0:00:14 > 0:00:20Every now and then, an idea takes form that changes everything -
0:00:20 > 0:00:24it revolutionises the way we see and understand the world around us.
0:00:24 > 0:00:26I believe that just such an idea
0:00:26 > 0:00:29took form in the medieval Islamic world.
0:00:29 > 0:00:32It's the idea that everything,
0:00:32 > 0:00:35from the stars above to the working of our own bodies,
0:00:35 > 0:00:41is not arbitrary or whimsical, but subject to certain systematic rules.
0:00:41 > 0:00:45And what's more, that we humans can work out what those rules might be
0:00:45 > 0:00:48and then, we can refine and test our theories
0:00:48 > 0:00:50through observation and experiments.
0:00:50 > 0:00:56In other words, it's the idea we now call the scientific method.
0:01:20 > 0:01:25'For me, the story of the scientific renaissance that took place in
0:01:25 > 0:01:28'the medieval Islamic world is a personal one.
0:01:31 > 0:01:36'This is my cousin Samir's house in the Iranian capital, Tehran.
0:01:36 > 0:01:39'I haven't seen some of the relatives
0:01:39 > 0:01:43'on my father's side of the family in over 30 years.'
0:01:44 > 0:01:49This is my not so tall, but very beautiful Auntie Anis.
0:01:50 > 0:01:53'The Al-Khalili family is originally
0:01:53 > 0:01:57from the city of Najaf in Iraq, south of Baghdad.
0:01:57 > 0:02:00'In fact, I grew up in Iraq.
0:02:00 > 0:02:04'But when Saddam Hussein came to power, the family split.
0:02:04 > 0:02:08'Many of the Al-Khalilis fled here to Iran.
0:02:08 > 0:02:12'As my mother's English, I came to Britain with my parents.'
0:02:14 > 0:02:18There, I pursued my passion for science
0:02:18 > 0:02:22and am now a professor of physics at the University of Surrey.
0:02:22 > 0:02:26But now, I find that my own scientific work
0:02:26 > 0:02:30and my Arabic and Islamic heritage are intertwined.
0:02:32 > 0:02:36On my journey through the Middle East, I discovered that
0:02:36 > 0:02:38an astonishing leap in scientific knowledge
0:02:38 > 0:02:41took place here 1,000 years ago
0:02:41 > 0:02:45under a powerful and flourishing Islamic Empire.
0:02:46 > 0:02:50Wealthy, powerful, successful cultures
0:02:50 > 0:02:54will produce enormous advances
0:02:54 > 0:02:57in understanding and in technique,
0:02:57 > 0:03:02and that's just what we find in Islam, in Baghdad,
0:03:02 > 0:03:07under a series of successful, powerful,
0:03:07 > 0:03:11wealthy and self-confident Islamic regimes.
0:03:12 > 0:03:17Over 1,000 years ago, the Islamic Empire was the largest in the world.
0:03:17 > 0:03:21It governed an estimated 60 million people -
0:03:21 > 0:03:24that was over 30% of the world's population.
0:03:28 > 0:03:31I found an archaeological fragment of this glorious past
0:03:31 > 0:03:35in a suburb of Tehran, not far from my cousin's house.
0:03:38 > 0:03:41These ancient walls tucked behind a backstreet
0:03:41 > 0:03:46on the outskirts of southern Tehran are literally all that remain
0:03:46 > 0:03:48of the ancient city of Ray.
0:03:48 > 0:03:53The city that the great Persian geographer Al-Muqaddasi described
0:03:53 > 0:03:55as one of the glories of Islam.
0:03:57 > 0:04:01Of course, Ray was just one of a number of cities
0:04:01 > 0:04:03that flourished under early Islamic rule.
0:04:03 > 0:04:05From Baghdad, its capital,
0:04:05 > 0:04:08the empire spread across thousands of miles
0:04:08 > 0:04:11from North Africa through to central Asia.
0:04:11 > 0:04:16Cities like Al-Askar, Basra, Merv, Gurganj, Bukhara,
0:04:16 > 0:04:19each powerful and thriving cities.
0:04:19 > 0:04:23Each would have been rich in trade, alive with culture.
0:04:23 > 0:04:26Each would have had its own libraries, its own academies.
0:04:26 > 0:04:29These were powerhouses of the new science.
0:04:29 > 0:04:32This really was a Golden Age.
0:04:32 > 0:04:34Think of that span of land.
0:04:34 > 0:04:39This is larger than any empire human civilisation
0:04:39 > 0:04:42had ever known. Within that span of land,
0:04:42 > 0:04:45you can plug in the Roman Empire and it will fill
0:04:45 > 0:04:48just maybe one-third of it, one-half of it or something like that.
0:04:48 > 0:04:52CHANTING IN ARABIC
0:04:58 > 0:05:01Reminders of this great Islamic Empire
0:05:01 > 0:05:03are everywhere in the Arab world today.
0:05:04 > 0:05:09This football match in the Syrian capital, Damascus, is being played
0:05:09 > 0:05:12at the Abbasid Stadium. That's the name of the family
0:05:12 > 0:05:17who ruled the Islamic Empire from 750 to 1258 AD.
0:05:26 > 0:05:31This large territory allowed them to raise enormous tax revenues
0:05:31 > 0:05:34to fund a search for knowledge and scholarship
0:05:34 > 0:05:38which became known as the Translation Movement.
0:05:38 > 0:05:43They sent scholars around the known world to gather up great books
0:05:43 > 0:05:46and have them translated into Arabic.
0:05:46 > 0:05:51It's a legacy that's still alive in the minds of most modern Arabs.
0:06:08 > 0:06:12For medieval Islamic leaders, scientific knowledge
0:06:12 > 0:06:16was crucial to successfully running a vast empire.
0:06:18 > 0:06:22They did have a big and sophisticated governmental administration,
0:06:22 > 0:06:26and that needed knowledge. If you wanted to be an administrator
0:06:26 > 0:06:30and had to assess taxes, you needed to know about mathematics.
0:06:30 > 0:06:36It also wants to be able to build monumental buildings. That requires a knowledge of architecture,
0:06:36 > 0:06:40and mathematical skills to construct fine buildings safely.
0:06:40 > 0:06:44Medicine just to keep the elite happy and healthy.
0:06:44 > 0:06:47Those are the areas of knowledge
0:06:47 > 0:06:51which are first translated from other languages into Arabic.
0:06:57 > 0:07:01The legacy of the medieval Islamic Empire
0:07:01 > 0:07:03is scattered across a vast region.
0:07:03 > 0:07:07There's architectural masterpieces,
0:07:07 > 0:07:10like the Ummayyad Mosque in Damascus,
0:07:10 > 0:07:12the Jame Mosque in Isfahan,
0:07:12 > 0:07:17and Al-Azhar University and mosque in Cairo.
0:07:17 > 0:07:21And then there are many ruins that still hint at past glories,
0:07:21 > 0:07:27like this, a crumbling 8th-century palace deep in the Syrian Desert.
0:07:28 > 0:07:32And this, a huge Muslim palace called Madinat Al-Zahra,
0:07:32 > 0:07:35currently being excavated in Southern Spain.
0:07:37 > 0:07:42These are the impressive ruins of Madinat Al-Zahra,
0:07:42 > 0:07:46the fantastic palace city built outside Cordoba
0:07:46 > 0:07:49in the 9th century by Abd al-Rahman III,
0:07:49 > 0:07:54who was the greatest of all the Andalucian caliphs.
0:07:54 > 0:07:58At the time that it was ruined, Cordoba was in fact
0:07:58 > 0:08:02the largest and most important city in Europe,
0:08:02 > 0:08:05a rival to Baghdad in the east
0:08:05 > 0:08:09for a centre for Islamic scholarship and science.
0:08:12 > 0:08:15And as I travelled, I saw how science,
0:08:15 > 0:08:19especially numerical record-keeping and measurement,
0:08:19 > 0:08:24was crucial to dealing with the challenges of running a vast empire.
0:08:29 > 0:08:32This is the mighty River Nile
0:08:32 > 0:08:35as it flows through the Egyptian capital, Cairo.
0:08:35 > 0:08:40Since antiquity, its unpredictable floods have determined the fate
0:08:40 > 0:08:44of Egypt's people, bringing years of lean and plenty.
0:08:44 > 0:08:49By the 8th century, Cairo was part of the Islamic Empire
0:08:49 > 0:08:52and the new rulers took the first step
0:08:52 > 0:08:56to understanding this mighty river in a scientific way.
0:08:56 > 0:08:59They built a device to measure it.
0:09:03 > 0:09:04Ha!
0:09:06 > 0:09:09It's an amazing structure, right?
0:09:09 > 0:09:14'Dr Nader El-Bizri of the Institute of Ismaili Studies,
0:09:14 > 0:09:18'is showing me the Nileometer. It's basically a huge colonnade
0:09:18 > 0:09:22'that was built in a chamber connected by tunnels to the river.
0:09:22 > 0:09:25'As the water rose or fell,
0:09:25 > 0:09:29'its height could be read from the central column.'
0:09:29 > 0:09:34The central colonnade here is ultimately a measuring instrument.
0:09:34 > 0:09:39It is very precise. It's almost one inch between a marking and another.
0:09:39 > 0:09:43Presumably they need to know seasonal variations in the height.
0:09:43 > 0:09:46And to try to have some sort of record,
0:09:46 > 0:09:49so that they could measure against certain years,
0:09:49 > 0:09:52- where a year was known for a high level of flood...- Yes.
0:09:52 > 0:09:55..versus another year known for its drought.
0:09:55 > 0:10:00- Then they might perhaps take some precautions.- Yes.
0:10:00 > 0:10:05'The data collected from the Nileometer had one practical use.
0:10:05 > 0:10:08'By creating an objective record of the river's behaviour,
0:10:08 > 0:10:11'it allowed the rulers of the time to calculate
0:10:11 > 0:10:15'how much tax to levy on Egypt's farmers.
0:10:15 > 0:10:19'But whatever its uses, what I love about the Nileometer
0:10:19 > 0:10:23'is how it shows that to understand the world,
0:10:23 > 0:10:26'you have to build devices to measure it.'
0:10:26 > 0:10:30If you think very hard, it's never obvious
0:10:30 > 0:10:37that measurement can make sense of the world around us.
0:10:37 > 0:10:41The world appears, as a Western philosopher once put it,
0:10:41 > 0:10:48like a buzzing, blooming confusion, and the idea that we as a group
0:10:48 > 0:10:53have tools which are reliable, which have sufficient integrity,
0:10:53 > 0:10:58which have an intellectual grip that can make sense
0:10:58 > 0:11:03of the basic phenomena we see around us, that's an astonishing idea.
0:11:11 > 0:11:16'And one medieval Islamic ruler made measurement a personal obsession,
0:11:16 > 0:11:21'giving it a scale and ambition that was truly unprecedented.'
0:11:21 > 0:11:24His name was Al-Ma'mun,
0:11:24 > 0:11:30and he became the caliph, or ruler, of the Islamic Empire in 813 AD.
0:11:30 > 0:11:33Al-Ma'mun lived in a culture without portraiture,
0:11:33 > 0:11:37so all we have are later impressions of what he might have looked like.
0:11:39 > 0:11:43Al-Ma'mun funded a range of scientific research,
0:11:43 > 0:11:47but one particular project was a personal favourite of his.
0:11:47 > 0:11:52And given that he ruled over such a large territory,
0:11:52 > 0:11:56it's hardly surprising what it was - map-making.
0:11:57 > 0:12:00In the second decade of the 9th century AD,
0:12:00 > 0:12:04Al-Ma'mun commissioned a new map of the world,
0:12:04 > 0:12:08and his scientists did a pretty impressive job.
0:12:08 > 0:12:12It was a vast improvement on all maps that had come before.
0:12:12 > 0:12:16What we see here is that they've really got the Mediterranean,
0:12:16 > 0:12:20its shape and how it links in with the Black Sea, the Middle East,
0:12:20 > 0:12:24even the whole of Asia as far as China and Japan.
0:12:24 > 0:12:28They've even got the Indian Ocean and the East coast of Africa.
0:12:28 > 0:12:32It all looks pretty impressive for the known world at the time.
0:12:32 > 0:12:36Of course, what Al-Ma'mun ultimately wanted to know
0:12:36 > 0:12:41was how much of the Earth as a whole did he possess.
0:12:41 > 0:12:45And this begged the question, just how big is the Earth?
0:12:49 > 0:12:54It's a sign of amazing ambition that groups of scholars
0:12:54 > 0:13:00and craftsmen together can, as it were, capture the world.
0:13:00 > 0:13:04Where does that ambition and that confidence come from?
0:13:04 > 0:13:07Part of it comes from religious faith.
0:13:07 > 0:13:11Because the world was made
0:13:11 > 0:13:16by someone a bit like us, but much smarter,
0:13:16 > 0:13:20if we're smart enough, the thought was,
0:13:20 > 0:13:24we could probably make sense of a bit of what he did.
0:13:24 > 0:13:27And that's very clear as a motivation
0:13:27 > 0:13:31in a lot of Islamic, as in a lot of Christian, science.
0:13:31 > 0:13:36And more specifically, the practice of Islam demanded
0:13:36 > 0:13:40that its followers have a very clear idea
0:13:40 > 0:13:43of the size and shape of the world.
0:13:43 > 0:13:46This is crucial information for Muslims, because,
0:13:46 > 0:13:49wherever they are in the world, they need to know
0:13:49 > 0:13:53the direction to Mecca for their prayer. This is known as al-qibla.
0:13:53 > 0:13:56Now, over such a large territory,
0:13:56 > 0:13:59finding the direction to Mecca is not a trivial problem.
0:14:01 > 0:14:04This problem was wonderfully illustrated
0:14:04 > 0:14:08when a mosque was built recently in Washington DC.
0:14:08 > 0:14:10Some worshippers were confused,
0:14:10 > 0:14:13because the direction they were told to face when praying
0:14:13 > 0:14:17was slightly north and not south-east as they expected.
0:14:17 > 0:14:20After all, Mecca is south-east of Washington
0:14:20 > 0:14:25and, on a flat map, it does appears to lie in that direction.
0:14:25 > 0:14:28But on a curved sphere, the shortest distance
0:14:28 > 0:14:34between any two points follows what's called a great circle.
0:14:34 > 0:14:39So, for example, this great circle line between Washington and Mecca
0:14:39 > 0:14:41is quite different to what you might expect,
0:14:41 > 0:14:44so the direction to Mecca from Washington
0:14:44 > 0:14:49actually points slightly north-east rather than south-east.
0:14:49 > 0:14:53Of course, this is complicated stuff, but the key point
0:14:53 > 0:14:56for Islamic scholars is that knowing the direction to Mecca
0:14:56 > 0:15:00requires a knowledge of how steeply the Earth curves,
0:15:00 > 0:15:03and that means knowing how big it is.
0:15:04 > 0:15:09So Al-Ma'mun commissioned his very best scientists to measure it.
0:15:10 > 0:15:13- Hello.- Hello.
0:15:13 > 0:15:15Nice to meet you.
0:15:15 > 0:15:18'To understand how they did it, I'm meeting up
0:15:18 > 0:15:22'with Professor Sami Chaloubi from Aleppo University in Syria,
0:15:22 > 0:15:25'who's an expert in early Islamic science.
0:15:32 > 0:15:35'Professor Chaloubi began by explaining the measuring technique,
0:15:35 > 0:15:38'which Al-Ma'mun's scientists first used
0:15:38 > 0:15:41'and which they had inherited from the Greeks.'
0:15:41 > 0:15:43We're now talking about this,
0:15:43 > 0:15:47the earlier Eratosthenes technique of measuring the circumference.
0:15:47 > 0:15:52It was repeated by the Abbasid astronomers.
0:15:52 > 0:15:56It was to measure the distance between two points
0:15:56 > 0:15:58and then look at the angle of inclination of the sun.
0:15:58 > 0:16:03So in Egypt, in Aswan down in the south, they regard the sun
0:16:03 > 0:16:06as being vertical - this is near to the equator -
0:16:06 > 0:16:10and they worked out how far away from the vertical the sun was
0:16:10 > 0:16:13if they measured it from the north of Egypt,
0:16:13 > 0:16:17in Alexandria, which is on the Mediterranean coast.
0:16:17 > 0:16:20'Al-Ma'mun's astronomers repeated the Greek experiments
0:16:20 > 0:16:25'in Syria and Iraq by measuring the angle of the sun in the sky at noon
0:16:25 > 0:16:28'at one known location.
0:16:28 > 0:16:31'They then walked due north to a second location,
0:16:31 > 0:16:35'carefully measuring the distance they travelled.'
0:16:35 > 0:16:37At the second location,
0:16:37 > 0:16:41they once again measured the angle of the sun at noon.
0:16:41 > 0:16:44This angle would have been slightly smaller than the first one.
0:16:46 > 0:16:49With these figures, Al-Ma'mun's astronomers
0:16:49 > 0:16:53were able to estimate the Earth's circumference.
0:16:53 > 0:16:56They got a value of 24,000 miles -
0:16:56 > 0:17:01within 4% of the correct value. Not bad, you might think.
0:17:01 > 0:17:05But this method was flawed and ultimately unreliable.
0:17:05 > 0:17:10The main problem was that measuring the distance between two locations
0:17:10 > 0:17:12was incredibly difficult. It could only be done
0:17:12 > 0:17:15by the unreliable method of counting paces
0:17:15 > 0:17:17as you walked through the burning desert.
0:17:19 > 0:17:24A more reliable and sophisticated method for estimating the Earth's size was needed,
0:17:24 > 0:17:29and two centuries after Al-Ma'mun died, it came.
0:17:29 > 0:17:33What made it possible was a great leap of imagination
0:17:33 > 0:17:35and the fact that, by 900 AD,
0:17:35 > 0:17:38much of the world's mathematical knowledge
0:17:38 > 0:17:40had been translated into Arabic,
0:17:40 > 0:17:44so scholars could scrutinise and improve on it.
0:17:44 > 0:17:47Out of this obsession with scholarly learning
0:17:47 > 0:17:50came a true mathematical visionary -
0:17:50 > 0:17:54Abu Rayhan Muhammad Ibn Ahmad Al-Biruni.
0:17:54 > 0:17:57And like all Islamic scholars of the time,
0:17:57 > 0:18:00Al-Biruni was obsessed with the science and mathematics
0:18:00 > 0:18:04of the ancient Greeks, Babylonians and Indians.
0:18:04 > 0:18:08And because of the success of the Translation Movement,
0:18:08 > 0:18:12he had literally on his desk the great work on geometry by Euclid,
0:18:12 > 0:18:16Ptolemy's Almagest, the Indian text the Sindhind,
0:18:16 > 0:18:20and the famous work on algebra by Al-Khwarizmi.
0:18:20 > 0:18:24CONVERSATION IN ARABIC
0:18:24 > 0:18:27'Professor Chaloubi has brought along the book
0:18:27 > 0:18:31'in which Al-Biruni describes how he combined algebra and geometry
0:18:31 > 0:18:34'with some very simple and practical measurements
0:18:34 > 0:18:39'to solve the epic problem of how to calculate the size of the Earth.'
0:18:39 > 0:18:43- Biruni's text. - And this his...?
0:18:43 > 0:18:45- Al-Qanoon Al-Masoodi. - The Masoodi Canon.
0:18:45 > 0:18:50This is Biruni's Canon, which I've been trying to get hold of,
0:18:50 > 0:18:54where he describes this fantastic experiment.
0:18:54 > 0:18:56Oh, you've found the page.
0:18:56 > 0:18:57Yes.
0:18:59 > 0:19:02'Having read Al-Biruni's description of how to
0:19:02 > 0:19:06'estimate the size of the world, I wanted to try it for myself.'
0:19:10 > 0:19:13First, he had to find a fairly high mountain
0:19:13 > 0:19:17from the top of which he could see a flat horizon -
0:19:17 > 0:19:19in this case, the sea.
0:19:20 > 0:19:23What I love about this story is that,
0:19:23 > 0:19:26with a few simple measurements around this small mountain peak,
0:19:26 > 0:19:31you can work out the size of the whole world.
0:19:31 > 0:19:35Al-Biruni's first step was to work out the height of the mountain.
0:19:35 > 0:19:41He did this by going to two points at sea level a known distance apart
0:19:41 > 0:19:45and then measuring the angles from these points to the mountain top.
0:19:48 > 0:19:52So, to measure the angle to the mountain top,
0:19:52 > 0:19:56Biruni had to use a device like this, called an astrolabe.
0:19:56 > 0:19:58It's basically a giant protractor.
0:19:58 > 0:20:02It has the angles in degrees marked around the outside
0:20:02 > 0:20:05and a pointer to help him determine his line of sight.
0:20:05 > 0:20:09So, if we try now and determine the angle to the top,
0:20:09 > 0:20:14it has to hang freely. And then... OK, so if you let it hang...
0:20:14 > 0:20:18'I'd like to stress, if you haven't noticed already, that Al-Biruni
0:20:18 > 0:20:22'would have made his measurements more meticulously than I am.
0:20:22 > 0:20:27'He did them again and again to get consistently reliable results.'
0:20:27 > 0:20:31OK, that's about it.
0:20:31 > 0:20:34And that is 24.5 degrees.
0:20:34 > 0:20:37OK, so now, we've determined one angle,
0:20:37 > 0:20:40we now have to go and pick our second spot along the beach.
0:20:44 > 0:20:47'The distance from the first to the second point
0:20:47 > 0:20:50'must be measured accurately - in this case, it's 100 metres -
0:20:50 > 0:20:54'and the two points must be in a straight line with the mountain.
0:21:01 > 0:21:05'I measured the second angle to be about 26.5 degrees and now
0:21:05 > 0:21:10'had enough information to calculate the height of the mountain.
0:21:11 > 0:21:16'Using trigonometry and algebra, Al-Biruni used a formula
0:21:16 > 0:21:19'that relates the height of the mountain to what are known
0:21:19 > 0:21:24'as the tangents of the angles he measured. Using my measurements,
0:21:24 > 0:21:28'I get a figure for this mountain of about 530 metres.
0:21:31 > 0:21:33'I now need only one more measurement
0:21:33 > 0:21:37'to get the size of the Earth, and to get that,
0:21:37 > 0:21:40'I have to climb to the top of the mountain.'
0:21:41 > 0:21:43What Biruni did next was measure
0:21:43 > 0:21:47the angle of the line of sight to the horizon
0:21:47 > 0:21:49as it dips below the horizontal.
0:21:49 > 0:21:52We're going to try and reproduce that,
0:21:52 > 0:21:55so if you can lift it up so that it's hanging...
0:21:57 > 0:22:01..and if I locate the horizon...
0:22:01 > 0:22:03OK.
0:22:03 > 0:22:08..which is about half a degree, about the value that Biruni got.
0:22:10 > 0:22:14Now, here's the really ingenious part.
0:22:14 > 0:22:17Biruni had measured four quantities -
0:22:17 > 0:22:21three angles and a distance. He used two of the angles and the distance
0:22:21 > 0:22:24to work out the height of the mountain.
0:22:24 > 0:22:27Al-Biruni now had everything he needed.
0:22:27 > 0:22:31In essence, Al-Biruni imagined a huge right-angled triangle,
0:22:31 > 0:22:33which has as its three corners
0:22:33 > 0:22:38the mountain top, the horizon and the centre of the Earth.
0:22:38 > 0:22:41Trigonometry told him that the angle he had measured
0:22:41 > 0:22:46and the height of the mountain are related to the radius of the Earth,
0:22:46 > 0:22:49and algebra allowed him to calculate it.
0:22:49 > 0:22:52With this formula, Biruni is able to arrive
0:22:52 > 0:22:54at a value for the circumference of the Earth
0:22:54 > 0:22:59that's within 200 miles of the exact value which we know it to be today,
0:22:59 > 0:23:01about 25,000 miles.
0:23:01 > 0:23:05That's to within an accuracy of less than 1%.
0:23:05 > 0:23:09A remarkable achievement for someone 1,000 years ago.
0:23:20 > 0:23:26For me, Biruni's experiment is an early dramatic example
0:23:26 > 0:23:29of a scientist using mathematical reasoning
0:23:29 > 0:23:31to extend humanity's reach.
0:23:31 > 0:23:35He really pushes the idea that abstract geometrical rules
0:23:35 > 0:23:40governing idealised shapes like perfect circles and triangles
0:23:40 > 0:23:43can help us to comprehend the real world.
0:23:43 > 0:23:46Einstein used precisely the same approach,
0:23:46 > 0:23:49admittedly with much more advanced mathematics,
0:23:49 > 0:23:53when he developed his General Theory of Relativity
0:23:53 > 0:23:56almost 1,000 years after Biruni.
0:23:56 > 0:24:02But both Einstein and Biruni were united by a single common idea -
0:24:02 > 0:24:07with mathematics, humanity can embrace the universe.
0:24:16 > 0:24:20In this story of the birth of the scientific method,
0:24:20 > 0:24:24the Islamic scholars' ability to master sophisticated mathematics
0:24:24 > 0:24:27is the first crucial ingredient.
0:24:35 > 0:24:40The second crucial ingredient is the use of experiment in science.
0:24:40 > 0:24:44Without experiment, theory remains meaningless and sterile.
0:24:44 > 0:24:47It's experimentation that allows theory
0:24:47 > 0:24:49to be held up against the real world.
0:24:49 > 0:24:52It gives it physical meaning.
0:24:52 > 0:24:54But whereas sophisticated mathematics
0:24:54 > 0:24:59grew out of the Empire's obsession with the world's learning through the Translation Movement,
0:24:59 > 0:25:02practical experiment came from the daily needs
0:25:02 > 0:25:05of a powerful and expanding civilisation.
0:25:11 > 0:25:17The driving force of the expanding medieval Islamic Empire was trade.
0:25:17 > 0:25:20It boomed from around 700 AD onwards,
0:25:20 > 0:25:26creating a massive demand for metalworkers, glass-blowers,
0:25:26 > 0:25:31tile-makers, craftsmen of every possible kind.
0:25:32 > 0:25:35When this collided with scholarly tradition,
0:25:35 > 0:25:37symbolised by the Translation Movement,
0:25:37 > 0:25:42it had seismic consequences for science.
0:25:42 > 0:25:45The sciences absolutely depend -
0:25:45 > 0:25:49astronomy is a wonderful example, chemistry is another -
0:25:49 > 0:25:54on really intense relationships between craft traditions
0:25:54 > 0:26:00of instrument making, of working with metal and fire,
0:26:00 > 0:26:05of working with medicines, drugs, plants, and scholarship -
0:26:05 > 0:26:10highly sophisticated literary and mathematical analysis.
0:26:10 > 0:26:15And the Islamic world is just such a place.
0:26:16 > 0:26:21By around 800 AD, the great cities of the Islamic Empire
0:26:21 > 0:26:23dominated the world's trade.
0:26:23 > 0:26:29To its markets came silks, spices, drugs, fruit,
0:26:29 > 0:26:32perfumes and gold from as far afield
0:26:32 > 0:26:36as India and China in the east and Spain in the west.
0:26:36 > 0:26:40Anything that could be traded was.
0:26:51 > 0:26:55A wonderful relic of this medieval trade boom
0:26:55 > 0:26:57are the great Caravanserais,
0:26:57 > 0:27:01like this one in the Syrian capital, Damascus.
0:27:01 > 0:27:05This huge vaulted building was designed as a resting place
0:27:05 > 0:27:09for all the traders and their animals who visited the city.
0:27:14 > 0:27:20On their ground floors were wide spaces for animals and goods
0:27:20 > 0:27:23and, above, there were rooms for the rich merchants
0:27:23 > 0:27:27to refresh themselves before another day of haggling.
0:27:29 > 0:27:32One 10th-century traveller talks of
0:27:32 > 0:27:35the "riches and beauties of the bazaars",
0:27:35 > 0:27:38and that the income of the provinces and localities
0:27:38 > 0:27:42was between 700 and 800 million dinars.
0:27:50 > 0:27:53Markets like this in the Egyptian capital, Cairo,
0:27:53 > 0:27:56still capture the intensity of medieval trade.
0:27:56 > 0:28:00And still surviving in the modern world of the internet
0:28:00 > 0:28:03and the mobile phone is a fantastic example
0:28:03 > 0:28:09of how traders 1,000 years ago communicated across a vast empire.
0:28:09 > 0:28:13THEY SPEAK ARABIC
0:28:13 > 0:28:15So this is a carrier pigeon.
0:28:15 > 0:28:18Its base is here, so wherever you took it all over Egypt,
0:28:18 > 0:28:20it would make its way back to this guy.
0:28:24 > 0:28:28There's a famous story that a rich Cairo merchant
0:28:28 > 0:28:31by the name of Al-Nawr wanted to grow cherry trees,
0:28:31 > 0:28:34so he sent a message by carrier pigeon
0:28:34 > 0:28:37to a contact of his in Damascus, asking for some seeds.
0:28:37 > 0:28:40His contact sent back 500 birds,
0:28:40 > 0:28:43each one carrying a small bag with seeds in it.
0:28:43 > 0:28:46The whole process took just three days.
0:28:46 > 0:28:48Sort of a medieval FedEx, really.
0:28:50 > 0:28:53By 700 AD, the Islamic Empire
0:28:53 > 0:28:57was taking the first steps towards mass production.
0:29:00 > 0:29:05And in this world where knowledge of materials, metals
0:29:05 > 0:29:09and how they're worked became increasingly important,
0:29:09 > 0:29:11one practice flourished.
0:29:13 > 0:29:18It's the practice that was inextricably linked with magic -
0:29:18 > 0:29:22specifically the dream to turn base metals into gold.
0:29:24 > 0:29:27The mysterious practice of alchemy.
0:29:29 > 0:29:33The ancient art of alchemy was a mystical system of belief
0:29:33 > 0:29:35based on spells, symbols and magic.
0:29:35 > 0:29:40But I believe it took Islamic scholars to turn this quasi-religion
0:29:40 > 0:29:44into something much more scientific - chemistry.
0:29:47 > 0:29:50Increasingly, the knowledge of the alchemists
0:29:50 > 0:29:53found more and more practical applications.
0:29:53 > 0:29:58For instance, when during the last decade of the 7th century,
0:29:58 > 0:30:01the ruler of the Islamic Empire, Abd al-Malik,
0:30:01 > 0:30:05made the bold decision to create a common currency
0:30:05 > 0:30:09for all his dominions, he turned to alchemists for help.
0:30:11 > 0:30:15The proportion of gold to other alloyed metals
0:30:15 > 0:30:18that you have to put into the dinar to make the dinar useable,
0:30:18 > 0:30:22otherwise pure gold will become very soft and you can't use it -
0:30:22 > 0:30:26that proportion is adjusted by, believe it or not,
0:30:26 > 0:30:29in this period, the alchemists.
0:30:29 > 0:30:33It is the alchemists who knew how to combine metals together
0:30:33 > 0:30:36and how to get the proportions of this gold to silver
0:30:36 > 0:30:38and gold to bronze and so on.
0:30:48 > 0:30:51- Salaam alaikum.- Salaam alaikum.
0:30:52 > 0:30:55'I hunted down tangible evidence
0:30:55 > 0:30:57'of the skill of medieval Islamic alchemists
0:30:57 > 0:31:01'in the old market in the Syrian capital, Damascus.'
0:31:01 > 0:31:04This is an Islamic dinar.
0:31:04 > 0:31:07The date of this is 128 after Hijri.
0:31:07 > 0:31:13- So the middle of the 8th century? - Almost, almost.- Almost 740s.- Yes.
0:31:13 > 0:31:18'This 1,300-year-old coin, made of an alloy of different metals,
0:31:18 > 0:31:22'isn't just durable - it's also malleable enough
0:31:22 > 0:31:25'to be inscribed with intricate Arabic writing.'
0:31:25 > 0:31:29"No God instead of Allah" and then...
0:31:29 > 0:31:31'Coin-making is one of the many examples
0:31:31 > 0:31:35'of how the practical needs of a booming economy
0:31:35 > 0:31:41'began to turn the magical practice of alchemy into modern chemistry.'
0:31:41 > 0:31:46What's striking about chemistry in the medieval Islamic world
0:31:46 > 0:31:50is the sheer quantity of manuscripts that deal with the subject.
0:31:50 > 0:31:53There are literally thousands that survive dealing with subjects
0:31:53 > 0:31:57as varied as metallurgy, glass-making,
0:31:57 > 0:32:01tile-making, dyeing, perfumery, weaponry.
0:32:01 > 0:32:04There's even a description on how to distil alcohol.
0:32:04 > 0:32:09All this activity clearly points to a bustling economy,
0:32:09 > 0:32:13with consumers, soldiers, engineers, architects
0:32:13 > 0:32:17all demanding innovation and all demanding new technology.
0:32:19 > 0:32:24A great example of applied chemistry in the medieval Islamic world
0:32:24 > 0:32:27was the manufacture of soap.
0:32:27 > 0:32:31This stuff - solid soap that you can really clean yourself with -
0:32:31 > 0:32:35was virtually unknown in Northern Europe until the 13th century,
0:32:35 > 0:32:39when it started being imported from Islamic Spain and North Africa.
0:32:39 > 0:32:42By that time, the manufacture of soap in the Islamic world
0:32:42 > 0:32:45had become virtually industrialised.
0:32:45 > 0:32:50The town of Fez boasted some 27 different soap makers,
0:32:50 > 0:32:54and cities like Nablus, Damascus and, of course, Aleppo
0:32:54 > 0:32:57became world-renowned for the quality of their soaps.
0:32:58 > 0:33:00A 12th-century document
0:33:00 > 0:33:05has the world's first detailed description of how to make soap.
0:33:05 > 0:33:09It mentions a key ingredient and it's a substance
0:33:09 > 0:33:14that became crucial to modern chemistry - an alkali.
0:33:14 > 0:33:17Now, alkaline substances are crucial to soap-making.
0:33:17 > 0:33:20But what's interesting is that our word "alkali"
0:33:20 > 0:33:25derives from the Arabic "al-qali", which means "ashes".
0:33:25 > 0:33:29That's because, back then, alkalis were manufactured from the ashes
0:33:29 > 0:33:32of the roots of certain plants like saltworts.
0:33:36 > 0:33:40Islamic chemists' new understanding of alkalis and other new chemicals
0:33:40 > 0:33:45gave another industry a lift, too - glass-making.
0:33:51 > 0:33:54The Islamic chemists discovered
0:33:54 > 0:33:56that they could change the colour of glass
0:33:56 > 0:34:00using newly discovered chemicals like manganese salts.
0:34:01 > 0:34:06And they built industrial furnaces, some several storeys high,
0:34:06 > 0:34:10to manufacture glass in huge quantities.
0:34:10 > 0:34:12The legacy of their skills
0:34:12 > 0:34:17can still be seen in beautiful stained-glass windows.
0:34:19 > 0:34:26Islamic chemists also developed many other colours, pigments and dyes
0:34:26 > 0:34:30using their new alkalis and metals like lead and tin.
0:34:31 > 0:34:34These helped architects to decorate mosques,
0:34:34 > 0:34:36like this one in the Iranian city of Isfahan,
0:34:36 > 0:34:40in a glorious range of colours and designs.
0:34:48 > 0:34:55'Chemistry was also driven by the booming market in perfumes.'
0:34:55 > 0:34:58Salaam alaikum.
0:34:58 > 0:35:02'In the main market of Damascus, traders still make up
0:35:02 > 0:35:06'your favourite scent as they would have 1,000 years ago.'
0:35:06 > 0:35:10So it basically has a base of alcohol and then he adds to it
0:35:10 > 0:35:16the oils from the plants you want - jasmine and rosewater and mint.
0:35:16 > 0:35:19But these days, they'll use...
0:35:19 > 0:35:23- Very nice.- Yeah, I think I'll buy some of that.
0:35:25 > 0:35:28'Perfumiers pushed chemists
0:35:28 > 0:35:30'to come up with ever more ingenious techniques
0:35:30 > 0:35:36'for extracting subtle and fragile fragrances from flowers and plants.
0:35:39 > 0:35:43'They responded by refining and really establishing a technique
0:35:43 > 0:35:48'that all chemists would instantly recognise today - distillation.'
0:35:48 > 0:35:52Many of the techniques originate with Islamic scholars, or even earlier.
0:35:52 > 0:35:56'Dr Andrea Sella, a chemist from University College London,
0:35:56 > 0:35:59'shows me how distillation was used.'
0:35:59 > 0:36:04Distillations would have been done in devices related to these.
0:36:04 > 0:36:08This is what's now called a retort. We don't really use them any more,
0:36:08 > 0:36:12but "retort" comes from the word "to bend" - in other words,
0:36:12 > 0:36:16a flask which has been bent over, and that's crucial.
0:36:16 > 0:36:19'The shape means that a gas produced in the flask
0:36:19 > 0:36:22'is forced to condense in the spout,
0:36:22 > 0:36:27'and it's the main way of extracting scents from flowers and plants.
0:36:27 > 0:36:31The idea here is you heat at this end and you collect at the other.
0:36:31 > 0:36:34We should actually take a look and see if we can do
0:36:34 > 0:36:37a quick distillation with rose petals.
0:36:37 > 0:36:40First, we need to just put in a little bit of water.
0:36:40 > 0:36:43The water and steam will essentially control the temperature.
0:36:43 > 0:36:46What we don't want is for this to get too hot.
0:36:46 > 0:36:49'The trick with this kind of distillation
0:36:49 > 0:36:52'is to use heat to release the scent molecules,
0:36:52 > 0:36:55'but at the same time making sure
0:36:55 > 0:36:58'that these delicate substances
0:36:58 > 0:37:01'aren't destroyed in the process.'
0:37:01 > 0:37:04You actually use the steam to control the temperature, and the steam
0:37:04 > 0:37:07will carry those smells over.
0:37:07 > 0:37:12You can see the liquid coming up, condensing in the long tube
0:37:12 > 0:37:16- and there is already liquid coming through...- Yeah.
0:37:16 > 0:37:22..and that should be carrying with it some of the rose water smell.
0:37:24 > 0:37:26Mmm, yes, you can really smell it.
0:37:28 > 0:37:33This picture shows a 14th-century perfume distillery.
0:37:33 > 0:37:35Middle Eastern perfumes
0:37:35 > 0:37:38where known to have been sold as far away as India and China.
0:37:41 > 0:37:45The Islamic chemists also played a pivotal role
0:37:45 > 0:37:49in another more gruesome industry - weaponry.
0:37:52 > 0:37:57Historical records during the Crusades talk in terrified tones
0:37:57 > 0:38:00of how the Muslims would attack the Christians
0:38:00 > 0:38:02with burning missiles and grenades,
0:38:02 > 0:38:05striking fear into the hearts of the defenders.
0:38:05 > 0:38:09Many of these used a substance known as Greek Fire.
0:38:11 > 0:38:14Islamic chemists improved on Greek Fire
0:38:14 > 0:38:20by using and refining a naturally occurring resource - petroleum.
0:38:21 > 0:38:25They developed the idea of distilling petroleum, or naft,
0:38:25 > 0:38:29to create a lighter, extremely flammable oil which they mixed
0:38:29 > 0:38:34with other volatile chemicals to make them burn furiously,
0:38:34 > 0:38:37and the result was clearly terrifying.
0:38:40 > 0:38:44What all these medieval Islamic texts on chemistry have in common
0:38:44 > 0:38:47is their great attention to detail,
0:38:47 > 0:38:50which is clearly based on careful experimentation.
0:38:50 > 0:38:53In fact, the whole idea of a laboratory,
0:38:53 > 0:38:57where chemical and industrial processes can be tried out,
0:38:57 > 0:38:59really takes hold at this time.
0:39:02 > 0:39:07The ingenuity of medieval Islamic chemists is impressive.
0:39:07 > 0:39:09But I wanted to know something deeper.
0:39:09 > 0:39:13What contribution did they make to our modern understanding
0:39:13 > 0:39:15of the principles behind chemistry?
0:39:15 > 0:39:21This is the centrepiece of modern chemistry - the periodic table.
0:39:21 > 0:39:24It lists all the known elements.
0:39:24 > 0:39:29Its key idea is to group substances with similar properties together.
0:39:29 > 0:39:33On the far right, for instance, are the inert gases.
0:39:33 > 0:39:36On the far left are the volatile metals.
0:39:36 > 0:39:40The periodic table is triumph of classification,
0:39:40 > 0:39:43giving scientists a way of organising
0:39:43 > 0:39:46their knowledge of the material world.
0:39:46 > 0:39:49Classification is simply a way to think clearly.
0:39:49 > 0:39:54What you need when you have some ideas about how the world works is
0:39:54 > 0:39:57that gives you a schema and you chop the world into categories,
0:39:57 > 0:40:03and that helps you to understand, to make sense of what's around you.
0:40:03 > 0:40:07People had been trying to classify the material world
0:40:07 > 0:40:11since ancient times. The Greeks, for instance, thought there were just
0:40:11 > 0:40:17four worldly elements - air, earth, fire and water.
0:40:17 > 0:40:21But this idea was a philosophical one and had little practical value.
0:40:22 > 0:40:26And that's what medieval Islamic chemists really changed.
0:40:26 > 0:40:29They used experimental observations
0:40:29 > 0:40:32to classify the stuff the world is made of.
0:40:32 > 0:40:37At the forefront of this was a medieval Islamic doctor and chemist
0:40:37 > 0:40:41called Ibn Zakariya Al-Razi, who was born here in the city of Ray,
0:40:41 > 0:40:46just outside the Iranian capital Tehran in 865 AD.
0:40:48 > 0:40:52Al-Razi's classification was very different from the Greek one.
0:40:52 > 0:40:55He argued, for instance, that minerals -
0:40:55 > 0:40:57roughly stuff we dig out of the ground -
0:40:57 > 0:41:00should be classified into six groups,
0:41:00 > 0:41:04depending on their observed chemical properties -
0:41:04 > 0:41:10the same guiding principle that lies behind the modern periodic table.
0:41:10 > 0:41:14Now, I've brought materials from his classification scheme.
0:41:14 > 0:41:17We have here what he called the spirits,
0:41:17 > 0:41:21we have the metallic bodies, we have the stones,
0:41:21 > 0:41:25then we have the attraments, the salts and finally the boraxes.
0:41:26 > 0:41:28'Each of Al-Razi's groups
0:41:28 > 0:41:32'had a profoundly different experimental behaviour.
0:41:32 > 0:41:36'For instance, spirits were flammable.
0:41:36 > 0:41:39'The metals were shiny and malleable.
0:41:39 > 0:41:43'Salts dissolved in water.
0:41:43 > 0:41:47'Of course, these classifications are not the way we do it today,
0:41:47 > 0:41:50'but the point is that, for the first time,
0:41:50 > 0:41:53'Al-Razi was grouping substances on the basis
0:41:53 > 0:41:59'of experimental observations, not philosophical musings.'
0:41:59 > 0:42:03We've come over 1,000 years since the work of Al-Razi.
0:42:03 > 0:42:06What sort of debt does modern chemistry
0:42:06 > 0:42:09owe to him for his classification?
0:42:09 > 0:42:14Well, I think with Razi, we start to see the first classification
0:42:14 > 0:42:17which really leads on to further experiments,
0:42:17 > 0:42:21the first schema which allows people to start doing rational work.
0:42:21 > 0:42:26And so, really, he lies at the start of almost formal chemistry,
0:42:26 > 0:42:30which ultimately leads to our periodic table.
0:42:34 > 0:42:36I believe that what we see
0:42:36 > 0:42:40in the work of the Islamic chemists and alchemists
0:42:40 > 0:42:44is the first tentative steps to a new science.
0:42:44 > 0:42:48Yes, by our standards, it contained a lot of magic and mumbo jumbo,
0:42:48 > 0:42:51but it placed an emphasis on experimentation
0:42:51 > 0:42:53that was truly revolutionary.
0:42:56 > 0:42:58But bigger and better was to come,
0:42:58 > 0:43:03because Islamic mathematics and the experimental techniques
0:43:03 > 0:43:07of Jabir Ibn Hayyan and Al-Razi were about to be welded together
0:43:07 > 0:43:11in a completely innovative way that would revolutionise their work
0:43:11 > 0:43:14and create the modern scientific age.
0:43:18 > 0:43:20Until the 9th or 10th centuries,
0:43:20 > 0:43:24ideas about science and how the natural world worked
0:43:24 > 0:43:28were dominated by the Greek philosopher Aristotle,
0:43:28 > 0:43:31and they were very different from ours today.
0:43:31 > 0:43:34He believed that mathematics was concerned
0:43:34 > 0:43:37only with an abstract world of perfect forms,
0:43:37 > 0:43:42of idealised shapes like circles, squares and triangles.
0:43:42 > 0:43:47It had no power to explain what we observe in the world around us,
0:43:47 > 0:43:52a world characterised by irregular, wonky shapes and constant change.
0:43:53 > 0:44:00"Physics" is a Greek word meaning "the science of change",
0:44:00 > 0:44:03and for the classical Greek tradition,
0:44:03 > 0:44:06there was a strong sense in which
0:44:06 > 0:44:12the science of change was in contradiction with mathematics.
0:44:12 > 0:44:16Mathematics dealt with perfect knowledge,
0:44:16 > 0:44:21with the unchanging world of mathematical forms.
0:44:21 > 0:44:24And it seemed, in principle, extremely unlikely
0:44:24 > 0:44:29that processes of coming into being and passing away,
0:44:29 > 0:44:32of growth and of decay,
0:44:32 > 0:44:34of qualitative change,
0:44:34 > 0:44:41could be captured with the beauties of geometry and mathematics.
0:44:45 > 0:44:48The story of how humanity shook off this idea
0:44:48 > 0:44:53and began to see that mathematics is actually an incredibly powerful way
0:44:53 > 0:44:57of describing the world around us is long and complicated.
0:44:59 > 0:45:03But for me, Islamic scientists played a crucial role,
0:45:03 > 0:45:08and I believe one man really led this movement to turn mathematics
0:45:08 > 0:45:14from a language of abstract thought into a truly practical science.
0:45:14 > 0:45:19He was, like me, from Iraq, and his name was Ibn Al-Haytham.
0:45:19 > 0:45:24What Al-Haytham and his contemporaries argued for
0:45:24 > 0:45:28was the possibility in a way of a single science,
0:45:28 > 0:45:33which would be both mathematical and philosophical,
0:45:33 > 0:45:38which would link together a physics - a science of change -
0:45:38 > 0:45:41with a mathematics - a science of quantity.
0:45:41 > 0:45:45And that seems to me to be radical and crucial
0:45:45 > 0:45:48for the construction of new forms of reliable knowledge.
0:45:48 > 0:45:55Ibn Al-Haytham was born in 965 AD in the southern Iraqi town of Basra,
0:45:55 > 0:45:59and other scholars regarded him as a prodigy.
0:45:59 > 0:46:03He shot to scientific fame just after the turn of the first millennium
0:46:03 > 0:46:06and was an incredibly innovative and brilliant scholar.
0:46:06 > 0:46:10His reputation as an intellect spread throughout the empire.
0:46:10 > 0:46:14But it was this reputation that'd almost cause him to lose everything
0:46:14 > 0:46:17when he took up the poisoned chalice
0:46:17 > 0:46:20of trying to tame one of the world's greatest rivers.
0:46:29 > 0:46:33There's a wonderful, if suspiciously apocryphal, story
0:46:33 > 0:46:38about how Ibn Al-Haytham's career as a scientist was transformed.
0:46:38 > 0:46:43It concerns the Nile and how, just after the turn of the millennium,
0:46:43 > 0:46:46Ibn Al-Haytham was asked by the ruler of Egypt
0:46:46 > 0:46:49to find a way of controlling it. Could he prevent
0:46:50 > 0:46:55its unpredictable and potentially devastating floods and droughts?
0:46:55 > 0:46:59But it didn't take Ibn Al-Haytham long to realise
0:46:59 > 0:47:03that the Nile was way too large to control.
0:47:03 > 0:47:06On hearing this, the Caliph flew into a terrible rage
0:47:06 > 0:47:10and ordered Ibn Al-Haytham's execution.
0:47:10 > 0:47:14Ibn Al-Haytham responded by feigning madness.
0:47:14 > 0:47:18The execution was called off and he was placed under house arrest.
0:47:20 > 0:47:24There, with time on his hands to contemplate, the story goes,
0:47:24 > 0:47:29Ibn Al-Haytham considered deep and fundamental questions in physics,
0:47:29 > 0:47:34and he began with a truly enigmatic and universal problem.
0:47:34 > 0:47:39He asked if the wonderful and entirely mysterious nature of light and vision
0:47:39 > 0:47:43could be explained by mathematics and geometry.
0:47:45 > 0:47:48Under house arrest, or perhaps here in the rooms
0:47:48 > 0:47:53of Al-Azhar University in Cairo, Ibn Al-Haytham carried out
0:47:53 > 0:47:57a series of experiments that created the modern science of optics.
0:47:58 > 0:48:01'I'm with Dr El-Bizri,
0:48:01 > 0:48:04'who has carefully studied Ibn Al-Haytham's work.
0:48:04 > 0:48:08'He explained that Ibn Al-Haytham first considered
0:48:08 > 0:48:11'the Aristotelian explanation for how we see,
0:48:11 > 0:48:15'an explanation that was completely un-mathematical.
0:48:15 > 0:48:19'Aristotle argued that we when we look at, say, a tree,
0:48:19 > 0:48:22'its essence or form emanates from it
0:48:22 > 0:48:26'and then mysteriously flows into our eyes.'
0:48:26 > 0:48:30So if I'm, for instance, now looking at the buildings
0:48:30 > 0:48:36and the trees on the banks of the Nile, I'm receiving the forms
0:48:36 > 0:48:41of these buildings and these trees in the eye
0:48:41 > 0:48:43abstracted from their matter.
0:48:45 > 0:48:46'According Dr El-Bizri,
0:48:46 > 0:48:50'Ibn Al-Haytham found this idea deeply unsatisfactory.
0:48:50 > 0:48:53'He wanted a mathematical explanation.
0:48:55 > 0:48:58'And looking back at existing Greek writings,
0:48:58 > 0:49:02'he found one, although it was obscure and bizarre.
0:49:04 > 0:49:07'This idea claimed that we see,
0:49:07 > 0:49:10'because light rays come out of the eye.'
0:49:10 > 0:49:14Ultimately, it says that vision occurs by way of the emission
0:49:14 > 0:49:20from the eye of light that is shaped in the form of a pyramid or a cone.
0:49:22 > 0:49:25This cone-shaped beam illuminates what we're looking at
0:49:25 > 0:49:29and is defined by nice geometric straight lines.
0:49:31 > 0:49:35It seems Ibn Al-Haytham liked this mathematical approach,
0:49:35 > 0:49:38but immediately spotted its flaws.
0:49:38 > 0:49:42If we see, he asked, because light comes out of the eye,
0:49:42 > 0:49:46why does it hurt when you look at a bright object like the sun
0:49:46 > 0:49:49but not hurt when you look at something dim?
0:49:49 > 0:49:53Or at night, can light from our eyes
0:49:53 > 0:49:57really be lighting up distant objects in the sky?
0:49:57 > 0:50:00So, in an inspired piece of thinking,
0:50:00 > 0:50:04Ibn Al-Haytham combined the two Greek ideas
0:50:04 > 0:50:09and defined our modern understanding of light and vision.
0:50:09 > 0:50:14Light, he said, does travel in straight lines that obey geometric laws.
0:50:14 > 0:50:20But instead of them coming out of the eye, these rays travel into it.
0:50:20 > 0:50:25It is the development of an entirely new theory, and also methodologically
0:50:25 > 0:50:28it is the beginnings of mathematising physics.
0:50:31 > 0:50:35What Ibn Al-Haytham did was take the principles of geometry,
0:50:35 > 0:50:38with its rules governing straight lines,
0:50:38 > 0:50:42and applied them to the real world. He then designed experiments
0:50:42 > 0:50:46to test whether the real world measured up to his mathematics.
0:50:48 > 0:50:51In about 1020, Ibn Al-Haytham published
0:50:51 > 0:50:55his ground-breaking geometric explanation of light
0:50:55 > 0:50:59in his Kitab al-Manazir, or Book of Optics.
0:50:59 > 0:51:02And what really marks this book out as science
0:51:02 > 0:51:06is that Ibn Al-Haytham carefully justifies his theories
0:51:06 > 0:51:11with detailed experiments that others can repeat and verify.
0:51:11 > 0:51:16He starts from first principles to find out how light travels.
0:51:21 > 0:51:24For his first experiment, Ibn Al-Haytham
0:51:24 > 0:51:29wanted to test the idea that light travels in straight lines.
0:51:29 > 0:51:34To do this, he took a straight tube on which he'd drawn a straight line
0:51:34 > 0:51:39down the side and a ruler with a straight line down the length of it.
0:51:39 > 0:51:41And by matching the two together,
0:51:41 > 0:51:45he was convinced then that the tube was straight.
0:51:45 > 0:51:49If he uses it to look at an object - in this case, a candle -
0:51:49 > 0:51:53he can see the candle through the tube, which is good evidence
0:51:53 > 0:51:57that the light is travelling up in a straight line. But to be sure,
0:51:57 > 0:52:00he then blocked the end of the tube.
0:52:00 > 0:52:04And then, by looking at the candle again, he can't see it,
0:52:04 > 0:52:09because what this does is confirm the light doesn't travel to his eye
0:52:09 > 0:52:13via any other route in a curved path outside the tube.
0:52:13 > 0:52:16Proof that light only travels in a straight line.
0:52:16 > 0:52:19Now, this might sound quite trivial and obvious to us,
0:52:19 > 0:52:23but Ibn Al-Haytham was starting from first principles.
0:52:23 > 0:52:27Then, through experiment, he extends
0:52:27 > 0:52:31his "light travels in straight lines" idea to many other phenomena.
0:52:31 > 0:52:35He explains how mirrors work, by arguing that the angle
0:52:35 > 0:52:40the ray comes in at is the same as the angle it bounces off at.
0:52:40 > 0:52:43He explains what we now call refraction,
0:52:43 > 0:52:48why objects look kinked in a glass of water - arguing that light rays
0:52:48 > 0:52:52bend when they move from one medium to another.
0:52:52 > 0:52:56And then he tackles the nature of vision.
0:52:56 > 0:52:59Ibn Al-Haytham wanted to understand
0:52:59 > 0:53:02how an object makes an image on the retina of the eye.
0:53:02 > 0:53:07So he built what he believed was a stripped down version of the eye,
0:53:07 > 0:53:11which is basically a black box with a tiny hole in it.
0:53:11 > 0:53:13This is what we call today the camera obscura.
0:53:13 > 0:53:19He next took his subject, in this case Anna, who's very brightly lit,
0:53:19 > 0:53:22and we now go inside the box to see what the image looks like.
0:53:25 > 0:53:29Now that I'm inside the camera obscura and I've allowed my eyes
0:53:29 > 0:53:32to get used to the dark, we can open the hole.
0:53:32 > 0:53:37And there we clearly see the image of Anna waving on the screen.
0:53:37 > 0:53:41But the image is inverted, because light travels in straight lines,
0:53:41 > 0:53:44so the light from her head has to move diagonally downwards
0:53:44 > 0:53:46to hit the bottom of the screen
0:53:46 > 0:53:50and light from her feet travels diagonally upwards to hit the top.
0:53:50 > 0:53:54But, more importantly, what this proved to Ibn Al-Haytham is
0:53:54 > 0:53:58there's a one-to-one correspondence between every point on the object -
0:53:58 > 0:54:02on Anna - and every point on her image on the screen.
0:54:04 > 0:54:06Just like a modern scientific paper,
0:54:06 > 0:54:11the attention to detail in the Kitab al-Manazir is incredible.
0:54:11 > 0:54:15His book isn't just a dry scientific treatise -
0:54:15 > 0:54:18it's a manual for future generations.
0:54:18 > 0:54:21In his work, he constantly justifies
0:54:21 > 0:54:25his theories about light with experimental observation
0:54:25 > 0:54:28and he describes his experiments in great detail,
0:54:28 > 0:54:32so that other people can repeat them and confirm his ideas.
0:54:32 > 0:54:36His message is, "Don't take my word for it, see for yourself."
0:54:36 > 0:54:40I believe that Ibn Al-Haytham was one of the very first people
0:54:40 > 0:54:43to ever work like this. This, for me,
0:54:43 > 0:54:47is the moment that science itself is summoned into existence
0:54:47 > 0:54:50and becomes a discipline in its own right.
0:54:58 > 0:55:03What I find so impressive about Ibn Al-Haytham is how,
0:55:03 > 0:55:06once he arrives at his mathematical theories,
0:55:06 > 0:55:10he then uses them to extend our knowledge of the real world.
0:55:10 > 0:55:15So, for instance, he used his new ideas about light to deduce
0:55:15 > 0:55:19that the Earth's atmosphere is of a finite thickness,
0:55:19 > 0:55:22and he even estimated what that thickness is.
0:55:23 > 0:55:29He did it basically by measuring how long twilight lasts.
0:55:29 > 0:55:33He rightly assumed that the reason it continues to be light
0:55:33 > 0:55:35after the sun has dropped below the horizon
0:55:35 > 0:55:40must be because its rays bend as they enter the Earth's atmosphere.
0:55:42 > 0:55:45The length of twilight and an educated guess
0:55:45 > 0:55:48for what we today call the air's refractive index
0:55:48 > 0:55:50gave Ibn Al-Haytham a way
0:55:50 > 0:55:54of estimating the thickness of the Earth's atmosphere.
0:55:54 > 0:55:58He came up with a figure of around 40 kilometres -
0:55:58 > 0:56:02about half of the modern value. That's pretty impressive.
0:56:02 > 0:56:05It really shows how mathematics
0:56:05 > 0:56:08extends the power of science to explain.
0:56:14 > 0:56:18On my journey so far, I've been overwhelmed by
0:56:18 > 0:56:22the sheer intellectual ambition of medieval Islamic scientists.
0:56:22 > 0:56:26When their leaders asked them to find out the size of the world,
0:56:26 > 0:56:31scholars like Al-Biruni used mathematics in startling new ways
0:56:31 > 0:56:35to reach out and describe the universe.
0:56:38 > 0:56:43And as trade and commerce boomed, scientists like Al-Razi
0:56:43 > 0:56:48responded by developing a new kind of experimental science - chemistry.
0:56:50 > 0:56:55But if there's one Islamic scientist we should remember above all others,
0:56:55 > 0:56:58it is, in my view, Ibn Al-Haytham,
0:56:58 > 0:57:03for doing so much to create what we now call the scientific method.
0:57:06 > 0:57:09The scientific method is, I believe,
0:57:09 > 0:57:14the single most important idea the human race has ever come up with.
0:57:14 > 0:57:18There is no other strategy that tells us how to find out
0:57:18 > 0:57:22how the universe works and what our place in it is.
0:57:22 > 0:57:26It's also delivered technologies that have transformed our lives.
0:57:26 > 0:57:29So, the next time you jet off on holiday or use a mobile phone
0:57:29 > 0:57:32or get vaccinated against a deadly disease,
0:57:32 > 0:57:36remember Ibn Al-Haytham, Ibn Sina, Al-Biruni
0:57:36 > 0:57:39and countless other Islamic scholars 1,000 years ago
0:57:39 > 0:57:43who struggled to make sense of the universe
0:57:43 > 0:57:45using crude mirrors and astrolabes.
0:57:45 > 0:57:48They didn't get all the right answers,
0:57:48 > 0:57:52but they did teach us how to ask the right questions.
0:58:04 > 0:58:08In the next episode, I travel to Syria and Northern Iran
0:58:08 > 0:58:12to find out about the great Islamic scientists
0:58:12 > 0:58:14who revolutionised astronomy,
0:58:14 > 0:58:16making it a truly modern science.
0:58:17 > 0:58:20And I'll also discover how the man many consider
0:58:20 > 0:58:25to be the father of the European scientific renaissance, Copernicus,
0:58:25 > 0:58:29borrowed from Islamic astronomical theories.
0:58:29 > 0:58:32And I'll unravel the mystery of how
0:58:32 > 0:58:36the Golden Age of Islamic science came to an end.
0:58:44 > 0:58:47Subtitles by Red Bee Media Ltd
0:58:47 > 0:58:50E-mail: subtitling@bbc.co.uk