Nova (1974–…): Season 42, Episode 21 - Inside Einstein's Mind - full transcript

It's a mysterious force
that shapes our universe

It feels familiar,

but it's far stranger
than anyone ever imagined

And yet, one man's
brilliant mind tamed it

Gravity

Using simple
thought experiments,

Albert Einstein made
an astonishing discovery:

time and space
are shaped by matter

You get rid of this force
of gravity,

and instead, we have
curvature of spacetime

Right now, the space around me



is being squeezed and stretched

He called it the "General Theory
of Relativity"

How did one person,
working almost entirely alone,

change everything we thought
we knew about the universe?

Einstein is toiling

as the world seems to fall apart

He was able with pure thought

to solve the riddle
of the universe

"Inside Einstein's Mind,"
right now on NOVA.

Gravity

The most familiar yet most
mysterious of nature's forces

100 years ago, Albert Einstein
made a mind-blowing discovery:

what we feel as gravity

is in fact the push and pull
of space and time itself



He called his idea
"general relativity"

It is perhaps
the most remarkable feat

of thinking about nature
to come from a single mind

General relativity

is undoubtedly one of the
greatest scientific theories

ever conceived

It's a theory of space, time,
and gravity

One mathematical sentence,

and from it, you can derive

the understanding
of the entire universe

on the largest scales,
and that is beautiful

Only now, a century
after it was first proposed,

do we have the technology

to explore the extremes
of Einstein's great theory

Supermassive black holes
at the center of galaxies

Waves of gravity that
distort space and time

The evolution
of our entire universe

How did a concept
that explains so much

come from the mind of one man?

Einstein had a magical talent

He could take a hard,
physical problem

and boil it down
to a powerful visual image,

a thought experiment

Suddenly he realizes,

"This is how the world works

All this abstract nonsense is
the correct theory of reality"

To gain an insight
into Einstein's mind

and the true wonder
of general relativity,

we need to trace
the crucial thought experiments

that led to his great
breakthrough

The seeds for his ideas

were planted
when he was just a child

Einstein grew up
in a small house in Munich,

in southern Germany

His unique personality
was evident early on

Like many great innovators,

Einstein was a rebel, a loner,

but deeply curious

He was slow in learning to speak
as a child,

so slow that his parents
consulted a doctor,

but he later said that
that's maybe why he thought

in visual thought experiments

His sister remembers him
building little card towers

using playing cards

He was a daydreamer,
but he was deeply persistent

Einstein's father, Hermann,

manufactured electrical
equipment

He nurtured his son's interest
in science

On one occasion,
he brought him a compass

Now, you and I maybe remember
getting a compass

when we were kids,
and we were like,

"Oh look, the needle twitches
and points north,"

but then we're on
to something else,

like, "Oh look,
there's a dead squirrel"

But for Einstein,
after getting that compass,

he developed a lifelong devotion

to understanding how things
can be forced to move

even though nothing's
touching them

The young Einstein
became gripped by a desire

to understand the underlying
laws of nature

He developed a unique way

of thinking
about the physical world

inspired by his favorite book

The book Einstein loved

told little stories,

like what it'd be like
to travel through space

or go through an electrical wire

And it made Einstein think
visually

These imagined situations

that we often call
"thought experiments"

became a defining feature
of Einstein's thinking

One of the critical
thought experiments

that Einstein began to play with

very young,
around the age of 16,

was trying to imagine
what would happen

if he could catch up
with a light wave

It's one thing to imagine
a light wave zooming past him

at some seemingly
impossible speed,

but what if he could somehow
just propel himself

really quickly?

What would it look like

if he could catch up
with that light wave?

What would he see?

He said it caused him
to walk around in such anxiety,

his palms would sweat

Now, you and I may remember

what was causing our palms
to sweat at age 16,

and it was not a light beam

But that's why he's Einstein

This dream-like thought
about the nature of light

was Einstein's first step
on the path to his great theory

It stayed with him throughout
his time at school and college

He was extremely gifted

in science and math
as a young person

and very bad at other classes,

mostly because
he kept cutting class

and being very rude
to his teachers

Many teachers
from his high school days on

were convinced he'd never amount
to anything

He was a discipline problem,
and he was bad news

He applies to the second best
university in Zurich,

the Zurich Polytech,
and gets rejected

I'd love to meet
the admissions director

who rejected Albert Einstein

But eventually he gets in,
and he does moderately well,

but not good enough
to get a teaching fellowship

And so he ends up
at the Bern Swiss patent office

as a third class examiner

Undaunted by his
university results,

Einstein started work
at the patent office in 1902,

age 23

Here, his job was to assess
the originality of new devices

He was immersed

in the kinds
of technical details

that he'd been fascinated by
as a very young kid

And here he was,
sitting in the kind of wave

of the modern age

This was the era
of electrification

So all the latest clever ideas
for switching technology,

for coordinating clocks
in particular,

those were all
passing through his office

Time zones had recently been
introduced in central Europe,

and accurately
synchronizing clocks

was a major challenge of the day

Switzerland was a world leader
in time technology

Dozens of patents to link clocks

passed through Einstein's office

He could whip through
these patent applications,

and then out of his drawer,
he'd pull his physics notes,

and his boss was very indulgent

and would sort of turn
a blind eye

as Einstein was doing
his theories in his spare time

It's really important
to remember that

theoretical physics was new
when Einstein was a young man

You could do quite a lot
of this work by reading

a relatively small number
of science journals

and making the calculations
yourself

Einstein's world in 1905

was dominated
by two kinds of physics

One was about 200 years old,

founded by Isaac Newton,
a British natural philosopher

For Newton, all there is
in the world is matter moving

Newton showed that the motion

of falling apples
and orbiting planets

are governed by the same force:

gravity

His equations are so effective,
we still use them today

to send probes to the farthest
reaches of the solar system

The other important theory
of Einstein's day

covered electricity
and magnetism

That branch of physics
had been revolutionized in 1865

by the Scottish physicist
James Clerk Maxwell

Maxwell's theory describes light

as an electromagnetic wave
that travels at a fixed speed

In Newton's world,
the speed of light is not fixed

Einstein could see that
there's a contradiction

between Newton and Maxwell

They just don't fit together

And one of the things
Einstein hated... hated...

Was contradiction

If there's one kind of physics
that says this

and another kind of physics
that says that

and they're different,

that's a sign that something's
gone wrong and it needs fixing

For months, Einstein wrestles

with the problem

Eventually,

to resolve this contradiction,

he focuses on a key element
of speed: time

He realized that

any statement about time

is simply a question
about what is simultaneous

For example, if you say
the train arrives at 7:00,

that simply means that
it gets to the platform

simultaneous with the clock
going to 7:00

In a brilliant
thought experiment,

he questions what "simultaneous"
actually means

and sees that the flow of time

is different for an observer
that is moving

versus one that is
standing still

He imagines a man
standing on a railway platform

Two bolts of lightning strike
on either side of him

The man is standing
exactly halfway between them

and the light from each strike
reaches his eyes

at exactly same moment

For him, the two strikes
are simultaneous

Then Einstein imagines a woman
on a fast-moving train,

Traveling at close to the speed
of light,

what would she see?

As the light travels out
from the strikes,

the train is moving towards one
and away from the other

Light from the front strike
reaches her eyes first

For the woman on the train,

time elapses
between the two strikes

For the man on the platform,

there is no time
between the strikes

This simple thought
has mind-blowing significance

Simultaneity,
and the flow of time itself,

depends on how you're moving

If there's no such thing
as simultaneity,

then there's no such thing
as absolute time everywhere

throughout the universe,
and Isaac Newton was wrong

This concept that time,
and space as well, are relative

became known as
special relativity

It led to remarkable results,

such as the famous equation
relating energy to mass

Einstein published
this article in 1905

to exactly no acclaim

Most people ignored it

This was not setting the world
on fire

Two years go by
before a very eminent physicist,

Johannes Stark, invites Einstein

to write a review article
on Einstein's own work,

precisely because no one
was paying attention

And he begins thinking
about ways to generalize

and to push his own results
from 1905

What if he considers
not only a train

moving at a fixed speed
past the platform?

What if that train begins
to speed up or slow down?

What if there's acceleration?

Adding acceleration to the
equations was his first task

Then there was that mysterious
Newtonian force of gravity

to contend with

In Newton's theory,

gravity is a force
that acts instantaneously

But special relativity says
that's impossible...

Nothing can travel
faster than light

What Newton's theory
tells you is that

suppose the sun
were to disappear,

the orbit of the earth should
change at that very moment

But the notion of
"at that very moment"

in two different places
is exactly one of these notions

that special relativity
has told you

isn't a good physics notion

So you've now got this challenge
of trying to work out

how to take the success
of Newton's theory of gravity

but fit it into this new
special relativistic picture

It was only when Einstein
began to understand the link

between gravity and acceleration

that things began
to fall into place

We all know that
when we are accelerated,

and of course now we have cars
and airplanes

to give us the physical feeling,

if you're in an airplane
and it's taking off,

you are pushed back
in your chair,

you feel actually kind of
a force pushing you back,

which feels very similar
to the force of gravity

But you need the brilliance
of Einstein

to explain why they are related

Suddenly, he hits
upon what he describes as

the happiest thought of his life

If gravity and acceleration
feel the same,

perhaps they are the same

Again, he examines the idea

in a beautiful
thought experiment

He imagines a man in a box

floating weightlessly
in a distant region of space

in zero gravity

Suddenly, the man stops floating

and accelerates downward
until he's standing in the box

What has happened?

Either the box
is now close to a planet

and the force of gravity
has pulled the man to the floor,

or someone has attached a rope

and the box is now
being pulled continuously

and accelerated upwards

So which is it?

Gravity?

Or acceleration?

Without being able
to see outside,

the man can't tell what's
causing his fall to the floor

Einstein realized

there is no way
to tell the difference

between sitting
in a gravitational field

and being accelerated

These are equivalent situations

The fact that these two effects
are the same,

give the same result,

means that gravity
is acceleration

It's not just like acceleration;

it's the same thing

It's a big breakthrough

Einstein's theory
of special relativity worked

for motion at a constant speed

By extending his ideas
to acceleration,

he could begin to formulate
a new theory of gravity

In 1912, Einstein is living
in Zurich with his wife Mileva

and two young sons,
Hans and Eduard

The academic world had realized
the importance

of special relativity,
and his career had taken off

He's now a professor

at the esteemed Swiss Federal
Institute of Technology,

but spends as much time as
possible working on his theory

He needs mathematics

that describes how objects move
in space and time

and soon realizes that
the best tool for the job

is a strange but powerful
concept called "spacetime"

If I think of space,

I know that I can find anything
if I know where it is

north-south, east-west,
and up-down, three points

But that doesn't mean
I can find it,

because I also have to know
where it is in time

And so if we start to think,

to know everything
about an event in the universe,

I have to know not just
its spatial coordinates,

but also its time coordinate

I can begin to think
about where it is in spacetime

Imagine a camera
filming an action,

capturing each moment in time
as a single frame

Einstein basically tells us,
"Think of the movie reel"

So you have
all these little pictures

Now, cut them apart one by one

and stack them on top
of each other,

you get this pile

And if you go up in the pile,
you go up in time

And now kind of glue them
all together into one big block,

and that block
has both space and time,

and that's the spacetime
continuum

It's almost looking at a movie
not frame by frame,

but seeing the whole movie
at once

They would now be
kind of two strands

going up in space and time,

and they would be
kind of spaghetti strands

In fact, we all are
spaghetti strands

moving in this spacetime

Einstein feels that spacetime
is the natural arena

in which his theory
of relativity should play out

But now he needs
sophisticated mathematics

By your standard or mine,
Einstein was good at math

He was Einstein

But he was not really
a mathematician per se

He didn't prove theorems,
he didn't pore over math books

He was a physicist

He did thought experiments

He thought of very tangible,
concrete situations

and what would happen

So when it came time for him
to really bear down

to the absolute cutting edge
mathematics of his day,

he required help

At university, Einstein had
skipped the geometry classes,

letting his friend Marcel
Grossman take notes for him

Grossman had excelled
in geometry

and was now chairman
of the math department

He suggests Einstein
uses advanced mathematics

in which the shape of space
and time could be curved

Because spacetime
has a geometry,

he thinks to himself,

"Well, maybe it's the actual
shape of spacetime itself

that is giving rise to gravity"

After months of work, Einstein
has an extraordinary idea

"What if spacetime
is shaped by matter,

and that's what we feel
as gravity?"

In struggling to figure out
what causes gravity then,

Einstein has this great insight

It is simply that a mass

distorts the shape of spacetime
around it

So you get rid of this force
of gravity,

and instead we have
curvature of spacetime

In Einstein's universe then,

if space were empty,
it would be flat

There'd be nothing going on

But as soon as you
put objects down,

they warp the space and time
around them,

and that causes a deviation
of the geometry

so that now things start moving

Everything wants to move
as simple as possible

through space and time

But Einstein tells us that mass
sculpts space and time,

and it's the curved motion
through this sculpture

that's the force of gravity

We have this feeling that

the reason I can feel pressure
on the soles of my feet,

that the reason things are going
to drop when I throw them,

are because there's a force

attracting us down
to the center of the earth

What general relativity tells
you is that's not the right way

to think about
what's going on there

What's really going on is that
your natural path in spacetime

would take you to the center
of the earth,

and what's actually happening is
the floor is getting in the way,

it's pushing you upwards

When we look at it, we go,
"Ah, the force of gravity"

But Einstein says, "No, no, no,
the curvature of spacetime"

It's a stunning insight

Just as an ant might feel forces
pulling it left and right

as it walks over crumpled paper

when it's simply the shape
of a surface dictating its path,

Einstein saw that what we feel
as the force of gravity

is in fact the shape of the
spacetime we're moving through

Einstein now has
everything he needs

to formulate his final theory
of gravity

But he makes a critical mistake

He misinterprets
one of his equations,

and unaware of his error,

continues working
on incorrect ideas

The point at which Einstein
is going to give

the most essential equations
of the theory,

Einstein considers
something like them

and then says,
"Ah, but these don't work,"

and then writes down
the wrong equations

What follows are alternations
of confidence and despair

as he convinces himself
that everything was fine

with this theory,
and then he realizes

that things aren't so good
with the theory

It is a long, dark period
for Einstein

as he struggles
to reconcile himself

with a theory
that is just not working

Two years later,
Einstein is in Berlin

At just 36 years old,
he has one of the most

prestigious positions in physics

But he is still struggling
with his theory

By 1915, he'd reached
the pinnacle of the profession

He's in the Prussian Academy

and a professor
at the University of Berlin

But his marriage
is falling apart,

his wife and his two kids
have moved back to Switzerland,

so he's pacing around
almost all alone

in this apartment in Berlin

And now he has a competitor

Einstein had enthusiastically
shared his ideas

with the brilliant mathematician
David Hilbert

Hilbert was so impressed,

he decided to work
on the theory himself

Einstein is now
in a race to the finish

with one of the world's
best mathematicians

This is unfolding

in a remarkably dramatic period
in history

World War I has begun
to ravage central Europe

Einstein is not just toiling
in the abstract;

he's toiling as the world
seems to fall apart

By November 1915, Einstein
is scheduled to present his work

in a series
of four weekly lectures

at the esteemed Prussian Academy

But he's struggling
to formulate his ideas

In the midst
of these challenges,

letters arrive
from his wife in Zurich

pressing the issue

of his financial obligations
to his family

and discussing contact
with his sons

As his lectures begin,

his theory is still
far from complete

The pressure on Einstein is huge

He would give a lecture,
revise it, give it again

Spot mistakes, correct them,
get up on the podium,

explain what was wrong
in the previous week's lecture,

correct it and then move on,

and then do that again and again
for four weeks running

His work to convince them
of the truth

of this absolutely radical
new theory of relativity

that he was proposing

is one of the most intense
periods of work

in the history of science

Somehow, he's able
to focus on his theory

with an incredible intensity,
and he makes his breakthrough

He tests his equations
on a problem

that Newton's theory of gravity
couldn't solve:

the orbit of Mercury

Mercury's path around the sun
has an anomaly

that Newton's theory
can't explain:

it deviates slightly
each time it goes round

Einstein calculates the orbit
with his new equations

The answer is correct,

exactly what astronomers
had observed

He'd found the final equations

for his general theory
of relativity

You have to think about the
hubris of being Albert Einstein

He had already thrown out
Newtonian mechanics

with special relativity,
and then he had gone off

on his little personal quest
to incorporate gravity

And at the end of the day,
he boils it down to a prediction

for a number
that had been observed:

the procession
of the orbit of Mercury

And, miraculously,
when the pages of algebra

work out to their end,
you get the right answer

And suddenly, it's not just
playing with equations anymore;

he realizes
this is how the world works

All this abstract nonsense is
the correct theory of reality

Einstein is at last able
to present a successful theory

That's a triumphant moment,

one of the great moments
in the history of physics,

and, for Einstein, a victory
very much against the odds,

and he'd won

On the 25th of November 1915,
Einstein lays out his findings

in his climactic fourth lecture
at the Prussian Academy

He presents general relativity

The theory can be written
as a single equation

It condenses
sprawling complexities

into a beautifully compact set
of symbols

So the formula is really simple:
G-mu-nu equals

G for the shape of spacetime

and T for the distribution
of mass and energy

So this very simple formula

captures all of Einstein
general relativity

It's a beautiful,
simple equation

but it's a lot of work
to unpack the symbols,

the mathematical symbols,

and see how
in this very simple formula,

the whole geometry
of the universe is hidden

It's kind of an acquired taste
to see the beauty

It's also a signature formula
for Einstein

The true mark of his genius
is that he combines two elements

that actually live
in different universes

The left hand side lives
in the world of geometry,

of mathematics

The right hand side lives
in the world of physics,

of matter and movement

And so perhaps the most powerful
ingredient of the equation

is this very simple
equal sign here,

these two lines that actually
are connecting the two worlds,

and it's quite appropriate
they're two lines

because it's two-way traffic

Matter tells space and time
to curve,

space and time tells matter
to move

When Einstein presented
his great theory,

few people understood it

He needed a way
to prove to the world

that the counterintuitive
features of his theory

were real

The general theory of relativity

made predictions of things
which looked really strange

For example,
the idea that light bends

when it passes near
a very heavy body

No one had ever looked for that

No one had ever observed it

Einstein was desperate,

desperate to get astronomers
to make that test

Einstein's theory predicts that

when light from a distant star
travels close to the sun,

the warped space around the sun
bends the light's path

In May 1919, the English
astronomer Arthur Eddington

traveled to the African island
of Principe to record images

that would show this phenomenon

What Eddington
had been able to do

was take photographs of stars

during a total eclipse
of the sun

so the moon blocked most
of the brightness of the sun

and little pinpricks of light
could be seen around the sun...

Otherwise, it would be lost
in the glare...

And Eddington and his colleagues
were able to measure

that the appearance
of those stars had been shifted

compared to where
they would have been

had that big mass of the sun
not been deflecting that light

from far away

So Eddington's able to show

that Einstein's general
relativity theory is right

and a revolution in science
has been accomplished

When the eclipse experiments
prove Einstein's theory right,

he rockets to fame
not just because he's explained

a new way of looking
at the universe,

but at the end of World War I,

you had the predictions
of a German scientist

be proven right
by some British astronomers,

and it becomes headlines
across the world

The New York Times says,

"Lights all askew
at the heavens,

men of science
more or less agog"

This is back when newspapers

knew how to write
great headlines

But Einstein kind of loves
this fact

that he is now an icon
of science

Einstein becomes
a worldwide celebrity,

the icon of genius
we still recognize today

The only person
who was more widely known

was Charlie Chaplin,

and they got on
like a house on fire

Chaplin said, "The reason
they all love me

"is because they understand
everything I do,

"and the reason they love you

"is that they don't understand
anything you do

Can you explain that?"

And Einstein said

But in 1930s Berlin,
the Nazi party is gaining power

As a Jewish scientist, Einstein
becomes increasingly caught up

in the political turmoil

Einstein's theories
became a target

They were deemed
aesthetically repugnant

to a kind of Aryan sensibility

So people attacked not just
Einstein the Jewish scientist,

but they would actually
have people

denouncing general relativity

In January, Nobel Prize
mathematician Albert Einstein

visited California

He begins to make trips
to America,

where he is welcomed
with open arms

Germany's loss, America's gain

And in 1933,
he settles in Princeton

with his second wife Elsa,

taking up a position at the
Institute for Advanced Study

Today, the Institute is headed
by Professor Robbert Dijkgraaf

He basically was still
very much by himself,

just actually
as he was in Berlin,

just concentrating
on his deep ideas

and struggling
with understanding the universe

Of course, his office was here

At the Institute,

Einstein worked to unify
his theory of gravity

with the other laws of physics

With Einstein,
you see this phenomena

you see with many great
scientists...

That they climb
this very high mountain

and instead of celebrating
their success,

they're privileged to see
a much wider landscape,

and they see all these mountains
behind it

And I think he was
very much aware

how much still there was
to be done

Till the very last days
of his life,

he was trying to push
these equations

and find a description
of nature, all of nature,

in terms of the geometry
of space and time

But general relativity was
fading from mainstream science

Physics was now focused

on the quantum theory
of atoms and tiny particles,

a theory incompatible
with Einstein's ideas,

but one that could be tested
in the lab

Most of general relativity

was then beyond the reach
of experiment

When Einstein died in 1955,
age 76,

his theory was seen as one

with little hope
of future discovery

The best theories in physics
always take us to places

where the people who invented
them didn't imagine

And a truly wonderful theory
like general relativity

predicts all sorts of things

that Einstein didn't conceive of

The theory has a life of its own

We understand general relativity
much better right now

than Albert Einstein ever did

Liftoff of space shuttle
Discovery

with the Hubble space telescope,
our window on the universe

Today, 100 years
after general relativity

was first presented

Telescopes released,
okay, thank you

new technology
is allowing us to explore

the most remarkable predictions
of the theory:

an expanding universe,

black holes,
ripples in spacetime,

and perhaps the most bizarre,

the idea that not just space,
but time itself

is distorted by heavy objects

To prove it,
a team of physicists

is carrying out
a remarkable experiment

They're using two atomic clocks
that are in near perfect sync,

accurate to a billionth
of a second

The master clock
remains at sea level

while they take the second clock

to the top of New Hampshire's
Mount Sunapee

General relativity tells us that
as you move away

from the mass of the planet,
time should speed up

After four days
at the top of the mountain,

the test clock is taken back
to the lab for comparison

There, they compare it
to the sea level master clock

We'll put that one
into Channel A

Four days ago,
they were ticking in unison

Master clock in Channel B

But what about now?

You guys ready?

This is it right here

The time interval counter
is gonna show us

the time difference
between these two clock ticks

20 nanoseconds

You can see the time
difference between them

represented here graphically

of the clock that was up
at the mountain for four days

and our master clock

Gravity, the distortion
of space and time,

becomes weaker as you move away
from the surface of the planet

So while the test clock
was up the mountain,

time sped up

It's now 20 nanoseconds,

20 billionths of a second,
ahead of the sea level clock,

This is really awesome

This distortion of time
has surprising consequences

The Global Positioning System,

something we all take
for granted,

wouldn't work without
taking this into account

The engineers who built
the GPS system

we use every day
to pinpoint locations

had to ensure it adjusted
for the time difference

between clocks on satellites
and receivers on the ground

If they didn't, GPS would be off
by six miles every day

Your GPS units

use the results
of general relativity

When you navigate in your car,

you perhaps should give a word
of thanks to Uncle Albert

Of all general relativity's
predictions

that new technology
has allowed us to explore,

there's one that's
straight out of science fiction:

a black hole

Everything that we're
familiar with in ordinary life

is made from matter

But not black holes

Black holes are made
from warped space and time

and nothing else

A black hole is an object
that is spherical,

like a star or like the Earth,

with a sharp boundary
called the horizon

through which nothing
can come out

So it casts a shadow
on whatever is behind it

It's just a black, black shadow,
unbelievably black

This simulation shows
the distortion of starlight

around a black hole

Even though Einstein knew his
theory predicted black holes,

he found it hard to believe they
would really exist in nature

In the 1960s,
Professor Kip Thorne

worked on the mathematical
concept of black holes

The idea made sense on paper,

and he began to feel that these
science fiction-like objects

might actually be real

Must be here somewhere,
it's in one of these piles

Kip Thorne made a bet with
fellow physicist Stephen Hawking

about whether or not
a strong source of x-rays

known as Cygnus X-1
was in fact a black hole

I think it's in here

Yeah, here we go, relativity,
stars and black holes

Yeah, there it is

So that is a copy
of the famous bet

"Stephen Hawking
bets a one-year subscription

"to Penthouse magazine

"against Kip Thorne's wager
of a four-year subscription

"to a political magazine called
Private Eye

"that Cygnus X-1 does not
contain a black hole of mass

"above the Chandrasekhar Limit

It's witnessed this 10th day
of December 1974"

Stephen Hawking had
a terribly deep investment

in it actually being
a black hole,

and so he made the bet against
himself as an insurance policy

that at least he would get
something out of it

if Cygnus X-1 turned out
not to be a black hole

The evidence mounted thereafter

over the period
of the '70s and '80s,

and in June 1990,

Stephen snuck into my office
and signed off on the bet,

that finally, the evidence
was absolutely overwhelming

that Cygnus X-1
really is a black hole

And Penthouse magazine arrived

He sent me the British version
of Penthouse,

which was ever
so much more raunchy

than the American Penthouse,
actually

Enough to make my face turn red
when I received it at first

Today, we have evidence
suggesting that

there are millions of black
holes in our galaxy alone

But perhaps the most profound
prediction of general relativity

is that our universe
had a hot, dense beginning

that we call the big bang

The discovery that distant
galaxies are moving away from us

and that there's a background
radiation permeating space

provided evidence
for the big bang

and a universe that's growing

With this picture
of an expanding universe,

there were natural questions

Is the universe slowing down
as it expands?

Is it so dense that someday,

it will come to a halt
and collapse?

Will the universe come
to an end?

These seemed like good questions

To find answers, in the 1990s,
Saul Perlmutter and his team

observed exploding stars,
called supernovae,

to track the growth
of the universe

When we made the measurement,
we discovered that the universe

isn't slowing down enough
to come to a halt

In fact,
it's not slowing at all;

it's speeding up!

The universe is expanding
faster and faster

But what's pushing it?

In order to explain
the acceleration of the universe

within Einstein's theory
of general relativity,

we're considering an energy
spread throughout all of space

that we've never seen before

We don't know what it is

We call it dark energy

And, if so, it would require

something like 70%
of all the stuff of the universe

to be in this form of previously
unknown dark energy

So this is a lot to swallow,

and you might imagine that
at that point,

you should go back
and revisit your theory

The problem is that Einstein's
theory is so elegant,

and it predicts many, many,
many digits of precision,

that it's very, very difficult
to come up

with any other theory

There is one final prediction
of general relativity

that remains untested:
gravitational waves

There are huge things
in the universe happening,

like black holes colliding
or stars exploding,

and they create these
gravitational waves...

Waves in the shape
of space and time

that travel through the universe
at the speed of light

And so right now,
the space around me

is being squeezed and stretched
by gravitational waves

just getting here
from, let's say, two black holes

colliding a billion
light years away

But the squeezing and stretching
is so minute,

I absolutely could not
personally detect it

And so what we're trying to do
is build an instrument that can

In Louisiana
and Washington state,

a vast experiment called LIGO

is in the final phases
of calibration

It's hoped that laser beams
traveling two-and-a-half miles

between precisely aligned
mirrors

will measure
the squeezing of space

caused by gravitational waves

This could open up an entirely
new window on the universe

For 100 years,
general relativity

has been proven to be correct
time and time again

But Einstein himself knew that
his great theory had limits

It remains incompatible

with the quantum world
of tiny atomic particles

Here at the Institute
for Advanced study,

where Einstein worked,

the world's leading
theoretical physicists

are trying to solve the problem
Einstein never could:

finding a single set of rules

that applies to both the cosmic
and atomic scales

A unified theory

The Holy Grail of physics

We are now in what at this time
is the school of physics

So here,
people are still struggling

with many of the same issues
that Einstein would struggle

and are still trying to capture
the laws of the universe

from the very small to the very
large in a single equation

And it's still blackboards
that are the weapon of choice

The brightest minds of the world
are coming here

to work 24 hours,
seven days a week,

struggling to grasp the great
mysteries of the universe

And I think we are still driven
by the same dream:

that at some point,

we can capture everything
in elegant mathematics

100 years after Einstein

transformed our understanding
of nature,

the stage is set
for the next revolution

When we finally move
beyond Einstein,

it might be another singular
genius that comes along...

Someone struggling in a poor
school in Kenya right now

that we don't know about

Or it might be
20 different people

with 20 different points of view

gradually building
brick-by-brick

to finally figure out
a more comprehensive view

that includes general
relativity in it

I think the most important thing

that you learn from Einstein
is just the power of an idea

If it's correct, you know,
it's just unstoppable

It's extremely encouraging that
he was able with pure thought

to solve the riddle
of the universe

Once we had general relativity,

the world changed completely

Our point of view on the world
changed completely

I mean, the origin
of the universe

is a prediction straight out
of general relativity

We didn't have that before

I often wonder
what Einstein would make

of today's theoretical physics

I think he would really be
saying, you know,

"Get on with it, get the right
story, get the details right"

You know, you have
the huge universe,

and it obeys
certain laws of nature,

but where in the universe are
these laws actually discovered?

Where are they studied?

And then you go
to this tiny planet

and there's this one individual,
Einstein, who captures this

And now there's
a small group of people

walking in his footsteps
and trying to push it further

And I often feel,

well, it's this small part
of the universe

that actually is reflecting
upon itself,

that tries to understand itself