All language subtitles for Through.the.Wormhole.S05E07.Is.Gravity.an.Illusion.720p.HDTV.x264-DHD

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.

♪ Through the Wormhole 05x07 ♪
Is Gravity an Illusion?
Original Air Date on July 2, 20

== sync, corrected by elderman ==
@elder_man

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.

And the fact that
it came out that simple

really was the great surprise.

We always had suspicions that
something like this was true.

But that it -- it works as
simply as it did --

that was really the big surprise
for us.

Zvi's work could mean
that when an apple falls,

the gravity that pulls it down
is just another manifestation

of the strong force.

The same force that holds

the nucleus of tiny atoms
together

could also be responsible
for holding

colossal celestial bodies
in orbit.

If so,
the universe is awash in gluons,

working together as gravitons.

Every time a pair of gluons

is exchanged
between massive objects,

the objects move
a little bit closer together.

Scientists are discovering

that our assumptions
about gravity

may be almost completely wrong.

A whole new side of gravity

could be waiting to be
discovered.

In fact, we may soon discover
objects that fall up.

Most physicists believe

that gravity is a force
that only attracts.

But cosmologists
have recently discovered

that galaxies appear
to be pushing each other apart

at an ever-increasing rate.

Perhaps it's time to reconsider

what we think we know
about gravity.

Dragan Hajdukovic
is a physicist

at the European Center
for Nuclear Research,

or C.E.R.N.,
in Geneva, Switzerland.

But he does his best work
when visiting

his home country
of Montenegro.

Dragan is using his time at home
to catch up with old friends

and work out a new theory
of gravity --

one that involves the dangerous
material in the universe --

antimatter.

I have a red apple,
which is made from matter,

and a blue one,
which is made from antimatter.

Fortunately,
it's not a true antimatter.

But if we assume that it is,
look what will happen.

Fortunately for us,

there isn't enough antimatter
in the vicinity of Earth

to ever blow it up.

But Dragan thinks that if there
were ever such a thing

as an antimatter apple,

it would have an unusual
gravitational property.

It is quite possible
that antimatter falls up.

Dragan suspects

that antimatter and matter
repel each other,

and that hidden pockets
of antimatter

could be responsible
for pushing the universe apart.

Physicists use the term
"quantum vacuum"

to describe the space

that fills
every corner of the cosmos.

Don't let the name fool you.

It's bubbling
with microscopic activity.

At every point
in the quantum vacuum,

tiny, innocuous pairs of matter
and antimatter particles

are popping
in and out of existence.

They exist for a split-second
before annihilating each other.

There are billions of billions
of billions of billions and --

let's stop, we can continue --

of pairs in the metacube
of the quantum vacuum.

So they must play a role
in theory of gravity.

Think of the quantum vacuum

like a typical Montenegrin town.

Every particle of matter
always dances with a partner.

When a pair of tiny dancers
pops into existence,

the gravity of the matter
is cancelled out

by the antigravity
of the antimatter.

So, normally, no matter how many
pairs of particles

and antiparticles are created,

the resulting
gravitational effect is zero.

But the quantum vacuum doesn't
always exist in a vacuum.

The universe is filled,

after all, with giant islands
of matter called galaxies.

If you put matter inside,

it spoils the symmetry,

and you have
gravitational effects.

At the end
of a Montenegrin folk dance,

male dancers are drawn
into the center

to form a massive structure.

The female dancers
are pushed outwards.

In Dragan's theory,

tiny particles of matter
and antimatter

in the quantum vacuum
follow the same steps.

Galaxies are made of matter.

They pull in the matter
in the quantum vacuum

and push its antimatter away.

So there's slightly less matter
and slightly more antimatter

in the space between galaxies.

So the quantum vacuum becomes
gravitationally repulsive

and galaxies are pushed apart.

Physicists can see
this galactic drift happening.

They are not sure where
the energy

that is causing it comes from,

so they call it dark energy.

But Dragan thinks dark energy

is gravity's
hidden dance partner.

Many physicists tried to explain
the existence of dark energy.

But once again, no one knows
what's dark energy.

Now, what's --
what's the simpler solution --

to invoke dark energy,

or to assume
gravitational repulsion

between matter
and antimatter?

Dragan's theory
is controversial.

But we may soon find out

if gravity has
a repulsive alter ego.

Back at C.E.R.N.,
Dragan's colleagues are using

the Large Hadron Collider
to produce antihydrogen.

If it falls up,

we may finally have
an explanation for dark energy.

Or it could be another
false step on the road

to understanding gravity.

I think that our understanding
is incomplete.

If you try to explain
astronomical phenomena

by our best physics,
it's a disaster.

Our gravitational
theories are broken.

Neither Einstein's theory
nor quantum physics

explains all of what we observe.

Is gravity a trick of the mind?

Or, perhaps,
gravity is what's real,

and reality itself
is the illusion.

Flat because our planet is so large,

Change your perspective
by flying high enough,

and you can see the curvature
of Earth.

If gravity is an illusion,

can we find a new perspective
on it

and see it for what it is?

Princeton University's
Herman Verlinde

is soul searching.

Multiple experiments have shown
that Einstein's theory,

that gravity is the warping
of space and time,

appears to be correct.

But an equally powerful theory,
quantum mechanics,

says that Einstein's theory
cannot explain

what gravity is made of.

Einstein told us that if you
move through space,

you don't notice it,

because space is empty.
It's not made out of anything.

But quantum theory
tells you that actually,

that there must be a granularity
to space,

just like this sand.

Einstein's theory says that

the particle that carries
gravitational force,

the graviton, must float
on the completely smooth surface

of empty space,
like the surface of the sea.

But according
to quantum mechanics,

space is not smooth at all.

It is made up of little grains,
which make for a bumpy ride.

It is a disagreement
that has plagued physicists

for over a century.

But Herman is beginning to think
both theories may be correct,

because reality itself
may be deceiving us.

Einstein famously
got into trouble

by thinking that reality
should really exist,

uh, and he called that
an objective reality.

But in physics,
we know that the --

the world is not quite
what it seems.

Objects that travel
at the speed of light,

like a photon or a graviton,
will see

a dramatically different version
of reality.

When the ball approaches
the speed of light,

something
very strange happens.

The rest of the world seems
to become shorter.

And the faster
the ball goes,

the shorter the rest
of the world becomes,

until it becomes flat
like a plane.

If you were a graviton,

you would be convinced that
you were always standing still

and the entire universe was
a flat sheet in front of you.

We observe particles in our
reality moving in linear paths.

But from a particle's
point of view,

there may be no such thing
as moving at all.

In the late 1960s,
mathematician Roger Penrose

proposed a new way
to see the world.

He said that particles that move
at the speed of light,

like photons
and the theoretical graviton,

experience an alternate reality
he called twistor space,

where points are lines
and lines are points.

In twistor space,

the path that the graviton
travels become points,

so it's a new set of coordinates
for space and for time.

The idea of a hidden reality

seemed preposterous
50 years ago.

But a more recent idea
in physics

suggests Penrose was ahead
of his time.

It is a theory physicists call
the holographic principle.

The holographic principle

is the idea things
that we see in space

are actually sort of
a reflection

of some other reality
on holographic screen.

It's as if
the actual reality

is sitting
on the walls of this room.

Herman is marrying
these two ideas

into twistor holography.

It's a reality-bending theory

where Einstein's gravity
and quantum mechanics

get along just fine.

Einstein's theory requires

that the graviton
move through smooth space.

But in twistor holography,

the path of the graviton's
movement is a point.

It doesn't matter whether

the graviton is floating
on water or sand,

because in this reality,

the graviton stays
completely still.

If Herman is correct, gravity is
real in an altered reality.

And what we experience as
reality could be an illusion,

constructed from something else.

It's kind of like watching
a good TV show.

You might not realize
that an invisible group

behind the scenes created it.

And cut.

Uh, tell me about reality
in life and in physics.

In physics,

reality is sometimes
not unique

and sometimes not...Objective

and sometimes deceptive.

You're sitting here
and you're real to me,

but who knows?
Maybe someone is tricking me.

If gravity is
the universe's greatest mirage,

then it must be created
from something.

A groundbreaking theory
now argues

that gravity could be
another form...

...of pure heat.

The ancient Greeks believed
that fire

was a fundamental element
of the universe.

But thermodynamics, the study
of how microscopic objects

create macroscopic effects,
proved the Greeks incorrect.

Fire is a phenomenon created

from the furious motion
of hot atoms.

Now a bold new theory is setting
the world of physics ablaze.

It suggests that, like fire,

gravity is
a thermodynamic mirage.

The science community
is heralding a recent discovery

as one
of the greatest revelations

of gravitational physics,

and it's all thanks to this man.

No, it's not Herman Verlinde.

It's his identical twin brother,
Erik.

Well, as a child,
Herman and I

discussed a lot about
what we found interesting.

When we would read something,
we would talk about it, and --

and we shared our excitement
in physics.

Erik and Herman lived
similar lives in Holland.

They both got their PhDs in
physics from Utrecht University

and even married two sisters.

But Erik's parallel path
would take a dramatic turn

when a little chaos
showed up at his doorstep.

I was vacationing,
and I came back from a run,

and I came into my apartment,
and then I saw

someone had broken in
and stolen my car key,

my laptop, my passport.
Many things got lost.

Physicists use
the term "entropy"

to describe the amount of chaos
in a system.

Entropy in the universe
is always increasing.

In physics and in life,

things naturally go from order
to disorder.

Turning entropy into order
requires energy,

just like when Erik
had to expend energy

to restore order to his house.

While dealing
with the unexpected chaos,

Erik was hit with a flash
of inspiration.

There is a deep connection
between entropy and gravity.

Imagine traveling to the surface
of a neutron star

where the intense gravity
would make you weigh

140 trillion times more
than you do on Earth.

It's enough to
significantly raise the entropy

of the atoms inside you.

As objects
fall toward a massive body,

they experience an ever stronger
gravitational pull.

And so their entropy
also goes up.

What I realized is that
what causes gravity

is that the apple,
when it's here,

has less entropy than
when it's down on the floor.

And nature tries
to increase entropy,

or tends to increase
entropy.

This is why,
if I let go of the apple,

it will try to get as
much entropy as possible,

and this is why
it's falling.

Erik believes that
objects with mass

feel the force of gravity

because the universe
is increasing

the amount of disorder,
or entropy, deep inside them.

A force that is created
from entropy

is nothing new to physicists
who understand thermodynamics.

In fact, the entropy
inside a hot air balloon

will lift you up into the sky.

So a hot air balloon
contains molecules.

Those molecules are moving.

They want to increase
the entropy,

and this they can do

by getting more space
inside the balloon.

And if the balloon expands,

it actually can do so
by moving up.

The hot air inside the balloon

tries to increase its entropy
by pushing outward and upward.

This results in an emergent
force called buoyancy.

Buoyancy is not a true force.

It's created from the entropy
of air molecules.

Erik thinks that gravity

is also created from the entropy
of something else,

perhaps from disorder

in the very fabric
of space and time.

Erik doesn't yet know
what it is created from,

but he feels sure

gravity cannot be a fundamental
force of the universe.

From the fact that I can derive
gravity from changes in entropy,

that basically means we have
to think about gravity

in a different way.

Instead of assuming it
as a fundamental force,

we can now view it as something
that can be emergent.

We might find out
the truth about gravity

if we could feel it
more intensely.

This is impossible on earth,
where gravity is weak.

But there is a place
in the universe

where gravity reigns supreme...

inside a black hole.

Here, it may completely
incinerate matter

in a wall of gravitational fire.

In unusual situations...

You don't always get

what you expect.

But sometimes

unusual situations lead
to new insights.

To find
the truth about gravity,

physicists are studying it

in a place where
they expect it to...

...Act very strangely.

Physicist Sean Carroll

has a lot on his mind.

Gravity is the hardest problem
in physics,

and he's tackling it head-on.

The fact that gravity is hard
was a surprise to everybody.

We're really gonna need
a breakthrough,

a different way
of thinking about gravity.

Physicists know

where to look for new insights
about gravity...

Inside a black hole.

These cosmic monsters form
when stars collapse.

The entire mass of the star

is compressed
into a single point...

...where gravity reaches
its theoretical maximum.

Surrounding every black hole is
an invisible, intangible shell

known as the event horizon,

the point beyond
which not even light

can escape
the black hole's gravity.

No one knows
what actually exists

on the other side
of this boundary.

The gravitational field in that
region of space is so strong

that it's a one-way ticket.

You can go in, and you can
explore around inside,

but you can never
come back out.

Theoretical physicists like Sean

turn to their imaginations
for answers.

Suppose you're astronaut Alice,
a daring cosmic explorer

willing to take the plunge
into a black hole.

Our current best theory
of gravity says that

you wouldn't even notice
there was an event horizon.

There are certain
cherished principles

that we like to hold on to.

One of them is simply called
no drama.

You could pass right
through the event horizon,

and it wouldn't look
any different

than any other place
in the universe.

So there's no drama when
you're near the black hole.

Physicists have long believed

that when you cross
the event horizon,

nothing dramatic happens

until you're deep inside
the black hole,

and the rising
gravitational intensity

turns you into human spaghetti.

But scientists are learning

that this time-honored story
might not hold up.

The laws of gravity may
break down at the event horizon.

Inside, gravity could be
something entirely different

or not exist at all.

Physicists started to notice
contradictions

after calculating how particles
in and around black holes

connect to each other through
a process called entanglement.

Entanglement says
I could have two electrons,

and I don't know what either
one of them is doing,

but if they're entangled
by measure one,

and I see
it's spinning clockwise,

then I know instantly the other
one is also spinning clockwise.

Another cherished
principle of physics

states that particles
are strictly monogamous.

They can only entangle
with one partner at a time,

no matter what.

But our understanding
of the physics of black holes

seemed to imply that particles
at the event horizon

needed to have
more than one entangled partner.

This was a scenario no physicist
was willing to entertain.

So this is what we call

the Almheiri-Marolf-
Polchinski-Sully paradox,

after the four
Santa Barbara physicists

who proposed it.

The four physicists

proposed a dramatic solution
to the paradox.

It was time to let go
of the cherished principle

of no drama
at the event horizon.

In fact,
something very dramatic happens.

If you went to a event horizon
of a black hole

and visited there, you would be
incinerated by a wall of fire.

Black holes may be surrounded

by a wall of fire so powerful

that it either incinerates
any particle going into it,

or perhaps incinerates the very
fabric of space and time.

If there's a firewall,
that means there's --

somehow, there's a boundary.
There's an edge.

And when you hit that region,
we're not sure what happens.

It seems like maybe
what happens

is that whatever is there
is not space and time anymore.

It's still quantum mechanics,

but it's not good old gravity
and spacetime

as Einstein would have
understood it.

Past the black hole firewall,

gravity could take on
an entirely new form.

If we could find out
exactly what that form is,

we may learn
the true nature of gravity

everywhere else in the cosmos.

Seeing the event horizon
of a black hole

was once thought
to be impossible.

But this astronomer thinks
he has a shot at it.

He's building
the largest telescope

the world has ever seen.

26,000 light-years away,

there's a place
where we could learn

the true nature of gravity.

It's the supermassive black hole
at the center of our galaxy.

Astronomers think
this hole in space

is not much bigger than our sun.

Seeing something that size
so far away

would take a telescope
the size of our planet.

So...Why not build one?

Astronomer Shep Doeleman's
career was launched

when he answered
the call to adventure

and landed...

here.

What excited me about

this particular brand
of radio astronomy

was that you got
to travel the world,

and I said,
"well, that's for me.

I definitely want to go out
into the field and do that."

And then when I got here,

they said "well, largely,
that work's been done."

Shep does most of
his work trapped in his office,

where he often escapes
by daydreaming...

About being the first astronomer
to observe a black hole.

It's one of the hardest problems
in his field,

because astronomers
can only observe objects

that radiate light.

When you ask yourself what
a black hole looks like,

you -- you really have to
begin with,

why do we see black holes
at all?

By definition,
they should be invisible.

When light enters
a black hole, it's gone forever.

But not all of the light around
a black hole gets sucked in.

Some of it bends
around the event horizon,

creating a shadow image
of the black hole.

That image could reveal
how gravity behaves

at the event horizon.

But by the time
the light reaches us,

the signal is so diluted
that shep would need a telescope

thousands of miles across
to pick it up.

So...He set out to build one.

Shep is traveling to exotic
locations around the world,

coordinating a massive
international collaboration.

In the spring of 2015,

nearly all of the world's
high-precision telescopes

will point towards the center
of our galaxy.

So at the center of our galaxy
is an extraordinary object.

It's a supermassive black hole.

And because it is so massive,

and because it's relatively
close to us, we have a shot,

we have a chance
to resolve it.

To resolve
an image of this black hole,

Shep's team devised
a method that turns

a collection of
individual telescopes

into one virtual telescope
the size of our planet.

Well, right now I'm
in the center of the earth,

represented by this ball field.

And we're gonna see water
flying out of a nozzle,

and you can think of that
as light

coming from a cosmic object,
say a black hole.

And a single telescope
can only capture

a small amount of that data.

We're gonna put telescopes
around the entire ball field,

and they're gonna capture all
the water flow and sample,

very comprehensively,
all the data

that we need to make an image
of the object.

When matter falls
into a supermassive black hole,

it spews radiation
out into space.

Shep is trying to reconstruct

the shape of the light
as it leaves its source.

It's just like water
leaving a nozzle.

The further it travels,
the more the spray spreads out.

But if enough collectors
are spread out

over a wide enough area,

the amount caught in each one

would allow you to reconstruct
the shape of the nozzle.

The nozzle of the hose is
spraying information out.

With a single telescope,

or a single cup,
you can only record

or capture part
of the information

coming from the nozzle.

But with many cups spread out
all over the field,

you sample
the full information field

from the object
you're looking at,

in this case, the nozzle.

And you can recreate
and understand

what was happening
when the water left

that very small volume.

Shep's planet-sized
virtual telescope

should have enough resolution
to determine

the gravitational physics
at the edge of a black hole.

Gravity is a theory.

It works very well
on the earth,

but we haven't put it
to ultimate tests.

We haven't put it to the test
where gravity is dominant,

at the edge of a black hole.

So this is one place

where gravity could
conceivably break down.

And it's very important
to test these theories,

because it's the only way
we understand

the nature of reality,

really, the only way we
understand the fundamental basis

of what we believe
about the universe.

Gravity feels real.

It holds all of us to this
little rock we call home.

But gravity may not be
what it seems.

If gravity is an illusion,

then it's time to call
into question

everything we think we know
about the cosmos.

Only when we let go
of what we feel to be correct

can we taste the real truth.

== sync, corrected by elderman ==
@elder_man