All language subtitles for BBC.Science.and.Islam.2of3.HDTV.x264.AC3.MVGroup

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

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

I believe that
just such an idea

took form
in the medieval Islamic world.

It's the idea that everything,

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

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

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

and then, we can refine
and test our theories

through observation
and experiments.

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

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

'the medieval Islamic world
is a personal one.

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

'I haven't seen
some of the relatives

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

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

'The Al-Khalili family
is originally

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

'In fact, I grew up in Iraq.

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

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

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

There, I pursued
my passion for science

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

But now, I find that my own
scientific work

and my Arabic and Islamic heritage
are intertwined.

On my journey through the
Middle East, I discovered that

an astonishing leap
in scientific knowledge

took place here 1,000 years ago

under a powerful
and flourishing Islamic Empire.

Wealthy, powerful,
successful cultures

will produce enormous advances

in understanding and in technique,

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

under a series
of successful, powerful,

wealthy and self-confident
Islamic regimes.

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

It governed an estimated
60 million people -

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

I found an archaeological fragment
of this glorious past

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

These ancient walls tucked behind
a backstreet

on the outskirts of southern Tehran
are literally all that remain

of the ancient city of Ray.

The city that the great Persian
geographer Al-Muqaddasi described

as one of the glories of Islam.

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

that flourished
under early Islamic rule.

From Baghdad, its capital,

the empire spread across
thousands of miles

from North Africa
through to central Asia.

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

each powerful and thriving cities.

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

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

These were powerhouses
of the new science.

This really was a Golden Age.

Think of that span of land.

This is larger than any empire
human civilisation

had ever known.
Within that span of land,

you can plug in the Roman Empire
and it will fill

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

CHANTING IN ARABIC

Reminders of this great
Islamic Empire

are everywhere
in the Arab world today.

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

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

who ruled the Islamic Empire
from 750 to 1258 AD.

This large territory allowed them
to raise enormous tax revenues

to fund a search
for knowledge and scholarship

which became known
as the Translation Movement.

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

and have them translated
into Arabic.

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

For medieval Islamic leaders,
scientific knowledge

was crucial to successfully
running a vast empire.

They did have a big and sophisticated
governmental administration,

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

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

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

and mathematical skills to construct
fine buildings safely.

Medicine just to keep the elite
happy and healthy.

Those are the areas of knowledge

which are first translated
from other languages into Arabic.

The legacy of the
medieval Islamic Empire

is scattered across a vast region.

There's architectural masterpieces,

like the Ummayyad Mosque
in Damascus,

the Jame Mosque in Isfahan,

and Al-Azhar University and mosque
in Cairo.

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

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

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

currently being excavated
in Southern Spain.

These are the impressive ruins
of Madinat Al-Zahra,

the fantastic palace city
built outside Cordoba

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

who was the greatest of all
the Andalucian caliphs.

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

the largest and most important city
in Europe,

a rival to Baghdad in the east

for a centre for Islamic
scholarship and science.

And as I travelled,
I saw how science,

especially numerical record-keeping
and measurement,

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

This is the mighty River Nile

as it flows through
the Egyptian capital, Cairo.

Since antiquity, its unpredictable
floods have determined the fate

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

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

and the new rulers
took the first step

to understanding this mighty river
in a scientific way.

They built a device to measure it.

Ha!

It's an amazing structure, right?

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

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

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

'As the water rose or fell,

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

The central colonnade here is
ultimately a measuring instrument.

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

Presumably they need to know
seasonal variations in the height.

And to try to
have some sort of record,

so that they could measure
against certain years,

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

..versus another year
known for its drought.

Then they might perhaps
take some precautions. Yes.

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

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

'it allowed the rulers of the time
to calculate

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

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

'is how it shows
that to understand the world,

'you have to build devices
to measure it.'

If you think very hard,
it's never obvious

that measurement can make
sense of the world around us.

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

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

have tools which are reliable,
which have sufficient integrity,

which have an intellectual grip
that can make sense

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

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

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

His name was Al-Ma'mun,

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

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

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

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

but one particular project
was a personal favourite of his.

And given that he ruled over
such a large territory,

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

In the second decade
of the 9th century AD,

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

and his scientists
did a pretty impressive job.

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

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

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

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

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

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

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

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

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

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

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

Where does that ambition and
that confidence come from?

Part of it comes from
religious faith.

Because the world was made

by someone a bit like us,
but much smarter,

if we're smart enough,
the thought was,

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

And that's very clear
as a motivation

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

And more specifically,
the practice of Islam demanded

that its followers
have a very clear idea

of the size and shape
of the world.

This is crucial information
for Muslims, because,

wherever they are in the world,
they need to know

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

Now, over such a large territory,

finding the direction to Mecca
is not a trivial problem.

This problem was
wonderfully illustrated

when a mosque was built recently
in Washington DC.

Some worshippers were confused,

because the direction they were
told to face when praying

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

After all,
Mecca is south-east of Washington

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

But on a curved sphere,
the shortest distance

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

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

is quite different
to what you might expect,

so the direction
to Mecca from Washington

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

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

for Islamic scholars is that
knowing the direction to Mecca

requires a knowledge of how
steeply the Earth curves,

and that means
knowing how big it is.

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

Hello. Hello.

Nice to meet you.

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

'with Professor Sami Chaloubi
from Aleppo University in Syria,

'who's an expert
in early Islamic science.

'Professor Chaloubi began by
explaining the measuring technique,

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

'and which they had inherited
from the Greeks.'

We're now talking about this,

the earlier Eratosthenes technique
of measuring the circumference.

It was repeated
by the Abbasid astronomers.

It was to measure the distance
between two points

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

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

as being vertical -
this is near to the equator -

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

if they measured it from
the north of Egypt,

in Alexandria, which is
on the Mediterranean coast.

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

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

'at one known location.

'They then walked due north
to a second location,

'carefully measuring
the distance they travelled.'

At the second location,

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

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

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

were able to estimate
the Earth's circumference.

They got a value of 24,000 miles -

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

But this method was flawed
and ultimately unreliable.

The main problem was that measuring
the distance between two locations

was incredibly difficult.
It could only be done

by the unreliable method
of counting paces

as you walked through
the burning desert.

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

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

What made it possible was
a great leap of imagination

and the fact that, by 900 AD,

much of the world's
mathematical knowledge

had been translated into Arabic,

so scholars could scrutinise
and improve on it.

Out of this obsession
with scholarly learning

came a true
mathematical visionary -

Abu Rayhan
Muhammad Ibn Ahmad Al-Biruni.

And like all Islamic scholars
of the time,

Al-Biruni was obsessed with
the science and mathematics

of the ancient Greeks,
Babylonians and Indians.

And because of the success
of the Translation Movement,

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

Ptolemy's Almagest,
the Indian text the Sindhind,

and the famous work on algebra
by Al-Khwarizmi.

CONVERSATION IN ARABIC

'Professor Chaloubi
has brought along the book

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

'with some very simple
and practical measurements

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

Biruni's text.
And this his...?

Al-Qanoon Al-Masoodi.
The Masoodi Canon.

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

where he describes
this fantastic experiment.

Oh, you've found the page.

Yes.

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

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

First, he had to find
a fairly high mountain

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

in this case, the sea.

What I love about
this story is that,

with a few simple measurements
around this small mountain peak,

you can work out
the size of the whole world.

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

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

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

So, to measure the angle
to the mountain top,

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

It's basically a giant protractor.

It has the angles in degrees
marked around the outside

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

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

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

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

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

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

OK, that's about it.

And that is 24.5 degrees.

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

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

'The distance from the first
to the second point

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

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

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

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

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

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

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

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

'I now need
only one more measurement

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

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

What Biruni did next was measure

the angle of the line of sight
to the horizon

as it dips below the horizontal.

We're going
to try and reproduce that,

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

..and if I locate the horizon...

OK.

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

Now, here's the really
ingenious part.

Biruni had measured
four quantities -

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

to work out the height
of the mountain.

Al-Biruni now had
everything he needed.

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

which has as its three corners

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

Trigonometry told him
that the angle he had measured

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

and algebra allowed him
to calculate it.

With this formula,
Biruni is able to arrive

at a value
for the circumference of the Earth

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

about 25,000 miles.

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

A remarkable achievement
for someone 1,000 years ago.

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

of a scientist using
mathematical reasoning

to extend humanity's reach.

He really pushes the idea that
abstract geometrical rules

governing idealised shapes like
perfect circles and triangles

can help us to comprehend
the real world.

Einstein used precisely
the same approach,

admittedly with much more
advanced mathematics,

when he developed
his General Theory of Relativity

almost 1,000 years after Biruni.

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

with mathematics,
humanity can embrace the universe.

In this story of the birth
of the scientific method,

the Islamic scholars' ability
to master sophisticated mathematics

is the first crucial ingredient.

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

Without experiment, theory
remains meaningless and sterile.

It's experimentation
that allows theory

to be held up
against the real world.

It gives it physical meaning.

But whereas
sophisticated mathematics

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

practical experiment
came from the daily needs

of a powerful and expanding
civilisation.

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

It boomed from around
700 AD onwards,

creating a massive demand
for metalworkers, glass-blowers,

tile-makers,
craftsmen of every possible kind.

When this collided with
scholarly tradition,

symbolised by
the Translation Movement,

it had seismic consequences
for science.

The sciences absolutely depend -

astronomy is a wonderful example,
chemistry is another -

on really intense relationships
between craft traditions

of instrument making,
of working with metal and fire,

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

highly sophisticated literary
and mathematical analysis.

And the Islamic world is
just such a place.

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

dominated the world's trade.

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

perfumes and gold
from as far afield

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

Anything that could be traded was.

A wonderful relic
of this medieval trade boom

are the great Caravanserais,

like this one
in the Syrian capital, Damascus.

This huge vaulted building
was designed as a resting place

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

On their ground floors were
wide spaces for animals and goods

and, above, there were rooms
for the rich merchants

to refresh themselves
before another day of haggling.

One 10th-century traveller talks of

the "riches and beauties
of the bazaars",

and that the income
of the provinces and localities

was between
700 and 800 million dinars.

Markets like this in
the Egyptian capital, Cairo,

still capture
the intensity of medieval trade.

And still surviving in the
modern world of the internet

and the mobile phone is
a fantastic example

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

THEY SPEAK ARABIC

So this is a carrier pigeon.

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

it would make its way
back to this guy.

There's a famous story
that a rich Cairo merchant

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

so he sent a message
by carrier pigeon

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

His contact sent back 500 birds,

each one carrying a small bag
with seeds in it.

The whole process
took just three days.

Sort of a medieval FedEx, really.

By 700 AD, the Islamic Empire

was taking the first steps
towards mass production.

And in this world where knowledge
of materials, metals

and how they're worked became
increasingly important,

one practice flourished.

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

specifically the dream to
turn base metals into gold.

The mysterious practice of alchemy.

The ancient art of alchemy
was a mystical system of belief

based on spells,
symbols and magic.

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

into something much more
scientific - chemistry.

Increasingly,
the knowledge of the alchemists

found more and more
practical applications.

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

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

made the bold decision
to create a common currency

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

The proportion
of gold to other alloyed metals

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

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

that proportion is adjusted by,
believe it or not,

in this period, the alchemists.

It is the alchemists who knew
how to combine metals together

and how to get the proportions
of this gold to silver

and gold to bronze and so on.

Salaam alaikum. Salaam alaikum.

'I hunted down tangible evidence

'of the skill
of medieval Islamic alchemists

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

This is an Islamic dinar.

The date of this is 128 after Hijri.

So the middle of the 8th century?
Almost, almost. Almost 740s. Yes.

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

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

'to be inscribed
with intricate Arabic writing.'

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

'Coin-making is
one of the many examples

'of how the practical needs
of a booming economy

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

What's striking about chemistry
in the medieval Islamic world

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

There are literally thousands that
survive dealing with subjects

as varied as metallurgy,
glass-making,

tile-making, dyeing,
perfumery, weaponry.

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

All this activity clearly
points to a bustling economy,

with consumers, soldiers,
engineers, architects

all demanding innovation
and all demanding new technology.

A great example of applied chemistry
in the medieval Islamic world

was the manufacture of soap.

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

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

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

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

had become virtually
industrialised.

The town of Fez boasted some
27 different soap makers,

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

became world-renowned
for the quality of their soaps.

A 12th-century document

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

It mentions a key ingredient
and it's a substance

that became crucial
to modern chemistry - an alkali.

Now, alkaline substances
are crucial to soap-making.

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

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

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

of the roots of certain plants
like saltworts.

Islamic chemists' new understanding
of alkalis and other new chemicals

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

The Islamic chemists discovered

that they could change
the colour of glass

using newly discovered chemicals
like manganese salts.

And they built industrial furnaces,
some several storeys high,

to manufacture glass
in huge quantities.

The legacy of their skills

can still be seen in
beautiful stained-glass windows.

Islamic chemists also developed many
other colours, pigments and dyes

using their new alkalis
and metals like lead and tin.

These helped architects
to decorate mosques,

like this one
in the Iranian city of Isfahan,

in a glorious range
of colours and designs.

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

Salaam alaikum.

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

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

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

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

But these days, they'll use...

Very nice. Yeah, I think
I'll buy some of that.

'Perfumiers pushed chemists

'to come up with
ever more ingenious techniques

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

'They responded by refining and
really establishing a technique

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

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

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

'shows me how distillation
was used.'

Distillations would have been done
in devices related to these.

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

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

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

'The shape means that
a gas produced in the flask

'is forced to condense
in the spout,

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

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

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

a quick distillation
with rose petals.

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

The water and steam will essentially
control the temperature.

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

'The trick
with this kind of distillation

'is to use heat
to release the scent molecules,

'but at the same time making sure

'that these delicate substances

'aren't destroyed in the process.'

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

will carry those smells over.

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

and there is already liquid
coming through... Yeah.

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

Mmm, yes, you can really smell it.

This picture shows
a 14th-century perfume distillery.

Middle Eastern perfumes

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

The Islamic chemists
also played a pivotal role

in another more gruesome
industry - weaponry.

Historical records during the
Crusades talk in terrified tones

of how the Muslims
would attack the Christians

with burning missiles
and grenades,

striking fear
into the hearts of the defenders.

Many of these used a substance
known as Greek Fire.

Islamic chemists
improved on Greek Fire

by using and refining a naturally
occurring resource - petroleum.

They developed the idea of
distilling petroleum, or naft,

to create a lighter, extremely
flammable oil which they mixed

with other volatile chemicals
to make them burn furiously,

and the result
was clearly terrifying.

What all these medieval Islamic
texts on chemistry have in common

is their great attention to detail,

which is clearly based
on careful experimentation.

In fact, the whole idea
of a laboratory,

where chemical and industrial
processes can be tried out,

really takes hold at this time.

The ingenuity of medieval
Islamic chemists is impressive.

But I wanted to know
something deeper.

What contribution did they make
to our modern understanding

of the principles
behind chemistry?

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

It lists all the known elements.

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

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

On the far left
are the volatile metals.

The periodic table
is triumph of classification,

giving scientists
a way of organising

their knowledge
of the material world.

Classification is
simply a way to think clearly.

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

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

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

People had been trying
to classify the material world

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

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

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

And that's what medieval Islamic
chemists really changed.

They used experimental observations

to classify the stuff
the world is made of.

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

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

just outside the Iranian capital
Tehran in 865 AD.

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

He argued, for instance,
that minerals -

roughly stuff
we dig out of the ground -

should be classified
into six groups,

depending on their observed
chemical properties -

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

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

We have here
what he called the spirits,

we have the metallic bodies,
we have the stones,

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

'Each of Al-Razi's groups

'had a profoundly different
experimental behaviour.

'For instance,
spirits were flammable.

'The metals were
shiny and malleable.

'Salts dissolved in water.

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

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

'Al-Razi was grouping substances
on the basis

'of experimental observations,
not philosophical musings.'

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

What sort of debt
does modern chemistry

owe to him
for his classification?

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

which really leads on
to further experiments,

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

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

which ultimately leads
to our periodic table.

I believe that what we see

in the work of the Islamic chemists
and alchemists

is the first tentative steps
to a new science.

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

but it placed an emphasis
on experimentation

that was truly revolutionary.

But bigger and better was to come,

because Islamic mathematics
and the experimental techniques

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

in a completely innovative way
that would revolutionise their work

and create
the modern scientific age.

Until the 9th or 10th centuries,

ideas about science
and how the natural world worked

were dominated by
the Greek philosopher Aristotle,

and they were very different
from ours today.

He believed that mathematics
was concerned

only with an abstract world
of perfect forms,

of idealised shapes like circles,
squares and triangles.

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

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

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

and for the classical
Greek tradition,

there was a strong sense in which

the science of change was in
contradiction with mathematics.

Mathematics dealt
with perfect knowledge,

with the unchanging world
of mathematical forms.

And it seemed, in principle,
extremely unlikely

that processes of coming
into being and passing away,

of growth and of decay,

of qualitative change,

could be captured with the beauties
of geometry and mathematics.

The story of how humanity
shook off this idea

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

of describing the world around us
is long and complicated.

But for me, Islamic scientists
played a crucial role,

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

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

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

What Al-Haytham
and his contemporaries argued for

was the possibility in a way
of a single science,

which would be
both mathematical and philosophical,

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

with a mathematics -
a science of quantity.

And that seems to me
to be radical and crucial

for the construction of new forms
of reliable knowledge.

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

and other scholars regarded him
as a prodigy.

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

and was an incredibly innovative
and brilliant scholar.

His reputation as an intellect
spread throughout the empire.

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

when he took up
the poisoned chalice

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

There's a wonderful,
if suspiciously apocryphal, story

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

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

Ibn Al-Haytham was asked
by the ruler of Egypt

to find a way of controlling it.
Could he prevent

its unpredictable and potentially
devastating floods and droughts?

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

that the Nile was way too large
to control.

On hearing this, the Caliph
flew into a terrible rage

and ordered
Ibn Al-Haytham's execution.

Ibn Al-Haytham responded
by feigning madness.

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

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

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

and he began with a truly
enigmatic and universal problem.

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

could be explained by mathematics
and geometry.

Under house arrest,
or perhaps here in the rooms

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

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

'I'm with Dr El-Bizri,

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

'He explained that Ibn Al-Haytham
first considered

'the Aristotelian explanation
for how we see,

'an explanation that was
completely un-mathematical.

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

'its essence or form
emanates from it

'and then mysteriously
flows into our eyes.'

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

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

of these buildings
and these trees in the eye

abstracted from their matter.

'According Dr El-Bizri,

'Ibn Al-Haytham found this idea
deeply unsatisfactory.

'He wanted
a mathematical explanation.

'And looking back at existing
Greek writings,

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

'This idea claimed that we see,

'because light rays
come out of the eye.'

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

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

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

and is defined by nice
geometric straight lines.

It seems Ibn Al-Haytham liked
this mathematical approach,

but immediately spotted its flaws.

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

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

but not hurt when you look
at something dim?

Or at night,
can light from our eyes

really be lighting up
distant objects in the sky?

So, in an inspired piece
of thinking,

Ibn Al-Haytham combined
the two Greek ideas

and defined our modern
understanding of light and vision.

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

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

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

it is the beginnings
of mathematising physics.

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

with its rules governing
straight lines,

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

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

In about 1020,
Ibn Al-Haytham published

his ground-breaking
geometric explanation of light

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

And what really marks
this book out as science

is that Ibn Al-Haytham carefully
justifies his theories

with detailed experiments
that others can repeat and verify.

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

For his first experiment,
Ibn Al-Haytham

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

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

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

And by matching the two together,

he was convinced then
that the tube was straight.

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

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

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

he then blocked
the end of the tube.

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

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

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

Proof that light only travels
in a straight line.

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

but Ibn Al-Haytham was starting
from first principles.

Then, through experiment,
he extends

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

He explains how mirrors work,
by arguing that the angle

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

He explains what
we now call refraction,

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

bend when they move
from one medium to another.

And then
he tackles the nature of vision.

Ibn Al-Haytham wanted
to understand

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

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

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

This is what we call today
the camera obscura.

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

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

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

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

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

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

so the light from her head
has to move diagonally downwards

to hit the bottom of the screen

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

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

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

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

Just like
a modern scientific paper,

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

His book isn't just
a dry scientific treatise -

it's a manual
for future generations.

In his work,
he constantly justifies

his theories about light
with experimental observation

and he describes his experiments
in great detail,

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

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

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

to ever work like this.
This, for me,

is the moment that science itself
is summoned into existence

and becomes a discipline
in its own right.

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

once he arrives
at his mathematical theories,

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

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

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

and he even estimated
what that thickness is.

He did it basically by measuring
how long twilight lasts.

He rightly assumed that the reason
it continues to be light

after the sun has dropped
below the horizon

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

The length of twilight
and an educated guess

for what we today call
the air's refractive index

gave Ibn Al-Haytham a way

of estimating the thickness
of the Earth's atmosphere.

He came up with
a figure of around 40 kilometres -

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

It really shows how mathematics

extends the power of science
to explain.

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

the sheer intellectual ambition
of medieval Islamic scientists.

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

scholars like Al-Biruni used
mathematics in startling new ways

to reach out
and describe the universe.

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

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

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

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

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

The scientific method is,
I believe,

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

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

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

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

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

or get vaccinated
against a deadly disease,

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

and countless other
Islamic scholars 1,000 years ago

who struggled
to make sense of the universe

using crude mirrors and astrolabes.

They didn't get
all the right answers,

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

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

to find out about
the great Islamic scientists

who revolutionised astronomy,

making it a truly modern science.

And I'll also discover
how the man many consider

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

borrowed from Islamic
astronomical theories.

And I'll unravel
the mystery of how

the Golden Age of Islamic science
came to an end.

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