The quantum tree: photosynthesis – Jim al-Khaili (EN►EN/ES/IT/NL)

Transcript of video

Quantum biology casts its spell
over every living creature.

We’ve seen that birds, mammals, insects
and amphibians are governed…

by the strangest laws of science.

But the most dramatic recent breakthrough
concerns the single vital process…

on wich all these forms of life depend.

The conversion of air and sunlight
into plants.

This fine specimen is a Larix Decidua
or a European larch.

It’s about a hundred 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 kickstart
a series of chemical reactions…

that underpins all life on earth:

Every second, of every day, sixteen thousand tons
of new plant life are created on earth.

And for me it is 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 a 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…

physisists could hardly believe it.

It was like a revelation, it was very exciting.

Because I was used to work on problems,
that were quite abstract.

I am a theoretician,
but I always relate in 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…
I don’t know…

scientifically it was an inspiration to my life
as a scientist.

I would say I fell in love with this field.

Textbook biology says the colour of green plants
comes from chlorophile molecules.

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

This energy is then transferred
incredibly quickly…

to the 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 chlorophile molecule.

This creates a tiny package of energy,
called an “Exoton”.

The Exoton then bounces its way
through a forest of chlorophile molecules,

untill it reaches
what’s called the reaction center.

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

that create the all important
bio-molecules of life.

The problem is: the Exoton needs to find
its way to the reaction center in the first place.

Textbook biology can’t explain
how the Exoton does this.

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

It just bounces around like a pin-ball,
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 Exoton eventually
does reach the reaction center…

it’s by pure chance.

If the exoton just blindly and randomly
hops between the chlorophile molecules,

it would take to long
to reach the reaction center…

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 lights from the sun.

They confirmed the Exoton 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 mistery lies in: then what is the explanation
of what we’re observing in the lab.

The solution is that plants obey
the most famous law in all of quantum mechanics.

The uncertainty principle.

It says you can never be certain
that the Exoton is in one specific place.

Instead it behaves like a quantum wave,
smearing itself out across the cell.

The Exoton 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 exoton 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 exoton is trying every route
to the reaction center at once,

it’s bound to find the fastes possible way
to deliver its energy.

It’s hard to express how incredible
this discovery seems to physisists like me.

Biological cells are full of the random jiggeling
of billions of atoms and molecules [as particles].

But somehow, Exotons 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.

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.

We’ll have to come together
to actually understand…

what is 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.


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