Ibn_al-Haytham

{{dablink|This article is about the scientist. For the crater on the Moon named after him, see [[Alhazen (crater)]].}}
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{{Infobox_Muslim scholars |


notability = [[Islamic science|Muslim scientist]]|
era = [[Islamic Golden Age]]|
color = #cef2e0 |


image_name = Ibn_haithem_portrait.jpg|
image_caption = Ibn al-Haytham depicted in an Iraqi 10,000-dinar note. |
signature = |


name = '''Abū ‘Alī al-{{Unicode|Ḥ}}asan ibn al-{{Unicode|Ḥ}}asan ibn al-Haytham'''|
title= '''Ibn al-Haytham''' and '''Alhacen'''|
birth = 965|
death = 1039|
Maddhab = |
school tradition= [[Ash'ari]]|
Ethnicity = [[Arab]] or [[Persian Empire|Persian]] |
Region = [[Iraq]] ([[Mesopotamia]]) and [[Egypt]] |
main_interests = [[Anatomy]], [[Islamic astronomy|Astronomy]], [[Muslim inventions|Engineering]], [[Islamic mathematics|Mathematics]], [[Mechanics]], [[Islamic medicine|Medicine]], [[Optics]], [[Ophthalmology in medieval Islam|Ophthalmology]], [[Early Islamic philosophy|Philosophy]], [[Physics]], [[Early Muslim sociology|Psychology]], [[Islamic science|Science]] |
notable idea= Pioneer in [[optics]], [[scientific method]], [[scientific skepticism]], [[experimental science]], [[experimental physics]], [[experimental psychology]], [[psychophysics]], [[phenomenology]], [[visual perception]], [[analytic geometry]], [[elliptical geometry]], [[hyperbolic geometry]], [[non-Euclidean geometry]], non-[[Ptolemaic astronomy]], [[astrophysics]] and [[celestial mechanics]] |
influences = [[Aristotle]], [[Euclid]], [[Ptolemy]], [[Galen]], [[Muhammad]], [[Abu al-Hasan al-Ash'ari]], [[Banū Mūsā]], [[Thabit ibn Qurra]], [[al-Kindi]], [[Ibn Sahl]], [[Abū Sahl al-Qūhī]] |
influenced = [[Omar Khayyam|Khayyam]], [[al-Khazini]], [[Mo'ayyeduddin Urdi|al-Urdi]], [[al-Tusi]], [[Qutb al-Din al-Shirazi|al-Shirazi]], [[Kamāl al-Dīn al-Fārisī|al-Farisi]], [[Ibn al-Shatir]], [[Roger Bacon]], [[John Peckham|Peckham]], [[Witelo]], [[Gersonides]], [[Alfonso]], [[da Vinci]], [[Gerolamo Cardano|Cardano]], [[Francis Bacon]], [[Pierre de Fermat|Fermat]], [[Johannes Kepler|Kepler]], [[Willebrord Snellius|Snell]], [[René Descartes|Descartes]], [[Christiaan Huygens|Huygens]], [[James Gregory|Gregory]], [[Guillaume de l'Hôpital|de l'Hopital]], [[Isaac Barrow|Barrow]], [[John Wallis|Wallis]], [[Giovanni Girolamo Saccheri|Saccheri]] |
works = ''[[Book of Optics]]'', ''Analysis and Synthesis'', ''Balance of Wisdom'', ''Discourse on Place'', ''Doubts Concerning Ptolemy'', ''Maqala fi'l-qarastun'', ''On the Configuration of the World'', ''Opuscula'', ''The Model of the Motions'', ''The Resolution of Doubts'', ''Treatise on Light'', ''Treatise on Place'' |
}}

'''{{transl|ar|ALA|Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham}}''' ([[Arabic language|Arabic]]: أبو علي الحسن بن الحسن بن الهيثم, [[Latin]]ized: '''Alhacen''' or (deprecated) '''Alhazen''') (965 – 1039), was an [[Arab]]<ref name=Smith>Smith (1992).</ref> or [[Persian Empire|Persian]]<ref name=MacTutor/> [[Muslim]] [[polymath]]<ref>Hamarneh:
{{quote|"A great man and a universal genius, long neglected even by his own people."}}</ref><ref>Bettany:
{{quote|"Ibn ai-Haytham provides us with the historical personage of a versatile universal genius."}}</ref>
who made significant contributions to the principles of [[optics]], as well as to [[anatomy]], [[Islamic astronomy|astronomy]], [[Muslim inventions|engineering]], [[Islamic mathematics|mathematics]], [[Islamic medicine|medicine]], [[Ophthalmology in medieval Islam|ophthalmology]], [[Early Islamic philosophy|philosophy]], [[physics]], [[Early Muslim sociology|psychology]], [[Ash'ari]] [[Kalam|theology]], [[visual perception]], and to [[Islamic science|science]] in general with his introduction of the [[scientific method]]. He is sometimes called '''al-Basri''' (Arabic: البصري), after his birthplace in the city of [[Basra]] in [[Iraq]] ([[Mesopotamia]]), then ruled by the [[Buyid dynasty]] of [[Persian Empire|Persia]].<ref name=Persia>[http://ublib.buffalo.edu/libraries/asl/exhibits/stamps/em.html Electromagnetic Theory and Light]</ref>

Ibn al-Haytham is regarded as the father of [[optics]] for his influential ''[[Book of Optics]]'', which correctly explained and proved the modern intromission theory of [[visual perception|vision]], and for his [[experiment]]s on optics, including experiments on [[lens (optics)|lenses]], [[mirror]]s, [[refraction]], [[Reflection (physics)|reflection]], and the dispersion of [[light]] into its constituent [[colours]].<ref name=Deek/>
He studied [[binocular vision]] and the [[moon illusion]], speculated on the [[speed of light|finite speed]], [[rectilinear propagation]] and [[Electromagnetism|electromagnetic]] aspects of light,<ref>Hamarneh, p. 119.</ref> and argued that [[Ray (optics)|rays]] of light are streams of [[photon|energy particles]]<ref>Rashed (2007), p. 19.</ref> travelling in straight lines.<ref>J. J. O'Connor and E. F. Robertson (2002). [http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Light_1.html Light through the ages: Ancient Greece to Maxwell], ''[[MacTutor History of Mathematics archive]]''.</ref>
Due to his formulation of a modern [[quantitative]], [[empiricism|empirical]] and [[experiment]]al approach to [[physics]] and [[science]], he is considered the pioneer of the modern [[scientific method]]<ref name=Agar>David Agar (2001). [http://users.jyu.fi/~daagar/index_files/arabs.html Arabic Studies in Physics and Astronomy During 800 - 1400 AD]. [[University of Jyväskylä]].</ref><ref name=Gorini/> and the originator of [[experimental science]]<ref>Omar (1977)</ref> and [[experimental physics]],<ref>Rüdiger Thiele (2005). "In Memoriam: Matthias Schramm", ''Arabic Sciences and Philosophy'' '''15''', p. 329–331. [[Cambridge University Press]].</ref> and some have described him as the "first [[scientist]]" for these reasons.<ref>Steffens.</ref>
He is also considered by some to be the founder of [[psychophysics]] and [[experimental psychology]]<ref name=Khaleefa>Khaleefa.</ref> for his experimental approach to the [[psychology]] of [[visual perception]],<ref name=Steffens>Steffens, Chapter 5.</ref> and a pioneer of the philosophical field of [[phenomenology]].
His ''Book of Optics'' has been ranked alongside [[Isaac Newton]]'s ''[[Philosophiae Naturalis Principia Mathematica]]'' as one of the most influential books in the [[history of physics]].<ref name=Salih>Salih, Al-Amri, El Gomati.</ref>

Among his other achievements, Ibn al-Haytham described the [[pinhole camera]] and invented the [[camera obscura]] (a precursor to the modern [[camera]]),<ref name=Wade/> discovered [[Fermat's principle]] of least time and the law of [[inertia]] (known as [[Newton's first law of motion]]),<ref name=Salam/> discovered the concept of [[momentum]] (part of [[Newton's second law of motion]]),<ref name=Nasr/> described the [[Gravitation|attraction]] between [[mass]]es and was aware of the [[Magnitude (mathematics)|magnitude]] of [[acceleration]] due to [[Gravitation|gravity]] at a distance,<ref name=Bizri>El-Bizri (2006).</ref> discovered that the [[Astronomical object|heavenly bodies]] were accountable to the [[Physical law|laws of physics]], presented the earliest critique and reform of the [[Geocentric model|Ptolemaic model]], first stated [[Wilson's theorem]] in [[number theory]], pioneered [[analytic geometry]] and the first theorems on [[non-Euclidean geometry]], formulated and solved [[#Alhazen's problem|Alhazen's problem]] geometrically, developed and proved the earliest general formula for [[infinitesimal]] and [[integral]] [[calculus]] using [[mathematical induction]],<ref name=Katz/> and in his optical research laid the foundations for the later development of [[telescope|telescopic]] astronomy,<ref name=Marshall>Marshall.</ref> as well as for the [[microscope]] and the use of optical aids in [[Renaissance]] [[art]].<ref name=Power/>

==Overview==
===Biography===
Abū ‘Alī al-Hasan ibn al-Hasan ibn al-Haytham was born in the [[Arab]] city of [[Basra]], [[Iraq]] ([[Mesopotamia]]), then part of the [[Buyid dynasty]] of [[Persian Empire|Persia]],<ref name=Persia/> and he probably died in [[Cairo]], [[Egypt]].<ref name=MacTutor>{{MacTutor Biography|id=Al-Haytham|title=Abu Ali al-Hasan ibn al-Haytham}}</ref> Known in the West as Alhacen or Alhazen, Ibn al-Haytham was born in 965 in [[Basra]], and was educated there and in [[Baghdad]].

One account of his career has him summoned to Egypt by the mercurial [[caliph]] [[al-Hakim bi-Amr Allah|Hakim]] to regulate the [[flooding]] of the [[Nile]]. After his field work made him aware of the impracticality of this scheme, and fearing the caliph's anger, he [[feigned madness]]. He was kept under [[house arrest]] until Hakim's death in 1021. During this time, he wrote his influential ''[[Book of Optics]]'' and scores of other important treatises on [[physics]] and [[mathematics]]. He later traveled to [[Spain]] and, during this period, he had ample time for his scientific pursuits, which included [[optics]], mathematics, physics, [[medicine]], and the development of scientific methods — on all of which he has left several outstanding books.

===Works===
Ibn al-Haytham was a pioneer in [[optics]], [[Islamic astronomy|astronomy]], [[Muslim inventions|engineering]], [[Islamic mathematics|mathematics]], [[Islamic science|physics]], and [[psychology]]. His optical writings influenced many Western intellectuals such as [[Roger Bacon]], [[John Pecham]], [[Witelo]], and [[Johannes Kepler]].<ref>Lindberg (1967).</ref>

Yasmeen M. Faruqi writes:
{{quote|"In seventeenth century Europe the problems formulated by Ibn al-Haytham (965-1041) became known as “Alhazen’s problem”. [...] Al-Haytham’s contributions to [[geometry]] and [[number theory]] went well beyond the [[Archimedes|Archimedean]] tradition. Al-Haytham also worked on [[analytical geometry]] and the beginnings of the link between [[algebra]] and geometry. Subsequently, this work led in [[pure mathematics]] to the harmonious fusion of algebra and geometry that was epitomised by [[René Descartes|Descartes]] in [[geometric analysis]] and by [[Isaac Newton|Newton]] in the [[calculus]]. Al-Haytham was a scientist who made major contributions to the fields of [[mathematics]], [[physics]] and [[astronomy]] during the latter half of the tenth century."<ref>Faruqi, p. 395-396.</ref>}}

According to medieval biographers, Ibn al-Haytham wrote more than 200 works on a wide range of subjects,<ref name=Ezine>Steffens ([[cf.]] Bradley Steffens, "Who Was the First Scientist?", ''Ezine Articles'').</ref> of which at least 96 of his scientific works are known. Most of his works are now lost, but more than 50 of them have survived to some extent. Nearly half of his surviving works are on mathematics, 23 of them are on astronomy, and 14 of them are on optics, with a few on other areas of science.<ref name=Rashed>Rashed (2002), p. 773.</ref> Not all of his surviving works have yet been studied, but some of his most important ones are described below. These include:

*''[[Book of Optics]]'' (1021)
*''Analysis and Synthesis''
*''Balance of Wisdom''
*''Discourse on Place''
*''Maqala fi'l-qarastun''
*''Doubts Concerning Ptolemy'' (1028)
*''On the Configuration of the World''
*''Opuscula''
*''The Model of the Motions of Each of the Seven Planets'' (1038)
*''The Resolution of Doubts''
*''Treatise on Light''
*''Treatise on Place''

===Scientific method===
Rosanna Gorini wrote the following on Ibn al-Haytham's introduction of the [[scientific method]]:
{{quote|"According to the majority of the historians al-Haytham was the pioneer of the modern scientific method. With his book he changed the meaning of the term optics and established experiments as the norm of proof in the field. His investigations are based not on abstract theories, but on experimental evidences and his experiments were systematic and repeatable."<ref name=Gorini>Gorini.</ref>}}

Roshdi Rashed wrote the following on Ibn al-Haytham:
{{quote|"His work on optics, which includes a theory of vision and a theory of light, is considered by many to be his most important contribution, setting the scene for developments well into the 17th century. His contributions to geometry and number theory go well beyond the archimedean tradition. And by promoting the use of experiments in scientific research, al-Haytham played an important part in setting the scene for modern science."<ref name=Rashed/>}}

Ibn al-Haytham developed rigorous [[experiment]]al methods of controlled [[Test method|scientific testing]] in order to verify theoretical [[Hypothesis|hypotheses]] and substantiate [[Inductive reasoning|inductive]] [[conjecture]]s.<ref name=Bizri/> Ibn al-Haytham's scientific method was very similar to the modern scientific method and consisted of the following procedures:<ref name=Ezine/>

#[[Observation]]
#Statement of [[problem]]
#Formulation of [[hypothesis]]
#Testing of hypothesis using [[experiment]]ation
#Analysis of experimental [[result]]s
#Interpretation of [[data]] and formulation of [[conclusion]]
#[[Publication]] of findings

In ''The Model of the Motions'', Ibn al-Haytham also describes an early version of [[Occam's razor]], where he employs only minimal hypotheses regarding the properties that characterize astronomical motions, as he attempts to eliminate from his planetary model the [[cosmology|cosmological]] hypotheses that cannot be observed from [[Earth]].<ref name=Rashed-35-36>Rashed (2007), p. 35-36.</ref>

From Ibn al-Haytham to the present day, the emphasis of the scientific method has always been on seeking [[truth]]:

{{quote|"Truth is sought for its own sake. And those who are engaged upon the quest for anything for its own sake are not interested in other things. Finding the truth is difficult, and the road to it is rough. ..."<ref>Alhazen (Ibn Al-Haytham) ''Critique of Ptolemy'', translated by S. Pines, ''Actes X Congrès internationale d'histoire des sciences'', Vol '''I''' Ithaca 1962, as referenced on p.139 of Shmuel Sambursky (ed. 1974) ''Physical Thought from the Presocratics to the Quantum Physicists'' ISBN 0-87663-712-8</ref>}}

===Legacy===
Ibn al-Haytham was one of the most eminent [[physicist]]s, whose developments in [[optics]] and the [[scientific method]] were particularly outstanding. Ibn al-Haytham's work on optics is credited with contributing a new emphasis on [[experiment]]. His influence on [[physical science]]s 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.<ref name=Deek/> The scientific method is considered to be so fundamental to [[science|modern science]] that some — especially [[Philosophy of science|philosophers of science]] and practicing scientists — consider earlier inquiries into nature to be ''pre-scientific''.<ref>[[Robert Briffault|Briffault]], p. 190-202:
{{quote|"What we call science arose as a result of new methods of experiment, observation, and measurement, which were introduced into Europe by the [[Arab]]s. [...] Science is the most momentous contribution of [[Arab world|Arab civilization]] to the [[Modern Times|modern world]], but its fruits were slow in ripening. Not until long after [[Moors|Moorish]] culture had sunk back into darkness did the giant to which it had given birth, rise in his might. It was not science only which brought Europe back to life. Other and manifold influences from the civilization of Islam communicated its first glow to European life. [...] The debt of our science to that of the Arabs does not consist in startling discoveries or revolutionary theories; science owes a great deal more to Arab culture, it owes its existence....The ancient world was, as we saw, pre-scientific. The astronomy and mathematics of Greeks were a foreign importation never thoroughly acclimatized in Greek culture. The Greeks systematized, generalized and theorized, but the patient ways of investigations, the accumulation of positive knowledge, the minute methods of science, detailed and prolonged observation and experimental inquiry were altogether alien to the Greek temperament. [...] What we call science arose in Europe as a result of new spirit of enquiry, of new methods of experiment, observation, measurement, of the development of mathematics, in a form unknown to the Greeks. That spirit and those methods were introduced into the European world by the Arabs."}}
</ref>
Due to its importance in the [[history of science]], some have considered his development of the scientific method to be the most important scientific development of the [[2nd millennium|second millennium]].<ref name=Power>Richard Power ([[University of Illinois]]), [http://online.physics.uiuc.edu/courses/phys199epp/fall06/Powers-NYTimes.pdf Best Idea; Eyes Wide Open], ''[[New York Times]]'', April 18, 1999.</ref>

[[Nobel Prize]] winning physicist [[Abdus Salam]] wrote:
{{quote|"Ibn-al-Haitham (Alhazen, 965-1039 CE) was one of the greatest physicists of all time. He made experimental contributions of the highest order in optics. He enunciated that a ray of light, in passing through a medium, takes the path which is the easier and 'quicker'. In this he was anticipating [[Fermat's principle|Fermat's Principle of Least Time]] by many centuries. He enunciated the law of [[inertia]], later to become [[Newton's laws of motion|Newton's first law of motion]]. Part V of [[Roger Bacon]]'s "''Opus Majus''" is practically an annotation to Ibn al Haitham's ''Optics''."<ref name=Salam>[[Abdus Salam|Salam]], in Lai.</ref>}}

[[George Sarton]], the "father of the history of science", wrote in the ''Introduction to the History of Science'':
{{quote|"[Ibn al-Haytham] was not only the greatest Muslim physicist, but by all means the greatest of [[Middle Ages|mediaeval times]]."<ref>[[George Sarton]], ''Introduction to the History of Science'', "The Time of Al-Biruni".</ref>}}
{{quote|"Ibn Haytham's writings reveal his fine development of the experimental faculty. His tables of corresponding [[Angle of incidence|angles of incidence]] and refraction of light passing from one medium to another show how closely he had approached discovering the [[Snell's law|law of constancy of ratio of sines]], later attributed to [[Willebrord Snellius|Snell]]. He accounted correctly for twilight as due to [[atmospheric refraction]], estimating the sun's depression to be 19 degrees below the horizon, at the commencement of the phenomenon in the mornings or at its termination in the evenings."<ref>Dr. A. Zahoor and Dr. Z. Haq (1997). [http://www.cyberistan.org/islamic/Introl1.html Quotations from Famous Historians of Science], Cyberistan.</ref>}}

Robert S. Elliot wrote the following on the ''[[Book of Optics]]'':
{{quote|"Alhazen was one of the ablest students of optics of all times and published a seven-volume treatise on this subject which had great celebrity throughout the medieval period and strongly influenced Western thought, notably that of Roger Bacon and Kepler. This treatise discussed [[Lens (optics)|concave]] and [[convex]] [[mirror]]s in both [[Cylinder (geometry)|cylindrical]] and [[sphere|spherical]] geometries, anticipated [[Fermat's principle|Fermat's law of least time]], and considered refraction and the magnifying power of lenses. It contained a remarkably lucid description of the optical system of the eye, which study led Alhazen to the belief that light consists of rays which originate in the object seen, and not in the eye, a view contrary to that of Euclid and Ptolemy."<ref>Elliott, Chapter 1.</ref>}}

The ''Biographical Dictionary of Scientists'' wrote the following on Ibn al-Haytham::
{{quote|"He was probably the greatest scientist of the Middle Ages and his work remained unsurpassed for nearly 600 years until the time of Johannes Kepler."<ref>"Alhazen", in Abbott, p. 75.</ref>}}

The Latin translation of his main work, ''Kitab al-Manazir'', exerted a great influence upon Western science: for example, on the work of [[Roger Bacon]], who cites him by name,<ref>Lindberg (1996), p. 11, passim.</ref> and on [[Johannes Kepler|Kepler]]. It brought about a great progress in [[experiment]]al methods. His research in [[catoptrics]] centered on spherical and [[parabola|parabolic]] mirrors and [[spherical aberration]]. He made the important observation that the ratio between the [[angle of incidence]] and [[refraction]] does not remain constant, and investigated the [[magnification|magnifying]] power of a [[lens (optics)|lens]]. His work on catoptrics also contains the important problem known as [[#Alhazen's problem|Alhazen's problem]].

The list of his books runs to 200 or so, yet very few of the books have survived. Even his monumental treatise on optics survived only through its Latin translation. During the Middle Ages his books on [[cosmology]] were translated into Latin, [[Hebrew language|Hebrew]] and other languages.

The [[Alhazen (crater)|Alhazen crater]] on the [[Moon]] was named in his honour. Ibn al-Haytham is also featured on the obverse of the Iraqi 10,000 dinars banknote issued in 2003. The [[asteroid]] "59239 Alhazen" was also named in his honour, while [[Iran]]'s largest laser research facility, located in the [[Atomic Energy Organization of Iran]] headquarters in [[Tehran]], is named after him as well.

==Physics==
===''Book of Optics''===
{{main|Book of Optics}}

His seven volume treatise on [[optics]], ''Kitab al-Manazir'' (''Book of Optics'') (written from 1011 to 1021),<ref>Steffens ([[cf.]] [http://www.ibnalhaytham.net/custom.em?pid=571860 Reviews of ''Ibn al-Haytham: First Scientist''], ''The Critics'', [[Barnes & Noble]].)</ref> which has been ranked alongside [[Isaac Newton]]'s ''[[Philosophiae Naturalis Principia Mathematica]]'' as one of the most influential books ever written in [[physics]],<ref name=Salih/> drastically transformed the understanding of [[light]] and [[Visual perception|vision]]. In [[classical antiquity]], there were two major theories on vision. The first theory, the [[Emission theory (vision)|emission theory]], was supported by such thinkers as [[Euclid]] and [[Ptolemy]], who believed that sight worked by the eye emitting [[Ray (optics)|rays]] of [[light]]. The second theory, the intromission theory, supported by [[Aristotle]] and his followers, had physical forms entering the eye from an object. Ibn al-Haytham argued on the basis of common observations (such as the eye being dazzled or even injured if we look at a very bright light) and logical arguments (such as how a ray could proceeding from the eyes reach the distant stars the instant after we open our eye) to maintain that we cannot see by rays being emitted from the eye, nor through physical forms entering the eye. He instead developed a highly successful theory which explained the process of vision as rays of light proceeding to the eye from each point on an object, which he proved through the use of [[experiment]]ation.<ref>Lindberg (1976), p. 60-67.</ref>

Ibn al-Haytham proved that rays of light travel in straight lines, and carried out a number of experiments with [[lens (optics)|lenses]], [[mirror]]s, [[refraction]], and [[Reflection (physics)|reflection]].<ref name=Deek/> He was also the first to reduce reflected and refracted light rays into vertical and horizontal components, which was a fundamental development in geometric optics.<ref>Albrecht Heeffer. [http://logica.rug.ac.be/albrecht/thesis/Heeffer-CMSRAfinal.pdf Kepler’s near discovery of the sine law: A qualitative computational model], [[Ghent University]], [[Belgium]].</ref> He also discovered a result similar to [[Snell's law|Snell's law of sines]], but did not quantify it and derive the law mathematically.<ref>[[A. I. Sabra|Sabra]] (1981). ([[cf.]] Pavlos Mihas, [http://www.ihpst2005.leeds.ac.uk/papers/Mihas.pdf Use of History in Developing ideas of refraction, lenses and rainbow], p. 5, Demokritus University, [[Thrace]], [[Greece]].)</ref> Ibn al-Haytham is also credited with the invention of the [[camera obscura]] and [[pinhole camera]].<ref name=Wade>Wade, Finger.</ref>

''Optics'' was [[Latin translations of the 12th century|translated into Latin]] by an unknown scholar at the end of the 12th century or the beginning of the 13th century.<ref>Crombie, p. 147, n. 2.</ref> It was printed by [[Friedrich Risner]] in 1572, with the title ''Opticae thesaurus: Alhazeni Arabis libri septem, nuncprimum editi; Eiusdem liber De Crepusculis et nubium ascensionibus'' [http://www.mala.bc.ca/~mcneil/cit/citlcalhazen1.htm]. Risner is also the author of the name variant "Alhazen"; before Risner he was known in the west as Alhacen, which is the correct transcription of the Arabic name.<ref>Smith (2001).</ref> This work enjoyed a great reputation during the [[Middle Ages]]. Works by Alhacen on geometrical subjects were discovered in the [[Bibliothèque nationale]] in [[Paris]] in 1834 by E. A. Sedillot. Other manuscripts are preserved in the [[Bodleian Library]] at [[Oxford]] and in the library of [[Leiden]]. Ibn al-Haytham's optical studies were influential in a number of later developments, including the [[telescope]], which laid the foundations of telescopic astronomy,<ref name=Marshall/> as well as of the modern [[camera]], the [[microscope]], and the use of optical aids in [[Renaissance]] [[art]].<ref name=Power/>

===Other treatises on optics===
Besides the ''[[Book of Optics]]'', Ibn al-Haytham wrote a number of other treatises on [[optics]]. His ''Risala fi l-Daw’'' (''Treatise on Light'') is a supplement to his ''Kitab al-Manazir'' (''Book of Optics''). The text contained further investigations on the properties of [[luminance]] and its [[radiance|radiant]] dispersion through various [[Transparency (optics)|transparent and translucent]] media. He also carried out further observations, investigations and examinations on the [[anatomy]] of the [[eye]], the [[camera obscura]] and [[pinhole camera]], [[Optical illusion|illusions]] in [[visual perception]], the [[meteorology]] of the [[rainbow]] and the [[density]] of the [[atmosphere]], various [[celestial]] phenomena (including the [[eclipse]], [[twilight]], and [[moonlight]]), [[refraction]], [[catoptrics]], [[dioptrics]], [[sphere|spherical]] and [[parabola|parabolic]] mirrors, and [[Magnifying glass|magnifying lenses]].<ref name=Bizri/>

In his treatise, ''Mizan al-Hikmah'' (''Balance of Wisdom''), Ibn al-Haytham discussed the [[density]] of the [[Earth's atmosphere|atmosphere]] and related it to [[altitude]]. He also studied [[atmospheric refraction]]. He discovered that the [[twilight]] only ceases or begins when the Sun is 19° below the horizon and attempted to measure the height of the atmosphere on that basis.<ref name=Deek>Dr. Mahmoud Al Deek. "Ibn Al-Haitham: Master of Optics, Mathematics, Physics and Medicine", ''Al Shindagah'', November-December 2004.</ref>

===Astrophysics===
In [[astrophysics]] and the [[celestial mechanics]] field of [[physics]], Ibn al-Haytham, in his ''Epitome of Astronomy'', discovered that the [[Astronomical object|heavenly bodies]] "were accountable to the [[Physical law|laws of physics]]".<ref>Duhem, p. 28.</ref>

Ibn al-Haytham's ''Mizan al-Hikmah'' (''Balance of Wisdom'') dealt with [[statics]], astrophysics, and celestial mechanics. He discussed the theory of [[Gravitation|attraction]] between [[mass]]es, and it seems that he was also aware of the [[Magnitude (mathematics)|magnitude]] of [[acceleration]] due to [[Gravitation|gravity]] at a distance.<ref name=Bizri/>

His ''Maqala fi'l-qarastun'' is a treatise on [[Center of mass|centers of gravity]]. Little is currently known about the work, except for what is known through the later works of [[al-Khazini]] in the 12th century. In this treatise, Ibn al-Haytham formulated the theory that the [[Weight|heaviness]] of bodies varies with their distance from the center of the [[Earth]].<ref>Professor Mohammed Abattouy (2002). "The Arabic Science of weights: A Report on an Ongoing Research Project", ''The Bulletin of the Royal Institute for Inter-Faith Studies'' '''4''', p. 109-130.</ref>

===Mechanics===
In the [[dynamics]] and [[kinematics]] fields of [[mechanics]], Ibn al-Haytham's ''Risala fi’l-makan'' (''Treatise on Place'') discussed theories on the [[Motion (physics)|motion]] of a body. He maintained that a body moves [[perpetual motion|perpetually]] unless an external force stops it or changes its direction of motion.<ref name=Bizri/> This was a precursor to the law of [[inertia]] later stated by [[Galileo Galilei]] in the 16th century and now known as [[Newton's first law of motion]].<ref name=Salam/>

Ibn al-Haytham also discovered the concept of [[momentum]], part of [[Newton's second law of motion]], around the same time as his contemporary, [[Avicenna]].<ref name=Nasr>Seyyed [[Hossein Nasr]], "The achievements of Ibn Sina in the field of science and his contributions to its philosophy", ''Islam & Science'', December 2003.</ref>

==Astronomy==
===''Book of Optics''===
{{main|Book of Optics}}

Chapters 15-16 of the ''Book of Optics'' dealt with [[Islamic astronomy|astronomy]]. Ibn al-Haytham was the first to discover that the [[celestial spheres]] do not consist of [[solid]] matter, and he also discovered that the heavens are less dense than the air. These views were later repeated by [[Witelo]] and had a significant influence on the [[Copernican heliocentrism|Copernican]] and [[Tychonic system]]s of astronomy.<ref>Edward Rosen (1985), "The Dissolution of the Solid Celestial Spheres", ''Journal of the History of Ideas'' '''46''' (1), p. 13-31 [19-20, 21].</ref>

===''Doubts Concerning Ptolemy''===
In his ''Al-Shukūk ‛alā Batlamyūs'', variously translated as ''Doubts Concerning Ptolemy'' or ''Aporias against Ptolemy'', written between 1025 and 1028, Ibn al-Haytham criticized many of [[Ptolemy]]'s works, including the ''[[Almagest]]'', ''Planetary Hypotheses'', and ''Optics'', pointing out various contradictions he found in these works. He considered that some of the mathematical devices Ptolemy introduced into astronomy, especially the [[equant]], failed to satisfy the physical requirement of uniform circular motion, and wrote a scathing critique of the physical reality of Ptolemy's astronomical system, noting the absurdity of relating actual physical motions to imaginary mathematical points, lines and circles:<ref>Langerman, p. 8-10</ref>

{{quote|"Ptolemy assumed an arrangement (''hay'a'') that cannot exist, and the fact that this arrangement produces in his imagination the motions that belong to the planets does not free him from the error he committed in his assumed arrangement, for the existing motions of the planets cannot be the result of an arrangement that is impossible to exist.... [F]or a man to imagine a circle in the heavens, and to imagine the planet moving in it does not bring about the planet's motion."<ref>Sabra (1978b), p. 121, n. 13.</ref><ref>[http://setis.library.usyd.edu.au/stanford/entries/copernicus/index.html Nicolaus Copernicus], [[Stanford Encyclopedia of Philosophy]] (2004).</ref>}}

Ibn al-Haytham further criticized Ptolemy's model on other [[empirical]], [[observation]]al and [[experiment]]al grounds,<ref>[[A. I. Sabra]] (1998), "Configuring the Universe: Aporetic, Problem Solving, and Kinematic Modeling as Themes of Arabic Astronomy", ''Perspectives on Science'' '''6''' (3), p. 288-330 [300].</ref> such as Ptolemy's use of [[conjectural]] undemonstrated theories in order to "save appearances" of certain [[phenomena]], which Ibn al-Haytham did not approve of due to his insistence on [[scientific demonstration]]. Unlike some later astronomers who criticized the Ptolemaic model on the grounds of being incompatible with [[Aristotelian physics|Aristotelian natural philosophy]], Ibn al-Haytham was mainly concerned with empirical observation and the internal contradictions in Ptolemy's works.<ref>[[Shlomo Pines]] (1986), ''Studies in Arabic Versions of Greek Texts and in Mediaeval Science'', p. 438-439. [[Brill Publishers]], ISBN 9652236268.</ref>

In his ''Aporias against Ptolemy'', Ibn al-Haytham commented on the difficulty of attaining scientific knowledge:

{{quote|"Truth is sought for itself [but] the truths, [he warns] are immersed in uncertainties [and the scientific authorities (such as Ptolemy, whom he greatly respected) are] not immune from error..."<ref name=Sabra>[[A. I. Sabra|Sabra]] (2003).</ref>}}

He held that the criticism of existing theories — which dominated this book — holds a special place in the growth of scientific knowledge:

{{quote|"Therefore, the seeker after the truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them, the one who submits to argument and demonstration, and not to the sayings of a human being whose nature is fraught with all kinds of imperfection and deficiency. Thus the duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency."<ref name=Sabra/>}}

===''On the Configuration of the World''===
In his ''On the Configuration of the World'', despite his criticisms directed towards Ptolemy, Ibn al-Haytham continued to accept the physical reality of the [[geocentric model]] of the universe,<ref>Some writers, however, argue that Alhazen's critique constituted a form of [[heliocentrism|heliocentricity]] (see Qadir, p. 5-6, 10).</ref> presenting a detailed description of the physical structure of the [[celestial spheres]] in his ''On the Configuration of the World'':
{{quote|"The earth as a whole is a round sphere whose center is the center of the world. It is stationary in its [the world's] middle, fixed in it and not moving in any direction nor moving with any of the varieties of motion, but always at rest."<ref>Langerman, chap. 2, sect. 22, p. 61.</ref>}}

While he attempted to discover the physical reality behind Ptolemy's mathematical model, he developed the concept of a single [[celestial spheres|orb (''falak'')]] for each component of Ptolemy's planetary motions. This work was eventually translated into [[Hebrew]] and [[Latin]] in the 13th and 14th centuries and subsequently had an important influence during the European Middle Ages and [[Renaissance]].<ref>Langerman, p. 34-41.</ref><ref>Gondhalekar (2001), p. 21.</ref>

===''The Model of the Motions''===
Ibn al-Haytham's ''The Model of the Motions of Each of the Seven Planets'', written in 1038, was an important book on astronomy. The surviving manuscript of this work has only recently been discovered, with much of it still missing, hence the work has not yet been published in modern times. Following on from his ''Doubts on Ptolemy'' and ''The Resolution of Doubts'', Ibn al-Haytham described the first non-Ptolemaic model in ''The Model of the Motions''. His reform was not concerned with [[cosmology]], as he developed a systematic study of [[Celestial mechanics|celestial]] [[kinematics]] that was completely [[geometry|geometric]]. This in turn led to innovative developments in [[infinitesimal]] [[geometry]].<ref>Rashed (2007).</ref>

His reformed [[empirical]] model was the first to reject the [[equant]]<ref>Rashed (2007), p. 20, 53.</ref> and [[eccentricity|eccentrics]],<ref>Rashed (2007), p. 33-34.</ref> separate [[natural philosophy]] from astronomy, free celestial kinematics from cosmology, and reduce physical entities to geometrical entities. The model also propounded the [[Earth's rotation]] about its axis,<ref>Rashed (2007), p. 20, 32-33.</ref> and the centres of motion were geometrical points without any physical significance, like [[Johannes Kepler]]'s model centuries later.<ref>Rashed (2007), p. 51-52.</ref>

In the text, Ibn al-Haytham also describes an early version of [[Occam's razor]], where he employs only minimal hypotheses regarding the properties that characterize astronomical motions, as he attempts to eliminate from his planetary model the cosmological hypotheses that cannot be observed from [[Earth]].<ref name=Rashed-35-36/>

===Refutation of astrology===
Ibn al-Haytham distinguished [[Islamic astrology|astrology]] from astronomy, and he refuted the study of astrology, due to the methods used by astrologers being [[conjectural]] rather than [[empirical]], and also due to the views of astrologers conflicting with orthodox [[Islam]].<ref>[[George Saliba]] (1994), ''A History of Arabic Astronomy: Planetary Theories During the Golden Age of Islam'', p. 60, 67-69. [[New York University Press]], ISBN 0814780237.</ref>

==Mathematics==
In [[Islamic mathematics|mathematics]], Ibn al-Haytham builds on the mathematical works of [[Euclid]] and [[Thabit ibn Qurra]], and goes on to systemize [[infinitesimal]] [[calculus]], [[conic section]]s, [[number theory]], and [[analytic geometry]] after linking [[algebra]] to [[geometry]].

===Alhazen's problem===
His work on [[catoptrics]] in ''Book V'' of the ''Book of Optics'' contains the important problem known as ''Alhazen's problem''. It comprises drawing lines from two points in the plane of a circle meeting at a point on the [[circumference]] and making equal angles with the normal at that point. This leads to an [[Quartic equation|equation of the fourth degree]]. This eventually led Ibn al-Haytham to derive the earliest formula for the sum of [[fourth power]]s; and by using an early [[proof]] by [[mathematical induction]], he developed a method for determining the general formula for the sum of any [[integral]] [[Exponentiation|powers]]. This was fundamental to the development of [[infinitesimal]] and [[integral]] [[calculus]].<ref name=Katz>Katz.</ref>

While Ibn al-Haytham solved the problem using [[conic section]]s and a geometric proof, Alhazen's problem remained influential in Europe, as later mathematicians such as [[Christiaan Huygens]], [[James Gregory]], [[Guillaume de l'Hôpital]], [[Isaac Barrow]] and many others attempted to find an algebraic solution to the problem, using various methods including [[analytic geometry|analytic methods of geometry]] and derivation by [[complex number]]s.<ref name=Smith/> Mathematicians were not able to find an algebraic solution to the problem until the end of the 20th century.<ref name=Steffens/>

===Geometry===
In [[geometry]], Ibn al-Haytham developed [[analytical geometry]] by establishing the linkage between [[algebra]] and [[geometry]]. Ibn al-Haytham also discovered a formula for adding the first 100 natural numbers (which may later have been intuited by [[Carl Friedrich Gauss]] as a youth). Ibn al-Haytham used a geometric proof to prove the formula.<ref>J. Rottman. ''A first course in Abstract Algebra'', Chapter 1.</ref>

Ibn al-Haytham made the first attempt at proving the [[Euclidean geometry|Euclidean]] [[parallel postulate]] using a [[proof by contradiction]],<ref>Michelle Eder (2000), [http://www.math.rutgers.edu/~cherlin/History/Papers2000/eder.html Views of Euclid's Parallel Postulate in Ancient Greece and in Medieval Islam], [[Rutgers University]].</ref> where he introduced the concept of [[Motion (physics)|motion]] and [[Transformation (geometry)|transformation]] into geometry.<ref>Victor J. Katz (1998), ''History of Mathematics: An Introduction'', p. 269, [[Addison-Wesley]], ISBN 0321016181: {{quote|"In effect, this method characterized parallel lines as lines always equidisant from one another and also introduced the concept of motion into geometry."}}</ref> His proof was also the first to employ the [[Lambert quadrilateral]] and [[Playfair's axiom]], both of which were not known in Europe until the 18th century.<ref name=Smith/> Some have referred to the Lambert quadrilateral as the "Ibn al-Haytham–Lambert quadrilateral" as a result.<ref>Boris Abramovich Rozenfelʹd (1988), ''A History of Non-Euclidean Geometry: Evolution of the Concept of a Geometric Space'', p. 65. Springer, ISBN 0387964584.</ref> His theorems on [[quadrilateral]]s, including the Lambert quadrilateral, were the first theorems on [[elliptical geometry]] and [[hyperbolic geometry]], and along with his alternative postulates, such as Playfair's axiom, his work marked the beginning of [[non-Euclidean geometry]] and had a considerable influence on its development among later Muslim geometers such as [[Omar Khayyám]] and [[Nasīr al-Dīn al-Tūsī]] and European geometers such as [[Witelo]], [[Gersonides]], [[Alfonso]], [[John Wallis]] and [[Giovanni Girolamo Saccheri]].<ref>Boris A. Rosenfeld and Adolf P. Youschkevitch (1996), "Geometry", in Roshdi Rashed, ed., ''[[Encyclopedia of the History of Arabic Science]]'', Vol. 2, p. 447-494 [470], [[Routledge]], London and New York: {{quote|"Three scientists, Ibn al-Haytham, Khayyam and al-Tusi, had made the most considerable contribution to this branch of geometry whose importance came to be completely recognized only in the ninteenth century. In essence their propositions concerning the properties of quadrangles which they considered assuming that some of the angles of these figures were acute of obtuse, embodied the first few theorems of the hyperbolic and the elliptic geometries. Their other proposals showed that various geometric statements were equivalent to the Euclidean postulate V. It is extremely important that these scholars established the mutual connection between tthis postulate and the sum of the angles of a triangle and a quadrangle. By their works on the theory of parallel lines Arab mathematicians directly influenced the relevant investiagtions of their European couterparts. The first European attempt to prove the postulate on parallel lines - made by Witelo, the Polish scientists of the thirteenth century, while revising Ibn al-Haytham's ''Book of Optics'' (''Kitab al-Manazir'') - was undoubtedly prompted by Arabic sources. The proofs put forward in the fourteenth century by the Jewish scholar Gersonides, who lived in southern France, and by the above-mentioned Alfonso from Spain directly border on Ibn al-Haytham's demonstration. Above, we have demonstrated that ''Pseudo-Tusi's Exposition of Euclid'' had stimulated borth J. Wallis's and G. Saccheri's studies of the theory of parallel lines."}}</ref>

In [[Euclidean geometry|elementary geometry]], Ibn al-Haytham attempted to solve the problem of [[squaring the circle]] using the area of [[Lune (mathematics)|lune]]s, but later gave up on the impossible task.<ref name=MacTutor/> Ibn al-Haytham also tackled other problems in elementary ([[Euclidean geometry|Euclidean]]) and advanced ([[Apollonius of Perga|Apollonian]] and [[Archimedes|Archimedean]]) geometry, some of which he was the first to solve.<ref name=Sabra/>

===Number theory===
His contributions to [[number theory]] includes his work on [[perfect number]]s. In his ''Analysis and Synthesis'', Ibn al-Haytham was the first to realize that every even perfect number is of the form 2''n''−1(2''n'' − 1) where 2''n'' − 1 is [[Prime number|prime]], but he was not able to prove this result successfully ([[Leonhard Euler|Euler]] later proved it in the 18th century).<ref name=MacTutor/>

Ibn al-Haytham solved problems involving [[congruence relation|congruences]] using what is now called [[Wilson's theorem]]. In his ''Opuscula'', Ibn al-Haytham considers the solution of a system of congruences, and gives two general methods of solution. His first method, the canonical method, involved Wilson's theorem, while his second method involved a version of the [[Chinese remainder theorem]].<ref name=MacTutor/>

==Philosophy==
===Phenomenology===
In [[Early Islamic philosophy|philosophy]], Ibn al-Haytham is considered a pioneer of [[phenomenology]]. He articulated a relationship between the physical and observable [[World (philosophy)|world]] and that of [[intuition]], [[psychology]] and [[mental function]]s. His theories regarding [[knowledge]] and [[perception]], linking the domains of science and religion, led to a philosophy of [[existence]] based on the direct observation of [[reality]] from the observer's point of view. Much of his thought on phenomenology was not further developed until the 20th century.<ref>Dr Valérie Gonzalez, "Universality and Modernity", ''The Ismaili United Kingdom'', December 2002, p. 50-53.</ref>

===Place===
Ibn al-Haytham's ''Risala fi’l-makan'' (''Treatise on Place'') presents a critique of [[Aristotle]]'s concept of [[place]] ([[topos]]). Aristotle's ''[[Physics (Aristotle)|Physics]]'' stated that the place of something is the two-dimensional boundary of the containing body that is at rest and is in contact with what it contains. Ibn al-Haytham disagreed and demonstrated that place (al-makan) is the imagined three-dimensional void between the inner surfaces of the containing body. He showed that place was akin to [[space]], foreshadowing [[René Descartes]]'s concept of place in the ''Extensio'' in the 17th century.

Following on from his ''Treatise on Place'', Ibn al-Haytham's ''Qawl fi al-Makan'' (''Discourse on Place'') was an important treatise which presents [[geometry|geometrical]] demonstrations for his geometrization of [[place]], in opposition to [[Aristotle]]'s philosophical concept of place, which Ibn al-Haytham rejected on mathematical grounds. [[Abd-el-latif]], a supporter of Aristotle's philosophical view of place, later criticized the work in ''Fi al-Radd ‘ala Ibn al-Haytham fi al-makan'' (''A refutation of Ibn al-Haytham’s place'') for its geometrization of place.<ref>El-Bizri (2007).</ref>

===Theology===
Ibn al-Haytham was a devout [[Muslim]],<ref>[http://www.ibnalhaytham.net/custom.em?pid=571860 Review of ''Ibn al-Haytham: First Scientist''], [[Kirkus Reviews]], December 1, 2006.</ref> who is said to have been a supporter of the orthodox [[Ash'ari]] school of [[Islamic theology]],<ref>[[Ziauddin Sardar]], [http://www.cgcu.net/imase/islam_science_philosophy.htm Science in Islamic philosophy]</ref> and opposed to the views of the [[Mu'tazili]] school,<ref>Bettany, p. 251.</ref> though he may have been a Mu'tazili supporter himself at some point in his life.<ref>Hodgson (2006), p. 53.</ref> Some also claim he may have possibly been a follower of [[Shia Islam]].<ref>Sabra 1978a, p. 178-216.{{page number}}</ref>

Ibn al-Haytham also wrote a work on Islamic theology, in which he discusses [[prophet]]hood and develops a system of philosophical criteria to discern true prophethood from false claimants in his time.<ref>C. Plott (2000), ''Global History of Philosophy: The Period of Scholasticism'', Pt. II, p. 464. ISBN 8120805518, [[Motilal Banarsidass]] Publ.</ref>

Ibn al-Haytham attributed his [[experiment]]al [[scientific method]] and [[scientific skepticism]] to his [[Islam]]ic faith. The [[Qur'an]], for example, placed a strong emphasis on [[empiricism]].<ref>{{quote|"Observe nature and reflect over it."|[[Qur'an]]}} ([[cf.]] C. A. Qadir (1990), ''Philosophy and Science in the lslumic World'', [[Routledge]], London) ([[cf.]] Bettany, Laurence (1995), "Ibn al-Haytham: an answer to multicultural science teaching?", ''Physics Education'' '''30''': 247-252 [247])</ref><ref>{{cite quran|17|36|quote=You shall not accept any information, unless you verify it for yourself. I have given you the hearing, the eyesight, and the brain, and you are responsible for using them.}}</ref><ref>{{cite quran|2|164|quote=Behold! In the creation of the heavens and the earth; in the alternation of the night and the day; in the sailing of the ships through the ocean for the benefit of mankind; in the rain which Allah Sends down from the skies, and the life which He gives therewith to an earth that is dead; in the beasts of all kinds that He scatters through the earth; in the change of the winds, and the clouds which they trail like their slaves between the sky and the earth - (Here) indeed are Signs for a people that are wise.}}</ref> He also believed that [[human]] beings are inherently flawed and that only [[God]] is perfect. He [[reason]]ed that to discover the [[truth]] about [[nature]], it is necessary to eliminate human [[opinion]] and [[error]], and allow the [[universe]] to speak for itself.<ref name=Ezine/> He wrote in his ''Doubts Concerning Ptolemy'':

{{quote|"Therefore, the seeker after the truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them, the one who submits to argument and [[Scientific demonstration|demonstration]], and not to the sayings of a human being whose nature is fraught with all kinds of imperfection and deficiency. Thus the duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either [[prejudice]] or [[leniency]]."<ref name=Sabra/>}}

In ''The Winding Motion'', Ibn al-Haytham further wrote that [[faith]] should only apply to [[prophets of Islam]] and not to any other authorities, in the following comparison between the Islamic prophetic tradition and the demonstrative [[science]]s:

{{quote|"From the statements made by the noble [[Sheikh|Shaykh]], it is clear that he believes in [[Ptolemy]]'s words in everything he says, without relying on a demonstration or calling on a proof, but by pure imitation ([[taqlid]]); that is how [[Ulema|experts in the prophetic tradition]] have faith in Prophets, may the blessing of God be upon them. But it is not the way that mathematicians have faith in specialists in the demonstrative sciences."<ref>Rashed (2007), p. 11.</ref>}}

Ibn al-Haytham described his search for truth and [[knowledge]] as a way of leading him closer to God:

{{quote|"I constantly sought knowledge and truth, and it became my belief that for gaining access to the [[Wiktionary:effulgence|effulgence]] and closeness to God, there is no better way than that of searching for truth and knowledge."<ref>C. Plott (2000), ''Global History of Philosophy: The Period of Scholasticism'', Pt. II, p. 465. ISBN 8120805518, [[Motilal Banarsidass]] Publ.</ref>}}

==Other contributions==
===Arts===
{{main|Hockney-Falco thesis}}

At a scientific conference in February 2007, [[Charles M. Falco]] argued that Ibn al-Haytham's work on optics may have influenced the use of optical aids by [[Renaissance]] [[art]]ists. 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."<ref>[[Charles M. Falco|Falco, Charles M.]] "Ibn al-Haytham and the Origins of Modern Image Analysis", presented at a plenary session at the International Conference on Information Sciences, Signal Processing and its Applications, 12–15 February 2007. Sharjah, United Arab Emirates (U.A.E.). [http://www.optics.arizona.edu/ssd/FalcoPlenaryUAE.pdf]</ref>

===Biomedical sciences===
Ibn al-Haytham discussed the topics of [[Islamic medicine|medicine]], [[Ophthalmology in medieval Islam|ophthalmology]] and [[eye surgery]] in the [[anatomical]] and [[physiological]] portions of the ''[[Book of Optics]]'' and in his commentaries on [[Galen]]ic works.<ref>Steffens ([[cf.]] [http://ummahpulse.com/index.php?option=com_content&task=view&id=85&Itemid=54 Review by Sulaiman Awan])</ref> He made several improvements to [[eye surgery]] and accurately described the process of sight,<ref>Bashar Saad, Hassan Azaizeh, Omar Said (October 2005). "Tradition and Perspectives of Arab Herbal Medicine: A Review", ''Evidence-based Complementary and Alternative Medicine'' '''2''' (4), p. 475-479 [476]. [[Oxford University Press]]</ref> the structure of the [[eye]], image formation in the eye and the [[visual system]]. He also discovered the underlying principles of [[Hering's law of equal innervation]], [[binocular vision]], [[motion perception]], vertical [[horopter]]s, and [[binocular disparity]].<ref name=Howard>{{cite journal | author=Ian P. Howard | year=1996 | title=Alhazen's neglected discoveries of visual phenomena | journal=Perception | volume=25 | issue=10 | pages=1203 – 1217}}</ref>

===Engineering===
In [[Inventions in the Muslim world|engineering]], one account of his career as a [[civil engineer]] has him summoned to Egypt by the [[Fatimid]] [[Caliph]] [[al-Hakim bi-Amr Allah]] to regulate the [[flooding]] of the [[Nile]] River. He carried out a detailed scientific study of the annual [[inundation]] of the Nile River, and he drew plans for building a [[dam]], at the site of the modern-day [[Aswan Dam]]. His field work, however, later made him aware of the impracticality of this scheme, and he soon [[feigned madness]] in order to avoid punishment from the Caliph.<ref>C. Plott (2000), ''Global History of Philosophy: The Period of Scholasticism'', Pt. II, p. 459. ISBN 8120805518, [[Motilal Banarsidass]] Publ.</ref>

According to [[al-Khazini]], Ibn al-Haytham also wrote a treatise providing a description on the [[construction]] of a [[water clock]].<ref>[[Ahmad Y Hassan]], [http://www.history-science-technology.com/Articles/articles%206.htm Al-Jazari And the History of the Water Clock]</ref>

===Psychology===
Ibn al-Haytham is considered the founder of [[experimental psychology]],<ref name=Khaleefa/> for his pioneering work on the [[psychology]] of [[visual perception]].<ref name=Steffens/> Ibn al-Haytham made many subjective reports regarding vision and can therefore be argued to be the first "psychologist".

In the ''[[Book of Optics]]'', Ibn al-Haytham was the first scientist to argue that vision occurs in the brain, rather than the eyes. He pointed out that personal experience has an effect on what people see and how they see, and that vision and perception are subjective. He explained possible errors in vision in detail, and as an example described how a small child with less experience may have more difficulty interpreting what he or she sees. He also gave an example of how an adult can make mistakes in vision due to experience that suggests that one is seeing one thing, when one is really seeing something else.<ref name=Steffens/>

Some also consider him a founder of [[psychophysics]].<ref name=Khaleefa/> However, there is no evidence that he used quantitative psychophysical techniques.

==See also==
*[[Islamic Golden Age]]
*[[Islamic science]]
*[[List of Muslim scientists]]
*[[List of Arab scientists and scholars]]
*[[List of Iraqis]]
*[[Optics]]
*[[Scientific method]]
*[[History of science]]

==Notes==

{{reflist|2}}

==References==
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* El-Bizri, Nader (2007). "In Defence of the Sovereignty of Philosophy: Al-Baghdadi's Critique of Ibn al-Haytham's Geometrisation of Place", ''Arabic Sciences and Philosophy'' '''17''', p. 57-80. [[Cambridge University Press]].
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* Gondhalekar, Prabhakar M. (2001). ''The Grip of Gravity: The Quest to Understand the Laws of Motion and Gravitation''. [[Cambridge University Press]]. ISBN 0521803160.
* Gorini, Rosanna (2003). "Al-Haytham the Man of Experience: First Steps in the Science of Vision", ''International Society for the History of Islamic Medicine''. Institute of Neurosciences, Laboratory of Psychobiology and Psychopharmacology, Rome, Italy.
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* {{Citation
| last =Hodgson
| first =P. E. (Peter Edward)
| author-link =
| publication-date =2006-01-15
| year =2006
| title =Theology And Modern Physics
| publication-place =Burlington, VT
| publisher =Ashgate Publishing
| id =DDC: 201.653, LCC: BL265.P4 H63 2005
| isbn =9780754636229
| oclc =56876894
}}.
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* Omar, Saleh Beshara (1977). ''Ibn al-Haytham's Optics: A Study of the Origins of Experimental Science''. Minneapolis: Bibliotheca Islamica. ISBN 0-88297-015-1.
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* Rashed, Roshdi (2002). "A Polymath in the 10th century", ''[[Science (journal)|Science]]'' '''297''' (5582), p. 773.
* Rashed, Roshdi (2007). "The Celestial Kinematics of Ibn al-Haytham", ''Arabic Sciences and Philosophy'' '''17''', p. 7-55. [[Cambridge University Press]].
* [[A. I. Sabra|Sabra, A. I.]] (1971), "The astronomical origin of Ibn al-Haytham’s concept of experiment", in ''Actes du XIIe congrès international d’histoire des sciences'', vol. 3, p. 133-136. Albert Blanchard, Paris. Reprinted in Sabra, A. I. (1994), ''Optics, Astronomy and Logic: Studies in Arabic Science and Philosophy'', Collected Studies Series, 444, Variorum, Aldershot, ISBN 0-86078-435-5.
*{{cite book |last=Sabra |first=Abd al-Hamid |editor=Seyyed Hossein Nasr |others= |title=Ibn al-Haytham and the Visual Ray Hypothesis |url= |edition= |series=Ismaili Contributions to Islamic Culture |year=1978a |publisher=Shambhala Publications |location=Boston |isbn=0-877-73731-2 |pages=pp. 178-216 |quote= }}
* Sabra, A. I. (1978b), "An Eleventh-Century Refutation of Ptolemy's Planetary Theory", in Erna Hilfstein, Paweł Czartoryski, Frank D. Grande, ed. (1978), ''Science and History: Studies in Honor of Edward Rosen'', p. 117-131, Studia Copernicana XVI, Ossolineum, Wrocław.
* Sabra, A. I. (1981). ''Theories of Light from Descartes to Newton''. [[Cambridge University Press]].
* Sabra, A. I. (2003). [http://www.harvardmagazine.com/on-line/090351.html Ibn al-Haytham: Brief life of an Arab mathematician], ''[[Harvard Magazine]]'', October-December 2003.
* H. Salih, M. Al-Amri, M. El Gomati (2005). "The Miracle of Light", ''A World of Science'' '''3''' (3). [[UNESCO]].
* [[Abdus Salam|Salam, Abdus]] (1984), "Islam and Science", in C. H. Lai (1987), ''Ideals and Realities: Selected Essays of Abdus Salam'', 2nd ed., World Scientific, [[Singapore]], p. 179-213.
* {{Cite book
| publisher = American Philosophical Society
| isbn = 9780871699145
| last = Smith
| first = A. Mark
| title = Alhacen's theory of visual perception: a critical edition, with English translation and commentary, of the first three books of Alhacen's De aspectibus, the medieval Latin version of Ibn al-Haytham's Kitab al-Manazir. Vol 1
| location = Philadelphia
| date = 2001
| pages = xxi
}}
* Smith, John D. (1992). "The Remarkable Ibn al-Haytham", ''The Mathematical Gazette'' '''76''' (475), p. 189-198.
* Steffens, Bradley (2006). ''Ibn al-Haytham: First Scientist'', Morgan Reynolds Publishing, ISBN 1599350246.
* Wade, Nicholas J. and Finger, Stanley (2001), "The eye as an optical instrument: from camera obscura to Helmholtz's perspective", ''Perception'' '''30''' (10), p. 1157-1177.

==Further reading==
===Primary sources===
* Langermann, Y. Tzvi, ed. and trans. ''Ibn al-Haytham's'' On the Configuration of the World, Harvard Dissertations in the History of Science. New York: Garland, 1990. ISBN 0824000412
* Sabra, A. I., ed. ''The Optics of Ibn al-Haytham, Books I-II-III: On Direct Vision. The Arabic text, edited and with Introduction, Arabic-Latin Glossaries and Concordance Tables.'' Kuwait: National Council for Culture, Arts and Letters, 1983.
* Sabra, A. I., ed. ''The Optics of Ibn al-Haytham. Edition of the Arabic Text of Books IV-V: On Reflection and Images Seen by Reflection.'' 2 vols., Kuwait: The National Council for Culture, Arts and Letters, 2002.
* Sabra, A. I., trans. ''The Optics of Ibn al-Haytham. Books I-II-III: On Direct Vision. English Translation and Commentary.'' 2 vols. Studies of the Warburg Institute, vol. 40. London: The Warburg Institute, University of London, 1989. ISBN 0-85481-072-2
* Smith, A. Mark, ed. and trans. ''Alhacen's Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen's'' De aspectibus,'' the Medieval Latin Version of Ibn al-Haytham's'' Kitāb al-Manāzir, 2 vols. Transactions of the American Philosophical Society, 91.4-5, Philadelphia, 2001. ISBN 0-87169-914-1
* Smith, A. Mark, ed. and trans. ''Alhacen on the Principles of Reflection: A Critical Edition, with English Translation and Commentary, of Books 4 and 5 of Alhacen's ''De Aspectibus,'' the Medieval Latin version of Ibn-al-Haytham's'' Kitāb al-Manāzir, 2 vols. Transactions of the American Philosophical Society, 96.2-3, Philadelphia, 2006. ISBN 0-87169-962-1

===Secondary literature===
* [[Charles M. Falco|Falco, Charles M.]] "Ibn al-Haytham and the Origins of Modern Image Analysis" presented at a plenary session at the International Conference on Information Sciences, Signal Processing and its Applications, 12–15 February 2007. Sharjah, United Arab Emirates (U.A.E.).[http://www.optics.arizona.edu/ssd/FalcoPlenaryUAE.pdf] In this lecture, Falco speculates that Ibn al-Haytham may have influenced the use of optical aids in Renaissance art. (See [[Hockney-Falco thesis]].)
* Omar, Saleh Beshara. ''Ibn al-Haytham and Greek optics: a comparative study in scientific methodology''. PhD Dissertation, Univ. of Chicago, Dept. of Near Eastern Languages and Civilizations, June 1975.

== External links ==
* {{MacTutor Biography|id=Al-Haytham|title=Abu Ali al-Hasan ibn al-Haytham}}
* {{ScienceWorldBiography | urlname=Alhazen | title=Alhazen (ca. 965-1039)}}
* [http://www-personal.umich.edu/~jbourj/money4.htm Ibn al-Haitham on two Iraqi banknotes]
* http://www.daviddarling.info/encyclopedia/A/Alhazen.html
* [http://www.islamonline.net/english/Science/2001/08/article11.shtml Alhazen Master of Optics]
* [http://unesdoc.unesco.org/images/0014/001412/141236E.pdf The Miracle of Light - a UNESCO article on Ibn Haitham]
* Roshdi Rashed. [http://www.sciencemag.org/cgi/reprint/297/5582/773.pdf "A Polymath in the 10th century"], ''[[Science (magazine)|Science]]'', 297 (2002): 773
* [[A. I. Sabra]], [http://www.harvardmagazine.com/on-line/090351.html "Ibn al-Haytham: Brief life of an Arab mathematician"]
* [http://www.cgie.org.ir/shavad.asp?id=123&avaid=1917 Biography of Ibn Haytham](in Persian)
* [http://www.kuark.org/kscience/index.php/archives/ibn-al-haytham-965-1039-his-life-and-works KuarkScience - Ibn al-Haytham:His Life and Works]

{{Islamic mathematics}}

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