Ibn al-Haytham or known to Europeans as Alhazen (965 in Basra - 1040 in Cairo) was a Muslim scientific thinker and polymath who made significant contributions to optics, physics, astronomy, mathematics, and the study of perception. Spending most of his life in Cairo, Alhazen argued that certain of Ptolemy's (90 - 168) earth-centered (geocentric) ideas in astronomy violated ideas of uniform circular motion and physical reality.
He was most original in his theory of light and vision, where he proceeded by experiment and induction, and again voiced skepticism of past authorities such as Euclid's (300 BC) extramission theory of vision. Alhazen rejected the classical concept of the visual cone emanating from the eye, pointing to the faultiness of assuming that some form of radiance could flow from the eye the moment it was opened and illuminate the entire heavens. He validated the intromission hypothesis of vision by explaining that a person experiences
Alhazen earned his living by transcribing all the geometric works by Greek mathematician Euclid and selling it for cash. Incidentally he developed a technical mastery of straight lines and motion. Finding employment at the court of the powerful caliph Al-Hakim in Cairo, who encouraged the enterprise of learning and technique in order to obsessively control all elements in the world around him. Desiring to command the Nile river, the caliph commissioned Alhazen to stop the annual Nile flooding. Alhazen, though assuming the project, quickly understood its doomed failure and pretended to be insane in order to escape the caliph's vengeful wrath. Unfortunately the plan did not succeed and he was sentenced to ten years in aphotic confinement.
Under police control in miserly conditions Alhazen began to meditate on what he could see, becoming obsessed with light and dark. He questioned the classical idea, the accepted dogma for a thousand years, that sight was due to light coming out of a human eye and touching an object to produce vision (extramission). He explained that a person experiences severe pain in the eye when looking at a very bright object like the sun, which contradicted extramission because such pain should not be felt if the eye was the source of the light rays.
If light is independent of the eye, how then do objects redirect light into our eyes
he realized there was a clue in the ways mirrors work ; he studied those patterns and confirmed the symmetry that the angle of incidence and reflection equate (the angle at which light hits an object is the same as its reflection), analogous to the way a ball strikes at and rebounds from a wall.
He made a breakthrough in realizing that light reflects off of all objects not just mirrors and precisely developed via mathematics how light bounces off (reflection) and bends through (refraction) and object.
In the year 1021, twelve years later, the caliph died and Alhazen was set free and produced seven volumes fundamentally covering light and vision, transforming its mathematical rules and enacting the modern study of optics.