Ḥasan Ibn al-Haytham (c. 965 – c. 1040), known in the Latin West as Alhazen, was an Arab mathematician, astronomer and physicist regarded as one of the most influential scientists of the medieval Islamic Golden Age. His seven-volume Book of Optics (Kitāb al-Manāẓir) overturned long-held Greek theories of vision and set out a rigorous, experiment-based approach to natural philosophy that anticipated the modern scientific method. [1]
Early life
Ibn al-Haytham was born around 965 in Basra, then part of the Abbasid Caliphate, in present-day Iraq. He received his education in Basra and Baghdad before moving to Egypt, which was ruled by the Fatimid Caliphate. Contemporary accounts report that he was summoned to Cairo by the caliph al-Ḩākim to devise a scheme for regulating the flooding of the Nile. [2]
According to a widely repeated tradition, Ibn al-Haytham concluded that the project was impractical and, to avoid the caliph's anger, feigned madness until al-Ḩākim's death. Whatever the circumstances, he spent his most productive years in Cairo, where he wrote, taught and copied mathematical texts for a living.
The Book of Optics
His masterwork, the Book of Optics, was composed in Cairo in the early eleventh century. In it he rejected the classical “emission” theory, which held that vision resulted from rays leaving the eye, and argued instead that sight occurs when light reflected from objects enters the eye. [1]
The treatise examined reflection, refraction, the anatomy of the eye, and optical illusions, and it contained early descriptions of the camera obscura. Translated into Latin as De aspectibus, it profoundly shaped later European scholars, including Roger Bacon, Witelo and Johannes Kepler. [4]
The experimental method
Ibn al-Haytham is often described as an early advocate of the experimental method, insisting that hypotheses be tested against observation and measurement rather than accepted on authority. He wrote of the need to scrutinise the work of predecessors critically:
Other work
Beyond optics, Ibn al-Haytham wrote extensively on mathematics and astronomy. His work in geometry addressed the problem now known as “Alhazen's problem,” and he produced critiques of Ptolemaic astronomy that influenced later reforms of planetary theory. [3]
Legacy
Ibn al-Haytham died in Cairo around 1040. His emphasis on observation, controlled experiment and mathematical reasoning earned him a lasting place in the history of science, and the lunar crater Alhazen and an asteroid are named in his honour. [2]
