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