BBC - Atom - Part 1 of 3 - The Clash of the Titans

BBC - Atom - Full Series - Part 1 of 3 - The Clash of the Titans .............................................- Part 2 of 3 - The Key to the Cosmos .............................................- Part 3 of 3 - The Illusion of Reality
In this three-part documentary series, Professor Jim Al-Khalili tells the story of one of the greatest scientific discoveries ever: that the material world is made up of atoms.

This is the story of the greatest
scientific discovery ever.

The discovery that everything
is made of atoms.

The vast variety and richness
of everything we see around us
in the world and beyond,

how it's built up,
how it all fits together

is all down to atoms

and the mysterious laws they obey.

As scientists delved deep into the
atom, into the very heart of matter,

they unravelled Nature's
most shocking secrets.

They had to abandon everything
they believed in

and create a whole new science.

A science that today underpins
the whole of physics,
chemistry, biology,

and maybe even life itself.

But for me, the story of
how humanity solved the mystery
of the atom

is both inspiring and remarkable.

It's a story of great geniuses.

Of men and women driven by their
thirst for knowledge and glory.

It's a story of false starts
and conflicts, of ambition
and revelation.

A story that lead us through
some of the most exciting
and exhilarating ideas

ever conceived of by the human race.

And for a working physicist like me,

it's the most important story
there is.

On 5th October, 1906,

in a hotel room near Trieste,

a German scientist called
Ludwig Boltzmann hanged himself.

Boltzmann had a long history
of psychological problems

and one of the key factors
in his depression

was that he'd been vilified,
even ostracised,

for believing something that today
we take for granted.

He believed that matter cannot be
infinitely divisible
into ever smaller pieces.

Instead, he argued that ultimately
everything is made of basic
building blocks -

atoms.

It seems incredible now
that Boltzmann's revelation
was so controversial.

But 100 years ago,

arguing atoms were real
was considered by most
to be a waste of time.

Although philosophers
since the Greeks

had speculated that the world
might be made out of some kind of
basic unit of matter,

they realised that they were
far too small to see

even under the most powerful
microscopes.

Speculating about them was therefore
a complete waste of time.

But then, in the middle
of the 19th century,

whether or not the atom was real

was suddenly a question
of burning importance.

The reason was this.

Steam.

By the 1850s, it was changing
the world.

It powered the mighty engines,

the trains, the ships, the factories
of the Industrial Revolution.

So figuring out how to use it
more effectively

became a matter
of crucial commercial, political
and military significance.

Not surprisingly, then,

it became the key question
of 19th-century science.

The demand to build more powerful
and efficient steam engines

in turn created an urgent need

to understand and predict
the behaviour of water and steam

at high temperatures and pressures.

Ludwig Boltzmann
and his scientific allies

showed that if you imagined steam
as made of millions of tiny
rigid spheres,

atoms,

then you could create some powerful
mathematical equations.

And those equations are capable of
predicting the behaviour of steam

with incredible accuracy.

But these same equations plunged
Boltzmann and his fellow atomists
into controversy.

Their enemies argued that since
the atoms referred to in their
calculations were invisible,

they were merely
a mathematical convenience

rather than real physical objects.

To claim that imaginary entities
were real seemed presumptuous,

even blasphemous.

Boltzmann's critics argued that
it was sacrilegious

to reduce God's miraculous creation

down to a series of collisions
between tiny inanimate spheres.

Boltzmann was condemned as
an irreligious materialist.

The tragic irony
of Boltzmann's story

is that when he took his own life
in 1906,

he was unaware that
he'd been vindicated.

You see, a year before he died,

a young scientist had published
a paper

which undeniably, irrefutably,
proclaimed the reality of the atom.

You might have heard of
this young scientist.

His name was Albert Einstein.

In 1905, the year before
Boltzmann's suicide,

Albert Einstein was 26 years old.

His brash arrogance had upset
most of his professors and teachers

and he was barely employable.

Then he got his girlfriend pregnant.

That was followed
by a hasty marriage.

He needed a job. Any job.
Having not quite distinguished
himself at university,

he took up a job as a patents clerk
here in Berne in Switzerland.

He'd moved into this small
one-bedroom apartment on Kramgasse

with his young wife Mileva.

Despite dire personal straits,

the young Einstein
had a burning ambition.

He was desperate to make his mark
as a physicist.

And in 1905, during one
miraculous year,

the mark he made
was truly incredible.

Having an undemanding job
meant that young Einstein had
plenty of time on his hands

both at work and here
in this tiny apartment

to think deep thoughts.

In the space of just a few months,
he was to publish several papers

that would change science for ever.

Now, everyone's heard of
his Theory of Relativity,

even if they don't understand it.

His paper on the nature of light
would win him the Nobel Prize
a few years later.

But ironically, it wasn't either
of these two papers

that had the most impact
on the discovery of atoms.

The one that made all the difference

was a short paper on how tiny grains
of pollen danced in water.

Almost 80 years earlier, in 1827,

a Scottish botanist
called Robert Brown

sprinkled pollen grains
in some water

and examined it
through a microscope.

What he found was really strange.

Instead of the pollen grains
floating gently in the water,

they danced around furiously,

almost as though they were alive.
Now,

while this so-called
"Brownian motion" was strange,

scientists soon forgot about it.

They found it mundane, even boring.
Who cared if the pollen
jiggled about in the water?

And what had the jiggling to do
with atoms anyway?

For nearly 80 years, Brown's
discovery remained a little-known
scientific anomaly.

Then Einstein changed everything.

In one staggering insight,

Einstein saw that Brownian motion
was all about atoms.

In fact, he realised that the
jiggling of pollen grains in water

could settle the raging debate about
the reality of atoms for ever.

His argument was simple.

The pollen will only jiggle
if they were being jostled
by something else.

So Einstein said that the water must
be made of tiny atom-like particles

which themselves are jiggling

and continually buffeting
the pollen.

If there were no atoms,

then the pollen would stay still.

So Boltzmann and his contemporaries

had been rowing furiously
about this question for nothing.

The answer was there all along.

Einstein proved that
for Brownian motion to happen,

atoms must exist.

Einstein's paper went way beyond
just verbal arguments.

With flawless mathematics,

he proved that the dance
of the pollen

revealed the size of the atom.

And it's mind-numbingly tiny.

One tenth of a millionth
of a millimetre across!

A single human hair, itself
one of the narrowest things visible
to the naked eye,

is over one million atoms wide.

Let me put it another way.

There are more atoms
in a single glass of water

than there are glasses of water
in all the oceans of the world!

It sort of hurts your head
just to think about it.

Einstein's paper ended the debate

about whether the atom was real
or not.

And Boltzmann had been
totally vindicated.

The atom had to be real.

By the early years
of the 20th century,

the atom had arrived.

Scientists who'd argued
that the atom was real
were no longer heretics.

In a dramatic sudden reversal,

they became the new orthodoxy.

But they were to pay a huge price
for their success.

Before they'd had a chance
to congratulate each other
on discovering the atom,

it ripped the rug out
from under their feet

and sent them spiralling
into a bizarre and at times
terrifying new world.

And it all kicked off here

in what by 1910 was the world's
centre for atomic physics -

Manchester.

Two of the most extraordinary men
in the history of science

worked here in the physics
department of Manchester University
between 1911 and 1916.

They were Ernest Rutherford
and Niels Bohr,

on the face of it,
two very different personalities

and the unlikeliest
of collaborators.

Rutherford was from a remote part
of New Zealand

and grew up on a farm.

Bohr was born in Copenhagen,

wealthy and erudite,
virtually an aristocrat.

Rutherford was the ultimate
experimentalist.

He loved technology

and ingenious arrangements
of batteries, coils, magnets
and radioactive rocks.

But he was also blessed
with a profound intuition.

In contrast, Bohr was
the ultimate theoretician.

To him, science was about deep
thought and abstract mathematics.

Pen and paper, chalk and blackboard
were his tools.

Logic was his path to truth.

Although their approaches
to their work couldn't have been
more different,

they had one thing in common.

They were prepared to ditch three
centuries of scientific convention

if it didn't fit what
they believed to be true.

They were genuine revolutionaries.

Rutherford and Bohr were two of
the most extraordinary minds
ever produced by the human race.

But it would take every bit
of their dogged tenacity

and inspirational brilliance

to take on the atom.

In 1907, Ernest Rutherford took over
the physics department
in Manchester.

This was a period of
momentous scientific change.

Just over ten years earlier,
in Germany,

came the first demonstration of
weird rays that see through flesh

to reveal our bones.

These rays were so inexplicable

scientists didn't know
what to call them.

So they were named x-rays.

A couple of years after that,
in Cambridge,

it was shown that powerful
electric currents

could produce strange streams of
tiny glowing charged particles

that were called electrons.

And in 1896 in Paris,

came the most significant discovery
of all.

One that, more than any other, would
unlock the secrets of the atom.

The metal uranium was shown to emit
a strange and powerful energy

that was named radioactivity.

It seemed straight out of
science fiction.

Radioactive metals were warm
to touch.

They could even burn the skin.

And the rays could pass through
solid matter as if it wasn't there.

It truly was a marvel
of the modern age.

Rutherford was obsessed
with radioactivity.

All sorts of questions plagued him.

How was it made? Why did it come
in different forms?

How far could it travel
through a vacuum or through air?

Did it alter the materials
that it encountered?

In Manchester, together with
his assistants, Hans Geiger -
of Geiger counter fame -

and Ernest Marsden, he devised
a series of experiments

that would probe the enigma
of radioactivity.

1909. Manchester University.

These are the props.

Gold leaf, beaten until it's just
a few atoms thick.

A moveable phosphorescent screen

that flashed when struck
by radioactive waves.

And inside this box
is the star attraction.

A tiny piece of the metal radium.

Radium is an extraordinarily
powerful source

of the kind of radioactivity that
Rutherford had named alpha-rays.

They weren't really rays.
They were more like a steady stream
of particles.

Radium spat out these particles
like a machine gun
that never ran out of bullets.

Rutherford set his students
a simple-enough task.

Use the radium gun.

Shoot the alpha-radioactivity
at the gold leaf

and with the phosphorescent plate,

count the number of particles
that come out the other side.

In practice, that meant
sitting alone in the dark

and counting tiny,
almost invisible, flashes
on the phosphorescent screen.

It was deeply tedious,
but Rutherford insisted
that they keep at it.

Weeks passed and the team of
researchers found nothing unusual.

The alpha particles seemed to punch
through the gold

almost as though it wasn't there.

Very occasionally, they would swerve
slightly as they went through.

Hardly front-page news!

Now comes what must be the most
consequential off-the-cuff remark

in the history of science.

One that changed the world.

The story goes that Rutherford
bumped into his assistant, Geiger,
in the corridor.

Geiger reported that so far
they'd seen nothing unusual.

In response, Rutherford could have
easily nodded and walked on,

but he didn't.

He later claimed that he said what
he said at the time

for the sheer hell of it.

But I don't believe him.

Rutherford had great scientific
intuition

and I think he had a hunch that
something was about to happen.

Here's what he said to Geiger.

"Tell young Marsden to see if
he can detect any alpha particles

"on the same side of the gold leaf
as the radium source."

In other words, see if any alpha
particles are bouncing back.

Now, it's an extraordinary
suggestion from Rutherford

and one that he had
no logical reason to make.

After all, Geiger and Marsden
had spent weeks

seeing the alpha particles do
nothing but stream straight through
the gold leaf,

almost as though it wasn't there.

Why would any bounce back?

But Geiger and Marsden were young
and in awe of the big New Zealander.

They did their master's bidding
and went back into their dark lab

and watched patiently.

For days, they saw
absolutely nothing.

They strained their eyes
to the point of myopia

but didn't see a single alpha
particle bouncing back off the gold.

It seemed that Rutherford's
suggestion really was a stupid one.

But then the impossible happened.

One afternoon in 1909,

Geiger burst into Rutherford's
office with some astonishing news.

Very, very occasionally,

an alpha particle would indeed
ricochet back off the gold leaf.

Geiger calculated that only one in
8,000 alpha particles would do this.

It's a tiny percentage,

but Rutherford's mind reeled
with the news.

He would later say it was like
firing a shell at a piece
of tissue paper

and have it bounce back at you.

There and then, Rutherford knew
he'd struck physics gold.

Although it would take him
over a year

to fully understand why the alpha
particles would do this,

when he did, he would show humanity
for the first time

the inside of an atom.

People had barely got used to
the idea that atoms existed.

But now Rutherford knew
that this minute world,

one tenth of a millionth
of a millimetre across,

had its own internal structure.

Within the atomic,
there's a sub-atomic world.

And Ernest Rutherford believed
he knew what it looked like.

Rutherford realised that
the bouncing alpha particle

revealed an atom
that was totally unexpected.

It had no familiar analogy
on Earth.

So Rutherford looked for one
in the heavens.

He pictured the atom
as a tiny solar system.

Electrons, tiny particles
of negative electricity,

orbit around a minute
positively-charged object

called the nucleus.

Rutherford calculated that the
nucleus was 10,000 times smaller
than the atom itself.

That's why only one in 8,000
alpha particles bounced back.

They're the ones that hit
the tiny nucleus by chance.

The rest whizz by
without hitting anything.

The first astonishing consequence
of this idea

is that Rutherford's atom
is almost entirely empty space.

That's why nearly all the alpha
particles race through the gold
atoms as if there's nothing there.

There really is nothing there.

Consider the bizarre implications
of Rutherford's atom

by imagining it on a bigger scale.

If the nucleus were the size
of a football,

then the nearest electron would be
in orbit half a mile away.

The rest of the atom would be
completely empty space.

Let me explain it another way.

If you were to suck out
all the empty space
from every atom in my body,

then I would shrink down to a size
smaller than a grain of salt.

Of course, I'd still weigh the same.

If you did the same thing
to the entire human race,

then all six billion of us

would fit inside a single apple!

The atom was unlike anything
we had ever encountered before.

And it would only get stranger
and stranger!

Almost immediately,
a problem surfaced,

and it was a big one.

According to the tried and trusted
science of the time,

the electrons should lose
their energy,

run out of speed
and spiral into the nucleus

in less than the blink of an eye.

Rutherford's atom contradicted
the known laws of science.

The atom didn't care that it defied
scientific convention.

It's almost entirely empty space
and it's gonna stay that way.

I show no signs of shrinking down
to the size of a grain of salt.

And the Earth is, well,
the size of the Earth.

It's not getting smaller.

It's worth remembering
the time scale.

In six short years
from 1905 through to 1911,

the atom had announced its existence

with the fact that it was
unimaginably small.

Then it revealed that it was mainly
empty space.

And now it didn't obey
the known laws of physics.

Not surprisingly, all the
established scientists of the day,

including Einstein, were baffled.

Scientific ideas they'd put
their faith in all their lives

had failed completely
to explain the atom.

The atom now required
a new generation of scientists

to follow in Rutherford's footsteps.

Bold, brilliant and above all,
young.

It was crucial they had no loyalty
or attachment

to ideas held by
previous generations.

One of the first of this new breed
was Niels Bohr.

He sailed from Denmark in 1911

and made his way to English soil.

Having finished his studies
in Copenhagen,

Bohr decided to move abroad and be
at the centre of the new physics.

The trail led him to Britain,
Manchester University
and Ernest Rutherford.

Bohr had a brilliant mind,

at times hampered by a pathological
obsession with detail.

In fact, the story goes that Bohr
taught himself English

by reading Dickens' Pickwick Papers
over and over again.

Bohr was so captivated by
Rutherford's picture of the atom

that he made it his mission
to solve the puzzles

of why the atom didn't collapse

and why there was
so much empty space.

As one of the new breed
of theoretical physicists,

he was fearless in his thinking

and was prepared to abandon
common sense and human intuition

to find an explanation.

So, in a leap of genius,

he started to look for clues
about the atom's structure

not by looking at matter

but by examining the mysterious
and wonderful nature of light.

Now, atoms and light
are clearly connected.

Most substances glow
when they're heated.

For centuries people had realised
that different substances

glow with their own distinctive
colours, a bit like a signature.

So the green of copper, the yellow
of sodium and the red of lithium.

These colours associated with
different substances
are called "spectra".

And Bohr's great insight

was to realise that spectra are
telling us something about the inner
structure of the atom,

that they could explain
all that empty space.

Bohr's idea was to take Rutherford's
solar system model of the atom

and replace it with something
that's almost impossible
to imagine or visualise.

So sensible ideas like empty space
and particles moving around orbits
fade away.

They're replaced with something

that is one of the most
misunderstood and misused concepts
in the whole of science -

the quantum jump.

Now, it takes most working
physicists many years

to come to terms with quantum jumps.

Bohr himself said that if
you think you've understood it,

then you haven't thought
about it enough.

So I'm going to take a deep breath

and in under 30 seconds try
and explain to you

one of the most complicated concepts
in the whole of science

but one that underpins
the entire universe.

Bohr described the atom
not as a solar system

but as a multi-storey building.

The ground floor is where
the nucleus lives,

with the electrons occupying
the floors above.

Mysterious laws mean the electrons
can only live ON the floors,

never in-between.

Other mysterious laws
mean that sometimes

they can instantaneously jump
from one floor to another.

These are what we call
quantum jumps.

Now, Bohr had absolutely no idea
what these laws were.

But thinking like this allowed him
to make a startling prediction.

When an electron jumps from
a higher floor to a lower one,

it gives off light.

More significantly,

the colour of the light depends on
how big or small the quantum jump
the electron makes.

So an electron jumping from the
third floor to the second floor

might give off red light.

And an electron jumping from the
tenth floor to the second floor,

blue light.

To test his new theory,

Bohr used it to make a prediction.

Could it explain
the mysterious signature
in the spectrum of hydrogen?

After months of calculating
furiously,

he finally came up with the result.

And his prediction
was surprisingly accurate.

For the first time ever,

it looked like the spectrum
could be explained.

And back in 1913, that was big news.

But Bohr's new idea rested on
a single seriously-controversial
supposition.

Why should the electrons
and the atom

behave as though they were
in a multi-storey building?

And why should they magically
perform quantum jumps
from one storey to another?

There was no precedent for it
anywhere else in science.

When one physicist claimed
that the jumps were nonsense,

Bohr replied,
"Yes, you're completely right!

"But that doesn't prove
the jumps don't happen,

"only that you cannot
visualise them."

But not being able to visualise
things seemed to go against
the whole purpose of science.

Older scientists in particular
felt that science was supposed to
be about understanding the world,

not about making up arbitrary rules
that seem to fit the data.

Conflict between the two generations
of scientists was inevitable.

Bohr's weird new atom
and his crazy quantum jumps

were a shot across the bow
of traditional classical science

and the old school reacted angrily.

Leading the traditionalists

was giant of the physics world
Albert Einstein.

He hated Bohr's ideas

and he was going to fight them.

Anything to save the world of order
and common sense

from this assault by madness.

Bohr, though, was undeterred
and as the 1920s dawned,

the battle lines for one of the
greatest conflicts in all science
were drawn.

Einstein spent much
of the early 1920s

arguing against Niels Bohr,
with mixed success.

His celebrity status gave him power

so when he said he loathed ideas
like quantum jumping

that seemed plucked out of thin air,
people listened.

Then in 1925, a letter landed
on his desk

that turned out to be manna
from physics heaven.

Here finally was an idea
that described the atomic world

with the tried and trusted
principles of traditional science.

Einstein was ecstatic.
He told friends,

"Finally, a veil has been lifted
on how the universe works."

The letter came with the PhD thesis
of a young Frenchman.

And behind it lay
an extraordinary tale.

During the First World War, a young
French student spent his time

at the top of the Eiffel Tower,
as a radio operator.

His name was Prince Louis
de Broglie.

He came from French aristocracy
but he was devoted to physics.

He was so wealthy he built his own
laboratory off the Champs-Elysees.

After the war, De Broglie became
gripped by the mysteries and
controversies surrounding the atom.

And then his war-time experience
as a radio operator

gave him an intriguing idea.

Perhaps radio waves
could explain the atom.

Although invisible, they behave
very much like water waves.

Like ripples spreading out
across a pond,

radio waves obeyed
mathematical equations

that were reliable
and well understood and had been
worked out decades earlier.

So for his PhD thesis, De Broglie
imagined a kind of radio wave

pushing the electron
around the atom.

He called it a pilot wave.

This pilot wave would also hold
the electron tightly in its orbit,

stopping the atom from collapsing.

There were no strange instant
quantum jumps,

just intuitive common sense
familiar waves.

The relief felt by the
traditionalists was palpable.

"The atom is all about waves",
they cried,

and we understand what waves are.

Einstein and the traditionalists
felt that victory was within
their grasp.

They believed they had Bohr and the
new atomic science with its crazy
quantum jumps on the ropes.

But Niels Bohr wasn't the kind
of man to roll over and give up.

Even though he'd explained
the spectrum of hydrogen,

with his new revolutionary theory,

he had nothing like Einstein's
worldwide recognition.

But in his native Denmark,

his theory was enough
to make him a star.

Flushed with success, Niels Bohr
returned to Copenhagen in 1916,
a conquering hero.

His new-found celebrity status

meant he found it very easy
to raise money for research.

In fact, it was funding
from the Carlsberg brewery

that helped build
his new research institute.

You could say it was beer
that helped us understand
the secrets of the atom!

This institute became a leading
centre for research in theoretical
physics that survives to this day.

I came here in the early 1990s to
carry out research on nuclear halos.

And even then, this was the place
to be to do that sort of research.

This is the main lecture room
in the Niels Bohr Institute.

It doesn't look very impressive as
far as lecture halls are concerned,

but it's full of great
quirky details.

I remember lecturing here
a few years back

and I know that Niels Bohr himself
designed some of the machinery that
raised and lowered blackboards.

There's an incredible series
of boards,

one underneath the other,

of boards filled with his formulae

so that he wouldn't ever need
to rub out any of his equations.

It sort of goes on and on.

Bohr's reputation for radical
and unconventional ideas

made Copenhagen a magnet for young,
ambitious physicists.

They were keen to make their mark

and be a part of Bohr's
innovative new science,

which came to be known as
quantum mechanics.

In 1924, in defiance of Einstein and
De Broglie's traditional explanation

of the atom, the radicals revealed
a new theory,

based on Bohr's quantum jumps.

It was to be their most ambitious
and most controversial idea yet.

It was first developed by Wolfgang
Pauli, one of Bohr's rising stars.

Pauli took Bohr's bizarre
"quantum jumps" idea

and turned it into one of
the most important concepts
in the whole of science.

And I don't say that lightly.

Pauli's idea goes by the uninspiring
title of the Exclusion Principle.

But I think a better title would be
"God's best-kept secret"

because it explains
the vast variety of Creation.

The question Pauli's idea
tried to answer was this.

Every atom is made of
the same simple components.

So why do they appear to us
in so many different guises?

In such a rich variety of colours,
textures and chemical properties?

For instance, gold and mercury.

Two very different elements.
Gold is solid,

mercury is liquid. Gold is inert,
mercury is highly toxic.

And yet they differ
by just one electron.

Gold has 79 and mercury has 80.

So how does one tiny electron
make all that difference?

What Pauli did was pluck another
quantum rule out of thin air.

Remember Bohr's multi-storey atom?

The nucleus is the ground floor

with the electrons progressively
filling the floors above.

Pauli said there's another quantum
rule which states crudely

that each floor can only accommodate
a fixed number of electrons.

So if we want to add
another electron to the atom,

it has to check for a vacancy
in the top floor.

And if that floor is full,

another floor or shell is created
above it for the electron.

In this way, a single electron

can radically change the shape
of the atom

and this, in turn,
affects how the atom behaves

and how it fits together
with other atoms.

So Pauli's principle
really is the basis

upon which the whole of chemistry,
and ultimately biology, rests.

Pauli's Exclusion Principle
was a major breakthrough
for Bohr's quantum mechanics.

For the first time, it seemed
to offer us a real understanding

of the incredible variety
in the world around us

and possibly life itself.

Its success blew a large hole
in Einstein's defence
of the old physics.

And like quantum jumping, it was
straight out of the weird rule book
of atomic physics.

Pauli didn't explain why
his principle worked.
He said it just did.

Einstein and the traditionalists
hated it.

For them, this sounded like
arrogant, unscientific nonsense.

But they needed to hit back,
and hit back hard.

So far, the debates
about the new atomic physics

had been polite and gentlemanly.

Now the two sides wheeled out
their biggest guns.

Two of the greatest names
in physics.

They were two very contrasting
characters who loathed each other.

For the new revolutionary science

was a buttoned-up,
uber-competitive German

called Werner Heisenberg.

For the conservatives was
a debonair, Byronesque Austrian

called Irwin Schroedinger.

Irwin Schroedinger,

passionate and poetic,
a philosopher and a romantic.

He wrote books on the Ancient
Greeks, on philosophy, on religion,

he was influenced by Hinduism.

He was also a very flamboyant
character,

cool, suave, sophisticated,

a dapper dresser
and a big hit with the ladies.

Schroedinger's promiscuity
was legendary.

He had a string of girlfriends
throughout his married life,

some much younger than him.

In 1925, 38-year-old Schroedinger

stayed at the Alpine resort of Arosa
in Switzerland

for a secret liaison
with an old girlfriend

whose identity remains a mystery
to this day.

But their passion proved to be
the catalyst for Schroedinger's
creative genius.

Another physicist said of
Schroedinger's week of
sexually-inspired physics,

"He had two tasks that week.

"Satisfy a woman and solve
the riddle of the atom.

"Fortunately, he was up to both."

He took De Broglie's idea
of mysterious pilot waves guiding
electrons around an atom

one crucial step further.

He argued that the electron
actually was a wave of energy

vibrating so fast it looked like
a cloud around the atom,

a cloud-like wave of pure energy.

What's more, he came up with
a powerful new equation

which completely described
this wave

and so described the whole atom

in terms of traditional physics.

The equation he came up with we now
call Schroedinger's wave equation.

It's incredibly powerful.

What's unique about it

is that it features a new quantity
called the wave function

which Schroedinger claimed
completely described the behaviour
of the sub-atomic world.

Schroedinger's equation and
the picture of the atom it painted,

created during a sexually-charged
holiday in the Swiss Alps,

once again allowed scientists
to visualise the atom

in simple terms.

It's hard to over-estimate the
relief Schroedinger's idea brought

to the traditional physics
community.

Strange though his picture
of the atom was,

at least it was a picture

and scientists love pictures.

They allowed them to use
their intuition.

But there was still a deep nagging
problem,

one that the radicals felt
Schroedinger just couldn't
reconcile.

His new theory still couldn't
account for Bohr's strange,
instantaneous quantum jumps.

The time had come for the radicals
to hit back.

In the summer of the same year,

one of Niels Bohr's protegees,
Werner Heisenberg,

was travelling to an obscure island
off the north coast of Germany.

He was fiercely competitive
and took Schroedinger's ideas
as a personal affront.

He felt strongly that
the strangeness of the instant
quantum jumps

was actually the key
to understanding the atom.

He thought the atom was so unique
and unusual,

it shouldn't be compromised
through a simple analogy

like a wave or an orbit,

or even a multi-storey building.

He believed it was time to give up
any picture of the atom at all.

Werner Heisenberg, one of the true
geniuses of the 20th century.

Young, athletic, a great mountain
climber, an excellent pianist,

he was also an exceptional student.

At the age of just 20, he was well
on his way to finishing his PhD

and being courted by the great
universities across Europe.

Now, in the summer of 1925,

he was suffering from a particularly
bad bout of hay fever.

His face was swollen up
almost beyond recognition.

He decided to escape alone, here,

to this beautiful but isolated
island of Helgeland.

He walked along the beaches,
he swam, he climbed the rocks

and he pondered.

Ever since he'd encountered
atomic physics,

Heisenberg felt in his bones
that all human attempts
to visualise the atom,

to model it with familiar images,
would always fail.

The atom, he believed,
was too capricious,

too strange to ever be explained
that simply.

So he decided to abandon
all pictures of it

and describe it using
pure mathematics alone.

But as he pondered, he realised the
atom didn't just defy visualisation,

it even defied
traditional mathematics.

It was while he was here
on Helgeland

that Heisenberg had
an incredible revelation.

He realised that in order
to describe certain properties
of atoms,

He had to use a strange new type
of mathematics.

It seems that certain properties
like where an electron is at a given
time and how fast it's moving,

when multiplied together, the order
in which you multiply them matters.

Let me try and explain.

If we multiply two numbers together,
it doesn't matter which order
we do it in.

So three times four is clearly
the same as four times three.

But when it came to atoms,

Heisenberg realised that the order
in which he multiplied quantities
together gave a different answer.

This quickly led him
to other discoveries

and he was convinced that
he'd cracked a code in the atom,

that he'd somehow found
the hidden mathematics within.

He was so excited.
He was also very scared.

That night, he climbed
to the top of a rock

and sat there waiting till dawn.

He called it his
"Night of Helgeland".

Back at university in Goettingen, he
told his colleague Max Born about it

and they then worked together
intensely for several months

developing a whole new theory
of the atom.

A theory that today we call
matrix mechanics.

Matrix mechanics uses complex arrays
of numbers,

rather like a spreadsheet.

By manipulating these arrays,

Heisenberg and his mentor
the brilliant physicist Max Born

could accurately predict
atomic behaviour.

But for Einstein
and the traditionalists,

this was pure scientific heresy.

An atom can't actually be
a matrix of numbers.

Surely we're made of atoms,
not numbers?

Back in Copenhagen,

Bohr and Pauli were thrilled with
matrix mechanics.

So what if we couldn't imagine
the atom as a physical object?

They exalted in the purity
of the mathematics

and launched into vicious attacks
against Schroedinger's
vulgar sensual waves.

Heisenberg wrote, "The more
I reflect on the physical portion
of Schroedinger's equation,

"the more disgusting I find it.

"In fact, it's just bullshit."

But Schroedinger was equally
scathing of Heisenberg,

saying he was repelled by his
methods and found his mathematics
monstrous.

In Munich in 1926, their enmity
began to reach boiling point.

Schroedinger was to give a lecture
on his wave equation.

Heisenberg scraped together
the money to travel to Munich
for the lecture.

To finally come face to face
with his rival.

What was at stake was more than
just Heisenberg's reputation.

He believed Schroedinger's
simplistic approach

wasn't just misguided,
but totally wrong.

And his intention
was nothing less than
to destroy Schroedinger's theory.

Schroedinger delivers his lecture
on the new wave mechanics

to a packed audience.
Standing room only.

He writes down
his new wave equation.

To Schroedinger, this describes
a real physical picture of the atom.

with electrons as waves
surrounding the atomic nucleus.

24-year-old Werner Heisenberg
is in the audience.

He can hardly contain himself.

At the end of the lecture he
stands up and delivers a monologue
attacking Schroedinger's approach.

For Heisenberg it's impossible to
ever have a picture

of what the atom is really like.

The audience is on
Schroedinger's side.

They much prefer his simple
physical interpretation

to Heisenberg's abstract,
complicated mathematics.

Heisenberg is booed. He's told
to sit down and be quiet.

He leaves the lecture sad
and depressed.

Heisenberg returned to Copenhagen
with his confidence severely dented.

There at the institute, he and Bohr
reached their darkest moment.

Almost all of the scientific
community was against them.

They felt isolated, desperate.
Their backs were against the wall.

Despite this, they stubbornly
refused to give up
their controversial theory.

This attic room was Heisenberg's
study back in 1926.

Bohr would come up here
night after night

where he and Heisenberg
would argue about the meaning
of quantum mechanics.

They would argue so passionately,

that on one occasion
Heisenberg was reduced to tears.

And then, as Heisenberg stared
out of his attic window in despair

at the park below,

an extraordinary thought
occurred to him.

It struck him why an atom
can't be visualised,

why it can't be understood
intuitively.

It's not just because it's tiny,
tricky and difficult.

It's because it's inherently
unknowable.

He realised that there was
a fundamental limit to how much we
can know about the sub-atomic world.

For instance, if we know where
an electron is at a particular
moment in time,

then we cannot know
how fast it's moving.

But if we knew its speed,
we wouldn't know its position.

This ambiguity isn't a shortcoming
in the theory itself.

Nor is it due to the clumsiness
of the way we carry out
our measurements,

but a fundamental truth
about the way Nature behaves

at the sub-atomic scale.

It became known as Heisenberg's
Uncertainty Principle.

And it's probably the most profound,
incredible, yet unsettling concepts

in the whole of science.

What Heisenberg had uncovered
through his abstract
matrix mechanics

was a deep and shocking truth
about the atomic world.

Atoms are wilfully obscure.

We can never fully know an atom's
position and speed simultaneously.

The atomic world just refuses
to allow that to happen.

It was completely mind-boggling.

But once they accepted it,

Heisenberg and Bohr found the boost
of confidence to be even more bold.

They realised uncertainty
forced them to put paradox right
at the very heart of the atom.

Atoms are not just unimaginable.
They're self-contradictory.

They behave both like particles
and waves.

And it gets weirder.

When you're not looking at an atom,
it behaves like a spread-out wave.

But when you look to see
where it is,

it behaves like a particle.

This is insane!

First, atoms couldn't be visualised
at all,

now they change completely
in character depending on whether
or not you're looking at them.

The Uncertainty Principle
had changed everything.

It revealed a shocking contradiction
at the heart of Nature.

Everything we see is made of atoms.

And yet atoms themselves
are unknowable.

They can only be understood
through mathematics.

For the first time for Bohr and
Heisenberg everything about the atom
fell into place.

By the autumn of 1927,

full of confidence
and smarting for a fight,

they knew they were finally ready
to take on the conservatives.

For this physics showdown,

they chose the Solvay Conference
in Brussels.

All the world's leading atomic
physicists would attend.

If Bohr and Heisenberg
were successful,

they would lead a total
scientific revolution.

This is amazing.
I'm looking at original footage

of the Solvay delegates
coming out of these doors.

There's Bohr talking to Schroedinger
and there's Heisenberg behind them.

There's Pauli, strange-looking guy.

There's Einstein coming down
with a big smile on his face.

For the week of the conference,
all that the delegates could think
and talk about

was Bohr's quantum mechanics.

With uncertainty now a central
plank,

it was a truly formidable theory.

And over the week,
the final showdown played out

between Bohr and his arch-rival,
Albert Einstein.

Einstein hated quantum mechanics.

Every morning he'd come to Bohr
with an argument

he felt picked a hole
in the new theory.

Bohr would go away, very disturbed,
and think very hard about it,

and later he'd come back with
a counter-argument that dismissed
Einstein's criticism.

This happened day after day until
by the end of the conference,

Bohr had brushed aside
all of Einstein's criticisms

and Bohr was regarded
as having been victorious.

And with that,
his vision of the atom,

which became known as
the Copenhagen Interpretation,

was suddenly at the very heart
of atomic physics.

At the end of the conference, they
all gathered for the team photo.

Never before or since have so many
great names of physics

been together in one place.

At the front, the elder statesman
of physics, Hendrik Lorentz,

flanked on either side by
Madame Curie and Albert Einstein.

Einstein's looking rather glum
because he's lost the argument.

Louis de Broglie has also failed
to convince the delegates
of his views.

Victory goes to Niels Bohr.

He's feeling very pleased
with himself.

Next to him, one of the unsung
heroes of quantum mechanics,

the German Max Born who developed
so much of the mathematics.

And behind them, the two
young disciples of Bohr,

Heisenberg and Pauli.

Pauli is looking rather smugly
across as Schroedinger,

a bit like the cat
who's got the milk.

This was the moment in physics
when it all changed.

The old guard was replaced
by the new.

Chance and probability became
interwoven into the fabric
of Nature itself

and we could no longer describe
atoms in terms of simple pictures

but only using pure abstract
mathematics.

The Copenhagen view
had been victorious.

Although Einstein went to his grave
never believing quantum mechanics,

Solvay 1927 was the turning point

at which the rest of
the science establishment

came to embrace
the Copenhagen Interpretation.

And that interpretation
is still accepted today.

All the physics that I use
in my research,

certainly the quantum mechanics
that I teach my students

and that fills the text books
on my shelves

is based on ideas that were hammered
out and crystallised here at the
Solvay Conference in October 1927.

In a sense, everything I know
about the way the world around me
is made up

started here.

The quantum mechanical description
of the atom

is one of the crowning glories
of human creativity.

Over the last 80 years, it has been
proven right, time after time

and its authority has never been
in doubt.

It's a monumental
scientific achievement.

Between 1905 and 1927,

science changed our view
of the world.

It also changed our view
of science itself.

As scientists probed the tiniest
building blocks of matter,

they created the most successful
and powerful theory ever -

quantum mechanics.

It allows us to describe
what everything in the universe
is made of,

how it interacts
and how it all fits together.

But it comes at a huge price.

At its most fundamental level,

we have to accept that Nature is
ruled by chance and probability.

Heisenberg's Uncertainty Principle

dictates that there are certain
limits on the sorts of questions
we can ask the atomic world.

Most crucially, while we now know
so much more

about what an atom is
and how it behaves,

we have to give up any possibility
of imagining what it looks like.

Our human nature has forced us
to ask questions of everything
we see around us in the world.

What we've discovered has been
beyond our wildest imagination.