Ibn al-Haytham (Alhazen) ابن الهيثم

965–1040 CE

Arab physicist, mathematician, and astronomer whose Kitab al-Manazir (Book of Optics) is a foundational scientific work in human history. Working in Fatimid Cairo, he fundamentally overturned the Greek theory of vision (which held that the eye emits rays) and proved that vision occurs when light enters the eye — the correct theory that became the basis of modern optics. He pioneered the experimental scientific method, insisting that theories must be tested through controlled experiments and verified through reproducible observations. He conducted detailed experiments with lenses, mirrors, refraction, and the camera obscura (a precursor to the modern camera).

Why They Mattered

Ibn al-Haytham is often called 'the first true scientist' for his systematic insistence on experimentation over philosophical speculation. His Book of Optics replaced centuries of incorrect Greek optical theory and established the correct understanding of how vision works. His experimental methodology — hypothesis, experiment, verification — anticipated the European scientific method by over 500 years. His work on the camera obscura influenced the development of modern photography.

Intellectual Role

Ibn al-Haytham's role in Islamic civilization distinguished him as a preeminent figure in the study of optics and the foundation of the scientific method. Often referred to as the 'father of optics', his work represented a significant departure from earlier Greek theories, particularly the emission theory of vision. Instead, he proposed that vision occurs when light enters the eye, a groundbreaking revelation encapsulated in his monumental treatise, Kitab al-Manazir (Book of Optics). In contrast to his contemporaries, who relied heavily on philosophical speculation, Ibn al-Haytham championed …

Legacy

His Book of Optics influenced Roger Bacon, Johannes Kepler, René Descartes, and Isaac Newton — making him a pivotal figure in the history of science. His emphasis on experimental verification over philosophical authority makes him a foundational figure of the scientific method. He appears on the Iraqi 10,000-dinar note, and a crater on the moon is named after him (Alhazen). UNESCO recognized his contributions by declaring 2015 the International Year of Light, partly in his honor.