All language subtitles for BBC.The.Secrets.of.Quantum.Physics.2of2.Let.There.be.Life.576p.PDTV.x264.AAC.MVGroup.org-eng

Welcome to a new and very strange world of nature.

It's been taken over by the weird subatomic particles of

quantum physics.

CHURCH BELL RINGS

As a physicist, I've spent my working life studying

how these particles behave in the laboratory.

But now I'm heading out into the natural world.

I'm on a mission to prove that quantum physics can solve

the greatest mysteries in biology.

This is a real adventure for me.

I'm very much out of my comfort zone trying to apply

the very careful ideas I'm familiar with in a physics laboratory

to the messy world of living things.

I believe that quantum physics could hold many of life's secrets.

That deep in the cells of animals,

particles glide through walls like ghosts.

That when plants capture sunlight...

..their cells are invaded by shimmering waves

that can be everywhere at the same time.

And that even our human senses

are tuning in to strange quantum vibrations.

In the fantastic world of quantum biology,

life is a game of chance,

played by quantum rules.

This is what I hope to convince you of,

to show you that quantum mechanics is essential in explaining

many of the important processes in life, and potentially, that

quantum mechanics may even underpin the very existence of life itself.

My quest begins with one of the most majestic sights in nature.

Migration.

Every winter, barnacle geese arrive right on cue

at the same Scottish river.

The end of an epic 2,000-mile voyage from Svalbard,

high above the Arctic Circle.

Of course, many birds head south for winter

then back home for summer.

But for decades, exactly how birds navigated with such accuracy

was one of the greatest mysteries in biology.

So the most recent discovery has caused a sensation.

In the past few years,

one species of bird has helped create a scientific revolution.

I was one of many physicists who was shocked to discover that it

navigates using one of the strangest tricks in the whole of science.

It utilises a quirk of quantum mechanics,

one that bamboozled even the greatest of physicists,

from Richard Feynman to Albert Einstein himself.

So you might be surprised to discover the identity of this

mysterious creature.

Say hello to the Quantum Robin.

This is the European robin.

Every year, she migrates from northern Europe

to the tip of Spain and back.

In this laboratory in the woods,

biologist Henrik Mouritsen is trying to solve the mystery

of how she does it.

But he's found himself in MY world,

the strange world of quantum mechanics.

Quantum mechanics describes the very weird behaviour of

subatomic particles.

Down in this realm of the very small,

we have to abandon common sense and intuition.

Instead, this is a world where objects can spread out like waves.

Quantum particles can be in many places at once

and send each other mysterious communications.

I set out to understand how the bird finds its way,

but it just turned out that the data

more and more pointed towards this as

the only explanation that could bring all the different results together.

Henrik's investigating a longstanding theory -

that robins navigate by the Earth's magnetic field.

His laboratory is an ingenious magnetic birdcage.

And these plastic cones lined with scratch-sensitive paper

provide the key measurements.

Henrik's artificial magnetic field is like the Earth's, except that

HE can point it in any direction he likes.

Inside their cones, the robins always respond to the field,

leaving scratches in a single direction.

The big mystery is HOW.

The Earth's magnetic field is incredibly weak,

far too weak for any living creature to detect.

But Henrik has found an intriguing clue

by giving the Quantum Robin a mask.

We have a little leather hood similar to what you put on a falcon,

you know, but just for a robin,

and you have then a hole in front of one eye

or a hole in front of the other eye.

And what we can see is that if you cover up the right eye, you turn off

their magnetic compass processing in the left part of the brain.

If you cover up this eye,

you turn the compass off in this part of the brain.

The robin's magnetic compass seems to be in her eyes.

I can show you what's going on using my own eye.

Now, we use our eyes for vision,

but we also have a second light-detecting mechanism.

If I shine this torch into my eye,

you can see that my pupil closes down.

It's basically a defence mechanism to protect my eyes.

My eye is responding to particles of light - or photons.

The energy provided by the photons

is clearly enough to activate chemical reactions.

After all, that's what controls my eye muscles.

Light must be causing similar chemical reactions

in the robin's eyes.

In fact, it's the power supply for a unique form of magnetic compass...

..inside her cells...

..in the weird world of subatomic particles...

..a place where only quantum physics

can explain what's going on.

To see why, imagine the chemical reactions in the robin's eye

taking place in mountains and valleys of energy.

To get a reaction to start,

you have to push molecules to the top of a mountain.

Thanks to Henrik's experiments,

we now know that light does most of the hard work.

But when it reaches the very peak,

the molecule becomes incredibly sensitive to the slightest touch.

The key point here is that the robin's chemical compass is now

balanced on an energy peak between two valleys.

Going one way produces one set of chemical products -

the other, a different set.

Now, even a tiny change in the Earth's magnetic field can tip the

molecule over the top, but the way this happens defies common sense.

The final piece of the puzzle

depends on one of the truly

mind-boggling ideas in physics.

But don't worry if you find it

hard to understand -

even Albert Einstein

called it "spooky".

The idea is called quantum entanglement.

It involves particles that seem to communicate faster

than the speed of light.

In 1935, Einstein published a famous paper

arguing that it was impossible.

But Einstein was wrong.

In recent years, extremely delicate experiments have shown that

subatomic particles really are entangled.

It means they can subtly

and instantaneously influence each other across space.

And now it seems the same thing is going on inside the robin's eye.

When a photon enters the robin's eye,

it creates what's called an entangled pair of electrons.

Here's how it works. Each electron has two possible states.

For simplicity, I'm choosing to call them Red and Green.

Now, here's the weird thing.

Until I measure it, it's neither one nor the other,

but both at the same time.

Think of the electrons like spinning discs.

They're simultaneously red AND green.

But by firing a dart...

..I can force the first electron to be one or the other.

So far, it's just a game of chance.

I don't know what I'll get until I try it.

So I know my first electron is red.

Suppose I now measure the second electron.

You'd think I'd have a 50/50 chance of getting red or green.

After all, that's what you'd expect in the normal, everyday world.

But you'd be wrong.

In quantum entanglement, the electrons are mysteriously linked.

For example, if I get red on the first...

..I ALWAYS get red on the second.

It's not a game of chance any more.

It's as if the first electron is telling the second one what to do.

That's why Einstein called it spooky.

The electrons seem to know that they should both have the same colour,

no matter how far apart they are.

The really important part is that

the two electrons needn't be the same colour.

They can be entangled in a different way,

so that if the first electron is red...

..the second one is always green.

It seems that this mysterious connection is the ultimate secret

of the Quantum Robin's compass...

..because the direction of the Earth's magnetic field

can influence the outcome.

Near the equator, they may be more likely to be red-red.

But near the Pole, they may be more likely to be red-green.

And that's the vital factor that finally tips the balance of

the robin's chemical compass.

Tiny variations in the Earth's magnetic field change the way

electrons in the robin's eye are entangled,

and that's just enough to trigger her compass.

Now, finally, we can see how something as weak as the Earth's

magnetic field can tip that balance one way or the other.

If the message changes,

the chemical reaction tips a different way...

..changing the robin's compass reading.

Suddenly it looks like it's a fundamentally quantum mechanical

phenomenon in birds.

It would be one of the first, if not THE first, in biology.

Biologists better get used to the weirdness of physics.

The robin is navigating by "spooky" quantum entanglement.

To see subtle quantum effects,

even in a controlled, austere environment of a physics lab,

is really difficult.

And yet here's the robin doing it with ease.

These experiments are real and verifiable, and yet even though

I'm seeing them with my own eyes, I still find it hard to believe.

Bird navigation has brought physics

and nature together as the science of quantum biology.

There's a whole new world to explore.

But its pioneers have found that it doesn't just affect birds.

It affects every single one of us.

Because the latest experiments say

you're doing quantum physics right now.

And believe it or not, you're doing it with your nose.

Hello, Jem!

Hello.

Hello, little girl! Hello...

Our sense of smell is remarkable,

and quite different from our other senses of sight and hearing.

Among the thousands of scents that we can recognise,

many of them may well trigger very powerful memories and emotions.

It's as though our sense of smell is

wired directly to our inner consciousness.

It's also different in another way.

The other senses of sight and hearing rely on us detecting waves -

light and sound.

But our sense of smell involves detecting particles -

chemical molecules.

Recently, scientists have begun to realise that when it comes to

our sense of smell, something very mysterious is going on.

GUNSHOT

For decades, biologists thought they knew exactly how our noses

sniffed out different chemicals.

But physicists like Jenny Brookes think there could be a new

ingredient in the mix.

And it smells like quantum mechanics.

A lot of people speak of the sense of smell and olfaction,

and the science of olfaction as being a problem that's been solved

and we know all about it - and we do know a lot about it.

We know about the ingredients,

we know about the equipment that we use to smell.

But I would argue that there's a little bit more to understand.

To understand more, I need someone to help me with a smell test.

And Jem is going to sniff him out.

Every human being gives off a cocktail of chemicals.

Jem's nose could detect a single gram of it

dissolved over an entire city.

So she has no trouble finding the man I'm looking for.

Meet Colin the gardener, a man who's used to smelling the flowers.

Right, then, Colin, I'm going to put your sniffing skills to the test.

- Cool.
- I've got a selection of chemicals here,

and I want you to tell me what they remind you of.

OK.

I'll start you off easily.

COLIN SNIFFS

Oh, that's...

- ..like a minty, minty vapour rub...
- It is, yeah.
- ..sort of thing.

- Yeah, this is...
- Something what you'd rub...

- This is men...menthol.
- Menthol.
- Yeah.
- But it's that essence.

Right, here's the next one.

Ah. You should be able to recognise this one.

That's baking with my daughter.

- Mm-hm.
- Erm, icing sugar sort of thing...

- Vanilla.
- Vanilla, yeah.

When our noses detect a chemical,

they fire a nerve signal to our brains.

But different chemicals create different sensations.

The standard explanation for this is to do with

the shape of the molecules.

The conventional theory that goes back to the 1950s

says that the scent molecule has a particular shape that allows it

to fit in to the receptor molecules in our nose.

If it has the right shape, it's like a hand in a glove,

or a key in a lock. In fact, it's called the lock and key mechanism.

With the wrong shape, it won't fit into the receptor.

But with the right shape, it fits into the receptor,

triggering that unique smell sensation.

Different receptors are wired to different parts of our brains.

So, when a menthol molecule locks into its specific receptor,

it triggers that minty fresh sensation.

But the lock and key theory has always had a problem...

..and Colin's next test will show you why.

OK, how about...

this one?

Quite a strong smell.

Oh, that's...

- Yeah.
- What does it remind you of? What does it conjure up?

What memories?

I think Christmas.

- Christmas cake.
- Yeah. Marzipan.

Marz...marz...yeah, that's it, yeah.

- Almonds.
- Very, yeah.

Colin identified the smell of marzipan or almonds.

In fact, it's due to a scent molecule called benzaldehyde.

What I didn't give him to smell was this other chemical - cyanide.

Both benzaldehyde and cyanide have the same smell,

they both smell of almonds,

but these molecules are both very different shapes,

so the lock and key mechanism,

as an explanation for how we smell, can't be the whole story.

So why would two molecules with different shapes smell the same?

Quantum biology has a head-spinning explanation.

It says our noses aren't smelling chemical molecules...

..they're LISTENING to them.

It's not just the shape of a scent molecule that matters.

Let's take a closer look at this model of a cyanide molecule.

The white ball here is a hydrogen atom,

and the grey sticks are the bonds that hold it together

with the carbon and nitrogen.

But the reality isn't as simple as that.

I can give you a better sense of what's going on

if we look at this larger white ball.

You see, atoms don't just sit still.

The bonds that hold them together are like vibrating strings,

and that gives us a whole new way of thinking about smell.

The bizarre new quantum theory of smell is all about vibrating bonds.

HE PLAYS HARMONICS ON GUITAR

Chemical molecules are playing music for our noses.

Imagine a receptor molecule in my nose is like my guitar.

Before it can make a sound, a scent molecule has to enter my nose,

and when that scent molecule is in place, its chemical bonds

provide the strings, and it's ready to be played.

The receptor molecules contain quantum particles -

electrons.

As they leap from one atom to another, they vibrate the bonds of

the scent molecule,

like my fingers plucking a guitar string.

GUITAR NOTE CHIMES

What's remarkable about this theory is that it tells us

our sense of smell is about the vibrations of molecules,

or wave-like behaviour,

and not so much about the shape of a particular scent molecule.

Our sense of smell may be much more like our sense of hearing.

HE PLUCKS HIGH NOTE

A particular molecule, say that of grass,

will vibrate at a particular frequency.

HE PLUCKS LOW NOTE

But a different molecule, say, that of mint,

will vibrate at a different frequency.

HE PLUCKS MID-RANGE NOTE

PLUCKED NOTE REVERBERATES

HIGHER NOTE REVERBERATES

This would explain why cyanide smells like almonds.

The two molecules have different shapes,

but their chemical bonds just happen to vibrate

at the same frequency.

The constant vibration in the odorant is almost

literally like a particle of sound.

So, yeah, we're saying that the process of smell could be

exactly like an acoustic resonance event,

it could be very analogous to, erm, hearing and seeing, actually.

But can we really be listening with our noses?

A bizarre theory needs a bizarre experiment to test it.

Here's how it works.

This molecule has a musky aroma, like perfume.

But if the theory is right,

then I should be able to change its smell by changing its vibrations.

The musky molecule contains

lots of hydrogen atoms like this

bonded to carbon atoms, but what if I were to replace all these atoms

with a different form of hydrogen called deuterium?

Now, it won't change the shape of the molecule,

but it will change the way it vibrates.

And here's why - deuterium is twice as heavy as normal hydrogen,

and so it vibrates more slowly.

Now, different vibrations mean different smells,

so if I were to make a new form of this chemical,

all packed with deuterium atoms instead of normal hydrogen,

it should smell different.

Quantum biologists found a unique way to carry out this experiment.

A smell comparison,

using the most sensitive noses they could find.

INSECTS BUZZ

Fruit flies.

First, the flies were trained to avoid the modified version

of the musky molecule.

To be honest,

I haven't got a clue how you go about training a fruit fly,

but apparently you can.

In the laboratory, the flies had to pass through a kind of maze.

They were then given a choice.

Go right for the nice, musky smell,

or left, for the nasty, modified version.

HE STRUMS GENTLY

They could definitely smell the difference.

They always preferred the original and turned right.

The fruit fly experiment gives hard evidence

that quantum smell theory really works.

But ultimately, it works in harmony with the lock and key theory.

First, the scent molecule fits into the receptor...

..then those molecular vibrations take over.

Incredible as it seems, flies, humans

and dogs may be smelling the sound of quantum biology.

Our sense of smell is fascinating and mysterious as it is,

but to think that when I encounter a particular scent

and that sets off a whole wave of memories

and emotions in my mind, that it's underpinned,

that it's triggered by quantum mechanics,

I think makes it even more remarkable.

CROWS CAW

The mysterious influence of quantum physics

reaches into every corner of the natural world.

In fact, it inhabits the walls

of every living cell on Earth.

Because the latest experiments suggest a magical solution

to one of the greatest mysteries of nature.

The miracle of metamorphosis.

The transformation of a tadpole into a frog

has never been fully explained.

In little more than six weeks, the tadpole breaks down,

then reassembles in its adult form.

But the big mystery is how it happens so fast.

When you think about it, there's nothing more extraordinary

than a tadpole turning into a frog.

Take its tail, for example.

Over a period of several weeks, it gets reabsorbed into the body

and the proteins and fibres that make up the flesh

get recycled to form the frog's new limbs.

But for this to happen,

trillions and trillions of chemical reactions work together,

breaking molecules, forming new ones in a carefully orchestrated dance.

But the fibres that hold flesh together are very, very strong.

They're a bit like these ropes holding my raft together.

In order to dismantle the raft, I'd have to undo these very tight knots.

You could think of it like this...

..a tadpole is held together by long robes of proteins

knotted together by chemical bonds.

The bonds are so strong that they should last for years,

much longer than the tadpole's entire life span.

So how can it turn into a frog in just a few weeks?

The explanation involves one of the most important molecules of life.

Tiny widgets in all our cells called enzymes.

The enzymes are the actual machinery of the cell.

They are actually the little machines inside cells

that do the chemical transformations that are involved in everyday life.

They are absolutely crucial.

And the reason they're so crucial is because what they are able to do

is to accelerate chemical reactions by enormous amounts.

Let me show you just how quickly enzymes get to work.

Inside this bottle is a substance called hydrogen peroxide.

You're probably most familiar with it

as the chemical used to bleach hair.

In fact, I obtained this sample

from my local hairdressers.

Hydrogen peroxide is also produced in the body,

and it's the job of the liver to get rid of it.

The way it does that is using an enzyme

which breaks down hydrogen peroxide into water and oxygen.

Now, to show you just how quickly this enzyme works,

I'm going to do a quick demonstration.

I've got some liver here which I've chopped up

in order to release the enzyme.

Now, watch what happens when I add this liver mixture

containing the enzyme to the hydrogen peroxide.

Watch how quickly the oxygen is released.

CROWS CAW

Just 100 grams of liver fired my rocket nearly 20 feet.

Liver enzymes make the breakdown of hydrogen peroxide

incredibly efficient.

It happens a trillion times faster.

That's a million, million times faster than it would otherwise.

In metamorphosis, it's enzymes

that dismantle the tadpole's tail.

And that means breaking down

an incredibly tough protein

called collagen.

Collagen is one of the most important proteins in the biological world.

It's the protein which actually gives that resilience, that elasticity

to tendons, to cartilage,

and of course to our skin, as well.

And in the tail of the tadpole, it provides the kind of scaffold

that supports that structure.

Now, when the tadpole is transformed into the frog,

what you need to do is to essentially have an enzyme,

collagenase, which will literally snip the collagen down

into small pieces and thereby take that scaffold apart.

But how do enzymes break chemical bonds apart so incredibly fast?

Let me show you why it's a problem only quantum biology can solve.

Think of it this way, all these different parts of the knot

are like subatomic particles - electrons, protons -

that hold the different parts of the molecule together.

Now, to untie the knot, enzymes have to move protons about.

But as you can see, this takes quite a bit of effort

and a lot of time if there are many knots to unpick.

Physicists have a fancy way of saying

"put in effort to get something done".

They say you have to overcome an energy barrier.

OK, here's my energy barrier.

And here's my proton.

To break a bond apart,

it needs enough energy to get over the barrier.

The trouble is, when we work out how long this would take,

it's much too slow to break down a tadpole's tale.

But this is where protons turn into ghosts.

I wouldn't blame you for thinking that this is an idea

that a clever theoretician has come up with,

that it's just mere speculation - something that we have no proof of.

But we do. It takes place all the time.

In the quantum world,

protons don't have to go over barriers.

They can tunnel...

straight through.

Tunnelling strikes at the very heart of what is most strange

about quantum mechanics.

It's like nothing we see in our everyday world.

A quantum particle can tunnel from one place to another

even if it has to pass through an impenetrable barrier.

They are not solid objects like balls in our everyday world.

They have spread out, fuzzy,

wavelike behaviour that allows them to leak through an energy barrier.

A particle can disappear on one side of the barrier

and instantaneously reappear on the other.

In nuclear physics, this effect is a proven fact.

Without quantum tunnelling, the Sun simply wouldn't shine.

But I never thought I'd see it...

..in a tadpole.

It's hard to stress just how weird this process is.

It's as though I would approach a solid brick wall and,

like a phantom, disappear from one side and reappear on the other.

The most important advantage of tunnelling is its speed.

It happens incredibly quickly -

much faster than if protons go OVER the barrier.

As a nuclear physicist, quantum tunnelling is my bread and butter.

Subatomic particles like protons do it all the time.

But what has this got to do with biology?

The answer is that without quantum ghosts,

the metamorphosis of a tadpole would be impossible.

Remember, chemical bonds are basically knots.

Tunnelling unties them - fast.

Have a look at these two knots.

Now, on the face of it they look identical,

but there's a subtle difference.

This knot has the two short ends

of the rope on the same side.

Whereas this one

has the two short ends on opposite sides.

Now, you'd think that wouldn't make a difference, but it does.

You see, THIS knot...

..is very hard to break,

whereas THIS one...

..is easy.

Quantum tunnelling...

..turns strong knots into weak ones.

So in a tadpole,

the entire collagen scaffold breaks apart easily.

And finally, other enzymes rebuild it in the shape of a frog.

The quantum tunnelling of particles is one of those weird features

of the subatomic world

that a physicist like me is very familiar with.

After all, it's responsible for radioactive decay

and it goes on inside the Sun.

It's the reason why the Sun and all stars shine.

But to discover this going on inside every cell of every

living organism on the planet, because every cell contains enzymes,

now, THAT I find truly amazing.

Quantum biology casts its spell over every living creature.

We've seen that birds, mammals, insects

and amphibians are governed by the strangest laws in science.

But the most dramatic recent breakthrough concerns

the single vital process on which all these forms of life depend.

The conversion of air and sunlight

into plants.

This fine specimen is a Larix decidua, or European larch.

It's about 100 feet high and right at this moment,

passing just this side of the planet Venus,

is a bullet with this tree's name on it.

The bullet is a photon

nearing the end of its long journey from the Sun.

Its ultimate destiny is to kick-start

a series of chemical reactions that underpins all life on Earth...

..photosynthesis.

Every second of every day,

16,000 tonnes of new plant life are created on Earth.

And for me, it's incredible to think that our existence

on this planet depends on what happens

in the next trillionth of a second.

The crucial first stage of photosynthesis

is the capture of energy from the Sun.

It's nearly 100% efficient,

vastly superior to any human technology.

But the way that every plant on Earth achieves this

is one of the great puzzles in biology.

When it turned out that quantum weirdness might hold the answer,

physicists could hardly believe it.

It was like a revelation.

It was very exciting, because I was

used to working on problems

that were quite abstract experiments.

I am a theoretician, but I always related my theory

to experiments that were very clean in the lab,

things that you can control.

But now, finding out that the things that I knew can help me

to understand better how nature works,

really, scientifically, it was like a...

a new inspiration to my life,

so I would say I fell in love with this field.

Textbook biology says the colour of green plants

comes from chlorophyll molecules.

Inside the living cells, they absorb light from the Sun.

This energy is then transferred incredibly quickly

to the food-making factory at the heart of the cell.

The entire event takes

just a millionth of a millionth of a second.

When the photon hits the cell,

it knocks an electron out of the middle of a chlorophyll molecule.

This creates a tiny packet of energy called an exciton.

The exciton then bounces its way

through a forest of chlorophyll molecules

until it reaches what is called the reaction centre.

Now, that is where its energy is used to drive chemical processes

that create the all-important biomolecules of life.

The problem is, the exciton needs to find its way to the reaction centre

in the first place.

Textbook biology can't explain how the exciton does this.

Because, of course, it doesn't know where it's going.

It just bounces around like a pinball

in a process called a random walk.

Sooner or later,

it will pass through every single part of the cell.

But this isn't the most efficient way to get around.

Because when the exciton eventually does reach the reaction centre...

..it's by pure chance.

If the exciton just blindly and randomly

hops between the chlorophyll molecules,

it would take too long to reach the reaction centre

and would have lost its energy as waste heat.

But it doesn't. Something very different must be going on.

The vital clue comes from recent experiments

that stunned the world of science.

Chemists fired lasers at plant cells

to simulate the capture of light from the Sun.

They confirmed the exciton wasn't bouncing along a haphazard route

through the cell.

This original understanding didn't explain what

we were observing in the lab.

So the mystery lies in, OK,

so then, what is the explanation for what we are observing in the lab?

The solution is that plants obey the most famous law

in all of quantum mechanics...

..the uncertainty principle.

It says it you can never be certain

that the exciton is in one specific place.

Instead, it behaves like a quantum wave,

smearing itself out across the cell.

The exciton doesn't simply move from A to B.

In a bizarre but very real sense,

it's heading in every direction at the same time.

It's spreading itself out as a wave

so that it can explore all possible routes simultaneously.

This strikes at the very heart

of what's so strange about quantum mechanics.

The exciton wave isn't just going this way or that way,

it's following all paths at the same time.

That's what gives it such incredible efficiency.

The beauty of it is...

..if the exciton is trying every route

to the reaction centre at once...

..it's bound to find the fastest possible way to deliver its energy.

It's hard to express how incredible this discovery seems

to physicists like me.

Biological cells are full of the random jiggling

of billions of atoms and molecules.

But somehow, excitons maintain their form

as beautiful, perfect quantum waves,

transporting the energy that guarantees life on Earth.

It opened a whole new scientific path for me.

And I really enjoy the fact that

to be able to understand fully what is happening there or in the plants,

you have to interact with scientists

that have completely different approaches

like biologists and chemists.

But we all have to come together

to actually understand what is the relevant of this,

the relevance of this.

So, for me, this is one of the most exciting parts of this field.

Real scientific experiments leave no doubt.

The strange hand of quantum mechanics has shaped

the entire living world.

It's not a surprise that you should find quantum tricks being used

in biological systems.

The reason is, because they're better.

Quantum entanglement is normally seen

in the tightly-controlled conditions of the physics lab.

But now, we know that robins use it

to navigate with extraordinary precision.

Quantum vibrations mean our noses LISTEN to chemicals...

..enhancing our perception of the world around us.

The living cells of all animals depend on protons

that vanish and reappear like ghosts...

..speeding up the vital processes of life.

And photosynthesis reveals the big picture.

A shimmering world

where quantum waves capture the Sun's energy in an instant.

Sometimes, people say, "Ah, but physicists have been

"looking for this for decades".

Well, biology has had millions of years.

The ultramodern science of quantum mechanics

is an ancient fact of life.

For the end of my journey,

I want to take these ideas to their logical conclusion.

Of course, as a scientist,

any speculations I have have to be backed up by careful experiments.

So I want to concoct a thought experiment that helps me

to answer the biggest biological question I can think of.

Does quantum physics play any role

in the mechanism of evolution itself?

In 1859, Charles Darwin stunned the world

with his Theory Of Evolution By Natural Selection.

He went on to explain the differences

between humans and other apes.

150 years later, there's no doubt that Darwin's theory

accounts for every living organism

on land and sea.

But I'd like to explore the latest,

extraordinary interpretation of his ideas.

STIRRING STRINGS

Could there be a quantum theory of evolution?

MUSIC: Adagio of Spartacus and Phrygia from Spartacus Suite No.2 by Aram Khachaturian

Can quantum evolution explain how the snail got its shell?

The snails I'm used to seeing in my back garden

tend to have rather bland, boring shells.

So have a look at this beauty.

The patterns on its shell very perfectly match

the lines on the stem.

It's called a banded snail. Cepaea nemoralis.

And the pattern isn't there by accident.

Come and have a look at this.

Less well adapted snails

are more likely to be found here.

This stone is called a thrush's anvil.

The song thrush is the snail's main predator.

It catches the snail

and smashes its shell against the stone to get to the snail.

Now, what I can see here

is that there aren't many banded snail shells,

suggesting that its colours camouflage it very well,

hiding it from the bird.

Darwin's theory says

that evolution depends on variation within a species.

Snails with camouflage are more likely to survive and reproduce...

..passing on their shells to the next generation

so that the species as a whole becomes better adapted.

So, variation - the random differences between snails -

is the driving force behind their evolution.

Now, all species evolve and adapt to their environment.

But the question I'd like to explore is

whether quantum mechanics plays a role in this.

The only way to find out

is by scientific experiments.

So, my adventures in quantum biology finally bring me home.

To the University of Surrey.

Here, in the laboratories,

I'm planning a new analysis of the most celebrated molecule in science.

Deoxyribonucleic acid, or DNA.

Its double helix holds the genetic code for every living organism.

It's a remarkable fact that Darwin himself had no idea

what created variation in the species.

The structure of DNA wasn't discovered until 1953

by Francis Crick and James Watson.

The most famous feature of DNA is of course

its beautiful double helix structure.

But that's just scaffolding.

The real genetic secret lies in between.

The four different-coloured molecules are called bases.

The colour code on one side - say blue, red, blue -

forms a gene that parents pass on to their offspring.

A gene is a bit like a jigsaw puzzle.

It fits together like this.

A full strand of the double helix forms a coloured pattern.

But the other strand always pairs up the same way.

A blue base always goes with yellow

and green always goes with red.

Because only those colours have the right shape to fit together.

What Crick and Watson realised was that this provides

a mechanism for passing on the genetic code.

When cells reproduce, the two strands of DNA separate,

ready to be copied.

But red still goes with green...

..and yellow still goes with blue.

So bit by bit,

the cell creates two new strands.

Two perfect copies of the entire genetic code.

So far, there's no genetic variation.

This new copy is identical to the original.

But here's the interesting bit.

During the copying process, something very important can happen.

Sometimes, mistakes creep in.

They're called mutations.

Let's have a look at these two bases here.

The two prongs that hold them together are subatomic particles.

They're protons.

They're basically the bonds between the strands of DNA.

These protons can jump across to the other side.

If the strands split when the protons have jumped across,

they find themselves in the wrong position.

Now, this red base will no longer bind to a green base.

Instead, it has to bond to a yellow base.

Slotting this back in,

we see that now this copy is no longer identical to the original

because I have a yellow base here instead of a green one.

We've brought in a genetic mutation.

Jumping protons would change the snail's DNA.

It could make a new gene for camouflaged shells.

The question is, how do protons jump?

It's my belief that quantum's spookiness can take over.

Now, for these mutations to take place,

the protons have to overcome an energy barrier.

And if you remember what happened with enzymes,

well, you can probably guess what's coming next.

Protons can behave as if barriers don't exist.

They tunnel straight through.

But does this ghostly effect really happen?

My colleagues in biology are already looking

for the very first evidence of quantum mutations.

Biologists didn't really even know about quantum mechanics,

so when you tell them that particles can be in two places at once,

they kind of say, "Well, not in my cells, they can't!"

Our experiment involves samples of bacteria.

The first sample is prepared in normal water,

containing hydrogen nuclei, or protons.

When the bacteria reproduce, we simply count the mutations.

But if our theory is correct,

then we should be able to change the rate at which mutations occur.

Remember how we tested the quantum theory of smell?

What if I replaced the proton with its big brother, the deuteron?

This is the nucleus of an atom of deuterium.

Now, crucially, a deuteron is twice as heavy as a proton

and this should influence how easy it is for

the deuteron to quantum tunnel.

Quantum mechanics is full of surprises.

Protons tunnel easily.

Deuterons...don't.

These heavier particles are much more likely to bounce straight back.

So the second sample of bacteria is prepared in heavy water,

which is full of deuterons.

Our theory says you should get far fewer mutations.

And, so far, the results are extremely encouraging.

The preliminary experiments that we've done gives us a hint

that the mutation rate is indeed depressed in deuterated water.

We find that it is lower. So my hunch is that we're right,

but we'll have to wait a little while before we're sure.

Final proof lies in the future.

Even if we're right,

quantum tunnelling is a rare form of mutation.

But our results promise hard evidence

for a new explanation of one of the most fundamental processes of life.

Even the merest possibility of a new quantum mechanism

for evolution itself is tremendously exciting.

In fact, the story of quantum biology is only just beginning.

What the frog, the robin, the fruit fly and the tree have shown us

is that real quantum effects are going on in nature all the time.

And if there's anything we've learnt

from the history of quantum mechanics, it's this -

we can never be certain where new discoveries will take us next.

Quantum biology is a revolution in science.

But it's time I got back to the physics department.