SciFri 3.18.05

Muhammad ibn Musa Al-Khwarizmi, born in what is now Uzbekistan around A.D. 780, gave his name to the word "algorism," which became "arithmetic."

Lighting the Dark Ages--ancient Arab and Persian scholars

By Deane Morrison

Published on March 18, 2005

The period between the fall of the Roman Empire and the beginning of the Renaissance has been called the Dark Ages because during that time, the light of learning lay dormant in Europe. But elsewhere, and perhaps nowhere more than in the Arab-Muslim world, it not only shone but brightened.

The eve of a visit to campus by Ismail Serageldin is a good time to look at the contributions of Arabs and Persians to modern science and mathematics. Director of Egypt's Library of Alexandria (Bibliotheca Alexandrina), Serageldin, a proponent of agricultural and scientific progress in developing countries, heads an institute whose namesake, the original library at Alexandria, was a mecca for scholars in the ancient world.

The Persian scientist Rhazes, also called Abu-Bakr Muhammad ibn Zakariyya Ar-Razi, was born near what is now Tehran about A.D. 845 and was the first to distinguish clearly between smallpox and measles. He described his experiments so well that modern scientists can reproduce them.

To get an idea how pervasive the influence of Arab mathematicians was during the Middle Ages, visit the MacTutor History of Mathematics Archive and look for biographies of mathematicians born between A.D. 500 and A.D. 999. You'll find the vast majority of names are Arabic.

One of those names is Muhammad ibn Musa Al-Khwarizmi, born in what is now Uzbekistan around A.D. 780. Never heard of him? He's well known in mathematical circles for a work in which he preserved and expanded on the work of Diophantus, a Greek. The work was titled "ilm al-jabr wal muqabalah," "the science of transposition and cancellation." The Arabic "al-jabr" became the Latin "algebra," the name given to the branch of mathematics Diophantus had founded. Al-Khwarizmi's own name got twisted into "algorism," meaning "the art of calculating," what we now call arithmetic.

Even more important, Al-Khwarizmi drew on the work of Hindu as well as Greek mathematicians, picking up the Hindu numerals, including the zero, which was unknown to users of Roman numerals. His work was translated into Latin, and the numerals--called Arabic numerals, despite their Hindu origin--went with it. The numerals were passed to Europe through the Italian mathematician Leonardo Fibonacci. It took a while, but the Arabic numerals turned mathematical calculations upside down. Today, no one can envision doing long division or any number of other manipulations without them.

The Persian scientist Rhazes, also called by the Arabic name Abu-Bakr Muhammad ibn Zakariyya Ar-Razi, was born near what is now Tehran about A.D. 845. He studied medicine and became the chief physician of Baghdad's biggest hospital. He is credited with being the first to distinguish clearly between smallpox and measles and described his experiments so well that modern scientists can reproduce them. Rhazes also concocted what is now called plaster of Paris and described how it could be made into casts to keep broken bones in place.

The most prominent physicist of the Middle Ages was Alhazen (Arabic name: Abu-'Ali Al-Hasan ibn Al-Haytham), born in Basra (Iraq) about A.D. 965. Fascinated by optics, he corrected an old notion that people see by rays of light emanating from the eyes and reflecting from objects. Alhazen realized that the sun or some other source emits light before it's reflected off objects and into the eye. He also explained that lenses magnify objects because of the curvature of their surface, not because of any intrinsic property of the material the lens is made from. He did much work on reflection and refraction of light, including studies of the rainbow and the focusing of light through lenses. He made a pinhole camera and parabolic mirrors, the type now used in telescopes. The world had to wait nearly six centuries--until the days of German astronomer Johannes Kepler, who was heavily influenced by a Latin translation of Alhazen's work--to see further progress in optics.

The dry air and clear skies of the Middle East led Arabian science to make its most famous marks. Pick up a star chart, and you'll see all kinds of Arabic names for stars. There's Algol, the winking "eye of the demon" in the constellation Perseus; Aldebaran, the eye of Taurus, the bull (from Al Dabaran, "follower"--of the Pleiades star cluster); and Betelgeuse, the brightest star in Orion. The name Betelgeuse is from the Arabic Ibt al Jauzah, or Armpit of the Central One, via a long line of intermediate names.

"Arab and other Muslim astronomers made numerous observations of star positions," says U of M astronomy professor Terry Jones. "Much of the ancient Arabs' contribution to astronomy consisted of preserving and refining the knowledge of others, especially Greeks and Egyptians."

For example, Arabian astronomer Albategnius (Arabic name: Abu-'Abdullah Muhammad ibn Jabir al-Battani), born in what is now southeastern Turkey around A.D. 858, made a mark by improving on the work of the ancient astronomer Ptolemy, who had drawn up a model of the universe with the Earth at the center. Albategnius noted, among other things, the position of the sun among the constellations at the moment the sun appears smallest--that is, when Earth is farthest from the sun. Observing the sun's position for himself at that moment, he realized the sun was no longer in the position where Ptolemy had said. He concluded that this position changed slowly and calculated a rather accurate value for the motion. Today, we know this phenomenon happens because the Earth's elliptical orbit itself rotates. Albategnius became the most respected of Arabian astronomers in the eyes of Medieval Europeans.

To read more on the development of science during ancient and Medieval times, see Isaac Asimov's Biographical Encyclopedia of Science and Technology, the source for much of this article. Ismail Serageldin will deliver the Freeman Lecture at 2:30 p.m. Wednesday, March 23, in the Cargill Building. It's free, but you must register at www.freemanforum.org; or call 612-624-3009.