Tuesday, March 23, 2010


Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham (Arabic: ابو علي، الحسن بن الحسن بن الهيثم, Persian: ابن هیثم, Latinized: Alhacen or (deprecated) Alhazen) (965 in Basra - c. 1039 in Cairo) was an Arab or Persian scientist and polymath. He made significant contributions to the principles of optics, as well as to physics, anatomy, astronomy, engineering, mathematics, medicine, ophthalmology, philosophy, psychology, visual perception, and to science in general with his early application of the scientific method. He is sometimes called al-Basri (Arabic: البصري), after his birthplace in the city of Basra. He was also nicknamed Ptolemaeus Secundus ("Ptolemy the Second") or simply "The Physicist" in medieval Europe.
Ibn al-Haytham is regarded as the "father of modern optics" for his influential Book of Optics which proved the intromission theory of vision and refined it into essentially its modern form. He is also recognized so for his experiments on optics, including experiments on lenses, mirrors, refraction, reflection, and the dispersion of light into its constituent colours. He studied binocular vision and the Moon illusion, described the finite speed of light, and argued that it is made of particles travelling in straight lines. Due to his formulation of a modern quantitative and empirical approach to physics and science, he is considered the pioneer of the modern scientific method and the originator of the experimental nature of physics and science. Author Bradley Steffens describes him as the "first scientist". He is also considered by A. I. Sabra to be the founder of experimental psychology for his approach to visual perception and optical illusions, and a pioneer of the philosophical field of phenomenology or the study of consciousness from a first-person perspective. His Book of Optics has been ranked with Isaac Newton's Philosophiae Naturalis Principia Mathematica as one of the most influential books in the history of physics, for starting a revolution in optics and visual perception.
Ibn al-Haytham's achievements include many advances in physics and mathematics. He gave the first clear description and correct analysis of the camera obscura. He enunciated Fermat's principle of least time and the concept of inertia (Newton's first law of motion), and developed the concept of momentum. He described the attraction between masses and was aware of the magnitude of acceleration due to gravity at-a-distance. He stated that the heavenly bodies were accountable to the laws of physics and also presented a critique and reform of Ptolemaic astronomy. He was the first to state Wilson's theorem in number theory, and he formulated the Lambert quadrilateral and a concept similar to Playfair's axiom now used in non-Euclidean geometry. Moreover, he formulated and solved Alhazen's problem geometrically using early ideas related to infinitesimal calculus and mathematical induction.

Ibn al-Haythem made significant improvements in optics, physical science, and the scientific method which influenced the development of science for over five hundred years after his death. Ibn al-Haytham's work on optics is credited with contributing a new emphasis on experiment. His influence on physical sciences in general, and on optics in particular, has been held in high esteem and, in fact, ushered in a new era in optical research, both in theory and practice. The scientific method is considered to be so fundamental to modern science that some—especially philosophers of science and practising scientists—consider earlier inquiries into nature to be pre-scientific.
Richard Powers nominated Ibn al-Haytham's scientific method and scientific skepticism as the most influential idea of the second millennium. Recipient of the Nobel Prize in Physics Abdus Salam considered Ibn-al-Haytham "one of the greatest physicists of all time." George Sarton, the father of the history of science, wrote that "Ibn Haytham's writings reveal his fine development of the experimental faculty" and considered him "not only the greatest Muslim physicist, but by all means the greatest of mediaeval times." Robert S. Elliot considers Ibn al-Haytham to be "one of the ablest students of optics of all times." The author Bradley Steffens considers him to be the "first scientist", and Professor Jim Al-Khalili also considers him the "world's first true scientist". The Biographical Dictionary of Scientists wrote that Ibn al-Haytham was "probably the greatest scientist of the Middle Ages" and that "his work remained unsurpassed for nearly 600 years until the time of Johannes Kepler." At a scientific conference in February 2007 as a part of the Hockney-Falco thesis, Charles M. Falco argued that Ibn al-Haytham's work on optics may have influenced the use of optical aids by Renaissance artists. Falco said that his and David Hockney's examples of Renaissance art "demonstrate a continuum in the use of optics by artists from circa 1430, arguably initiated as a result of Ibn al-Haytham's influence, until today." The Latin translation of his main work, Kitab al-Manazir (Book of Optics), exerted a great influence on Western science: for example, on the work of Roger Bacon, who cites him by name, and on Johannes Kepler. It brought about a great progress in experimental methods. His research in catoptrics (the study of optical systems using mirrors) centred on spherical and parabolic mirrors and spherical aberration. He made the observation that the ratio between the angle of incidence and refraction does not remain constant, and investigated the magnifying power of a lens. His work on catoptrics also contains the problem known as "Alhazen's problem". Meanwhile in the Islamic world, Ibn al-Haytham's work influenced Averroes' writings on optics, and his legacy was further advanced through the 'reforming' of his Optics by Persian scientist Kamal al-Din al-Farisi (d. ca. 1320) in the latter's Kitab Tanqih al-Manazir (The Revision of [Ibn al-Haytham's] Optics). The correct explanations of the rainbow phenomenon given by al-Fārisī and Theodoric of Freiberg in the 14th century depended on Ibn al-Haytham's Book of Optics. The work of Ibn al-Haytham and al-Fārisī was also further advanced in the Ottoman Empire by polymath Taqi al-Din in his Book of the Light of the Pupil of Vision and the Light of the Truth of the Sights (1574). He wrote as many as 200 books, although only 55 have survived, and many of those have not yet been translated from Arabic. Even some of his treatises on optics survived only through Latin translation. During the Middle Ages his books on cosmology were translated into Latin, Hebrew and other languages. The crater Alhazen on the Moon is named in his honour, as was the asteroid "59239 Alhazen".
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