All language subtitles for BBC - Light Fantastic 1 (Let There Be Light)

And God said: Let there be
light, and there was light.

God is light. In all cultures,
there is an intimate association

between illumination and divinity,
between light and creation.

Light is color. Light is energy. It
fuels life and it feeds the spirit.

It inspires art, religion and science.

Light holds the secrets of the universe.

For thousands of years,
humanity has tried to unlock the

mysteries of light in its search
for the nature of God himself.

Woe unto them that call
evil good and good evil,

that put darkness for light,
and light for darkness.

This is the story of that
long quest to try understand

light because it leads to
an understanding of God.

Extraordinarily, we will see, that
enlightenment, that modern science

itself emerges from this religious
quest to understand the nature of light.

The journey into the mysteries of light

begins here, in Sicily,
over 2,000 years ago.

This luminous isle was home to some of
the most renowned Greek philosophers.

And it was they who first began to
question the nature of light and how we see.

Light is surely fascinating
for the Greek thinkers because

it offers a clue to the whole
structure of the universe.

It seems to fill space, and it allows
a kind of penetration of the world.

Greek exploration of light would lead to
discoveries that would change the world.

The Greeks lived in a world
bathed in light, but in order to

understand light in order to bring
it within the realm of reason,

it was necessary in a way to abstract from
the light that surrounded them, to choose

appearances, to choose phenomena where light
was behaving in a special, or strange way.

So, for example, why did distant
objects appear so much smaller,

or why do objects
completely change their

position and shape when
you put them under water.

By thinking about these specific
questions, these particular puzzles,

Greek philosophers made the most

extraordinary advances
in our understanding of

light and of its relationship between the
eye, the mind, and the world beyond us.

The first comprehensive
theory of light and

vision is attributed
to a wealthy scholar who

grew up in the shadows
of mountain Etna, the

giant smoldering volcano
on the island of Sicily.

His name was Empedocles.

Empedocles was a Sicilian philosopher,

physician and poet, who
lived 2,500 years ago.

Empedocles believed himself
to be divinely inspired

to reveal the properties
of light and of nature.

Indeed, according to one story, believe
it or not, in order to prove that he was

a God himself, he jumped into the crater
of this great volcano on Sicily, Etna.

Then we can guess that he
ended up as a mere mortal, but

his ideas about vision
acquired their own immortality.

Empedocles put forward the
extraordinary idea that we see

objects because light streams
out of our eyes and touches them,

and it makes an enormous amount of sense
that modelly something like a lighthouse,

I am seeing things because something
streams from my eyes towards them,

and as my gaze touches
them, they come into view.

Now, that may seem at first
glance that this idea is crazy,

but his idea that light
streams from our eyes

towards objects became
the fundamental basis

on which later Greek mathematicians
and philosophers will construct some

of the most important theories we
have about light, vision and optics.

Among them was the renowned
mathematician, Euclid.

Euclid used Empedocles'
theory to make the single most

important breakthrough in
the understanding of light.

Reason loves problems and
above all, it loves showing you

there is a problem where you
didn't think there was one.

Here is an example that
Euclid really focused on:

why do objects further away seems so small
in comparison with objects near our eye.

The height of a distant
column, which we know

in our minds, is much
bigger than our finger,

looks to our eyes to be exactly the
same as the finger held near our eye.

Euclid came up with an elegant solution:

the eye, the top of the finger, and the
top of the column must fly on the same line,

and for that to be true, the rays from
the eye must follow straight lines.

It was a fundamental breakthrough,
for the first time, light

could be explained, predicted by
the new discipline of mathematics.

What it showed as a
dramatic discovery was

that the geometry of
straight lines in triangles

can completely master problems of
light, and vision out there in the world.

And this mastery of light
had far reaching consequences.

It would help transform
navigation into a rigorous

skill based on the position
of the sun and the stars.

Greek navigators opened
up new trade routes,

and Greek culture and learning dominated
the known world as far east as India.

But nothing lasts forever.

In the wake of the great
achievements of the Greek

philosophers of light, the
world entered a period of crisis.

The Mediterranean world was wrecked
by war, invasion, destruction.

Libraries were burnt,
communities of scholars broken up.

Much of the teaching of the
ancient scholars was lost, but

here in Sicily, their work
would suffer a much kinder fate.

Conquered from North Africa,
Sicily soon fell under Islamic rule.

Most of what survived of that great Greek
optical theories was transmitted to the West

through the scholars of
Islam who arrived in the

Mediterranean world at
the end of 7th century,

and then for hundreds of years,
edited, translated, and debated

what the classical Greek
scholars had already established.

For Islam, with its notion
of a single God and a single

creation, light played an
absolutely fundamental role.

It was the medium through which God
made and communicated with his world.

Indeed, the very idea that
knowledge and spirituality is

associated with light is
essentially a Muslim doctrine.

The brightness of faith
put light, put optics

right to the center
of Islamic scholarship.

It is not surprising it
seems to me, that one of the

founders of modern optical
doctrine is a great Muslim scholar.

His name was Abin Al Haitan, or as
he became known in the west, Al-hazan.

Al-hazan would make
one the most significant

discoveries in history about
how light and vision worked.

But, bizarrely, his journey
into the mysteries of light

began with a tyrannical
king and a troublesome river.

There is a long history of clever men
trying to get work at powerful courts and

governments, and the career of Al-hazan
fits perfectly into this kind of story.

He was born in Basra
in the 10th century.

And he earned his living by each year
copying out all the works in geometry of

the great Greek mathematician Euclid,
and then selling those copies for cash.

So his understanding of
the behaviors of straight

lines and motion was
really second to none.

Al-hazan found an employment
at the court of the slightly

eccentric, extremely powerful
caliph in Cairo, Al Hakim.

Al Hakim encouraged learning
and technique because he

wished to control everything
in the world around him.

Everything. He simply couldn't
stand the idea that there

were elements in the world
that he couldn't order around.

And the river Nile, the source
of all of Egypt's wealth,

was something that the caliph
really wanted to master.

The caliph ordered
Al-hazan to stop the Nile

flooding. Failure would
result in almost certain death.

Now Al-hazan of course lacked
the modern technology of tide

control and flood control which
many European cities now have.

He knew and he was beaten, so
he drummed up a cunning plan.

He would pretend to be mad and in that
way, perhaps escape the caliph's wrath.

The plan didn't exactly
work; Al-hazan was thrown into

jail and stayed in confinement
for more than 10 years.

Sitting in the darkness, under police
control, he began to meditate on what

he could see and on what he couldn't;
he became obsessed with light and dark.

Al-hazan began to realize that there was
something wrong about the idea that we

see because stuff comes out of our eyes,
and touches or grasps the objects in sight.

Here is one of these problems that
occurred to him: sitting in the

darkness, and then looking suddenly
at the sun, his eyes really hurt.

Staring at sun was intensely
painful after that time in the dark.

It seemed improbable to
Al-hazan that if rays were indeed

emitted by the eye, that they
should cause him such pain.

He began to piece together an
entirely different explanation.

Al-hazan's big new idea was that
we see because there were rays,

traveling through space in
straight lines, towards our eyes.

He had overturned more than
1000 years of accepted dogma

But if light is independent
of the eye, how do objects

redirect the light into
our eyes when we see them?

Al-hazan realized there was a
clue in the way mirrors work.

Mirrors obviously reflect
light, and by studying

those patterns of
reflection very closely,

Al-hazan was able to confirm the
idea that the angle at which a ray

hits the mirror is the same as
the angle at which it is reflected.

There is a symmetry there.

It is as though a ball is striking
a wall and then bouncing off.

So there is a relationship between the
ideas of light ray is straight line and

its fundamental understanding of the
basic geometry of the law of reflection.

Al-hazan had the genius
to realize that light

bounces like a ball off all
objects, not just mirrors.

He worked out the precise
mathematical laws of light's

most important properties:
reflection and refraction.

Laws on which everything depends,
from spectacles to space telescopes.

12 years after locking out
Al-hazan away, the caliph died.

Al-hazan was freed.

He began obsessively refining his ideas.

His 7 volume work became the
fundamental text on light and vision,

insights which made entire
modern science of optics possible.

Light was transformed, governed
by mathematical rules and laws.

Light was leaving the abstract
world and entering the real one.

Within 2 centuries of
Al-hazan's death, militant

Christianity mobilized against
Islam in the Mediterranean.

The holy Catholic Church, determined
to demonstrate its divine authority,

seized on the work of the
great Islamic scholars,

and used Al-hazan's breakthroughs to
further a Christian knowledge of light.

It appeared between 1,000
and 1200 AD. The translation

of these texts by scholars
from Arabic into Latin,

their transmission to new schools and
universities of Western Europe would produce

something like a
revolution of learning, a

completely new approach
to the study of nature.

But the Christian church's interest in
light was not simply to prove its grasp of

nature, rather to use it as an instrument
to both control and inspire its flock.

Mastering light became absolutely central
to this project, for medieval Christianity;

there was an extraordinary strong
relationship between light and divinity

Light was the first substance to appear on
the world, God had said: Let there be light.

At the same time, light became a way of

fiatrocolizing, of dramatizing
the truth of the faith.

In ways that is now almost impossible
for us to imagine, the churches were

bright with candle light, with stained
glass of the most extraordinary colors.

A whole theatre of the
faith, whose working in many

ways depended on the
mastery of light and color.

As the Christian scholars investigated color
and how to make it, what they found would

become the central
theme of one of the most

vicious controversies in
the history of the church

The story begins with Roger Bacon,
a 13th century Franciscan friar,

Bacon, more of less, for the
first time in the west, really

studied the work of Al-hazan, the
great Islamic authority on optics.

Bacon learned from Al-hazan,
the structure of the

eye, how light and vision
happen, the way light bends,

and began to study the effect
of glass on light, on colors.

By thinking hard of the new
glass technologies of the 13th

century, Bacon made the most
extraordinary breakthrough.

He began to see the ways in
which curved glasses could change

the figure, the shape and the
size of objects that we looked at.

Bacon wrote down accounts of
new fangled spectacles, of bits

of curved glass which made
distant objects appear very near,

which made tiny objects vast, which
could put colored images into the sky,

its excitement is palpable.

The new fangled spectacles that
would correct the problems of vision.

Bacon was enchanted by these things.

A new universe of light, of
glass, of color opened before him.

Bacon didn't just observe
and think in some vague

way about how light behave
in the world at large.

He brought it into the
workshop an experimented

it, on isolated aspects
of light's behavior.

He watched how it distorted
through water and glass,

and he noticed how in the
sunlight, droplets of water seem

to produce the same colors as
the ones he saw in rainbows.

Bacon seems to have become
obsessed by the rainbow,

but it wasn't obsession
that was bordering on heresy.

Towards the ends of the book of
genesis, Christians learned that

after the great flood which destroyed
all but a few select faithful,

God put into the heaven
a mark of his covenant,

that he would never again
visit destruction upon them.

The rainbow stood for that extraordinary

relationship between the
believers and their god,

yet Bacon was driven to explain
the rainbow, using logic and reason.

Its colors were a puzzle,
a challenge to his wit,

and he could make them
experimentally here on earth.

He would amaze his audiences by
swallowing a mouthful of water

and then spitting it out in an
arc through a beam of sunlight.

He was reproducing colors which you could
see in heaven here on earth experimentally.

It dawned on Roger Bacon that Gods'
miraculous rainbow must obey rules

similar to the mathematical laws of
reflection Al-hazan had discovered.

There was the danger, Bacon was
transgressing all sorts of boundaries,

the relationship between what
was natural and what was divine

and above all, he made no secret
of the fact that he, Roger Bacon,

was the unique individual who
could really see the truth of things

If there is one thing more
impressive, more striking, than Bacon's

extraordinary ability to
understand the phenomenon of nature,

it was Bacon's ability to make enemies;

He was explaining a miracle
through natural causes.

For Bacon, it was religious suicide

For denying the possibility
of miracles, and declaring

that everything that happens
is the result of natural law,

you shall be taken from this
place to a place of confinement.

Bacon was arrested and put
into close confinement in Paris.

He spent more than 2 decades there, locked
up in his cell, studying and writing.

But damned, because he dared
to speak out, he dared to trying

explain the wonders of creation,
using natural principles alone.

Roger Bacon died in less than
2 years after his release,

but despite the church's best effort to
suppress his work, his legacy lived on.

Not only had he described
how rainbows are the result of

refraction and reflection in
individual droplets of water,

he'd also explored the use of glass
lenses as a way of improving vision.

In time, Bacon would be remembered as
doctum mirabilis, the wonderful teacher.

But it would be religious
scholars like Bacon that

would plunge the church into
a crisis of its own making.

Chaos, madness, disorder.

This always been the
enemy of those in power.

Getting the time right, imposing
rules and system on everyday life.

for the Catholic Church, control of the

calendar, the rituals
of the year was the most

important outward invisible
sign of its control,

of its legitimacy, of
its inspiration from God,

and it would turn out that the technical
mastery of light would solve the

church's problems of imposing order on
a fallen, chaotic, and disorderly world

The Catholic Church was in
crisis, millions of believers

were defecting, protesting
against the pop's authority,

and it stake in this violent
struggle was the timing of Easter.

It is the movement of light
that dominates our sense of

time, and it seems to me that
the principal way in which

religions exert their authority
over our lives is precisely

through their control of time,
and their control of light.

For the Christian church, the
calendar of the year was set

around the most important of
Christian festivals: Easter.

Easter was the moment
when all believers marked

that extraordinary moment
when the world was plunged

into darkness because of
the death of the son of

the God, and his miraculous
resurrection into light.

This was the basis of faith.

Now Easter's date has been
set by the church as happening

on the first Sundee after the
first full moon of the spring.

Not being able to predict when Easter
fell brought chaos to the Catholic Church.

Without a precise system
for calculating future

spring equinoxes, Easter
was celebrated weeks late.

This inability to say
exactly when Easter fell was

becoming visible evidence
of the church's weakness.

What was required was an accurate
way of calculating when spring started

and from the 1500 on, great churches
were turned into a time and light machines

Here is how you can turn a
church into a solar clock.

The idea is that you draw a hole,
high in the wall of the church,

you see, how the hole
is surrounded by image

of the sun, and the
crown of the pope himself.

That hole will let through sunlight
when the sun is passing overhead at noon.

The image of the hole then
falls like a bright dot on a long

brass rod aligned north and
south on the floor of the church.

Here is the clever bit. Now noon in
winter, the sun is still pretty low,

so the image of the sun will fall
far to the northern end of the rod,

and during the course of
the year, that spot will

move inexorably towards
it, towards the south,

until we get to high summer
and then back again, through

the autumn, back towards
the northern end of our line.

The area that the astronomers and
priests cared about the most is here,

this defines whether sun is on
the day of the spring equinox,

that moment when the length of daylight
and the length of the night are identical,

because it was on this position that
the calculation of Easter relied.

This position defines the moment of equinox,
the limit of Easter, Terminvs Paschae.

By carefully noting where
the spring equinox fell year

after year, the observers saw
patterns beginning to emerge,

and from these patterns, they
could extrapolate with incredible

accuracy when future equinoxes
would occur for centuries ahead.

For the church, order and its own authority
appear to be restored, but not for long.

A tension begins to emerge,

On the one hand, the great churches are

clearly instruments of
astronomical learning,

the great wealth of the church
is being spent on patronizing and

supporting research into light, the
sun, the planets and astronomical time.

And this is at exactly the same moment
as the new theories in astronomy,

that the Earth is not
the center of the world,

that the Sun doesn't
move around the Earth,

are being developed by those who,
from the Churches' point of view, would

call the church into question and
threaten its scripture in divine authority.

As the war raged over the very nature of
the universe, 2 men would emerge, wielding

light and color as the weapons with which
they settle the matter, once and for all.

On the Catholic side,
was Rene Descartes,

and against him, Isaac Newton.

The church needed to show
that what did it said was true,

the set of undeniable rules
with which no one could argue.

The church needed an intellect who
was also a defender of the faith.

And they found one, in the unlikely
form of a coffee house philosopher.

Rene Descartes was the second son of a
wealthy landed family from central France;

he thought all there was in the world was
just machinery, including our own bodies.

He thought that food was just
a kind of fuel for these bodies.

Descartes believed that this idea would
be the perfect theory for the church.

God, he said, was the
ultimate clock maker.

Descartes liken the universe to a giant
machine, created and set in motion by God,

and obeying a set of predictable rules.

Well this really counted within
his understanding of light. Light,

he thought, could be completely
understood through mechanics.

Descartes' starting point to proving
his mechanical system was to focus his

attention on what he believed to the
ultimate optical instrument, the eye.

In Descartes' world, everything was
a machine, animals and humans too.

As far as Descartes was concerned,
the only difference between

beasts and humans was that humans
have souls and animals just don't.

If animals are machines, then the way to
find out how the culgris that make them

take actually work is to start cutting
them open, to make the flesh and blood speak

and that is exactly what he did to eyes.

If he could show that the eyes
were a machine, then, he argued,

that would be proof enough on
which to stand his entire theory.

What we have here, cat's eye ball, and I
just trim off the spare tissue around it.

This is exactly what
Descartes would have to do.

He said he scrapped it off
on his pair of scissors.

So I gonna make a few incisions in
the eyes so that I can get at the lens,

so I am just cutting the lens clear
of the tissues close to the iris.

Those are the lens, you can see, coming
away now. We will move it to that pot.

Well I have got a picture
of Descartes himself here.

So let's try, have a look
at that picture of Descartes

and seeing what I can see
through the lens itself.

It was the first real
demonstration that the

eye produced an inverted
image on the retina.

Up until then, there were various theories
for how the retina detected the image,

but we now, of course, from Descartes'
works, it is an inverted image,

of course we don't see it
inverted, because the nerve

system correct it for us
through the wires into the brain,

so we actually get the
world upright in the way.

Descartes' experiment with the
ox's eye was a real breakthrough.

He had shown how the shape
of the lens, the front of the

eye would change depending
on how far a way objects were.

That made the eye an
ideal mechanical system,

and that is what really
Descartes cared about.

The lens in the eye, acted
exactly like a glass lens,

Descartes had his evidence that
the eye was indeed a machine.

With this proof, Descartes could answer
the most complex questions of the day.

He could even explain
the mystery of color.

In Descartes' mechanical universe,
light was spinning particles

and color appeared when white light
particles spun faster or slower.

So the key to Descartes'
theory was that white light was

pure, and colors, merely a
temporary distortion of white light.

A mechanical universe
built by an orderly

systematic God was
exactly what Rome needed to

reassert its claim that
the Catholic Church alone

truly understood the
workings of the universe.

But theirs was a victory
that was short lived.

Across the water, in protestant England,
anger was building over the arrogant

declarations by Descartes
and the roman church

that they own the
knowledge of the world.

Standing against Descartes and his
views were man like Isaac Newton.

Newton saw Descartes as alien,
French, Catholic, rationalist,

and authoritarian and above all,
Descartes was wrong about light.

Isaac Newton would wrench light
from the Catholic Church's grip.

By his own admission, his obsession with

light would drive him
to the brink of madness.

In hunting for the shadow, I sacrificed my
piece of mind, a matter of real substance.

Isaac Newton came here to Cambridge
as a young student in the early 1660's.

It was here that all
his genuinely creative

science, philosophy, and
religious ideas were formed.

Light meant everything to Isaac Newton.

He thought of it as an
almost divine principle.

He thought that the
world have been made by a

single, wise, omnipotent,
clever, mathematical God.

A God, who to be frank,
rather resembled Isaac Newton.

There is a being, who made
all things, who has all

things in his power, and who
is therefore, to be feared.

And so in investigating light
and color, what Newton thought he

was doing was peeling deep into
the mysteries of God's creation.

And it was in 1664, aged just 21, that

Newton first began to
study light and vision.

Newton's reputation, then as
now, was an intensely solitary

man, of few friends, violent
tempetais, and obsessive energy.

Newton's first thoughts
about light and color were

prompted by an extraordinary
degree of self examination.

It is as though he turned his
attention inwards, into his own minds

He would stare at the suns for
hours and then shut himself in a dark

room, and by will alone, he try
to summon up the image of the sun

And then himself experiments
got much more dramatic.

He wanted to see if there was a
difference between the images we

see because of pressure, because
of something pushing on our eyes,

and the images we see when
we simply think or dream.

So what he did was to
take a wooden needle,

and put it between his
eyeball and the bone, and push.

Don't try this at home.

If you do this, Newton
found, that you get colored

circles appearing just
above the focus of your eye

and the colored circles followed the
order of the colors of the rainbow.

Newton was so focused, so concentrated
on the most might-new details

of that phenomenon of light that
even at the risk of his own eyesight,

that he was driven to see if there was
a way of making the optical phenomenon,

that appeared inside our own eyes as
in our minds appear in the outside world

so that others can see them.

With prisms and lenses and mirrors,
Newton recon you can do just that.

Newton had one aim to show
the world that Descartes'

mechanical theories about light
and color were utter nonsense.

Now a certain gentleman has suggested

that colors are mechanical and it is the

prism that changes the
white light into colors,

but this theory is not only
insufficient, but unintelligible,

Newton would design a series
of experiments on whose

replicability the whole status of
his new theory of light depended.

Newton made of a very tiny
hole in the window shutters,

allowing a beam of sunlight
to fall on the opposite

wall, and then he intercepted
the sunbeam with a prism.

He positioned the prism
very, very carefully

so that the angle at
which the sunlight hits the

prism was the same as the
angle at which they left.

Finally, after weeks' effort,
he made a breakthrough.

What Newton have done was to
make an artificial rainbow.

He saw red, orange, yellow,
green, blue, indigo, and violet.

And he invented a word for the sun's image,
colored as it was, this word was spectrum.

For the first time, Newton had precisely
measured the colors in a ray of sunlight.

Centuries later, knowledge
of the spectrum would extend

to X-rays, radio waves,
ultra-violet, and infra-red.

It would even reveal what
stars themselves are made of.

Yet for Newton, this was
only the starting point.

The spectrum was the key weapon in his holy
war over the true nature of divine light.

What I proposed was not to explain
the properties of light by hypothesis,

as so many before me have done,

but to prove them by
reason out of experiments.

The most important of Newton's
experiments was what came

to be called the crucial
experiment, experiment of cruces.

Newton reckoned he found an
absolute demonstration that shows

that Descartes' story about
the origin of color is rubbish.

And if you could show that
story is rubbish, then the

whole of Descartes' philosophy
falls to bits and bang,

which is the price Newton was
after, the whole of this bad religion

that Descartes and his allies
are peddling would be swept away.

And it all hung on a single
question, is white light pure,

and do Prisms make colors by
modifying it as Descartes claimed.

Newton tested this assertion by
carefully drilling a hole in the

screen and allowing just the red
part of the spectrum to pass through

Now this was the moment of truth.

If Descartes was right, then
a second prism would cause the

red light to be modified and
new colors would be produced;

if Newton was right, the red
light would remain the same.

That was Newton's crucial experiment.

Why is it crucial? Because it shows
that prisms don't change colors.

They analyze them. If the red
light coming from the original

spectrum is really primitive,
basic, elementary and simple,

it can't be analyzed any further when
it passes through the second prism.

So this simultaneously
suggested that white

light really is a mixture
of 7 different colors.

And that, here is a color, red, for
example, which is truly primitive.

My observations, though
paradoxical, are clear.

It is each separate color that is pure, and
it is the white light, that is the mixture.

Once side is that Newton has
assembled a kind of bank balance

of experiments, which he reckoned,
were completely convincing.

He behaved exactly as a 17 century

experimenter in England
was supposed to behave.

He put them together as a series of letters
and sent them from Cambridge to the royal

society, as a series
of recipes, which he

invited the experimental
community to repeat.

Newton had shown that all
of his contemporary' ideas

about light and colors
were just completely wrong.

He had rewritten the book of light.

In 1703, Isaac Newton became president
of the royal society of London.

Newton released his great
book: On light and color.

It was almost immediately
recognized as one of the

greatest works of modern
experimental philosophy.

The time has finally come, to put
the nature of light beyond question.

What had started as an
argument over the divine nature

of light had turned into
something far, far bigger.

Newton's dogged insistence that any
explanation of light had to be grounded

on strict experimental observation,
heralded the dawn of enlightenment.

And it is this enlightenment that result

ultimately spawned the
modern scientific world view

The old questions were
religious questions,

where do we come from, what are
we made of, what is our future.

But in the 17th century, with Isaac
Newton, something unprecedented happened.

A new way of finding out
creation was invented.

The experimental method, experiments
on light, deliver us to a modern

version of the world�� to our own way
of understanding how the world works.

Science had been created, and by its light,
the world would never looked the same again.

Next on light fantastic, how
we learn to manipulate light,

how for Galileo to Hershaw,
the simple tools of light,

overthrew the entire
model of the universe.