Atom (2007–…): Season 1, Episode 3 - The Illusion of Reality - full transcript
In 1912, in a hot air balloon
about three miles above the ground,
an Austrian scientist called
Victor Hess made one of the most
astonishing discoveries in science.
Up here Hess found that incredibly
mysterious rays of energy
were pouring in from outer space
and streaming through the Earth.
They were incredibly powerful,
yet unlike anything seen before.
They were called cosmic rays.
At the same time
in laboratories down below,
scientists were studying equally
mysterious and powerful energy rays
pouring out from the interior
of atoms - known as radioactivity.
Mysterious rays from the vast
emptiness of space and mysterious
rays from deep within the atom,
the tiniest building block.
No one really understood what they
were or if they might be connected.
Then an incredible story unfolded.
Cosmic rays and radioactivity
turned out to be connected in a way
so shocking that it beggars belief.
The discovery of this connection
would force us to rethink
the nature of reality itself.
The world we think we know,
the solid, reassuring world
of our senses,
is just a tiny sliver
of an infinitely weirder universe
than we could ever conceive of.
Our reality is just an illusion.
In the years up to the mid-1920s,
the atom revealed
its strange secrets to us
at a prodigious rate,
as it produced one scientific
revolution after another.
In 1897, Marie Curie studied
strange rays pouring out
of some rare metals.
She called them radioactivity.
Then, in 1905, Albert Einstein
conclusively proved the existence
and size of an atom
by studying
the way pollen moves in water.
A few years later, the New Zealander
Ernest Rutherford performed
an experiment in Manchester
that revealed to him the shape
of the interior of an atom.
Scientists were shocked to discover
that the atom is almost entirely
empty space.
The question then became,
"How could this empty atom possibly
make the solid world around us?"
The answer to that was worked out
by a group of revolutionary
physicists in Denmark.
They proposed that the world
of the atom ran on principles
which were completely different
to any mankind had ever seen before.
It meant that the atom, the basic
building block of everything
in the universe, was unique.
And perhaps
outside human comprehension.
Then a scientist explored the
nucleus, the tiny heart of the atom.
They found it bursting
with powerful energy.
This discovery gave them
the potential to bring about
the destruction of the Earth,
but in a shocking turnaround,
it also gave them
a fundamental understanding
of how the universe was created.
And yet, despite this,
the journey to understand
the strange and capricious atom
had only just started.
In 1927, a young man was studying
at the Mathematics Department
of Cambridge University.
Shy, awkward, clumsy
and frighteningly brilliant,
his name was
Paul Adrien Maurice Dirac.
It's probably fair to say that
Paul Dirac isn't a household name.
But it should be. He was recently
voted, by other physicists,
as the second-greatest
English physicist of all time,
second only to Newton.
And he deserves the accolade.
All the brilliant minds
that pioneered atomic physics
were left trailing by Dirac,
aghast at the sheer boldness
and lateral thinking in his work.
When Einstein read a paper by
the then 24-year-old Dirac, he said,
"I have trouble with Dirac.
"This balancing on the dizzying path
between genius and madness
is awful."
In 1927, for reasons no one
has ever really fathomed,
Paul Dirac set himself a task
that was monumental in its scope -
to unify science.
To bring its scattered parts
into one beautiful entity.
And what this meant, above all,
was to unite the two most difficult
and counter-intuitive ideas
in history.
Here's what Dirac was trying
to reconcile.
First there's quantum mechanics,
mathematical equations describing
the atom and its component parts.
Then there's Einstein's
Special Theory of Relativity,
which at first seems unrelated.
It deals with loftier matters
like the nature of space and time.
One of its consequences is that
objects behave very differently
when they travel
close to the speed of light.
The first thing you might ask is
why would anyone want to reconcile
two such different theories?
Well, by the late 1920s,
the equations of quantum mechanics
were consistently getting the wrong
answers when describing electrons,
one of the constituents of atoms,
as they move at very high speed.
But for Dirac there was
a much more esoteric motivation.
He was once quoted as saying,
"A physical theory
must have mathematical beauty".
So for him, the fact that quantum
mechanics and relativity weren't
reconciled wasn't just inconvenient,
it was downright ugly.
So around 1925, in Cambridge,
Dirac put his extraordinary mind,
a mind that even Einstein had
trouble keeping up with, to work.
This is Room A4, New Court.
It was Dirac's original study.
The original fireplace
has been boarded up,
but it was here that Dirac tried
to understand and bring together
the two new ideas of physics.
Word is Dirac would sit here
in front of his blazing fireplace
and try to understand and bring
together these two different
theories into one unified picture,
one single equation.
For three frustrating years,
he laboured alone on the problem.
Then, one evening in early 1928,
he had an amazing revelation.
The only way I can explain
what happened is to say that
the equations of quantum mechanics
and special relativity
coalesced inside Dirac's mind.
Einstein's description of space and
time somehow stretched and squeezed
the existing equations of the atom.
They bent and twisted them
into new weird and wonderful shapes.
Then, guided by his unshakeable
belief that nature's laws
must be beautiful,
Dirac homed in on one equation,
an entirely new description
of what goes on inside the atom.
Dirac knew it was right
because it had mathematical beauty.
Here it is, the Dirac equation.
Don't try to understand it.
Just look at it and marvel.
As human achievements go, it's up
there with King Lear, Beethoven's
Fifth or The Origin of the Species.
Hidden in these symbols is the
perfect description of how reality
works at a fundamental level.
It's the key
to nature's secret code.
With perfect mathematical elegance,
Dirac's equation describes
an atomic particle
travelling at any speed,
right up to the speed of light.
That much Dirac was expecting
to achieve, but when he looked
at his own equation more carefully,
he noticed something breathtakingly
revolutionary about it.
He later said his equation
knew more than he did.
In essence, Dirac's equation was
telling him there's another universe
we've never noticed before.
That's because instead of
his equation having one answer,
it has two.
The first describes the universe
we know, made of the atoms
we're familiar with.
The second describes
a mirror image to our universe,
made of atoms whose properties
are somehow reversed.
Science fiction fans will know
what's coming. As well as matter,
Dirac's equation predicts
the existence of antimatter.
Dirac's theory seemed to say that
for everything in our known world,
for every part of an atom,
every particle, there can exist
a corresponding anti-particle
with the same mass, but exactly
opposite in every other way.
And just like a world in a mirror,
the universe made of antimatter
atoms would look and work
just like ours.
It would be perfectly possible
for me to be made out of antimatter.
Anti-me would look and behave
exactly the same as original me.
And it's possible that out there
in the vast expanses of the cosmos,
there are stars and planets and even
living beings made of antimatter.
There's one final prediction
of the Dirac equation.
It states that matter
and antimatter must never
come into contact. If they do,
they will annihilate each other
in a conflagration of pure energy.
The combined mass of matter
and antimatter would convert
completely into energy,
according to Einstein's
famous equation, E=MC2.
So if I ever do meet
my doppelganger, we would explode
with an energy equivalent to
a million Hiroshima-sized
atom bombs.
All this sounds like science fiction
and the idea of antimatter
has inspired huge swathes of it.
But the truth is antimatter,
particularly antimatter electrons,
called positrons
are made routinely now
in laboratories.
Positrons are used in sophisticated
medical imaging devices
called PET scanners
that can see through our skulls
and accurately map pictures
of our brains.
But back in the 1920s, the initial
reaction to Dirac's equation among
physicists was deeply sceptical.
Even Dirac had trouble
believing his own results.
Antimatter seemed
such a preposterous concept.
Then came resounding confirmation
of the Dirac equation
and all its paradoxical implications
and it came from the most
unexpected place - outer space.
In 1932, physicist Carl Anderson
was working here at Caltech
in Los Angeles
when he made an amazing discovery.
He'd been studying cosmic rays.
These are high-energy subatomic
particles that continuously bombard
the Earth from outer space.
To do this, he used a device
called a cloud chamber.
This is basically a vessel filled
with a fine mist of water vapour.
This shows up the tracks
of the particles as they stream down
through the vapour.
Placed inside a magnetic field,
these tracks are deflected one way
or the other,
depending on the electric charge
of the particle. Positive tracks
go one way, negative the other.
Anderson found evidence of particles
that look exactly like electrons,
but which are deflected
in the opposite direction.
He had discovered
Dirac's anti-electrons,
particles of antimatter.
The Dirac equation
is an impressive achievement.
Its prediction of the existence
of antimatter, using abstract
mathematics alone, would be enough
to make it a significant milestone
in the history of human thought.
But within just a few years
of publication, first Dirac
and then others sensed
that his new equation
was telling them something profound,
something completely new
about nature. And they were right.
But the revelation hidden within
Dirac's equation would take the best
efforts of the greatest minds
30 years to uncover.
The problem
with Dirac's equation was this -
although it was incredibly powerful
and led to the discovery
of antimatter,
ultimately it could only describe
a single electron. It fails
completely to explain what happens
when there is more than one electron
present. What was needed
was a new theory to explain
how electrons interact
with each other.
And that turned out to be
the most difficult question
of the mid-20th Century,
but when an answer came,
it was to bring with it
an unexpected revelation.
This office in Caltech
used to belong
to the great Richard Feynman.
In our story of so many geniuses
of science,
Feynman stands, in my view,
second only to Einstein in the list
of greatest 20th Century physicists.
Feynman wasn't just
a common or garden genius.
Many referred to him as a magician,
he was so smart,
such an innovative thinker.
Like Einstein, he became this
mythical figure, a household name.
Feynman was a larger-than-life
character with a huge personality.
He loved cultivating
and telling anecdotes about himself.
He used to frequent strip clubs,
he had affairs with his students
and was rumoured to go to orgies,
but his greatest contribution
to physics was the part he played
in developing the next phase
of quantum mechanics.
Feynman and his contemporaries
were attempting to pick up
the atomic torch from Paul Dirac
and develop a theory that took
our understanding of the atom
literally a quantum leap further.
Like Dirac's antimatter equation
before, the intention
of the new theory was unification.
They wanted to understand
how electrons affect each other.
In other words, it aimed to explain
how everything works together
through the electromagnetic field.
They called their unification
project quantum electrodynamics
or QED.
The project was a formidable
challenge, but the end result
was magnificent -
nothing less than
the most far-reaching and accurate
scientific theory ever conceived.
For instance, it predicts
a certain property of the electron
called its magnetic moment
to have a value of...
Experiments measure precisely
the same number. That's an agreement
between theory and experiment
to one part in ten billion. It's
an unprecedented level of agreement.
It's like measuring the distance
between London and New York
to within the thickness of a hair.
The phenomenal accuracy
of quantum electrodynamics
shows it to underpin
almost everything we experience
in the physical world.
It's as close to a theory of
everything as we have ever come.
It defies the laws of nature -
the atomic scale.
It explains shape, colour, texture
and the way almost everything
interacts and fits together.
It encompasses everything
from the biochemistry of life to
why we don't fall through the floor.
So what does QED actually say?
Well, this is where the going
gets very tough.
It may be a wonderful
scientific description of nature,
but trying to understand what
Feynman was doing with his theory
is almost impossible.
This is what he himself said
when he introduced his theory:
"It is my task to convince you
not to turn away
because you don't understand it.
"My physics students don't
understand it. That's because
I don't understand it. Nobody does."
If the inventor of the theory
doesn't understand, what possible
hope is there for the rest of us?
With that disclaimer,
I'm going to try to explain anyway.
First, you have to abandon your
most basic intuition about nature.
You have to give up the notion
that empty space is empty.
Let me try to explain.
If I were to suck out
all the air from this jar,
you'd quite rightly say
that having removed all the atoms,
I'm left with a vacuum,
a volume of pure emptiness.
Quantum electrodynamics flies
in the face of this idea
by saying that the vacuum is NOT,
I repeat not, a place where
nothing exists and nothing happens.
Instead, it's full of stuff.
And it's heaving with activity.
How can this possibly be true?
Well, let's imagine
one tiny point in the emptiness.
Common sense tells us
that there's nothing there,
but quantum physics tells us
there's only nothing there ON
AVERAGE. This forces us to rethink
our understanding of reality.
Think of empty space like
a bank account, which on average
has nothing in it.
This is a concept I'm familiar with!
Some days it might be £100
in credit, others £100 overdrawn.
But on average
it has a zero balance.
Empty space turns out to have
similar accounting skills,
but it can borrow energy
rather than money
and this is literally borrowed
from the future, provided
it's paid back very quickly.
In practice this means the borrowed
energy can be used to create
a particle and an anti-particle,
which are spontaneously formed
from the void, provided that
a fraction of a second later
they annihilate each other
and disappear.
Energy is borrowed out of nowhere.
It's turned into matter.
The matter then self-destructs
back into energy.
And this happens in an instant
all over the void.
In fact, in a stunning confirmation
of Dirac's antimatter theory,
the vacuum seethes with huge numbers
of matter and antimatter particles,
continually being created
and annihilated.
Down at the smallest scale,
space is a constant storm
of creation and destruction.
Physicists call it
the quantum foam.
The particles in the quantum foam
come and go so quickly,
we're completely unaware of them.
We refer to them as virtual
particles, but if we could slow time
down almost to a standstill,
we'd be able to see this seething
activity, this constant creation and
annihilation of matter and energy
that's the fabric of reality itself.
From this comes the most
jaw-dropping idea of all.
Quantum electrodynamics says that
the matter we think of as the stuff
that makes up the everyday world,
the world that we see and feel,
is basically just a kind of leftover
from all the feverish activity
that virtual particles get up to
in the void.
So you, me, the Earth,
the stars, everything,
is basically just a part
of a deeper, infinitely more complex
reality than we ever imagined.
Of course, when Feynman first
started to develop his revolutionary
ideas in Caltech in the mid '40s,
his contemporaries were horrified
because at that time
the general opinion was that
the quantum electrodynamics project
was an unmitigated disaster.
The theory couldn't be solved.
The equations had no sensible
solutions. The mathematics
had spiralled out of control.
But Feynman believed that he could
see a way through the mathematical
complexity to a new truth.
What Feynman did, with all the
arrogance and confidence of youth,
was slash through
the insanely complicated maths.
Feynman developed a new series
or revolutionary,
but almost childlike, diagrams
to explain his new ideas.
Their elegant simplicity flew
in the face of the complex maths
of traditional quantum mechanics.
Conflict seemed inevitable.
Then, in 1948, at the age of 30,
Richard Feynman decided to unveil
his controversial version
of quantum electrodynamics
with his idiosyncratic diagrams
to the physics world.
And he chose
the most important science
conference of the American calendar.
Set on the coast of Pennsylvania,
the Shelter Island Conference was
a physics celebrity circus.
Present were Niels Bohr, so-called
"father of atomic physics",
the discoverer of antimatter
Paul Dirac and the man
behind America's atom bomb,
Robert Oppenheimer.
The atmosphere at the start
of the conference was grim.
Confidence in quantum
electrodynamics was at rock bottom.
It seemed a hopeless mess.
One after another, the physicists
stood up and droned on despairingly
about failing to find a solution.
Then it was the turn
of Richard Feynman.
Barely 30 years old, he stood up
and took his place in front of the
world's most illustrious scientists
and started to unveil
his new diagrams and equations.
What happened next was astonishing.
A row broke out, not over Feynman's
weird description of reality -
What happened next was astonishing.
A row broke out, not over Feynman's
weird description of reality -
physicists were used to weird -
but because he dared to visualise
what was going on.
Instead of using arcane,
complicated mathematics,
Feynman was describing what all
his virtual particles were up to,
using his simple pictures.
There was uproar. Niels Bohr,
the father of quantum mechanics,
leapt from his chair in disgust.
He hated Feynman's diagrams
because they went completely against
everything he'd devoted his life to.
He believed that atomic particles
could not be visualised
under any circumstances.
Feynman defended his new theory,
trying to explain that the diagrams
were simply a tool to help visualise
his new equations.
But the rest of the scientists,
including Dirac, wouldn't hear it,
calling him an idiot who understood
nothing about quantum mechanics.
Feynman ended his lecture
bruised, but unrepentant.
He knew that his diagrams
and equations were correct.
If only he could convince
the others.
That evening, Feynman met
another young physicist
called Julian Schwinger.
He was the same age as Feynman
and had been identified as
a child prodigy at the age of 12.
Although he and Feynman had been
working independently and approached
the problem very differently,
they'd reached
identical conclusions.
With their new equations, they could
solve quantum electrodynamics
and with Feynman's diagrams
they produced a theory
of awesome power.
Together now as allies,
they planned a full-frontal attack
on Niels Bohr and the conservatives.
By the end of the conference,
the mood in the Pennsylvanian
roadhouse had changed
from one of frustrated hopelessness
to one of excitement and idealism.
Over the next few years,
their theory was fleshed out
and rapidly became
the most accurate and powerful
theory mankind had ever had.
Despite finally being tamed,
quantum electrodynamics' talk
of empty space seething with energy
we can't feel and virtual particles
we can't see
does make many people, including
physicists, a little suspicious.
And many sceptics might say
these ghostly objects
that allegedly fill the vacuum
aren't actually real.
Yes, the complicated mathematical
equations seem to require them,
but that doesn't itself mean
they exist. They might just be
mathematical fantasies
with no basis in reality.
Well, I have bad news
for the sceptics.
Since the late 1950s,
direct evidence that empty space
isn't in the slightest bit empty
but is, in fact, seething with
activity has been observed time
and time again in laboratories.
And what's wonderful about the proof
that emptiness isn't empty
is that the first clue came
from a jar of mayonnaise.
In 1948, a physicist called Hendrik
Casimir was working at the Philips
Research Laboratories in Holland
on the seemingly obscure problem
of colloidal solutions.
This is just a fancy name
for substances like paint
and mayonnaise
which consist of tiny solid
particles suspended in a liquid.
You see, no one knew why mayonnaise
wasn't runny. Why doesn't it behave
like a normal liquid?
It's as if some strange force holds
the molecules of mayonnaise
together, making it viscous.
And that got Casimir thinking.
In an astonishing insight,
Casimir realised that the mysterious
force that attracts molecules
of mayonnaise together
is related to the mysterious
virtual particles in empty space.
And even better, he came up with
an experiment that would reveal
these particles for all to see.
It took another ten years
of tinkering in labs
to carry out Casimir's experiment,
but in essence it's quite simple.
You suspend two metal plates very
close to each other in a vacuum.
These plates aren't magnetic
or electrically charged, so you'd
expect them to sit there immobile,
unaffected by each other.
In fact, over time, they start
to move towards each other
due to a tiny force
that pushes them together.
And this force doing the pushing,
Casimir showed, was caused
by the virtual particles
that fill the vacuum.
Like wind pushing the sail of a boat
at sea, the stuff that emptiness is
made of pushes the plates together.
The fact that nothingness,
pure emptiness, could exert
a small, but real mechanical force
is surely one of nature's
greatest magic tricks.
In their more fanciful moments,
physicists speculate
that this so-called vacuum energy
might one day be harnessed.
They imagine it powering
intergalactic spaceships carrying
humans across the cosmos.
Who knows if this will ever come
to pass, but that mayonnaise
might lead to space travel
is a connection
Douglas Adams would be proud of.
Quantum electrodynamics is,
by any measure,
a truly magnificent discovery.
It's one great pinnacle
of our story, a glorious conclusion
to five amazing decades of science.
In quantum electrodynamics,
the atom had given us a theory
that explains much of our universe
with stunning accuracy.
But since quantum electrodynamics'
triumphant arrival in the late '40s,
our story becomes rather messy
and awkward.
As a result of quantum
electrodynamics, scientists were
convinced that the vast majority
of everything in the universe
consisted of essentially
just two things - atoms and light.
Light was made out of tiny particles
called photons.
And atoms were made out of
three components - the electron,
the proton and the neutron.
And because of antimatter, there
were anti-protons, anti-neutrons
and positrons -
a bit strange,
but pleasingly symmetrical.
Everything in the physics garden
was rosy thanks to the rules
of quantum electrodynamics,
but then, much to the profound
irritation of every working
physicist,
a load of new and exotic particles
suddenly appeared like party
gatecrashers to spoil the fun.
Exotic entities that didn't fit in
to any known theories were appearing
in physics labs with such frequency
that scientists couldn't keep up
with naming them all.
The neutrino, the positive pion,
the negative pion, the kaon,
the lambda, the delta...
And each of these had
their antimatter counterparts.
When one new particle, the muon,
was discovered, a physicist quipped,
"Who ordered that?"
The whole thing was a mess
and physicists despairingly refer
to it as the particle zoo.
It began to seem as though
every time scientists solved
one of nature's mysteries,
the atom would present them
with something even more weird.
Within just a few years,
atomic physics had gone from
a position of quiet confidence
to total chaos.
And, of course, to make some sense
of this new mystery would require -
yes, you've guessed it -
another scientific revolution.
The third genius in our story
is Murray Gell-Mann.
Gell-Mann was a child prodigy.
By 15, he'd already started at Yale
to study Physics
and finished his PhD by his early
20s. His incredible intelligence
terrified those around him.
He spoke many languages
and seemed to have a deep knowledge
of any subject you threw at him.
Like Richard Feynman, whom he joined
here at Caltech in the early '60s,
he seemed to have this ability
to see beyond the mathematics
to the underlying
secrets of nature below.
Together, Gell-Mann and Feynman
made an awesome duo.
This office, Number 456,
used to belong to Feynman.
What's great is that just two doors
along the corridor was the office
of Murray Gell-Mann.
There was an intense academic
rivalry between these two giants,
but they fed off the creativity.
They were very different.
Feynman played the buffoon,
Gell-Mann the cultured elitist.
Gell-Mann used to get upset
by Feynman's loud voice.
Feynman enjoyed winding him up.
But during the 1960s and '70s,
these two geniuses here at Caltech
dominated the world
of particle physics.
Their bitter rivalry pushed them
both to the very limits
of their imaginations
and Gell-Mann especially was
desperate to prove himself
over Feynman
by bringing order
to the particle zoo.
Within the feverishly intellectual
atmosphere of Caltech,
Gell-Mann's mind did something
very strange.
He started working with
a different kind of mathematics
to deal with the preponderance
of subatomic particles.
He used an obscure form of maths
called group theory. As its name
suggests, this is a theory
that analyses groups of numbers and
symbols and tries to organise them
into simple patterns.
It's like working
with an abstract form of origami.
Using this technique, Gell-Mann
started working all known particles
into an organised system,
which he called the Eightfold Way,
after a Buddhist poem.
But then he had his most awesome
revelation. Gell-Mann realised
that his group theory pointed
to a deeper underlying mathematical
truth, with the potential
to rewrite the atomic rule book.
What Gell-Mann's mathematics
revealed to him was that
in order to make coherent patterns
of all the new particles
in his Eightfold Way,
he had to acknowledge a deeper,
underlying, fundamental reality.
Once again, it turned out
that things were not at all
as they seemed.
Physicists had been comfortable
with the notion that atoms have
three different kinds of particles -
electrons orbiting around
the outside of a nucleus
made up of proton and neutrons.
Gell-Mann had the temerity
to suggest that protons and neutrons
were themselves composed
of more elementary particles,
particles that he called quarks.
Murray Gell-Mann was cultured
and arrogant, but at heart
lacked confidence.
He knew that for his colleagues,
even those used to
the strangeness of the atom,
quarks were a step too far.
And, in any case,
there'd been no evidence
of anything remotely like a quark.
He was convinced his new theory
would be declared outlandish
or just wrong,
so Gell-Mann sat on his revelation
and one of the greatest ideas
in science was almost lost forever.
Then something extraordinary
turned up, just a few hundred miles
north of his office.
This is the Stanford Linear
Accelerator, south of San Francisco.
What you can see is one end of what
is basically a giant electron gun.
A beam of high-energy electrons
is fired through a tunnel
that starts off over two miles away
in the hills, travels under
the freeway and comes out here
where it enters the experimental
area. The grey building
is End Station A,
where one of the most important
discoveries in physics was made.
It was built during the 1960s,
when it was - and still is today -
the longest single building
on Earth. Although 40 years old,
there's construction work going on,
and it's still being used
for fundamental research today.
I'm now inside the two-mile-long
linear accelerator building.
The red objects on your right
are called klystrons
and they provide the power
that boosts the electron beam
20 feet beneath us.
Such is the acceleration,
these electrons will, within
the first few metres, have reached
99% the speed of light.
Let me put it another way.
If these electrons were to start off
their journey at the same time
as you fire a bullet from a gun,
they would have covered
the full two-mile distance before
the bullet has left the barrel.
The electron beam now travelling
at almost the speed of light would
have arrived at the target area.
There would have been, in 1968,
where I'm standing now,
a large tank of hydrogen -
basically, protons. The electrons
would smash into the protons
and scatter off through tubes
to be picked up by huge detectors
that filled the hall outside.
And as they did this, physicists got
their biggest ever confirmation
that there might be a deeper set of
rules underpinning the particle zoo.
What they had discovered
from the way the electrons scattered
with their extremely high energy
was conclusive proof that protons
had internal structure.
In other words, protons were made
of more elementary particles.
Here were Gell-Mann's quarks.
This was an astonishing moment.
For decades, people were confident
that the components of the atomic
nucleus - the proton and neutron -
were absolutely fundamental.
And now, for the first time, there
was evidence of something deeper.
The quark is a tricky
and elusive beast.
There are six different kinds
or flavours of quark -
up, down, strange, charm,
top and bottom.
Also, quarks never exist
in isolation, only in combination
with other quarks.
This makes them
impossible to see directly.
We can only infer their presence.
Despite these caveats, the quark
brought some semblance of order
to the particle zoo.
In recent years,
it's allowed us to concoct
a simple, yet powerful description
of how the universe is built up.
Basically, everything
in the universe made of atoms
is built up from just quarks
and electrons. That's it.
This now brings us
pretty well up to date.
The discovery of the quark in 1967
was the last significant
experimental discovery of a new type
of fundamental particle.
Some say we may yet discover
the quark is made of something
even stranger. And it's possible.
But for now it's as good as it gets.
Our journey from Einstein's proof
of the existence of atoms in 1905
until now
has been extraordinary.
We've learnt so much
about the atomic world,
from the size and shape of the atom
to how its centre holds
the secret of the universe itself.
From how it reveals an unknown world
of antimatter to how empty space is
far from empty.
From what we thought was a basic
building block of the universe
to the discovery of something
even more fundamental inside it.
And yet, despite all the powerful
science which we've uncovered,
something doesn't quite add up.
There are two
startling and worrying anomalies.
The first of these is now at the
forefront of theoretical physics
across the world
and it concerns one of the oldest
scientific principles there is.
Gravity. It's been thoroughly
understood since Einstein,
but never really been part
of atomic theory, until now.
Suddenly there's a glimmer of hope
from ideas that sound
almost too crazy to be possible.
Some of these are called string
theories, that regard all subatomic
particles as tiny vibrating strings
that have higher dimensions of space
trapped inside them.
Some, called brain theories,
suggest that our entire
space and time
is just a membrane
floating through the multiverse.
Another, called quantum loop
gravity, suggests
that nothing really exists at all
and everything is ultimately made up
of tiny loops in space and time
themselves.
But despite gravity's unwillingness
to fit in with quantum theory,
I believe there's something worse
lurking in the quantum shadows,
something truly nightmarish.
Late into the night at physics
conferences all over the world,
over drinks at the bar
when we huddle together to debate
and discuss our strangest ideas,
there are still things
that really, really bother us.
Chief among these are the quantum
mechanical laws that atoms obey.
In particular, one aspect of them.
Something called
the measurement problem.
If you want to see fear
in a quantum physicist's eyes,
just say "the measurement problem".
The measurement problem is this -
an atom only appears in a particular
place if you measure it.
In other words, an atom is
spread out all over the place
until a conscious observer
decides to look at it.
So the act of measurement,
or observation,
creates the entire universe.
Just to show how mad this idea is,
I'm going to explain one of the most
famous hypothetical experiments
in the whole of science.
It's called
the Schrodinger's Cat Experiment.
Erwin Schrodinger was
a founding father of atomic theory.
In the mid-1930s he devised
a thought experiment to highlight
the absurdity of quantum mechanics.
He suggested you take a box
in which you place
an unopened container of cyanide,
connected to a radiation detector
and some radioactive material.
If an atom in the material
emits a particle,
this is picked up by the detector,
which releases the cyanide.
Next you take Schrodinger's cat,
which in this case is a lovely
Norwegian forest cat called Dawkins.
I should point out
that this isn't real cyanide.
You place the cat in the box,
you close the lid...and wait.
Here's the conundrum -
according to traditional
quantum mechanics, known as
the Copenhagen Interpretation,
all the time the box is closed,
the radioactive atom inside
has yet to make up its mind
whether it has decayed
and spat out a particle.
So we have to describe it as having
both decayed and not decayed
at the same time.
Think about what this means.
Since the radioactive particle
triggers the release of the poison,
the cat is both poisoned
AND not poisoned.
So until we open the lid
to check on the fate of the cat,
what's called making a measurement,
it's not just that we don't know,
but that the cat is literally both
dead and alive at the same time.
This is clearly a paradox.
Or is it?
The paradox of Schrodinger's cat
and the contradictory nature
of the measurement problem
really does force us to accept that
tiny objects down at the atomic
scale obey their own set
of profoundly strange rules.
But at larger scales,
those of everyday experience,
those rules vanish
and an utterly new set of nice,
intuitive rules take over.
How can this be?
Some argue that, in fact,
the quantum weirdness of the atom
might actually be writ large
across the cosmos,
that we may have to rethink
everything known about the universe.
Welcome to the many worlds
interpretation of quantum mechanics
and its chief adherent,
David Deutsch, of Oxford University.
Deutsch proposes that reality itself
is profoundly misunderstood.
He says that what quantum mechanics
actually describes
is not one universe,
but an infinite number
of parallel universes.
He calls it a multiverse,
in which every possible quantum
mechanical outcome for each
and every atom in the universe
exists somewhere.
So an atom and its electron
are multiversal objects.
And that multiversal object is
what quantum mechanics is describing.
Now that means that the parallel
universe aspect of reality
as described by quantum theory
must apply to objects of all sizes -
humans, stars, galaxies, everything.
And that's why we call it
the parallel universe theory
rather than just
parallel electrons theory.
Because we are made of atoms.
That's right.
The same theory that says the atoms
exist in more than one place
says that we humans also exist
in more than one place
in different universes.
And there are some universes
where you and I don't exist at all.
'The highly-respected author
and physicist, Paul Davies,
has an even more bizarre idea.
'He suggests that the strangeness
of the measurement problem explains
how the universe came into being.'
The experimenter today in the lab
can make a measurement
that affects the nature of reality
as it was five billion years ago.
There's a sort of feedback loop
between the existence
of living organisms and observers
and the laws and conditions
which have given rise to them.
Otherwise it just seems
a bit miraculous that the universe
happens to have started out
with the right laws and conditions
that lead to observers like ourselves
who can make measurements
and make sense of it all.
But quantum mechanics provides
just such a feedback through time.
It allows this backwards in time
effect. Not causation.
It's not that we here now can change
the past to fix it so that we exist,
but we have an influence on the past
through quantum measurements we make.
But there's a pragmatic side
to the debate, too.
Other scientists are worried
that these bizarre and metaphysical
speculations
leave the world of measurement and
laboratory experiment far behind.
Professor Andrew Jackson of the
Niels Bohr Institute in Copenhagen
says that ultimately we shouldn't
worry about the interpretation or
the measurement problem or the cat.
He says we shouldn't be concerned
about the so-called true nature
of reality.
It's enough that the theory works.
All of the things we can measure
give us questions we can answer
from quantum mechanics.
So the quantum mechanics itself,
without the need for interpretation,
provides us with answers
or predictions regarding the result
of every experiment we can do.
So I don't know...
That's enough for me. Yeah.
So you don't think quantum mechanics
needs a unique interpretation
because it doesn't add anything?
It doesn't add anything
and I don't think it will lead us
to the next step.
An interpretation doesn't change
the results or the rules
and that's why it's not testable.
The whole purpose of the last 200
years in physics, this incredible
leap forward that we've made,
has come because experiment
confronted theory and led to new
theory when theory broke down
and back and forth and back and
forth. Interpretations don't do that.
Interpretations only give us
some kind of a way of believing
we understand what quantum mechanics
tells us, but that's a fixed point.
There's no new content to it.
Quantum mechanics is
counterintuitive
and goes against common sense.
What do you say to people
who insist on wanting to know
what an atom is doing
when you're not looking at it?
I'm not sure I'm quoting,
Feynman or Dirac,
but the answer is,
"Shut up and calculate".
So shut up and use the maths. Right.
"Shut up and calculate"?
Is this really scientific pragmatism
or just dogmatic fundamentalism?
The reason that this is unacceptable,
philosophically,
can I think be best understood by
comparing it with an earlier episode
in the history of physics,
namely the Inquisition's attitude
several hundred years ago
to the idea that the Earth goes round
the Sun, not the Sun round the Earth.
They wanted to promote a compromise
with Galileo where they would admit
that the positions of the stars
and planets and Sun in the sky
are exactly as predicted
by that theory,
but that it was presumptuous
of humans
to purport to be able to describe
the underlying reality -
why the stars appeared there.
The same thing happened
with quantum mechanics.
A group of people who didn't like
the implications of the theory
about reality
realised you could use it in practice
by just using its predictions.
That is a move you can always make
with any scientific theory. You can
always deny it describes reality.
You can't be proved wrong
by experiment, but as a philosophical
position it's a dead end. Sterile.
I think it's fair to say that most
physicists use quantum mechanics
to describe the subatomic world
without worrying too much
about the interpretation.
Personally,
I'm not in favour of this view.
I don't have a preferred
interpretation, but believe nature
must behave in a particular way.
So only one of the interpretations
can be correct
and, to be quite honest, we probably
haven't found the final answer yet,
but I think
it's only a matter of time.
I certainly don't subscribe
to "Shut up and calculate".
I prefer the "Shut up
WHILE you calculate" view.
I'm happy to do my calculations
to study atoms,
but when I'm away from my work, I
still worry about what it all means.
In the last 100 years
we have peered deep inside the atom,
the basic building block of
the universe, and inside this tiny
object we found a strange, new world
governed by exotic laws
that at times seemed
to defy reason.
Atoms present us
with dizzying contradictions.
They can behave both as particles
or waves, they appear to be
in more than one place,
they force us to rethink
what we mean by past and future,
by cause and effect,
and they tell us strange things
about where the universe came from
and where it's going.
Pretty amazing stuff for something
a millionth of a millimetre across.
That's why Niels Bohr, the father
of atomic physics, once said
that when it comes to atoms
language can only be used as poetry.
What's fascinating to me is
that although we've learnt
an incredible amount about atoms,
our scientific journey
has only just begun.
Although we know how a single atom
or just a few atoms behave,
the way trillions of them
come together in concert
to create the world around us
is still largely a mystery.
To give you one dramatic example -
the atoms that make up my body
are identical to the atoms
in the rocks, the trees, the air,
even the stars. And yet they come
together to create a conscious being
who can ask the question,
"What is an atom?"
Explaining all that is surely
the next great challenge in science.
about three miles above the ground,
an Austrian scientist called
Victor Hess made one of the most
astonishing discoveries in science.
Up here Hess found that incredibly
mysterious rays of energy
were pouring in from outer space
and streaming through the Earth.
They were incredibly powerful,
yet unlike anything seen before.
They were called cosmic rays.
At the same time
in laboratories down below,
scientists were studying equally
mysterious and powerful energy rays
pouring out from the interior
of atoms - known as radioactivity.
Mysterious rays from the vast
emptiness of space and mysterious
rays from deep within the atom,
the tiniest building block.
No one really understood what they
were or if they might be connected.
Then an incredible story unfolded.
Cosmic rays and radioactivity
turned out to be connected in a way
so shocking that it beggars belief.
The discovery of this connection
would force us to rethink
the nature of reality itself.
The world we think we know,
the solid, reassuring world
of our senses,
is just a tiny sliver
of an infinitely weirder universe
than we could ever conceive of.
Our reality is just an illusion.
In the years up to the mid-1920s,
the atom revealed
its strange secrets to us
at a prodigious rate,
as it produced one scientific
revolution after another.
In 1897, Marie Curie studied
strange rays pouring out
of some rare metals.
She called them radioactivity.
Then, in 1905, Albert Einstein
conclusively proved the existence
and size of an atom
by studying
the way pollen moves in water.
A few years later, the New Zealander
Ernest Rutherford performed
an experiment in Manchester
that revealed to him the shape
of the interior of an atom.
Scientists were shocked to discover
that the atom is almost entirely
empty space.
The question then became,
"How could this empty atom possibly
make the solid world around us?"
The answer to that was worked out
by a group of revolutionary
physicists in Denmark.
They proposed that the world
of the atom ran on principles
which were completely different
to any mankind had ever seen before.
It meant that the atom, the basic
building block of everything
in the universe, was unique.
And perhaps
outside human comprehension.
Then a scientist explored the
nucleus, the tiny heart of the atom.
They found it bursting
with powerful energy.
This discovery gave them
the potential to bring about
the destruction of the Earth,
but in a shocking turnaround,
it also gave them
a fundamental understanding
of how the universe was created.
And yet, despite this,
the journey to understand
the strange and capricious atom
had only just started.
In 1927, a young man was studying
at the Mathematics Department
of Cambridge University.
Shy, awkward, clumsy
and frighteningly brilliant,
his name was
Paul Adrien Maurice Dirac.
It's probably fair to say that
Paul Dirac isn't a household name.
But it should be. He was recently
voted, by other physicists,
as the second-greatest
English physicist of all time,
second only to Newton.
And he deserves the accolade.
All the brilliant minds
that pioneered atomic physics
were left trailing by Dirac,
aghast at the sheer boldness
and lateral thinking in his work.
When Einstein read a paper by
the then 24-year-old Dirac, he said,
"I have trouble with Dirac.
"This balancing on the dizzying path
between genius and madness
is awful."
In 1927, for reasons no one
has ever really fathomed,
Paul Dirac set himself a task
that was monumental in its scope -
to unify science.
To bring its scattered parts
into one beautiful entity.
And what this meant, above all,
was to unite the two most difficult
and counter-intuitive ideas
in history.
Here's what Dirac was trying
to reconcile.
First there's quantum mechanics,
mathematical equations describing
the atom and its component parts.
Then there's Einstein's
Special Theory of Relativity,
which at first seems unrelated.
It deals with loftier matters
like the nature of space and time.
One of its consequences is that
objects behave very differently
when they travel
close to the speed of light.
The first thing you might ask is
why would anyone want to reconcile
two such different theories?
Well, by the late 1920s,
the equations of quantum mechanics
were consistently getting the wrong
answers when describing electrons,
one of the constituents of atoms,
as they move at very high speed.
But for Dirac there was
a much more esoteric motivation.
He was once quoted as saying,
"A physical theory
must have mathematical beauty".
So for him, the fact that quantum
mechanics and relativity weren't
reconciled wasn't just inconvenient,
it was downright ugly.
So around 1925, in Cambridge,
Dirac put his extraordinary mind,
a mind that even Einstein had
trouble keeping up with, to work.
This is Room A4, New Court.
It was Dirac's original study.
The original fireplace
has been boarded up,
but it was here that Dirac tried
to understand and bring together
the two new ideas of physics.
Word is Dirac would sit here
in front of his blazing fireplace
and try to understand and bring
together these two different
theories into one unified picture,
one single equation.
For three frustrating years,
he laboured alone on the problem.
Then, one evening in early 1928,
he had an amazing revelation.
The only way I can explain
what happened is to say that
the equations of quantum mechanics
and special relativity
coalesced inside Dirac's mind.
Einstein's description of space and
time somehow stretched and squeezed
the existing equations of the atom.
They bent and twisted them
into new weird and wonderful shapes.
Then, guided by his unshakeable
belief that nature's laws
must be beautiful,
Dirac homed in on one equation,
an entirely new description
of what goes on inside the atom.
Dirac knew it was right
because it had mathematical beauty.
Here it is, the Dirac equation.
Don't try to understand it.
Just look at it and marvel.
As human achievements go, it's up
there with King Lear, Beethoven's
Fifth or The Origin of the Species.
Hidden in these symbols is the
perfect description of how reality
works at a fundamental level.
It's the key
to nature's secret code.
With perfect mathematical elegance,
Dirac's equation describes
an atomic particle
travelling at any speed,
right up to the speed of light.
That much Dirac was expecting
to achieve, but when he looked
at his own equation more carefully,
he noticed something breathtakingly
revolutionary about it.
He later said his equation
knew more than he did.
In essence, Dirac's equation was
telling him there's another universe
we've never noticed before.
That's because instead of
his equation having one answer,
it has two.
The first describes the universe
we know, made of the atoms
we're familiar with.
The second describes
a mirror image to our universe,
made of atoms whose properties
are somehow reversed.
Science fiction fans will know
what's coming. As well as matter,
Dirac's equation predicts
the existence of antimatter.
Dirac's theory seemed to say that
for everything in our known world,
for every part of an atom,
every particle, there can exist
a corresponding anti-particle
with the same mass, but exactly
opposite in every other way.
And just like a world in a mirror,
the universe made of antimatter
atoms would look and work
just like ours.
It would be perfectly possible
for me to be made out of antimatter.
Anti-me would look and behave
exactly the same as original me.
And it's possible that out there
in the vast expanses of the cosmos,
there are stars and planets and even
living beings made of antimatter.
There's one final prediction
of the Dirac equation.
It states that matter
and antimatter must never
come into contact. If they do,
they will annihilate each other
in a conflagration of pure energy.
The combined mass of matter
and antimatter would convert
completely into energy,
according to Einstein's
famous equation, E=MC2.
So if I ever do meet
my doppelganger, we would explode
with an energy equivalent to
a million Hiroshima-sized
atom bombs.
All this sounds like science fiction
and the idea of antimatter
has inspired huge swathes of it.
But the truth is antimatter,
particularly antimatter electrons,
called positrons
are made routinely now
in laboratories.
Positrons are used in sophisticated
medical imaging devices
called PET scanners
that can see through our skulls
and accurately map pictures
of our brains.
But back in the 1920s, the initial
reaction to Dirac's equation among
physicists was deeply sceptical.
Even Dirac had trouble
believing his own results.
Antimatter seemed
such a preposterous concept.
Then came resounding confirmation
of the Dirac equation
and all its paradoxical implications
and it came from the most
unexpected place - outer space.
In 1932, physicist Carl Anderson
was working here at Caltech
in Los Angeles
when he made an amazing discovery.
He'd been studying cosmic rays.
These are high-energy subatomic
particles that continuously bombard
the Earth from outer space.
To do this, he used a device
called a cloud chamber.
This is basically a vessel filled
with a fine mist of water vapour.
This shows up the tracks
of the particles as they stream down
through the vapour.
Placed inside a magnetic field,
these tracks are deflected one way
or the other,
depending on the electric charge
of the particle. Positive tracks
go one way, negative the other.
Anderson found evidence of particles
that look exactly like electrons,
but which are deflected
in the opposite direction.
He had discovered
Dirac's anti-electrons,
particles of antimatter.
The Dirac equation
is an impressive achievement.
Its prediction of the existence
of antimatter, using abstract
mathematics alone, would be enough
to make it a significant milestone
in the history of human thought.
But within just a few years
of publication, first Dirac
and then others sensed
that his new equation
was telling them something profound,
something completely new
about nature. And they were right.
But the revelation hidden within
Dirac's equation would take the best
efforts of the greatest minds
30 years to uncover.
The problem
with Dirac's equation was this -
although it was incredibly powerful
and led to the discovery
of antimatter,
ultimately it could only describe
a single electron. It fails
completely to explain what happens
when there is more than one electron
present. What was needed
was a new theory to explain
how electrons interact
with each other.
And that turned out to be
the most difficult question
of the mid-20th Century,
but when an answer came,
it was to bring with it
an unexpected revelation.
This office in Caltech
used to belong
to the great Richard Feynman.
In our story of so many geniuses
of science,
Feynman stands, in my view,
second only to Einstein in the list
of greatest 20th Century physicists.
Feynman wasn't just
a common or garden genius.
Many referred to him as a magician,
he was so smart,
such an innovative thinker.
Like Einstein, he became this
mythical figure, a household name.
Feynman was a larger-than-life
character with a huge personality.
He loved cultivating
and telling anecdotes about himself.
He used to frequent strip clubs,
he had affairs with his students
and was rumoured to go to orgies,
but his greatest contribution
to physics was the part he played
in developing the next phase
of quantum mechanics.
Feynman and his contemporaries
were attempting to pick up
the atomic torch from Paul Dirac
and develop a theory that took
our understanding of the atom
literally a quantum leap further.
Like Dirac's antimatter equation
before, the intention
of the new theory was unification.
They wanted to understand
how electrons affect each other.
In other words, it aimed to explain
how everything works together
through the electromagnetic field.
They called their unification
project quantum electrodynamics
or QED.
The project was a formidable
challenge, but the end result
was magnificent -
nothing less than
the most far-reaching and accurate
scientific theory ever conceived.
For instance, it predicts
a certain property of the electron
called its magnetic moment
to have a value of...
Experiments measure precisely
the same number. That's an agreement
between theory and experiment
to one part in ten billion. It's
an unprecedented level of agreement.
It's like measuring the distance
between London and New York
to within the thickness of a hair.
The phenomenal accuracy
of quantum electrodynamics
shows it to underpin
almost everything we experience
in the physical world.
It's as close to a theory of
everything as we have ever come.
It defies the laws of nature -
the atomic scale.
It explains shape, colour, texture
and the way almost everything
interacts and fits together.
It encompasses everything
from the biochemistry of life to
why we don't fall through the floor.
So what does QED actually say?
Well, this is where the going
gets very tough.
It may be a wonderful
scientific description of nature,
but trying to understand what
Feynman was doing with his theory
is almost impossible.
This is what he himself said
when he introduced his theory:
"It is my task to convince you
not to turn away
because you don't understand it.
"My physics students don't
understand it. That's because
I don't understand it. Nobody does."
If the inventor of the theory
doesn't understand, what possible
hope is there for the rest of us?
With that disclaimer,
I'm going to try to explain anyway.
First, you have to abandon your
most basic intuition about nature.
You have to give up the notion
that empty space is empty.
Let me try to explain.
If I were to suck out
all the air from this jar,
you'd quite rightly say
that having removed all the atoms,
I'm left with a vacuum,
a volume of pure emptiness.
Quantum electrodynamics flies
in the face of this idea
by saying that the vacuum is NOT,
I repeat not, a place where
nothing exists and nothing happens.
Instead, it's full of stuff.
And it's heaving with activity.
How can this possibly be true?
Well, let's imagine
one tiny point in the emptiness.
Common sense tells us
that there's nothing there,
but quantum physics tells us
there's only nothing there ON
AVERAGE. This forces us to rethink
our understanding of reality.
Think of empty space like
a bank account, which on average
has nothing in it.
This is a concept I'm familiar with!
Some days it might be £100
in credit, others £100 overdrawn.
But on average
it has a zero balance.
Empty space turns out to have
similar accounting skills,
but it can borrow energy
rather than money
and this is literally borrowed
from the future, provided
it's paid back very quickly.
In practice this means the borrowed
energy can be used to create
a particle and an anti-particle,
which are spontaneously formed
from the void, provided that
a fraction of a second later
they annihilate each other
and disappear.
Energy is borrowed out of nowhere.
It's turned into matter.
The matter then self-destructs
back into energy.
And this happens in an instant
all over the void.
In fact, in a stunning confirmation
of Dirac's antimatter theory,
the vacuum seethes with huge numbers
of matter and antimatter particles,
continually being created
and annihilated.
Down at the smallest scale,
space is a constant storm
of creation and destruction.
Physicists call it
the quantum foam.
The particles in the quantum foam
come and go so quickly,
we're completely unaware of them.
We refer to them as virtual
particles, but if we could slow time
down almost to a standstill,
we'd be able to see this seething
activity, this constant creation and
annihilation of matter and energy
that's the fabric of reality itself.
From this comes the most
jaw-dropping idea of all.
Quantum electrodynamics says that
the matter we think of as the stuff
that makes up the everyday world,
the world that we see and feel,
is basically just a kind of leftover
from all the feverish activity
that virtual particles get up to
in the void.
So you, me, the Earth,
the stars, everything,
is basically just a part
of a deeper, infinitely more complex
reality than we ever imagined.
Of course, when Feynman first
started to develop his revolutionary
ideas in Caltech in the mid '40s,
his contemporaries were horrified
because at that time
the general opinion was that
the quantum electrodynamics project
was an unmitigated disaster.
The theory couldn't be solved.
The equations had no sensible
solutions. The mathematics
had spiralled out of control.
But Feynman believed that he could
see a way through the mathematical
complexity to a new truth.
What Feynman did, with all the
arrogance and confidence of youth,
was slash through
the insanely complicated maths.
Feynman developed a new series
or revolutionary,
but almost childlike, diagrams
to explain his new ideas.
Their elegant simplicity flew
in the face of the complex maths
of traditional quantum mechanics.
Conflict seemed inevitable.
Then, in 1948, at the age of 30,
Richard Feynman decided to unveil
his controversial version
of quantum electrodynamics
with his idiosyncratic diagrams
to the physics world.
And he chose
the most important science
conference of the American calendar.
Set on the coast of Pennsylvania,
the Shelter Island Conference was
a physics celebrity circus.
Present were Niels Bohr, so-called
"father of atomic physics",
the discoverer of antimatter
Paul Dirac and the man
behind America's atom bomb,
Robert Oppenheimer.
The atmosphere at the start
of the conference was grim.
Confidence in quantum
electrodynamics was at rock bottom.
It seemed a hopeless mess.
One after another, the physicists
stood up and droned on despairingly
about failing to find a solution.
Then it was the turn
of Richard Feynman.
Barely 30 years old, he stood up
and took his place in front of the
world's most illustrious scientists
and started to unveil
his new diagrams and equations.
What happened next was astonishing.
A row broke out, not over Feynman's
weird description of reality -
What happened next was astonishing.
A row broke out, not over Feynman's
weird description of reality -
physicists were used to weird -
but because he dared to visualise
what was going on.
Instead of using arcane,
complicated mathematics,
Feynman was describing what all
his virtual particles were up to,
using his simple pictures.
There was uproar. Niels Bohr,
the father of quantum mechanics,
leapt from his chair in disgust.
He hated Feynman's diagrams
because they went completely against
everything he'd devoted his life to.
He believed that atomic particles
could not be visualised
under any circumstances.
Feynman defended his new theory,
trying to explain that the diagrams
were simply a tool to help visualise
his new equations.
But the rest of the scientists,
including Dirac, wouldn't hear it,
calling him an idiot who understood
nothing about quantum mechanics.
Feynman ended his lecture
bruised, but unrepentant.
He knew that his diagrams
and equations were correct.
If only he could convince
the others.
That evening, Feynman met
another young physicist
called Julian Schwinger.
He was the same age as Feynman
and had been identified as
a child prodigy at the age of 12.
Although he and Feynman had been
working independently and approached
the problem very differently,
they'd reached
identical conclusions.
With their new equations, they could
solve quantum electrodynamics
and with Feynman's diagrams
they produced a theory
of awesome power.
Together now as allies,
they planned a full-frontal attack
on Niels Bohr and the conservatives.
By the end of the conference,
the mood in the Pennsylvanian
roadhouse had changed
from one of frustrated hopelessness
to one of excitement and idealism.
Over the next few years,
their theory was fleshed out
and rapidly became
the most accurate and powerful
theory mankind had ever had.
Despite finally being tamed,
quantum electrodynamics' talk
of empty space seething with energy
we can't feel and virtual particles
we can't see
does make many people, including
physicists, a little suspicious.
And many sceptics might say
these ghostly objects
that allegedly fill the vacuum
aren't actually real.
Yes, the complicated mathematical
equations seem to require them,
but that doesn't itself mean
they exist. They might just be
mathematical fantasies
with no basis in reality.
Well, I have bad news
for the sceptics.
Since the late 1950s,
direct evidence that empty space
isn't in the slightest bit empty
but is, in fact, seething with
activity has been observed time
and time again in laboratories.
And what's wonderful about the proof
that emptiness isn't empty
is that the first clue came
from a jar of mayonnaise.
In 1948, a physicist called Hendrik
Casimir was working at the Philips
Research Laboratories in Holland
on the seemingly obscure problem
of colloidal solutions.
This is just a fancy name
for substances like paint
and mayonnaise
which consist of tiny solid
particles suspended in a liquid.
You see, no one knew why mayonnaise
wasn't runny. Why doesn't it behave
like a normal liquid?
It's as if some strange force holds
the molecules of mayonnaise
together, making it viscous.
And that got Casimir thinking.
In an astonishing insight,
Casimir realised that the mysterious
force that attracts molecules
of mayonnaise together
is related to the mysterious
virtual particles in empty space.
And even better, he came up with
an experiment that would reveal
these particles for all to see.
It took another ten years
of tinkering in labs
to carry out Casimir's experiment,
but in essence it's quite simple.
You suspend two metal plates very
close to each other in a vacuum.
These plates aren't magnetic
or electrically charged, so you'd
expect them to sit there immobile,
unaffected by each other.
In fact, over time, they start
to move towards each other
due to a tiny force
that pushes them together.
And this force doing the pushing,
Casimir showed, was caused
by the virtual particles
that fill the vacuum.
Like wind pushing the sail of a boat
at sea, the stuff that emptiness is
made of pushes the plates together.
The fact that nothingness,
pure emptiness, could exert
a small, but real mechanical force
is surely one of nature's
greatest magic tricks.
In their more fanciful moments,
physicists speculate
that this so-called vacuum energy
might one day be harnessed.
They imagine it powering
intergalactic spaceships carrying
humans across the cosmos.
Who knows if this will ever come
to pass, but that mayonnaise
might lead to space travel
is a connection
Douglas Adams would be proud of.
Quantum electrodynamics is,
by any measure,
a truly magnificent discovery.
It's one great pinnacle
of our story, a glorious conclusion
to five amazing decades of science.
In quantum electrodynamics,
the atom had given us a theory
that explains much of our universe
with stunning accuracy.
But since quantum electrodynamics'
triumphant arrival in the late '40s,
our story becomes rather messy
and awkward.
As a result of quantum
electrodynamics, scientists were
convinced that the vast majority
of everything in the universe
consisted of essentially
just two things - atoms and light.
Light was made out of tiny particles
called photons.
And atoms were made out of
three components - the electron,
the proton and the neutron.
And because of antimatter, there
were anti-protons, anti-neutrons
and positrons -
a bit strange,
but pleasingly symmetrical.
Everything in the physics garden
was rosy thanks to the rules
of quantum electrodynamics,
but then, much to the profound
irritation of every working
physicist,
a load of new and exotic particles
suddenly appeared like party
gatecrashers to spoil the fun.
Exotic entities that didn't fit in
to any known theories were appearing
in physics labs with such frequency
that scientists couldn't keep up
with naming them all.
The neutrino, the positive pion,
the negative pion, the kaon,
the lambda, the delta...
And each of these had
their antimatter counterparts.
When one new particle, the muon,
was discovered, a physicist quipped,
"Who ordered that?"
The whole thing was a mess
and physicists despairingly refer
to it as the particle zoo.
It began to seem as though
every time scientists solved
one of nature's mysteries,
the atom would present them
with something even more weird.
Within just a few years,
atomic physics had gone from
a position of quiet confidence
to total chaos.
And, of course, to make some sense
of this new mystery would require -
yes, you've guessed it -
another scientific revolution.
The third genius in our story
is Murray Gell-Mann.
Gell-Mann was a child prodigy.
By 15, he'd already started at Yale
to study Physics
and finished his PhD by his early
20s. His incredible intelligence
terrified those around him.
He spoke many languages
and seemed to have a deep knowledge
of any subject you threw at him.
Like Richard Feynman, whom he joined
here at Caltech in the early '60s,
he seemed to have this ability
to see beyond the mathematics
to the underlying
secrets of nature below.
Together, Gell-Mann and Feynman
made an awesome duo.
This office, Number 456,
used to belong to Feynman.
What's great is that just two doors
along the corridor was the office
of Murray Gell-Mann.
There was an intense academic
rivalry between these two giants,
but they fed off the creativity.
They were very different.
Feynman played the buffoon,
Gell-Mann the cultured elitist.
Gell-Mann used to get upset
by Feynman's loud voice.
Feynman enjoyed winding him up.
But during the 1960s and '70s,
these two geniuses here at Caltech
dominated the world
of particle physics.
Their bitter rivalry pushed them
both to the very limits
of their imaginations
and Gell-Mann especially was
desperate to prove himself
over Feynman
by bringing order
to the particle zoo.
Within the feverishly intellectual
atmosphere of Caltech,
Gell-Mann's mind did something
very strange.
He started working with
a different kind of mathematics
to deal with the preponderance
of subatomic particles.
He used an obscure form of maths
called group theory. As its name
suggests, this is a theory
that analyses groups of numbers and
symbols and tries to organise them
into simple patterns.
It's like working
with an abstract form of origami.
Using this technique, Gell-Mann
started working all known particles
into an organised system,
which he called the Eightfold Way,
after a Buddhist poem.
But then he had his most awesome
revelation. Gell-Mann realised
that his group theory pointed
to a deeper underlying mathematical
truth, with the potential
to rewrite the atomic rule book.
What Gell-Mann's mathematics
revealed to him was that
in order to make coherent patterns
of all the new particles
in his Eightfold Way,
he had to acknowledge a deeper,
underlying, fundamental reality.
Once again, it turned out
that things were not at all
as they seemed.
Physicists had been comfortable
with the notion that atoms have
three different kinds of particles -
electrons orbiting around
the outside of a nucleus
made up of proton and neutrons.
Gell-Mann had the temerity
to suggest that protons and neutrons
were themselves composed
of more elementary particles,
particles that he called quarks.
Murray Gell-Mann was cultured
and arrogant, but at heart
lacked confidence.
He knew that for his colleagues,
even those used to
the strangeness of the atom,
quarks were a step too far.
And, in any case,
there'd been no evidence
of anything remotely like a quark.
He was convinced his new theory
would be declared outlandish
or just wrong,
so Gell-Mann sat on his revelation
and one of the greatest ideas
in science was almost lost forever.
Then something extraordinary
turned up, just a few hundred miles
north of his office.
This is the Stanford Linear
Accelerator, south of San Francisco.
What you can see is one end of what
is basically a giant electron gun.
A beam of high-energy electrons
is fired through a tunnel
that starts off over two miles away
in the hills, travels under
the freeway and comes out here
where it enters the experimental
area. The grey building
is End Station A,
where one of the most important
discoveries in physics was made.
It was built during the 1960s,
when it was - and still is today -
the longest single building
on Earth. Although 40 years old,
there's construction work going on,
and it's still being used
for fundamental research today.
I'm now inside the two-mile-long
linear accelerator building.
The red objects on your right
are called klystrons
and they provide the power
that boosts the electron beam
20 feet beneath us.
Such is the acceleration,
these electrons will, within
the first few metres, have reached
99% the speed of light.
Let me put it another way.
If these electrons were to start off
their journey at the same time
as you fire a bullet from a gun,
they would have covered
the full two-mile distance before
the bullet has left the barrel.
The electron beam now travelling
at almost the speed of light would
have arrived at the target area.
There would have been, in 1968,
where I'm standing now,
a large tank of hydrogen -
basically, protons. The electrons
would smash into the protons
and scatter off through tubes
to be picked up by huge detectors
that filled the hall outside.
And as they did this, physicists got
their biggest ever confirmation
that there might be a deeper set of
rules underpinning the particle zoo.
What they had discovered
from the way the electrons scattered
with their extremely high energy
was conclusive proof that protons
had internal structure.
In other words, protons were made
of more elementary particles.
Here were Gell-Mann's quarks.
This was an astonishing moment.
For decades, people were confident
that the components of the atomic
nucleus - the proton and neutron -
were absolutely fundamental.
And now, for the first time, there
was evidence of something deeper.
The quark is a tricky
and elusive beast.
There are six different kinds
or flavours of quark -
up, down, strange, charm,
top and bottom.
Also, quarks never exist
in isolation, only in combination
with other quarks.
This makes them
impossible to see directly.
We can only infer their presence.
Despite these caveats, the quark
brought some semblance of order
to the particle zoo.
In recent years,
it's allowed us to concoct
a simple, yet powerful description
of how the universe is built up.
Basically, everything
in the universe made of atoms
is built up from just quarks
and electrons. That's it.
This now brings us
pretty well up to date.
The discovery of the quark in 1967
was the last significant
experimental discovery of a new type
of fundamental particle.
Some say we may yet discover
the quark is made of something
even stranger. And it's possible.
But for now it's as good as it gets.
Our journey from Einstein's proof
of the existence of atoms in 1905
until now
has been extraordinary.
We've learnt so much
about the atomic world,
from the size and shape of the atom
to how its centre holds
the secret of the universe itself.
From how it reveals an unknown world
of antimatter to how empty space is
far from empty.
From what we thought was a basic
building block of the universe
to the discovery of something
even more fundamental inside it.
And yet, despite all the powerful
science which we've uncovered,
something doesn't quite add up.
There are two
startling and worrying anomalies.
The first of these is now at the
forefront of theoretical physics
across the world
and it concerns one of the oldest
scientific principles there is.
Gravity. It's been thoroughly
understood since Einstein,
but never really been part
of atomic theory, until now.
Suddenly there's a glimmer of hope
from ideas that sound
almost too crazy to be possible.
Some of these are called string
theories, that regard all subatomic
particles as tiny vibrating strings
that have higher dimensions of space
trapped inside them.
Some, called brain theories,
suggest that our entire
space and time
is just a membrane
floating through the multiverse.
Another, called quantum loop
gravity, suggests
that nothing really exists at all
and everything is ultimately made up
of tiny loops in space and time
themselves.
But despite gravity's unwillingness
to fit in with quantum theory,
I believe there's something worse
lurking in the quantum shadows,
something truly nightmarish.
Late into the night at physics
conferences all over the world,
over drinks at the bar
when we huddle together to debate
and discuss our strangest ideas,
there are still things
that really, really bother us.
Chief among these are the quantum
mechanical laws that atoms obey.
In particular, one aspect of them.
Something called
the measurement problem.
If you want to see fear
in a quantum physicist's eyes,
just say "the measurement problem".
The measurement problem is this -
an atom only appears in a particular
place if you measure it.
In other words, an atom is
spread out all over the place
until a conscious observer
decides to look at it.
So the act of measurement,
or observation,
creates the entire universe.
Just to show how mad this idea is,
I'm going to explain one of the most
famous hypothetical experiments
in the whole of science.
It's called
the Schrodinger's Cat Experiment.
Erwin Schrodinger was
a founding father of atomic theory.
In the mid-1930s he devised
a thought experiment to highlight
the absurdity of quantum mechanics.
He suggested you take a box
in which you place
an unopened container of cyanide,
connected to a radiation detector
and some radioactive material.
If an atom in the material
emits a particle,
this is picked up by the detector,
which releases the cyanide.
Next you take Schrodinger's cat,
which in this case is a lovely
Norwegian forest cat called Dawkins.
I should point out
that this isn't real cyanide.
You place the cat in the box,
you close the lid...and wait.
Here's the conundrum -
according to traditional
quantum mechanics, known as
the Copenhagen Interpretation,
all the time the box is closed,
the radioactive atom inside
has yet to make up its mind
whether it has decayed
and spat out a particle.
So we have to describe it as having
both decayed and not decayed
at the same time.
Think about what this means.
Since the radioactive particle
triggers the release of the poison,
the cat is both poisoned
AND not poisoned.
So until we open the lid
to check on the fate of the cat,
what's called making a measurement,
it's not just that we don't know,
but that the cat is literally both
dead and alive at the same time.
This is clearly a paradox.
Or is it?
The paradox of Schrodinger's cat
and the contradictory nature
of the measurement problem
really does force us to accept that
tiny objects down at the atomic
scale obey their own set
of profoundly strange rules.
But at larger scales,
those of everyday experience,
those rules vanish
and an utterly new set of nice,
intuitive rules take over.
How can this be?
Some argue that, in fact,
the quantum weirdness of the atom
might actually be writ large
across the cosmos,
that we may have to rethink
everything known about the universe.
Welcome to the many worlds
interpretation of quantum mechanics
and its chief adherent,
David Deutsch, of Oxford University.
Deutsch proposes that reality itself
is profoundly misunderstood.
He says that what quantum mechanics
actually describes
is not one universe,
but an infinite number
of parallel universes.
He calls it a multiverse,
in which every possible quantum
mechanical outcome for each
and every atom in the universe
exists somewhere.
So an atom and its electron
are multiversal objects.
And that multiversal object is
what quantum mechanics is describing.
Now that means that the parallel
universe aspect of reality
as described by quantum theory
must apply to objects of all sizes -
humans, stars, galaxies, everything.
And that's why we call it
the parallel universe theory
rather than just
parallel electrons theory.
Because we are made of atoms.
That's right.
The same theory that says the atoms
exist in more than one place
says that we humans also exist
in more than one place
in different universes.
And there are some universes
where you and I don't exist at all.
'The highly-respected author
and physicist, Paul Davies,
has an even more bizarre idea.
'He suggests that the strangeness
of the measurement problem explains
how the universe came into being.'
The experimenter today in the lab
can make a measurement
that affects the nature of reality
as it was five billion years ago.
There's a sort of feedback loop
between the existence
of living organisms and observers
and the laws and conditions
which have given rise to them.
Otherwise it just seems
a bit miraculous that the universe
happens to have started out
with the right laws and conditions
that lead to observers like ourselves
who can make measurements
and make sense of it all.
But quantum mechanics provides
just such a feedback through time.
It allows this backwards in time
effect. Not causation.
It's not that we here now can change
the past to fix it so that we exist,
but we have an influence on the past
through quantum measurements we make.
But there's a pragmatic side
to the debate, too.
Other scientists are worried
that these bizarre and metaphysical
speculations
leave the world of measurement and
laboratory experiment far behind.
Professor Andrew Jackson of the
Niels Bohr Institute in Copenhagen
says that ultimately we shouldn't
worry about the interpretation or
the measurement problem or the cat.
He says we shouldn't be concerned
about the so-called true nature
of reality.
It's enough that the theory works.
All of the things we can measure
give us questions we can answer
from quantum mechanics.
So the quantum mechanics itself,
without the need for interpretation,
provides us with answers
or predictions regarding the result
of every experiment we can do.
So I don't know...
That's enough for me. Yeah.
So you don't think quantum mechanics
needs a unique interpretation
because it doesn't add anything?
It doesn't add anything
and I don't think it will lead us
to the next step.
An interpretation doesn't change
the results or the rules
and that's why it's not testable.
The whole purpose of the last 200
years in physics, this incredible
leap forward that we've made,
has come because experiment
confronted theory and led to new
theory when theory broke down
and back and forth and back and
forth. Interpretations don't do that.
Interpretations only give us
some kind of a way of believing
we understand what quantum mechanics
tells us, but that's a fixed point.
There's no new content to it.
Quantum mechanics is
counterintuitive
and goes against common sense.
What do you say to people
who insist on wanting to know
what an atom is doing
when you're not looking at it?
I'm not sure I'm quoting,
Feynman or Dirac,
but the answer is,
"Shut up and calculate".
So shut up and use the maths. Right.
"Shut up and calculate"?
Is this really scientific pragmatism
or just dogmatic fundamentalism?
The reason that this is unacceptable,
philosophically,
can I think be best understood by
comparing it with an earlier episode
in the history of physics,
namely the Inquisition's attitude
several hundred years ago
to the idea that the Earth goes round
the Sun, not the Sun round the Earth.
They wanted to promote a compromise
with Galileo where they would admit
that the positions of the stars
and planets and Sun in the sky
are exactly as predicted
by that theory,
but that it was presumptuous
of humans
to purport to be able to describe
the underlying reality -
why the stars appeared there.
The same thing happened
with quantum mechanics.
A group of people who didn't like
the implications of the theory
about reality
realised you could use it in practice
by just using its predictions.
That is a move you can always make
with any scientific theory. You can
always deny it describes reality.
You can't be proved wrong
by experiment, but as a philosophical
position it's a dead end. Sterile.
I think it's fair to say that most
physicists use quantum mechanics
to describe the subatomic world
without worrying too much
about the interpretation.
Personally,
I'm not in favour of this view.
I don't have a preferred
interpretation, but believe nature
must behave in a particular way.
So only one of the interpretations
can be correct
and, to be quite honest, we probably
haven't found the final answer yet,
but I think
it's only a matter of time.
I certainly don't subscribe
to "Shut up and calculate".
I prefer the "Shut up
WHILE you calculate" view.
I'm happy to do my calculations
to study atoms,
but when I'm away from my work, I
still worry about what it all means.
In the last 100 years
we have peered deep inside the atom,
the basic building block of
the universe, and inside this tiny
object we found a strange, new world
governed by exotic laws
that at times seemed
to defy reason.
Atoms present us
with dizzying contradictions.
They can behave both as particles
or waves, they appear to be
in more than one place,
they force us to rethink
what we mean by past and future,
by cause and effect,
and they tell us strange things
about where the universe came from
and where it's going.
Pretty amazing stuff for something
a millionth of a millimetre across.
That's why Niels Bohr, the father
of atomic physics, once said
that when it comes to atoms
language can only be used as poetry.
What's fascinating to me is
that although we've learnt
an incredible amount about atoms,
our scientific journey
has only just begun.
Although we know how a single atom
or just a few atoms behave,
the way trillions of them
come together in concert
to create the world around us
is still largely a mystery.
To give you one dramatic example -
the atoms that make up my body
are identical to the atoms
in the rocks, the trees, the air,
even the stars. And yet they come
together to create a conscious being
who can ask the question,
"What is an atom?"
Explaining all that is surely
the next great challenge in science.