NARRATOR: 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 (Columbia University): Why don't
we ever see events unfold in reverse order?
According to the laws of physics, this can
happen.
NARRATOR: 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.
BRIAN GREENE: I'm going to have what he's
having.
NARRATOR: Here, our universe may be one of
numerous parallel realities, the three-dimensional
world, merely a mirage; the distinction between
past, present and future, just an illusion.
BRIAN GREENE: But how could this be? How could
we be so wrong about something so familiar?
DAVID GROSS: Does it bother us? Absolutely.
STEVEN WEINBERG (The University of Texas at
Austin): There's no principle built into the
laws of nature that says theoretical physicists
have to be happy.
NARRATOR: It's a game-changing perspective
that opens up a whole new world of possibilities.
Coming up: the realm of tiny atoms and particles,
the quantum realm. The laws here seem impossible...
BRIAN GREENE: There's a sense in which things
don't like to be tied down to just one location.
NARRATOR: ...yet they're vital to everything
in the universe.
ALLAN ADAMS (Massachusetts Institute of Technology):
There's no disagreement between quantum mechanics
and any experiment that's ever been done.
NARRATOR: What do they reveal about the nature
of reality? Take a Quantum Leap on the Fabric
of the Cosmos, right now, on NOVA.
BRIAN 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,
BRIAN GREENE 2: There's a sense in which things
don't like to be tied down to just one location...
BRIAN GREENE: ...or to follow just one path.
It's almost as if things were in more than
one place at 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 looked 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.
ALLAN ADAMS: It's the best theory we have.
SETH LLOYD (Massachusetts Institute of Technology):
There are literally billions of pieces of
confirming evidence for quantum mechanics.
WALTER LEWIN (Massachusetts Institute of Technology):
It has passed so many tests of so many bizarre
predictions.
ALLAN ADAMS: There's no disagreement between
quantum mechanics and any experiment that's
ever been done.
BRIAN GREENE: 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: for example, 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 (Harvard University): 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 (Massachusetts Institute of Technology):
It wouldn't give out a smear, kind of a complete
rainbow of light; it would give out, sort
of, pencil beams of light, at very specific
colors.
PETER GALISON: And it was something of a mystery,
how to understand what was going on.
BRIAN 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 itself,
in the structure of the atom.
He thought that atoms resembled tiny solar
systems, with even tinier particles called
electrons orbiting around a nucleus, much
the way the planets orbit around the sun.
But Bohr proposed that, unlike the solar system,
electrons could not move in just any orbit,
instead, only certain orbits were allowed.
PETER GALISON: And he had a, a really surprising
and completely counter physical idea, which
was that there were definite states, fixed
orbits that these electrons could have, and
only those orbits.
BRIAN 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."
S. JAMES GATES, JR. (University of Maryland):
If it weren't for the quantum leap, you would
have this schmear 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.
BRIAN 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.
DAVID KAISER: An electron had to be here or
there and simply nowhere in between. And that's,
that's like nothing we experience in everyday
life.
WALTER LEWIN: 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.
BRIAN GREENE: As mysterious as it might be,
the evidence quickly mounted showing that
Bohr was right. 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 1920s, 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.
MAX TEGMARK (Massachusetts Institute of Technology):
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.
BRIAN 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 1920s, 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 is 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?
LEONARD SUSSKIND (Stanford University): Particles
are particles; waves are waves. How can a
particle be a wave?
S. JAMES GATES, JR.: 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."
LEONARD SUSSKIND: 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?
BRIAN GREENE: Back in the 1920s, 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 Schrí¶dinger came up
with an equation that seemed to describe it.
STEVEN WEINBERG: Schrí¶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 moosh.
PETER GALISON: There was a lot of argument
about exactly what this represented. Finally,
a physicist named Max Born came up with a
new and revolutionary idea for what the wave
equation described.
BRIAN GREENE: Born said that the wave is not
a smeared out electron or anything else previously
encountered in science. Instead, he declared
it 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.
STEVEN 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.
DAVID KAISER: And that's just very strange,
right? So the electron, on its own, seems
to be a jumble of possibilities.
PETER FISHER (Massachusetts Institute of Technology):
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?" Well, I mean, that bugs anyone,
anytime.
BRIAN GREENE: 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 Schrí¶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 percent
of them would end up here, 7.9 percent 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 we'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.
CROUPIER: One.
BRIAN GREENE: But it does know the probability
that I'll win. In this game it's one in 38.
CROUPIER: Twenty-one.
Twenty-nine!
BRIAN GREENE: 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.
ED FARHI (Massachusetts Institute of Technology):
At base, nature is described by an inherently
probabilistic theory. And that is highly counterintuitive
and something which many people would find
difficult accepting.
BRIAN 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.
WALTER LEWIN: 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.
BRIAN 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 U.S., almost, would stop functioning.
BRIAN 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.
ALLAN 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.
STEVEN 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 19th
century: steam engines, telegraph signals...
MAX 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.
BRIAN 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 1920s
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."
DAVID KAISER: That's what Einstein was, 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.
Einstein was convinced something was missing
from quantum theory, something that would
describe all the detailed features of particles,
like their location even when you were not
looking at them. But at the time, few physicists
shared his concern. 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.
PETER GALISON: 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.
BRIAN 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 1935, Einstein thought he'd finally
found the Achilles heel of quantum mechanics,
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."
WALTER LEWIN: The most bizarre, the most absurd,
the most crazy, the most ridiculous prediction
that quantum mechanics makes is entanglement.
BRIAN 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."
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 that he called it spooky:
"spooky action at a distance."
ALAIN ASPECT (Institut d'Optique, Palaiseau):
When you have one particle here and one particle
there, and they are separated enough that
there is no signal able to allow them to communicate,
and they still seem to be talking to each
other, that is a big mystery.
STEVEN WEINBERG: 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.
DAVID KAISER: 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?
WALTER LEWIN: So there's no way they can communicate
with each other, so it is completely bizarre.
Einstein just could not accept that entanglement
worked this way, convincing himself that only
the math was weird, not reality.
BRIAN GREENE: He agreed that entangled particles
could exist, but he thought 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 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'll 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.
ALAIN ASPECT: Einstein comes and says, "Look,
if there is a strong relation, it means that
the direction of the spins were already determined
before you do the measurement."
BRIAN GREENE: 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 1955, Einstein died, still convinced that
quantum mechanics offered, at best, an incomplete
picture of reality.
In 1967, 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 Ph.D. in astrophysics.
The only thing standing in his way was his
grade in quantum mechanics.
JOHN CLAUSER (J. F. Clauser & Associates):
When I was still a graduate student, try as
I might, I could not understand quantum mechanics.
BRIAN 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.
JOHN CLAUSER: I was convinced that the quantum
mechanical view was probably wrong.
BRIAN 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.
JOHN CLAUSER: I came to the conclusion that,
"My god, this is one of the most profound
results I've ever seen."
BRIAN 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.
ALLAN ADAMS: Bell turned the question into
an experimental question.
DAVID KAISER: It wasn't just going to be about
philosophy or, or trading pieces of paper.
ALLAN ADAMS: And the experiment that he envisioned
could be done.
DAVID KAISER: You could really set up an actual
experiment to, to force the issue.
BRIAN GREENE: Clauser set about constructing
a machine that would finally settle the debate.
JOHN CLAUSER: 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.
BRIAN GREENE: Clauser's machine could measure
thousands of pairs of entangled particles
and compare them in many different directions.
As the results started coming in, Clauser
was surprised and not happy.
JOHN CLAUSER: I kept asking myself, "What
have I done wrong? What mistakes have I made
in this?"
BRIAN GREENE: Clauser repeated his experiments,
and soon French physicist Alain Aspect developed
some even more sophisticated tests.
In Aspect's test, the only way that measuring
one of the particles could directly influence
the other would be for a signal to travel
between them faster than the speed of light,
something Einstein himself had shown impossible.
The only remaining explanation was spooky
action, and so Aspect's experiment removed
virtually all doubt.
ALAIN ASPECT: Quantum mechanics is true, even
in the most mysterious and the most weird
situation.
BRIAN GREENE: The results of these experiments
are truly shocking. 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.
JOHN CLAUSER: 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.
WALTER LEWIN: 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.
BRIAN 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.
STAR TREK CLIP Beam me aboard!
Energize.
Energize!
BRIAN 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 (University of Vienna): We
do the experiments here, on the Canary Islands,
because you have two observatories. And, after
all, it's a nice environment.
BRIAN 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-guided telescope
to the island of Tenerife, 89 miles away.
Next, 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, the team is able to use that comparison
to transform the entangled photon on the distant
island into an identical copy of that third
photon.
It will be as if the third photon has teleported
across the sea, without traversing the space
between the islands.
ANTON ZEILINGER: We, sort of, extract the
information carried by the original and make
a new original there.
BRIAN 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.
BRIAN GREENE: 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 or particles here in New
York that's entangled with another chamber
of particles in Paris.
ATTENDANT: Right this way, Mr. Greene.
BRIAN GREENE: I would step into a pod that
acts sort of like a scanner or 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.
ATTENDANT: Bonjour, Monsieur Greene.
BRIAN GREENE: Hi, there.
So, here I am in Paris, an exact replica of
myself. And I'd better be, because measuring
the quantum states of all my particles in
New York has destroyed the original me.
EDWARD 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.
BRIAN GREENE: 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.
ANTON 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. And
if this is the case, then it is the original.
JOHN CLAUSER: I wouldn't step into that machine.
BRIAN GREENE: Whether or not human teleportation
ever becomes a reality, the fuzzy uncertainty
of quantum mechanics has all sorts of other
potential applications.
Here at M.I.T., Seth Lloyd is one of many
researchers trying to harness quantum mechanics
in powerful new ways.
SETH 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?
BRIAN GREENE: Lloyd's weird lemonade comes
in the form of a quantum computer.
These are the guts of a quantum computer.
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.
SETH 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.
BRIAN 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.
SETH LLOYD: 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.
BRIAN 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.
SETH LLOYD: Then it means you can do computations
in ways that our classical brains could not
have dreamed of.
BRIAN GREENE: In theory, quantum bits could
be made from anything that acts in a quantum
way, like an electron or an atom. 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 the 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'd 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 even 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 tornados.
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.
MAX TEGMARK: 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.
ED FARHI: 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.
STEVEN WEINBERG: After you learn quantum mechanics,
you're never really the same again.
BRIAN 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
is both shocking and thrilling, bringing us
that much closer to fully understanding
the
fabric of
the cosmos.
