Einstein and Hawking: Unlocking the Universe (2019) - full transcript
In the 1960s,
radio telescopes around the world
started to pick up strange signals
from outer space.
They appeared to be coming
from tiny objects of massive density,
neutron stars.
These mysterious objects
had been predicted by Einstein's
theory of relativity
and their discovery meant
other predictions of relativity
might also exist...
objects like black holes.
Understanding these mysterious
monsters of the universe
kick-started the careers
of a young group of physicists
including Stephen Hawking.
It was a golden age, relativity,
as we sorted out,
under Hawking's leadership,
the theory of black holes.
It soon became clear that black holes
were very peculiar places.
We think of a black hole as a thing,
as an object,
but really
it's a region of space time.
A black hole is a region of space
time where gravity is so strong
that once you enter that region,
you just cannot ever leave it.
Black holes are fissures
in the fabric of the universe,
surrounded by an invisible boundary
called the event horizon.
Nothing that crosses that horizon
can ever get away.
Falling through the event horizon
is a bit like going over
Niagara Falls in a canoe.
If you are above the Falls, you can
get away if you paddle fast enough
but once you are over the edge,
you are lost.
A black hole is really defined
by that event horizon.
It separates us
fundamentally and for ever
from the inside of the black hole.
You can fall in
but you cannot come out.
The consequence is once something
has fallen into a black hole,
it appears to be lost
from the universe for ever.
From the outside, you can't tell
what is inside a black hole.
You can throw television sets,
diamond rings
or even your worst enemies
into a black hole
and all the black hole will remember
is the total mass
and the state of rotation.
It was these monsters that
Stephen Hawking was working on
in Cambridge in the mid 1970s.
And in 1974,
he made an enormous breakthrough.
Up to 1974, everyone,
including me,
thought that nothing
could get out of a black hole.
Then I discovered
that the uncertainty principle
of quantum mechanics
allowed particles to leak out.
By adding quantum mechanics, Hawking
made the stunning discovery
that actually black holes
could evaporate.
Black holes are not
what you thought they were.
Black holes can actually radiate.
Yeah, that was an in-your-face
shocking idea that he put forward.
Quantum mechanics implies
that the whole of space
is filled with pairs of virtual
particles and anti-particles
that are constantly materialising in
pairs, and annihilating each other.
Now in the presence of a black hole,
one member of a pair of virtual
particles may fall into the hole,
leaving the other member
without a partner.
As particles escape
from a black hole,
the hole will lose mass and shrink.
Eventually the black hole will lose
all its mass and disappear.
The discovery that black holes
emitted particles
was soon named Hawking Radiation.
It showed that black holes were even
stranger than we had imagined.
How can a black hole evaporate?
It seemed so peculiar and very
counter-intuitive but it made sense.
The calculations were checked over
and over again and it made sense.
This is completely counter
to everything
we thought that we understood
about black holes in the year 1970.
By combining general relativity
with quantum mechanics,
Hawking had shown the enduring power
of Einstein's theory.
But as Einstein himself
would discover,
that theory also had a dark side.
It could be used to unleash
devastation on the earth.
Back in the 1920s, Einstein found
that interest in his work
had extended beyond
the world of theoretical physics
and into the realm
of populist politics.
Long before there was even
a formal Nazi party,
as early as spring of 1920,
there were rallies to denounce
not just Albert Einstein
but rather to denounce
general relativity.
They would rent out sports arenas
and opera houses
and large, large stadiums,
thousands of people in attendance,
to basically chant
'Down with warping space time.'
It was seen as a symbol
of all that had gone wrong
with so-called Jewish physics.
It became clear it was not
going to be safe for him.
After the Nazis came to power,
Einstein fled Germany in 1933
and settled here in Princeton,
New Jersey,
working at the Institute
for Advanced Study.
And as a lifelong pacifist,
he was appalled
at the prospect of another war,
especially since he knew his own work
could have a devastating impact
on its outcome.
Einstein did not want to get
that involved in the war effort.
I think everyone was extremely
surprised that this 1905 paper,
E = MC2, could have an implication
for killing people.
So we come to Einstein's most famous
equation, E = MC2.
And like many of his equations,
it has this magical property
of equating two things that you
wouldn't expect to be equal.
On the left hand side we find E,
the energy.
On the right hand side, M, the mass.
And so this equation tells us
that energy and mass
are essentially the same.
They're equivalent.
They can be exchanged.
And the exchange rate
is C squared.
C is the speed of light,
it's huge.
So C squared
is a tremendously large number.
So one way to read the equation
is that a huge amount of energy
can be converted
into a small amount of matter
but reading the equation
from the opposite end,
it tells us that a small amount
of matter can be converted
into a huge amount of energy.
The power of E = MC2
went far beyond the theoretical.
In the early 1920s, Einstein's friend
Arthur Eddington realised
that this famous equation was the
secret to how stars, like our sun,
produced such vast amounts
of heat and light.
Deep in the hearts of stars,
pressures and temperatures
are so high that hydrogen nuclei
slam into each other,
fusing and eventually creating
helium nuclei.
And in that process, a tiny amount
of mass is converted into energy.
Albert Einstein realised
that perhaps we could harness
that process here on Earth
and create energy of our own.
Or create a weapon.
Worried the Germans had already
started a nuclear programme,
Einstein and fellow physicist
Leo Szilard
wrote to President Roosevelt,
urging him to develop a bomb.
Roosevelt responded by setting up
the Manhattan Project.
They achieved their goal
in just three years.
This is the Trinity monument.
On July 16th 1945, the world's
very first nuclear bomb
was set off right here in this spot.
The bomb, nicknamed Gadget,
was winched to the top
of a hundred foot tower
that stood right here.
The observers retreated
and just before dawn,
the bomb was detonated.
At 5.29 am, the device exploded
with an energy equivalent
to twenty kilo-tonnes of TNT.
The roar of the shock wave was felt
over one hundred miles away.
The surrounding mountains were
illuminated brighter than daytime
and the mushroom cloud reached
seven and a half miles in height.
All that power was released
when inside the bomb,
just 0.9 grams of matter
were converted into energy
and that's the power of E = MC2.
Just three weeks later, on August 6th
1945, another bomb was dropped
over the Japanese city of Hiroshima.
At exactly 8.15 in the morning,
0.6 grams of matter
was converted into energy,
incinerating seventy thousand people.
The devastating power of Einstein's
equation had been unleashed.
Now it's always been a mixed legacy
for the history of physics, right?
Like we like to think of ourselves
discovering secrets of the universe
not as blowing things up, but there
is this necessary interplay
between the discoveries we make
and the technological capabilities
that we have here on Earth
that physicists have to accept,
and of course Einstein always had
mixed feelings about it later on
because he was at heart a pacifist.
For the rest of his life,
Einstein campaigned for nuclear
disarmament and peace.
The nuclear bomb
was a devastating demonstration
of how Einstein's theories could be
used to practical effect.
Ever since then,
humanity has been building
increasingly complicated machines
that use Einstein's theory
not for destruction, but to unlock
the mysteries of the universe.
This is the entrance
to the Large Hadron Collider.
Buried deep below
the Swiss/French border,
it is the world's biggest machine.
Sudan Paramesvaran is a scientist who
uses the LHC to travel back in time.
The point of the LHC
is to try and understand
how the universe
came into its current state
from the Big Bang
all those billions of years ago,
and one way that we can do that
is to try and re-create
some of those early conditions.
Sudan's work relies on
the concept of time dilation,
developed by Albert Einstein.
Time dilation is only noticeable
at close to the speed of light
but in the LHC,
we can see it in action.
Beams of protons are fired
through these tubes
and smashed into each
other at very high speed.
In the middle of this pipe is where
the actual protons are travelling.
We accelerate them using
very powerful magnets.
They're actually
travelling round the ring
eleven thousand times a second,
very, very close
to the speed of light.
So when the protons collide,
they actually smash up into lots
of little different things.
A lot of new particles are created.
We think the particles
created in these collisions
are similar to those that existed
in the moments after the Big Bang.
Studying them can help us
understand the early universe
and that's where
time dilation comes in.
Okay, so what we have here
is a visual representation
of a collision.
The protons are colliding right
in the middle of our detector
and then everything comes out
from that point.
Each of these tracks
represents an individual particle
created in the collisions.
Many of them blink out of existence
in a fraction of a second.
This is actually
the decay of a B-meson
and its typical lifetime is only a
millionth of a millionth of a second
so it's tiny, and that would make it
very difficult for us
to actually investigate it.
It would decay very close
to the primary point here.
Now because it's travelling
close to the speed of light,
its clock is running
a little bit slower.
This means that it's actually able
to travel this distance before decay
and so the fact that
it undergoes time dilation
gives us
an avenue of physics to explore
which we otherwise
wouldn't be able to do.
The time dilation we see in the LHC
is Einstein's theory of relativity
in action...
this time for peaceful means.
We have answered many mysteries
about the universe
using Einstein's theories.
But even in the 21st century
there are still more discoveries
to be made...
discoveries that will
elegantly tie together
the work of Albert Einstein
on relativity
and Stephen Hawking on black holes.
Black holes are stranger
than anything dreamed up
by science fiction writers
but they are firmly
matters of science fact.
Despite all our advances
in technology,
we have still never seen a black hole
and it's that search for
an elusive glimpse of a black hole
that brings Dan Marrone
to the mountains of Arizona.
Black holes are one of those things
that I feel like everyone
is interested in, right?
The fact that we've never even
seen one is kind of amazing.
We're so confident they're there
but yet show me a picture
and you can't.
Dan is on a mission to do something
no one has ever done before,
take a picture of a black hole.
Ordinarily, it would be impossible
to photograph a black hole,
like picking out a shadow
on an already-dark sky.
But Dan is hoping to capture a black
hole in a particular phase of life,
while it is feeding.
The gravitation pull
of black holes is so strong
that they can consume
entire stars.
This simulation shows what we think
happens as a star is ripped apart.
What you see is the bright splatter
of the debris
falling around the black hole
from the neighbouring star,
and it turns out,
maybe even ironically,
that the darkest objects
fundamentally conceivable
become the brightest beacons
in the universe.
The event horizon, where the
whirlpool is at its fiercest,
is one of the most extreme
environments in the universe.
It is what Dan and his colleagues
are trying to take a picture of.
This is the sub-millimetre telescope
on Mount Graham in Arizona.
A radio telescope,
it can probe the depths
of the universe in broad daylight.
We'd like to see that material
circling the drain and disappearing.
We'd like to see the light itself
not escaping,
a shadow in front of the black hole
where the light
is disappearing into it.
Dan's sights are set
on the very heart of our galaxy.
Astronomers have been tracking
the motion of the stars
around the galactic core
for more than twenty years.
How's the weather this evening?
The weather's good.
The enormous speed
at which they are moving
suggests that they are orbiting
something huge and unseen.
They believe it is
a super-massive black hole,
over forty million kilometres across
and four million times
the mass of our sun.
It is known as Sagittarius A♪.
The event horizon around it
should be one of the brightest spots
in the galaxy...
but it is still so small
and so far away
that to image it takes
the largest telescope ever built.
So right now the telescope
is pointed at Sagittarius A♪.
We have to look through
the entire plain of the galaxy
and so if you look
with a visible light telescope,
you can't actually see it
as a black hole.
All the dust in the way
blocks the light
and so we have to do this
with a radio telescope.
And in fact we're not
just looking through one
but we're looking with a whole array
of them scattered over the earth.
The event horizon telescope
is a huge network.
As well as this dish on Mount Graham,
there are dishes in Europe,
on Hawaii, in Chile
and at the South Pole,
all of which are simultaneously aimed
at the very centre of the galaxy.
When the data
from all of them is combined,
it creates a telescope
the size of the Earth.
It is hoped it could soon produce
our first detailed view
of an event horizon
and the material around it
spiralling into oblivion.
But while we wait
for that first elusive image...
there is already a technology
that can detect Stephen Hawking's
beloved black holes
and may answer
one of the final great mysteries
of Einstein's theory of relativity.
These are offices at LIGO.
We can use any of these rooms
if you want
but if you want my office,
we're heading there.
It's full of junk.
This is the office they give
emeritus old professors,
that's what they do with them,
so a lot of my papers and junk
is all around.
There's a picture of my mentor
right over there.
You can see him,
his name is Jerrold Zacharias.
He's the first guy who ever
said to me that, you know,
you're not as dumb as you look.
That was very important.
You need somebody in your life
to tell you that.
Rainer Weiss, Rai to his friends,
is now a Nobel prize-winning
Emeritus Professor at MIT
but in 1967
he was just a junior faculty member
who was fascinated by a particular
piece of Einstein's theory...
gravitational waves.
In 1916,
Einstein himself had calculated
that objects moving through
the fabric of space-time
should cause it to ripple,
like waves on a pond.
At first Einstein thought
that these waves would be so tiny
they would be
impossible to measure.
Later in life, he was not sure
they existed at all.
If you ask me whether there are
gravitational waves or not,
I must answer that I don't know but
it is a highly interesting problem.
Rai thought gravitational waves
did exist
and has spent a lifetime
trying to find them
so he came up with a system
that could potentially detect
the most miniscule waves
in space-time.
It was called laser interferometry.
So here's the idea.
There's a laser
which is the cylinder.
There is something called a beam
splitter which divides the light.
Half of the light will get reflected
to a mirror that's over here,
and then sent back
to this beam splitter,
and the other half hits this mirror
and comes back to the beam splitter.
Then two beams will head
towards a photo detector
and you'll see something
interesting.
No light goes to the photo detector.
Light cancels.
Now what happens is you change the
length on one arm, make it longer,
make the light shorter
on the other arm.
You see light does go
to the photo detector
when the paths are not equal
any more and that,
the fact that light goes
to the photo detector here,
when the paths are no longer equal
and may have been disturbed by that
gravitational wave to do this,
that's the way
the detection is made.
It's really as simple as that.
If Rai's calculations were right,
his system would be able to pick up
movements in the mirrors
of just
a few trillionths of a metre.
I heard about the idea,
I did some numbers
and it was obvious that Rai
had gone crazy or something.
I just couldn't believe
that he could really,
anyone could really pull this off
and then I spent the rest
of my career eating crow
and trying to help him pull it off.
When Kip Thorne,
a theoretical physicist
and close friend of Stephen Hawking,
joined the project,
his job was to work out whether there
were any events in the universe
powerful enough to produce
gravitational waves
that Rai's system could detect.
As a theorist,
I had the best handle anyone had.
It was not a great handle
but the best handle anyone had
on the strengths of the sources.
What Kip needed was a source
of gravitational energy
so strong it would shake the fabric
of the entire universe,
the sort of energy
that would be released
if two black holes collided.
You began with two massive stars.
This one collapsed
and formed a black hole
and then later that one collapsed
and formed a black hole,
and then create a binary
going around each other.
That binary emits
gravitational waves,
spirals the other closer and closer
and the black holes collide.
But we'd never seen
pairs of black holes.
We couldn't see pairs of black holes
because black holes
don't emit any electromagnetic waves
as they go round each other, they
only produce gravitational waves,
so the only way we would ever
see them was with our detectors.
To try to detect the gravitational
signals from colliding black holes,
Kip Thorne and Rai Weiss embarked
on one of the most expensive
scientific ventures ever attempted.
After years of planning,
construction started in Livingston,
Louisiana in 1994.
The lasers would be fired
up these arms,
each four kilometres long,
before reflecting off the mirrors
and returning to sensors
so finely tuned they could in theory
detect a shortening of the arms
caused by gravitational waves
of just a million million millionth
of a metre.
Three thousand miles away
in Hanford, Washington,
an identical facility was built.
For any detection to be confirmed,
it would have to be picked up by both
detectors at the same time.
The instruments were activated
in 2002.
For eight years
they listened to the universe.
By 2010, they had heard
absolutely nothing.
For the LIGO team,
the pressure was mounting.
We had convinced the NSF
and Congress
that they should spend
a billion dollars on this
and we had nothing to show for it.
Doubling down, they shut the project
for another five years
to install an even more precise
set of detectors.
It was a high stakes gamble.
In September 2015,
almost exactly a hundred years
after Einstein published
his theory of general relativity,
Rai Weiss's detectors
were reactivated.
Just two days later, both sites
recorded an unusual signal.
Ladies and gentlemen, we have
detected gravitational waves.
We did it!
After working on the problem
for almost fifty years,
it was a massive vindication
for Rai and his friend Kip.
I want to first remind you
of Einstein's 1915 big discovery,
was the, really the formulation
of these field equations.
He applied these field equations
to the idea of gravitational waves.
Almost the first day
of the real run,
we saw what is in front of you
on the screen here,
and let me play it for you.
That isn't much. It's a little blip.
That's all you heard.
But let me change, this is a trick.
We made it
so that you can hear it better
by changing the frequency
of everything.
And that chirp is the characteristic
of this particular source,
and that was something
which was quite astounding to us.
Long, long ago, in a galaxy
far, far away, a pair of black holes
each around thirty times
the mass of the sun
circled each other,
moving faster and closer.
The point when we first see
the gravitational waves,
they may be
a thousand kilometres apart,
each one roughly
a hundred kilometres in size
and they're going around and around
creating stronger and stronger
warping of space and time.
As they near each other,
they warp space and time in a wild
way, very much like a storm at sea.
And then, the black holes coalesce.
In that instant,
three times the mass of the sun
is converted into pure energy...
but none of that energy
is emitted as light.
It is all released
as gravitational waves.
So there's a huge amount of energy.
Turns out to be fifty times higher
than the total power output
of all the stars in the universe
put together.
By far the largest explosion
in terms of power output,
except the Big Bang,
that we ever had any evidence of.
As they travel through space at the
speed of light, the waves dissipate,
getting smaller and smaller
until 1.3 billion years later...
they passed through Rai's detectors.
I wish I could have
told Einstein directly
that we had seen a black hole
doing this.
That would have been
just a wonderful experience,
to see the expression on his face
after we'd told him that.
The discovery of gravitational waves
is the ultimate triumph
of Einstein's theory of relativity,
a theory that has been repeatedly
tested and proven to be correct.
Einstein died in 1955.
In just half a century, he had
re-imagined the entire universe.
Albert Einstein enters the world
when it's one way
and by the time he leaves the world,
it's completely different.
We now live in a world
where we understand
the universe had a beginning
and we can tell
how long ago it was.
Those are stunning achievements
and stunning shifts,
both in our scientific
and our cultural perspective.
He was a figure that is rare,
you know, once in a hundred years,
maybe once in five hundred years.
Stephen Hawking's greatest
contribution to physics
was his discovery
that black holes could evaporate.
If his theory of Hawking radiation
was correct,
it would have profound implications
for the way we understand
the entire universe.
In Haifa, Israel,
Jeff Steinhauer has spent a decade
searching for evidence
of Hawking radiation,
using artificial black holes
that he makes out of sound.
So here we go.
All the equipment that you see
is for the sake
of this small point right in there
where the artificial black hole is.
We start out with these very cold
atoms in this tube-like volume
and it's only .1 millimetres long.
We then apply a blue laser beam
which causes some of the atoms
to be accelerated to supersonic
speed and so in this region,
they're flowing slower
than the speed of sound
and here they're flowing faster
than the speed of sound.
So here, in the supersonic region,
a sound wave trying to move against
the flow will actually fall back.
It can't go forward
against the very fast flow.
In his artificial black hole,
Jeff has created an event horizon.
Once the sound wave is over
that line, it cannot escape,
just as light cannot
escape a real black hole,
and when Jeff takes photos
of his sonic event horizon,
he sees something very strange, the
tell-tale signs of Hawking radiation.
You see this band?
This band is an observation
of sound waves being emitted
from the horizon of the black hole.
This experiment is the first time
that Hawking radiation
has been observed.
It is an amazing discovery which
suggests that Hawking radiation
may be a fundamental feature
of black holes.
If that's true,
it means that given enough time,
all black holes will evaporate
and that prospect has troubling
implications for the rest of physics.
A central principle of all physics,
in fact it's written into
the laws of quantum theory,
is that information
cannot be destroyed.
Consider this newspaper.
It has information on every page
and if I were to throw it
on this fire,
it's quickly consumed by the flames
and it looks like the information
is destroyed
but if I were able
to take all the ashes,
collect all the smoke
and all the heat,
and analyse and reconstruct
the past of all the particles,
then I should be able
to reconstruct what's on every page.
And this is because
the laws of physics allow us
to tell the entire future
and the entire past of any system.
No one's saying it's easy
but it is possible as long
as you have all the information.
We call this determinism.
Scientists believe that
the principle of determinism
applies to all systems,
no matter how big or complex.
It should even apply
to the entire universe.
So if I were to somehow
know the position and state
of every particle in the universe,
I could apply the laws of physics
and know the entire
future of the universe
and the entire past of the universe.
But there is a catch because if,
as Hawking predicted,
black holes could evaporate in such
a way that they leave behind
no trace of the material
that was inside,
then information could be lost
and even if only a small amount
of information is lost,
then everything is lost.
You can't re-construct the past
and you can't predict the future.
It seems trivial but actually
it was a massive problem
that shook
the very foundations of physics
and this became known
as the information paradox.
If determinism, the predictability
of the universe,
breaks down with black holes,
it could break down
in other situations.
Even worse,
if determinism breaks down,
we can't be sure
of our past history either.
The history books and our memories
could just be illusions.
It is the past
that tells us who we are.
Without it, we lose our identity.
The information paradox has troubled
physicists for decades.
If Hawking was right
and black holes did destroy
the information they contained,
then they would also destroy
almost everything we know
about modern physics.
It created this big rift
between those who were adherents
to quantum thinking
and those who were
adherents to relativity,
the quantum people saying
the information must get out.
We don't know how,
we don't see how, but it must.
And the relativists saying
you know maybe,
maybe the information's just lost.
I'm inclined to suspect
that information is truly lost
down black holes
but mine is the minority
point of view.
Who cares if black holes evaporate
and swallow little bits of
information as they go?
But in the forty-plus years
since then,
it's kind of been like a snowball.
The importance of this problem
has grown and grown.
The information paradox was a problem
that Stephen Hawking worked on
for over four decades
and in 2015, he came up with
a major breakthrough.
Many scientists felt that
information should not be lost
but no one could suggest a mechanism
by which it be preserved.
The arguments went on for years.
Finally, I found what I think
is the answer.
I realised that a black hole
can store the information
in what is called super-translations
of the horizon.
Hawking's new idea was that as
objects fall into a black hole,
they disturb the event horizon,
leaving behind
a pattern of turbulence
which could preserve the information
about everything
that's fallen inside.
I am now working with my colleagues,
Malcolm Perry at Cambridge, and
Andrew Strominger at Harvard,
on whether this
can resolve the paradox.
If information
is stuck on the horizon,
it has not fallen
into the black hole
and you can't directly observe it
from outside
but what will happen is it will
influence the Hawking radiation
that comes out of the black hole
and that may be enough to help you
resolve the information paradox.
When we first came upon it,
we were up until late at night.
He said he hadn't been
this excited in forty years...
and he started working on it
basically full time.
Together, the scientists wrote
three papers on the subject...
edging closer to a solution
to the information paradox.
It was Hawking's last great idea.
Sadly this is the last paper
that Stephen wrote.
He was fully engaged with it
right till the very end.
Hawking died in March 2018
at the age of 76,
over half a century after he had been
given just two years to live.
He was kind of magical to be around.
When I miss him the most
is when we figure something out.
I'd like to tell him.
Such was his contribution to science,
his ashes were interred
in Westminster Abbey
alongside Isaac Newton
and Charles Darwin.
Stephen was one of the great minds
of the 20th century
in terms of his impact
on our understanding
of the laws that govern
the universe.
I miss Stephen greatly.
It was a tremendous loss
for me personally.
His gravestone engraved
with the equation describing
Hawking radiation.
Stephen Hawking's legacy
will clearly be a vital part
in the unfolding story
of putting gravity
and quantum mechanics together.
And as we go forward,
everything that we do
in some sense will go right back
to Stephen Hawking.
Time.
We think of it
as regular as clockwork,
ticking out the steady
progress of the universe,
but time is not constant.
It holds the key
to the secrets of the universe
and the two people who helped us
unlock those mysteries
are joined by
a cosmic coincidence of timing.
On March 14th 1879,
Albert Einstein was born.
Einstein gave to us all
a set of tools
that literally help us organise
the world around us to this day.
And on March 14th 2018,
Stephen Hawking died.
I think Stephen should be remembered
as one of the most remarkable people
of the 21st century.
He is someone who in a thousand
years from now will be remembered.
His name will be known.
That's not true for most of us.
Between them, they have transformed
our understanding
of the entire universe.
As a working physicist,
I look at these two giants
and I have nothing but gratitude.
They revealed the world to be so
much more than it would have been,
and without them,
who knows if we would have gotten
to this wondrous stage
in our understanding.
I have a real feeling of achievement
that I made a modest but significant
contribution to human knowledge
despite my condition.
radio telescopes around the world
started to pick up strange signals
from outer space.
They appeared to be coming
from tiny objects of massive density,
neutron stars.
These mysterious objects
had been predicted by Einstein's
theory of relativity
and their discovery meant
other predictions of relativity
might also exist...
objects like black holes.
Understanding these mysterious
monsters of the universe
kick-started the careers
of a young group of physicists
including Stephen Hawking.
It was a golden age, relativity,
as we sorted out,
under Hawking's leadership,
the theory of black holes.
It soon became clear that black holes
were very peculiar places.
We think of a black hole as a thing,
as an object,
but really
it's a region of space time.
A black hole is a region of space
time where gravity is so strong
that once you enter that region,
you just cannot ever leave it.
Black holes are fissures
in the fabric of the universe,
surrounded by an invisible boundary
called the event horizon.
Nothing that crosses that horizon
can ever get away.
Falling through the event horizon
is a bit like going over
Niagara Falls in a canoe.
If you are above the Falls, you can
get away if you paddle fast enough
but once you are over the edge,
you are lost.
A black hole is really defined
by that event horizon.
It separates us
fundamentally and for ever
from the inside of the black hole.
You can fall in
but you cannot come out.
The consequence is once something
has fallen into a black hole,
it appears to be lost
from the universe for ever.
From the outside, you can't tell
what is inside a black hole.
You can throw television sets,
diamond rings
or even your worst enemies
into a black hole
and all the black hole will remember
is the total mass
and the state of rotation.
It was these monsters that
Stephen Hawking was working on
in Cambridge in the mid 1970s.
And in 1974,
he made an enormous breakthrough.
Up to 1974, everyone,
including me,
thought that nothing
could get out of a black hole.
Then I discovered
that the uncertainty principle
of quantum mechanics
allowed particles to leak out.
By adding quantum mechanics, Hawking
made the stunning discovery
that actually black holes
could evaporate.
Black holes are not
what you thought they were.
Black holes can actually radiate.
Yeah, that was an in-your-face
shocking idea that he put forward.
Quantum mechanics implies
that the whole of space
is filled with pairs of virtual
particles and anti-particles
that are constantly materialising in
pairs, and annihilating each other.
Now in the presence of a black hole,
one member of a pair of virtual
particles may fall into the hole,
leaving the other member
without a partner.
As particles escape
from a black hole,
the hole will lose mass and shrink.
Eventually the black hole will lose
all its mass and disappear.
The discovery that black holes
emitted particles
was soon named Hawking Radiation.
It showed that black holes were even
stranger than we had imagined.
How can a black hole evaporate?
It seemed so peculiar and very
counter-intuitive but it made sense.
The calculations were checked over
and over again and it made sense.
This is completely counter
to everything
we thought that we understood
about black holes in the year 1970.
By combining general relativity
with quantum mechanics,
Hawking had shown the enduring power
of Einstein's theory.
But as Einstein himself
would discover,
that theory also had a dark side.
It could be used to unleash
devastation on the earth.
Back in the 1920s, Einstein found
that interest in his work
had extended beyond
the world of theoretical physics
and into the realm
of populist politics.
Long before there was even
a formal Nazi party,
as early as spring of 1920,
there were rallies to denounce
not just Albert Einstein
but rather to denounce
general relativity.
They would rent out sports arenas
and opera houses
and large, large stadiums,
thousands of people in attendance,
to basically chant
'Down with warping space time.'
It was seen as a symbol
of all that had gone wrong
with so-called Jewish physics.
It became clear it was not
going to be safe for him.
After the Nazis came to power,
Einstein fled Germany in 1933
and settled here in Princeton,
New Jersey,
working at the Institute
for Advanced Study.
And as a lifelong pacifist,
he was appalled
at the prospect of another war,
especially since he knew his own work
could have a devastating impact
on its outcome.
Einstein did not want to get
that involved in the war effort.
I think everyone was extremely
surprised that this 1905 paper,
E = MC2, could have an implication
for killing people.
So we come to Einstein's most famous
equation, E = MC2.
And like many of his equations,
it has this magical property
of equating two things that you
wouldn't expect to be equal.
On the left hand side we find E,
the energy.
On the right hand side, M, the mass.
And so this equation tells us
that energy and mass
are essentially the same.
They're equivalent.
They can be exchanged.
And the exchange rate
is C squared.
C is the speed of light,
it's huge.
So C squared
is a tremendously large number.
So one way to read the equation
is that a huge amount of energy
can be converted
into a small amount of matter
but reading the equation
from the opposite end,
it tells us that a small amount
of matter can be converted
into a huge amount of energy.
The power of E = MC2
went far beyond the theoretical.
In the early 1920s, Einstein's friend
Arthur Eddington realised
that this famous equation was the
secret to how stars, like our sun,
produced such vast amounts
of heat and light.
Deep in the hearts of stars,
pressures and temperatures
are so high that hydrogen nuclei
slam into each other,
fusing and eventually creating
helium nuclei.
And in that process, a tiny amount
of mass is converted into energy.
Albert Einstein realised
that perhaps we could harness
that process here on Earth
and create energy of our own.
Or create a weapon.
Worried the Germans had already
started a nuclear programme,
Einstein and fellow physicist
Leo Szilard
wrote to President Roosevelt,
urging him to develop a bomb.
Roosevelt responded by setting up
the Manhattan Project.
They achieved their goal
in just three years.
This is the Trinity monument.
On July 16th 1945, the world's
very first nuclear bomb
was set off right here in this spot.
The bomb, nicknamed Gadget,
was winched to the top
of a hundred foot tower
that stood right here.
The observers retreated
and just before dawn,
the bomb was detonated.
At 5.29 am, the device exploded
with an energy equivalent
to twenty kilo-tonnes of TNT.
The roar of the shock wave was felt
over one hundred miles away.
The surrounding mountains were
illuminated brighter than daytime
and the mushroom cloud reached
seven and a half miles in height.
All that power was released
when inside the bomb,
just 0.9 grams of matter
were converted into energy
and that's the power of E = MC2.
Just three weeks later, on August 6th
1945, another bomb was dropped
over the Japanese city of Hiroshima.
At exactly 8.15 in the morning,
0.6 grams of matter
was converted into energy,
incinerating seventy thousand people.
The devastating power of Einstein's
equation had been unleashed.
Now it's always been a mixed legacy
for the history of physics, right?
Like we like to think of ourselves
discovering secrets of the universe
not as blowing things up, but there
is this necessary interplay
between the discoveries we make
and the technological capabilities
that we have here on Earth
that physicists have to accept,
and of course Einstein always had
mixed feelings about it later on
because he was at heart a pacifist.
For the rest of his life,
Einstein campaigned for nuclear
disarmament and peace.
The nuclear bomb
was a devastating demonstration
of how Einstein's theories could be
used to practical effect.
Ever since then,
humanity has been building
increasingly complicated machines
that use Einstein's theory
not for destruction, but to unlock
the mysteries of the universe.
This is the entrance
to the Large Hadron Collider.
Buried deep below
the Swiss/French border,
it is the world's biggest machine.
Sudan Paramesvaran is a scientist who
uses the LHC to travel back in time.
The point of the LHC
is to try and understand
how the universe
came into its current state
from the Big Bang
all those billions of years ago,
and one way that we can do that
is to try and re-create
some of those early conditions.
Sudan's work relies on
the concept of time dilation,
developed by Albert Einstein.
Time dilation is only noticeable
at close to the speed of light
but in the LHC,
we can see it in action.
Beams of protons are fired
through these tubes
and smashed into each
other at very high speed.
In the middle of this pipe is where
the actual protons are travelling.
We accelerate them using
very powerful magnets.
They're actually
travelling round the ring
eleven thousand times a second,
very, very close
to the speed of light.
So when the protons collide,
they actually smash up into lots
of little different things.
A lot of new particles are created.
We think the particles
created in these collisions
are similar to those that existed
in the moments after the Big Bang.
Studying them can help us
understand the early universe
and that's where
time dilation comes in.
Okay, so what we have here
is a visual representation
of a collision.
The protons are colliding right
in the middle of our detector
and then everything comes out
from that point.
Each of these tracks
represents an individual particle
created in the collisions.
Many of them blink out of existence
in a fraction of a second.
This is actually
the decay of a B-meson
and its typical lifetime is only a
millionth of a millionth of a second
so it's tiny, and that would make it
very difficult for us
to actually investigate it.
It would decay very close
to the primary point here.
Now because it's travelling
close to the speed of light,
its clock is running
a little bit slower.
This means that it's actually able
to travel this distance before decay
and so the fact that
it undergoes time dilation
gives us
an avenue of physics to explore
which we otherwise
wouldn't be able to do.
The time dilation we see in the LHC
is Einstein's theory of relativity
in action...
this time for peaceful means.
We have answered many mysteries
about the universe
using Einstein's theories.
But even in the 21st century
there are still more discoveries
to be made...
discoveries that will
elegantly tie together
the work of Albert Einstein
on relativity
and Stephen Hawking on black holes.
Black holes are stranger
than anything dreamed up
by science fiction writers
but they are firmly
matters of science fact.
Despite all our advances
in technology,
we have still never seen a black hole
and it's that search for
an elusive glimpse of a black hole
that brings Dan Marrone
to the mountains of Arizona.
Black holes are one of those things
that I feel like everyone
is interested in, right?
The fact that we've never even
seen one is kind of amazing.
We're so confident they're there
but yet show me a picture
and you can't.
Dan is on a mission to do something
no one has ever done before,
take a picture of a black hole.
Ordinarily, it would be impossible
to photograph a black hole,
like picking out a shadow
on an already-dark sky.
But Dan is hoping to capture a black
hole in a particular phase of life,
while it is feeding.
The gravitation pull
of black holes is so strong
that they can consume
entire stars.
This simulation shows what we think
happens as a star is ripped apart.
What you see is the bright splatter
of the debris
falling around the black hole
from the neighbouring star,
and it turns out,
maybe even ironically,
that the darkest objects
fundamentally conceivable
become the brightest beacons
in the universe.
The event horizon, where the
whirlpool is at its fiercest,
is one of the most extreme
environments in the universe.
It is what Dan and his colleagues
are trying to take a picture of.
This is the sub-millimetre telescope
on Mount Graham in Arizona.
A radio telescope,
it can probe the depths
of the universe in broad daylight.
We'd like to see that material
circling the drain and disappearing.
We'd like to see the light itself
not escaping,
a shadow in front of the black hole
where the light
is disappearing into it.
Dan's sights are set
on the very heart of our galaxy.
Astronomers have been tracking
the motion of the stars
around the galactic core
for more than twenty years.
How's the weather this evening?
The weather's good.
The enormous speed
at which they are moving
suggests that they are orbiting
something huge and unseen.
They believe it is
a super-massive black hole,
over forty million kilometres across
and four million times
the mass of our sun.
It is known as Sagittarius A♪.
The event horizon around it
should be one of the brightest spots
in the galaxy...
but it is still so small
and so far away
that to image it takes
the largest telescope ever built.
So right now the telescope
is pointed at Sagittarius A♪.
We have to look through
the entire plain of the galaxy
and so if you look
with a visible light telescope,
you can't actually see it
as a black hole.
All the dust in the way
blocks the light
and so we have to do this
with a radio telescope.
And in fact we're not
just looking through one
but we're looking with a whole array
of them scattered over the earth.
The event horizon telescope
is a huge network.
As well as this dish on Mount Graham,
there are dishes in Europe,
on Hawaii, in Chile
and at the South Pole,
all of which are simultaneously aimed
at the very centre of the galaxy.
When the data
from all of them is combined,
it creates a telescope
the size of the Earth.
It is hoped it could soon produce
our first detailed view
of an event horizon
and the material around it
spiralling into oblivion.
But while we wait
for that first elusive image...
there is already a technology
that can detect Stephen Hawking's
beloved black holes
and may answer
one of the final great mysteries
of Einstein's theory of relativity.
These are offices at LIGO.
We can use any of these rooms
if you want
but if you want my office,
we're heading there.
It's full of junk.
This is the office they give
emeritus old professors,
that's what they do with them,
so a lot of my papers and junk
is all around.
There's a picture of my mentor
right over there.
You can see him,
his name is Jerrold Zacharias.
He's the first guy who ever
said to me that, you know,
you're not as dumb as you look.
That was very important.
You need somebody in your life
to tell you that.
Rainer Weiss, Rai to his friends,
is now a Nobel prize-winning
Emeritus Professor at MIT
but in 1967
he was just a junior faculty member
who was fascinated by a particular
piece of Einstein's theory...
gravitational waves.
In 1916,
Einstein himself had calculated
that objects moving through
the fabric of space-time
should cause it to ripple,
like waves on a pond.
At first Einstein thought
that these waves would be so tiny
they would be
impossible to measure.
Later in life, he was not sure
they existed at all.
If you ask me whether there are
gravitational waves or not,
I must answer that I don't know but
it is a highly interesting problem.
Rai thought gravitational waves
did exist
and has spent a lifetime
trying to find them
so he came up with a system
that could potentially detect
the most miniscule waves
in space-time.
It was called laser interferometry.
So here's the idea.
There's a laser
which is the cylinder.
There is something called a beam
splitter which divides the light.
Half of the light will get reflected
to a mirror that's over here,
and then sent back
to this beam splitter,
and the other half hits this mirror
and comes back to the beam splitter.
Then two beams will head
towards a photo detector
and you'll see something
interesting.
No light goes to the photo detector.
Light cancels.
Now what happens is you change the
length on one arm, make it longer,
make the light shorter
on the other arm.
You see light does go
to the photo detector
when the paths are not equal
any more and that,
the fact that light goes
to the photo detector here,
when the paths are no longer equal
and may have been disturbed by that
gravitational wave to do this,
that's the way
the detection is made.
It's really as simple as that.
If Rai's calculations were right,
his system would be able to pick up
movements in the mirrors
of just
a few trillionths of a metre.
I heard about the idea,
I did some numbers
and it was obvious that Rai
had gone crazy or something.
I just couldn't believe
that he could really,
anyone could really pull this off
and then I spent the rest
of my career eating crow
and trying to help him pull it off.
When Kip Thorne,
a theoretical physicist
and close friend of Stephen Hawking,
joined the project,
his job was to work out whether there
were any events in the universe
powerful enough to produce
gravitational waves
that Rai's system could detect.
As a theorist,
I had the best handle anyone had.
It was not a great handle
but the best handle anyone had
on the strengths of the sources.
What Kip needed was a source
of gravitational energy
so strong it would shake the fabric
of the entire universe,
the sort of energy
that would be released
if two black holes collided.
You began with two massive stars.
This one collapsed
and formed a black hole
and then later that one collapsed
and formed a black hole,
and then create a binary
going around each other.
That binary emits
gravitational waves,
spirals the other closer and closer
and the black holes collide.
But we'd never seen
pairs of black holes.
We couldn't see pairs of black holes
because black holes
don't emit any electromagnetic waves
as they go round each other, they
only produce gravitational waves,
so the only way we would ever
see them was with our detectors.
To try to detect the gravitational
signals from colliding black holes,
Kip Thorne and Rai Weiss embarked
on one of the most expensive
scientific ventures ever attempted.
After years of planning,
construction started in Livingston,
Louisiana in 1994.
The lasers would be fired
up these arms,
each four kilometres long,
before reflecting off the mirrors
and returning to sensors
so finely tuned they could in theory
detect a shortening of the arms
caused by gravitational waves
of just a million million millionth
of a metre.
Three thousand miles away
in Hanford, Washington,
an identical facility was built.
For any detection to be confirmed,
it would have to be picked up by both
detectors at the same time.
The instruments were activated
in 2002.
For eight years
they listened to the universe.
By 2010, they had heard
absolutely nothing.
For the LIGO team,
the pressure was mounting.
We had convinced the NSF
and Congress
that they should spend
a billion dollars on this
and we had nothing to show for it.
Doubling down, they shut the project
for another five years
to install an even more precise
set of detectors.
It was a high stakes gamble.
In September 2015,
almost exactly a hundred years
after Einstein published
his theory of general relativity,
Rai Weiss's detectors
were reactivated.
Just two days later, both sites
recorded an unusual signal.
Ladies and gentlemen, we have
detected gravitational waves.
We did it!
After working on the problem
for almost fifty years,
it was a massive vindication
for Rai and his friend Kip.
I want to first remind you
of Einstein's 1915 big discovery,
was the, really the formulation
of these field equations.
He applied these field equations
to the idea of gravitational waves.
Almost the first day
of the real run,
we saw what is in front of you
on the screen here,
and let me play it for you.
That isn't much. It's a little blip.
That's all you heard.
But let me change, this is a trick.
We made it
so that you can hear it better
by changing the frequency
of everything.
And that chirp is the characteristic
of this particular source,
and that was something
which was quite astounding to us.
Long, long ago, in a galaxy
far, far away, a pair of black holes
each around thirty times
the mass of the sun
circled each other,
moving faster and closer.
The point when we first see
the gravitational waves,
they may be
a thousand kilometres apart,
each one roughly
a hundred kilometres in size
and they're going around and around
creating stronger and stronger
warping of space and time.
As they near each other,
they warp space and time in a wild
way, very much like a storm at sea.
And then, the black holes coalesce.
In that instant,
three times the mass of the sun
is converted into pure energy...
but none of that energy
is emitted as light.
It is all released
as gravitational waves.
So there's a huge amount of energy.
Turns out to be fifty times higher
than the total power output
of all the stars in the universe
put together.
By far the largest explosion
in terms of power output,
except the Big Bang,
that we ever had any evidence of.
As they travel through space at the
speed of light, the waves dissipate,
getting smaller and smaller
until 1.3 billion years later...
they passed through Rai's detectors.
I wish I could have
told Einstein directly
that we had seen a black hole
doing this.
That would have been
just a wonderful experience,
to see the expression on his face
after we'd told him that.
The discovery of gravitational waves
is the ultimate triumph
of Einstein's theory of relativity,
a theory that has been repeatedly
tested and proven to be correct.
Einstein died in 1955.
In just half a century, he had
re-imagined the entire universe.
Albert Einstein enters the world
when it's one way
and by the time he leaves the world,
it's completely different.
We now live in a world
where we understand
the universe had a beginning
and we can tell
how long ago it was.
Those are stunning achievements
and stunning shifts,
both in our scientific
and our cultural perspective.
He was a figure that is rare,
you know, once in a hundred years,
maybe once in five hundred years.
Stephen Hawking's greatest
contribution to physics
was his discovery
that black holes could evaporate.
If his theory of Hawking radiation
was correct,
it would have profound implications
for the way we understand
the entire universe.
In Haifa, Israel,
Jeff Steinhauer has spent a decade
searching for evidence
of Hawking radiation,
using artificial black holes
that he makes out of sound.
So here we go.
All the equipment that you see
is for the sake
of this small point right in there
where the artificial black hole is.
We start out with these very cold
atoms in this tube-like volume
and it's only .1 millimetres long.
We then apply a blue laser beam
which causes some of the atoms
to be accelerated to supersonic
speed and so in this region,
they're flowing slower
than the speed of sound
and here they're flowing faster
than the speed of sound.
So here, in the supersonic region,
a sound wave trying to move against
the flow will actually fall back.
It can't go forward
against the very fast flow.
In his artificial black hole,
Jeff has created an event horizon.
Once the sound wave is over
that line, it cannot escape,
just as light cannot
escape a real black hole,
and when Jeff takes photos
of his sonic event horizon,
he sees something very strange, the
tell-tale signs of Hawking radiation.
You see this band?
This band is an observation
of sound waves being emitted
from the horizon of the black hole.
This experiment is the first time
that Hawking radiation
has been observed.
It is an amazing discovery which
suggests that Hawking radiation
may be a fundamental feature
of black holes.
If that's true,
it means that given enough time,
all black holes will evaporate
and that prospect has troubling
implications for the rest of physics.
A central principle of all physics,
in fact it's written into
the laws of quantum theory,
is that information
cannot be destroyed.
Consider this newspaper.
It has information on every page
and if I were to throw it
on this fire,
it's quickly consumed by the flames
and it looks like the information
is destroyed
but if I were able
to take all the ashes,
collect all the smoke
and all the heat,
and analyse and reconstruct
the past of all the particles,
then I should be able
to reconstruct what's on every page.
And this is because
the laws of physics allow us
to tell the entire future
and the entire past of any system.
No one's saying it's easy
but it is possible as long
as you have all the information.
We call this determinism.
Scientists believe that
the principle of determinism
applies to all systems,
no matter how big or complex.
It should even apply
to the entire universe.
So if I were to somehow
know the position and state
of every particle in the universe,
I could apply the laws of physics
and know the entire
future of the universe
and the entire past of the universe.
But there is a catch because if,
as Hawking predicted,
black holes could evaporate in such
a way that they leave behind
no trace of the material
that was inside,
then information could be lost
and even if only a small amount
of information is lost,
then everything is lost.
You can't re-construct the past
and you can't predict the future.
It seems trivial but actually
it was a massive problem
that shook
the very foundations of physics
and this became known
as the information paradox.
If determinism, the predictability
of the universe,
breaks down with black holes,
it could break down
in other situations.
Even worse,
if determinism breaks down,
we can't be sure
of our past history either.
The history books and our memories
could just be illusions.
It is the past
that tells us who we are.
Without it, we lose our identity.
The information paradox has troubled
physicists for decades.
If Hawking was right
and black holes did destroy
the information they contained,
then they would also destroy
almost everything we know
about modern physics.
It created this big rift
between those who were adherents
to quantum thinking
and those who were
adherents to relativity,
the quantum people saying
the information must get out.
We don't know how,
we don't see how, but it must.
And the relativists saying
you know maybe,
maybe the information's just lost.
I'm inclined to suspect
that information is truly lost
down black holes
but mine is the minority
point of view.
Who cares if black holes evaporate
and swallow little bits of
information as they go?
But in the forty-plus years
since then,
it's kind of been like a snowball.
The importance of this problem
has grown and grown.
The information paradox was a problem
that Stephen Hawking worked on
for over four decades
and in 2015, he came up with
a major breakthrough.
Many scientists felt that
information should not be lost
but no one could suggest a mechanism
by which it be preserved.
The arguments went on for years.
Finally, I found what I think
is the answer.
I realised that a black hole
can store the information
in what is called super-translations
of the horizon.
Hawking's new idea was that as
objects fall into a black hole,
they disturb the event horizon,
leaving behind
a pattern of turbulence
which could preserve the information
about everything
that's fallen inside.
I am now working with my colleagues,
Malcolm Perry at Cambridge, and
Andrew Strominger at Harvard,
on whether this
can resolve the paradox.
If information
is stuck on the horizon,
it has not fallen
into the black hole
and you can't directly observe it
from outside
but what will happen is it will
influence the Hawking radiation
that comes out of the black hole
and that may be enough to help you
resolve the information paradox.
When we first came upon it,
we were up until late at night.
He said he hadn't been
this excited in forty years...
and he started working on it
basically full time.
Together, the scientists wrote
three papers on the subject...
edging closer to a solution
to the information paradox.
It was Hawking's last great idea.
Sadly this is the last paper
that Stephen wrote.
He was fully engaged with it
right till the very end.
Hawking died in March 2018
at the age of 76,
over half a century after he had been
given just two years to live.
He was kind of magical to be around.
When I miss him the most
is when we figure something out.
I'd like to tell him.
Such was his contribution to science,
his ashes were interred
in Westminster Abbey
alongside Isaac Newton
and Charles Darwin.
Stephen was one of the great minds
of the 20th century
in terms of his impact
on our understanding
of the laws that govern
the universe.
I miss Stephen greatly.
It was a tremendous loss
for me personally.
His gravestone engraved
with the equation describing
Hawking radiation.
Stephen Hawking's legacy
will clearly be a vital part
in the unfolding story
of putting gravity
and quantum mechanics together.
And as we go forward,
everything that we do
in some sense will go right back
to Stephen Hawking.
Time.
We think of it
as regular as clockwork,
ticking out the steady
progress of the universe,
but time is not constant.
It holds the key
to the secrets of the universe
and the two people who helped us
unlock those mysteries
are joined by
a cosmic coincidence of timing.
On March 14th 1879,
Albert Einstein was born.
Einstein gave to us all
a set of tools
that literally help us organise
the world around us to this day.
And on March 14th 2018,
Stephen Hawking died.
I think Stephen should be remembered
as one of the most remarkable people
of the 21st century.
He is someone who in a thousand
years from now will be remembered.
His name will be known.
That's not true for most of us.
Between them, they have transformed
our understanding
of the entire universe.
As a working physicist,
I look at these two giants
and I have nothing but gratitude.
They revealed the world to be so
much more than it would have been,
and without them,
who knows if we would have gotten
to this wondrous stage
in our understanding.
I have a real feeling of achievement
that I made a modest but significant
contribution to human knowledge
despite my condition.