Through the Wormhole

We feel it every moment of our lives.

But for physicists...

It is the oldest unsolved mystery of the cosmos.

Why does gravity make everything attract?

Cutting-edge theory is closing in on unexpected answers.

Could gravity be another force in disguise...

A shadow of a holographic reality,

or a rippling mirage?

Do we, Earth, the Sun, and the stars

really have weight?

Or is gravity an illusion?

Space, time, life itself...

The secrets of the cosmos lie through the wormhole.

The gravitational pull of the sun

keeps Earth from flying off into space.

Earth's gravity keeps us firmly planted on the ground.

This all seems real enough.

But scientists are peering deep into the fabric of the universe

and are discovering that gravity...

...may not be what it seems to be.

Can something feel real but not actually be real?

There were some days growing up

when there just wasn't anything to do.

So we would play simple games

like target practice with rocks.

Gravity always worked.

No matter what I dropped, I always expected it to fall.

Physicists have their own expectations about gravity.

They believe it to be a fundamental force,

an intrinsic cog in the machinery of the universe.

But experimentalist Nergis Mavalvala

isn't taking anything for granted.

So, a fundamental force that -- like gravity,

that describes how massive objects interact

should be true anywhere you look in the universe.

Isaac Newton showed that every object with mass

attracts every other object with mass.

The greater the mass and the closer they are,

the greater the gravitational attraction.

Over 200 years later,

Albert Einstein explained why this happens.

Space and time are interwoven into a fabric called spacetime.

Einstein believed that spacetime could bend.

This distortion is what we experience as gravity.

And that's how he understood that objects with mass

attract to each other.

They follow the curvature of spacetime.

So Einstein's picture of -- of gravity was

that mass tells spacetime how to curve,

and then the curvature of spacetime

tells mass how to move.

Einstein also predicted

that when all objects with mass move,

they trigger tiny gravitational ripples

in the fabric of spacetime.

Gravitational waves should permeate the heavens above us.

Nergis believes we should be able to detect those waves,

if they are big enough.

So if I drop an apple in the middle of a pond...

And I try to detect the ripple at the shore,

it's not going to make it.

It was too small of a wave.

Luckily for Nergis,

bodies much more massive than apples

cause a stir in the heavens.

Awesome! Whoa!

Around the cosmos,

intense gravitational events,

like the collision of galaxies...

...or the explosions of giant stars...

...should be sending massive volleys

of gravitational waves towards Earth.

Nergis has created a way to detect them

with the help of collaborators like Mike Landry.

Nergis and Mike

are part of the largest experiment ever built

by the National Science Foundation.

It is known as

the Laser Interferometer Gravitational Wave observatory,

or L.I.G.O.,

in this behemoth,

laser beams fire down two vacuum tubes

arranged in an "L" shape.

Each arm is 4 kilometers long.

The laser beams can measure the length of each arm

with an accuracy of better than 1 millionth

of the width of an atom.

If a gravitational wave from any intense cosmic event

up to 500 trillion trillion miles away

passes through the Earth,

the space inside the tubes will ripple.

The lasers will detect the change,

and the alarm bells will ring.

After almost a decade of listening to the heavens,

L.I.G.O. picked up the sound...

...of crickets.

We didn't observe a gravitational wave

in the initial science runs of L.I.G.O.

Nergis, Mike, and the thousands of scientists at L.I.G.O.

Have one more shot.

They're working on advanced upgrades

that will increase L.I.G.O.'s sensitivity tenfold.

But there's no guarantee they'll ever get a signal.

Well, if we don't detect gravitational waves

with advanced L.I.G.O., well, first, I'll cry.

But then, I think, it's actually very exciting either way.

If we don't see gravitational waves,

then it's going to start off a different kind of revolution,

where there'll be a lot of head-scratching

about, "what is it about nature we don't understand?"

Nergis is hopeful.

In fact, in march of 2014, a group of astronomers

claimed to have detected gravitational waves

produced by the big bang.

But some scientists take

the deafening silence at L.I.G.O.

as evidence that gravity may not be a fundamental force.

When an apple falls to the earth,

something else could be pulling it down.

Physicists believe that everything in the universe,

even the pulse of energy that we call force,

is made from particles.

Gravity should be no exception.

Zvi Bern is a particle physicist

with a very active imagination.

He's imagining what a game of mini golf would look like

if the balls were shrunk

to the size of subatomic particles

and ruled by the laws of quantum mechanics.

Quantum mechanics is full of the strangest things

you can imagine.

The concept of a particle being at one point,

that becomes a very fuzzy concept in quantum mechanics.

Subatomic particles are unlike anything

you can see with your naked eye.

They become fuzzy when no one looks at them.

Sometimes they can appear out of nowhere...

and then suddenly vanish.

Some of these appearing and disappearing particles...

...transmit the fundamental forces of nature --

electromagnetism, the strong force,

the weak force, and, supposedly, gravity.

I have here a golf ball.

The golf ball represents a photon.

The photon is the carrier of the electromagnetic force.

The electromagnetic force attracts or repels

anything with an electric charge.

The next golf balls --

these represent the W and the Z boson.

The W and the Z boson --

these are the carriers of the weak nuclear interaction.

The weak force causes

the nucleus of a radioactive atom

to break apart.

The next golf ball -- it represents the gluon.

The gluon is the carrier of the strong nuclear interaction.

The strong force binds particles together

to form an atomic nucleus.

Gravity should also be carried by a particle,

but no one has ever observed this so-called graviton.

In fact, when physicists try to calculate

how the theoretical graviton might work,

they quickly get lost in impossible math.

Gravity, unfortunately, is one of our most complicated theories

in the way it interacts.

And what happens is as you do these calculations,

very quickly you start encountering expressions

which no computer in the world,

or all the world's computer --

they couldn't possibly do those calculations.

But Zvi has a trick up his sleeve

to calculate whether or not the graviton exists.

Quantum theory, like mini golf, is a game of probability.

Trying to hit a hole-in-one is difficult.

There are so many ways the ball could go.

But break up the hole into smaller pieces,

and things are much more manageable.

Together with some colleagues,

we developed an idea that we called the Unitarity Method.

And the basic idea of that is, you take the bigger problem

of these interactions, these complications,

and then you chop it into smaller pieces.

And then, by solving the smaller problems

and assembling it, you can do a lot better than

if you were just trying to solve the whole problem at once.

When Zvi and his colleagues

applied their Unitarity Method to gravitons,

an unexpected result came back.

What we discovered about the graviton

is that, in a very precise way,

it can be interpreted as two copies of gluons.

Which binds the nuclei of atoms together

through the strong force.

But Zvi and his colleagues believe gluons

could also be responsible for gravity.

The graviton could actually be a pair of gluons.

Everything became instantly clear,

like a moment of insight, the "Eureka!" moment.

This is our "Eureka!" moment,

where -- where we really knew that we understood it.