- hace 4 meses
Categoría
📺
TVTranscripción
00:00All human cultures build up a lot of the stories they tell each other,
00:14their rituals, their religions and their science, by thinking about light.
00:25Men of God declared light divine.
00:30Scientists bent it through glass to see to the depths of space and the minute interiors of cells.
00:41It seemed, by understanding the truth about light, we would understand the truth about everything.
00:50But it turned out, and this is surely one of the great paradoxes of the light stories
00:58that we've been telling.
00:59It turned out that the more people could manipulate light, the more puzzling and tricky light turned
01:08out to be.
01:09And in the very same idea that light and truth go together, it turns out that a great deal
01:18of what light gives us is an illusion.
01:25In 1664, the great natural philosopher Isaac Newton performed his ground-breaking experiment,
01:41showing that a prism can split white light into coloured rays.
01:56But above all, what Newton did with his prism was to set up a great challenge for future generations.
02:08He'd shown white light as a mixture of colours.
02:11But beyond that, he admitted to being completely mystified.
02:19colour was light's last mystery.
02:33Understanding colour would be the key that would unlock the truth about light.
02:38And as it did, it would change everything.
02:41Science, art, and even our understanding of the human mind.
03:00The first step in this story, into the heart of light, needed one of the greatest upheavals
03:05in history.
03:10The Industrial Revolution began in the late 18th century textile mills of North West England.
03:24People were forced to think about light, and particularly colour, in a new and urgent way.
03:31Controlling colour counted because the British market was being flooded by brightly coloured cloths
03:41from India, from Asia.
03:43British industrialists countered this flood with their own cloths and their own industrially manufactured dyes.
03:53Standardising those colours, getting chemical control over how they were made,
03:59and then making sure they mixed tightly with the dyed cloth was the key to market success.
04:10Perhaps the most dramatic impact of the new colour industries was the way it changed folks' sense of what was natural,
04:20what was artificial.
04:22Colours which had previously been understood as matching natural objects,
04:27the blue of the sky, the green of grass, the red of the rose, could be made completely artificially.
04:37Artificial dyes revealed that many people didn't see a coloured cloth the same way as others did.
04:49For the first time, people realised there was a mystery about the way we see colour.
04:56It's inevitable that the puzzle of getting colour judgements systematically wrong appears precisely at the place and the time of mass colour industrialisation.
05:14The man who matters was John Dalton.
05:23John Dalton, the gifted son of an impoverished weaver, threw himself into the new chemistry of the Industrial Revolution.
05:32He's best known now for proposing the atomic theory of matter, but his first scientific paper was based on his realisation that there was something awry with his own colour perception.
05:46Dalton, who was a Quaker showed several signs of getting colour wrong or judging it badly.
05:53When he went to Quaker meetings, he would sometimes turn up dressed in the most inappropriately bright colours, in a red gown.
06:03Not the sort of thing that a dour, solid Quaker citizen should be wearing.
06:11For the first time in history, Dalton started to systematically analyse his own sense of colour.
06:19He went back to nature and to his childhood fascination with botany.
06:24The bright pink flowers of clover seemed bright blue to him.
06:34The pink geranium, the pelargonium, seemed absolutely blue when he collected it outside.
06:43And then when he brought it into the house and looked at it by candlelight, it changed, strangely, from being blue to being yellow.
06:52Dalton meditated on this problem. Was it special to him?
06:58Dalton, who worked as a school teacher, asked his pupils whether they had the same problem.
07:05And it turned out that in a class of about two dozen, four or five boys suffered from exactly the same puzzle.
07:13Dalton was the first person to identify and scientifically study colour blindness.
07:28Dalton himself thought it was caused by a physical property of the eye.
07:34And he came up with a gruesome way of testing this idea.
07:37In Dalton's will, he instructed his medical adviser, Ransom, to take out one of his eyes and dissect it.
07:52Because Dalton guessed that the reason for his colour blindness was that there was a blue liquid inside his eye.
08:00Ransom followed Dalton's will to the letter.
08:05He extracted one of the great man's eyeballs and cut it open.
08:11There was no blue liquid.
08:14Ransom instead describes the eyeball as pellucid.
08:19It let the light through perfectly.
08:21It showed no staining, no colour.
08:25There was no blue liquid inside.
08:28That couldn't be the explanation of Dalton's own colour blindness.
08:33Instead, and this was what was really suggestive,
08:37the problem must be to do with some kind of judgement.
08:42Something more psychological.
08:44Something between the brain and the back of the eye.
08:47Dalton may have got the cause of colour blindness wrong.
08:54But he proved that the condition ran in families.
08:58And that it came in just a few common forms.
09:08He published these revolutionary findings in the new industrial age's greatest city.
09:13Dalton's great lecture of October 1794 at the Manchester Literary and Philosophical Society set the stage for nothing less than a revolution in the science of light and colour.
09:30The commercial imperatives of the industrial revolution would lead to the discovery that the mind has a role to play in how we see colour.
09:45The booming factories and towns of 18th century Europe urgently needed brighter and more efficient lamps and lanterns.
09:54Designing them would revolutionise our understanding of the true nature of light.
10:09Now put the lens in.
10:11Out.
10:12The key figure in this story was an American émigré living in Europe called Benjamin Thompson.
10:19Thompson did one of the most intriguing experiments ever on the behaviour of light.
10:25But it started because he was trying to save money for his employers, the city of Munich.
10:30The Munich government gave him a really important job, which was to clean every single beggar off the Munich streets and put them in a newly designed workhouse, which Benjamin Thompson constructed.
10:50As a reward, Thompson became a count, Count Rumford.
10:57Now one of the things his workhouse was going to need was lighting.
11:03And so Rumford decided to do a series of extraordinarily precise experiments to work out what the cheapest kind of lighting could possibly be.
11:15One set of experiments that he was really keen on doing was seeing if it was possible to compare, say, the brightness of a candle with the brightness of sunlight.
11:28Now obviously he'd need to stop down the sunlight that was coming into his lab.
11:33So what he did was to use a series of coloured filters in order to bring the light down.
11:38But as he put coloured filters in front of sunlight or lamps, he noticed something absolutely extraordinary.
11:50So look at the shadow through this red filter and you see that the shadow is now a rather beautiful turquoise.
12:00And the shadow cast by this lamp, which was black, has gone red.
12:09Well, we might be able to see why the shadow on the left has gone red, because we've put a red filter in front of the light that's illuminating that shadow.
12:20But what is going on with the other colour? That was Rumford's big problem.
12:27At this point, Rumford tried to eliminate from his field of view everything except the turquoise shadow.
12:34He decided to look at the turquoise shadow through a tube painted black on the inside.
12:47And this was even spookier.
12:51To Rumford's utter amazement, when he used his tube so the only thing in his field of view was the blue shadow, its blueness disappeared.
13:01I was not able even to tell when the coloured glass was before the lamp and when it was not.
13:10And though the assistant often exclaimed at the striking brilliancy of the shadow's colour, I could not discern in it the least appearance of any colour at all.
13:21He couldn't see any colour change, whatever the assistant was doing. He saw a uniform shadow. That was really hard to understand.
13:34Two people see the same thing differently. There could only be one explanation.
13:41The colour exhibited by one of the shadows only is real. That of the other is imaginary, being an optical deception occasioned in some way unknown to us.
13:56These colours that we see are actually the work of our own brains. They're not simply out there in the world.
14:06I'm back again again. Away.
14:09Rumford had shown, for reasons he didn't understand, that the human mind can add its own colours into the dull, colourless grey of a shadow.
14:19Rumford himself hoped that the effect of this discovery on the future of art and painting would be revolutionary, and so it was.
14:35Contemporary painters, like Joseph Turner, realised that coloured shadows would make their paintings more authentic, more psychologically real.
14:45This is the fighting Temeraire. The shadowed side of the tugboat, instead of being grey, is tinged with violet, to bring out the melancholy mood of the sunset.
15:00The shadows in Claude Monet's paintings of Rouen Cathedral are alive with colour, yellow to evoke the haze of the midday sun, purple for the dying light of twilight.
15:19Rumford reckoned that the implications of the fact that colours are partly made up by the mind would then go far beyond painting.
15:28Rumford kind of had a dream.
15:32Rumford kind of had a dream.
15:35If colours are subjective, then you ought to be able to use them to entertain people, to seduce people in fact.
15:44The idea was that you could key the keyboard of a harpsichord to coloured lights, and when you played a note, a colour would appear.
15:57Rumford called this device an optical harpsichord. He never actually built one. It was too difficult with 18th century technology.
16:14It took 200 years for Rumford's dream of light and music to come true.
16:21But back in the late 1700s, people were observing more and more aspects of light and colour which they had no way of explaining.
16:26But back in the late 1700s, people were observing more and more aspects of light and colour which they had no way of explaining.
16:38What had caused John Dalton's colour blindness? What was causing Rumford's coloured shadows? What was needed was a breakthrough in the understanding of what light is.
16:53And that breakthrough came in the early 1800s, but not from someone who was investigating light, but from someone investigating light.
17:12sound.
17:34The hero of this story was a wealthy and precocious Cambridge medical student called Thomas Young.
17:48Now as a member of a college, and a wealthy one at that, Thomas Young liked horse riding, he liked music, and he liked placing bets.
17:56And there's a bet recorded in the gambling book at the college, that Thomas Young, as a student, bet.
18:03That before he graduated, he would write the best essay ever on sound.
18:11He thought he did, no one else did, and he lost the bet.
18:15But that essay argued, that if you listen hard to organ pipes, you're unlocking the mystery of the way sound travels.
18:25An amazing truth about light would be hidden in Young's essay about sound.
18:32His initial interest was to investigate a fact that people had known since antiquity.
18:38Sound travels in waves.
18:44For instance, columns of air in organ pipes vibrate up and down, rather like ripples of water going back and forth in a lake.
18:53Young studied the unusual and distinctive ways in which sound waves behave, particularly when they overlap.
19:05Imagine that you play a single note on the organ.
19:11And it sounds pure.
19:14Now if you add another note, which is out of tune.
19:19You begin to hear beats, which are related to the difference in frequency between the two notes.
19:35When two waves meet, they can either add or subtract.
19:40You get pulses of addition and difference.
19:49Young now made a dramatic leap of imagination.
19:52He realized that light must work in the same way that sound does.
19:58That light must work in the same way.
19:59If you shine a beam of light through a card with two slits in it, as the two light beams emerging from the slits, recombine, you see a pattern of bright and dark bands.
20:17The two beams of light cancel each other out in places, just as the two sound waves do.
20:30That could only mean one thing. Light, like sound, was a wave.
20:41Today, everything from fibre optics to spectacle design is based on the idea that light is a wave.
20:52But at the time, it was an incredible idea. From Newton on, the existing notion of light was that it was a stream of tiny corpuscles or particles.
21:02Young's radical idea was greeted with howls of derision.
21:13Young's lectures on his new theory that light travelled in waves were very controversial.
21:20It was going right against 150 years of models of light as a particle.
21:28Young hit back, and the example that came to mind was a pond.
21:36Think of waves travelling on the surface of a pond, and you could see the way light moved.
21:42Young's lectures, with their watery model of light, were a powerful argument for a new wave theory,
21:51which would explain how we see and how light travels.
22:04The idea that light was a wave is now heralded as one of the great discoveries of science.
22:11It meant colour was at last comprehensible.
22:17Just as different frequencies of sound give you different notes,
22:22different frequencies of light give you different colours.
22:26Now, in essence, the idea was really simple.
22:32And it was illustrated during the 19th century by pretty simple machines like this.
22:44Now, imagine that this is a wave of light.
22:48What Young asked is, what happens when light waves of this kind enter our eyes?
22:56It seemed obvious to him that what the retina is doing is vibrating.
23:04It's not some kind of passive scream that gets hit by particles.
23:08It's a vibrating membrane.
23:11And the faster it vibrates, explains the difference in colours.
23:16So that blue-making rays are vibrating really fast, red rays much more slowly.
23:25And Young even guessed something really important about the way we sense colour.
23:36If light's a wave, and colours are different frequencies of that wave,
23:42then maybe in the very back of the eye we have different kinds of senses,
23:47which pick up different kinds of vibrations.
23:52Young experimented with spinning colour wheels,
23:55and he saw that if spun fast enough,
23:58just three colours, red, green and blue,
24:02can combine to appear as white.
24:06What Thomas Young concluded from this
24:09is that the vast panoply of colours humans think they see
24:14come from combining our responses to just three frequencies of light,
24:20red, green and blue.
24:26Now that model's right.
24:28This would begin to explain the kinds of colour blindness
24:33that his friend John Dalton was exhibiting.
24:36Because if one set of receptors wasn't working properly,
24:40you wouldn't pick up that kind of colour.
24:43That was Young's idea.
24:45Dalton, the man who'd begun the study of colour perception,
24:50provided bizarre posthumous confirmation of Young's idea.
24:55In 1995, 150 years after his death,
25:00doctors extracted DNA from Dalton's eyeball,
25:04which, amazingly, had been preserved by a Manchester Scientific Society.
25:09Dalton's DNA showed that he was blind to red and green.
25:19Back in the 19th century,
25:21understanding the mystery of how we see colour
25:24couldn't have come at a better time.
25:26Colour perception was now a matter of life and death.
25:30In 1875, in Sweden, near the town of Holland,
25:48In 1875, in Sweden, near the town of Lagerlunda, a train missed a red signal and hurtled towards
26:05another in the middle of the night. Nine people died. Hundreds were injured.
26:10The local professor, a guy called Holmgren, guessed that one of the guys on the northbound
26:20train was probably colourblind and had mistaken a red light for green and sent the train hurtling
26:28to its destruction. In Britain, where there were more railway lines than anywhere else,
26:39the government lurched into action. Experts from the scientific establishment were hired
26:47to do tests on whether there were good ways of spotting the colourblind amongst drivers and pilots.
27:01The leader of the inquiry was Lord Rayleigh, a very well-connected and very wealthy gentleman.
27:08Rayleigh was an expert on light and sound, and he'd already studied the rather bizarre fact that a lot
27:16of his brothers-in-law, including the eminent Tory politician Arthur Balfour, seemed to suffer from
27:23a strange form of colourblindness in which they were over-sensitive to red lights, not, you would have
27:30thought, a normal problem among Tories. But what Rayleigh then did was to introduce a system of
27:36absolutely rigorous colour testing on the working class.
27:40Building on Young's three colour theory, Rayleigh devised the first ever colourblindness tests for every train driver and boat pilot in the country, and by the early 1900s, the modern colour perception tests, which most people now take,
27:48were developed.
28:08In fact, back in Victorian times, the human ability to discriminate between subtle differences
28:14in colour was at the heart of massive controversy.
28:21It was widely accepted that all people, not just the colour blind, see colour slightly differently.
28:29And some Victorian scientists believed that if they could accurately measure this variation, they would prove categorically the most repugnant of all European ideas, white supremacy.
28:45Colour perception played an absolutely crucial role in European ideas about human nature itself.
28:54The coming fashion for racist explanations of the difference between human groups cashed out its ideas in the area of differential sensitivity to colours.
29:11This is how it worked. It was believed that animals had faster, better attuned senses than humans.
29:21And at the time, it was also believed that black people were lower down the evolutionary scale, so more like animals.
29:30And to prove that fact, all you had to show was that their responses to light and colour were better.
29:38In 1898, a group of Cambridge-based scientists and medics went from England to the Torres Straits, the islands between Australia and New Guinea.
29:52One of the most important members of the expedition was a man named William Rivers.
29:58Rivers was an extraordinary figure. He was a brilliant physiologist and medic.
30:04He'd written the definitive account of optics and vision and colour perception.
30:10What Rivers was going to do was to set up a psychology lab on the beach.
30:15This is one of the actual bits of equipment Rivers took to the Torres Straits to assess natives' colour perception.
30:25It's called a tintometer and it was designed to test human sensitivity to subtle changes in colour.
30:33What Rivers was going to do was to test how Torres Strait Islanders matched colours.
30:42So, for example, he might take a particular red and drop it in to this tube and then invite the islanders to select a glass colour which corresponded to that.
30:58Like that. And then the islander would look down the tube and agree that these two colours are the same or that this one should be slightly darker or slightly lighter.
31:11What this allowed Rivers to do then was to construct numerical colour scales for Islanders colour perception and test whether Islanders or others could make finer colour discriminations.
31:28Day after day, Bemused Islanders queued up to look at tinted slides, spinning discs and have their reaction times measured.
31:53But Rivers was in for a big surprise. What he found, by and large, the range of discrimination of colours that he found amongst the islanders was not that different from the range of discrimination of colours amongst the English.
32:12In other words, the English differed from each other as much in their colour discrimination as they did on average from any Torres Strait Islander.
32:23The psychic unity of humankind. Most people see things in roughly the same way.
32:34To Rivers' eternal credit, when he found that this evidence contradicted his original hypothesis, he simply ditched it.
32:46On his return to England, Rivers spearheaded a movement that argued that there was no scientific evidence for the superiority of European culture over any other.
33:03Well, for many of us, I think Rivers is an extraordinary hero. He understood extremely well that European culture, Cambridge culture, could be studied in exactly the way that other cultures were studied by European scientists.
33:25He has a wonderful story about what it would be like if an islander from the Pacific came to Cambridge and began to study the Cambridge natives.
33:36Surely, Rivers pointed out, this islander would naturally assume that the natives of Cambridge had some kind of primitive or sentimental or superstitious mentality which completely explained their bizarre rituals and strange behaviour.
33:53Studying the human response to light created two new sciences, psychology and anthropology.
34:07But light itself remained enigmatic. Thomas Young's idea of light waves was accepted. But what were these waves made of? The answer would come from studying an aspect of light that is not at first obvious. The fact that light doesn't just show us the world, it changes it.
34:28As anyone who's had a rather bad sunburn will tell you, light doesn't leave the bodies it touches unaffected. On the contrary, light is a powerful chemical, physiological and biological agent which can have the most huge effects on anything with which it interacts.
34:52The story of this discovery of the most miraculous of light's properties begins in the late 1700s in industrial England with one of the greatest English chemists, Joseph Priestley.
35:13Joseph Priestley, a Yorkshireman of impeccable intellectual credentials, tough-minded, radical, materialist and ambitious, was one of the leading natural philosophers of late 18th century Britain.
35:34And for Priestley and his closest friends, light and life went together.
35:41In this experiment, Priestley put a mouse into a sealed bell jar to test what happened to the air as the mouse breathed in and out.
35:54Fairly quickly, the mouse sickened, got exhausted and died.
36:01This air, he reckoned, must be really bad, really bad not just for living animals but for plants as well.
36:12So into the jar, Priestley introduced a set of growing plants and he left them there for several weeks.
36:22To his amazement, they grew happily.
36:26Whatever was in the air that killed the mouse seemed to make plants flourish.
36:39Priestley decided to test what it was in the air where the mouse had died that was responsible for encouraging the life of plants.
36:52He would simply introduce another mouse.
36:56The result was absolutely amazing.
36:59He found, provided that a plant was growing there, that the animal would suddenly revive.
37:06This was what he called a luxury air, which only a couple of mice and myself have had the privilege of breathing.
37:17And there was more.
37:19What Priestley found was that the quality of the air wasn't just improved by growing the plant in it.
37:26If you shone a light on the plant, the air quality went shooting up.
37:33What it showed was that light shining on the green matter in plants could restore the air to an almost paradisiac quality,
37:45where it would keep animals alive for unparalleled periods of time, where flames would burn with extraordinary life.
37:54Light and life went together.
38:00We now know Priestley's discovery as photosynthesis, the remarkable way plants absorb the energy from light,
38:08and in the process, convert carbon dioxide into oxygen.
38:13Light doesn't just show us the world.
38:16It's a form of energy that's essential for all life.
38:26The discovery that light was energy, and could effect powerful chemical changes, would have surprising results.
38:33It would open up a world that no one had ever seen before.
38:38The story begins with Tom Wedgwood, son of the famous potter Josiah.
38:54Tom Wedgwood's experiments would kick-start one of the most revolutionary technologies of all time, photography.
39:04It began with Tom trying to help out the family business.
39:08Wedgwood pots were famous for their hand-drawn decorations,
39:13and Tom wanted to find a way of decorating pots automatically.
39:22So what Wedgwood did was to prepare a special chemical mixture made up of silver nitrate and common salt.
39:32Others had noticed that silver nitrate goes black when light shines on it.
39:37But Wedgwood experimented with ways of using this to draw patterns, what he called sun prints.
39:45What I'm going to do is to make a sun print by wrapping my silver nitrate with this foil, and then exposing it suddenly to a very bright light.
40:01What we get are these blackened images where the silver nitrate has been hit by the light.
40:17Deluged as we are by fantastic photographic images, these grey splodges look rather unimpressive.
40:25But in 1770, they gave a glimpse of a wonderful future.
40:32Wedgwood and his collaborators were absolutely fascinated by this process of sun printing.
40:38Because what it meant was that there might be a way of preserving forever the information that light carries to the eye.
40:48The dream of enlightenment immortality was turning into the reality of photography.
40:56Within 50 years of Wedgwood's experiments, paper soaked in silver nitrate was being used to capture real images.
41:04Photography became a craze.
41:08The exposure is going to have to be about 30 seconds.
41:11Okay.
41:12Stand probably with your head or your shoulders so that they can be supported by the mantelpiece behind you.
41:20Right.
41:21Now, this could make you a bit uncomfortable. Could you draw yourself up a little?
41:26Photography pandered to the vanity of middle class Europeans, because having your own portrait was now affordable.
41:35One.
41:36Photography was a very seductive and popular art, but I think it was also seen as extremely threatening.
41:45All sorts of social boundaries were broken down or breached by the new photographic process.
41:51Things you weren't supposed to see, places you weren't supposed to look at, images that were not for popular consumption, the boundary between elite taste and vulgar industrial taste.
42:06All these fences were being torn down by the chemical process of photography.
42:1229, 30.
42:13Thank you very much.
42:14Photography was crucial to Florence Nightingale's campaigns to improve military hospitals.
42:29It helped found the Salvation Army, and it brought home to the public the horrors of the American Civil War.
42:42But photography would do more than uncover social secrets.
42:46The ability to capture light would reveal unimagined truths about the natural world.
42:54It would revolutionize biology, engineering, and ultimately through physics, take us into a new dimension.
43:01It started with a simple question. What happens when a horse gallops?
43:14In the age of the horse, it was an old question as to how exactly they move.
43:23When they're galloping, do their feet all simultaneously come off the ground?
43:29Now, that was an ancient question, but you couldn't solve it with the naked eye.
43:33Edward Muybridge, a photographer on the west coast of America, was commissioned, for a bet, to use this newfangled technology to prove once and for all how a horse really moved.
43:49Muybridge's plan was to use 24 cameras placed in a row across the racetrack, each attached to a tripwire.
43:57And when the horse gallop passed, its exact movement at that instant would be caught on camera.
44:13Muybridge then developed the photos and had a series of amazing images of horses moving quickly.
44:22It was true that at one point in the gallop, the horse takes all its feet off the ground.
44:31Something you could never see with the naked eye, which the camera had now revealed for the first time.
44:40But the ability to freeze motion with a photograph was far more than a gimmick.
44:45Others believed that if they could examine animal motion in fine enough detail, they would be able to replicate it, artificially.
44:54A French scientist, Etienne-Jules Marais, had a particularly audacious dream.
45:01Using Muybridge's cameras, he hoped to discover the secrets of flight.
45:06But it turned out pretty quickly that birds are just too quick and move in far too complicated a way to be able to be photographed the way Muybridge took pictures of horses.
45:29So Marais cast about for another kind of camera.
45:36And he found one. A camera that worked like a gun.
45:40When you fired it, it took an enormous number of shots each second.
45:44So what Marais would do would be to point this gun at a bird and follow it through the sky, taking first hundreds and then thousands of shots each second.
45:59The scientific study of bird motion now became possible.
46:14And by the end of the century, Marais photographs not just of flying birds, but also of how wings control and are effective.
46:28By the air flow around them were being used to design the very first effective flying machines.
46:41Photography not only revealed what you couldn't see with the naked eye.
46:47It let humans reveal their own dreams.
46:51Marais' bird photos directly inspired the Wright brothers, who built the first aeroplane.
46:59And his camera was adapted into the first movie camera by the Lumiere brothers.
47:04By 1900, in this world of new technological wonders, scientists finally believed they could explain what light was.
47:21Building on Thomas Young's idea that light is a wave, the great Scottish scientist James Clerk Maxwell showed what these mysterious waves were.
47:36Pulses of electromagnetic energy.
47:42Humanity's long quest to understand light seemed over.
47:45Light, it was argued, was completely understood.
47:53We know what it is, we know where it came from, and we know where it's going.
47:58Light is a form of electromagnetic radiation which travels through empty space at a finite measured speed.
48:06And the physics of light, the technology of light became a kind of symbol of the great successes of physics and engineering and the whole of science.
48:16But there was a dramatic twist in the tale.
48:22Enter a Swiss patent clerk called Albert Einstein.
48:27Aged just 25, using the idea that light was an energy wave, Einstein was forced to conclude that all the laws of physics needed to be completely rewritten.
48:39To understand how Einstein could think so differently from his predecessors, picture the world in which he grew up.
48:54So imagine you were living in a European city around 1900.
48:59Your world had completely changed.
49:01You saw people whizzing past on bicycles, the first horseless carriages, motor cars.
49:08You could go to the cinema and see exact reproductions of what it was like to move really fast through space, through time.
49:18Einstein's was the first generation that went to the cinema, and like most people, he loved watching how time could be played with.
49:32Speed it up, slowed down, and even frozen.
49:39Einstein began to realise that time might be variable in the real world too, and that you'd experience it if you could travel like a beam of light.
49:51And he certainly began to imagine what it would be like sitting on a light beam, travelling through space.
49:58All sorts of paradoxical effects, he quickly worked out, would follow.
50:05Flying along a light beam into the depths of space, Einstein would see a reality completely different to the normal one.
50:14Time would stop. Distance would stretch out.
50:19It was just as weird as a cinema trick.
50:21And then in 1915, he published on his general theory of relativity.
50:30An astonishing intellectual achievement, it declared that humanity's most basic intuitions about space, time and light cannot be trusted.
50:41Now, Einstein's big idea was that when light travels near a heavy object, like our sun, it bends.
50:59What the gravitation of a very heavy object does, is to distort space and time.
51:05Near very heavy objects, straight lines curve.
51:14Put another way, a vast entity like a star makes empty space, the void itself, curve.
51:25It seemed bizarre, but if Einstein's incredible idea was right, it could be proved by looking at the stars.
51:33Near the sun, light will change direction. It will curve.
51:42And the apparent position of stars beyond the sun will shift.
51:48We'll be able to see stars in positions that weren't there before.
51:53But normally, the sun is so bright that it blanks out the stars that are in the sky behind it.
52:03There is only one rare occasion when we can see the stars behind the sun, and that is during a total eclipse.
52:12During an eclipse, the sun's disk is completely darkened. The temperature drops, and the sky seems to be extremely dark.
52:30Some of the stars, which the sun's light otherwise is too bright for us to see, some of those stars suddenly become visible.
52:39What you want to do, is take a photo of a star you can see just past the sun's edge.
52:45Now that would mean that the light ray from that star is coming really close to the sun.
52:52And if Einstein's right, then that light ray will bend a bit, and the star will seem to have shifted from where it normally is when the sun's not there.
53:02Einstein worked really, really hard to try and get astronomers to watch stars during a solar eclipse.
53:14Because if those stars seemed to shift position a bit, then his theory would be proved right.
53:21In 1919, there was a total solar eclipse, and a team of the finest British astronomers, led by Arthur Eddington,
53:41armed with the best telescopes and photographic equipment, went to Africa and Brazil to prove
53:47whether Einstein's mad ideas about space and time were true.
53:54The scientific world held its breath and waited for the result.
54:00It took months to do all the comparisons and calculations, but at a meeting of the prestigious Royal Astronomical Society in London,
54:10in November 1919, Eddington and his colleagues were able to stand up and say,
54:15our photographic data proves unambiguously that Einstein is right.
54:22A small shift of stars had completely changed the world.
54:28All of a sudden, literally overnight, Einstein became a world celebrity, the new Newton, a global hero.
54:37There were cartoons of the whole of Earth, with a single flag attached to the planet, saying simply, Einstein lived here.
54:48He became not just a celebrity, but a kind of figure of what it was to be a scientist, what it was to be a genius,
54:59and I guess what it is to have seen the secrets of the universe.
55:05Indeed, one person who visited Einstein said, visiting Einstein is like visiting the fourth dimension.
55:11He stopped being a human being. He became a force of nature.
55:14And the drama with which this revolutionary discovery was proclaimed put the new science of light right at the centre of the news media.
55:28It made the physics of light into a global event.
55:32But above all, what Einstein had done was overturn 3,000 years of thinking about light.
55:42Every philosopher, from the ancient Greeks to 9th century Arabs, from medieval monks to Isaac Newton,
55:51from Galileo to Maxwell, had unquestioningly accepted one fact about light.
55:59It travels in straight lines.
56:02And now Einstein had shown that even this was wrong.
56:12So Einstein was right. Light doesn't travel in perfect geometrical straight lines.
56:18But it travels through a space and a time that's curved.
56:25That makes light, as it were, depart from the straight and narrow.
56:30Light had once been the sign of reliability.
56:35It had been a tool for astronomers.
56:38It had been their basic technique for finding out how the cosmos works.
56:43Now it turned out that far from being a tool, light was a puzzle.
56:50It was a problem.
56:52It twisted. It turned. It bent. It strayed.
56:56Einstein's world became a world in which light needed to be teased apart.
57:04And in which the message that light brought from the most distant stars was a puzzle and a challenge to human intellect.
57:14Stay with us tonight for a powerful West Indian family drama about gun crime and a tricky father-son relationship.
57:28The critically acclaimed Elmina's Kitchen by Kwame Kwe Amar, next.
57:32At economethak h
57:35at West Indianapolis
57:37at the decades.
57:39At the妹 West.
57:41At Elling the road is nothing, OK
57:42married in the murderer for the past,
57:45John Murray.
57:46At the帶off at the abundantly screen,
57:48with a human defined identity,
57:50theオン fø� sina pas
Sé la primera persona en añadir un comentario