Islamic Science: The Discoveries That Shaped the Modern World

What set the science of the Islamic world apart was not only what it discovered, but how. Scholars did not simply trust the ancient authorities. They tested them.

The clearest example is Ibn al-Haytham (known in Europe as Alhazen, around 965 to 1040). Working in Cairo, he showed that we see because light enters the eye, overturning the old Greek idea that the eye sends out rays. He proved it with controlled experiments, including the earliest clear description of the camera obscura, and wrote it up in his Book of Optics. His insistence that a claim must be checked against evidence is one of the earliest statements of the experimental method, and it ran through the whole enterprise. Muslim science began, in large part, in the Golden Age city of Baghdad and spread from there.

Around 820, a scholar at Baghdad's House of Wisdom named al-Khwarizmi wrote a book on solving equations. Its title gave us the word algebra, and the Latin form of his own name gave us algorithm. He also championed the Hindu numeral system, including zero as a placeholder, which spread through the Muslim world and then to Europe, where we still call the symbols Arabic numerals.

Others built on him. Omar Khayyam, better known in the West as a poet, solved cubic equations geometrically and helped reform the calendar. Muslim mathematicians developed trigonometry into a full discipline, driven in part by the practical need to find the direction of prayer and the times of the day from any point on earth.

The Muslim world built true hospitals, called bimaristans, with separate wards, pharmacies, record-keeping and teaching, open to rich and poor alike. The medicine practised in them was written down in books that outlasted the buildings.

Al-Razi (Rhazes, around 865 to 925) was a sharp clinical observer who was the first to clearly distinguish smallpox from measles. Ibn Sina (Avicenna, 980 to 1037) gathered the medical knowledge of his age into the Canon of Medicine, which remained a standard textbook in European universities for roughly 600 years. In Cordoba, al-Zahrawi wrote a surgical encyclopaedia, complete with drawings of the instruments he invented, that helped found modern surgery.

Ibn al-Haytham's work on light did more than explain vision. It laid groundwork for the study of lenses and reflection that European scientists picked up centuries later, when his Book of Optics reached them in Latin. It is why he is often called the father of modern optics.

Chemistry took shape in the same period. Jabir ibn Hayyan, working in the 8th century, is remembered for turning alchemy toward careful, repeatable procedure. He and those who followed him refined distillation, crystallisation and the handling of acids, and built much of the standard laboratory apparatus. The words alcohol, alkali, alembic and alchemy all came into English from Arabic.

In 9th-century Baghdad, the three Banu Musa brothers wrote the Book of Ingenious Devices, describing around a hundred mechanical inventions, from trick fountains to self-adjusting instruments. Three centuries later al-Jazari went further. His Book of Knowledge of Ingenious Mechanical Devices (1206) described elaborate water clocks, automatic musicians and hand-washing machines, and along the way used crankshafts, camshafts and valves, components at the heart of machines to this day.

His most famous design was the elephant clock, a water-powered clock built as a working sculpture, combining an Indian elephant, Chinese dragons, an Egyptian phoenix and a Greek water mechanism into a single celebration of a connected world.

Astronomy was the queen of the Islamic sciences. Observatories mapped the heavens with growing precision, and so many stars still carry Arabic names, among them Aldebaran, Altair and Betelgeuse. In 964, the astronomer al-Sufi recorded the Andromeda galaxy, the first known account of a galaxy beyond our own.

The same curiosity turned to the earth itself. Al-Biruni estimated the planet's circumference with striking accuracy, and the geographer al-Idrisi produced one of the finest world maps of the Middle Ages for the court of Sicily. Astronomy is a story large enough for its own page: read Islam and the stars.

None of this stayed in one place. From the 12th century, scholars in Toledo and Sicily translated Arabic science into Latin, and Europe studied it for centuries. Ibn al-Haytham shaped how Europeans thought about light and proof. Ibn Sina trained their physicians. Al-Khwarizmi taught them to calculate. This transmission is one of the threads that made the European Renaissance possible.

The debt is even in the vocabulary of science: algebra, algorithm, alcohol, alkali, cipher, zenith and nadir all came from Arabic. The Islamic Golden Age was not a detour in the history of science. It was one of its main roads.