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00:00The world at night, seen from outer space.
00:10Millions of lights glitter across the surface of the globe.
00:16And in these twinkling lights is the story of how light created the modern world.
00:23About 150 years ago, light stopped living in heaven and started living in the material world.
00:33It became a kind of good you could buy and sell. It was artificial.
00:39And mastering artificial light has unlocked the secret of light itself.
00:45A secret so extraordinary that it would revolutionize our understanding of the way the world works.
00:56But it's come at a price that we're still learning to live with.
01:15In 1847, a 16-year-old Edinburgh schoolboy was taken to see one of the minor scientific wonders of the Victorian world.
01:39It was this, a prism made from a special crystal found in Iceland.
01:46And what it did was something completely surprising to scientists at the time.
01:52It played tricks with light.
01:56It's transparent. It lets the light through.
02:01Nothing puzzling there, but wait.
02:03Two of these crystals, combined, make the light go out.
02:11They extinguish the light.
02:19Light seemed to be violating all the known laws of nature.
02:23Now, the Scottish schoolboy was called James Clerk Maxwell.
02:33And his fascination with what the strange crystals did to light set him on a journey that would unravel the mysterious and astonishing nature of light itself.
02:47Maxwell lived at a time when Britain was the workshop of the world.
03:05Its traders, merchants and engineers dominated the globe.
03:11They understood how heat, pressure and sound worked.
03:24Its architects could build the most extraordinary structures.
03:28They could bring light into the interior of the very buildings themselves.
03:32Yet light itself baffled them.
03:49Maxwell was captivated by mysteries like this.
03:53Young Maxwell liked playing with things.
03:57He wanted to know their particular go.
04:01It was a phrase that was never out of his mouth.
04:04He would look at bells and locks and keys and how water flowed and the strange properties of light.
04:12And so he set about making his own optical instrument to explore the peculiar properties of the Iceland crystals.
04:23What we now know as polarising lenses.
04:27It's based on a very simple idea.
04:33The light falls onto this mirror here and then along the tube and you can look at it through a second mirror at the end.
04:42Now, Maxwell wasn't that concerned with the fact that polarisation allows light through or else it stops it.
04:51That wasn't the primary concern for him.
04:55No.
04:56What he wanted to do was to use this device to see things you could not see with the naked eye.
05:07He started with a seemingly unremarkable piece of glass.
05:12Maxwell would heat it until it was red hot, far too hot to touch.
05:16And then plunge it into ice cold water and it would suddenly set.
05:23There would be lines of tension inside the glass.
05:26We can't see them.
05:28But when Maxwell put them into his instrument.
05:33And then looked through the mirrors.
05:36What he saw were the most amazing patterns.
05:40These are frozen stress lines, things you just can't see with the naked eye.
05:52But with Maxwell's instrument, these crucial lines of frozen stress become visible and beautiful.
06:00How could brute physical forces affect something as intangible as light?
06:16And we know just how fascinated he was because we've got here the watercolours that he did himself when young,
06:24of the colours he could see through his instrument.
06:33These colours were speaking to Maxwell.
06:36Because what they suggested was that there must be some kind of relationship between the forces acting inside some stuff like glass.
06:46And the way light travelled through it.
06:51And that was really odd.
06:53What could be the relationship between pressure and tension.
06:57And the way light travelled.
07:00And the colours that it showed.
07:02Light was posing a series of problems for people that they just didn't seem to be smart enough to solve.
07:23Only a couple of years before the young Maxwell had started working with those polarising prisms.
07:36Light had posed a really big challenge that it was very hard to understand.
07:42It was this experiment here.
07:45Again it used nickel prisms.
07:47Between the prisms you put a piece of very heavy glass and you shine light through the prisms and the glass.
07:57What you do now is put a very strong electromagnet near it.
08:02And when you turn the magnet on, the light changes.
08:07Now this was a very, very peculiar phenomenon.
08:14How could magnets affect light?
08:22And there were yet other mysteries to do with light.
08:26I mean it was well known that light heats things up a bit.
08:30But it turned out that stuff would get really warm through some kind of radiation even where you couldn't see any light.
08:43What was the curious relationship between light and heat?
08:48And light sensitive paper would turn black even though there was no visible light around.
08:55It was as though there was much more to light than met the eye.
09:01Light was a trickster.
09:03It was the central problem for physicists to understand.
09:16The riddles set by light became a standing provocation to the confidence of Victorian scientists.
09:22If they could solve what light was, they could pull together chemistry and mechanics, electricity and magnetism.
09:37Solving the problems of light would put them on the path to the first adequate unified theory of the world.
09:46It became one of the hottest topics in Victorian science.
09:59So when Maxwell went to Cambridge University, light was almost inevitably one of his main areas of study.
10:07Maxwell has come down to us as an odd character.
10:24He pondered the maths of why cats always fall on their feet.
10:30And why paper fell in particular patterns.
10:39Could there be some kind of law behind them that would enable him to draw up universal rules for how the world worked?
10:49He even tried his hand at poetry, though, as history will probably judge, with much less success.
11:02When a telegraph cable under the Atlantic failed to work, Maxwell wrote an ode.
11:08Under the sea, no little signals are coming to me. Under the sea, something has surely gone wrong.
11:20And it's broke, broke, broke. What is the cause of it does not transpire.
11:27But something has broken the telegraph wire.
11:30Yet behind the amateur versifier was a brilliant analytical mind, which was to fuse two traditions which until now had never seen eye to eye.
11:46Maths and engineering.
11:48Down here in the University of Cambridge, a bastion of the Church of England, it was as though the Industrial Revolution had never happened.
12:06Not only that, but there were whole sciences that really mattered to engineering,
12:10like the science of heat, about steam engines, or electricity and magnetism, that were simply banned from the undergraduate curriculum,
12:18because they were too radical, they were too new for the sensitive palates of Cambridge undergraduates.
12:23So when Maxwell arrived here, he knew what he was in for.
12:27He brought his own equipment with him, his own prisms and lenses and polarimeters.
12:32In family letters, he called them his dirt, as though he really understood the way in which Cambridge dons might think about
12:38what engineering meant in a bastion of theology and mathematics.
12:49The clash of these two traditions would enable Maxwell to explore light in a totally new way.
12:56Yet surprisingly, the biggest revelation about light would come from another problem that fascinated Victorian society.
13:11The relation between electricity and magnetism.
13:15In 1831, Michael Faraday had demonstrated that if you wave a magnet near a coil of copper wire, it would produce an electric current.
13:37What nobody could explain was why.
13:48Maxwell set about looking for a mathematical explanation.
13:58He had to invent a new mathematical language.
14:03And what this gave him, after a huge amount of work, were four stunning equations that showed for the first time the precise relationship between electricity and magnetism.
14:24And magnetism.
14:30But there was more, because hidden in them was something else.
14:35The truth about light.
14:41The particular excitement about this set of equations is that they start off by describing the phenomena not of light,
14:53but of electricity and magnetism.
14:58And if you represent the way in which electric and magnetic forces interact with these four equations,
15:04you start to see, as Maxwell gradually realized with extraordinary excitement,
15:11that light, electricity and magnetism have something to do with each other.
15:15But then there's more, an extraordinary, sudden moment of realization, that this number, which appears in the equations, describes the speed with which waves travel in electromagnetic space.
15:32And it turns out, Maxwell was astonished, it turns out that the speed with which these waves move is exactly the same as the speed of light.
15:44There could only be one explanation.
15:51Light, electricity and magnetism must be the same kind of thing.
15:59Light is an electromagnetic wave.
16:02It was one of the biggest insights into how the world works in the history of science.
16:15Most of his contemporaries found it impossible to grasp.
16:20People stumbled along behind him in his wake, either not understanding his lectures or simply not being able to follow the leaps of imagination which Maxwell engaged in.
16:36When he was a student and when he was a professor, what his colleagues used to say about him was that Maxwell is always right but you can't always see why.
16:46That Maxwell never made a mistake but it was impossible to check exactly how he got from where he started to the startling ideas with which he ended up.
17:06Yet for Maxwell, the world now fitted together beautifully.
17:11If light is an electromagnetic wave, then the different colours of the spectrum correspond to waves vibrating at different frequencies.
17:25There's red at one end. This is light that's vibrating pretty slowly.
17:30And then as the speed of vibration increases, we see the colours, from red to orange, all the way up to blue and violet.
17:41Violet light vibrating extremely fast.
17:49Other mysteries also fell into place, like the apparent presence of light, even when it can't be seen.
17:55Beyond the edges of what we can see, beyond the visible spectrum, there's something very spooky indeed.
18:04There's invisible light. There's a radiation we can't see.
18:10Faster than blue, faster than violet, there's ultraviolet light.
18:15It was this form of invisible light that was mysteriously fogging photographic paper.
18:32At the other end, vibrating slower than the red, is infrared heat radiation.
18:37This is the mysterious source of heat that scientists had found associated with light.
18:45The spectrum gets wider and wider.
18:51The very neatness of the whole edifice gave Maxwell enormous satisfaction.
18:58One of the things that Maxwell thought was that there's a really deep relationship between the beauty of mathematics and the reality of his science.
19:13If something's true, Maxwell reckoned, you must be able to express it in an aesthetic form.
19:20And that's what the equations are doing for him.
19:25They summarise this idea that there's a profound relationship between the way the world works and our understanding that the way the world works is beautiful.
19:39This is beautiful.
19:45In the years to come, these four equations would have an enormous impact.
19:52They would influence every new technological development forever after.
19:57The relation between light and civilisation has always been pretty important.
20:10But after Maxwell's equations, nothing was ever going to be the same again.
20:14He was going to bring light into dark corners and his tools and techniques were going to completely change the history of the world.
20:21Society was about to change forever.
20:30Though not necessarily for the better.
20:35Maxwell's equations arrived at a time when Victorian Britain was hungry for new forms of light.
20:59Gas was hot, smelly and occasionally dangerous.
21:10Now there was a serious alternative.
21:20Maxwell's equations unlocked the potentiality of electromagnetism.
21:26What could now happen was that people could master magnets to generate a constant and reliable electrical supply.
21:37And that electrical supply at last made electric lighting viable.
21:45It's a really good example of the way in which something that might seem abstract and out of this world is brought down to Earth.
21:56The way that intelligent and inventive men would be able to exploit the potential and make lots of money.
22:04One of these men was a chemist working in the north of England.
22:09Newcastle was a boom city of the 19th century.
22:28It was full of entrepreneurs and businessmen with an eye on the main chance.
22:32And the learning and skill to follow any business opportunity.
22:37One of them was the local manufacturing chemist, Joseph Swan.
22:42A gentleman of letters, but with the keen eye to spot any commercial opportunity that would come his way.
22:49Victorian engineers were already experimenting with primitive ways of using electricity to make light.
23:03Electric light pulled in an enormous number of people's interests.
23:08It drew on state-of-the-art engineering.
23:11But the problem was that the current form of electric light in use, arc lighting, just wasn't cutting it.
23:17It didn't really work.
23:19It was unstable. It was noisy. It burst.
23:21There had to be a better way of bringing illumination into the home and into the factory.
23:31Swan set about finding a solution.
23:34One alternative to lighting by electric sparks would be to use the fact that some substances glow.
23:47They incandesce when you pass electricity through them.
23:51The problem with that kind of electric glow is that anything that glows so brightly is likely to burn and disappear.
24:06The solution would be to get it to glow in a vacuum where there's no air so combustion couldn't happen.
24:15And this turned out to be crucial for the development of electric light.
24:20It was like a really successful convergence of technologies.
24:25At just the moment when electric generators were reliable enough to produce the electric inputs for these lights,
24:34at the same time, big vacuum pumps came on stream that could suck all the air out of bulbs
24:42and maintain really, really low air pressure.
24:47With this convergence of technologies, it became possible to think of having a light bulb with a glowing filament in a vacuum.
25:02But what should the filament be made of?
25:05Now, Swan knew that carbon, when it's heated up, could be made to glow very brightly.
25:10But what kind of substance should he carbonise?
25:18He looked at paper, he looked at a range of substances, but then one day he decided to try carbonising this cotton.
25:27So he would pack the cotton into this container of charcoal and seal it and put it in an almost airtight container in the oven and bake it.
25:44After he'd baked it, he got this.
25:48The first viable filament for an electric light.
25:53And with this carbonised cotton filament, he was able to make electric light bulbs like these, shaped like a lemon and glowing bright red.
26:06Swan's new bulb was a technological triumph.
26:16Joseph Swan's new incandescent electric light was an instant hit with the posh and the wealthy amongst Victorian leaders.
26:34Britain's industrial class.
26:51Now, one of Swan's best and closest friends was Sir William Armstrong, Mr Tyneside.
26:57Armstrong was an enormously wealthy and ambitious Victorian entrepreneur and Swan's new invention was just the sort of thing he needed to impress his wealthy customers.
27:12They'd be brought to Newcastle on Armstrong's boats, they'd be greeted by Armstrong's employees, they would be taken up to Armstrong's country residence on one of his own private railway trains, steaming up the hill through the dark forests.
27:35And what they found when they arrived was this.
27:46Cragside.
27:54Cragside was really Armstrong's pride and joy.
27:57He turned it into a kind of showcase for state-of-the-art modern technology.
28:03It was described in the newspapers as the palace of a modern magician.
28:08This house became an electrified palace.
28:13It was the very first house to be lit by the new-fangled incandescent electric light bulbs.
28:24More than 40 of them delivering the illumination of more than a thousand candles.
28:33Here's a wonderful example.
28:36This is an incandescent electric light bulb pretending to be a gas lamp, pretending to be a candle, pretending to be a medieval heraldic lion.
28:51It's a perfect image of the way in which Armstrong and Swan's new electric technology brilliantly adapted itself to the aristocratic values of the late 19th century.
29:02Yet there was a major flaw in Swan's plan to use Cragside to encourage others to buy light bulbs.
29:19To keep his house electric, William Armstrong had one very big advantage.
29:26He had this.
29:28He had his own river.
29:34Which he used to run a big hydroelectric scheme to supply the electric power that kept Cragside lit with electric light.
29:49Now, if Joseph Swan's scheme was going to have any future at all,
29:54it couldn't possibly rely on people like William Armstrong with their own private electrical supply.
30:02What was needed was a public supply of electricity.
30:07In the closing decades of the 19th century, there was really only one place that was going to happen.
30:24Swan had lit a house.
30:393,000 miles away in New Jersey was a man who wanted to light the world.
30:45Thomas Alva Edison had also just invented an incandescent light bulb.
30:55But the parallel with Swan stops right there.
31:01Edison was in every way larger than life.
31:05He was a kind of modern hero that no one had ever seen before.
31:10A mixture of engineer and entrepreneur, businessman and visionary.
31:15In 1878, Edison set about building the world's first public electricity supply.
31:33He had to invent every single component,
31:36from the insulation surrounding the cables to the meters, fuses, switches,
31:42and, above all, the light fittings that made it work.
31:50But that was just the beginning.
31:52Making electric light available is one thing.
31:54Making it economic is quite another.
31:59The Edison revolution had only just begun.
32:03Perhaps the most important problem that the Edison system faced
32:16was that you only need to turn the lights on at night.
32:19And that meant that electric light was only going to be used
32:23for a very limited part of each 24 hours.
32:26Now, you can't easily store electric power.
32:30And it's really inefficient and costly only to run an electric system
32:35for a very limited period of the night.
32:40The answer was to persuade a sceptical public
32:43to buy more and more devices which ran on electricity
32:47that would make sure that they were customers of the electric companies
32:52on a 24-7 basis.
33:00Edison's revolutionary insight was that to sell electricity,
33:04he needed to sell a lifestyle.
33:06Lifestyle.
33:13Plenty of time, there's plenty of time,
33:16plenty of time for play.
33:19I want to tell you a bit about electric cooking.
33:23So free, so reliable, and so labour-saving.
33:29Well, I never.
33:31Come on now.
33:32Get her to sign up for the thing.
33:34Oh, think of the husband.
33:35It'll cost him far less than all those doctor's bills for his indigestion.
33:39That's not salesmanship.
33:40It's just kindness to animals.
33:47No stone was left unturned to convince a sceptical public
33:51that electric lighting was the new future.
33:54One electric light promoter, a man called William Preece,
34:02went to bizarre lengths.
34:07In my house, I use lamps that require 30 volts.
34:11I often put the wires into the mouths of my little children.
34:15They don't much like it, but it doesn't harm them.
34:18Well, I never.
34:20Well, I never.
34:22Well, I never.
34:24Isn't that clever?
34:25There's plenty of time, plenty of time for play.
34:31Edison's campaign to market electricity and the electric light bulb
34:37really set the tone for consumer marketing ever since.
34:42Because what Edison realised was that he wasn't so much selling light bulbs,
34:47he was selling dreams, dreams of light, of leisure, of less work.
34:54People were buying Edison's light bulbs, not so much because they needed them,
34:59but because they had that dream, that vision of a world of light.
35:05And that technique that Edison started with his sales campaigns
35:10for electric light bulbs has dominated marketing ever since.
35:14It's been kept going, whether you're selling cars
35:18or whether you're marketing computers.
35:25Today, light bulbs are everywhere.
35:29They've become the symbol of a modern, thrusting, 24-hour, 7-day-a-week society.
35:36It's a world which has harnessed the genius of Maxwell
35:48with the brilliance of Edison
35:52to give us more control over our environment than ever before.
35:56Or has it?
36:08For many, it's encouraged a world in which most people may, in reality,
36:13have less control than before.
36:15Why is it exactly that we live in a 24-7 society?
36:24Is it because we really want to?
36:27Or is it rather because it's the dictates of the machines
36:32that they become profitable if they're switched on all the time?
36:36Is it that we live in a world because we've chosen to live in a world
36:42that's lit every single day and every single night?
36:46Or is it not rather the demand for profit and engineering
36:51that keeps the world going just as it does?
36:55So it looks as though these technologies of artificial light
36:59give us an unprecedented control over the world around us.
37:05But maybe, just maybe, we're the victims.
37:09We're under the control of machines and the market.
37:16Yet for scientists, the real impact of the light bulb
37:20has had nothing to do with control.
37:23In fact, it's been the very opposite.
37:29The light bulb was going to blow apart the laws of physics
37:37and reveal a world that's more uncertain, more unpredictable,
37:42and more dangerous than its inventors dreamt of.
37:45In the mid-1890s, in the town of Würzburg, a German scientist had embarked on a series of new experiments with light.
38:06His name was Wilhelm Röntgen, and what interested Röntgen was a new piece of equipment recently developed from the light bulb.
38:17It was a vacuum tube, a long glass tube from which almost all the air had been pumped out.
38:26You couldn't make one of these without the technology which was being used to make light bulbs.
38:31The most extraordinary thing about this was that if you passed an electric current through the vacuum tube,
38:39it started to glow.
38:42It started to glow brightly.
38:49The tube was empty, yet something was glowing.
38:52It became known as a cathode ray.
39:01Röntgen was intrigued, but as he played around with it, he came across something even more extraordinary.
39:07When he increased the charge and took a photograph of a hand, he could suddenly see the bones through the skin.
39:20They became known as X-rays.
39:25These X-rays made a sensation.
39:41You could see through flesh, clothes, you could see embarrassing things, perhaps, under people's clothing.
39:54Anti-X-ray devices were sold.
39:58Lead pants to prevent your privates becoming visible under this new kind of light.
40:04There were cartoons about X-rays.
40:09There were X-ray shops.
40:11There was even the idea that X-rays were some kind of spooky ray that came from your eye through objects,
40:20so that you could penetrate them in some kind of inexplicable way.
40:25They were the news media sensation of the 1890s.
40:29These mysterious rays of light seemed to confirm for many people that there was something beyond the natural world.
40:43A supernatural world.
40:47Cathode rays.
40:49X-rays.
40:51All sorts of weird and strange radiations.
40:53Went along with an explosion in interest in spiritualism.
41:00In fact, I think spiritualism made more sense in a world where there were kinds of light and kinds of rays that you couldn't see,
41:11but showed you things that were otherwise invisible.
41:15After all, how do you communicate with the dead?
41:19By some kind of ray, which passes a barrier, which otherwise seems impermeable.
41:26Well, that's what X-rays do.
41:29X-rays travel through glass and flesh, and they show you things that otherwise no human could ever see.
41:37In the decades to come, as scientists pieced together what was really going on,
41:47it became clear that X-rays have nothing to do with the supernatural.
41:54They're merely another part of the electromagnetic spectrum.
41:58At the top of that spectrum, vibrating quite fast, is blue and violet light, and beyond it the light we can't see.
42:10Ultraviolet.
42:12And now a form of radiation emerges that is very high frequency indeed, vibrating extremely fast.
42:20X-radiation.
42:29But the visible glow in the vacuum tube would lead scientists somewhere very different.
42:40It wouldn't help them communicate with the dead, but in its own way it would be just as revolutionary.
42:58One of the centres of research into the strange characteristics of vacuum tubes was Cambridge.
43:09Here, Maxwell's research lab was now run by a physicist called J.J. Thompson.
43:15It's one of Thompson's misfortunes to have gone down in history for an incident that's almost absurd in its triviality.
43:33In the 1920s, he's reputed to have shouted at a couple of undergraduates training for the 1924 Olympics in the Great Court at Trinity College.
43:42One of them went on to win gold.
43:49But Thompson, like Maxwell, was a brilliant scientist, and in the closing decades of the 19th century, he designed his own cathode ray tube to investigate this very peculiar form of light.
44:03This is a replica of what Thompson designed.
44:11And what's special about it is that it allows the cathode rays to be affected simultaneously by electric and magnetic forces.
44:22And the experiment that J.J. Thompson did with this tube would have the most dramatic consequences.
44:28Thompson was not a practical man. In fact, he was notoriously clumsy.
44:37Yet, using his new tube, he performed a series of hugely important experiments.
44:42He would turn the cathode ray tube on. You'd see a glow and a bright point at the other end of the tube.
44:55Turn the electromagnets on. The position of the dot moves.
45:01The magnets are deflecting the cathode rays.
45:05Thompson repeated the experiment time and time again and measured the size of the deflection.
45:21Whatever was coming down the tube was clearly not a wave.
45:25It only made sense if it was a stream of particles.
45:34Thompson then plugged the figures into Maxwell's famous equations.
45:41And the result he got was absolutely dramatic.
45:44He found that the particles making up cathode rays are tiny, much, much smaller than atoms.
45:54And that was an earth-shattering result.
45:56Nobody had ever produced any evidence that there was anything smaller than an atom before.
46:12Indeed, some scientists didn't even believe in atoms.
46:15Years later, Thompson was to describe his findings in a lecture to the prestigious Institute of Electrical Engineers.
46:29Could anything at first sight seem more impractical than a body which is so small that its mass is an insignificant fraction of the mass of an atom, the hydrogen,
46:47which itself is so small, that a crowd of these atoms, equal in number to the population of the whole world, would be too small to have been detected by any means, then no science.
47:08Today, we know these tiny particles as electrons.
47:19This was really revolutionary stuff.
47:22And what was so exciting about it was that the technology to begin to pull atoms apart,
47:30to begin to tell a story about the most fundamental building blocks of the world,
47:35came straight from light technology.
47:39Vacuum pumps, light bulbs, vacuum tubes.
47:44It was by thinking about those bits of machinery that the atom began to be torn apart.
47:51Yet it's one of history's great ironies that at the time nobody realised science was on the verge of a breakthrough that would turn physics and the world on their heads.
48:12By the end of the 19th century, most scientists in Europe and overseas reckoned that, in many ways, the task of physics was over.
48:31The basic problems had been solved.
48:33We knew how light, electricity and magnetism worked.
48:38We understood the problems of heat and engineering.
48:42Physics turned into a search, not for great new theories, but just for better measurements.
48:49One of these measurements concerned the production of light bulbs by now a hugely important and influential commercial activity.
49:05The light and power system was the most important financial area of European world industry.
49:19Getting the right answer to problems of electric light and electric power meant big bucks worldwide.
49:26The problem the industry faced seemed scientifically trivial.
49:35What they wanted was to get the maximum amount of light out of a bulb for the minimum amount of electric energy going in.
49:43So the physicists were asked, do some sums and calculate what the relationship is between the amount of electric energy heating up a piece of metal wire
49:53and the amount of light coming out when that wire starts to radiate.
50:01No one thought that this was going to be a deeply important theoretical problem.
50:06It mattered to people's bank balances.
50:08It didn't seem to matter to physical theory very much.
50:14The man the industry turned to was a German physicist called Max Planck.
50:20Planck looked at Maxwell's celebrated equations which describe the relationship between light and energy.
50:32It was then that he had a shock.
50:37What these equations suggested was that the more energy you put in and the hotter the system got, the more light and heat it should radiate.
50:47Maxwell's equations have predicted that the energy levels would continue to build up infinitely until an object was radiating a catastrophic amount of light and heat.
51:06And it would atomize.
51:07But this simply isn't true.
51:14Think about what happens, for example, when you have a metal bar just resting on the fire.
51:19As it starts to get hotter, it begins to glow, initially just red, and then all the other frequencies begin to kick in.
51:27So it goes from red through blue to white heat.
51:29But no matter how hot it gets, it's never going to explode.
51:38This was a prediction from Maxwell's theory that completely failed.
51:43The apparently infallible Maxwell had made a mistake.
51:55It was a body blow to physics.
51:58As Planck tried to untangle what was going on here, he came up with an idea that was completely counterintuitive.
52:15Now, because Maxwell thought light was a wave, Maxwell reckoned that when bodies got hotter and hotter, there was absolutely no reason why they shouldn't emit more and more light.
52:29Planck then came up with a really cunning scheme to try and make the theory fit the data.
52:37Planck's problem was similar to the one Thomson had faced.
52:46Thomson had had to decide whether cathode rays were waves or particles.
52:53Planck faced an identical dilemma and came up with an extraordinary solution.
53:00What Max Planck was saying, and for him it was a quick technical fix,
53:05was that sometimes light seems to be behaving like a wave, but sometimes it seems to be behaving a bit like a particle.
53:13Now, after a bit, it quickly emerges that that's a really revolutionary idea.
53:20It completely undermines the basis of modern physics.
53:24Because light turns out to have a split personality.
53:28It has a wave nature on Mondays, Wednesdays and Fridays, as one of the physicists said,
53:33and a particle nature on Tuesdays, Thursdays and Saturdays.
53:37Suddenly, young physicists had a big, new, world-shattering problem to work on.
53:43And they'd staked their careers on trying to understand light schizophrenia.
53:49Everything in physics that had been taken for granted was now up for grabs,
53:59and every ambitious young physicist wanted a piece of the action.
54:04Abstract atomic physics developing at present will one day fit more.
54:10It turned into one of the most exciting and creative periods in the history of science.
54:17Quantum physics was born.
54:20If one was not shocked by quantum theory, he has not understood it.
54:25Planck's revolutionary explanation of light forced a fundamental rethink of the basic properties of matter.
54:34The number of scientific knowledge has been enormously extended,
54:40and theoretical knowledge has become vastly more profound.
54:44And what began to emerge was a whole new world of tiny, subatomic particles no one until now had ever imagined could exist.
54:59To Thomson's discovery of the electron were added new particles like neutrons and protons.
55:07This zoo of particles was just impossible to pull together.
55:16Physicists, for their meat and drink, night and day, tried to work out a better story about how these things could be pulled together.
55:24And the problem didn't just stay inside physics labs.
55:29No, physicists would write science fiction stories, make movies and plays to try and get the public interested.
55:35And they did.
55:37Protons are creaking and jittering.
55:39Electrons are rolling and cluttering.
55:42Light comes rushing with a wince.
55:44Oh, this nonsense makes no sense.
55:46No, no.
55:51The bubbling excitement eventually resulted in a completely different picture of what the atom is like.
55:58It's like a planetary system.
56:00There's a central nucleus stuffed with neutrons and protons,
56:03and around that nucleus orbit the negatively charged electrons.
56:08But what really mattered was that this atom was bubbling with energy.
56:14The atom itself could be an inexhaustible source of power.
56:19A new physics was born.
56:21A physics of the atomic age.
56:31Atomic physics gave us nuclear fission.
56:34A terrifying new power was born.
56:38A new power was born.
56:47Out of the ashes emerges a completely different, completely new vision of what light really is like.
56:55And it's a very surprising one, because it's a vision of uncertainty, not at all a mechanical world in which effects follow causes in a rigorous chain of consequences.
57:10This is the world view of modern quantum mechanics.
57:21A world view in which light shifts its character between wave and particle.
57:29It has completely changed the way we think about light.
57:33And it's completely changed the way we think about the world.
57:37Ironically, the more we've uncovered its mysteries, the greater those mysteries have grown.
57:46Next on Light Fantastic, how light gave us trickery of cinema and Einstein's truth about the universe.
58:08Powerful drama coming up tonight.
58:10Two psychiatrists disagree about the best care for a black patient who thinks he's the son of Idi Amin, in Joe Pennell's Blue Orange, next.
58:24Outro Music
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