Nova (1974–…): Season 38, Episode 23 - The Fabric of the Cosmos: Quantum Leap - full transcript

Lying just beneath
everyday reality

is a breathtaking world,

where much of what we perceive
about the universe is wrong.

Physicist and best-selling
author Brian Greene takes you

on a journey that bends the
rules of human experience.

BRIAN GREENE:
Why don't we ever see events
unfold in reverse order?

According to the laws
of physics, this can happen.

It's a world
that comes to light

as we probe the most extreme
realms of the cosmos,

from black holes
to the Big Bang

to the very heart
of matter itself.



I'm going to have
what he's having.

Here, our universe may be one
of numerous parallel realities.

The three-dimensional world
may be just an illusion,

and there's no distinction

between past, present
and future.

GREENE:
But how could this be?

How could we be so wrong
about something so familiar?

Does it bother us?

Absolutely.

There's no principle
built into the laws of nature

that say that theoretical
physicists have to be happy.

It's a game-changing
perspective

that opens up a new world
of possibilities.

Coming up...



The realm of tiny atoms and
particles: the quantum realm.

The laws here seem impossible.

There's a sense in which things
don't like to be tied down

to just one location.

Yet they're vital
to everything in the universe.

There's no disagreement
between quantum mechanics

and any experiment
that's ever been done.

What do they reveal
about the nature of reality?

Take a "Quantum Leap" on
"The Fabric of the Cosmos,"

right now on NOVA.

Major funding for NOVA is
provided by the following:

And...

And by the Corporation
for Public Broadcasting

and by contributions
to your PBS station from:

Major funding
for "The Fabric of the Cosmos"

is provided by
the National Science Foundation.

And...

Supporting original research
and public understanding

of science, technology,
engineering and mathematics.

Additional funding
is provided by...

And the George D. Smith Fund.

GREENE:
For thousands of years,

we've been trying to unlock

the mysteries of how
the universe works.

And we've done pretty well,
coming up with a set of laws

that describes the clear
and certain motion

of galaxies and stars
and planets.

But now we know,
at a fundamental level,

things are a lot more fuzzy,

because we've discovered
a revolutionary new set of laws

that have completely transformed
our picture of the universe.

From outer space, to the heart
of New York City,

to the microscopic realm,

our view of the world
has shifted,

thanks to these strange
and mysterious laws

that are redefining our
understanding of reality.

They are the laws
of quantum mechanics.

Quantum mechanics rules over
every atom and tiny particle

in every piece of matter.

In stars and planets,

in rocks and buildings,

and in you and me.

We don't notice the strangeness
of quantum mechanics

in everyday life,

but it's always there,
if you know where to look.

You just have to change
your perspective

and get down
to the tiniest of scales,

to the level of atoms
and the particles inside them.

Down at the quantum level, the
laws that govern this tiny realm

appear completely different
from the familiar laws

that govern big,
everyday objects.

And once you catch
a glimpse of them,

you never look at the world
in quite the same way.

It's almost impossible to
picture how weird things can get

down at the smallest of scales.

But what if you could visit
a place like this,

where the quantum laws
were obvious,

where people and objects behave
like tiny atoms and particles?

You'd be in for quite a show.

Here, objects do things
that seem crazy.

I mean, in the quantum world,

there's a sense in which things
don't like to be tied down

to just one location,

or to follow just one path.

It's almost as if things were in
more than one place at a time.

And what I do here can have an
immediate effect somewhere else,

even if there's no one there.

And here's one of the strangest
things of all:

if people behaved like the
particles inside the atom,

then most of the time,

you wouldn't know exactly
where they were.

Instead, they could be
almost anywhere,

until you look for them.

Hey.

I'm going to have
what he's having.

So why do we believe
these bizarre laws?

Well, for over 75 years,

we've been using them
to make predictions

for how atoms and particles
should behave.

And in experiment
after experiment,

the quantum laws
have always been right.

It's the best theory we have.

There are literally
billions of pieces

of confirming evidence
for quantum mechanics.

It has passed so many tests
of so many bizarre predictions.

There's no disagreement
between quantum mechanics

and any experiment
that's ever been done.

The quantum laws
become most obvious

when you get down
to tiny scales, like atoms,

but consider this:

I'm made of atoms.

So are you.

So is everything else we see
in the world around us.

So it must be the case
that these weird quantum laws

are not just telling us
about small things.

They're telling us
about reality.

So how did we discover them,

these strange laws
that seem to contradict

much of what we thought
we knew about the universe?

Not long ago, we thought we had
it pretty much figured out.

The rules that govern
how planets orbit the Sun.

How a ball arcs through the sky.

How ripples move across
the surface of a pond.

These laws were all spelled out
in a series of equations

called classical mechanics,

and they allowed us to predict

the behavior of things
with certainty.

It all seemed to be making
perfect sense

until about a hundred years ago,

when scientists were
struggling to explain

some unusual properties
of light.

In particular, the kind of light
that glowed from gases

when they were heated
in a glass tube.

When scientists observed
this light through a prism,

they saw something
they'd never expected.

PETER GALISON:
If you heated up some gas and
looked at it through a prism,

it formed lines.

Not the continuous spectrum
that you see projected

by a piece of cut glass
on your table,

but very distinct lines.

DAVID KAISER:
It wouldn't give out a smear,

kind of complete rainbow
of light.

It would give out
sort of pencil beams of light

at very specific colors.

GALISON:
And it was something
of a mystery,

how to understand
what was going on.

GREENE:
An explanation for the
mysterious lines of color

would come from a band
of radical scientists

who, at the beginning
of the 20th century,

were grappling with the
fundamental nature

of the physical world.

And some of the most
startling insights

came from the mind
of Niels Bohr,

a physicist who loved to discuss
new ideas over ping-pong.

Bohr was convinced
that the solution to the mystery

lay at the heart of matter,
in the structure of the atom.

He thought that atoms resemble
tiny solar systems,

with even tinier particles
called electrons

orbiting around a nucleus,

much the way the planets
orbit around the Sun.

But unlike the solar system,
Bohr proposed that electrons

could not move
in just any orbit.

Instead, only certain orbits
were allowed.

GALISON:
And he had a really surprising

and completely
counterphysical idea,

which was that there
were definite states,

fixed orbits that these
electrons could have,

and only those orbits.

GREENE:
Bohr said that
when an atom was heated,

its electrons would
become agitated

and leap from one fixed orbit
to another.

Each downward leap would emit
energy in the form of light

in very specific wavelengths,

and that's why atoms produce
very specific colors.

This is where we get
the phrase "quantum leap."

JIM GATES:
If it weren't
for the quantum leap,

you would have this smear
of color coming out from an atom

as it got excited or de-excited.

But that's not what we see
in the laboratory.

You see very sharp reds
and very sharp greens.

It's the quantum leap

that's the origin and the author
of that sharp color.

GREENE:
What made the quantum leap
so surprising

was that the electron goes
directly from here to there,

seemingly without moving
through the space in between.

It was as if Mars suddenly
popped from its own orbit

out to Jupiter.

Bohr argued that the quantum
leap arises from a fundamental,

and fundamentally weird,
property of electrons in atoms,

that their energy comes
in discrete chunks

that cannot be subdivided,

specific minimum quantities
called "quanta."

And that's why there are only
discrete, specific orbits

that electrons can occupy.

KAISER:
An electron had to be
here or there,

and simply nowhere in between.

And that's like nothing
we experience in everyday life.

Think of your daily life.

When you eat food, you think
your food is quantized?

Do you think
that you have to take

a certain amount
of minimum food?

Food is not quantized.

But the energy of electrons
in an atom are quantized.

That is very mysterious,
why that is.

GREENE:
As mysterious as it might be

for tiny particles
in an atom to act this way,

the evidence quickly mounted,
showing that Bohr was right.

In more and more experiments,

electrons followed
a different set of rules

than planets or ping-pong balls.

Bohr's discovery
was a game-changer.

And with this new picture of the
atom, Bohr and his colleagues

found themselves
on a collision course

with the accepted laws
of physics.

The quantum leap
was just the beginning.

Soon, Bohr's radical views
would bring him head-to-head

with one of the greatest
physicists in history.

Albert Einstein was not
afraid of new ideas.

But during the 1 920s,
the world of quantum mechanics

began to veer in a direction
Einstein did not want to go,

a direction
that sharply diverged

from the absolute,
definitive predictions

that were the hallmark
of classical physics.

TEGMARK:
If you asked Einstein or other
physicists at the time

what it was
that distinguished physics

from all kind of flaky
speculation,

they would have said,

"It's that we can predict
things with certainty."

And quantum mechanics

seemed to pull the rug out
from under that.

GREENE:
One test in particular,

which would come to be known
as the double-slit experiment,

exposed quantum mysteries
like no other.

If you were looking
for a description of reality

based on certainty, your
expectations would be shattered.

We can get a pretty good feel
for the double-slit experiment,

and how dramatically it alters
our picture of reality,

by carrying out
a similar experiment,

not on the scale
of tiny particles

but on the scale
of more ordinary objects,

like those you'd find here
in a bowling alley.

But first I need to make

a couple of adjustments
to the lane.

You'd expect that if I roll

a few of these balls
down the lane,

they'll either be stopped
by the barrier

or pass through one
or the other slit

and hit the screen at the back.

And in fact,
that's just what happens.

Those balls that make it through
always hit the screen

directly behind either the left
slit or the right slit.

The double slit experiment
was much like this,

except instead of bowling balls,

you use electrons, which are
billions of times smaller.

You can picture them like this.

Let's see what happens if I
throw a bunch of these balls.

When electrons are hurled
at the two slits,

something very different happens
on the other side.

Instead of hitting
just two areas,

the electrons land all over
the detector screen,

creating a pattern of stripes,

including some right between
the two slits,

the very place you'd think
would be blocked.

So what's going on?

Well, to physicists,
even in the 1 920s,

this pattern could mean
only one thing:

waves.

Waves do all kinds
of interesting things,

things that bowling balls
would never do.

They can split.

They can combine.

If I sent a wave of water
through the double slits,

it would split in two,

and then the two sets of waves
would intersect.

Their peaks and valleys
would combine,

getting bigger in some places,
smaller in others,

and sometimes
they'd cancel each other out.

With the height of the water

corresponding to brightness
on the screen,

the peaks and valleys
would create a series of stripes

in what's known as
an interference pattern.

So how could electrons,
which are particles,

form that pattern?

How could a single electron end
up in places a wave would go?

Particles are particles.

Waves are waves.

How can a particle be a wave?

Unless you give up the idea
that it's a particle.

And think, "Aha!"

"This thing that I thought was
a particle was actually a wave."

A wave in an ocean,
that's not a particle.

The ocean is made
out of particles,

but the waves in the ocean
are not particles.

And rocks are not waves,
rocks are rocks.

So a rock is an example
of a particle,

an ocean wave is an example
of an ocean wave,

and now somebody's telling you
a rock is like an ocean wave.

What?

Back in the 1 920s,

when a version of this
experiment was first done,

scientists struggled to
understand this wavy behavior.

Some wondered if a single
electron, while in motion,

might spread out into a wave.

And the physicist
Erwin Schr?dinger

came up with an equation
that seemed to describe it.

STEVEN WEINBERG:
Schr?dinger thought
that this wave

was a description
of an extended electron,

that somehow an electron
got smeared out

and it was no longer a point,
but was like a mush.

There was a lot of argument

about exactly what
this represented.

GREENE:
Finally, a physicist
named Max Born

came up with a new
and revolutionary idea

for what the wave equation
described.

Born said that the wave
is not a smeared-out electron

or anything else previously
encountered in science.

Instead, he declared
it's something

that's really peculiar:
a probability wave.

That is, Born argued that the
size of the wave at any location

predicts the likelihood of the
electron being found there.

WEINBERG:
Where the wave is big,

that's not where most
of the electron is,

that's where the electron
is most likely to be.

And that's just
very strange, right?

So the electron on its own seems
to be a jumble of possibilities.

PETER FISHER:
You're not allowed to ask,

"Where is the electron
right now?"

You are allowed to ask,
"If I look for the electron

"in this little particular
part of space,

what is the likelihood
I will find it there?"

I mean, that bugs
anyone anytime.

As weird as it sounds,

this new way of describing how
particles like electrons move

is actually right.

When I throw a single electron,

I can never predict
where it will land,

but if I use
Schr?dinger's equation

to find the electron's
probability wave,

I can predict
with great certainty

that if I throw
enough electrons,

then, say, 33.1 %
would end up "here,"

7.9% would end up "there,"
and so on.

These kinds of predictions

have been confirmed
again and again by experiments.

And so, the equations
of quantum mechanics

turn out to be amazingly
accurate and precise,

so long as you can accept
that it's all about probability.

If you think
that probability means

you're reduced to guessing,

the casinos of Las Vegas
are ready to prove you wrong.

Try your hand at any one
of these games of chance,

and you can see
the power of probability.

Let's say I place
a $20 bet on number 29

here at the roulette table.

The house doesn't know
whether I'll win on this spin

or the next or the next.

One.

But it does know the probability
that I'll win.

In this game, it's one in 38.

21 .

(bell rings)

WOMAN:
29.

So even though I may win
now and then, in the long run,

the house always takes in
more than it loses.

The point is, the house doesn't
have to know the outcome

of any single card game,
roll of the dice,

or spin of the roulette wheel.

Casinos can still be confident
that over the course

of thousands of spins, deals,
and rolls, they will win,

and they can predict
with exquisite accuracy

exactly how often.

According to quantum mechanics,

the world itself is a game
of chance much like this.

All the matter in the universe

is made of atoms
and subatomic particles

that are ruled by probability,
not certainty.

EDWARD FARHI:
At base, nature is described

by an inherently
probabilistic theory.

And that is highly
counterintuitive,

and something which many people
would find difficulty accepting.

GREENE:
One person who found it
difficult was Einstein.

Einstein could not believe
that the fundamental nature

of reality, at the deepest
level, was determined by chance.

And this is what Einstein
could not accept.

Einstein said,
"God does not throw dice."

He didn't like the idea that we
couldn't with certainty say,

"This happens or that happens."

GREENE:
But a lot of other physicists

weren't so put off
by probability,

because the equations
of quantum mechanics

gave them the power
to predict the behavior

of groups of atoms
and tiny particles

with astounding precision.

Before long,
that power would lead

to some very big inventions.

Lasers, transistors,
the integrated circuit,

the entire field of electronics.

MAX TEGMARK:
If quantum mechanics
suddenly went on strike,

every single machine
that we have in the US, almost,

would stop functioning.

GREENE:
The equations
of quantum mechanics

would help engineers design
microscopic switches

that direct the flow
of tiny electrons

and control virtually
every one of today's computers,

digital cameras,
and telephones.

ADAMS:
All the devices that we live on,
diodes, transistors, just...

that form the basis of
information technology,

the basis of daily life in all
sorts of ways, they work.

And why do they work?

They work because
of quantum mechanics.

WEINBERG:
I'm tempted to say that
without quantum mechanics,

we'd be back in the dark ages,
but I guess more accurately,

without quantum mechanics we'd
be back in the 1 9th century.

Steam engines,
telegraph signals.

TEGMARK:
Quantum mechanics is the most
successful theory

that we physicists
have ever discovered.

And yet, we're still arguing

about what it means,

what it tells us about
the nature of reality.

GREENE:
In spite of all of its triumphs,

quantum mechanics remains
deeply mysterious.

It makes all this stuff run,
but we still haven't answered

basic questions
raised by Albert Einstein

all the way back
in the 1 920s and '30s,

questions involving probability
and measurement,

the act of observation.

For Niels Bohr, measurement
changes everything.

He believed that before you
measured or observed a particle,

its characteristics
were uncertain.

For example, an electron
in the double-slit experiment.

Before the detector at the back
pinpoints its location,

it could be almost anywhere,

with a whole range
of possibilities.

Until the moment you observe it,
and only at that point,

will the location's
uncertainty disappear.

According to Bohr's approach
to quantum mechanics,

when you measure a particle,

the act of measurement forces
the particle to relinquish

all of the possible places
it could have been

and select one definite location
where you find it.

The act of measurement
is what forces the particle

to make that choice.

Niels Bohr accepted
that the nature of reality

was inherently fuzzy.

But not Einstein.

He believed in certainty,

not just when something
is measured or looked at,

but all the time.

As Einstein said, "I like
to think the moon is there

even when I'm not
looking at it."

That's what Einstein
was so upset about.

Do we really think the reality
of the universe rests on

whether or not we happen
to open our eyes?

That's just bizarre.

GREENE:
Einstein was convinced something
was missing from quantum theory,

something that would describe

all the detailed features of
particles, like their locations,

even when you were
not looking at them.

But at the time, few physicists
shared his concern.

KAISER:
And Einstein just thought
it was giving up

on the job of the physicist.

It wasn't bad physics per se,
it just was totally incomplete.

That's Einstein's refrain.

Quantum mechanics is not
incorrect, it's as far as...

in so far as it goes,
but it's incomplete.

It doesn't capture
all of the things

that can be said or predicted
with certainty.

GREENE:
Despite Einstein's arguments,
Niels Bohr remained unmoved.

When Einstein repeated that
"God does not play dice,"

Bohr responded,
"Stop telling God what to do."

But in 1 935, Einstein
thought he'd finally found

the Achilles' Heel
of quantum mechanics.

(screaming)

Something so strange,

so counter to all logical views
of the universe,

he thought it held the key

to proving the theory
was incomplete.

It's called "entanglement."

LEWIN:
The most bizarre,

the most absurd, the most crazy,
the most ridiculous prediction

that quantum mechanics makes
is entanglement.

GREENE:
Entanglement is a theoretical
prediction

that comes from the equations
of quantum mechanics.

Two particles
can become entangled

if they're close together and
their properties become linked.

Remarkably,
quantum mechanics says

that even if you separated
those particles,

sending them
in opposite directions,

they could remain entangled,
inextricably connected.

To understand how profoundly
weird this is,

consider a property of electrons
called "spin."

(screaming)

Unlike a spinning top,
an electron's spin,

as with other quantum qualities,

is generally completely
fuzzy and uncertain

until the moment you measure it.

And when you do, you'll find

it's either spinning clockwise
or counterclockwise.

It's kind of like this wheel.

When it stops turning,

it will randomly land
on either red or blue.

Now imagine a second wheel.

If these two wheels behaved
like two entangled electrons,

then every time one landed red,

the other is guaranteed
to land on blue.

And vice-versa.

Now, since the wheels
are not connected,

that's suspicious enough.

But the quantum mechanics
embraced by Niels Bohr

and his colleagues
went even further,

predicting that if one
of the pair were far away,

even on the moon, with no wires
or transmitters connecting them,

still, if you look at one
and find red,

the other is sure to be blue.

In other words, if you measured
a particle here,

not only would you affect it,

but your measurement would also
affect its entangled partner,

no matter how distant.

For Einstein, that kind of weird
long-range connection

between spinning wheels
or particles was so ludicrous,

he called it spooky:
"spooky action at a distance."

What's surprising is that
when you make a measurement

of one particle, you affect
the state of the other particle.

You change its state.

There's no forces or pulleys
or, you know, telephone wires.

There's nothing connecting
those things, right.

How could my choice to act here

have anything to do
with what happens over there?

So there's no way they can
communicate with each other.

So it is completely bizarre.

GREENE:
Einstein just could not accept
entanglement worked this way,

convincing himself that only
the math was weird, not reality.

He agreed that entangled
particles could exist,

but he thought that there was
a simpler explanation

for why they were linked
that did not involve

a mysterious long-distance
connection.

Instead, he insisted
that entangled particles

were more like a pair of gloves.

Imagine someone separates
the two gloves,

putting each in a case.

Then that person delivers
one of those cases to me,

and sends the other case

to Antarctica.

Thanks.

Before I look inside my case,
I know that it has

either a left-hand
or a right-hand glove.

And when I open my case,
if I find a left-hand glove,

then at that instant,
I know the case in Antarctica

must contain a right-hand glove,

even though no one
has looked inside.

There's nothing mysterious
about this.

Obviously, by looking
inside the case,

I've not affected either glove.

This case has always
had a left-hand glove,

and the one in Antarctica

has always had
a right-hand glove.

That was set from the moment

the gloves were separated
and packed away.

Now, Einstein thought
that exactly the same idea

applies to entangled particles.

Whatever configuration
the electrons are in

must have been fully determined

from the moment
that they flew apart.

So who was right?

Bohr, who championed
the equations that said

that particles were like
spinning wheels

that could immediately link
their random results

even across great distances?

Or Einstein, who believed there
was no spooky connection,

but instead, everything
was decided

well before you looked?

Well, the big challenge
in figuring out who was right,

Bohr or Einstein,
is that Einstein is saying

a particle, say, has a definite
spin before you measure it.

"How do you check that?"
you say to Einstein.

He says, "Well, measure it

and you'll find
the definite spin."

Bohr would say, "But it's
the act of measurement

that brought that spin
to a definite state."

No one knew how to resolve
the problem,

so the whole question came
to be considered philosophy,

not science.

In 1 955, Einstein died, still
convinced that quantum mechanics

offered, at best, an incomplete
picture of reality.

In 1 967, at Columbia University,

Einstein's mission to challenge
quantum mechanics

was taken up
by an unlikely recruit.

John Clauser was on the verge of
earning a PhD in astrophysics.

The only thing
standing in his way

was his grade
in quantum mechanics.

JOHN CLAUSER:
When I was still a graduate
student, try as I might,

I could not understand
quantum mechanics.

GREENE:
Clauser was wondering
if Einstein might be right

when he made
a life-altering discovery.

It was an obscure paper

by a little-known Irish
physicist named John Bell.

Amazingly, Bell seemed
to have found a way

to break the deadlock
between Einstein and Bohr,

and show, once and for all,

who was right
about the universe.

CLAUSER:
I was convinced that
the quantum mechanical view

was probably wrong.

GREENE:
Reading the paper,

Clauser saw that Bell
had discovered

how to tell
if entangled particles

were really communicating
through spooky action,

like matching spinning wheels,

or if there was
nothing spooky at all

and the particles were already
set in their ways,

like a pair of gloves.

What's more, with some
clever mathematics,

Bell showed that if spooky
action were not at work,

then quantum mechanics
wasn't merely incomplete,

as Einstein thought:

it was wrong.

I came to the conclusion that,
"My God,

this is one of the most profound
results I've ever seen."

GREENE:
Bell was a theorist.

But his paper showed that
the question could be decided

if you could build a machine

that created and compared many
pairs of entangled particles.

Bell turned the question
into an experimental question.

It wasn't just going
to be about philosophy

or trading pieces of paper.

And the experiment that he
envisioned could be done.

You could really set up
an actual experiment

to force the issue.

GREENE:
Clauser set about
constructing a machine

that would finally
settle the debate.

Now, I was just this punk
graduate student at the time.

This really seemed like, "Wow."

There's always the slim chance

that you will find a result
that will shake the world.

GREENE:
Clauser's machine could measure

thousands of pairs
of entangled particles

and compare their spins
in many different directions.

As the results
started coming in,

Clauser was surprised,
and not happy.

I kept asking myself,
"What have I done wrong?

What mistakes
have I made in this?"

GREENE:
Clauser repeated his
experiments, and soon,

French physicist Alain Aspect

started doing similar tests.

Aspect got the same results.

GREENE:
Clauser's and Aspect's results
are truly shocking.

Even though they defy
our intuition,

they prove that the math
of quantum mechanics is right.

Entanglement is real.

Quantum particles
can be linked across space.

Measuring one thing can,
in fact,

instantly affect
its distant partner,

as if the space between them
didn't even exist.

The one thing that Einstein
thought was impossible,

spooky action at a distance,
actually happens.

I was again very saddened

that I had not overthrown
quantum mechanics,

because I still had
and, to this day,

still have great difficulty
in understanding it.

That is the most bizarre thing
of quantum mechanics.

It is impossible
to even comprehend.

Don't even ask me why.

Don't ask me, which you're
going to, how it works,

because it's
an illegal question.

All we can say

is that is apparently
the way the world ticks.

GREENE:
So, if we accept that the world

really does tick
in this bizarre way,

could we ever harness

the long-distance spooky action
of entanglement

to do something useful?

Well, one dream has been

to somehow transport
people and things

from one place to another

without crossing the space
in between.

In other words: teleportation.

"Beam me aboard!"

"Energize."

"Energizing!"

GREENE:
Star Trek has always made
"beaming," or teleporting,

look pretty convenient.

It seems like pure
science fiction,

but could entanglement
make it possible?

Remarkably, tests
are already underway

here on the Canary Islands,
off the coast of Africa.

ANTON ZEILINGER:
We do the experiments here
on the Canary Islands

because you have
two observatories.

And after all,
it's a nice environment.

GREENE:
Anton Zeilinger is a long way
from teleporting himself

or any other human,

but he is trying to use
quantum entanglement

to teleport tiny individual
particles,

in this case, photons,
particles of light.

He starts by generating
a pair of entangled photons

in a lab on the island
of La Palma.

One entangled photon
stays on La Palma,

while the other is sent by laser

to the island of Tenerife,
89 miles away.

Now, Zeilinger brings in
a third photon,

the one he wants to teleport,

and has it interact with the
entangled photon on La Palma.

The team studies
the interaction,

comparing the quantum states
of the two particles.

And here's the amazing part:

because of spooky action,

Zeilinger is able to use
that comparison

to transform the entangled
photon on the distant island

into an identical copy
of that third photon.

It's as if the third photon
has teleported across the sea,

without traversing the space
between the islands.

We sort of extract
the information

carried by the original

and make a new original there.

GREENE:
Using this technique,

Zeilinger has successfully
teleported dozens of particles.

But could this go even further?

Since we're made of particles,

could this process make human
teleportation possible one day?

ATTENDANT:
Welcome to New York City.

Let's say I want to get
to Paris for a quick lunch.

Well, in theory,

entanglement might someday
make that possible.

Here's what I'd need: a chamber
of particles here in New York

that's entangled with another
chamber of particles in Paris.

Right this way,
Mr. Greene.

GREENE:
I would step into a pod

that acts sort of like a scanner
or a fax machine.

While the device scans the huge
number of particles in my body--

more particles
than there are stars

in the observable universe--

it's jointly scanning the
particles in the other chamber,

and it creates a list that
compares the quantum state

of the two sets of particles.

And here's where entanglement
comes in:

because of spooky action
at a distance,

that list also reveals how the
original state of my particles

is related to the state
of the particles in Paris.

Next, the operator
sends that list to Paris.

There, they use the data

to reconstruct
the exact quantum state

of every single one
of my particles,

and a new me materializes.

It's not that the particles
traveled from New York to Paris.

It's that entanglement
allows my quantum state

to be extracted in New York
and reconstituted in Paris,

down to the last particle.

(French music plays)

Bonjour, Mr. Greene.

Hi there.

So here I am in Paris,
an exact replica of myself.

And I'd better be, because
measuring the quantum state

of all my particles in New York
has destroyed the original me.

FARHI:
It is absolutely required in the
quantum teleportation protocol

that the thing
that is teleported

is destroyed in the process.

And you know, that does
make you a little anxious.

I guess you would just
end up being a lump

of neutrons, protons,
and electrons.

You wouldn't look too good.

Now, we are a long way
from human teleportation today,

but the possibility
raises a question:

is the Brian Greene
who arrives in Paris really me?

Well, there should be
no difference

between the old me in New York
and the new me here in Paris.

And the reason is that,
according to quantum mechanics,

it's not the physical particles
that make me "me,"

it's the information
those particles contain.

And that information
has been teleported exactly

for all the trillions
of trillions of particles

that make up my body.

ZEILINGER:
It is a very deep
philosophical question,

whether what arrives
at the receiving station

is the original or not.

My position is that by original,

we mean something which has all
the properties of the original.

ATTENDANT:
Welcome to New York City.

ZEILINGER:
And if this is the case,
then it is the original.

I wouldn't
step into that machine.

(laughs)

Whether or not
human teleportation

ever becomes a reality,

the fuzzy uncertainty
of quantum mechanics

has all sorts of other
potential applications.

Here at MIT, Seth Lloyd
is one of many researchers

trying to harness quantum
mechanics in powerful new ways.

LLOYD:
Quantum mechanics is weird.

That's just the way it is.

So you know, life is dealing us
weird lemons,

can we make some weird lemonade
from this?

GREENE:
Lloyd's weird lemonade comes in
the form of a quantum computer.

LLOYD:
These are the guts
of a quantum computer.

GREENE:
This gold and brass contraption

might not look anything
like your familiar laptop,

but at its heart, it speaks
the same language: binary code,

a computer language spelled out
in zeros and ones, called bits.

LLOYD:
So the smallest chunk
of information is a bit.

And what a computer does is
simply busts up the information

into the smallest chunks,

and then flips them really,
really, really rapidly.

GREENE:
This quantum computer
speaks in bits,

but unlike a conventional bit,

which at any moment can be
either zero or one,

a quantum bit
is much more flexible.

You know, something here
can be a bit.

Here is zero, there is one.

That's a bit of information.

So if you can have something
that's here and there

at the same time, then you have
a quantum bit, or qubit.

GREENE:
Just as an electron
can be a fuzzy mixture

of spinning clockwise
and counterclockwise,

a quantum bit
can be a fuzzy mixture

of being a zero and a one,
and so a qubit can multitask.

LLOYD:
Then it means you can
do computations

in ways
that our classical brains

could not have dreamed of.

GREENE:
In theory, quantum bits
could be made from anything

that acts in a quantum way,
like an electron or an atom.

The qubits at the heart
of this computer

are tiny
super-conducting circuits

built with nanotechnology

that can run
in two directions at once.

Since quantum bits are so good
at multi-tasking,

if we can figure out

how to get qubits to work
together to solve problems,

our computing power could
explode exponentially.

To get a feel for why a quantum
computer would be so powerful,

imagine being trapped
in the middle of a hedge maze.

What you'd want is to find
a way out as fast as possible.

The problem is,
there are so many options.

And I just have to try them out
one at a time.

That means I'm going to hit
lots of dead ends,

go down lots of blind alleys,

and make lots of wrong turns

before I finally get lucky
and find the exit.

And that's pretty much

how today's computers
solve problems.

Though they do it very quickly,

they only carry out
one task at a time,

just like I can only investigate
one path at a time in the maze.

But if I could try all
of the possibilities at once,

it would be a different story.

And that's kind of how
quantum computing works.

Since particles can, in a sense,
be in many places at once,

the computer could investigate
a huge number of paths

or solutions at the same time,

and find the correct one
in a snap.

Now, a maze like this

only has a limited number
of routes to explore,

so a conventional computer

could find the way out
pretty quickly.

But imagine a problem

with millions or billions
of variables,

like predicting the weather
far in advance.

We might be able to forecast
natural disasters

like earthquakes or tornadoes.

Solving that kind of problem
right now would be impossible,

because it would take
a ridiculously huge computer,

but a quantum computer
could get the job done

with just a few hundred atoms.

And so the brain
of that computer...

it would be smaller
than a grain of sand.

There's no doubt we're getting
better and better

at harnessing the power
of the quantum world,

and who knows where that
could take us?

But we can't forget that
at the heart of this theory,

which has given us so much,
there is still a gaping hole.

All the weirdness down
at the quantum level--

at the scale of atoms
and particles--

where does the weirdness go?

Why can things
in the quantum world

hover in a state of uncertainty,

seemingly being partly here
and partly there,

with so many possibilities,
while you and I--

who, after all, are made
of atoms and particles--

seem to always be stuck
in a single definite state?

We are always
either here or there.

Niels Bohr offered
no real explanation

for why all the weird fuzziness
of the quantum world

seems to vanish
as things increase in size.

As powerful and accurate

as quantum mechanics
has proven to be,

scientists are still struggling
to figure this out.

Some believe that there is
some detail missing

in the equations
of quantum mechanics.

And so, even though there are
multiple possibilities

in the tiny world, the missing
details would adjust the numbers

on our way up from atoms
to objects in the big world

so that it would become clear

that all but one of those
possibilities disappear,

resulting in a single,
certain outcome.

Other physicists believe
that all the possibilities

that exist in the quantum world,
they never do go away.

Instead, each and every possible
outcome actually happens,

only most of them happen

in other universes
parallel to our own.

It's a mind-blowing idea,

but reality could go beyond
the one universe we all see

and be constantly branching off,

creating new,
alternative worlds,

where every possibility
gets played out.

This is the frontier
of quantum mechanics,

and no one knows
where it will lead.

The very fact that our reality
is much grander than we thought,

much more strange and mysterious
than we thought,

is to me also very beautiful
and awe-inspiring.

The beauty of science is that
it allows you to learn things

which go beyond
your wildest dreams.

And quantum mechanics
is the epitome of that.

After you learn
quantum mechanics,

you're never really
the same again.

GREENE:
As strange as quantum mechanics
may be,

what's now clear
is that there's no boundary

between the worlds
of the tiny and the big.

Instead, these laws
apply everywhere,

and it's just that their weird
features are most apparent

when things are small.

And so the discovery
of quantum mechanics

has revealed a reality,
our reality,

that's both shocking
and thrilling,

bringing us that much closer
to fully understanding

the fabric of the cosmos.

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