Original subtitles

There's never been a stranger idea

in the entire history of science.

Down at the smallest scale.

Smaller than our cells.

Smaller than atoms, could the world suddenly get bigger...

Branching out in new and totally unexpected ways?

A quest to understand the ultimate nature of reality

has gripped the greatest living minds

and is forcing us to consider a truly shocking possibility...

Are there more than three dimensions?

Space, time, life itself.

The secrets of the cosmos lie through the wormhole.

♪ Through the Wormhole 2x04 ♪ Are There More Than Three Dimensions? Original Air Date on June 29, 2011

== sync, corrected by elderman ==

Up, down, backward, forward, side to side.

If you want to get anywhere on Earth,

these three dimensions are the only ways you can go.

They describe any place in our reality.

Or do they?

Many scientists now believe

our world is not three-dimensional.

That somehow... there are other ways to move.

Discovering those hidden dimensions

is the biggest prize in physics

and would forever change the way we see the Universe.

When I was a boy down in the Mississippi Delta,

bugs swarmed all summer long.

Some of them could even walk on water.

But down below there were creatures

who would occasionally dart up and grab an unsuspecting bug.

The water bugs never seemed to see it coming.

Why not?

Was it because, to them, the pool had no depth,

no third dimension?

Could we be like water bugs,

unable to see the full extent of reality?

Susan Barry knows all too well the limits of human perception.

She was born with her eyes severely crossed.

As a baby, her brain's attempts

to fuse the separate two-dimensional images

from each eye into one 3-D image ran into serious trouble.

Now, when I was little, being cross-eyed,

if I, let's say, looked at the apple with my right eye,

my left eye would be turned in and looking at something else --

let's say, this clock.

So that would mean one eye is seeing the clock

and one eye is seeing the apple,

and the brain might interpret that

to think that the clock and the apple

were in the same place in space.

Now, if you think about that, that's an untenable situation.

Because how would you be able to know how to move

and interact with things

if you don't know where they are in space?

So, if your eyes are crossed like that,

you have to find a way to adapt,

and one way to adapt, the way that I used,

was I simply threw out the information from one eye,

the eye that was turned.

Freeman: Susan had eye surgeries when she was a child,

but they only changed her outward appearance.

She could only see two dimensions.

Nothing had any depth.

Everything, even her own reflection,

looked entirely flat.

And it seemed she would live that way forever.

For the past half century, there has been a belief

that if you did not develop the ability to see in 3-D

within the first years of life in early childhood,

you could not develop it as an adult.

Freeman: But in her late 40s,

Susan began a rigorous vision retraining program

to try to teach her eyes to lock onto the same target

and give her brain the chance to discover

an extra dimension of space.

One day, after her 48th birthday,

something incredible happened.

Barry: I went out to my car and I sat down in the driver's seat,

and I went to look at the steering wheel,

and it had popped out.

It was popped out in space with this palpable pocket of space

between the steering wheel and the dashboard.

And I had never seen anything like that.

And all that day, my stereo vision would emerge

like intermittently, unexpectedly,

and it would be amazing.

The sink faucets were really jutting out toward me,

and I can remember just admiring the sink faucets

and thinking that I had never seen an arc

as beautiful as the arc of those sink faucets.

Freeman: The sudden appearance of this extra dimension

was a revelation to Susan Barry.

But the idea that another dimension

beyond the three we know

might be hiding from all of us is now at the center

of the world's most important scientific investigations.

Harvard Professor of physics Lisa Randall

is at the forefront of this hunt.

She sees the world differently from you and me.

Randall: It was just one day I was walking to work,

and I realized I really did think that extra dimensions

could be out there.

Freeman: The main reason for her conviction

that there must be more than three dimensions?

This paperclip.

It's really strange.

If I take this tiny magnet, I can pick up this paperclip

even though the entire Earth is pulling down on this paperclip.

If you think about it, the force of magnetism

that is exerted on this paperclip is enough to compete

and actually overwhelm the force of gravity that's acting on it.

So there's a mystery there,

because why is electromagnetism so much stronger

than the force of gravity?

Freeman: Physicists have discovered

that we live in a world governed by four primal forces.

There is electromagnetism,

the force that affects objects with electric charge...

The strong nuclear force,

whose power is unleashed in nuclear weapons,

and the weak nuclear force that triggers radioactive decay.

These first three forces are all roughly equal in strength.

But the fourth force, gravity, is much weaker.

In fact, it's around a trillion, trillion, trillion times

weaker than the other three.

So we're trying to understand what can explain why gravity

is so much weaker than the other elementary forces.

And one of the possibilities that we start to think about

quite seriously in the last decade or two

is that there could actually be additional dimensions of space.

If that's true, it could be that gravity's weak

because it's actually concentrated

somewhere else in another dimension.

Freeman: The idea that extra dimensions

might be a hidden part of our reality is as old as Plato.

He imagined the world we live in

to be like the wall of a cave lit by firelight.

Shadows dance across our two-dimensional world

cast by objects in the body of the cave

in a third dimension that's hidden from us.

A three-dimensional geometrical shape like the tetrahedron,

which has four equal sides,

could cast a distorted shadow on the wall

so that one side looks much shorter than the others.

Just as an extra dimension

can hide the true length of one of the sides,

so, too, it might be hiding the true strength of gravity.

And Lisa Randall's efforts to learn about extra dimensions

begins, like Plato's, with studying shadows.

So here I have a three-dimensional cube.

Now, if I had a single projection,

I might actually confuse that,

for example, of just being a square,

which is two-dimensional.

However, by rotating the object

and looking from different angles

with different projections,

you can tell that what you have is a three-dimensional object.

By putting together the information,

you can deduce what's there.

Freeman: Just as a two-dimensional shadow

can help us learn the true shape of a three-dimensional cube,

we can explore a four-dimensional cube,

a hypercube, by looking at its three-dimensional shadows.

We can look at different projections of a hypercube.

What we would see

are things from one angle that might look a cube.

From other angles, it might look like a cube inside a cube.

It might look like it's turning itself inside out

because we're not really in the fourth dimension,

so it does things that we're not familiar with

because it has this whole other dimension of space

that it can play with.

Freeman: But if a fourth dimension does exist,

shouldn't we see objects changing shapes like this,

even turning themselves inside out?

Could it be that whatever exists in the fourth dimension

is somehow blocked from entering our world?

Or could they be hidden some other way?

Randall: So, if there are extra dimensions,

they have to be pretty well-hidden

for us not to have seen them.

So, why would that be?

It could be these other dimensions

are just so tiny we just don't notice them.

Freeman: But this scientist

thinks he's discovered a new way to detect them

and that dimensions we can't see

control the way everything in the Universe moves.

What would it look like

if we were to travel into a fourth dimension of space?

It's not easy to imagine.

But here's one way to get an idea.

Think of the palm of my hand as a world of only two dimensions.

If a three-dimensional ball were to pass through it,

what would the inhabitants of my palm see?

A circle that grew

and then shrunk down to a dot before disappearing.

So, if I could move into the fourth dimension,

my three-dimensional projection would distort, shrink,

and finally flicker out of this world, becoming totally dark.

U.C. Irvine Physicist Tim Tait

thinks most of the matter in the Universe

may have moved into the fourth dimension and gone dark.

He, too, spends most of his time

trying to escape the dimensions that normally confine us.

Tait: When you scuba dive,

you become immediately aware of the fact

that you have to control how high you are,

how deep, you know, you are in the water,

how close you are to the surface,

and so you instantly become aware of the fact

that there's another dimension

in a way that you can't really feel when you're on the ground.

Freeman: Tim believes that yet another dimension,

a fourth dimension, might be the key

to explaining one of the deepest mysteries of the Universe --

the mystery of dark matter.

In the recent years, we've become really aware of the fact

that when we account for all the stuff in our Universe,

there's stuff that's missing.

We can see it pulling on other things gravitationally,

but other than that, it doesn't leave any trace that it's there.

Freeman: Scientists are convinced dark matter exists

because it's affecting the way stars rotate around galaxies.

The gravitational pull of it is so strong,

that they estimate dark matter

outweighs normal matter by five to one.

We really don't know what dark matter is,

but there have been many ideas that have been proposed

to try to explain it,

and my own personal take on dark matter

is a theory with extra dimensions.

Freeman: Tim's idea is that dark matter could be evidence

that a fourth dimension exists,

a dimension that is almost impossible for us to see.

Tait: So an analogy for the extra dimension

would be looking at the anchor line of a boat.

When you look at the line from far away, you see a line.

You see a long, thin object,

and you don't realize that it actually has width,

that it has an extra direction that you can move

if you were sitting on the surface of it.

Close up, it's actually a cylinder.

It's big and fat, and you can move around the periphery of it.

Freeman: If particles are moving around this cylinder,

and if it were small enough,

they would look to us like they were not moving at all.

So this is our model for an extra dimension.

We have the Bob, which represents a particle.

As I spin the particle around,

as it goes in a circle with the string holding it in place,

and that represents it moving in the extra dimension.

So, let's see how that works.

So here we have it spinning around in the extra dimension.

As it gets closer and closer, it speeds up.

It moves faster and faster and has more energy.

Even though this particle looks like it's standing still,

it could actually be moving very, very fast

just in a very, very small circle.

Freeman: Any particle that is moving must have energy,

and according to the most famous equation in all physics,

if you have energy, you have mass.

That gave Tim a flash of inspiration

about what dark-matter particles might actually be

and how they might lead us

to discovering the fourth dimension.

Tait: So photons are particles of light,

but if there's another direction that photons can travel in,

we can actually get a dark-matter particle

by just taking these massless photons

and letting them move around in a circle in the extra dimension.

Freeman: If Tim's right,

dark matter is actually made of light,

massless particles that appear to have mass

because they are racing around

a tiny fourth-dimensional loop that's too small for us to see.

But how and when

did these photons leave our three-dimensional world

and enter the fourth dimension?

One way you can try to understand this

is if you think about a round-about in a playground.

It's spinning around really fast.

Actually get onto the round-about,

a child is gonna have to run around it at the same speed

that it's spinning.

But if it's spinning faster than the child can actually run,

then there's no way to get onto it safely.

Most particles we have today

just don't have that much energy.

But when the Universe was very young,

it was very small and it was very hot.

And at that time, particles had a lot more energy,

and they were able to actually get into the extra dimension.

Freeman: Right after the Big Bang,

super high-energy particles of light

may have blasted their way into the fourth dimension.

They have been stuck there ever since

and appear to us today as dark matter.

But Tim thinks there might be a way for them to get out,

and when they do, they could bring us proof

that the fourth dimension really exists.

If two photons are moving around this curled-up dimension

in opposite directions,

they might occasionally bump into one another.

When they collide, they annihilate and burst out

as an intense shower of energy into our 3-D Universe.

Even though this event is rare,

these collisions in the fourth dimension

should create a telltale signal.

Man: Engines start. Liftoff.

Freeman: In 2008, NASA launched the Fermi Space Telescope,

a probe designed to pick up the intense radiation, gamma rays,

created by cosmic cataclysms like exploding stars.

But it should also detect gamma rays from dark-matter photons

as they annihilate one another.

So, as it collects data, we understand the gamma-ray sky,

and we start to look for where the dark matter might be.

Freeman: Fermi has already discovered a sea of gamma rays

emanating from the center of our galaxy.

But much more work is needed

to prove this signal is coming from the fourth dimension.

Tait: So obviously, I hope that tomorrow we declare victory

and explore the extra dimension.

On the other hand,

I don't know exactly when we're gonna discover it.

I think, though, the prospects today are much better

than they have been in the past.

Freeman: The Fermi Telescope will continue gathering evidence

from the depths of space until around 2015.

But proof that there are more than three dimensions

may not come from so far away.

Right now the biggest experiment mankind has ever built

is trying to find them under the Swiss Alps.

The goal of science

is to reveal to us the deepest workings of nature.

And nothing in science attempts to go deeper than string theory.

String theory says that every single particle of matter

and energy in the Universe

is actually a tiny, vibrating string...

A string that vibrates not in three dimensions, but in nine.

If string theory is right, at every point in space,

there are six extra dimensions curled up incredibly tight.

These hidden dimensions

could solve all the mysteries of physics.

But there's a problem.

Since string theory was first proposed over 40 years ago,

there's not a single shred of evidence to support it.

Thousands of scientists are on the hunt for that evidence.

Under the foothills of the Alps in Geneva

lies the Large Hadron Collider, the LHC.

It's a 17-mile-long circular racetrack

designed to smash subatomic particles together

at phenomenal energies.

Caltech Physics Professor Maria Spiropulu

has been working at the atom smashers in Geneva

since she was an undergraduate.

She has seen trillions of particles fly

like subatomic shrapnel through the detectors.

The LHC, I think, is the most ambitious

and technologically complex scientific project

that humanity has ever attempted.

We got a billion collisions per second,

and this is a daunting task to record this data.

Freeman: Maria and her colleagues have sifted through

this immense pile of data

and identified dozens of tiny subatomic particles,

the basic building blocks of matter.

But they've never seen the strings

that lie at the heart of each of these particles.

String theory predicts that they must be

a trillion, trillion times smaller than an atom.

Put that another way --

if an atom were the size of the solar system,

a string would be the size of a light bulb.

And the smaller an object is,

the more energy it takes to see it.

The energy of the subatomic particles racing around the LHC

is staggeringly large.

Protons zip around this ring so fast that a beam of light

only outruns them by about eight miles an hour.

But to see fundamental strings

and their six curled-up dimensions

requires levels of energy almost beyond comprehension.

Spiropulu: If you want to make a collider

that will actually produce something like strings,

it would take an accelerator much bigger than the LHC,

much bigger than the Earth, the circumference of the Earth,

possibly much bigger than the Milky Way.

Freeman: But there may be a way to prove that string theory

and the six extra dimensions of space that come with it

is correct,

a way that does not require seeing tiny strings directly.

Joe Polchinski is one of the world's

leading string theorists.

Like many physicists,

he draws inspiration from being close to nature.

It's great to get out here in nature in the mountains

to think about things a bit.

When you get to the top of a climb,

you really get a much bigger picture.

Freeman: Joe has probably

delved deeper into the workings of string theory

than anyone else, and in doing so, he realized

something crucial was missing from the math.

So, we know that the basic building blocks of nature

have to be really small,

smaller than anything we've ever seen --

probably a whole lot smaller.

So, if these building blocks are strings, you know,

they're very elusive.

How do we know that they're there?

And so it's challenging.

And there was this one calculation we would do,

and the answer that the math was giving us

wouldn't match up with the physical picture

we thought we had.

It turned out that the problem was

the strings themselves were not enough.

What the math was telling us was there was another kind of thing,

another sort of object in the picture.

Freeman: In 1995, after many years of work,

Joe made his way through the torturous math

and discovered the source of strings.

He called these objects D-branes.

So we're out here on this nice hike out here in nature,

and we've got this beautiful spider web,

which is a nice model for some of these ideas.

So D-branes are these higher-dimensional objects.

They can be two-dimensional, three-dimensional, or even more.

And this spider web is two-dimensional, a sheet,

and like a sheet, it can flex and bend

the way D-branes can flex and bend.

Now, it's not a perfect model

because this web is stuck between these two branches,

but the D-branes can go on forever.

They could be of cosmic size,

stretching from one side of the Universe to another.

And if you look close,

you see that there are these little bugs stuck to it

the way strings get stuck to a D-brane.

Freeman: In Joe's theory, D-branes could take on

any of the nine dimensions

that exist in the mathematics of string theory.

Our entire Universe could be a three-dimensional brane,

a block of space to which all the strings,

all the matter in our Universe is stuck.

Now you have the branes doing what they do,

and you find that very possibly

the dimensions could be much larger than we thought about,

large enough to see particle accelerators,

large enough to maybe have effects on what we see

in astrophysics, in some of the physics we see from space.

Freeman: Thanks to Joe's discovery,

scientists around the world are fueled with fresh hope

that they may soon detect extra dimensions.

If you, me, every star, every galaxy in the cosmos

is stuck on a three-dimensional brane,

then a fourth dimension

wouldn't have to be a tiny fraction of an atom.

It could be much bigger.

The discovery of extra dimensions

would be one of the biggest breakthroughs

in the history of science.

But it might also spell disaster.

Because the experiment that proves they exist

might also create a black hole here on Earth.

In 1609, Galileo peered through his telescope

and spied the moons of Jupiter.

His discovery of those four tiny points of light,

invisible to the naked eye,

changed our understanding of our world.

Extra dimensions of space

will be much harder to see than Galileo's moons,

but if we discover them, it will change our understanding

of the entire Universe.

This piece of delicately balanced equipment

could be the device that discovers the fourth dimension.

It sits in a basement at the University of Washington

and belongs to this man.

Eric Adelberger, along with a small team,

has spent the last decade

watching this torsion balance twist back and forth,

hoping it reveals evidence

that there are more than three dimensions.

Gravity is really an amazing story.

It was the first of the fundamental forces

that the physicists learned about.

Isaac Newton had his theory of gravity,

which has been tested very well in the solar system.

But it's not really been tested very well at all

at very short distances.

And the short distances

are now where all the theoretical action is,

so to speak.

Freeman: The forces Eric needs to measure

are incredibly weak.

Even though the lab is underground,

his data is frequently marred by trains, rush-hour traffic,

even airplanes flying miles overhead.

The forces we're measuring are really extraordinarily tiny.

To get some idea, if you could cut a postage stamp

into a trillion little pieces somehow

and could weigh one of those little pieces somehow,

that's the kind of forces that we're measuring.

Freeman: If the force of gravity deviates from Newton's laws

at very small distances, it would be a telltale sign

that an extra microscopic dimension exists.

It's a principle Eric knows firsthand

from his passion outside the lab

tending another set of delicate objects.

A nice way to understand this is this analogy

between the way gravity spreads out

in varying number of dimensions

and the way flow of water spreads out

in varying number of dimensions.

We got a steady stream of water

that flows out of these two outlets at the top,

and it falls into a channel and is confined in one dimension.

And it runs down along the one dimension,

and we've made one channel twice as long as the other channel.

And we're gonna see -- measure the flow of water

by watching how much the level of the water in this bucket

changes compared to this bucket, where the water's had to travel

twice as far in that one dimension.

The amount of water

that's flowed through the longer one-dimensional channel

is just the same as the amount of water

that's flowed through the shorter one-dimensional channel.

So what this tells us about gravity is that if gravity

were operating in a one-dimensional world,

it would be the same if objects are close together

or if they're very far apart.

So now we're gonna see what happens

when the water flows in two dimensions.

In our two-dimensional experiment,

the beaker that was closer to the water source

got twice as much water

as the beaker that was farther from the source.

If these two beakers here were our measure of gravity,

we would know that we were in a two-dimensional world

because we got twice as much water over here.

Okay, now we're gonna see what happens

when the water spreads in three dimensions.

Freeman: When water spreads out in a three-dimensional world,

when you place the bucket twice as close to the source,

you get four times as much water.

So if we lined up the beakers from the three experiments,

we'd see that the 1-D beakers, the water was the same height,

2-D, the near beaker had twice the water,

and in the case of 3-D, it had four times the water.

Now, if we could imagine that we were living in four dimensions,

what would we see, we would expect to see

that the nearer beaker had eight times the amount of water

that the more distant one had.

Freeman: The more dimensions there are,

the faster the force of gravity changes with distance.

Well, we've measured gravity down to roughly 50 microns.

That's about half the diameter of a hair on your head, okay?

So far, Mr. Isaac Newton is still correct.

Freeman: If Eric can get even closer,

the hidden world of extra dimensions

could suddenly pop into view.

Adelberger: There are reasons to think

that, you know, the region between 50 and 10

might contain some real surprises, and, of course,

that's stimulating our enthusiasm

for doing the experiments.

Freeman: On the other side of the planet,

at the Large Hadron Collider,

Particle Physicist Maria Spiropulu is also looking

for unexpected changes in the force of gravity.

But if her experiment is successful,

she'll create something never before seen on Earth --

a black hole.

Spiropulu: It is quite possible the LHC experiment

can produce the so-called microscopic black holes.

Freeman: This is not the type of black hole

that is borne from a collapsing star,

where the core gets so compacted

that nothing can escape its gravitational pull.

What Maria is looking for

is evidence of a microscopic black hole.

If the LHC can force two particles

sufficiently close together,

and the extra dimensions are large enough,

gravity could start growing much stronger than expected,

eventually compacting the two particles enough

to form a tiny subatomic black hole.

But don't worry about moving to Mars just yet.

The black holes Maria and her colleagues expect to create

are tiny...

So tiny that they will evaporate in a fraction of a second.

The microscopic black holes, as soon as they are produced,

they immediately decay with a very, very short life-span.

There is a spray of these particles, and that is the clue

that such an object might have been created.

Freeman: The LHC has been looking for these black holes

for over a year.

So far they found no hint

of even a single black hole being created.

Extra dimensions remain elusive.

But Lisa Randall thinks that might be

because they're different from what most scientists expect.

She believes extra dimensions are warped

and that they are passageways to a parallel Universe.

Extra dimensions are not easy to see.

If they were, we'd have found them long ago.

Many scientists now believe

we'll never have the technology to find them.

But extra dimensions might still reveal themselves...

because they might be separating us from a parallel Universe.

An entire cosmos could be lurking

less than...a trillionth of an inch away.

Harvard Professor Lisa Randall

has a radical new idea about extra dimensions,

one that will change the way we see our entire Universe.

She began with string theory,

the idea that all the fundamental particles

are just vibrations of tiny nine-dimensional strings.

Then she added in Joe Polchinski's ideas

that strings making up all the stuff in our Universe

had to be stuck to a giant three-dimensional object

called a brane.

There are two types of strings --

strings with ends

and strings that are closed loops, like rubber bands.

And the strings with ends, those ends have to be somewhere.

They can't just be anywhere in higher-dimensional space.

They have to be on the surface of a brane.

And if that's true,

the particles associated with that string

will also be on the brane.

And it turns out that all the matter we know about,

and also the forces through which they interact,

might all be stuck on a brane through this mechanism,

except for gravity.

Because gravity is never associated with open string.

Gravity's associated with a closed string.

And closed strings have no ends.

There's no mechanism that makes it stick to a brane.

A closed string can be anywhere.

Freeman: Lisa's math suggested that gravity might be so weak

because the closed-loop strings

that carry this force, gravitons,

are being pulled away from our brane

and concentrated instead in a parallel Universe

that's separated from us by a fourth dimension.

Randall: You can imagine that these two buildings behind me

represent two different branes,

and we maybe are living only in that building or that brane.

If gravity is concentrated at the other building,

we might only get a tail end of gravity.

It might be that that could explain

why gravity is so weak for us.

Freeman: Gravitons flow freely between our brane

and the one that's across the fourth dimension.

But the gravity in that parallel world is so strong,

it compresses space

trillions upon trillions of times smaller than ours.

The space between these two brane worlds is warped.

As gravitons move

from the dense-gravity brane to our brane,

they spread out, and their force gets far weaker.

Things get rescaled

as you go from one place in an extra dimension to the other.

So whereas things might be extremely heavy here,

they could be exponentially lighter here,

which would naturally explain why gravity is so weak.

Freeman: Lisa Randall's idea of a warped fourth dimension

separating us from a parallel Universe,

where gravity is just as strong as the other forces of nature,

has set the world of physics alight.

Back at the Large Hadron Collider in Geneva,

the beams will soon be smashing together

with enough force to produce particles

that could prove this warped dimension really exists.

Randall: Well, if this idea is right,

you would actually be able to make particles

that essentially have momentum in another dimension.

Now, we don't see that other dimension.

What we see is the effect as if the particle had mass,

and the mass turns out to be the right mass

that it can be produced at the energies

of the Large Hadron Collider, we hope.

Freeman: Any day now, news may come from the Swiss Alps

that the world is fundamentally different

from the way we've always imagined it.

But there is one more twist to this epic hunt

for warped or curled-up extra dimensions.

One scientist thinks our search is doomed to failure.

She does not believe there are more than three dimensions.

She thinks there's only one.

How do you build a Universe?

Do you need three dimensions?

Or do you need four? Nine? Or more?

These are the most fundamental questions

scientists can ask about our reality.

But the simplest questions are often the hardest to answer.

Swarms of scientists at the Large Hadron Collider

and labs around the world

are hunting for evidence of extra dimensions,

be they warped or curled up in tiny loops.

They hope to make a major breakthrough

within the next few years.

But Renate Loll, a physicist at the University of Utrecht,

isn't holding her breath.

Of course, one of the problems you have in string theory

is that there's all these many dimensions.

Then you have to explain why you only see a few of them.

That would be wonderful if you could do that.

But currently that's too difficult

or no one has managed to show that.

Freeman: Renate believes

that the extra dimensions predicted by string theory

are merely a mathematical quirk

and the theory itself is likely to be wrong.

Of course, it raises the question of,

"Well, can we maybe do

without these extra dimensions whatsoever?"

Freeman: Renate Loll's dislike

for the extra dimensions of string theory

is matched only by her passion

to attack the same puzzle it was created to solve --

the mystery of gravity.

Einstein realized that gravity could be seen

as simply a bending of space by massive objects.

His theory of general relativity

was a masterpiece of modern physics.

But it left a serious problem unsolved --

how does gravity affect space on the microscopic level?

So if you ask questions

that have to do, say, with the very, very small

and that involves anything that has to do with gravity --

so, how do objects interact gravitationally

on very, very short scales --

then you need an extension of Einstein's theory

because it doesn't cover that range.

Freeman: Renate has taken on that challenge.

She's trying to develop new laws of gravity

that apply even at the smallest distances,

and she's testing them in computer simulations.

She begins with a collection of microscopic points of space

and attempts to stick them together with gravity.

In other words, she is growing space.

The last time this happened outside a computer

was about 13.7 billion years ago.

It was part of an event you've probably heard of --

the Big Bang.

Renate is working on a much smaller scale,

but the microscopic Universes she is cultivating

have some very unexpected properties.

Imagine you're given a space or just a piece of space

and you want to learn about what it is, and, in particular,

you may want to learn about what its dimension is.

So one experiment that you can actually do

to find out what the dimension is,

is to let an ink drop fall in it and then see what happens,

see how the ink spreads in the space.

Freeman: In water, ink spreads into three dimensions.

On a piece of blotting paper, it spreads into two.

But when Renate tested how things spread out

inside her computer-simulated Universes,

the results looked something like this.

Loll: Watch what happens now.

It filled out much less ones than we expected

on small scales,

and that's a true indication

that the dimension's actually smaller

than what we expected.

It's smaller than three.

Freeman: Renate's simulations

looked like they had three dimensions,

but at root, they only had one.

If her theories of gravity are right,

it suggests that solid space is not solid at all.

Down at the smallest scales,

it might be built from a mesh of one-dimensional lines.

Is this the fundamental truth about how space is formed?

Is one dimension all there really is?

So the order is, one would think of the dimension of a space

as fixed, just God-given.

It's just there.

But what happens on very, very small scales?

And there's the story we find is totally different.

The space appears to have a smaller and smaller dimension

as you explore it on smaller and smaller scales.

Freeman: Other scientists are not convinced

Renate's one-dimensional Universe is correct.

Their bets are hedged on a Universe

with many extra dimensions.

The truth is still elusive.

But it's not out of reach.

Randall: It's a problem we really want to solve.

We really think there has to be an answer --

really tells us that something has to be there,

and it could tell us

that there's some really exotic, underlying matter

or physics or forces that we haven't thought about yet.

In the end, there is, you know, some theory.

There's some simple, elegant theory out there

that accounts for all of nature, for everything we see,

and we feel like we could be very, very close to it.

So when you have shocking questions,

it takes sometimes shocking ideas and answers

to try to put your arms around this.

Are there nine dimensions or only one?

Is this hidden space warped or curled up in tiny loops?

We don't know yet.

But we can be evermore sure of one thing.

The three-dimensional world we thought we lived in

is only what we see.

Reality is almost certainly a lot stranger.

== sync, corrected by elderman ==