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 worldŁ¬ 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.