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00:00And God said let there be light, and there was light.
00:30God is light.
00:43God is light.
00:45In all cultures there's an intimate association between illumination and divinity, between
00:52light and creation.
01:03Light is colour.
01:06Light is energy.
01:09It fuels life and it feeds the spirit.
01:16It inspires art, religion and science.
01:25Light holds the secrets of the universe.
01:35For thousands of years humanity has tried to unlock the mysteries of light in its search
01:42for the nature of God himself.
01:47And there is no need.
01:55Woe unto them that call evil good, and good evil.
02:02That put darkness for light, and light for darkness.
02:10This is the story of that long quest to try and understand light, because it leads to
02:24an understanding of God.
02:26Extraordinarily, we'll see that enlightenment, that modern science itself emerges from this
02:34religious quest to understand the nature of light.
02:58The journey into the mysteries of light begins here, in Sicily, over 2,000 years ago.
03:05This luminous isle was home to some of the most renowned Greek philosophers.
03:11And it was they who first began to question the nature of light, and how we see.
03:21Light is surely fascinating for the Greek thinkers, because it offers a clue to the whole structure
03:29of the universe.
03:31It seems to fill all space, and it allows a kind of penetration of the world.
03:46The Greek exploration of light would lead to discoveries that would change the world.
03:56The Greeks lived in a world bathed in light.
04:00But in order to understand light, in order to bring it within the realm of reason, it was
04:05necessary in a way to abstract from the light that surrounded them.
04:10To choose appearances, to choose phenomena, where light was behaving in a special or strange
04:18way.
04:23So for example, why do distant objects appear so much smaller?
04:28Or why do objects completely change their position and shape when you put them underwater?
04:35By thinking about these specific questions, these particular puzzles, Greek philosophers made
04:40the most extraordinary advances in our understanding of light and of its relationship between the
04:47I, the mind, and the world beyond us.
04:54The first comprehensive theory of light and vision is attributed to a wealthy scholar who
05:09grew up in the shadow of Mount Etna, the giant smouldering volcano on the island of Sicily.
05:18His name was Empedocles.
05:36Empedocles was a Sicilian philosopher, physician and poet who lived 2,500 years ago.
05:45He believed himself to be divinely inspired to reveal the properties of light and of nature.
05:53Indeed according to one story, believe it or not, in order to prove that he was a god himself,
06:00he jumped into the crater of this great volcano on Sicily, Etna.
06:06I think we can guess that he ended up as a mere mortal.
06:14But his ideas about vision acquired their own immortality.
06:20Empedocles put forward the extraordinary idea that we see objects because light streams out of our eyes and touches them.
06:31And it makes an enormous amount of sense. The model is something like a lighthouse.
06:36I'm seeing things because something streams from my eyes towards them.
06:43And as my gaze touches them, they come into view.
06:51Now it may seem at first glance that this idea is crazy.
06:56But his idea that light streams from our eyes towards objects became the fundamental basis on which later Greek mathematicians and philosophers would construct some of the most important theories we have about light, vision and optics.
07:12What is the most important?
07:17Among them was the renowned mathematician Euclid.
07:21Euclid used Empedocles theory to make the single most important breakthrough in the understanding of light.
07:30Reason loves problems and above all, it loves showing you that there is a problem where you didn't think there was one.
07:48Here's an example that Euclid really focused on.
07:51Why do objects further away seem so small in comparison with objects nearer our eye?
08:00The 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 a finger held near our eye.
08:14Euclid came up with an elegant solution.
08:19The eye, the top of the finger and the top of the column must lie on the same line.
08:26And for that to be true, the rays from the eye must follow straight lines.
08:33It was a fundamental breakthrough.
08:35For the first time, light could be explained, predicted by the new discipline of mathematics.
08:44What this showed, and it was a dramatic discovery, was that the geometry of straight lines and triangles can completely master problems of light and vision out there in the world.
08:58And this mastery of light had far reaching consequences.
09:14It would help transform navigation into a rigorous skill based on the position of the sun and the stars.
09:25Greek navigators opened up new trade routes.
09:30And Greek culture and learning dominated the known world, as far east as India.
09:38But nothing lasts forever.
09:42In the wake of the great achievements of the Greek philosophers of light, the world entered a period of crisis.
10:08The Mediterranean world was wracked by war, invasion, destruction.
10:15Libraries were burnt, communities of scholars broken up.
10:26Much of the teaching of the ancient scholars was lost.
10:31But here, in Sicily, their work would suffer a much kinder fate.
10:40Conquered from North Africa, Sicily soon fell under Islamic rule.
10:46Most of what survived of the great Greek optical theories was transmitted to the West through the scholars of Islam,
11:08who arrived in the Mediterranean world at the end of the 7th century and then for hundreds of years edited, translated and debated what the classical Greek scholars had already established.
11:23For Islam, with its notion of the single God and the single creation, light played an absolutely fundamental role.
11:31It was the medium through which God made and communicated with his world.
11:43Indeed, the very idea that knowledge and spirituality is associated with light is essentially a Muslim doctrine.
11:52The brightness of faith put light, put optics right at the centre of Islamic scholarship.
12:11It's not surprising, it seems to me, that one of the founders of modern optical doctrine is a great Muslim scholar.
12:26His name was Ibn al-Haytham, or, as he became known in the West, Alhazen.
12:35Alhazen would make one of the most significant discoveries in history about how light and vision worked.
12:45But, bizarrely, his journey into the mysteries of light began with a tyrannical king and a troublesome river.
13:04There's a long history of clever men trying to get work at powerful courts and governments.
13:20And the career of Alhazen fits perfectly into this kind of story.
13:25He was born in Basra in the 10th century.
13:28Now, he earned his living by, each year, copying out all the works in geometry of the great Greek mathematician Euclid,
13:36and then selling those copies for cash.
13:38So his understanding of the behaviour of straight lines and motion was really second to none.
13:45Alhazen found employment at the court of the slightly eccentric and extremely powerful caliph in Cairo, Al-Hakim.
13:57Al-Hakim encouraged learning and technique because he wished to control everything in the world around him.
14:09Everything.
14:10He simply couldn't stand the idea that there were elements in the world that he couldn't order around.
14:18And the river Nile, the source of all of Egypt's wealth, was something that the caliph really wanted to master.
14:33The caliph ordered Alhazen to stop the Nile flooding. Failure would result in almost certain death.
14:42Now, Alhazen, of course, lacked the modern technology of tide control and flood control, which many European cities now have.
14:52He knew when he was beaten. So he dreamt up a cunning plan. He would pretend to be mad and in that way perhaps escape the caliph's wrath.
15:04The plan didn't exactly work. Alhazen was thrown into jail and stayed in confinement for more than ten years.
15:23Alhazen was thrown into jail and was thrown into jail and was thrown into jail.
15:37in the darkness, under police control.
15:40He began to meditate on what he could see
15:44and what he couldn't.
15:45He became obsessed with light and dark.
16:02Alhazan began to realize there was something wrong
16:05about the idea that we see
16:07because stuff comes out of our eyes
16:10and touches or grasps the objects in sight.
16:15Here's one obvious problem that occurred to him.
16:19Sitting in the darkness
16:21and then looking suddenly at the sun,
16:23his eyes really hurt.
16:25Staring at the sun was intensely painful
16:28after that time in the dark.
16:35It seemed improbable to Alhazan
16:41that if rays were indeed emitted by the eye,
16:44that they should cause him such pain.
16:51He began to piece together an entirely different explanation.
16:56Alhazan's big new idea was that we see because there are rays
17:13travelling through space in straight lines towards our eyes.
17:18He had overturned more than 1,000 years of accepted dogma.
17:29But if light is independent of the eye,
17:32how do objects redirect the light into our eyes when we see them?
17:37Alhazan realized there was a clue in the way mirrors work.
17:48Mirrors obviously reflect light.
17:52And by studying those patterns of reflection very closely,
17:56Alhazan was able to confirm the idea
17:59that the angle at which a ray hits the mirror
18:03is the same as the angle at which it's reflected.
18:08There's a symmetry there.
18:20It's as though a ball is striking a wall and then bouncing off.
18:24So there's a relationship between the idea of a light ray as a straight line
18:32and this fundamental understanding
18:34of the basic geometry of the law of reflection.
18:44Alhazan had the genius to realize
18:47that light bounces like a ball off all objects, not just mirrors.
18:54He'd worked out the precise mathematical laws
18:57of light's most important properties,
19:00reflection and refraction.
19:03Laws on which everything depends.
19:07From spectacles to space telescopes.
19:13Twelve years after locking Alhazan away,
19:17the caliph died.
19:20Alhazan was freed.
19:24He began obsessively refining his ideas.
19:33His seven-volume work became the fundamental text
19:37on light and vision.
19:39Insights which made the entire modern science of optics possible.
19:48Light was transformed, governed by mathematical rules and laws,
19:53light was leaving the abstract world
19:56and entering the real one.
20:14Within two centuries of Alhazan's death,
20:15militant Christianity mobilised against Islam in the Mediterranean.
20:27The Holy Catholic Church,
20:28determined to demonstrate its divine authority,
20:32seized on the work of the great Islamic scholars
20:34and used Alhazan's breakthroughs
20:35to further a Christian knowledge of light.
20:39Alhazan's breakthroughs to further a Christian knowledge of light.
20:43In the period between about 1,000 and 1,200 A.D.,
20:59the translation of these texts by scholars from Arabic into Latin,
21:02their transmission to the new schools and universities of Western Europe
21:07would produce something like a revolution of learning,
21:11a completely new approach to the study of nature.
21:16But the Christian Church's interest in light wasn't simply to improve its grasp of nature,
21:23rather to use it as an instrument to both control and inspire the light.
21:25to both control and inspire its flock.
21:34Mastering light became abstract,
21:35but the Christian Church's interest in light
21:37wasn't simply to improve its grasp of nature,
21:41rather to use it as an instrument to both control and inspire its flock.
21:47Mastering light became absolutely central to this project.
21:59For medieval Christianity,
22:01there was an extraordinarily strong relationship between light and divinity.
22:07Light was the first substance to appear in the world.
22:11God had said, let there be light.
22:16At the same time, light became a way of theatricalising,
22:22of dramatising the truths of the faith.
22:26In ways it's now almost impossible for us to imagine,
22:29the churches were bright with candlelight,
22:33with stained glass of the most extraordinary colours.
22:37A whole theatre of the faith,
22:41whose working in many ways depended on the mastery of the faith,
22:45light and colour.
22:51As the Christian scholars investigated colour and how to make it,
22:56what they found would become the central theme
22:59of one of the most vicious controversies in the history of the Church.
23:04The story begins with Roger Bacon, a 13th century Franciscan friar.
23:19Bacon, more or less for the first time in the West,
23:22really studied the work of Alhazen, the great Islamic authority on optics.
23:28Bacon learnt from Alhazen the structure of the eye,
23:32how light and vision happen, the way light bends,
23:36and began to study the effect of glass on light, on colours.
23:42By thinking hard about the new glass technologies of the 13th century,
23:57Bacon made the most extraordinary breakthrough.
24:00He began to see the ways in which curved glasses could change the figure,
24:10the shape and the size of objects that we looked at.
24:14Bacon wrote down accounts of newfangled spectacles,
24:27of bits of curved glass, which made distant objects appear very near,
24:33which made tiny objects vast, which could put coloured images into the sky.
24:39His excitement is palpable.
24:42The newfangled spectacles that would correct the problems of vision,
24:47Bacon was enchanted by these things.
24:52A new universe of light, of glass, of colour opened before him.
24:58Bacon didn't just observe and think in some vague way about how light behaved in the world at large.
25:12He brought it into the workshop and experimented on isolated aspects of light's behaviour.
25:20He watched how it distorted through water and glass.
25:26And he noticed how in the sunlight, droplets of water seemed to produce the same colours as the ones he saw in rainbows.
25:40Bacon seems to have become obsessed by the rainbow.
25:43But it was an obsession that was bordering on heresy.
25:55Towards the end of the book of Genesis, Christians learnt that after the great flood,
26:01which had destroyed all but a few select faithful,
26:06God had put into the heaven a mark of his covenant,
26:11that he would never again visit destruction upon them.
26:16The rainbow stood for that extraordinary relationship between the believers and their God.
26:23Yet Bacon was driven to explain the rainbow using logic and reason.
26:33Its colours were a puzzle, a challenge to his wit.
26:38And he could make them experimentally here on earth.
26:48He would amaze his audiences by swallowing a mouthful of water,
26:52and then spitting it out in an arc through a beam of sunlight.
26:56He was reproducing colours which you could see in heaven, here on earth, experimentally.
27:04It dawned on Roger Bacon that God's miraculous rainbow must obey rules
27:11similar to the mathematical laws of reflection Al-Hazen had discovered.
27:16There was the danger.
27:20Bacon was transgressing all sorts of boundaries,
27:25the relationship between what was natural and what was divine.
27:28And above all, he made no secret of the fact that he, Roger Bacon,
27:34was the unique individual who could really see the truth of things.
27:38If there was one thing more impressive, more striking,
27:42than Bacon's extraordinary ability to understand the phenomena of nature,
27:47it was Bacon's ability to make enemies.
27:50He was explaining a miracle through natural causes.
27:56For Bacon, it was religious suicide.
28:13For denying the possibility of miracles,
28:15and declaring that everything that happens is the result of natural law,
28:21you shall be taken from this place to a place of confinement.
28:39Bacon was arrested and put into close confinement in Paris.
28:44He spent more than two decades there, locked up in his cell,
28:49studying and writing.
28:51But damned.
28:53Because he dared to speak out.
28:56He dared to try and explain the wonders of creation
29:01using natural principles alone.
29:04Roger Bacon died less than two years after his release.
29:13But despite the church's best efforts to suppress his work,
29:17his legacy lived on.
29:19Not only had he described how rainbows are the result of refraction
29:25and reflection in individual droplets of water,
29:29he'd also explored the use of glass lenses
29:33as a way of improving vision.
29:36In time, Bacon would be remembered as Doctor Mirabilis,
29:41the wonderful teacher.
29:46But it would be religious scholars like Bacon
29:48that would plunge the church into a crisis of its own making.
29:53Chaos, madness, disorder.
30:00These have always been the enemy of those in power.
30:06Getting the time right, imposing rule and system on everyday life.
30:15For the Catholic Church, control over the calendar, the rituals of the year,
30:19was the most important outward and visible sign of its control, of its legitimacy, of its inspiration from God.
30:32And 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.
31:01The Catholic Church was in crisis.
31:18Millions of believers were defecting, protesting against the Pope's authority.
31:24And at stake in this violent struggle was the timing of Easter.
31:29It's the movement of light that dominates our sense of time.
31:36And it seems to me that the principle way in which religions exert their authority over our lives
31:42is precisely through their control of time and their control of light.
31:48For the Christian Church, the calendar of the year was set around the most important of Christian festivals, Easter.
31:57Easter 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 God and his miraculous resurrection into light.
32:12This was the basis of faith.
32:19Now, Easter's date had been set by the church as happening on the first Sunday after the first full moon of the spring.
32:34Not being able to predict when Easter fell brought chaos to the Catholic Church.
32:44Without a precise system for calculating future spring equinoxes, Easter was celebrated weeks late.
32:53This inability to say exactly when Easter fell was becoming visible evidence of the church's weakness.
33:08What was required was an accurate way of calculating when spring started.
33:16And from the 1500s on, great churches were turned into time and light machines.
33:29Here's how you can turn a church into a solar clock.
33:33The idea is that you drill a hole high in the wall of the church.
33:37You see how the hole is surrounded by an image of the sun and the crown of the Pope himself.
33:46That hole will let through sunlight when the sun is passing overhead at noon.
34:04The 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.
34:16Here's the clever bit.
34:17Here's the clever bit.
34:19Now, at noon in winter, the sun is still pretty low.
34:23So the image of the sun will fall far to the northern end of the rod.
34:29And during the course of the year, that spot will move inexorably towards us, towards the south until we get to high summer, and then back again through the autumn, back towards the northern end of our line.
34:48The area that the astronomers and priests cared about the most is here.
35:01This defines where the sun is on the day of the spring equinox.
35:07That moment when the length of daylight and the length of the night are identical.
35:14Because it was on this position that the calculation of Easter relied.
35:19This position defines the moment of equinox, the limit of Easter, Terminus Pascae.
35:28By carefully noting where the spring equinox fell year after year, the observers saw patterns beginning to emerge.
35:45And from these patterns, they could extrapolate with incredible accuracy when future equinoxes would occur for centuries ahead.
36:00For the church, order and its own authority appeared to be restored.
36:06But not for long.
36:12A tension begins to emerge.
36:15On the one hand, the great churches are clearly instruments of astronomical learning.
36:22The great wealth of the church is being spent on patronising and supporting research into light, the sun, the planets and astronomical time.
36:34And this is at exactly the same moment as the new theories in astronomy, that the earth is not the centre of the world, that the sun does not move round the earth, are being developed by those who, from the church's point of view, would call Mother Church into question and threaten its scriptural and divine authority.
37:01As the war raged over the very nature of the universe, two men would emerge, wielding light and colour as the weapons with which they'd settle the matter once and for all.
37:16On the Catholic side was René Descartes.
37:22And against him, Isaac Newton.
37:30The church needed to show that what it said was true, the set of undeniable rules with which no one could argue.
37:39The church needed an intellect who was also a defender of the faith.
37:55And they found one in the unlikely form of a coffee house philosopher.
38:00René Descartes was the second son of a wealthy landed family from central France.
38:10He thought that all there is in the world is just machinery, including our own bodies.
38:17He thought that food was just a kind of fuel for these bodies.
38:20Descartes believed that this idea would be the perfect theory for the church.
38:29God, he said, was the ultimate clockmaker.
38:34Descartes likened the universe to a giant machine created and set in motion by God and obeying a set of predictable rules.
38:47And where this really counted was in his understanding of light.
38:54Light, he thought, could be completely understood through mechanics.
39:00Descartes' starting point to proving his mechanical system was to focus his attention on what he believed to be the ultimate optical instrument, the eye.
39:11In Descartes' world, everything was a machine. Animals and humans too.
39:26As far as Descartes was concerned, the only difference between beasts and humans was that humans have souls and animals just don't.
39:33If animals are machines, then the way to find out how the cogwheels that make them tick actually work is to start cutting them open.
39:44To make the flesh and blood speak. And that's exactly what he did to eyes.
39:49If he could show that the eye was a machine, then, he argued, that would be proof enough on which to stand his entire theory.
40:02Well, we have here a cow's eyeball and I'll just trim off the spare tissue around it.
40:13This is exactly what Descartes would have had to do.
40:17He said he scraped it off. I'll use a pair of scissors.
40:21So, I'm going to make a few incisions in the eye so that I can get at the lens.
40:32So, I'm just cutting the lens clear of the tissue close to the iris.
40:40There's the lens you can see coming away now. I'll move it into that pot.
40:45Well, I've got a picture of Descartes himself here.
40:53So, let's try and have a look at our picture of Descartes.
40:58Seeing what I can see through the lens itself.
41:04It was the first real demonstration that the eye produced an inverted image on the retina.
41:09Up until then, there were various theories for how the retina detected the image.
41:14But we now know, of course, from Descartes' work, that it is an inverted image.
41:19Of course, we don't see it inverted because the nervous system corrects it for us with the wiring into the brain.
41:25So that we actually get the world up the right way.
41:34Descartes' experiment with the ox's eye was a real breakthrough.
41:37He'd shown how the shape of the lens at the front of the eye would change depending on how far away objects were.
41:46That made the eye an ideal mechanical system and that's really what Descartes cared about.
41:56The lens in the eye acted exactly like a glass lens.
42:01Descartes had his evidence that the eye was indeed a machine.
42:05With this proof, Descartes could answer the most complex questions of the day.
42:15He could even explain the mystery of colour.
42:21In Descartes' mechanical universe, light was spinning particles and colour appeared when white light particles spun faster or slower.
42:32So the key to Descartes' theory was that white light was pure and colours merely a temporary distortion of white light.
42:42A 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.
43:04But theirs was a victory that was short-lived.
43:07Across the water in Protestant England, anger was building over the arrogant declarations by Descartes and the Roman Church that they owned the knowledge of the world.
43:23Standing against Descartes and his views were men like Isaac Newton.
43:33Newton saw Descartes as alien, French, Catholic, rationalist and authoritarian.
43:39And above all, Descartes was wrong about light.
43:47Isaac Newton would wrench light from the Catholic Church's grip.
43:53But by his own admission, his obsession with light would drive him to the brink of madness.
44:05In hunting for a shadow, I sacrificed my peace of mind, a matter of real substance.
44:17Isaac Newton came here to Cambridge as a young student in the early 1660s.
44:42It was here that all his genuinely creative science, philosophy and religious ideas were formed.
44:55Light meant everything to Isaac Newton.
45:00He thought of it as an almost divine principle.
45:03He thought that the world had been made by a single, wise, omnipotent, clever, mathematical God.
45:13A God who, to be frank, rather resembled Isaac Newton.
45:16There is a being who made all things, who has all things in his power, and who is therefore to be feared.
45:33And so, in investigating light and colour, what Newton thought he was doing was peering deep into the mysteries of God's creation.
45:48And it was in 1664, aged just 21, that Newton first began to study light and vision.
46:08Newton's reputation, then as now, was as an intensely solitary man.
46:14A few friends, violent enmities, and obsessive energy.
46:30Newton's first thoughts about light and colour were prompted by an extraordinary degree of self-examination.
46:36It's as though he turned his attention inwards, into his own mind.
46:46He would stare at the sun for hours, and then shut himself in a dark room, and by will alone, he'd try to summon up the image of the sun.
46:57And then his self-experiments got much more dramatic.
47:10He wanted to see if there was a difference between the images we see because of pressure, because of something pushing on our eye, and the images we see when we simply think or dream.
47:33So what he did was to take a wooden needle, and put it between his eyeball and the bone, and push.
47:47Don't try this at home.
47:51If you do this, Newton found, that you get coloured circles appearing just above the focus of your eye.
48:01And the coloured circles followed the order of the colours of the rainbow.
48:05Newton was so focused, so concentrated on the most minute details of phenomena like that, even at the risk of his own eyesight,
48:19that he was driven to see if there was a way of making the optical phenomena that appear inside our own eyes, in our own minds,
48:27appear in the outside world, so that others could see them.
48:31With prisms and lenses and mirrors, Newton reckoned you could do just that.
48:41Newton had one aim.
48:44To show the world that Descartes' mechanical theories about light and colour were utter nonsense.
48:51Now, a certain gentleman has suggested that colours are mechanical,
49:03and that it is the prism that changes the white light into colours.
49:09But this theory is not only insufficient, but unintelligible.
49:14Newton would design a series of experiments on whose replicability the whole status of his new theory of light depended.
49:31Newton made a very tiny hole in the window shutters, allowing a beam of sunlight to fall on the opposite wall.
49:42And then he intercepted the sunbeam with a prism.
49:47He positioned the prism very, very carefully, so that the angle at which the sunlight hit the prism was the same as the angle at which it left.
50:01Finally, after weeks of effort, he made a breakthrough.
50:10What Newton had done was to make an artificial rainbow.
50:16He saw red, orange, yellow, green, blue, indigo and violet.
50:23And he invented a word for the sun's image, coloured as it was.
50:31This word was spectrum.
50:38For the first time, Newton had precisely measured the colours in a ray of sunlight.
50:45Centuries later, knowledge of the spectrum would extend to X-rays and radio waves, ultraviolet and infrared.
50:58It would even reveal what the stars themselves are made of.
51:05Yet, for Newton, this was only the starting point.
51:15The spectrum was the key weapon in his holy war over the true nature of divine light.
51:23What I proposed was not to explain the properties of light by hypotheses, as so many before me have done, but to prove them by reason of experiments.
51:42The most important of Newton's experiments was what came to be called the crucial experiment, experimentum crucis.
51:55Newton reckoned he'd found an absolute demonstration that shows that Descartes' story about the origin of colour is rubbish.
52:05And if you could show that story as rubbish, then the whole of Descartes' philosophy falls to bits.
52:12And then, which is the prize Newton was after, the whole of this bad religion that Descartes and his allies are peddling would be swept away.
52:27And it all hung on the single question.
52:29Is white light pure, and do prisms make colours by modifying it, as Descartes claimed?
52:42Newton tested this assertion by carefully drilling a hole in a screen
52:48and allowing just the red part of the spectrum to pass through.
52:53Now this was the moment of truth.
53:05If Descartes was right, then a second prism would cause the red light to be modified
53:13and new colours would be produced.
53:17If Newton was right, the red light would remain the same.
53:21The same.
53:39That was Newton's crucial experiment.
53:42Why is it crucial?
53:44Because it shows that prisms don't change colours.
53:48They analyse them.
53:51If the red light coming from the original spectrum is really primitive, basic, elementary and simple,
53:59it can't be analysed any further when it passes through the second prism.
54:06So this simultaneously suggested that white light really is a mixture of several different colours,
54:12and that here's a colour, red for example, which is truly primitive.
54:21My observations, though paradoxical, are clear.
54:25It is each separate colour that is pure, and it is the white light that is the mixture.
54:37Once Isaac Newton had assembled a kind of bank balance of experiments which he reckoned were completely convincing.
54:47He behaved exactly as a 17th century experimenter in England was supposed to behave.
54:54He 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.
55:05Newton had shown that all of his contemporaries' ideas about light and colours were just completely wrong.
55:18He had rewritten the Book of Light.
55:23In 1703, Isaac Newton became president of the Royal Society of London.
55:29Newton released his great book on light and colour.
55:36It was almost immediately recognised as one of the greatest works of modern experimental philosophy.
55:49The time has finally come to put the nature of light beyond question.
55:56What had started as an argument over the divine nature of light had turned into something far, far bigger.
56:14Newton's dogged insistence that any exploration of light had to be grounded in strict experimental observation
56:23heralded the dawn of enlightenment.
56:36And it is this enlightenment that has ultimately spawned the modern scientific world view.
56:44The old questions were religious questions.
57:03Where do we come from? What are we made of? What is our future?
57:07But in the 17th century, with Isaac Newton, something unprecedented happened.
57:22A new way of finding out creation was invented.
57:26The experimental method, experiments on light deliver us to a modern vision of the world.
57:37To our own way of understanding how the world works.
57:41Science had been created.
57:53And by its light, the world would never look the same again.
57:58Next on Light Fantastic, how we learnt to manipulate light.
58:13How, from Galileo to Herschel, the simple tools of light overthrew the entire model of the universe.
58:21Stay with us tonight for the antics of a series of out of control emperors who brought the Roman Empire to its knees.
58:34Its decline and fall, in the words of historian Edward Gibbon, next.
58:37HELL, CESAR!
58:53HELL, CESAR!
58:55HELL, CESAR!
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