The Fabric of the Cosmos

QUANTUM LEAP PBS Airdate: November 16, 2011

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.

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 gonna have what he's having.

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

The three-dimensional world may be just an illusion.

And there's no distinction between past, present and future.

But how could this be?

How could be we so wrong about something so familiar?

Does it bother us? Absolutely.

There's no principle built into the laws of nature

that says that theoretical physicists have to be happy.

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.

There is 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 has 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.

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 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.

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 behaviour 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.

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.

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.

And it was something of a mystery, how to understand what was going on.

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 laid at the heart of matter,

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.

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.

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".

If it weren't for the quantum leap,

you would have this schmear of color coming out

from the atom as it got excited or de-excited.

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.

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.

An electron has to be here or there and simply nowhere in between.

And that's, 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.

As mysterious as it might be for tiny particles and 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 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 prediction

that were the hallmark of classical physics.

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.

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.