Ibn al-Haytham was the first to correctly explain the theory of vision,[14] and to argue that vision occurs in the brain, pointing to observations that it is subjective and affected by personal experience.[15] He also stated the principle of least time for refraction which would later become Fermat's principle.[16] He made major contributions to catoptrics and dioptrics by studying reflection, refraction and nature of images formed by light rays.[17][18] Ibn al-Haytham was an early proponent of the concept that a hypothesis must be supported by experiments based on confirmable procedures or mathematical reasoning—an early pioneer in the scientific method five centuries before Renaissance scientists,[19][20][21][22] he is sometimes described as the world's "first true scientist".[12] He was also a polymath, writing on philosophy, theology and medicine.[23]
Born in Basra, he spent most of his productive period in the Fatimid capital of Cairo and earned his living authoring various treatises and tutoring members of the nobilities.[24] Ibn al-Haytham is sometimes given the bynameal-Baṣrī after his birthplace,[25] or al-Miṣrī ("the Egyptian").[26][27] Al-Haytham was dubbed the "Second Ptolemy" by Abu'l-Hasan Bayhaqi[28] and "The Physicist" by John Peckham.[29] Ibn al-Haytham paved the way for the modern science of physical optics.[30]
^El-Bizri 2010, p. 11: "Ibn al-Haytham's groundbreaking studies in optics, including his research in catoptrics and dioptrics (respectively the sciences investigating the principles and instruments pertaining to the reflection and refraction of light), were principally gathered in his monumental opus: Kitåb al-manåóir (The Optics; De Aspectibus or Perspectivae; composed between 1028 CE and 1038 CE)."
^Rooney 2012, p. 39: "As a rigorous experimental physicist, he is sometimes credited with inventing the scientific method."
^Baker 2012, p. 449: "As shown earlier, Ibn al-Haytham was among the first scholars to experiment with animal psychology.
^Also Alhacen, Avennathan, Avenetan, etc.; the identity of "Alhazen" with Ibn al-Haytham al-Basri "was identified towards the end of the 19th century". (Vernet 1996, p. 788)
^Esposito, John L. (2000). The Oxford History of Islam. Oxford University Press. p. 192.: "Ibn al-Haytham (d. 1039), known in the West as Alhazan, was a leading Arab mathematician, astronomer, and physicist. His optical compendium, Kitab al-Manazir, is the greatest medieval work on optics."
^For the description of his main fields, see e.g. Vernet 1996, p. 788 ("He is one of the principal Arab mathematicians and, without any doubt, the best physicist.") Sabra 2008, Kalin, Ayduz & Dagli 2009 ("Ibn al-Ḥaytam was an eminent eleventh-century Arab optician, geometer, arithmetician, algebraist, astronomer, and engineer."), Dallal 1999 ("Ibn al-Haytham (d. 1039), known in the West as Alhazan, was a leading Arab mathematician, astronomer, and physicist. His optical compendium, Kitab al-Manazir, is the greatest medieval work on optics.")
^Roshdi Rashed, Ibn al-Haytham's Geometrical Methods and the Philosophy of Mathematics: A History of Arabic Sciences and Mathematics, Volume 5, Routledge (2017), p. 635