips itself apart, you could in some ways

create a new universe through a new Big Bang.

So you could get this replicating system.

- [Speaker 7] It could well be that the Big Bang was just

one of an infinite number of events

in a much larger universe.

So there are many ways that the universe could have always

existed, or essentially has a time

arrow that goes back to an infinite length into the past.

- [Speaker 10] Once you think that you have

universes giving rise to--

to new universes in a sort of like a birth like process,

I don't think there's any reason to think, um--

that-- that process goes back finitely

as opposed to infinitely.

I think at this point, we have no experimental data

because we're positing things that we

no longer can have any kind of experimental access to.

We can only really get to, um, see the stuff that's going

on in our own universe.

And even then, not all of that.

- [Narrator] If an edge or boundary

to the universe exists, then nothing has to exist.

Although saying nothing exists suggests there is something

there in the first place.

Nothing is an equally hard concept for humans

to understand, as is infinity.

(OMINOUS MUSIC)

- [Speaker 1] Beyond the edge of the universe,

if the universe had an edge and there being nothing, I guess

why can't there be nothing?

- [Speaker 2] The idea of nothing is--

is just as inconceivable and possibly unhelpful as infinity.

- [Speaker 5] Nothing is as hard

a concept to get our heads around as infinitely something.

- [Speaker 7] I find nothingness more

uncomfortable than infinity.

Infinity makes sense to me.

Nothingness having something truly

born out of absolutely nothing, that logically seems--

does not make sense to me.

- [Narrator] To try to answer the question of whether nothing

exists, scientists conducted experiments where they created

an absolute vacuum in space.

What they discovered was completely unexpected.

- [Speaker 5] We think if you take this pocket in front of me

and you take all those atoms out,

and you keep pumping them out and it looks empty in the most

pure vacuum imaginable, far beyond anything,

even in the depths of space, you take every single atom out,

and then you look and you realize

there's still something there.

- [Speaker 4] There is a seething froth of virtual

particles coming into and out of existence

that's irreducible.

You can't get rid of it.

You know, I could get rid of the sound,

I could get rid of the neutrinos,

I could get rid of the-- the air,

but I cannot get rid of the structure of the vacuum,

which are these irreducible particles coming

into and out of existence.

So the idea of saying that there's nothing there

is kind of a silly old-fashioned thing.

Just throw it out.

There is no such thing as nothing.

- [Narrator] Perhaps this is true within our universe.

But if there was an outside of the universe,

could there be absolute nothingness?

- [Speaker 7] You know, your choice is nothingness in its

absolute form or infinity.

Something just exists forever and always has existed.

Those are your two choices.

They're both uncomfortable.

We have to live with one or the other.

(DEEP LOW HUMMING)

(COSMIC ROARING)

- [Narrator] Infinity is thought to exist in our own

universe inside the very strange phenomenon

known as the black hole.

A black hole is created when a star dies

and collapses in on itself, creating

a center of infinite density.

Everything that gets close to the black hole

gets sucked in and can never escape.

These strange but common holes in space and time

bend all dimensions, and any physical laws we understand

do not apply at the center of a black hole.

Black holes were discovered relatively recently

and have been the fascination of physicists worldwide.

- [Speaker 9] We actually have things that go to infinity

in our own universe.

So black holes.

black holes are a singularity where a star or an object

has collapsed in on itself, and gravity

has increased and increased and increased

as you go to the single singular

point of the black hole.

And at that very singular point, the level,

the strength of gravity is infinite.

(COSMIC ROARING)

- [Narrator] So here we have proof that infinity exists.

A proof of concept, albeit inside a huge black hole

in space where we can never explore.

How can we be sure that infinity truly

exists within a black hole?

- [Speaker 11] What we have in the universe are things which

are consequences of physical laws, and black holes are

consequences of physical laws.

We know that you can create giant stars

and we see giant stars in the universe.

We know that giant stars die, right?

They run out of fuel, their nuclear furnaces go out

and these stars collapse.

What happens when they collapse?

Well, their mass starts to crash down and crash down,

and using our best physical theories,

we ask what happens to that mass, and it just keeps going,

and it crashes down and forms a black hole.

What's not understood is that region at the very center where

things seem to go wrong, where we get our infinities,

and that's the regime where we know

we have to worry about quantum mechanics, as well as gravity.

- [Narrator] So conceptually, there is infinity inside

a black hole, in the same way as infinite

density existed in the birth of our universe, the Big Bang.

Again, we don't have the physics to date

to explore these theoretical infinities,

but we can accurately speculate as

to the behaviors of an object falling into a black hole.

- [Speaker 7] So black holes are a place where,

you know, space and time as we know them come to an end.

- [Speaker 4] Imagine we have a black hole here,

and let's send anybody into this,

and we're going to say, please signal us as you're falling.

Beep-beep, beep-beep, beep-beep.

And they're falling, falling.

And then their beep-beep starting to beep, beep, beep.

And their clocks are getting slower.

You may have seen the movie "Interstellar,"

where one hour on the surface of this planet near the event

horizon of a supermassive black hole,

is equivalent to seven years on the spaceship that's orbiting,

that's further away from the black hole.

And, uh, similarly, when you fall into a black hole,

your watch is-- you think, oh, it's just

click, click, click, click.

But viewed from the outside you're seeing beep, beep, beep.

And then when you reach the event horizon,

the black hole, then the person hangs there forever.

From the outside, you cannot fall into a black hole,

but from the viewpoint of that person, you go right into it.

So there's a whole universe inside the event

horizon of a black hole that is disconnected

from our space time.

But you can get to it, but you just can't go back.

It's a one-way entrance.

(COSMIC HUMMING)

- [Speaker 7] When I was a kid, people often described just

black holes as connecting to other

universes or somehow being their own little universe.

An interesting notion.

There's a lot of similarities between the horizon

of a black hole and for example,

the horizon that allows us not to see beyond the universe.

- [Narrator] Many speculations have been posited

as to their purpose in the universe,

and some have thought that they are the portals

to other universes.

Another speculation is that the center of a black hole

creates a new Big Bang, which in turn creates a new universe.

Whatever this bizarre phenomenon is,

we can only speculate about the realities inside a black hole.

- [Speaker 4] Could a black hole be

the machine or process in our universe

that creates another universe?

And that could very well be the case.

We have a big star.

We know that stars more massive than let's say, about

20 solar masses, they go boom.

They don't-- they create a neutron

star and then they create a black hole,

if it's more massive.

And that black hole, there it sits.

And we know that inside of there

is not part of our universe.

We have no way of getting information

from inside the black hole.

That kind is like a free for all

for a theoretical cosmologist to say,

sure, there's a-- there's a whole universe in there.

And matter of fact, my dead grandmother

lives in there or something.

You could invent all kinds of crazy things

because it's kind of hidden away.

We wave our hands an awful lot, try

to be consistent with the physics we do know, but inside,

whether we have a whole new universe, uh, sure, why not?

(LAUGHS)

- [Narrator] A new discovery has

been made in the last 20 years that has science baffled.

(MYSTERIOUS MUSIC)

Everything that we knew of in the universe amounts to only 5%

of everything that there is, leaving a massive 95% of space

unaccounted for.

We now know that space is made up

of two unknown, undefined elements named

dark energy and dark matter.

Dark energy being the most recent discovery in only 1998.

We know they exist because of the effects

that they exert on the universe,

but we can't see or understand their properties.

Dark energy is known to repel the stuff of the universe,

while dark matter is thought to bind galaxies together.

These two elements are thought to make up 95% of everything

in the universe, and we have no idea as to what they are.

- [Speaker 6] We have these two big mysteries

in the universe at the moment.

One is dark matter.

There's something that's binding galaxies and clusters

together at some particle that we don't know about,

but in various supersymmetric theories and so on you can see,

yeah, there's room for particles like that.

We'll probably find them eventually,

and then we'll understand what dark matter is.

And then there's dark energy, which is something else again,

and that's to do with the structure of space and time.

There is something in our universe

which is making the universe accelerate.

And we call it dark energy-- it sounds like we know what it is.

We don't.

No-- we haven't got the foggiest idea

what dark energy is.

Current dark energy is not really a good name

because it's saying--

it's asserting that we know it's a sort of energy.

We don't even know that.

All we have is an observational effect.

There is something that is making the universe accelerate.

- [Speaker 9] Our universe has grown over the 13.8 billion

years, so much and so fast, that light from

the furthest objects in the universe

can never actually catch up.

So if we have the universe growing like this,

and we have a galaxy over here, well, the universe is growing

and so this light is never going to catch up.

And this is essentially a consequence of something

called dark energy.

- [Speaker 12] We now have been able to detect things like dark

energy, which we only see by their gravitational influence,

so we don't feel it on our hands.

We can't see it with our eyes, but what we can see

is it moving around the things around us.

The analogy I make is with the wind.

We can't see the wind, but we can see the wind pushing

around the leaves of trees.

Now, it's remarkable to think that just 200 years ago, we

didn't know what the wind was.

We didn't have a particle theory of matter.

We didn't have the periodic table.

We didn't know what carbon and oxygen and nitrogen were.

- [Speaker 6] And right now we've got no

really good way of pinning down what

is causing that dark energy.

So there's a few ideas knocking around.

There's a few tests that people are proposing.

There's a lot of people planning

experiments to test those ideas over the next decade or so.

- [Speaker 12] Maybe it will take us another couple

of hundred years, but maybe we'll find out that

there's a whole dark matter chemistry

going on out there that we, uh, have yet to understand.

- [Speaker 5] A few decades ago, the actual extent,

what we thought of as the entirety of the universe,

is now resigned to just 5%.

So that is the atoms, other types of particles

in our standard model.

We have once again undergone this revolution

in our understanding of our place

and really relegated us to a--

an afterthought, a very interesting, very diverse,

very complex afterthought, but really fundamentally

the universe with a five cents on the dollar,

the bits that make up you and I and all of the stars.

(EXPLOSION)

- [Narrator] Our universe is thought to have burst

into existence 13.8 billion years ago

from basically nothing, no matter

time or space existed before.

But a new theory is emerging that is

gaining more and more acceptance

and is based on solid physics.

It is the theory that our universe is one

of many infinite universes.

(ENIGMATIC MUSIC)

It is thought that these universes may be completely

disconnected from each other, and may have vastly different

properties or dimensions.

- [Speaker 11] The multiverse theory is that our universe is

not alone, that there are a multitude of different

universes out there, hidden in some higher dimensional sort

of space time, and we're just one of almost infinite

number of other universes.

- [Speaker 1] But this idea of infinite universes,

I think is really exciting to contemplate,

and I don't know if we'll find the answer in my lifetime

or not, but I'm very excited about more

people exploring the idea.

- [Speaker 2] Multiverses are both heartening to me

and disappointing because we're just

one of the universe's in an infinite number.

But if there are an infinite number of universes,

that means that there are an infinite number

of possibilities that anything and everything exists.

And that idea is heartening.

- [Narrator] Infinity is already

a concept that is stretching our understanding

to the limits.

But an infinite universe and infinitely many infinite

universes is clearly beyond our science.

What are the possible models or variations

of the multiverse that have been contemplated to date?

- [Speaker 13] I think today a popular

model is that our universe is one amongst many.

If you think of soap bubbles in the sink

when you're washing up in the morning,

you see thousands of soap bubbles

all interlocked and some bubbles are big

and some bubbles are small, and some bubbles are getting bigger

and other bubbles are shrinking.

People think of the universe, maybe

in the same way, that we-- we are one bubble in a very

complex multi-bubble universe.

So our bubble is huge and expanding,

and we know it's expanding.

We even know it's accelerating bubble from work that was done

here in Australia in the 90s.

And so there'll be other bubbles that

may be also expanding near US and other bubbles

that may be shrinking.

So I think people would say that the universe is probably

finite in terms of our universe,

but there are many other universe bubbles

expanding and contracting that go on and on for

presumably forever.

- [Narrator] Another possibility is that other

universes exist alongside our own universe,

but in different dimensions to our three

of space and one of time.

- [Speaker 7] It is possible to have an infinite universe

that is itself embedded in an infinite

sea of infinite universes.

That is all possible, and it seems counterintuitive,

but the universe, if you want to think of it,

just basically imagine our universe

is embedded not in four dimensions, in five dimensions.

So our universe is infinite in those four dimensions,

but then another one is just next door

in the fifth dimension, and again, it's

infinite in its dimensions.

Now, I'm not saying that's the way the universe is,

but that illustrates the possibility of having

an infinite number of universes,

each infinite separated, just need an extra dimension.

- [Speaker 11] When you talk about something like

a multiverse, you could be talking about universes like

our own, which have four dimensions,

three of space and one of time, but embedded

in a higher dimensional space.

So each of those individual universes

could be spatially infinite inside a large volume.

- [Narrator] There is a new theory that universes

are suspended in an even larger structure made up of membranes.

These are known as branes, and they contain universes.

- [Speaker 9] Some very compelling theories, which I--

I personally believe suggest that there

could be a larger framework, something called a brane.

So a brane, not this brain-- um,

that says there's billions of universes, which each have

billions of galaxies, which each have billions

of stars and planets and planets

and so on and so on and so on.

But then there's no reason to think, well, that brain is

actually a part of a larger framework

called a blaa, which each has billions of brains,

which each have billions of universes

and billions of galaxies.

And so there's always going to be something bigger.

(DEEP SPACE RUMBLING)

- [Narrator] And infinitely many infinite universes makes

everything that could happen happen

an infinite number of times.

This is the many worlds theory, which leads to conclusions

as wild as we all have infinite copies of ourselves living

in infinitely many universes, each with the same

or vastly different outcomes.

Sounds crazy?

Not according to physicists who have

proposed this very outcome.

- [Speaker 2] It wouldn't surprise me if there were

infinite multiverses, an infinite number

of reproductions of Earth and of us

and somewhere Elvis lived.

(DISTANT SHOUTING)

(DISTANT MUSIC PLAYING)

- [Speaker 9] There is probably something having an identical

conversation right now in at least one of hundreds

billion worlds, I would say.

- [Speaker 6] Everything that could conceivably happen, might

happen in some other universe.

I-- I love it because every mistake I've made in my life,

there's some other universe where Reynolds

has made the right decision.

- [Speaker 14] The sort of theories that are proposed

about possible multiple universes where we're all

actually existing in some slightly different form,

and so on.

I mean, they all sound counterintuitive in a sense.

They almost sound crazy, but they're

not being promoted as just some sort of crazy idea.

They are the consequences of analysis of the physics.

And I guess I would just say, well, you know, maybe.

- [Speaker 15] Why do we get infinite copies of things?

Well, basically because quantum mechanics

says that anything can happen.

So if you have a bit of the universe that

looks like our bit, well, there's

nothing special about that.

So that bit of the universe, if you just wait long enough,

will be duplicated.

Very, very low probability, but if you have an infinite amount

of time to wait, then everything that's possible

will happen.

You'll win the lottery, you'll lose the lottery.

- [Speaker 16] And so the idea is that since each of us is

composed of a finite number of atoms,

and these atoms have large but finite number

of configurations, that if you have infinite

number of universes, that the same

configuration exists there.

And so this is the idea of having copies, which could be

slightly different or even identical

if the multiverse exists.

- [Speaker 15] You kind of live forever

because there's always a finite chance that whatever

kills you didn't happen.

Now, that will get rarer and rarer and rarer,

and the chances that you're going

to be the one that lives forever gets less

and less likely each time.

But it's still logically possible,

and everything that's essentially logically

and physically possible will happen

in this vast, large universe.

Once things are infinitely large,

it doesn't only seem possible, it seems inevitable.

- [Speaker 11] So if there are an infinite number of other

universes, then of course, an infinite number of them will,

uh, be dead, but also an infinite

number of them will be alive.

But then you're playing games with infinities, right?

Which is what you can do with infinities.

- [Narrator] And playing games with

infinities is as mind-blowing as any

game we could conceive of.

The following bears testament to this.

- [Speaker 2] If you have infinite possibilities,

then surely one of those possibilities

is a universe in which other infinite

universes cannot occur.

And if our universe exists, then it

must mean that our universe is that universe that excludes

all other infinite universes.

- [Narrator] Concepts like these are not easy to get

your head around, and neither is the idea that

every history event has happened

in an infinite number of ways.

(EXPLOSION)

(OMINOUS MUSIC)

- [Speaker 11] There are infinite numbers of identical

patches, and in those identical patches,

the history of the universe gets played out identically,

and that there would be a patch, in fact,

an infinite number of patches where we're having this

conversation, plus an infinite number

of patches where we're not.

An infinite number of patches, where the lights are on,

and an infinite number of patches

where the lights are off or you're

talking to somebody else.

- [Narrator] The multi-world theory is understandably

a controversial one, so much so that some people

dismiss the whole concept.

- [Speaker 15] These questions about

infinite copies of things do trouble people,

and I think rightly so.

Uh, so some people say, you know what?

It is sufficiently troubling that I want the universe

to, like, be pretty small, because then

you can get away without having copies of things.

But I think a lot of other people

like the excitement of-- of having infinite amount of stuff

in the universe, makes everything possible.

And if everything's possible, that's kind of fun.

- [Speaker 9] I think it is very possible that within

the next century, we will have a good understanding

or evidence that multiverses are really

true in some way or another.

I think our universe is too big to be that boring

and just have one universe.

- [Narrator] Speculations are endless

when it comes to such enormous concepts such as multiverses.

But where does that lead us when

it comes to our own possible infinite universe?

- [Speaker 6] It makes the problem of infinity even worse

that not only do you have to think of our three dimensions,

but you think, well, there might actually be an infinite

number of other universes.

Maybe there's other infinities going off in other dimensions,

and you have to contend with those as well.

So the multiverse makes our problem of conceiving

infinity even worse.

It doesn't help. (LAUGHS)

(CALM MUSIC)

- [Narrator] Our universe consists of four dimensions,

three of space and one of Time.

Is it possible that other dimensions exist

and we are blissfully unaware?

Imagine sitting in a quiet room and all that you hear

is the faint bird sound around you.

But imagine the mass of radio, cell phone and TV signals that

are passing through your body constantly

until you have a radio or TV tuned

into the correct frequency.

Then you would have no idea of these TV, radio

programs or conversations that are

being constantly communicated.

Perhaps there are other entities that are coexisting

that are on completely different dimension to us,

and their existence and conversations

are as silent as the TV signals and radio that

pass through us constantly.

Dimensions could be of such a vastly different nature

or scale that we may never, as humans,

know or understand their existence.

(MYSTERIOUS MUSIC)

- [Speaker 17] Are there even more dimensions beyond

what we imagine already?

Erm, I wouldn't be surprised.

In fact, I'd almost be surprised if they weren't.

- [Speaker 18] The possibilities are all there,

so they can exist in different dimensions

all at the same time.

- [Narrator] Are dimensions simply different versions

of reality that don't interact with us and we

can't interact with them?

- [Speaker 2] You could conjecture

any kind of reality where things don't interact with us.

But it's that if they're not interacting with us, then

it doesn't matter if they're in our world or not.

- [Narrator] However, science is taking the idea of other

dimensions very seriously.

- [Speaker 9] It's nice to think that there could be other

dimensions, and there could be 11 or 12, or however

you want to throw out there.

They very well could exist, and we just

don't realize we're interacting with them

or we haven't figured out how to interact with them.

That's all very true.

- [Narrator] How can we learn more about these

possible other dimensions?

- [Speaker 5] It is mainstream physics to talk

about extra dimensions.

Now, those dimensions can be very small.

They can be wrapped, um, up on themselves essentially.

And that can be of such small scales

that you miss it, that essentially

your hand just passes over and around

this wrapped up dimension.

- [Speaker 12] Extra dimensions are a very serious thing

that's being considered in physics as a possible

explanation for the fundamentals underlying

what we were observing.

- [Narrator] One of science's challenges is understanding

gravity and why it is so weak compared to the other forces.

Could other dimensions explain the gravity anomaly?

- [Speaker 12] Extra dimensions come up as a way to possibly

explain some really interesting physical conundrums,

like trying to link quantum physics and gravity.

People in, uh, the string theory fields

are using extra dimensions to try

to explain the nature of space and time,

so it is genuinely possible that there's other dimensions

that are out there that are either just too small for us

to experience or too large, and we don't have access to them.

So we live in a three dimensions of space world,

but maybe there are other dimensions that are experienced

by the particles that carry gravity, and maybe the charges

that particles have are determined

by the sizes of extra dimensions that they can see.

- [Speaker 5] Certain theories suggest that gravity can have

a wander through these dimensions,

and then come back into our four dimension,

and hence explain why it's so surprisingly weak

relative to the other forces.

There is the exact opposite scale, where

you have larger dimensions.

And in the same way that our universe, our four dimensions,

could indeed be the surface layer of a larger bulk, so

we are the membrane or the brain around a larger bulk,

just as a two-dimensional surface of a balloon

is encompassing this larger third dimension.

- [Narrator] Dimensions could explain a lot about

the things in our universe that at this stage,

simply don't add up.

Another mystery of our universe is how the ingredients

of our universe had to be incredibly

fine tuned for everything that we know to come into existence.

- [Speaker 19] She tasted the porridge in the big bowl,

but it was too hot.

She tasted the porridge in the middle sized bowl,

but it was too cold.

She tasted the porridge in the wee little bowl.

It was just right.

- [Narrator] Our world is in the so-called Goldilocks zone,

just right to support life.

(ENIGMATIC MUSIC)

Had things been even the tiniest bit different,

nothing would exist, stars, planets, or us.

This fine tuning has been compared to the likelihood

of a storm blowing through a junkyard

and producing the space shuttle,

or a golfer who gets a hole in one every single time

for his entire life.

Our world is in the so-called Goldilocks zone,

just right to support life.

Is this fine tuning a pure random coincidence?

Or is this a common outcome in the universe?

- [Speaker 11] There's a whole series of coincidences,

effectively, that seem to have conspired to allow our life

to be here on this planet.

If you mess around with the fundamental constant,

you mess around with the fundamental masses,

it's very easy to create a sterile universe.

I mean, the example is-- is very similar to human

being, right?

You're made of a bunch of atoms, you've got carbon,

you've got iron, you've got lots

of oxygen, lots of hydrogen.

There are many, many ways of arranging those atoms to create

an amorphous dead blob.

There's a very small number of ways to arrange them

to create a living person.

And it's a similar thing with the universe.

If you mess around with the fundamental makeup

of the universe, it's very easy to make a dead one.

(OMINOUS MUSIC)

- [Speaker 4] Is the universe somehow fine tuned?

Is there something special about our universe?

I think the answer to that is no.

There doesn't seem to be one.

I know some of my colleagues think that, oh,

since our universe-- the constants of our universe

seem to have been fine tuned to allow us to exist.

But I don't buy that.

I don't believe it's true because in order

to have fine tuning--

You know, when you have a radio, you have a knob

and you fine tune it by going like this.

When you do that, you need to know that there's

a range that you can sample.

And the reality is we do not know the range of that knob.

And if you don't know the range,

you can't even assign a meaning to the word fine tuned.

And that's why I think the whole argument falls apart.

And so I don't see any designer there.

I think there's-- things are some way, uh, whether they

could have been otherwise is--

you know, that's a function of people's imagination.

- [Speaker 13] The universe that

we live in has allowed for human

life to come into existence.

Planet Earth, if it was too much closer to the sun,

it would be too hot.

If it was too further away, it would be too cold.

If it was much more massive, then maybe DNA wouldn't grow.

And if it wasn't massive enough,

it wouldn't hold on to an atmosphere.

We live around the sun.

That's very boring and evolving very slowly,

very quiescent, not too violent,

which is great for life to occur over.

We live in a part of the galaxy that's not too violent.

We're way out in the-- in the outskirts, in the suburbs,

rather than in the center, where

there's a gigantic black hole spewing

out stuff in all directions.

So this idea is that this universe

is just so-- just right to allow

humans to come into existence.

But there could be many other universes

with different parameter sets where you would not

have evolved some sort of intelligent life,

certainly not human life.

So people are attracted to the idea

that our universe is a statistical fluke

that allowed for human life.

And there'll be infinite number of other universes

with different sets of fundamental parameters

of nature that evolve boring universes that collapse

quickly, that evolve universes that get much, much bigger,

accelerate much, much faster, and maybe other

universes beyond that that have seven, eight, 15 or

105 dimensions.

We just don't know.

- [Spekaer 12] Why is our universe hospitable to life?

It would be easy to imagine that if we had a slightly

different speed of light or charge

on the electron or something, then stars couldn't form

and complex chemistry couldn't exist.

It's actually quite finely balanced.

(GENTLE MUSIC)

So to explain that multiverses actually come in handy

because if there's lots of different universes with lots

of different possible constants of nature,

then we would just happen to find ourselves

in the one in which life was possible, because obviously

we're not going to find ourselves in one

in which life was impossible.

So if there's many, many universes,

that would explain, naturally why

we happen to find ourselves in the universe

that's hospitable to life.

- [Narrator] So multiverses could

explain a lot of unanswered questions about our universe.

Whether multiverses exist is still unknown.

But more and more physicists are starting

to embrace the theory.

Maybe one day we will find proof that they exist,

and we will have our minds and reality expanded once again.

(THEME MUSIC)