Horizon (1964–…): Season 46, Episode 4 - Who's Afraid of a Big Black Hole? - full transcript
There's something deeply disturbing
in deep space.
Something so incredibly massive,
it could swallow an entire star.
People tend to be fascinated by
things which are big and scary,
like dinosaurs,
and there's really nothing that's
bigger and scarier than a black hole.
Black holes are one of the most
destructive forces in nature.
But far from being monsters,
scientists now believe
they could hold the key to the
greatest mystery of all...
..where the universe came from.
Black holes are the doorway to
understanding the basic laws of
the universe around us.
The trouble is, they're
practically invisible and billions
of kilometres from Earth.
We think right there is a black hole.
Right there.
The more we try to understand them,
the stranger black holes become.
Everything we know about common
sense is thrown out the window.
The equations no
longer make any sense.
Black holes could force us to
abandon everything we thought
we knew about the universe.
There aren't questions
much bigger than this.
There's really a lot
that we don't understand.
We humans have evolved to make sense
of planet Earth and, so far,
we've made a pretty good stab at it.
In the last century, we've made
sense of the impossibly small...
..and the unimaginably large.
The enormity of space, and the
microscopic behaviour of atoms.
Yet there are some things that
threaten to elude us completely.
The harder we look,
the more questions we uncover.
Nowhere is this more true
than for a black hole.
I think of a black hole
as the symbol of what it is we
don't understand about the universe.
Black holes are one of the most
mysterious objects in the cosmos.
What are black holes made of?
Oh, OK. Already you've asked me
a question that I can't answer.
They fell out of Einstein's
theory of relativity in 1916,
and they've defied some of
our greatest minds ever since.
Are black holes made of anything?
Black holes... Hmm.
We don't really have any
idea what's going on, so....
I don't understand black holes.
I love black holes.
I love black holes
because I don't understand them.
There are many strange things in this
universe, but I think I've picked
the weirdest thing to actually study
which is the black hole.
Until recently, there wasn't
much evidence they existed at all,
because while we think they're
out there, we can't see them.
Black holes are, by definition,
completely black.
Nothing can escape it, even light,
and that's why it's called
a black hole,
because light can't come out of it.
Black holes, totally mysterious,
billions of kilometres away
and practically impossible to see.
Not that that's
stopped astronomers trying.
Doug Leonard even
thinks he's seen one,
or at least seen one form.
It took two years
and the Hubble space telescope.
It was only possible at all
because we think black holes
begin their lives as something
we've all seen in space - stars.
Stars, like our sun, are essentially
big, hot balls of gas
that have nuclear generators in their
core, that create all the heat
and light that we see shining.
Stars are enormous.
You could fit a million Earths
inside the sun, and the sun is not
even an abnormally large star.
But the most fascinating thing to
me about stars is that they die.
The theory is, black holes are born
when nature's most massive stars
burn off all their fuel
and violently collapse.
The cores of these massive stars
implode in less than a second.
They go from something
about the size of the Earth,
down to something
about the size of a small city.
And they don't stop there,
they continue imploding
all the way down to a point.
That point is what we
believe becomes a black hole.
And it's this process that
Doug Leonard believes he's spotted
when a massive explosion, supernova,
signalled the death of a star
in a remote galaxy billions and
billions of kilometres from Earth.
This is a picture of a galaxy
215 million light years away
and, indicated by the arrow,
this is the supernova,
a single star that exploded that, for
a short period of time, is as bright
as the entire galaxy that it's in.
And that
big blob there is the galaxy?
This big blob here
is the combined light
of tens of billions
of ordinary stars.
This is a close-up,
an extreme close-up, of the supernova
while it was still very, very bright.
Once the supernova was discovered,
we trawled the Hubble space telescope
archives
and found a picture of this exact
spot taken eight years earlier,
and what we found
at the location of the supernova
was this object, which is
actually an extremely bright star.
So what we did next was wait.
For two years, we waited for all the
fire arcs of this supernova explosion
to disappear and go out,
and we went back and took another
picture
of that exact spot in the sky,
and what we found was nothing.
The star was gone. It exploded as a
supernova and had now disappeared.
And we think right there
is a black hole.
Right there.
But I can't ever be
100% sure about that.
Is that because you can't see it?
Seeing nothing in black hole science
is a great thing.
You don't expect to see anything
when you're looking at a black hole.
As images of black holes go,
these few dark pixels are
about as good as it gets.
Without the death of a star,
there'd be no reason to suspect
there was a black hole there at all.
In fact, black holes are so hard to
see, most of what we know about them
hasn't come from those observing
the universe but from another group
of scientists - the theorists.
And the universe they study
is in their heads.
I think of theoretical physics
really as a great detective story
that you get to be part of.
The clues look so few and scant
that it seems like a hopeless case,
but if you work really hard at it,
often you can discover amazing stuff.
So it's amazing to me how much
one can actually learn about
reality just by detective work.
Black holes have existed in
theorists' minds and notebooks
for almost a century,
most notably in the mind and
notebook of Albert Einstein.
In 1916, Einstein changed
the way we see our world.
Purely by the power of thought,
and some clever mathematics,
he explained something we
all take for granted - gravity.
Gravity is the universal force
which holds everything together.
If you were to shut off gravity
right now, the sun would explode,
the Earth would fall apart,
and we'd be flung into outer space
at a thousand miles per hour.
So it's gravity that keeps
us rooted onto the Earth
and holds and binds the galaxy
and the solar system together.
Scientists had been able
to calculate the effects
of gravity for centuries.
But until Einstein, what caused it
had remained a mystery.
The answer was stranger
than anyone had imagined.
Einstein's great insight
was to realise that gravity is caused
by the bending of space and time.
So gravity is not really
pulling me down to the ground,
it is space that is pushing me down.
Einstein called his theory
general relativity.
The theory of relativity is infamous
for its difficulty.
I want to show that there's nothing
peculiarly difficult about it.
Space isn't simply an empty void,
it can be bent and stretched.
Let me illustrate this one example.
Let's imagine that this piece of
jelly is the space, then the presence
of matter is to distort the space.
All massive objects
like stars and planets
bend the space and time around them.
Any object that passes through
that warped space time will move
as if being pulled by a force,
and this is what we experience
as gravity.
Einstein's theory of relativity
does lead us into very
strange and unfamiliar paths.
Relativity is perfectly intelligible
to anybody who is willing to think.
Einstein's theory has withstood the
test of time for almost a century.
If there is one data point
out of place, we would have
to throw the entire theory out.
Everywhere we look in the heavens,
Einstein's theory comes
right on the spot.
But less than a year after it was
published, theorists realised
general relativity predicted
something so profoundly troubling,
many believed it couldn't
exist in the real world.
Anything very heavy and very small
would create such a strong
gravitational field
that space and time would be bent
and twisted to breaking point.
General relativity had predicted
the existence of black holes.
And it didn't just say
that they would exist...
general relativity allows
us to imagine what
it would be like to travel into one.
There's a beautiful analogy
between black holes and waterfalls
which actually lets us calculate all
properties of black holes exactly.
When you approach a waterfall,
the river flows faster and faster.
When you approach a black hole,
it's not the water that flows faster,
it's space itself.
The structure of a black hole
is similar to the relentless
flow of water over a waterfall.
It's an analogy that follows the
water from the river above
to the rocks below
and allows us to journey
into the very heart of a black hole.
If you're swimming upstream
from a waterfall,
there is an invisible line where the
water flows as fast as you can swim,
and if you cross that line,
it's the point of no return.
You wouldn't feel anything special,
but no matter how hard you struggle,
you can never escape
getting sucked all the way down.
For a black hole, the point of no
return is called the event horizon.
Past it, space is travelling inwards
faster than the speed of light.
Even if I can only swim at a maximum
speed, the water can obviously
fall much faster than that.
In the same way, even though
I can never go faster than
the speed of light through space,
space itself is allowed, in the black
hole, to fall as fast as it wants,
which means that everything
that's there, even a particle of
light trying to go upward,
will be sucked inexorably downwards
towards the centre.
Assuming your body
withstood the intense gravity,
leaving the universe forever
could be remarkably uneventful.
People used to think that you would
die at the event horizon, but we now
understand that for big black holes,
it's perfectly possible to still be
alive at this stage, you just have
no choice but to continue downward.
Everything would feel just normal
to you, you wouldn't even know
necessarily that you're doomed.
The only thing is that there's
no way you can ever get out again.
As you approach the
centre of the black hole,
you reach the inner horizon,
where everything falling in
meets matter being pushed out
by the hole's rotation,
similar to where the torrent
flowing over the falls
hits water rebounding back up.
Eventually, the inward flow
actually slows down to become slower
than the speed of light,
because the rotation of the black
hole causes a sort of repulsion.
At that point,
you have things colliding together
near the speed of light,
creating these ridiculously high
temperatures,
much hotter than inside of a star.
So hot that it would vaporise me
and any ordinary matter.
So that makes an ordinary traffic
accident seem tame in comparison,
now you're being hit by a truck
going almost 300,000km per second.
It's not a place
where I would wanna be.
The inner horizon is one of the
most extreme environments
in the universe.
According to general relativity,
the only place more extreme
is what lies beyond it.
Let me gather my thoughts
for a moment.
It's remarkably difficult for us
to actually calculate with Einstein's
equations what happens
inside the inner horizon.
But if I jumped into a black
hole, that's probably as
far down as I would get.
At the centre of a black hole,
the equations predict
something so strange,
it blows Einstein's greatest
achievement out of the water
and forces us to question
our understanding of the universe.
Einstein hoped that general
relativity would form the framework
for a new understanding of nature.
But at the heart of its
description of a black hole,
theorists found a problem
with Einstein's mathematics.
Something so disturbing,
his theory breaks down completely.
Einstein's equations of general
relativity simply say the following -
the Ricci curvature tensor
minus one half the metric tensor,
times the contracted curvature tensor
is proportional to the
stress energy tensor.
All this says that if I start
with a star, a black hole,
or even a universe,
that determines the curvature
that surrounds that
concentration of matter and energy.
But inside these equations,
there's a monster.
In the extreme gravity of the core
of a black hole,
Einstein's equations spiral wildly
out of control.
After every long tedious calculation,
I mostly get zeros but the
non-zero term is given as follows...
M is the mass of the black hole,
R describes the distance
from the black hole...
Here is the problem, right there...
when R is equal 0...
The point at
which physics itself breaks down.
So one over R
equals one over 0 equals infinity.
To a mathematician, infinity is
simply a number without limit.
To a physicist, it's a monstrosity.
It means that gravity is infinite at
the centre of a black hole, that
time stops. And what does that mean?
Space makes no sense, it means
the collapse of everything we
know about the physical universe.
In the real world,
there's no such thing as infinity,
therefore there is a fundamental flaw
in the formulation
of Einstein's theory.
According to Einstein then, all the
mass of the black hole is contained
within an infinitely small point
that takes up
precisely no space at all.
This impossible object of infinite
density and infinite gravity
is called the singularity.
We know what a singularity is.
A singularity is when
we don't know what to do.
To me what's so embarrassing
about a singularity
is that we can't predict anything
about what's gonna come out of it.
I could have a singularity
and - boom - out comes a
pink elephant with purple stripes.
And that's consistent with what
the laws of physics predicts,
because they don't predict anything.
A singularity is when our
understanding of nature breaks down,
that's what a singularity is.
Einstein realised
there was a problem
when he was shown this infinity,
but he thought that black holes could
never physically form, therefore
it was an academic question.
Sure, there was a problem, but it
didn't matter because mother nature
could never create a black hole.
In 1939, Einstein even wrote a paper
that appeared to prove black holes
would never be found
in the real world.
He hoped that there'd be some
physical mechanism that would stop
them from actually being produced.
And he really wanted to ask
the question
could they physically form? I think
he wanted to show the answer was no.
Given the physics known at the time,
his assumptions were reasonable,
but we've learned a lot of physics
since then so therefore we know that
his reasoning was incomplete.
At the time,
no-one had seen anything
to suggest Einstein was wrong.
For years, theorists were happy
that general relativity was a
complete understanding of
gravity in our universe.
Then, in the early 1970s,
astronomers made a breakthrough.
X-rays revealed hot gas
falling into objects
that were both extremely massive
and invisible to normal light.
For some, these images could
only be caused by black holes.
Material on the way into the
black hole can become very hot.
So hot that it becomes a million
degrees or even ten million degrees,
and that makes x-rays.
And just before this lump of material
disappears in the black hole,
it becomes a
bright flash of x-ray radiation.
Professor Reinhard Genzel is
Director of the Max-Planck Institute
for Extraterrestrial Physics.
He's spent the last 25 years
looking for proof of the existence
of one particular black hole.
While we can't see black holes as
such, we can see that they're there
and what they are
through their interaction
with visible objects like stars,
like gas in their vicinity.
Using radio telescopes,
astronomers had also seen objects
at the centres of galaxies
they suspected were black holes.
But to prove it, they'd need to
make more precise measurements.
Unfortunately, the nearest one
was 25,000 light years away
and totally obscured by dust.
It was
at the centre of our own galaxy.
It took Genzel and his team
nearly ten years
to develop an infrared telescope
capable of seeing enough detail
through the clouds of dust and
gas surrounding the galactic centre.
It took them a further 13 years of
painstaking observations before they
saw the thing they were looking for.
A star orbiting exceptionally
close to the centre.
Genzel knew that measuring
the star's orbit could tell him
about whatever it was orbiting.
So what we are seeing
are the innermost stars.
This green cross,
that's the centre of the Milky Way,
Sagittarius A star.
So in 2002, this star here
was very close to this
and the next year, it has moved
quite a substantial distance.
Because the galactic centre
is so far away,
this minute change means
the star is moving incredibly fast.
The separation which you see
is quite an enormous distance,
these are several light weeks.
And how far is that in kilometres?
OK...
So we have an hour, and we have a
day, and then take a week,
then we have the speed of light...
and so in kilometres, OK...
Wow, is that a big number -
180 billion kilometres.
Let me just check this so...
Yeah, a 180...180 billion kilometres.
I can't deal with that number.
It's hard to imagine what a
180 billion kilometres is.
Once you know the size
of a star's orbit and the time
it takes to go round,
it's a relatively simple calculation
to work out the mass
of the object it's orbiting.
Although tracking a single star
would be enough to measure
the mass of the central object,
Professor Genzal has mapped the
orbits of the 30 stars
closest to the galactic centre.
Here we have the innermost stars.
And these orbits we determine
uniquely from the motion
we have tracked over the years.
So it takes S2, this innermost star,
15 years to move once around
the centre of the Milky Way here.
The other stars are slower,
some of them take several
hundred years to move around.
From the size of each
of these orbits and the speed
the stars were travelling,
Professor Genzal calculated
the mass of the central object
and it was truly astronomical.
From these two numbers,
you already can determine uniquely
the central mass,
and we can do this
for each of these stars,
and we find that the mass is
always the same.
It's four million times
the mass of the sun.
Because the closest stars
pass so near to the centre,
this extraordinary mass, four
million times heavier than the sun,
must be in a very small space.
That really clinches this.
Because nothing fits in there,
into this relatively small volume
other than the massive black hole.
Even a schoolchild can analyse
the data and will come to the
same conclusion, it's very clear.
What Genzel had found
at the centre of our galaxy
was so heavy and so small,
it had to be a black hole,
but it was far too big
to have formed from
the collapse of a single star.
The black hole at the centre
of our galaxy is an object
which is much more massive
than the stellar black holes.
It's about four million times
the mass of the sun.
So we would call these
super massive black holes.
Although Professor Genzel
hadn't seen a black hole,
the indirect evidence
was so compelling
there could be little doubt
black holes were real
and it won him the 2008
Shaw Prize for Astronomy.
So the prize, the Shaw prize,
is a fairly large amount of money,
actually a million dollars,
which was given to me
and with no strings attached.
So I've given some of it
away to my colleagues,
some of it I kept myself and,
you know, people have convinced me
I should use some of that
to buy a new car.
Everything in our galaxy, the Earth,
the sun, a million million stars,
are all spinning around the super
massive black hole at the centre.
And ours isn't even
particularly impressive.
The super massive black hole
at the centre of our galaxy is
quite small relative
to other super massive black
holes that we know about.
There are galaxies,
not very far from ours,
in which we have seen
super massive black holes
up to a thousand times more massive,
several billion solar masses.
It now appears there's a super
massive black hole at the
centre of almost every galaxy.
And it could be that
these black holes aren't
simply agents of destruction,
because scientists have discovered
a unique relationship they share
with their parent galaxy.
So the mass of the
super massive black hole
is related to the mass of the parent
galaxy in a very simple way,
so I can show this
with a graph here.
So let me say, along one axis, I'll
show the mass of the black hole.
And I will measure this mass
in terms of the mass of the sun.
So let's say down here it is
a million times the mass of the sun.
Ten million, 100 million,
billion times the mass of the sun,
so that's the range of black
hole masses we have seen.
Along this axis, let me just
show you the mass of the galaxy.
Let me start with a billion
times the mass of the sun...
ten billion, 100 billion,
a million million solar masses.
Basically, when people measure
these two masses for
a large number of galaxies,
what they find is different
galaxies may come different places
here on this diagram.
And the miraculous thing is
that all these points seem to lie
more or less on a straight line
in this plot.
So there seems to be a...
some relation between the mass
of the black hole and the galaxy.
Roughly, the black hole
seems to be approximately
a thousand times less massive
than the galaxy in which it lives.
The existence of this kind of
a relation is rather surprising,
because what it means is
somehow the black hole is able
to influence the entire galaxy
and is actually modifying perhaps
how the galaxy forms and evolves.
This is the surprise
in this business.
In the last century,
black holes have gone
from being mathematical curiosities
to real objects in the cosmos,
millions of times the mass
of the sun and seemingly crucial
to the formation of galaxies.
I think black holes have got
maybe a little bit of a bad rap
as being the ultimate bad guys
in the universe.
It might well be that the monster
black holes in the middle of galaxies
actually helped the galaxies form
and therefore helped life
come on the scene.
As well as
super massive black holes,
astronomers believe there are also
billions of smaller stellar
black holes all over the cosmos.
How many black holes are there?
Roughly every galaxy has got
one big black hole in the middle,
super massive black hole,
and millions and millions
of smaller black holes.
Black holes are common,
they're a very common occurrence
in nature, fantastic thing.
Would we have thought it? No.
Think of all the galaxies,
each one with a raging
black hole in the centre.
Each one with perhaps thousands
of stellar black holes in them
and then you begin to realise
that black holes represent
one of the dominant forces
in the evolution of the universe.
Black holes, it turns out,
are everywhere.
And that means millions upon
millions of places where
Einstein's equations break down.
But physicists have always
known that relativity is
an incomplete theory of nature.
Although it beautifully describes
how gravity influences the motions
of planets, stars and galaxies,
it can never describe the world
at the smallest possible scale.
The realm of atoms and the
tiny particles that form them.
To do that,
they use a separate theory.
A theory called quantum mechanics.
You might wonder why we'd
wanna apply quantum mechanics
to something as large
as a massive black hole,
when quantum mechanics
deals with the very small.
And that's because, ultimately,
at the heart of a large black hole
is a singularity.
Whatever a singularity really is,
one thing we do know is
it must be very, very small.
It seems quite likely that,
in order to really
understand what goes inside a black
hole, we will need quantum mechanics,
that the final story
of how a black hole works
and what happens at the singularity
can only be understood when
quantum mechanics is included.
This subatomic world quantum
mechanics describes is nothing
like the world we experience.
Quantum mechanics tells us how the
world works at a fundamental level
and it is stranger
than you can imagine.
In the quantum world, the mere act
of observing changes what you see.
You can't say where something is,
only where it's likely to be
and anything that is possible,
no matter how unlikely,
happens all the time.
All of our notions about
how things behave change.
For example,
an object has a known location,
"I'm here, you're there,"
but at a quantum mechanical scale,
objects can be in many different
places at the same time, literally.
Yet as strange as quantum
mechanics is, theorists
believe the world it describes
is the true nature of reality.
Quantum mechanics is so weird,
it may sound like science fiction,
but it's not science fiction,
it's science fact,
and it's done better
than any other idea in physics.
It allows us to make the best
predictions we've ever made,
so like it or not,
it describes the world.
Quantum mechanics describes
everything, there's no escaping
quantum mechanics.
Every object is
a quantum mechanical object subject
to the laws of quantum mechanics.
And the world that we live in,
in the ultimate reality,
is a quantum world.
So there's no question
that there's some great truth
in quantum mechanics.
But there's one thing quantum
mechanics can't describe -
gravity.
And it's not normally a problem,
because atoms are so light,
the effect of gravity is irrelevant.
Most of the time,
quantum mechanics and gravity
leave each other in peace.
But there's one arena in which
they're both important,
and that arena is when things
are both very small
and the force of gravity
is very large.
And that's what happens
inside a black hole.
The singularity at the heart of
a black hole is both astronomically
heavy and infinitesimally small.
To understand it, quantum mechanics
alone wasn't enough.
It needed to be extended
to describe gravity.
A theory called quantum gravity.
The most obvious way
to create such a theory
was to make a quantum version
of Einstein's theory of relativity.
Proof of its success would be
a new understanding of black holes
that explained what really happens
in a singularity.
When physicists tried
to combine the two theories,
they encountered a familiar problem.
I insert this into the probability
that gravity will move from
one point to another point.
When I actually do this calculation,
I get yet another integral,
and when you do this integral,
you get something which
makes no sense whatsoever -
an infinity.
Total nonsense!
In fact, you get an infinite
sequence of infinities,
infinitely worse
than the divergences of
Einstein's original theory.
This is a nightmare
beyond comprehension.
The search for a theory of
quantum gravity had fallen apart,
because quantum mechanics and
general relativity proved to be
totally incompatible.
I think the most embarrassing
problem we have in theoretical
physics is that
we have these two different theories
which won't talk to each other.
We have Einstein's theory of
gravity, which beautifully describes
the very big and the very fast,
and then we have quantum physics,
which very successfully describes
the very small and yet, clearly,
nature has one unique way
of operating,
it's not schizophrenic,
and we humans just don't seem
to be able to find that way.
The failure of these two great
theories to understand black holes
means they are, at best,
an approximation to the laws
governing the universe.
The equations
no longer make any sense
and nobody knows exactly what
we're supposed to do about that.
Well, it's awful.
It means that physics is
having a nervous breakdown.
It means the collapse of physics
as we know it, you know?
Something is fundamentally wrong.
Nature is smarter than we are.
If we want to understand
the universe,
we must understand how
quantum mechanics and gravity
can live together and
so that's our challenge.
So it's quite a big question?
It's a huge question.
There aren't questions
much bigger than this.
We don't understand.
For nearly 100 years,
physics has been able to explain
the universe around us.
General relativity
perfectly describes the motions
of stars and galaxies.
And the world of atoms
is beautifully explained by
quantum mechanics.
Yet the discovery of black
holes means we don't
fully understand anything.
But far from being a problem,
black holes represent one of the
greatest opportunities in physics.
Black holes are the key to...
taking the next step,
the doorway to our next step
in understanding the basic laws
of the universe around us.
Unlocking the mysteries
of black holes could provide
the answer to the biggest question
every posed by the human mind.
Because there's one other place
where our current laws of nature
fail as dramatically as
they do in a black hole.
Any direction you look up
from the Earth at distant galaxies,
every single one of them is
moving away from us.
And the only way to make sense
of that is to think of the entire
universe just expanding.
This much we know
and have known for 80 years.
But then, there is an immediate
very profound implication.
If the universe is expanding,
long ago it was much more compact.
Nearly 14 billion years ago,
Einstein's theory says the
universe began in the Big Bang.
So just to get an idea
of the scale of the universe,
let's start with the Earth,
which is a pretty big object.
The sun is about a million times
more massive than the Earth
and most stars that we see in the
sky are about the size of the sun
and our galaxy has roughly
a million million of these stars.
And then the universe has roughly
a million million galaxies.
So that's a huge amount of stuff and
all that started from a singularity.
A point from which an initial
explosion got the expansion going.
That's the Big Bang.
For me, it's a weird concept,
as weird a concept
as it would be to any person who's
hearing about it for the first time.
But nature is doing it,
so that's what makes this exciting.
The singularity,
the impossible object found at the
heart of every black hole,
is the same impossible object found
at the very beginning of time.
The whole universe came out of
a singularity, all of us are the
product of a big singularity.
And so these singularities are very,
very interesting for many reasons.
There are two places in nature where
there apparently are singularities.
One is at the centre
of a black hole
and the other is at the beginning
of time itself at the Big Bang.
So it's quite likely,
if we understood the singularity
associated with the black hole,
we might resolve the question
of how the universe began
and where we came from.
Black holes could hold the key
to understanding what there was
before the universe existed.
But while we might seem
tantalisingly close,
black holes
and the theory that explains them
remain just out of reach.
Quantum gravity is the name
that we give to the solution
to this problem.
We don't really know
what quantum gravity is.
What's frustrating
with quantum gravity is that
previous revolutions in physics,
like quantum mechanics,
relativity theory,
were all brought on by
a lot of clues from nature
and, for quantum gravity,
we have almost no clues at all.
Right now, we're mostly stuck
with having to figure this out
with pencil and paper
just from theory.
The trouble is, although we know
black holes are everywhere,
we've never seen
a single one directly.
Have you ever seen a black hole?
No.
Have you ever seen a black hole?
No.
No-one has ever seen
a black hole directly.
Here is an object in outer space
that is beyond our mathematics,
beyond our physical theories,
demanding a theory beyond Einstein.
And, ironically, we can't see them.
But according to general relativity,
a black hole won't just create
a dark shadow in space,
this shadow would be surrounded
by a bright halo.
A black hole's immense gravity
warps the space around it,
focusing the starlight
coming from behind into a ring.
And, in theory at least,
we might even be able to see it.
You can see how they warp
with the space around them.
Shep Doeleman is
aiming to do just that.
He's devoted his career to
making the first direct
observations of a black hole.
I happen to really like
making the observations,
getting things done,
that there's a real joy
in assembling
a new kind of telescope.
There's a real joy in making
a new kind of measurement that
no-one has ever made before.
I guess that theoreticians feel the
same way when they think of an idea
that nobody has thought of before.
Shep is attempting to take a picture
of a shadow cast in space
by the super massive black hole
at the centre of our galaxy.
Directly observing how and
where general relativity fails
could provide vital clues
for the theory that replaces it.
Our observations are aimed squarely
at testing general relativity
in one of the most extreme
environments in the universe -
the event horizon of a black hole.
And it's there
that Einstein's theories
may break down.
For quantum gravity, seeing
the shadow exactly as predicted
by Einstein would be of little use.
If we see something that is not
consistent with general relativity,
the theorists will be extremely
interested and will want to know
everything about that
and that will point them in a new
direction for a theory of gravity.
We could look
at the centre of our galaxy,
see something completely unpredicted
around this black hole that would
send us back to the drawing board.
Shep is an astronomer at the
Haystack Observatory near Boston.
But the 37-metre telescope here
simply isn't big enough
to photograph the black hole
at the centre of our galaxy.
To do that, Shep needs a telescope
with 100,000 times the resolution.
And that requires a dish
4,500 kilometres across,
roughly the size of the
continental United States.
To observe the object we're after,
we have to create a telescope
that can see finer details
than any other telescope
in the history of astronomy.
The reason you haven't heard about
this massive telescope is because
it only exists in Shep's computer.
He hooked up radio telescopes from
across the continent, effectively
to product one giant virtual dish.
The way a normal telescope works is
it focuses all the light
because of its particular shape
into a single focal point.
When you link telescopes around the
world together, we don't have a lens.
We have to do it in a super
computer here in Massachusetts.
Shep's super computer,
the correlator,
pieces together the raw data
from all his separate telescopes
to build up a computer-generated
dish the size of America.
The level of detail you can see
with a single dish is limited
by the size of that dish.
But when you link telescopes
around the world together,
something magic happens.
You create a virtual dish
that's as big as the distance
between those dishes,
and that gives a level of detail
that's a thousand times finer
than you can get with a single dish.
Instead of creating pictures,
each of Shep's telescopes
produces reams upon reams of data.
And this is where we keep
all of the data when it comes
back from the telescopes,
each of these contains eight
very large hard disk drives and when
you have two modules together,
that contains as much data
as the US Library of Congress,
the largest library in the world,
and we have on these shelves
about 64 such libraries.
The amount of data is
just staggering, really.
We've spent a lot of money
in this project on disk drives.
There's so much data,
processing just a few nights'
observations takes months.
Hey, Mike, what's the latest
from the correlator?
Ah, actually a lot of interesting
things from last night.
You've got a full hour of direct
detections on the galactic centre.
These are great. Perfectly clear.
These are great, looks like this is
gonna be a great data set.
What about the other baselines?
That's excellent,
That is just excellent.
That's with zeroes,
that's with no corrections.
That's beautiful,
that is absolutely beautiful.
This gives me a lot of confidence
we'll be able to do what we wanna do.
Despite producing all this data,
Shep doesn't yet
have enough telescopes linked
together to build up a full image.
Yeah, so this is a great data set.
This is...
I'm very, very happy with this.
But this year, he might be able
to detect our first glimpse
of something that has,
until now, eluded us -
the shadow of the event horizon.
If someone said, "That's impossible,
you can't do it,"
I would say, "That's our job to try
and see things that can't be seen,
"to try to do things
that are great challenges."
The reason that we're interested
in this is, quite frankly,
because it's hard.
And if you'd asked me five years ago
if it was possible,
I flatly would have said no.
Shep believes that, within
ten years, his virtual telescope
will have the resolution to create
an image of a black hole
and put relativity
to the ultimate test.
That's very exciting for me
to know that we're almost there
and that with just a little more
effort, a little more ingenuity,
linking a few more telescopes
together, we'll be able to see
something extraordinary.
What would be the most
exciting thing to see?
Would you rather be the guy
who confirms Einstein's
predictions or the guy who...?
Yeah. Well, look, nobody wants
to be the person known as
the one who disproved Einstein.
At the same time, it would be
extremely exciting to be able to
make some observations
that would speak directly to
the validity of general relativity.
So either way, whether we see the
shadow as the right size or we see
the shadow as not the right size
would be incredibly exciting. I can't
decide which would be the best.
Whether the breakthrough comes
from a clue observed in the heavens
or theoretical detective work,
most physicists believe
we will eventually crack the
question of quantum gravity
and produce a unified theory
of everything.
A theory that could explain
the singularities at the heart
of a black hole
and may even provide the science
to predict what happened
before our universe existed.
I suspect that this is
a case where we need
a new Einstein
with a grand thought,
a completely new thought that
suddenly makes sense of things.
Many people think it's
never gonna happen, we humans
just aren't smart enough.
If we one day succeed
in finding this holy grail,
these equations of everything,
that's when the real work
begins to try and solve these
equations and predict stuff
and that'll keep physicists out of
harm's way for a long time, I think.
It doesn't dishearten me that
we don't understand everything
about the universe.
I find it wonderful and exciting.
It seems amazing
that we can understand anything
about the world around us.
It might seem as if it would
be easier if things like
black holes just went away,
but then, where would the fun be?
HE LAUGHS
We don't know what's out there.
People might give you an answer,
but they'll probably be wrong.
in deep space.
Something so incredibly massive,
it could swallow an entire star.
People tend to be fascinated by
things which are big and scary,
like dinosaurs,
and there's really nothing that's
bigger and scarier than a black hole.
Black holes are one of the most
destructive forces in nature.
But far from being monsters,
scientists now believe
they could hold the key to the
greatest mystery of all...
..where the universe came from.
Black holes are the doorway to
understanding the basic laws of
the universe around us.
The trouble is, they're
practically invisible and billions
of kilometres from Earth.
We think right there is a black hole.
Right there.
The more we try to understand them,
the stranger black holes become.
Everything we know about common
sense is thrown out the window.
The equations no
longer make any sense.
Black holes could force us to
abandon everything we thought
we knew about the universe.
There aren't questions
much bigger than this.
There's really a lot
that we don't understand.
We humans have evolved to make sense
of planet Earth and, so far,
we've made a pretty good stab at it.
In the last century, we've made
sense of the impossibly small...
..and the unimaginably large.
The enormity of space, and the
microscopic behaviour of atoms.
Yet there are some things that
threaten to elude us completely.
The harder we look,
the more questions we uncover.
Nowhere is this more true
than for a black hole.
I think of a black hole
as the symbol of what it is we
don't understand about the universe.
Black holes are one of the most
mysterious objects in the cosmos.
What are black holes made of?
Oh, OK. Already you've asked me
a question that I can't answer.
They fell out of Einstein's
theory of relativity in 1916,
and they've defied some of
our greatest minds ever since.
Are black holes made of anything?
Black holes... Hmm.
We don't really have any
idea what's going on, so....
I don't understand black holes.
I love black holes.
I love black holes
because I don't understand them.
There are many strange things in this
universe, but I think I've picked
the weirdest thing to actually study
which is the black hole.
Until recently, there wasn't
much evidence they existed at all,
because while we think they're
out there, we can't see them.
Black holes are, by definition,
completely black.
Nothing can escape it, even light,
and that's why it's called
a black hole,
because light can't come out of it.
Black holes, totally mysterious,
billions of kilometres away
and practically impossible to see.
Not that that's
stopped astronomers trying.
Doug Leonard even
thinks he's seen one,
or at least seen one form.
It took two years
and the Hubble space telescope.
It was only possible at all
because we think black holes
begin their lives as something
we've all seen in space - stars.
Stars, like our sun, are essentially
big, hot balls of gas
that have nuclear generators in their
core, that create all the heat
and light that we see shining.
Stars are enormous.
You could fit a million Earths
inside the sun, and the sun is not
even an abnormally large star.
But the most fascinating thing to
me about stars is that they die.
The theory is, black holes are born
when nature's most massive stars
burn off all their fuel
and violently collapse.
The cores of these massive stars
implode in less than a second.
They go from something
about the size of the Earth,
down to something
about the size of a small city.
And they don't stop there,
they continue imploding
all the way down to a point.
That point is what we
believe becomes a black hole.
And it's this process that
Doug Leonard believes he's spotted
when a massive explosion, supernova,
signalled the death of a star
in a remote galaxy billions and
billions of kilometres from Earth.
This is a picture of a galaxy
215 million light years away
and, indicated by the arrow,
this is the supernova,
a single star that exploded that, for
a short period of time, is as bright
as the entire galaxy that it's in.
And that
big blob there is the galaxy?
This big blob here
is the combined light
of tens of billions
of ordinary stars.
This is a close-up,
an extreme close-up, of the supernova
while it was still very, very bright.
Once the supernova was discovered,
we trawled the Hubble space telescope
archives
and found a picture of this exact
spot taken eight years earlier,
and what we found
at the location of the supernova
was this object, which is
actually an extremely bright star.
So what we did next was wait.
For two years, we waited for all the
fire arcs of this supernova explosion
to disappear and go out,
and we went back and took another
picture
of that exact spot in the sky,
and what we found was nothing.
The star was gone. It exploded as a
supernova and had now disappeared.
And we think right there
is a black hole.
Right there.
But I can't ever be
100% sure about that.
Is that because you can't see it?
Seeing nothing in black hole science
is a great thing.
You don't expect to see anything
when you're looking at a black hole.
As images of black holes go,
these few dark pixels are
about as good as it gets.
Without the death of a star,
there'd be no reason to suspect
there was a black hole there at all.
In fact, black holes are so hard to
see, most of what we know about them
hasn't come from those observing
the universe but from another group
of scientists - the theorists.
And the universe they study
is in their heads.
I think of theoretical physics
really as a great detective story
that you get to be part of.
The clues look so few and scant
that it seems like a hopeless case,
but if you work really hard at it,
often you can discover amazing stuff.
So it's amazing to me how much
one can actually learn about
reality just by detective work.
Black holes have existed in
theorists' minds and notebooks
for almost a century,
most notably in the mind and
notebook of Albert Einstein.
In 1916, Einstein changed
the way we see our world.
Purely by the power of thought,
and some clever mathematics,
he explained something we
all take for granted - gravity.
Gravity is the universal force
which holds everything together.
If you were to shut off gravity
right now, the sun would explode,
the Earth would fall apart,
and we'd be flung into outer space
at a thousand miles per hour.
So it's gravity that keeps
us rooted onto the Earth
and holds and binds the galaxy
and the solar system together.
Scientists had been able
to calculate the effects
of gravity for centuries.
But until Einstein, what caused it
had remained a mystery.
The answer was stranger
than anyone had imagined.
Einstein's great insight
was to realise that gravity is caused
by the bending of space and time.
So gravity is not really
pulling me down to the ground,
it is space that is pushing me down.
Einstein called his theory
general relativity.
The theory of relativity is infamous
for its difficulty.
I want to show that there's nothing
peculiarly difficult about it.
Space isn't simply an empty void,
it can be bent and stretched.
Let me illustrate this one example.
Let's imagine that this piece of
jelly is the space, then the presence
of matter is to distort the space.
All massive objects
like stars and planets
bend the space and time around them.
Any object that passes through
that warped space time will move
as if being pulled by a force,
and this is what we experience
as gravity.
Einstein's theory of relativity
does lead us into very
strange and unfamiliar paths.
Relativity is perfectly intelligible
to anybody who is willing to think.
Einstein's theory has withstood the
test of time for almost a century.
If there is one data point
out of place, we would have
to throw the entire theory out.
Everywhere we look in the heavens,
Einstein's theory comes
right on the spot.
But less than a year after it was
published, theorists realised
general relativity predicted
something so profoundly troubling,
many believed it couldn't
exist in the real world.
Anything very heavy and very small
would create such a strong
gravitational field
that space and time would be bent
and twisted to breaking point.
General relativity had predicted
the existence of black holes.
And it didn't just say
that they would exist...
general relativity allows
us to imagine what
it would be like to travel into one.
There's a beautiful analogy
between black holes and waterfalls
which actually lets us calculate all
properties of black holes exactly.
When you approach a waterfall,
the river flows faster and faster.
When you approach a black hole,
it's not the water that flows faster,
it's space itself.
The structure of a black hole
is similar to the relentless
flow of water over a waterfall.
It's an analogy that follows the
water from the river above
to the rocks below
and allows us to journey
into the very heart of a black hole.
If you're swimming upstream
from a waterfall,
there is an invisible line where the
water flows as fast as you can swim,
and if you cross that line,
it's the point of no return.
You wouldn't feel anything special,
but no matter how hard you struggle,
you can never escape
getting sucked all the way down.
For a black hole, the point of no
return is called the event horizon.
Past it, space is travelling inwards
faster than the speed of light.
Even if I can only swim at a maximum
speed, the water can obviously
fall much faster than that.
In the same way, even though
I can never go faster than
the speed of light through space,
space itself is allowed, in the black
hole, to fall as fast as it wants,
which means that everything
that's there, even a particle of
light trying to go upward,
will be sucked inexorably downwards
towards the centre.
Assuming your body
withstood the intense gravity,
leaving the universe forever
could be remarkably uneventful.
People used to think that you would
die at the event horizon, but we now
understand that for big black holes,
it's perfectly possible to still be
alive at this stage, you just have
no choice but to continue downward.
Everything would feel just normal
to you, you wouldn't even know
necessarily that you're doomed.
The only thing is that there's
no way you can ever get out again.
As you approach the
centre of the black hole,
you reach the inner horizon,
where everything falling in
meets matter being pushed out
by the hole's rotation,
similar to where the torrent
flowing over the falls
hits water rebounding back up.
Eventually, the inward flow
actually slows down to become slower
than the speed of light,
because the rotation of the black
hole causes a sort of repulsion.
At that point,
you have things colliding together
near the speed of light,
creating these ridiculously high
temperatures,
much hotter than inside of a star.
So hot that it would vaporise me
and any ordinary matter.
So that makes an ordinary traffic
accident seem tame in comparison,
now you're being hit by a truck
going almost 300,000km per second.
It's not a place
where I would wanna be.
The inner horizon is one of the
most extreme environments
in the universe.
According to general relativity,
the only place more extreme
is what lies beyond it.
Let me gather my thoughts
for a moment.
It's remarkably difficult for us
to actually calculate with Einstein's
equations what happens
inside the inner horizon.
But if I jumped into a black
hole, that's probably as
far down as I would get.
At the centre of a black hole,
the equations predict
something so strange,
it blows Einstein's greatest
achievement out of the water
and forces us to question
our understanding of the universe.
Einstein hoped that general
relativity would form the framework
for a new understanding of nature.
But at the heart of its
description of a black hole,
theorists found a problem
with Einstein's mathematics.
Something so disturbing,
his theory breaks down completely.
Einstein's equations of general
relativity simply say the following -
the Ricci curvature tensor
minus one half the metric tensor,
times the contracted curvature tensor
is proportional to the
stress energy tensor.
All this says that if I start
with a star, a black hole,
or even a universe,
that determines the curvature
that surrounds that
concentration of matter and energy.
But inside these equations,
there's a monster.
In the extreme gravity of the core
of a black hole,
Einstein's equations spiral wildly
out of control.
After every long tedious calculation,
I mostly get zeros but the
non-zero term is given as follows...
M is the mass of the black hole,
R describes the distance
from the black hole...
Here is the problem, right there...
when R is equal 0...
The point at
which physics itself breaks down.
So one over R
equals one over 0 equals infinity.
To a mathematician, infinity is
simply a number without limit.
To a physicist, it's a monstrosity.
It means that gravity is infinite at
the centre of a black hole, that
time stops. And what does that mean?
Space makes no sense, it means
the collapse of everything we
know about the physical universe.
In the real world,
there's no such thing as infinity,
therefore there is a fundamental flaw
in the formulation
of Einstein's theory.
According to Einstein then, all the
mass of the black hole is contained
within an infinitely small point
that takes up
precisely no space at all.
This impossible object of infinite
density and infinite gravity
is called the singularity.
We know what a singularity is.
A singularity is when
we don't know what to do.
To me what's so embarrassing
about a singularity
is that we can't predict anything
about what's gonna come out of it.
I could have a singularity
and - boom - out comes a
pink elephant with purple stripes.
And that's consistent with what
the laws of physics predicts,
because they don't predict anything.
A singularity is when our
understanding of nature breaks down,
that's what a singularity is.
Einstein realised
there was a problem
when he was shown this infinity,
but he thought that black holes could
never physically form, therefore
it was an academic question.
Sure, there was a problem, but it
didn't matter because mother nature
could never create a black hole.
In 1939, Einstein even wrote a paper
that appeared to prove black holes
would never be found
in the real world.
He hoped that there'd be some
physical mechanism that would stop
them from actually being produced.
And he really wanted to ask
the question
could they physically form? I think
he wanted to show the answer was no.
Given the physics known at the time,
his assumptions were reasonable,
but we've learned a lot of physics
since then so therefore we know that
his reasoning was incomplete.
At the time,
no-one had seen anything
to suggest Einstein was wrong.
For years, theorists were happy
that general relativity was a
complete understanding of
gravity in our universe.
Then, in the early 1970s,
astronomers made a breakthrough.
X-rays revealed hot gas
falling into objects
that were both extremely massive
and invisible to normal light.
For some, these images could
only be caused by black holes.
Material on the way into the
black hole can become very hot.
So hot that it becomes a million
degrees or even ten million degrees,
and that makes x-rays.
And just before this lump of material
disappears in the black hole,
it becomes a
bright flash of x-ray radiation.
Professor Reinhard Genzel is
Director of the Max-Planck Institute
for Extraterrestrial Physics.
He's spent the last 25 years
looking for proof of the existence
of one particular black hole.
While we can't see black holes as
such, we can see that they're there
and what they are
through their interaction
with visible objects like stars,
like gas in their vicinity.
Using radio telescopes,
astronomers had also seen objects
at the centres of galaxies
they suspected were black holes.
But to prove it, they'd need to
make more precise measurements.
Unfortunately, the nearest one
was 25,000 light years away
and totally obscured by dust.
It was
at the centre of our own galaxy.
It took Genzel and his team
nearly ten years
to develop an infrared telescope
capable of seeing enough detail
through the clouds of dust and
gas surrounding the galactic centre.
It took them a further 13 years of
painstaking observations before they
saw the thing they were looking for.
A star orbiting exceptionally
close to the centre.
Genzel knew that measuring
the star's orbit could tell him
about whatever it was orbiting.
So what we are seeing
are the innermost stars.
This green cross,
that's the centre of the Milky Way,
Sagittarius A star.
So in 2002, this star here
was very close to this
and the next year, it has moved
quite a substantial distance.
Because the galactic centre
is so far away,
this minute change means
the star is moving incredibly fast.
The separation which you see
is quite an enormous distance,
these are several light weeks.
And how far is that in kilometres?
OK...
So we have an hour, and we have a
day, and then take a week,
then we have the speed of light...
and so in kilometres, OK...
Wow, is that a big number -
180 billion kilometres.
Let me just check this so...
Yeah, a 180...180 billion kilometres.
I can't deal with that number.
It's hard to imagine what a
180 billion kilometres is.
Once you know the size
of a star's orbit and the time
it takes to go round,
it's a relatively simple calculation
to work out the mass
of the object it's orbiting.
Although tracking a single star
would be enough to measure
the mass of the central object,
Professor Genzal has mapped the
orbits of the 30 stars
closest to the galactic centre.
Here we have the innermost stars.
And these orbits we determine
uniquely from the motion
we have tracked over the years.
So it takes S2, this innermost star,
15 years to move once around
the centre of the Milky Way here.
The other stars are slower,
some of them take several
hundred years to move around.
From the size of each
of these orbits and the speed
the stars were travelling,
Professor Genzal calculated
the mass of the central object
and it was truly astronomical.
From these two numbers,
you already can determine uniquely
the central mass,
and we can do this
for each of these stars,
and we find that the mass is
always the same.
It's four million times
the mass of the sun.
Because the closest stars
pass so near to the centre,
this extraordinary mass, four
million times heavier than the sun,
must be in a very small space.
That really clinches this.
Because nothing fits in there,
into this relatively small volume
other than the massive black hole.
Even a schoolchild can analyse
the data and will come to the
same conclusion, it's very clear.
What Genzel had found
at the centre of our galaxy
was so heavy and so small,
it had to be a black hole,
but it was far too big
to have formed from
the collapse of a single star.
The black hole at the centre
of our galaxy is an object
which is much more massive
than the stellar black holes.
It's about four million times
the mass of the sun.
So we would call these
super massive black holes.
Although Professor Genzel
hadn't seen a black hole,
the indirect evidence
was so compelling
there could be little doubt
black holes were real
and it won him the 2008
Shaw Prize for Astronomy.
So the prize, the Shaw prize,
is a fairly large amount of money,
actually a million dollars,
which was given to me
and with no strings attached.
So I've given some of it
away to my colleagues,
some of it I kept myself and,
you know, people have convinced me
I should use some of that
to buy a new car.
Everything in our galaxy, the Earth,
the sun, a million million stars,
are all spinning around the super
massive black hole at the centre.
And ours isn't even
particularly impressive.
The super massive black hole
at the centre of our galaxy is
quite small relative
to other super massive black
holes that we know about.
There are galaxies,
not very far from ours,
in which we have seen
super massive black holes
up to a thousand times more massive,
several billion solar masses.
It now appears there's a super
massive black hole at the
centre of almost every galaxy.
And it could be that
these black holes aren't
simply agents of destruction,
because scientists have discovered
a unique relationship they share
with their parent galaxy.
So the mass of the
super massive black hole
is related to the mass of the parent
galaxy in a very simple way,
so I can show this
with a graph here.
So let me say, along one axis, I'll
show the mass of the black hole.
And I will measure this mass
in terms of the mass of the sun.
So let's say down here it is
a million times the mass of the sun.
Ten million, 100 million,
billion times the mass of the sun,
so that's the range of black
hole masses we have seen.
Along this axis, let me just
show you the mass of the galaxy.
Let me start with a billion
times the mass of the sun...
ten billion, 100 billion,
a million million solar masses.
Basically, when people measure
these two masses for
a large number of galaxies,
what they find is different
galaxies may come different places
here on this diagram.
And the miraculous thing is
that all these points seem to lie
more or less on a straight line
in this plot.
So there seems to be a...
some relation between the mass
of the black hole and the galaxy.
Roughly, the black hole
seems to be approximately
a thousand times less massive
than the galaxy in which it lives.
The existence of this kind of
a relation is rather surprising,
because what it means is
somehow the black hole is able
to influence the entire galaxy
and is actually modifying perhaps
how the galaxy forms and evolves.
This is the surprise
in this business.
In the last century,
black holes have gone
from being mathematical curiosities
to real objects in the cosmos,
millions of times the mass
of the sun and seemingly crucial
to the formation of galaxies.
I think black holes have got
maybe a little bit of a bad rap
as being the ultimate bad guys
in the universe.
It might well be that the monster
black holes in the middle of galaxies
actually helped the galaxies form
and therefore helped life
come on the scene.
As well as
super massive black holes,
astronomers believe there are also
billions of smaller stellar
black holes all over the cosmos.
How many black holes are there?
Roughly every galaxy has got
one big black hole in the middle,
super massive black hole,
and millions and millions
of smaller black holes.
Black holes are common,
they're a very common occurrence
in nature, fantastic thing.
Would we have thought it? No.
Think of all the galaxies,
each one with a raging
black hole in the centre.
Each one with perhaps thousands
of stellar black holes in them
and then you begin to realise
that black holes represent
one of the dominant forces
in the evolution of the universe.
Black holes, it turns out,
are everywhere.
And that means millions upon
millions of places where
Einstein's equations break down.
But physicists have always
known that relativity is
an incomplete theory of nature.
Although it beautifully describes
how gravity influences the motions
of planets, stars and galaxies,
it can never describe the world
at the smallest possible scale.
The realm of atoms and the
tiny particles that form them.
To do that,
they use a separate theory.
A theory called quantum mechanics.
You might wonder why we'd
wanna apply quantum mechanics
to something as large
as a massive black hole,
when quantum mechanics
deals with the very small.
And that's because, ultimately,
at the heart of a large black hole
is a singularity.
Whatever a singularity really is,
one thing we do know is
it must be very, very small.
It seems quite likely that,
in order to really
understand what goes inside a black
hole, we will need quantum mechanics,
that the final story
of how a black hole works
and what happens at the singularity
can only be understood when
quantum mechanics is included.
This subatomic world quantum
mechanics describes is nothing
like the world we experience.
Quantum mechanics tells us how the
world works at a fundamental level
and it is stranger
than you can imagine.
In the quantum world, the mere act
of observing changes what you see.
You can't say where something is,
only where it's likely to be
and anything that is possible,
no matter how unlikely,
happens all the time.
All of our notions about
how things behave change.
For example,
an object has a known location,
"I'm here, you're there,"
but at a quantum mechanical scale,
objects can be in many different
places at the same time, literally.
Yet as strange as quantum
mechanics is, theorists
believe the world it describes
is the true nature of reality.
Quantum mechanics is so weird,
it may sound like science fiction,
but it's not science fiction,
it's science fact,
and it's done better
than any other idea in physics.
It allows us to make the best
predictions we've ever made,
so like it or not,
it describes the world.
Quantum mechanics describes
everything, there's no escaping
quantum mechanics.
Every object is
a quantum mechanical object subject
to the laws of quantum mechanics.
And the world that we live in,
in the ultimate reality,
is a quantum world.
So there's no question
that there's some great truth
in quantum mechanics.
But there's one thing quantum
mechanics can't describe -
gravity.
And it's not normally a problem,
because atoms are so light,
the effect of gravity is irrelevant.
Most of the time,
quantum mechanics and gravity
leave each other in peace.
But there's one arena in which
they're both important,
and that arena is when things
are both very small
and the force of gravity
is very large.
And that's what happens
inside a black hole.
The singularity at the heart of
a black hole is both astronomically
heavy and infinitesimally small.
To understand it, quantum mechanics
alone wasn't enough.
It needed to be extended
to describe gravity.
A theory called quantum gravity.
The most obvious way
to create such a theory
was to make a quantum version
of Einstein's theory of relativity.
Proof of its success would be
a new understanding of black holes
that explained what really happens
in a singularity.
When physicists tried
to combine the two theories,
they encountered a familiar problem.
I insert this into the probability
that gravity will move from
one point to another point.
When I actually do this calculation,
I get yet another integral,
and when you do this integral,
you get something which
makes no sense whatsoever -
an infinity.
Total nonsense!
In fact, you get an infinite
sequence of infinities,
infinitely worse
than the divergences of
Einstein's original theory.
This is a nightmare
beyond comprehension.
The search for a theory of
quantum gravity had fallen apart,
because quantum mechanics and
general relativity proved to be
totally incompatible.
I think the most embarrassing
problem we have in theoretical
physics is that
we have these two different theories
which won't talk to each other.
We have Einstein's theory of
gravity, which beautifully describes
the very big and the very fast,
and then we have quantum physics,
which very successfully describes
the very small and yet, clearly,
nature has one unique way
of operating,
it's not schizophrenic,
and we humans just don't seem
to be able to find that way.
The failure of these two great
theories to understand black holes
means they are, at best,
an approximation to the laws
governing the universe.
The equations
no longer make any sense
and nobody knows exactly what
we're supposed to do about that.
Well, it's awful.
It means that physics is
having a nervous breakdown.
It means the collapse of physics
as we know it, you know?
Something is fundamentally wrong.
Nature is smarter than we are.
If we want to understand
the universe,
we must understand how
quantum mechanics and gravity
can live together and
so that's our challenge.
So it's quite a big question?
It's a huge question.
There aren't questions
much bigger than this.
We don't understand.
For nearly 100 years,
physics has been able to explain
the universe around us.
General relativity
perfectly describes the motions
of stars and galaxies.
And the world of atoms
is beautifully explained by
quantum mechanics.
Yet the discovery of black
holes means we don't
fully understand anything.
But far from being a problem,
black holes represent one of the
greatest opportunities in physics.
Black holes are the key to...
taking the next step,
the doorway to our next step
in understanding the basic laws
of the universe around us.
Unlocking the mysteries
of black holes could provide
the answer to the biggest question
every posed by the human mind.
Because there's one other place
where our current laws of nature
fail as dramatically as
they do in a black hole.
Any direction you look up
from the Earth at distant galaxies,
every single one of them is
moving away from us.
And the only way to make sense
of that is to think of the entire
universe just expanding.
This much we know
and have known for 80 years.
But then, there is an immediate
very profound implication.
If the universe is expanding,
long ago it was much more compact.
Nearly 14 billion years ago,
Einstein's theory says the
universe began in the Big Bang.
So just to get an idea
of the scale of the universe,
let's start with the Earth,
which is a pretty big object.
The sun is about a million times
more massive than the Earth
and most stars that we see in the
sky are about the size of the sun
and our galaxy has roughly
a million million of these stars.
And then the universe has roughly
a million million galaxies.
So that's a huge amount of stuff and
all that started from a singularity.
A point from which an initial
explosion got the expansion going.
That's the Big Bang.
For me, it's a weird concept,
as weird a concept
as it would be to any person who's
hearing about it for the first time.
But nature is doing it,
so that's what makes this exciting.
The singularity,
the impossible object found at the
heart of every black hole,
is the same impossible object found
at the very beginning of time.
The whole universe came out of
a singularity, all of us are the
product of a big singularity.
And so these singularities are very,
very interesting for many reasons.
There are two places in nature where
there apparently are singularities.
One is at the centre
of a black hole
and the other is at the beginning
of time itself at the Big Bang.
So it's quite likely,
if we understood the singularity
associated with the black hole,
we might resolve the question
of how the universe began
and where we came from.
Black holes could hold the key
to understanding what there was
before the universe existed.
But while we might seem
tantalisingly close,
black holes
and the theory that explains them
remain just out of reach.
Quantum gravity is the name
that we give to the solution
to this problem.
We don't really know
what quantum gravity is.
What's frustrating
with quantum gravity is that
previous revolutions in physics,
like quantum mechanics,
relativity theory,
were all brought on by
a lot of clues from nature
and, for quantum gravity,
we have almost no clues at all.
Right now, we're mostly stuck
with having to figure this out
with pencil and paper
just from theory.
The trouble is, although we know
black holes are everywhere,
we've never seen
a single one directly.
Have you ever seen a black hole?
No.
Have you ever seen a black hole?
No.
No-one has ever seen
a black hole directly.
Here is an object in outer space
that is beyond our mathematics,
beyond our physical theories,
demanding a theory beyond Einstein.
And, ironically, we can't see them.
But according to general relativity,
a black hole won't just create
a dark shadow in space,
this shadow would be surrounded
by a bright halo.
A black hole's immense gravity
warps the space around it,
focusing the starlight
coming from behind into a ring.
And, in theory at least,
we might even be able to see it.
You can see how they warp
with the space around them.
Shep Doeleman is
aiming to do just that.
He's devoted his career to
making the first direct
observations of a black hole.
I happen to really like
making the observations,
getting things done,
that there's a real joy
in assembling
a new kind of telescope.
There's a real joy in making
a new kind of measurement that
no-one has ever made before.
I guess that theoreticians feel the
same way when they think of an idea
that nobody has thought of before.
Shep is attempting to take a picture
of a shadow cast in space
by the super massive black hole
at the centre of our galaxy.
Directly observing how and
where general relativity fails
could provide vital clues
for the theory that replaces it.
Our observations are aimed squarely
at testing general relativity
in one of the most extreme
environments in the universe -
the event horizon of a black hole.
And it's there
that Einstein's theories
may break down.
For quantum gravity, seeing
the shadow exactly as predicted
by Einstein would be of little use.
If we see something that is not
consistent with general relativity,
the theorists will be extremely
interested and will want to know
everything about that
and that will point them in a new
direction for a theory of gravity.
We could look
at the centre of our galaxy,
see something completely unpredicted
around this black hole that would
send us back to the drawing board.
Shep is an astronomer at the
Haystack Observatory near Boston.
But the 37-metre telescope here
simply isn't big enough
to photograph the black hole
at the centre of our galaxy.
To do that, Shep needs a telescope
with 100,000 times the resolution.
And that requires a dish
4,500 kilometres across,
roughly the size of the
continental United States.
To observe the object we're after,
we have to create a telescope
that can see finer details
than any other telescope
in the history of astronomy.
The reason you haven't heard about
this massive telescope is because
it only exists in Shep's computer.
He hooked up radio telescopes from
across the continent, effectively
to product one giant virtual dish.
The way a normal telescope works is
it focuses all the light
because of its particular shape
into a single focal point.
When you link telescopes around the
world together, we don't have a lens.
We have to do it in a super
computer here in Massachusetts.
Shep's super computer,
the correlator,
pieces together the raw data
from all his separate telescopes
to build up a computer-generated
dish the size of America.
The level of detail you can see
with a single dish is limited
by the size of that dish.
But when you link telescopes
around the world together,
something magic happens.
You create a virtual dish
that's as big as the distance
between those dishes,
and that gives a level of detail
that's a thousand times finer
than you can get with a single dish.
Instead of creating pictures,
each of Shep's telescopes
produces reams upon reams of data.
And this is where we keep
all of the data when it comes
back from the telescopes,
each of these contains eight
very large hard disk drives and when
you have two modules together,
that contains as much data
as the US Library of Congress,
the largest library in the world,
and we have on these shelves
about 64 such libraries.
The amount of data is
just staggering, really.
We've spent a lot of money
in this project on disk drives.
There's so much data,
processing just a few nights'
observations takes months.
Hey, Mike, what's the latest
from the correlator?
Ah, actually a lot of interesting
things from last night.
You've got a full hour of direct
detections on the galactic centre.
These are great. Perfectly clear.
These are great, looks like this is
gonna be a great data set.
What about the other baselines?
That's excellent,
That is just excellent.
That's with zeroes,
that's with no corrections.
That's beautiful,
that is absolutely beautiful.
This gives me a lot of confidence
we'll be able to do what we wanna do.
Despite producing all this data,
Shep doesn't yet
have enough telescopes linked
together to build up a full image.
Yeah, so this is a great data set.
This is...
I'm very, very happy with this.
But this year, he might be able
to detect our first glimpse
of something that has,
until now, eluded us -
the shadow of the event horizon.
If someone said, "That's impossible,
you can't do it,"
I would say, "That's our job to try
and see things that can't be seen,
"to try to do things
that are great challenges."
The reason that we're interested
in this is, quite frankly,
because it's hard.
And if you'd asked me five years ago
if it was possible,
I flatly would have said no.
Shep believes that, within
ten years, his virtual telescope
will have the resolution to create
an image of a black hole
and put relativity
to the ultimate test.
That's very exciting for me
to know that we're almost there
and that with just a little more
effort, a little more ingenuity,
linking a few more telescopes
together, we'll be able to see
something extraordinary.
What would be the most
exciting thing to see?
Would you rather be the guy
who confirms Einstein's
predictions or the guy who...?
Yeah. Well, look, nobody wants
to be the person known as
the one who disproved Einstein.
At the same time, it would be
extremely exciting to be able to
make some observations
that would speak directly to
the validity of general relativity.
So either way, whether we see the
shadow as the right size or we see
the shadow as not the right size
would be incredibly exciting. I can't
decide which would be the best.
Whether the breakthrough comes
from a clue observed in the heavens
or theoretical detective work,
most physicists believe
we will eventually crack the
question of quantum gravity
and produce a unified theory
of everything.
A theory that could explain
the singularities at the heart
of a black hole
and may even provide the science
to predict what happened
before our universe existed.
I suspect that this is
a case where we need
a new Einstein
with a grand thought,
a completely new thought that
suddenly makes sense of things.
Many people think it's
never gonna happen, we humans
just aren't smart enough.
If we one day succeed
in finding this holy grail,
these equations of everything,
that's when the real work
begins to try and solve these
equations and predict stuff
and that'll keep physicists out of
harm's way for a long time, I think.
It doesn't dishearten me that
we don't understand everything
about the universe.
I find it wonderful and exciting.
It seems amazing
that we can understand anything
about the world around us.
It might seem as if it would
be easier if things like
black holes just went away,
but then, where would the fun be?
HE LAUGHS
We don't know what's out there.
People might give you an answer,
but they'll probably be wrong.