All language subtitles for Stephen Hawkings Grand Design S01E02 The Key to the Cosmos

Hello. My name is Stephen Hawking.

Physicist, cosmologist,
and something of a dreamer.

Although I can not move
and I have to speak through a computer...

In my mind, I am free.

Free to explore the most profound
mysteries of the cosmos.

Such as:
Why is the universe the way it is?

Why does it follow rules and laws?

Why is there order instead of chaos?

Finding out leads us
to the very deepest of secrets.

To the one principle that sit the heart of
everything in the cosmos.

Check it out.

The Aurora Australis
or Southern Lights...

seen from the International Space Station.

I've devoted my life to the
search for an explanation to such...

beautiful mysteries.

Because I believe it would lead us to
the secrets of the universe itself.

This is the search for one
I call the Grand Design:

The key to the cosmos.

The good news is,
I think we found it.

Almost.

Getting here has been
quite a journey.

It began one night
350 years ago...

In the small English town of Cambridge.

The year was 1665.

Death stroke the land as England fell
under the plagues, dark spell.

A student called Isaac Newton,
fled out...

To escape the threat.

We fortunately got away, because Newton
was a radical thinker...

who dare to see the universe
in a completely new way.

Newton took the first
steps in the search...

for the Grand Design by looking
for the mysterious laws that govern nature.

He asked, "Why the things move?"
"Why do they stop?"

and most famously:
"Why do they fall to earth?"

You might not think answer to such
simple questions would change the world...

But it did.

Because Newton realize there was a
force outwork deep within the fabrique of the universe...

that makes all objects attract
one another: the force of gravity.

Gravity works not just on Earth
but throughout the cosmos.

And its strength depends on
just a couple of fundamental things:

The mass of the objects and
their distance apart.

To find these answers, Newton invented a
completely new mathematical language, called...

The calculus.

You don't need to know how it works,
but it wasn't bad...

for a 23 year old.

Scientists all over the
world still use it every day.

Newton's work, made it possible
to predict everything...

from the orbits of planets
around the stars...

and the precise timing of eclipses...

to the trajectories of raindrops.

Today, we theoretical physicists are still
doing the same sort of things as Newton.

And thankfully we don't
have to worry about the plague.

Although our work may seem complex,
it's really quite simple.

We're trying to unravel the hidden
mechanism...

that underlies everything.

We can only do it just because
we stand on the shoulders of giants.

Scientists who piece by piece
discovered what makes...

the universe take.

Amongst those giants was another
of my scientific heroes:

James Clerk Maxwell.

Maxwell was fascinated by light...

which in 1861 led to him inventing
color photography.

But that was just the beginning
of what this remarkable man achieved.

It was when he began to investigate
a completely different round of physics...

that everything changed.

This was the strange, almost
magical connection...

between magnetism and electricity.

There is nothing complicated about it.

Move a magnet near a wire...

and you will cause electricity to
flow through the wire.

Put electricity through a wire,
and it would act like a magnet...

and deflect the compass.

So what connected them?

Maxwell's big idea was that
magnetism and electricity...

are actually two facets
of the same thing:

a wave of energy that was part electrical
part magnetical.

He called them:
electromagnetic waves.

But then came a surprise.

The mathematics told him this
electromagnetic waves...

travel at extraordinary speed:
186,000 miles per second.

The exact same speed that had already
been determined to be the speed of light.

This led to astounding conclusion:

Light is an electromagnetic wave, too.

Maxwell connected electricity,
magnetism, and light...

in a series of four equations...

that I consider to be
one of the greatest discoveries...

in the history of science.

The equations called Maxwell's laws...

govern everything from the auroras that
dawn over the north and south poles...

to the modern electrical
and communications technology...

that powers the planet.

Virtually every machine
in the modern world...

from the computer to a power station
to a washing machine...

works to the rules
Maxwell reviewed.

Electromagnetism quite literally
lights up our planet.

A fitting testament
to a great mind.

But light is much more interesting than
is Maxwell himself realized.

Although he didn't know it, he had actually
uncovered one of the fundamental clues...

of the Grand Design.

That clue is
the speed of light itself.

By the late nineteenth century it looked like...

some of the great mysteries of
the universe would be all wrapped up...

thanks to the groundbreaking
discoveries of Newton and Maxwell.

But then two American physicists
stumbled into a completely unexpected discovery.

Albert Michelson and Edward Morley
were investigating...

the implications of Maxwell's revelation
that light is a form of wave...

traveling at 186,000 miles per second.

They figured that just as water waves,
a wave of energy traveling in water...

and sound waves, a wave of
energy traveling through air...

so light waves must also travel
through... something.

They called this "something":
the luminiferous ether.

Michelson and Morley proposed
that space...

including the space
between the sun and the earth...

Was filled with this mysterious ether.

They believed that sunlight
must travel through the ether...

to reach earth.

Since the earth also
move around the sun...

They must be traveling through
this ether, too.

If so, this movement would
cause what they called an 'ether wind'...

to blow over the surface
of our planet.

Michelson and Morley believed this ether wind
should be detectable here on Earth...

and design an experiment
to measure its effects.

They ran their experiment
in a crowded basement.

But to understand
the principle behind it...

I thought we get them out of the lab
and stay out here on the beach.

Since the earth is constantly
orbiting the sun...

then the ether wind
would be ever-present...

and would effect the speed of light
here, on earth.

If a beam of light was traveling
with the ether wind behind them...

the light should move faster.

But if light was traveling
in the exact opposite direction,

and so was fighting oncoming ether wind,
the speed of light should slow down.

And the difference between those two
speeds should be measurable.

But they couldn't detect any difference.

Whichever way the light waves
were pointing...

They couldn't find any slowing down
or speeding.

This result was deeply disturbing.

The luminiferous ether could not exist.

What's more, it meant the speed of light
must be constant in all directions.

Modern experiments have repeatedly
confirmed this discovery.

The speed of light remains fixed regardless
of the direction in which it is traveling.

Michelson and Morley were
deeply embarrassed...

about having to report they being
wrong. The ether simply wasn't there.

But the experiment wasn't
a total disaster.

It's one of the most important
mistakes in the history of science.

Light is a wave that travels through
nothing. What a strange idea.

And the discovery that the speed
can not be varied, is also very odd.

Likely, we physicists
like strange things...

because it often leads to breakthroughs.

And this discovery led to the
biggest breakthrough of all:

The discovery that the speed
of light is fixed...

Would challenge everything we
scientists believed about the universe.

It would take another of my heroes,
Albert Einstein...

to discover the deep truth
about the nature of light.

To explain how he did it,
let me take you back to my childhood.

My old toy train is a perfect way of
illustrating Einstein's profound question...

of what the fixed speed of light
meant for the universe.

Einstein started with a simple question:

How fast is something like this
little train moving?

Well, this is the 1950s and toy trains
weren't all that good.

So let's say it's traveling
at about one mile per hour.

But change way you look at it from.
You get a different answer.

The earth spins on its axes
at around 1,000 miles per hour.

So, seen from up here, my train
is actually traveling much faster.

Of course, the earth as a whole is
orbiting the sun at 67,000 miles per hour.

And even the sun isn't stationary.
It is orbiting the center of the milky way.

And the Milky Way is moving
through space, too.

So how fast is the train
really moving?

Well, it all depends on way
you see it from.

It could be 1 mile per hour, 1,000
miles per hour, 60,000 miles per hour...

Or many times faster.

So what's the problem?

Anyone can understand that speed
is relative to your perspective.

But when you remember that unlike
the speed of the toy train...

the speed of light is fixed no matter
what your perspective...

then that common sense view things
starts to break down.

To explain why
Einstein imagined a train, too.

Only his was full-sized.

He devised a thought experiment, asking how
something as simple as the lighting of a cigarette light tip...

would look to people with different points of view.

He imagined a man playing with his lighter
in the center of a railway car...

being watched by two people
at either end.

Both at exactly the same
distance from the lighter.

Einstein said the interesting
question is not what do these people see...

But when do they see it.

Because they're in the same car
or moving together at the same speed...

the two observers see the light
at exactly the same time.

But what about someone outside?
What do she see?

From her perspective,
with the train moving forward...

the beam of light needs to travel a little bit further
before it reaches the man at the front.

On the other hand, the light moving towards the
man at the back...

has a slightly shorter distance to go,
since he is moving towards it.

So, she sees the light reach the man at the back
before it hits the chap at the front.

What that means is that an event
on a moving train...

takes place simultaneously
if you're on the train...

But at different times when you're
standing on the platform.

Stop a moment...

and think about
the implication of that.

It means that we can't say if the events
really happen at the same time or not.

Reality itself depends on
where you are.

Scale this up to the universe
as a whole, and it gets even weirder.

If reality depends on where you are...

Then how can you know what's
really going on in the universe.

What's more, what chance do we stand
to finding the key...

to how the universe works if
we can't even tell if...

two events are
simultaneous or not.

Don't worry, because Einstein thankfully
came out with the answer...

in his famous theory
of special relativity.

Einstein proposed that reality is flexible
because time itself is flexible.

It might sound strange, but
this flexibility is just the start...

of a whole new concept in physics.

Einstein went down to suggest that just
like magnetism, electricity and light...

both time and space are inextricably linked
in what he called "spacetime".

This spacetime is flexible as well.

It can be bended and warped
by the shear mass of heavy things

like stars, and planets...
and galaxies.

But what's really amazing, is this
distortions also explain...

that mysterious force discovered by Newton
so many years ago.

Gravity is
the warping of spacetime.

Now, curving space and time
may sound tricky wrap your head around.

But it's not.

Imagine a boat locked on the straight
course across the flat surface of a lake.

A lake that stretches away...
forever.

The flat lake is like
undistorted spacetime.

Now imagine a giant hole
appears beneath the lake...

and water begins to drain away.

The lake has become distorted,
just as spacetime is by a planet.

The effect would be to drag
the boat towards the hole...

so that it begins to curve around it.

Even though the boat
is still being driven in a straight line.

And it's exactly that same effect
a massive star or planet has...

on spacetime.

It causes spacetime
to distort around it,

pulling things towards it.

And that's why things fall to earth:
gravity.

Einstein had lurked deep into the fabrique of
the universe and seen its inner workings.

Ten years after he explained
the fixed speed of light...

He discovered that the distortion
of space and time...

produces gravity, a fundamental force of nature.

His work brought us much closer...

to discovering the secret key
to the cosmos.

But not even Einstein was
prepared for what happen next.

Although Einstein had begun
to reveal the universe's

hidden clockwork,

He still couldn't quite yet see
how it operated.

His theories drawn
the nature of light...

as a super fast electromagnetic wave
racing through the emptiness of space.

But they revealed nothing about what
these waves really are.

That challenge was taken up
in 1919 by a German theorist,

named Theodore Kaluza, a mathematician with
a passion for purity and elegance.

The next great scientist
in my pantheon of heroes.

Kaluza was a man who took all forms
of theory very seriously indeed.

It's said that he taught
himself to swim...

solely by reading a book
on this subject.

Kaluza was fearless in putting
theory into practice.

Luckily for Kaluza, the theory
of swimming was well understood.

But in 1919 that couldn't be said for
a theory that explain the universe:

A theory of everything.

Inspired by Einstein's success
in explaining gravity...

Kaluza wondered if the same idea
might be applied...

to electromagnetism and light.

Were light waves ever more complex
distortions of spacetime...

like ripples in the very
fabrique of the universe?

It was a bold assumption
and the answer was yes.

Despite that flash of genius
Kaluza's timing was unfortunate.

His ideas were swept aside by
new branch of physics...

that through everything into
questions: quantum mechanics.

This should happen when physics
attended attention...

to studying some of the very
smallest things in the universe.

Inside the atom, the universe was
revealed to be a strange chaotic place...

where the familiar rules of
physics just didn't seem to hold sway.

Just how odd this quantum world was...

would be revealed in the deceptively
simple experiment...

using tiny subatomic
particles called electrons.

a stream of electrons
was fired through two tiny slits...

towards a detector.

common sense tells us the electrons
should hit the detector...

in this two highlighted areas
right behind the slits.

But that's not what happened.

Instead, the detector picked up
a pattern of not just two lines...

but many.

This is simply not what anyone expected
electrons or any small lumps of matter to do.

The tiny electrons appeared
to be define the laws of physics.

To get your head around just
how weird this really is...

Let me scale up the electrons
to something a bit more familiar...

like a soccer ball.

This striker is about
to take a free kick.

Obviously, he'll do his best to hit the ball, pass
the defensive wall and the goalie, and into the net.

And they will do their best to
stop that from happen.

So far it all make sense.

But apply the rules of the
subatomic or quantum world...

and things work differently.

And that's why physicists
started to get very worry.

Instead of taking a single,
definable path...

the ball, like the electrons
will take any and every route.

Leaving the goalkeeper
without a chance.

Once in the goal,
the ball reverts back to one reality.

But in the moments before that,
it is everywhere and anywhere.

I told you it was weird.

It's hard to overstate just how
disturbing this view of reality is.

If everything is actually chaotic
at the subatomic level...

then could the project started by
Newton, continued by Maxwell...

and refined by Einstein and Kaluza
have boiled down to this...

something as random
as the game of roulette?

Perhaps the secrets of
the universe are ungraspable...

and beyond the power
of the human mind.

The seeming contradictions between the chaotic
workings of the subatomic world...

and the order of the rest of the world...

was a real problem for us physicists.

But not for long.

In the 50s, along came a man with
an instinctive grasp...

of randomness and probability.

Meet Richard Feynman: party animal,
inveterate gambler and something of a genius.

Feynman brought the mathematics
of his favorite vice...

to the uncertainty of the quantum world.

He argued that, just as a roulette ball
obeys the laws of chance...

So should an electron.

As any roulette player knows, even
though you can't predict for certain...

which number the ball will land on,

you can work out the odds.
1 in 37, as it happens.

Using probability, Feynman was able
to deduce the peculiar rules...

that govern how a particular quantum
event might come forward.

With that, the quantum world
was tamed...

and science itself brought back
from the break.

Richard Feynman did
physicists a great favor.

It's not just that some of his much needed
glamor rubbed off on us.

His discovery that the quantum world
could be predicted meant...

science could resume the
search for the Grand Design.

Physics now turned to finding
connections...

between what happens at the very smallest scale to
the universe at the very largest.

It did so baritoning to the
long neglected work...

of that eccentric German physicist
and self-taught swimmer:

Theodore Kaluza.

Physicists began looking at how his theories
might apply to some of the tiniest things in nature,

the world inside the atom,

where electrons spin around the center
nucleus composed of other particles...

called neutrons and protons.

Inside them, are even
smaller entities known as quarks.

Quarks are themselves made from something
we physicists call "strings"...

which are ever more intricate distortion
of space and time.

You can think of them as being
a bit like vibrating violin strings.

Just as a violin string can vibrate
to produce different musical notes...

each subatomic string
also vibrates, producing

a different
kind of fundamental particle.

And it's these tiniest particles
that give shape to the universe around us.

Building on the ideas of Kaluza and
Einstein, string theory suggests...

that the vibrations of the strings
produce tiny distortions...

in spacetime at a microscopic scale.

And they do so in a mindboggling
ten dimensions.

If the string vibrates in one way...

It produces a certain kind of
fundamental particle, say, a quark.

And if it vibrates in another way...

It creates a neutrino, which
is another kind of particle.

But here's the clever bit: String
theory has the potential to explain...

why these particles interact with
each other in the precise way they do...

just like the harmony
in a piece of music.

And this is where the laws of physics
come from.

The laws that control
everything in the universe.

From the behavior of black holes...

To the life and death of stars.

Take something as simple as a roll
of paper falling to the floor.

Or the flickering of the
magnetic compass needle.

The simplests but most fundamental
of actions.

all governed by
the rules of string theory.

Currently, there are several
different versions of this string theory,

which are all put together
and called "M-theory".

Nobody seems to know
what the M stands for.

It could be Master, Miracle, or Mystery.
Perhaps all three.

Either way, there is still
a lot of works to do.

But even before it's finished...

this M-theory is making
one remarkable prediction:

that ours is not the only universe.

There are many, many more.

Physics has come a long way
since Newton and Maxwell.

And I must say I'm very glad to have lived through
what I think will proved to be a historic turning point.

At the Perimeter Institute for
Theoretical Physics near Toronto...

my colleagues and I have been thinking
about what string theory could mean...

about our place in the universe.

One extraordinary prediction
string theory is making...

is that it should be hundreds
of billions of billions of other universes.

Perhaps more universes than there
are stars in the known cosmos.

To get your head rumished,
let's return to that idea that the...

strings of string theory
unlike notes played by...

a string quartet.

Each vibration of the strings gives rise to the
fundamental particles and to the forces of nature...

which between them, make up everything
in the universe.

But of course, the quartet could just
as well be playing a different tune...

with different vibrating notes.

And mathematically, that
different tune...

would produce different particles and different
forces of nature. Meaning, a different universe.

Change again, and that's
another universe.

So just as there are an endless number of
possible tunes, so our universe must be just...

one of billions of universes.

We can't see them because
they are beyond the limits...

of our own universe.

Each with their own
history and properties.

Some are unstable and collapse
back to where they came from.

Some will produce no stars or
planets and so be dark and cold.

Others will expand and
go on to produce stars and galaxies...

like ours.

As we pounder mist,
we should not be surprised...

to find ourselves in a universe
that is perfect for us.

Our very presence means our
universe must be just right.

So the search for the key
to the universe...

has had one unexpected result:

We have found the key to
every other universe, too.

It seems that M-theory is a system
of laws that governs everything:

The Grand Design.