The Fabric of the Cosmos

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 going to have what he's having.

Here, empty space teems with ferocious activity.

Our universe may be one of many,

and the three-dimensional world merely a mirage.

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 whole new world of possibilities.

Coming up...

Look around any train station,

and you can see how time rules our lives.

But time is not what it seems.

There may be no distinction

between past, present, and future.

If time isn't what we all think it is,

then what is it?

Did it have a beginning?

Will it have an end?

Where did it come from?

"The Illusion of Time"

on "The Fabric of the Cosmos," right now on NOVA.

Major funding for NOVA is provided by the followin "Once upon a time."

That magical phrase at the beginning of every good story.

But what is the story of time?

People say that time flies, that time is money,

we waste time, we kill time, we try to save time.

But what do we really know about time?

Well, like this river, time seems to flow endlessly

from one moment to the next.

And the flow of time seems to always be in one direction:

toward the future.

But that may not be right.

Discoveries over the last century

have shown that much of what we think about time

may be nothing more than an illusion.

Contrary to everyday experience, time may not flow at all.

Our past may not be gone.

Our future may already exist.

It turns out time itself can speed up or slow down.

And events that we think can unfold in only one direction

can also unfold in reverse.

But how could this be?

How could we be so wrong about something so familiar?

And if time isn't what we all think it is, then what is it?

Did it have a beginning?

Will it have an end?

Where did it come from?

We'd like to corner time as a thing,

but it defies that completely by being momentary,

by only having definitions that hearken back to the notion

of time itself.

Time is the thing that everyone knows intimately

until you ask them to tell you about it.

"What is time?" is really

the $64,000 question to physics.

There's basically no aspect of time

which I feel we really fully understand.

So how do you begin to unlock a mystery

as deep and elusive as time?

Well, one way is to measure it.

And using clocks of all different shapes, sizes,

and kinds, we've been measuring time

with ever-greater accuracy for thousands of years.

The first clock was one that you could say ticks just once a day:

the rotating Earth.

From the repetition of our planet's daily rotation

on its axis

to its yearly orbit around the sun,

we have always used the predictable,

consistent motion of the Earth to measure time.

We're always looking for things that repeat over and over again,

and that repetition, that cycle of things, forms a clock.

That's all time becomes is some repetitive process.

Measuring the Earth's motion with a sundial,

we divided the day into hours.

The Earth rotates once a day,

and we tick off the days

by looking at the rising and the setting of the sun.

With the swing of a pendulum,

we divided hours into minutes and seconds.

With the vibration of a quartz crystal,

we improved accuracy to the thousandths of a second.

But the National Institute of Standards and Technology

in Colorado is the place to go

if you really want to know what time it is.

This is U.S. official time.

It doesn't get any more accurate than this.

Here, they measure time with mind-boggling accuracy

using one of the smallest objects in the universe:

an atom of a rare metal called cesium.

Atoms have a natural frequency.

And anything that vibrates,

that is giving you repetitive motion, can be a clock.

The frequency at which the cesium atom ticks

is the official timekeeper for the world.

When a cesium atom is bombarded with energy,

it vibrates, or ticks, giving off pulses of light

over nine billion times a second.

We count the ticks of the cesium atom.

And the cesium atom ticks

at this 9,192,631,770 ticks in a second.

And so every time you count up to that number,

one second has gone by.

And you get one second after one second,

after one second after one second.

This is just astounding.

My watch gains or loses a second every couple of months.

We're talking about clocks that would only gain or lose a second

in 100 million years.

And that kind of story, where we take one measure of time

and replace it with something that we decide is more accurate,

has been the constant reform process of physics

over hundreds of years.

But no matter how accurate our clocks have become,

time remains a mystery.

Clocks can tell us what time it is,

but they haven't been able to tell us what time itself is.

What is it we're actually measuring?

We may not know what time is,

but the experience of the passage of time

is a fundamental part of our lives.

We're always thinking about time, remembering the past,

making plans for the future,

living our lives within time's constant tick, tick, tick.

I mean, look around any train station

and you can see how time rules our lives.

What may not be so obvious

is that the rise of train travel played a key role

in one of the most startling discoveries about time.

Tickets, please, sir.

Train running on time?

Yes, sir.

Thank you.

In the early days of train travel,

time posed a unique problem.

Back then, each town set their own particular time.

Noon was when the sun was directly overhead,

you know, more or less.

And what time it was in another city,

well, you know, that hardly mattered.

And to complicate things even further,

trains would carry the time of the city

where they began their journey.

So, if I was going from Paris to Geneva,

I would be on Paris time the whole way,

since that's where I started.

But were I going the other direction, from Geneva to Paris,

I'd be on Geneva time.

And as you began to have more and more train lines crossing,

and more and more different times

located at that interchange,

it became a nightmare of confusion.

The need to coordinate clocks over great distances

became a huge issue,

especially when the cities were connected by a single track.

And here's where the modern story of time begins.

As the need for synchronized clocks

became ever more critical,

a young physicist named Albert Einstein

took a job at the patent office in Bern, Switzerland.

It was a ringside seat

to all of the great inventions of the time.

The patents showed how new and exciting ways

to synchronize clocks with the exchange of telegraph signals,

clocks that were synchronized by radio waves,

all made the synchronization of time, and what time was,

and how it was measured,

something immediately important and exciting for Einstein.

Einstein would soon shake up the world

with a radical insight into the nature of time.

And these mechanical devices provided unexpected inspiration.

Einstein realized that these attempts to synchronize clocks--

they were much more than merely creative inventions.

Instead, he realized that they were revealing a deep crack

in our understanding of time itself.

Most people view time

in a pretty simple, straightforward way.

Time ticks the same for everyone everywhere.

It's a common-sense picture

established by the father of modern science, Isaac Newton.

Time for Isaac Newton is something that is

an immutable property of the universe.

Time always changes at the same rate.

Time just goes along,