The Empire of Reason Science and Islam


The Empire of Reason

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Every now and then, an idea takes form that changes everything -

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it revolutionises the way we see and understand the world around us.

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I believe that just such an idea

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took form in the medieval Islamic world.

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It's the idea that everything,

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from the stars above to the working of our own bodies,

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is not arbitrary or whimsical, but subject to certain systematic rules.

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And what's more, that we humans can work out what those rules might be

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and then, we can refine and test our theories

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through observation and experiments.

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In other words, it's the idea we now call the scientific method.

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'For me, the story of the scientific renaissance that took place in

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'the medieval Islamic world is a personal one.

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'This is my cousin Samir's house in the Iranian capital, Tehran.

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'I haven't seen some of the relatives

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'on my father's side of the family in over 30 years.'

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This is my not so tall, but very beautiful Auntie Anis.

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'The Al-Khalili family is originally

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from the city of Najaf in Iraq, south of Baghdad.

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'In fact, I grew up in Iraq.

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'But when Saddam Hussein came to power, the family split.

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'Many of the Al-Khalilis fled here to Iran.

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'As my mother's English, I came to Britain with my parents.'

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There, I pursued my passion for science

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and am now a professor of physics at the University of Surrey.

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But now, I find that my own scientific work

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and my Arabic and Islamic heritage are intertwined.

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On my journey through the Middle East, I discovered that

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an astonishing leap in scientific knowledge

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took place here 1,000 years ago

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under a powerful and flourishing Islamic Empire.

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Wealthy, powerful, successful cultures

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will produce enormous advances

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in understanding and in technique,

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and that's just what we find in Islam, in Baghdad,

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under a series of successful, powerful,

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wealthy and self-confident Islamic regimes.

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Over 1,000 years ago, the Islamic Empire was the largest in the world.

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It governed an estimated 60 million people -

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that was over 30% of the world's population.

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I found an archaeological fragment of this glorious past

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in a suburb of Tehran, not far from my cousin's house.

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These ancient walls tucked behind a backstreet

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on the outskirts of southern Tehran are literally all that remain

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of the ancient city of Ray.

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The city that the great Persian geographer Al-Muqaddasi described

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as one of the glories of Islam.

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Of course, Ray was just one of a number of cities

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that flourished under early Islamic rule.

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From Baghdad, its capital,

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the empire spread across thousands of miles

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from North Africa through to central Asia.

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Cities like Al-Askar, Basra, Merv, Gurganj, Bukhara,

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each powerful and thriving cities.

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Each would have been rich in trade, alive with culture.

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Each would have had its own libraries, its own academies.

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These were powerhouses of the new science.

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This really was a Golden Age.

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Think of that span of land.

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This is larger than any empire human civilisation

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had ever known. Within that span of land,

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you can plug in the Roman Empire and it will fill

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just maybe one-third of it, one-half of it or something like that.

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CHANTING IN ARABIC

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Reminders of this great Islamic Empire

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are everywhere in the Arab world today.

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This football match in the Syrian capital, Damascus, is being played

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at the Abbasid Stadium. That's the name of the family

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who ruled the Islamic Empire from 750 to 1258 AD.

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This large territory allowed them to raise enormous tax revenues

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to fund a search for knowledge and scholarship

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which became known as the Translation Movement.

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They sent scholars around the known world to gather up great books

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and have them translated into Arabic.

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It's a legacy that's still alive in the minds of most modern Arabs.

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For medieval Islamic leaders, scientific knowledge

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was crucial to successfully running a vast empire.

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They did have a big and sophisticated governmental administration,

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and that needed knowledge. If you wanted to be an administrator

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and had to assess taxes, you needed to know about mathematics.

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It also wants to be able to build monumental buildings. That requires a knowledge of architecture,

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and mathematical skills to construct fine buildings safely.

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Medicine just to keep the elite happy and healthy.

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Those are the areas of knowledge

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which are first translated from other languages into Arabic.

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The legacy of the medieval Islamic Empire

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is scattered across a vast region.

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There's architectural masterpieces,

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like the Ummayyad Mosque in Damascus,

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the Jame Mosque in Isfahan,

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and Al-Azhar University and mosque in Cairo.

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And then there are many ruins that still hint at past glories,

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like this, a crumbling 8th-century palace deep in the Syrian Desert.

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And this, a huge Muslim palace called Madinat Al-Zahra,

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currently being excavated in Southern Spain.

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These are the impressive ruins of Madinat Al-Zahra,

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the fantastic palace city built outside Cordoba

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in the 9th century by Abd al-Rahman III,

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who was the greatest of all the Andalucian caliphs.

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At the time that it was ruined, Cordoba was in fact

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the largest and most important city in Europe,

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a rival to Baghdad in the east

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for a centre for Islamic scholarship and science.

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And as I travelled, I saw how science,

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especially numerical record-keeping and measurement,

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was crucial to dealing with the challenges of running a vast empire.

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This is the mighty River Nile

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as it flows through the Egyptian capital, Cairo.

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Since antiquity, its unpredictable floods have determined the fate

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of Egypt's people, bringing years of lean and plenty.

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By the 8th century, Cairo was part of the Islamic Empire

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and the new rulers took the first step

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to understanding this mighty river in a scientific way.

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They built a device to measure it.

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Ha!

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It's an amazing structure, right?

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'Dr Nader El-Bizri of the Institute of Ismaili Studies,

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'is showing me the Nileometer. It's basically a huge colonnade

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'that was built in a chamber connected by tunnels to the river.

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'As the water rose or fell,

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'its height could be read from the central column.'

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The central colonnade here is ultimately a measuring instrument.

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It is very precise. It's almost one inch between a marking and another.

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Presumably they need to know seasonal variations in the height.

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And to try to have some sort of record,

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so that they could measure against certain years,

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-where a year was known for a high level of flood...

-Yes.

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..versus another year known for its drought.

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-Then they might perhaps take some precautions.

-Yes.

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'The data collected from the Nileometer had one practical use.

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'By creating an objective record of the river's behaviour,

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'it allowed the rulers of the time to calculate

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'how much tax to levy on Egypt's farmers.

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'But whatever its uses, what I love about the Nileometer

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'is how it shows that to understand the world,

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'you have to build devices to measure it.'

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If you think very hard, it's never obvious

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that measurement can make sense of the world around us.

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The world appears, as a Western philosopher once put it,

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like a buzzing, blooming confusion, and the idea that we as a group

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have tools which are reliable, which have sufficient integrity,

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which have an intellectual grip that can make sense

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of the basic phenomena we see around us, that's an astonishing idea.

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'And one medieval Islamic ruler made measurement a personal obsession,

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'giving it a scale and ambition that was truly unprecedented.'

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His name was Al-Ma'mun,

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and he became the caliph, or ruler, of the Islamic Empire in 813 AD.

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Al-Ma'mun lived in a culture without portraiture,

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so all we have are later impressions of what he might have looked like.

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Al-Ma'mun funded a range of scientific research,

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but one particular project was a personal favourite of his.

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And given that he ruled over such a large territory,

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it's hardly surprising what it was - map-making.

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In the second decade of the 9th century AD,

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Al-Ma'mun commissioned a new map of the world,

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and his scientists did a pretty impressive job.

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It was a vast improvement on all maps that had come before.

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What we see here is that they've really got the Mediterranean,

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its shape and how it links in with the Black Sea, the Middle East,

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even the whole of Asia as far as China and Japan.

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They've even got the Indian Ocean and the East coast of Africa.

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It all looks pretty impressive for the known world at the time.

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Of course, what Al-Ma'mun ultimately wanted to know

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was how much of the Earth as a whole did he possess.

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And this begged the question, just how big is the Earth?

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It's a sign of amazing ambition that groups of scholars

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and craftsmen together can, as it were, capture the world.

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Where does that ambition and that confidence come from?

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Part of it comes from religious faith.

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Because the world was made

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by someone a bit like us, but much smarter,

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if we're smart enough, the thought was,

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we could probably make sense of a bit of what he did.

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And that's very clear as a motivation

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in a lot of Islamic, as in a lot of Christian, science.

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And more specifically, the practice of Islam demanded

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that its followers have a very clear idea

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of the size and shape of the world.

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This is crucial information for Muslims, because,

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wherever they are in the world, they need to know

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the direction to Mecca for their prayer. This is known as al-qibla.

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Now, over such a large territory,

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finding the direction to Mecca is not a trivial problem.

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This problem was wonderfully illustrated

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when a mosque was built recently in Washington DC.

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Some worshippers were confused,

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because the direction they were told to face when praying

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was slightly north and not south-east as they expected.

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After all, Mecca is south-east of Washington

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and, on a flat map, it does appears to lie in that direction.

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But on a curved sphere, the shortest distance

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between any two points follows what's called a great circle.

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So, for example, this great circle line between Washington and Mecca

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is quite different to what you might expect,

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so the direction to Mecca from Washington

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actually points slightly north-east rather than south-east.

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Of course, this is complicated stuff, but the key point

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for Islamic scholars is that knowing the direction to Mecca

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requires a knowledge of how steeply the Earth curves,

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and that means knowing how big it is.

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So Al-Ma'mun commissioned his very best scientists to measure it.

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-Hello.

-Hello.

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Nice to meet you.

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'To understand how they did it, I'm meeting up

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'with Professor Sami Chaloubi from Aleppo University in Syria,

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'who's an expert in early Islamic science.

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'Professor Chaloubi began by explaining the measuring technique,

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'which Al-Ma'mun's scientists first used

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'and which they had inherited from the Greeks.'

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We're now talking about this,

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the earlier Eratosthenes technique of measuring the circumference.

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It was repeated by the Abbasid astronomers.

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It was to measure the distance between two points

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and then look at the angle of inclination of the sun.

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So in Egypt, in Aswan down in the south, they regard the sun

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as being vertical - this is near to the equator -

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and they worked out how far away from the vertical the sun was

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if they measured it from the north of Egypt,

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in Alexandria, which is on the Mediterranean coast.

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'Al-Ma'mun's astronomers repeated the Greek experiments

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'in Syria and Iraq by measuring the angle of the sun in the sky at noon

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'at one known location.

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'They then walked due north to a second location,

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'carefully measuring the distance they travelled.'

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At the second location,

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they once again measured the angle of the sun at noon.

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This angle would have been slightly smaller than the first one.

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With these figures, Al-Ma'mun's astronomers

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were able to estimate the Earth's circumference.

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They got a value of 24,000 miles -

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within 4% of the correct value. Not bad, you might think.

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But this method was flawed and ultimately unreliable.

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The main problem was that measuring the distance between two locations

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was incredibly difficult. It could only be done

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by the unreliable method of counting paces

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as you walked through the burning desert.

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A more reliable and sophisticated method for estimating the Earth's size was needed,

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and two centuries after Al-Ma'mun died, it came.

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What made it possible was a great leap of imagination

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and the fact that, by 900 AD,

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much of the world's mathematical knowledge

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had been translated into Arabic,

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so scholars could scrutinise and improve on it.

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Out of this obsession with scholarly learning

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came a true mathematical visionary -

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Abu Rayhan Muhammad Ibn Ahmad Al-Biruni.

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And like all Islamic scholars of the time,

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Al-Biruni was obsessed with the science and mathematics

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of the ancient Greeks, Babylonians and Indians.

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And because of the success of the Translation Movement,

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he had literally on his desk the great work on geometry by Euclid,

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Ptolemy's Almagest, the Indian text the Sindhind,

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and the famous work on algebra by Al-Khwarizmi.

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CONVERSATION IN ARABIC

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'Professor Chaloubi has brought along the book

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'in which Al-Biruni describes how he combined algebra and geometry

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'with some very simple and practical measurements

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'to solve the epic problem of how to calculate the size of the Earth.'

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-Biruni's text.

-And this his...?

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-Al-Qanoon Al-Masoodi.

-The Masoodi Canon.

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This is Biruni's Canon, which I've been trying to get hold of,

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where he describes this fantastic experiment.

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Oh, you've found the page.

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Yes.

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'Having read Al-Biruni's description of how to

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'estimate the size of the world, I wanted to try it for myself.'

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First, he had to find a fairly high mountain

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from the top of which he could see a flat horizon -

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in this case, the sea.

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What I love about this story is that,

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with a few simple measurements around this small mountain peak,

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you can work out the size of the whole world.

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Al-Biruni's first step was to work out the height of the mountain.

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He did this by going to two points at sea level a known distance apart

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and then measuring the angles from these points to the mountain top.

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So, to measure the angle to the mountain top,

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Biruni had to use a device like this, called an astrolabe.

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It's basically a giant protractor.

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It has the angles in degrees marked around the outside

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and a pointer to help him determine his line of sight.

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So, if we try now and determine the angle to the top,

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it has to hang freely. And then... OK, so if you let it hang...

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'I'd like to stress, if you haven't noticed already, that Al-Biruni

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'would have made his measurements more meticulously than I am.

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'He did them again and again to get consistently reliable results.'

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OK, that's about it.

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And that is 24.5 degrees.

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OK, so now, we've determined one angle,

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we now have to go and pick our second spot along the beach.

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'The distance from the first to the second point

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'must be measured accurately - in this case, it's 100 metres -

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'and the two points must be in a straight line with the mountain.

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'I measured the second angle to be about 26.5 degrees and now

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'had enough information to calculate the height of the mountain.

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'Using trigonometry and algebra, Al-Biruni used a formula

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'that relates the height of the mountain to what are known

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'as the tangents of the angles he measured. Using my measurements,

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'I get a figure for this mountain of about 530 metres.

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'I now need only one more measurement

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'to get the size of the Earth, and to get that,

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'I have to climb to the top of the mountain.'

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What Biruni did next was measure

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the angle of the line of sight to the horizon

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as it dips below the horizontal.

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We're going to try and reproduce that,

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so if you can lift it up so that it's hanging...

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..and if I locate the horizon...

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OK.

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..which is about half a degree, about the value that Biruni got.

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Now, here's the really ingenious part.

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Biruni had measured four quantities -

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three angles and a distance. He used two of the angles and the distance

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to work out the height of the mountain.

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Al-Biruni now had everything he needed.

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In essence, Al-Biruni imagined a huge right-angled triangle,

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which has as its three corners

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the mountain top, the horizon and the centre of the Earth.

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Trigonometry told him that the angle he had measured

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and the height of the mountain are related to the radius of the Earth,

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and algebra allowed him to calculate it.

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With this formula, Biruni is able to arrive

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at a value for the circumference of the Earth

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that's within 200 miles of the exact value which we know it to be today,

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about 25,000 miles.

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That's to within an accuracy of less than 1%.

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A remarkable achievement for someone 1,000 years ago.

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For me, Biruni's experiment is an early dramatic example

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of a scientist using mathematical reasoning

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to extend humanity's reach.

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He really pushes the idea that abstract geometrical rules

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governing idealised shapes like perfect circles and triangles

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can help us to comprehend the real world.

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Einstein used precisely the same approach,

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admittedly with much more advanced mathematics,

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when he developed his General Theory of Relativity

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almost 1,000 years after Biruni.

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But both Einstein and Biruni were united by a single common idea -

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with mathematics, humanity can embrace the universe.

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In this story of the birth of the scientific method,

0:24:160:24:20

the Islamic scholars' ability to master sophisticated mathematics

0:24:200:24:24

is the first crucial ingredient.

0:24:240:24:27

The second crucial ingredient is the use of experiment in science.

0:24:350:24:40

Without experiment, theory remains meaningless and sterile.

0:24:400:24:44

It's experimentation that allows theory

0:24:440:24:47

to be held up against the real world.

0:24:470:24:49

It gives it physical meaning.

0:24:490:24:52

But whereas sophisticated mathematics

0:24:520:24:54

grew out of the Empire's obsession with the world's learning through the Translation Movement,

0:24:540:24:59

practical experiment came from the daily needs

0:24:590:25:02

of a powerful and expanding civilisation.

0:25:020:25:05

The driving force of the expanding medieval Islamic Empire was trade.

0:25:110:25:17

It boomed from around 700 AD onwards,

0:25:170:25:20

creating a massive demand for metalworkers, glass-blowers,

0:25:200:25:26

tile-makers, craftsmen of every possible kind.

0:25:260:25:31

When this collided with scholarly tradition,

0:25:320:25:35

symbolised by the Translation Movement,

0:25:350:25:37

it had seismic consequences for science.

0:25:370:25:42

The sciences absolutely depend -

0:25:420:25:45

astronomy is a wonderful example, chemistry is another -

0:25:450:25:49

on really intense relationships between craft traditions

0:25:490:25:54

of instrument making, of working with metal and fire,

0:25:540:26:00

of working with medicines, drugs, plants, and scholarship -

0:26:000:26:05

highly sophisticated literary and mathematical analysis.

0:26:050:26:10

And the Islamic world is just such a place.

0:26:100:26:15

By around 800 AD, the great cities of the Islamic Empire

0:26:160:26:21

dominated the world's trade.

0:26:210:26:23

To its markets came silks, spices, drugs, fruit,

0:26:230:26:29

perfumes and gold from as far afield

0:26:290:26:32

as India and China in the east and Spain in the west.

0:26:320:26:36

Anything that could be traded was.

0:26:360:26:40

A wonderful relic of this medieval trade boom

0:26:510:26:55

are the great Caravanserais,

0:26:550:26:57

like this one in the Syrian capital, Damascus.

0:26:570:27:01

This huge vaulted building was designed as a resting place

0:27:010:27:05

for all the traders and their animals who visited the city.

0:27:050:27:09

On their ground floors were wide spaces for animals and goods

0:27:140:27:20

and, above, there were rooms for the rich merchants

0:27:200:27:23

to refresh themselves before another day of haggling.

0:27:230:27:27

One 10th-century traveller talks of

0:27:290:27:32

the "riches and beauties of the bazaars",

0:27:320:27:35

and that the income of the provinces and localities

0:27:350:27:38

was between 700 and 800 million dinars.

0:27:380:27:42

Markets like this in the Egyptian capital, Cairo,

0:27:500:27:53

still capture the intensity of medieval trade.

0:27:530:27:56

And still surviving in the modern world of the internet

0:27:560:28:00

and the mobile phone is a fantastic example

0:28:000:28:03

of how traders 1,000 years ago communicated across a vast empire.

0:28:030:28:09

THEY SPEAK ARABIC

0:28:090:28:13

So this is a carrier pigeon.

0:28:130:28:15

Its base is here, so wherever you took it all over Egypt,

0:28:150:28:18

it would make its way back to this guy.

0:28:180:28:20

There's a famous story that a rich Cairo merchant

0:28:240:28:28

by the name of Al-Nawr wanted to grow cherry trees,

0:28:280:28:31

so he sent a message by carrier pigeon

0:28:310:28:34

to a contact of his in Damascus, asking for some seeds.

0:28:340:28:37

His contact sent back 500 birds,

0:28:370:28:40

each one carrying a small bag with seeds in it.

0:28:400:28:43

The whole process took just three days.

0:28:430:28:46

Sort of a medieval FedEx, really.

0:28:460:28:48

By 700 AD, the Islamic Empire

0:28:500:28:53

was taking the first steps towards mass production.

0:28:530:28:57

And in this world where knowledge of materials, metals

0:29:000:29:05

and how they're worked became increasingly important,

0:29:050:29:09

one practice flourished.

0:29:090:29:11

It's the practice that was inextricably linked with magic -

0:29:130:29:18

specifically the dream to turn base metals into gold.

0:29:180:29:22

The mysterious practice of alchemy.

0:29:240:29:27

The ancient art of alchemy was a mystical system of belief

0:29:290:29:33

based on spells, symbols and magic.

0:29:330:29:35

But I believe it took Islamic scholars to turn this quasi-religion

0:29:350:29:40

into something much more scientific - chemistry.

0:29:400:29:44

Increasingly, the knowledge of the alchemists

0:29:470:29:50

found more and more practical applications.

0:29:500:29:53

For instance, when during the last decade of the 7th century,

0:29:530:29:58

the ruler of the Islamic Empire, Abd al-Malik,

0:29:580:30:01

made the bold decision to create a common currency

0:30:010:30:05

for all his dominions, he turned to alchemists for help.

0:30:050:30:09

The proportion of gold to other alloyed metals

0:30:110:30:15

that you have to put into the dinar to make the dinar useable,

0:30:150:30:18

otherwise pure gold will become very soft and you can't use it -

0:30:180:30:22

that proportion is adjusted by, believe it or not,

0:30:220:30:26

in this period, the alchemists.

0:30:260:30:29

It is the alchemists who knew how to combine metals together

0:30:290:30:33

and how to get the proportions of this gold to silver

0:30:330:30:36

and gold to bronze and so on.

0:30:360:30:38

-Salaam alaikum.

-Salaam alaikum.

0:30:480:30:51

'I hunted down tangible evidence

0:30:520:30:55

'of the skill of medieval Islamic alchemists

0:30:550:30:57

'in the old market in the Syrian capital, Damascus.'

0:30:570:31:01

This is an Islamic dinar.

0:31:010:31:04

The date of this is 128 after Hijri.

0:31:040:31:07

-So the middle of the 8th century?

-Almost, almost.

-Almost 740s.

-Yes.

0:31:070:31:13

'This 1,300-year-old coin, made of an alloy of different metals,

0:31:130:31:18

'isn't just durable - it's also malleable enough

0:31:180:31:22

'to be inscribed with intricate Arabic writing.'

0:31:220:31:25

"No God instead of Allah" and then...

0:31:250:31:29

'Coin-making is one of the many examples

0:31:290:31:31

'of how the practical needs of a booming economy

0:31:310:31:35

'began to turn the magical practice of alchemy into modern chemistry.'

0:31:350:31:41

What's striking about chemistry in the medieval Islamic world

0:31:410:31:46

is the sheer quantity of manuscripts that deal with the subject.

0:31:460:31:50

There are literally thousands that survive dealing with subjects

0:31:500:31:53

as varied as metallurgy, glass-making,

0:31:530:31:57

tile-making, dyeing, perfumery, weaponry.

0:31:570:32:01

There's even a description on how to distil alcohol.

0:32:010:32:04

All this activity clearly points to a bustling economy,

0:32:040:32:09

with consumers, soldiers, engineers, architects

0:32:090:32:13

all demanding innovation and all demanding new technology.

0:32:130:32:17

A great example of applied chemistry in the medieval Islamic world

0:32:190:32:24

was the manufacture of soap.

0:32:240:32:27

This stuff - solid soap that you can really clean yourself with -

0:32:270:32:31

was virtually unknown in Northern Europe until the 13th century,

0:32:310:32:35

when it started being imported from Islamic Spain and North Africa.

0:32:350:32:39

By that time, the manufacture of soap in the Islamic world

0:32:390:32:42

had become virtually industrialised.

0:32:420:32:45

The town of Fez boasted some 27 different soap makers,

0:32:450:32:50

and cities like Nablus, Damascus and, of course, Aleppo

0:32:500:32:54

became world-renowned for the quality of their soaps.

0:32:540:32:57

A 12th-century document

0:32:580:33:00

has the world's first detailed description of how to make soap.

0:33:000:33:05

It mentions a key ingredient and it's a substance

0:33:050:33:09

that became crucial to modern chemistry - an alkali.

0:33:090:33:14

Now, alkaline substances are crucial to soap-making.

0:33:140:33:17

But what's interesting is that our word "alkali"

0:33:170:33:20

derives from the Arabic "al-qali", which means "ashes".

0:33:200:33:25

That's because, back then, alkalis were manufactured from the ashes

0:33:250:33:29

of the roots of certain plants like saltworts.

0:33:290:33:32

Islamic chemists' new understanding of alkalis and other new chemicals

0:33:360:33:40

gave another industry a lift, too - glass-making.

0:33:400:33:45

The Islamic chemists discovered

0:33:510:33:54

that they could change the colour of glass

0:33:540:33:56

using newly discovered chemicals like manganese salts.

0:33:560:34:00

And they built industrial furnaces, some several storeys high,

0:34:010:34:06

to manufacture glass in huge quantities.

0:34:060:34:10

The legacy of their skills

0:34:100:34:12

can still be seen in beautiful stained-glass windows.

0:34:120:34:17

Islamic chemists also developed many other colours, pigments and dyes

0:34:190:34:26

using their new alkalis and metals like lead and tin.

0:34:260:34:30

These helped architects to decorate mosques,

0:34:310:34:34

like this one in the Iranian city of Isfahan,

0:34:340:34:36

in a glorious range of colours and designs.

0:34:360:34:40

'Chemistry was also driven by the booming market in perfumes.'

0:34:480:34:55

Salaam alaikum.

0:34:550:34:58

'In the main market of Damascus, traders still make up

0:34:580:35:02

'your favourite scent as they would have 1,000 years ago.'

0:35:020:35:06

So it basically has a base of alcohol and then he adds to it

0:35:060:35:10

the oils from the plants you want - jasmine and rosewater and mint.

0:35:100:35:16

But these days, they'll use...

0:35:160:35:19

-Very nice.

-Yeah, I think I'll buy some of that.

0:35:190:35:23

'Perfumiers pushed chemists

0:35:250:35:28

'to come up with ever more ingenious techniques

0:35:280:35:30

'for extracting subtle and fragile fragrances from flowers and plants.

0:35:300:35:36

'They responded by refining and really establishing a technique

0:35:390:35:43

'that all chemists would instantly recognise today - distillation.'

0:35:430:35:48

Many of the techniques originate with Islamic scholars, or even earlier.

0:35:480:35:52

'Dr Andrea Sella, a chemist from University College London,

0:35:520:35:56

'shows me how distillation was used.'

0:35:560:35:59

Distillations would have been done in devices related to these.

0:35:590:36:04

This is what's now called a retort. We don't really use them any more,

0:36:040:36:08

but "retort" comes from the word "to bend" - in other words,

0:36:080:36:12

a flask which has been bent over, and that's crucial.

0:36:120:36:16

'The shape means that a gas produced in the flask

0:36:160:36:19

'is forced to condense in the spout,

0:36:190:36:22

'and it's the main way of extracting scents from flowers and plants.

0:36:220:36:27

The idea here is you heat at this end and you collect at the other.

0:36:270:36:31

We should actually take a look and see if we can do

0:36:310:36:34

a quick distillation with rose petals.

0:36:340:36:37

First, we need to just put in a little bit of water.

0:36:370:36:40

The water and steam will essentially control the temperature.

0:36:400:36:43

What we don't want is for this to get too hot.

0:36:430:36:46

'The trick with this kind of distillation

0:36:460:36:49

'is to use heat to release the scent molecules,

0:36:490:36:52

'but at the same time making sure

0:36:520:36:55

'that these delicate substances

0:36:550:36:58

'aren't destroyed in the process.'

0:36:580:37:01

You actually use the steam to control the temperature, and the steam

0:37:010:37:04

will carry those smells over.

0:37:040:37:07

You can see the liquid coming up, condensing in the long tube

0:37:070:37:12

-and there is already liquid coming through...

-Yeah.

0:37:120:37:16

..and that should be carrying with it some of the rose water smell.

0:37:160:37:22

Mmm, yes, you can really smell it.

0:37:240:37:26

This picture shows a 14th-century perfume distillery.

0:37:280:37:33

Middle Eastern perfumes

0:37:330:37:35

where known to have been sold as far away as India and China.

0:37:350:37:38

The Islamic chemists also played a pivotal role

0:37:410:37:45

in another more gruesome industry - weaponry.

0:37:450:37:49

Historical records during the Crusades talk in terrified tones

0:37:520:37:57

of how the Muslims would attack the Christians

0:37:570:38:00

with burning missiles and grenades,

0:38:000:38:02

striking fear into the hearts of the defenders.

0:38:020:38:05

Many of these used a substance known as Greek Fire.

0:38:050:38:09

Islamic chemists improved on Greek Fire

0:38:110:38:14

by using and refining a naturally occurring resource - petroleum.

0:38:140:38:20

They developed the idea of distilling petroleum, or naft,

0:38:210:38:25

to create a lighter, extremely flammable oil which they mixed

0:38:250:38:29

with other volatile chemicals to make them burn furiously,

0:38:290:38:34

and the result was clearly terrifying.

0:38:340:38:37

What all these medieval Islamic texts on chemistry have in common

0:38:400:38:44

is their great attention to detail,

0:38:440:38:47

which is clearly based on careful experimentation.

0:38:470:38:50

In fact, the whole idea of a laboratory,

0:38:500:38:53

where chemical and industrial processes can be tried out,

0:38:530:38:57

really takes hold at this time.

0:38:570:38:59

The ingenuity of medieval Islamic chemists is impressive.

0:39:020:39:07

But I wanted to know something deeper.

0:39:070:39:09

What contribution did they make to our modern understanding

0:39:090:39:13

of the principles behind chemistry?

0:39:130:39:15

This is the centrepiece of modern chemistry - the periodic table.

0:39:150:39:21

It lists all the known elements.

0:39:210:39:24

Its key idea is to group substances with similar properties together.

0:39:240:39:29

On the far right, for instance, are the inert gases.

0:39:290:39:33

On the far left are the volatile metals.

0:39:330:39:36

The periodic table is triumph of classification,

0:39:360:39:40

giving scientists a way of organising

0:39:400:39:43

their knowledge of the material world.

0:39:430:39:46

Classification is simply a way to think clearly.

0:39:460:39:49

What you need when you have some ideas about how the world works is

0:39:490:39:54

that gives you a schema and you chop the world into categories,

0:39:540:39:57

and that helps you to understand, to make sense of what's around you.

0:39:570:40:03

People had been trying to classify the material world

0:40:030:40:07

since ancient times. The Greeks, for instance, thought there were just

0:40:070:40:11

four worldly elements - air, earth, fire and water.

0:40:110:40:17

But this idea was a philosophical one and had little practical value.

0:40:170:40:21

And that's what medieval Islamic chemists really changed.

0:40:220:40:26

They used experimental observations

0:40:260:40:29

to classify the stuff the world is made of.

0:40:290:40:32

At the forefront of this was a medieval Islamic doctor and chemist

0:40:320:40:37

called Ibn Zakariya Al-Razi, who was born here in the city of Ray,

0:40:370:40:41

just outside the Iranian capital Tehran in 865 AD.

0:40:410:40:46

Al-Razi's classification was very different from the Greek one.

0:40:480:40:52

He argued, for instance, that minerals -

0:40:520:40:55

roughly stuff we dig out of the ground -

0:40:550:40:57

should be classified into six groups,

0:40:570:41:00

depending on their observed chemical properties -

0:41:000:41:04

the same guiding principle that lies behind the modern periodic table.

0:41:040:41:10

Now, I've brought materials from his classification scheme.

0:41:100:41:14

We have here what he called the spirits,

0:41:140:41:17

we have the metallic bodies, we have the stones,

0:41:170:41:21

then we have the attraments, the salts and finally the boraxes.

0:41:210:41:25

'Each of Al-Razi's groups

0:41:260:41:28

'had a profoundly different experimental behaviour.

0:41:280:41:32

'For instance, spirits were flammable.

0:41:320:41:36

'The metals were shiny and malleable.

0:41:360:41:39

'Salts dissolved in water.

0:41:390:41:43

'Of course, these classifications are not the way we do it today,

0:41:430:41:47

'but the point is that, for the first time,

0:41:470:41:50

'Al-Razi was grouping substances on the basis

0:41:500:41:53

'of experimental observations, not philosophical musings.'

0:41:530:41:59

We've come over 1,000 years since the work of Al-Razi.

0:41:590:42:03

What sort of debt does modern chemistry

0:42:030:42:06

owe to him for his classification?

0:42:060:42:09

Well, I think with Razi, we start to see the first classification

0:42:090:42:14

which really leads on to further experiments,

0:42:140:42:17

the first schema which allows people to start doing rational work.

0:42:170:42:21

And so, really, he lies at the start of almost formal chemistry,

0:42:210:42:26

which ultimately leads to our periodic table.

0:42:260:42:30

I believe that what we see

0:42:340:42:36

in the work of the Islamic chemists and alchemists

0:42:360:42:40

is the first tentative steps to a new science.

0:42:400:42:44

Yes, by our standards, it contained a lot of magic and mumbo jumbo,

0:42:440:42:48

but it placed an emphasis on experimentation

0:42:480:42:51

that was truly revolutionary.

0:42:510:42:53

But bigger and better was to come,

0:42:560:42:58

because Islamic mathematics and the experimental techniques

0:42:580:43:03

of Jabir Ibn Hayyan and Al-Razi were about to be welded together

0:43:030:43:07

in a completely innovative way that would revolutionise their work

0:43:070:43:11

and create the modern scientific age.

0:43:110:43:14

Until the 9th or 10th centuries,

0:43:180:43:20

ideas about science and how the natural world worked

0:43:200:43:24

were dominated by the Greek philosopher Aristotle,

0:43:240:43:28

and they were very different from ours today.

0:43:280:43:31

He believed that mathematics was concerned

0:43:310:43:34

only with an abstract world of perfect forms,

0:43:340:43:37

of idealised shapes like circles, squares and triangles.

0:43:370:43:42

It had no power to explain what we observe in the world around us,

0:43:420:43:47

a world characterised by irregular, wonky shapes and constant change.

0:43:470:43:52

"Physics" is a Greek word meaning "the science of change",

0:43:530:44:00

and for the classical Greek tradition,

0:44:000:44:03

there was a strong sense in which

0:44:030:44:06

the science of change was in contradiction with mathematics.

0:44:060:44:12

Mathematics dealt with perfect knowledge,

0:44:120:44:16

with the unchanging world of mathematical forms.

0:44:160:44:21

And it seemed, in principle, extremely unlikely

0:44:210:44:24

that processes of coming into being and passing away,

0:44:240:44:29

of growth and of decay,

0:44:290:44:32

of qualitative change,

0:44:320:44:34

could be captured with the beauties of geometry and mathematics.

0:44:340:44:41

The story of how humanity shook off this idea

0:44:450:44:48

and began to see that mathematics is actually an incredibly powerful way

0:44:480:44:53

of describing the world around us is long and complicated.

0:44:530:44:57

But for me, Islamic scientists played a crucial role,

0:44:590:45:03

and I believe one man really led this movement to turn mathematics

0:45:030:45:08

from a language of abstract thought into a truly practical science.

0:45:080:45:14

He was, like me, from Iraq, and his name was Ibn Al-Haytham.

0:45:140:45:19

What Al-Haytham and his contemporaries argued for

0:45:190:45:24

was the possibility in a way of a single science,

0:45:240:45:28

which would be both mathematical and philosophical,

0:45:280:45:33

which would link together a physics - a science of change -

0:45:330:45:38

with a mathematics - a science of quantity.

0:45:380:45:41

And that seems to me to be radical and crucial

0:45:410:45:45

for the construction of new forms of reliable knowledge.

0:45:450:45:48

Ibn Al-Haytham was born in 965 AD in the southern Iraqi town of Basra,

0:45:480:45:55

and other scholars regarded him as a prodigy.

0:45:550:45:59

He shot to scientific fame just after the turn of the first millennium

0:45:590:46:03

and was an incredibly innovative and brilliant scholar.

0:46:030:46:06

His reputation as an intellect spread throughout the empire.

0:46:060:46:10

But it was this reputation that'd almost cause him to lose everything

0:46:100:46:14

when he took up the poisoned chalice

0:46:140:46:17

of trying to tame one of the world's greatest rivers.

0:46:170:46:20

There's a wonderful, if suspiciously apocryphal, story

0:46:290:46:33

about how Ibn Al-Haytham's career as a scientist was transformed.

0:46:330:46:38

It concerns the Nile and how, just after the turn of the millennium,

0:46:380:46:43

Ibn Al-Haytham was asked by the ruler of Egypt

0:46:430:46:46

to find a way of controlling it. Could he prevent

0:46:460:46:49

its unpredictable and potentially devastating floods and droughts?

0:46:500:46:55

But it didn't take Ibn Al-Haytham long to realise

0:46:550:46:59

that the Nile was way too large to control.

0:46:590:47:03

On hearing this, the Caliph flew into a terrible rage

0:47:030:47:06

and ordered Ibn Al-Haytham's execution.

0:47:060:47:10

Ibn Al-Haytham responded by feigning madness.

0:47:100:47:14

The execution was called off and he was placed under house arrest.

0:47:140:47:18

There, with time on his hands to contemplate, the story goes,

0:47:200:47:24

Ibn Al-Haytham considered deep and fundamental questions in physics,

0:47:240:47:29

and he began with a truly enigmatic and universal problem.

0:47:290:47:34

He asked if the wonderful and entirely mysterious nature of light and vision

0:47:340:47:39

could be explained by mathematics and geometry.

0:47:390:47:43

Under house arrest, or perhaps here in the rooms

0:47:450:47:48

of Al-Azhar University in Cairo, Ibn Al-Haytham carried out

0:47:480:47:53

a series of experiments that created the modern science of optics.

0:47:530:47:57

'I'm with Dr El-Bizri,

0:47:580:48:01

'who has carefully studied Ibn Al-Haytham's work.

0:48:010:48:04

'He explained that Ibn Al-Haytham first considered

0:48:040:48:08

'the Aristotelian explanation for how we see,

0:48:080:48:11

'an explanation that was completely un-mathematical.

0:48:110:48:15

'Aristotle argued that we when we look at, say, a tree,

0:48:150:48:19

'its essence or form emanates from it

0:48:190:48:22

'and then mysteriously flows into our eyes.'

0:48:220:48:26

So if I'm, for instance, now looking at the buildings

0:48:260:48:30

and the trees on the banks of the Nile, I'm receiving the forms

0:48:300:48:36

of these buildings and these trees in the eye

0:48:360:48:41

abstracted from their matter.

0:48:410:48:43

'According Dr El-Bizri,

0:48:450:48:46

'Ibn Al-Haytham found this idea deeply unsatisfactory.

0:48:460:48:50

'He wanted a mathematical explanation.

0:48:500:48:53

'And looking back at existing Greek writings,

0:48:550:48:58

'he found one, although it was obscure and bizarre.

0:48:580:49:02

'This idea claimed that we see,

0:49:040:49:07

'because light rays come out of the eye.'

0:49:070:49:10

Ultimately, it says that vision occurs by way of the emission

0:49:100:49:14

from the eye of light that is shaped in the form of a pyramid or a cone.

0:49:140:49:20

This cone-shaped beam illuminates what we're looking at

0:49:220:49:25

and is defined by nice geometric straight lines.

0:49:250:49:29

It seems Ibn Al-Haytham liked this mathematical approach,

0:49:310:49:35

but immediately spotted its flaws.

0:49:350:49:38

If we see, he asked, because light comes out of the eye,

0:49:380:49:42

why does it hurt when you look at a bright object like the sun

0:49:420:49:46

but not hurt when you look at something dim?

0:49:460:49:49

Or at night, can light from our eyes

0:49:490:49:53

really be lighting up distant objects in the sky?

0:49:530:49:57

So, in an inspired piece of thinking,

0:49:570:50:00

Ibn Al-Haytham combined the two Greek ideas

0:50:000:50:04

and defined our modern understanding of light and vision.

0:50:040:50:09

Light, he said, does travel in straight lines that obey geometric laws.

0:50:090:50:14

But instead of them coming out of the eye, these rays travel into it.

0:50:140:50:20

It is the development of an entirely new theory, and also methodologically

0:50:200:50:25

it is the beginnings of mathematising physics.

0:50:250:50:28

What Ibn Al-Haytham did was take the principles of geometry,

0:50:310:50:35

with its rules governing straight lines,

0:50:350:50:38

and applied them to the real world. He then designed experiments

0:50:380:50:42

to test whether the real world measured up to his mathematics.

0:50:420:50:46

In about 1020, Ibn Al-Haytham published

0:50:480:50:51

his ground-breaking geometric explanation of light

0:50:510:50:55

in his Kitab al-Manazir, or Book of Optics.

0:50:550:50:59

And what really marks this book out as science

0:50:590:51:02

is that Ibn Al-Haytham carefully justifies his theories

0:51:020:51:06

with detailed experiments that others can repeat and verify.

0:51:060:51:11

He starts from first principles to find out how light travels.

0:51:110:51:16

For his first experiment, Ibn Al-Haytham

0:51:210:51:24

wanted to test the idea that light travels in straight lines.

0:51:240:51:29

To do this, he took a straight tube on which he'd drawn a straight line

0:51:290:51:34

down the side and a ruler with a straight line down the length of it.

0:51:340:51:39

And by matching the two together,

0:51:390:51:41

he was convinced then that the tube was straight.

0:51:410:51:45

If he uses it to look at an object - in this case, a candle -

0:51:450:51:49

he can see the candle through the tube, which is good evidence

0:51:490:51:53

that the light is travelling up in a straight line. But to be sure,

0:51:530:51:57

he then blocked the end of the tube.

0:51:570:52:00

And then, by looking at the candle again, he can't see it,

0:52:000:52:04

because what this does is confirm the light doesn't travel to his eye

0:52:040:52:09

via any other route in a curved path outside the tube.

0:52:090:52:13

Proof that light only travels in a straight line.

0:52:130:52:16

Now, this might sound quite trivial and obvious to us,

0:52:160:52:19

but Ibn Al-Haytham was starting from first principles.

0:52:190:52:23

Then, through experiment, he extends

0:52:230:52:27

his "light travels in straight lines" idea to many other phenomena.

0:52:270:52:31

He explains how mirrors work, by arguing that the angle

0:52:310:52:35

the ray comes in at is the same as the angle it bounces off at.

0:52:350:52:40

He explains what we now call refraction,

0:52:400:52:43

why objects look kinked in a glass of water - arguing that light rays

0:52:430:52:48

bend when they move from one medium to another.

0:52:480:52:52

And then he tackles the nature of vision.

0:52:520:52:56

Ibn Al-Haytham wanted to understand

0:52:560:52:59

how an object makes an image on the retina of the eye.

0:52:590:53:02

So he built what he believed was a stripped down version of the eye,

0:53:020:53:07

which is basically a black box with a tiny hole in it.

0:53:070:53:11

This is what we call today the camera obscura.

0:53:110:53:13

He next took his subject, in this case Anna, who's very brightly lit,

0:53:130:53:19

and we now go inside the box to see what the image looks like.

0:53:190:53:22

Now that I'm inside the camera obscura and I've allowed my eyes

0:53:250:53:29

to get used to the dark, we can open the hole.

0:53:290:53:32

And there we clearly see the image of Anna waving on the screen.

0:53:320:53:37

But the image is inverted, because light travels in straight lines,

0:53:370:53:41

so the light from her head has to move diagonally downwards

0:53:410:53:44

to hit the bottom of the screen

0:53:440:53:46

and light from her feet travels diagonally upwards to hit the top.

0:53:460:53:50

But, more importantly, what this proved to Ibn Al-Haytham is

0:53:500:53:54

there's a one-to-one correspondence between every point on the object -

0:53:540:53:58

on Anna - and every point on her image on the screen.

0:53:580:54:02

Just like a modern scientific paper,

0:54:040:54:06

the attention to detail in the Kitab al-Manazir is incredible.

0:54:060:54:11

His book isn't just a dry scientific treatise -

0:54:110:54:15

it's a manual for future generations.

0:54:150:54:18

In his work, he constantly justifies

0:54:180:54:21

his theories about light with experimental observation

0:54:210:54:25

and he describes his experiments in great detail,

0:54:250:54:28

so that other people can repeat them and confirm his ideas.

0:54:280:54:32

His message is, "Don't take my word for it, see for yourself."

0:54:320:54:36

I believe that Ibn Al-Haytham was one of the very first people

0:54:360:54:40

to ever work like this. This, for me,

0:54:400:54:43

is the moment that science itself is summoned into existence

0:54:430:54:47

and becomes a discipline in its own right.

0:54:470:54:50

What I find so impressive about Ibn Al-Haytham is how,

0:54:580:55:03

once he arrives at his mathematical theories,

0:55:030:55:06

he then uses them to extend our knowledge of the real world.

0:55:060:55:10

So, for instance, he used his new ideas about light to deduce

0:55:100:55:15

that the Earth's atmosphere is of a finite thickness,

0:55:150:55:19

and he even estimated what that thickness is.

0:55:190:55:22

He did it basically by measuring how long twilight lasts.

0:55:230:55:29

He rightly assumed that the reason it continues to be light

0:55:290:55:33

after the sun has dropped below the horizon

0:55:330:55:35

must be because its rays bend as they enter the Earth's atmosphere.

0:55:350:55:40

The length of twilight and an educated guess

0:55:420:55:45

for what we today call the air's refractive index

0:55:450:55:48

gave Ibn Al-Haytham a way

0:55:480:55:50

of estimating the thickness of the Earth's atmosphere.

0:55:500:55:54

He came up with a figure of around 40 kilometres -

0:55:540:55:58

about half of the modern value. That's pretty impressive.

0:55:580:56:02

It really shows how mathematics

0:56:020:56:05

extends the power of science to explain.

0:56:050:56:08

On my journey so far, I've been overwhelmed by

0:56:140:56:18

the sheer intellectual ambition of medieval Islamic scientists.

0:56:180:56:22

When their leaders asked them to find out the size of the world,

0:56:220:56:26

scholars like Al-Biruni used mathematics in startling new ways

0:56:260:56:31

to reach out and describe the universe.

0:56:310:56:35

And as trade and commerce boomed, scientists like Al-Razi

0:56:380:56:43

responded by developing a new kind of experimental science - chemistry.

0:56:430:56:48

But if there's one Islamic scientist we should remember above all others,

0:56:500:56:55

it is, in my view, Ibn Al-Haytham,

0:56:550:56:58

for doing so much to create what we now call the scientific method.

0:56:580:57:03

The scientific method is, I believe,

0:57:060:57:09

the single most important idea the human race has ever come up with.

0:57:090:57:14

There is no other strategy that tells us how to find out

0:57:140:57:18

how the universe works and what our place in it is.

0:57:180:57:22

It's also delivered technologies that have transformed our lives.

0:57:220:57:26

So, the next time you jet off on holiday or use a mobile phone

0:57:260:57:29

or get vaccinated against a deadly disease,

0:57:290:57:32

remember Ibn Al-Haytham, Ibn Sina, Al-Biruni

0:57:320:57:36

and countless other Islamic scholars 1,000 years ago

0:57:360:57:39

who struggled to make sense of the universe

0:57:390:57:43

using crude mirrors and astrolabes.

0:57:430:57:45

They didn't get all the right answers,

0:57:450:57:48

but they did teach us how to ask the right questions.

0:57:480:57:52

In the next episode, I travel to Syria and Northern Iran

0:58:040:58:08

to find out about the great Islamic scientists

0:58:080:58:12

who revolutionised astronomy,

0:58:120:58:14

making it a truly modern science.

0:58:140:58:16

And I'll also discover how the man many consider

0:58:170:58:20

to be the father of the European scientific renaissance, Copernicus,

0:58:200:58:25

borrowed from Islamic astronomical theories.

0:58:250:58:29

And I'll unravel the mystery of how

0:58:290:58:32

the Golden Age of Islamic science came to an end.

0:58:320:58:36

Subtitles by Red Bee Media Ltd

0:58:440:58:47

E-mail: [email protected]

0:58:470:58:50

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