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Physics in medieval Islam included experimental physics, mathematical physics and theoretical physics.The fields of physics that were studied by Muslim scientists during this time also included optics and magnetism (which are both now part of electromagnetism), mechanics (including statics, dynamics, kinematics and motion), and astrophysics (see Islamic astronomy).These studies flourished in the Islamic world during the Islamic Golden Age, variously dated from the 8th century to the 16th century.


In medieval Islam, experimental physics began in Iraqmarker and Egyptmarker, with the work of the Muslim physicist, Ibn al-Haytham (known as Alhazen in the West), who is considered the "father of modern optics" and the most important physicist of the Middle Ages, for having developed the earliest experimental scientific method in his Book of Optics.

George Sarton, the "father of the history of science", wrote in his Introduction to the History of Science:

Matthias Schramm wrote in his Ibn al-Haythams Weg zur Physik:

Another important medieval Muslim physicist who contributed towards experimental physics was Abū Rayhān al-Bīrūnī, who developed the earliest experimental method for mechanics. Ibn al-Haytham and Al-Biruni also introduced the earliest experimental methods for astronomy and astrophysics, while Al-Biruni and Al-Khazini unified statics with dynamics into the science of mechanics and combined hydrostatics with dynamics to create the field of hydrodynamics.

Islam and physics

The Qur'an contains an "insistence that the Universe is ruled by a single set of laws" which was "rooted in the Islamic concept of tawhîd, the unity of God", as well its "greater respect for empirical data than was common in the preceding Greek civilization" which inspired Muslims to place a greater emphasis on empirical observation, in contrast to ancient Greek philosophers such as the Platonists and Aristotelians who expressed a general distrust towards the senses and instead viewed reason alone as being sufficient to understanding nature. The Qur'an's insistence on observation, reason and contemplation ("see", "think" and "contemplate"), on the other hand, led Muslims to develop an early scientific method based on these principles, particularly empirical observation. Muhammad Iqbal says that it was:

Ibn al-Haytham (Alhazen) attributed his experimental method and scientific skepticism to his Islamic faith. He believed that human beings are inherently flawed and that only God is perfect. He reasoned that to discover the truth about nature, it is necessary to eliminate human opinion and error, and allow the universe to speak for itself. 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 sciences:

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

Ali Kuşçu's (1403-1474) support for the Earth's rotation and his rejection of Aristotelian cosmology (which advocates a stationary Earth) was also motivated by religious opposition to Aristotelianism by orthodox Islamic theologians such as Al-Ghazali.

Scientific method

Muslim scientists placed a greater emphasis on experimentation than previous ancient civilizations (for example, Greek philosophy placed a greater emphasis on rationality rather than empiricism), which was due to the emphasis on empirical observation found in the Qur'an and Sunnah, (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]) and the rigorous historical methods established in the science of hadith. Muslim scientists thus combined precise observation, controlled experiment and careful records with a new approach to scientific inquiry which led to the development of the scientific method. In particular, the empirical observations and experiments of Ibn al-Haytham (Alhazen) in his Book of Optics (1021) is seen as the beginning of the modern scientific method, which he first introduced to optics and astrophysics. Rosanna Gorini writes:

Other early experimental methods were developed by Geber for alchemy and chemistry, by al-Kindi for the Earth sciences, and by Abū Rayhān al-Bīrūnī for astrophysics and mechanics. The most important development of the scientific method, the use of experimentation and quantification to distinguish between competing scientific theories set within a generally empirical orientation, was introduced by Muslim scientists.

Robert Briffault wrote in The Making of Humanity:

George Sarton wrote in the Introduction to the History of Science:

Oliver Joseph Lodge wrote in the Pioneers of Science:

Muhammad Iqbal wrote in The Reconstruction of Religious Thought in Islam:

Alhazenian method

Ibn al-Haytham, considered the "father of modern optics", used the scientific method to obtain the results in his famous Book of Optics (1021). In particular, he combined observations, experiments and rational arguments to show that his modern intromission theory of vision, where rays of light are emitted from objects rather than from the eyes, is scientifically correct, and that the ancient emission theory of vision supported by Ptolemy and Euclid (where the eyes emit rays of light), and the ancient intromission theory supported by Aristotle (where objects emit physical particles to the eyes), were both wrong. It is known that Roger Bacon was familiar with Ibn al-Haytham's work.

Ibn al-Haytham developed rigorous experimental methods of controlled scientific testing in order to verify theoretical hypotheses and substantiate inductive conjectures. Ibn al-Haytham's scientific method was similar to the modern scientific method in that it consisted of the following procedures:

  1. Observation
  2. Statement of problem
  3. Formulation of hypothesis
  4. Testing of hypothesis using experimentation
  5. Analysis of experimental results
  6. Interpretation of data and formulation of conclusion
  7. Publication of findings

An aspect associated with Ibn al-Haytham's optical research is related to systemic and methodological reliance on experimentation (i'tibar) and controlled testing in his scientific inquiries. Moreover, his experimental directives rested on combining classical physics (ilm tabi'i) with mathematics (ta'alim; geometry in particular) in terms of devising the rudiments of what may be designated as a hypothetico-deductive procedure in scientific research. This mathematical-physical approach to experimental science supported most of his propositions in Kitab al-Manazir (The Optics; De aspectibus or Perspectivae) and gounded his theories of vision, light and colour, as well as his research in catoptrics and dioptrics. His legacy was further advanced through the 'reforming' of his Optics by 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 development of the scientific method is considered to be fundamental to modern science and some — especially philosophers of science and practicing scientists — consider earlier inquiries into nature to be pre-scientific. Some consider Ibn al-Haytham to be the "first scientist" for this reason.

Ibn al-Haytham also employed scientific skepticism and criticism, and emphasized the role of empiricism. He also explained the role of induction in syllogism, and criticized Aristotle for his lack of contribution to the method of induction, which Ibn al-Haytham regarded as superior to syllogism, and he considered induction to be the basic requirement for true scientific research.

The Book of Optics was the first book to emphasize the role of experimentation as a form of proof in scientific inquiry. He was also the first scientist to adopt a form of positivism in his approach, centuries before a term for positivism was coined. In his Book of Optics, he wrote that "we do not go beyond experience, and we cannot be content to use pure concepts in investigating natural phenomena", and that the understanding of these cannot be acquired without mathematics. After assuming that light is a material substance, he does not discuss its nature any further but confines his investigations to the diffusion and propagation of light. The only properties of light he takes into account are that which can be treated by geometry and verified by experiment, noting that energy is the only quality of light that can be sensed.

The concept of Occam's razor is also present in the Book of Optics. For example, after demonstrating that light is generated by luminous objects and emitted or reflected into the eyes, he states that therefore "the extramission of [visual] rays is superfluous and useless." In The Model of the Motions, Ibn al-Haytham also uses a form 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.

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

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

Birunian and Avicennian methods

Abū Rayhān al-Bīrūnī (973-1048) also introduced an early scientific method in nearly every field of inquiry he studied. For example, in his treatise on mineralogy, Kitab al-Jamahir (Book of Precious Stones), Al-Biruni is "the most exact of experimental scientists", while in the introduction to his study of India, he declares that "to execute our project, it has not been possible to follow the geometric method" and develops comparative sociology as a scientific method in the field. He was also responsible for introducing the experimental method into mechanics, and was one of the first to conduct elaborate experiments related to astronomical phenomena.

Al-Biruni's scientific method was similar to the modern scientific method in many ways, particularly his emphasis on repeated experimentation. Biruni was concerned with how to conceptualize and prevent both systematic errors and random errors, such as "errors caused by the use of small instruments and errors made by human observers." He argued that if instruments produce random errors because of their imperfections or idiosyncratic qualities, then multiple observations must be taken, analyzed qualitatively, and on this basis, arrive at a "common-sense single value for the constant sought", whether an arithmetic mean or a "reliable estimate." He also introduced the method of checking tests during experiments.

In the Al-Burhan (On Demonstration) section of the The Book of Healing (1027), Avicenna discussed the philosophy of science and described an early scientific method of inquiry. He discusses Aristotle's Posterior Analytics and significantly diverged from it on several points. Avicenna discussed the issue of a proper methodology for scientific inquiry and the question of "How does one acquire the first principles of a science?" He asked how a scientist would arrive at "the initial axioms or hypotheses of a deductive science without inferring them from some more basic premises?" He explains that the ideal situation is when one grasps that a "relation holds between the terms, which would allow for absolute, universal certainty." Avicenna then adds two further methods for arriving at the first principles: the ancient Aristotelian method of induction (istiqra), and the method of examination and experimentation (tajriba). Avicenna criticized Aristotelian induction, arguing that "it does not lead to the absolute, universal, and certain premises that it purports to provide." In its place, he develops "a method of experimentation as a means for scientific inquiry."

In comparison to Avicenna's scientific method where "general and universal questions came first and led to experimental work", al-Biruni developed scientific methods where "universals came out of practical, experimental work" and "theories are formulated after discoveries", like with inductivism. Due to differences between their scientific methods, al-Biruni referred to himself as a mathematical scientist and to Avicenna as a philosopher, during a debate between the two scholars.


Geometrical optics

In optics, al-Kindi (c. 801–873) was one of the earliest important writers on geometrical optics in the Islamic world. In a work known in the west as De radiis stellarum, al-Kindi developed a theory "that everything in the world ... emits rays in every direction, which fill the whole world."

Ibn Sahl (c. 940-1000), a mathematician and physicist connected with the court of Baghdadmarker, wrote a treatise On Burning Mirrors and Lenses in 984 in which he set out his understanding of how curved mirrors and lens bend and focus light. Ibn Sahl is now credited with first discovering the law of refraction, usually called Snell's law. He used this law to work out the shapes of lenses that focus light with no geometric aberrations, known as anaclastic lenses.

Beginning of physical optics

Ibn al-Haytham (known in Western Europe as Alhacen or Alhazen) (965-1040), often regarded as the "father of optics" and a pioneer of the scientific method, formulated "the first comprehensive and systematic alternative to Greek optical theories." His key achievement was twofold: first, to insist that vision only occurred because of rays entering the eye and that rays postulated to proceed from the eye had nothing to do with it; the second was to define the physical nature of the rays discussed by earlier geometrical optical writers, considering them as the forms of light and color. This now forms the basis of modern physical optics. He developed a camera obscura to demonstrate that light and color from different candles passed through a single aperture in straight lines, without intermingling at the aperture. He then analyzed these physical rays according to the principles of geometrical optics. Ibn al-Haytham also employed the experimental scientific method as a form of demonstration in optics. He wrote many books on optics, most significantly the Book of Optics (Kitab al Manazir in Arabic), translated into Latin as the De aspectibus or Perspectiva, which disseminated his ideas to Western Europe and had great influence on the later developments of optics.

Ibn al-Haytham (Alhazen) (965-1039), in his broad theory of light and optics in his Book of Optics, explained vision, using geometry and anatomy, and stated that each point on an illuminated area or object radiates light rays in every direction, but that only one ray from each point, which strikes the eye perpendicularly, can be seen. The other rays strike at different angles and are not seen. He used the example of the camera obscura and pinhole camera, which produces an inverted image, to support his argument. This contradicted Ptolemy's theory of vision that objects are seen by rays of light emanating from the eyes. Alhacen held light rays to be streams of minute energy particles travelling in straight lines at a finite speed. He also speculated on the rectilinear propagation and electromagnetic aspects of light, and discovered that the speed of light is variable, with its speed decreasing in denser bodies. In order to establish that light travels in time and with finite speed, he undertook an experiment with a camera obscura and stated: “If the hole was covered with a curtain and the curtain was taken off, the light traveling from the hole to the opposite wall will consume time.” He also accurately described the refraction of light, and discovered the laws of refraction.

Alhazen also carried out the first experiments on the dispersion of light into its constituent colours. His major work Kitab al-Manazir was translated into Latin in the Middle Ages, as well as his book dealing with the colors of sunset. He dealt at length with the theory of various physical phenomena like shadows, eclipses, and the rainbow. He also attempted to explain binocular vision and the moon illusion. Through these extensive researches on optics, he is considered the pioneer of modern physical optics. Ibn al-Haytham also correctly argued that we see objects because the sun's rays of light, which he believed to be streams of tiny particles traveling in straight lines, are reflected from objects into our eyes. He understood that light must travel at a large but finite velocity, and that refraction is caused by the velocity being different in different substances. He also studied spherical and parabolic mirrors, and understood how refraction by a lens will allow images to be focused and magnification to take place. He understood mathematically why a spherical mirror produces aberration. 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, for initiating a scientific revolution in optics and visual perception.

Robert S. Elliot wrote the following on Ibn al-Haytham (Alhacen):

The Book of Optics established experimentation as the norm of proof in optics, and gave optics a physico-mathematical conception at a much earlier date than the other mathematical disciplines of mechanics and astronomy. The book was influential in both the Islamic world and in Western Europe.

Beginning of physiological optics

Ibn al-Haytham discussed the topics of medicine and ophthalmology in the anatomical and physiological portions of the Book of Optics and in his commentaries on Galenic works. He accurately described the process of sight, 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, vertical horopters and binocular disparity, and improved on the theories of binocular vision, motion perception and horopters previously discussed by Aristotle, Euclid and Ptolemy.

He discussed ocular anatomy, and was the first author to deal with the "descriptive anatomy" and "functional anatomy" of the eye independently. Much of his decriptive anatomy was faithful to Galen's gross anatomy, but with significant differences in his approach. For example, the whole area of the eye behind the iris constitutes what Ibn al-Haytham uniquely called the uveal sphere, and his description of the eye was devoid of any teleological or humoral theories associated with Galenic anatomy. He also described the eye as being made up of two interesecting globes, which was essential to his functional anatomy of the eye.

After describing the construction of the eye, Ibn al-Haytham makes his most original anatomical contribution in describing the functional anatomy of the eye as an optical system, or optical instrument. His mulitple light-source experiment via a reduction slit with the camera obscura, also known as the lamp experiment, provided sufficient empirical grounds for him to develop his theory of corresponding point projection of light from the surface of an object to form an image on a screen. It was his comparison between the eye and the beam-chamber, or camera obscura, which brought about his synthesis of anatomy and optics, giving rise to a new field of optics now known as "physiological optics". As he conceptualized the essential principles of pinhole projection from his experiments with the pinhole camera, he considered image inversion to also occur in the eye,Gul A. Russell, "Emergence of Physiological Optics", p. 689, in and viewed the pupil as being similar to an aperture. Regarding the process of image formation, however, he incorrectly agreed with Avicenna that the lens was the receptive organ of sight, but correctly hinted at the retina also being involved in the process.

Rainbow phenomenon

Ibn al-Haytham (Alhazen; 965-1039), attempted to provide a scientific explanation for the rainbow phenomenon. In his Maqala fi al-Hala wa Qaws Quzah (On the Rainbow and Halo), he "explained the formation of rainbow as an image, which forms at a concave mirror. If the rays of light coming from a farther light source reflect to any point on axis of the concave mirror, they form concentric circles in that point. When it is supposed that the sun as a farther light source, the eye of viewer as a point on the axis of mirror and a cloud as a reflecting surface, then it can be observed the concentric circles are forming on the axis." He was not able to verify this because his theory that "light from the sun is reflected by a cloud before reaching the eye" did not allow for a possible experimental verification. This explanation was later repeated by Averroes, and, though incorrect, provided the groundwork for the correct explanations later given by Kamāl al-Dīn al-Fārisī and Theodoric of Freiberg.

Ibn al-Haytham's contemorary, Ibn Sīnā (Avicenna; 980-1037), provided an alternative explanation, writing "that the bow is not formed in the dark cloud but rather in the very thin mist lying between the cloud and the sun or observer. The cloud, he thought, serves simply as the background of this thin substance, much as a quicksilver lining is placed upon the rear surface of the glass in a mirror. Ibn Sīnā would change the place not only of the bow, but also of the color formation, holding the iridescence to be merely a subjective sensation in the eye." This explanation, however, was also incorrect.

Qutb al-Din al-Shirazi (1236–1311) gave a fairly accurate explanation for the rainbow phenomenon. This was elaborated on by his student, Kamāl al-Dīn al-Fārisī (1260–1320), who gave a more mathematically satisfactory explanation of the rainbow. He "proposed a model where the ray of light from the sun was refracted twice by a water droplet, one or more reflections occurring between the two refractions." He verified this through extensive experimentation using a transparent sphere filled with water and a camera obscura. As he noted in his Kitab Tanqih al-Manazir (The Revision of the Optics), al-Farisi used a large clear vessel of glass in the shape of a sphere, which was filled with water, in order to have an experimental large-scale model of a rain drop. He then placed this model within a camera obscura that has a controlled aperture for the introduction of light. He projected light unto the sphere and ultimately deducted through several trials and detailed observations of reflections and refractions of light that the colors of the rainbow are phenomena of the decomposition of light. His research had resonances with the studies of his contemporary Theodoric of Freiberg (without any contacts between them; even though they both relied on Ibn al-Haytham's legacy), and later with the experiments of Descartes and Newton in dioptrics (for instance, Newton conducted a similar experiment at Trinity College, though using a prism rather than a sphere).

Later Islamic optics

Avicenna (980-1037) agreed that the speed of light is finite, as he "observed that if the perception of light is due to the emission of some sort of particles by a luminous source, the speed of light must be finite." Abū Rayhān al-Bīrūnī (973-1048) also agreed that light has a finite speed, and he stated that the speed of light is immensely faster than the speed of sound.

Abu 'Abd Allah Muhammad ibn Ma'udh, who lived in Al-Andalusmarker during the second half of the 11th century, wrote a work on optics later translated into Latin as Liber de crepisculis, which was mistakenly attributed to Alhazen. This was a "short work containing an estimation of the angle of depression of the sun at the beginning of the morning twilight and at the end of the evening twilight, and an attempt to calculate on the basis of this and other data the height of the atmospheric moisture responsible for the refraction of the sun's rays." Through his experiments, he obtained the accurate value of 18°, which comes close to the modern value.

In the late 13th and early 14th centuries, Qutb al-Din al-Shirazi (1236-1311) and his student Kamāl al-Dīn al-Fārisī (1260-1320) continued the work of Ibn al-Haytham, and they were the first to give the correct explanations for the rainbow phenomenon.

In 1574, Taqi al-Din (1526–1585) wrote the last major Arabic work on optics, entitled Kitab Nūr hadaqat al-ibsār wa-nūr haqīqat al-anzār (Book of the Light of the Pupil of Vision and the Light of the Truth of the Sights), which contains experimental investigations in three volumes on vision, the light's reflection, and the light's refraction. The book deals with the structure of light, its diffusion and global refraction, and the relation between light and colour. In the first volume, he discusses "the nature of light, the source of light, the nature of the propagation of light, the formation of sight, and the effect of light on the eye and sight". In the second volume, he provides "experimental proof of the specular reflection of accidental as well as essential light, a complete formulation of the laws of reflection, and a description of the construction and use of a copper instrument for measuring reflections from plane, spherical, cylindrical, and conical mirrors, whether convex or concave." The third volume "analyses the important question of the variations light undergoes while travelling in mediums having different densities, i.e. the nature of refracted light, the formation of refraction, the nature of images formed by refracted light." In his writings he also seems to describe an early rudimentary telescope.


Statics and dynamics

Al-Farabi (872-950) carried out an experiment concerning the existence of vacuum, in which he investigated handheld plungers in water. He concluded that air's volume can expand to fill available space, and he suggested that the concept of perfect vacuum was incoherent. However, Ibn al-Haytham (Alhazen, 965-1039) and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, and they supported the existence of a void. Using geometry, Ibn al-Haytham mathematically demonstrated that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body. Abū Rayhān al-Bīrūnī also states that there is no observable evidence that rules out the possibility of a vacuum. Also in the early 11th century, Avicenna (Ibn Sina, 980-1037) gauged the relative hotness and coldness of dry air using a rudimentary air thermometer.

Abū Rayhān al-Bīrūnī (973-1048), and later al-Khazini (fl. 1115-1130), were the first to apply experimental scientific methods to mechanics, especially the fields of statics and dynamics, particularly for determining specific weights, such as those based on the theory of balances and weighing. Muslim physicists unified statics and dynamics into the science of mechanics, and they combined the fields of hydrostatics with dynamics to give birth to hydrodynamics. They applied the mathematical theories of ratios and infinitesimal techniques, and introduced algebraic and fine calculation techniques into the field of statics. They were also generalized the theory of the centre of gravity and applied it to three-dimensional bodies. They also founded the theory of the ponderable lever and created the "science of gravity" which was later further developed in medieval Europe.Mariam Rozhanskaya and I. S. Levinova (1996), "Statics", p. 642, in :

In statics, al-Biruni measured the specific gravities of eighteen gemstones, and discovered that there is a correlation between the specific gravity of an object and the volume of water it displaces. He also introduced the method of checking tests during experiments, measured the weights of various liquids, and recorded the differences in weight between freshwater and saline water, and between hot water and cold water.

During his experiments on mechanics, al-Biruni invented the conical measure, in order to find the ratio between the weight of a substance in air and the weight of water displaced, and to accurately measure the specific weights of the gemstones and their corresponding metals, which are very close to modern measurements. Al-Biruni also realized that acceleration is connected with non-uniform motion.

In 1121, al-Khazini, in The Book of the Balance of Wisdom, invented a hydrostatic balance and proposed that the gravity or gravitational potential energy of a body varies depending on its distance from the centre of the Earth. In statics, al-Khazini clearly differentiated between force, mass, and weight, and he showed awareness of the weight of the air and of its decrease in density with altitude, and discovered that there was greater density of water when nearer to the Earth's centre.

The first suction pump was invented in 1206 by the Arabian engineer and inventor, Al-Jazari. The suction pump later appeared in Europe from the 15th century. Taqi al-Din's six-cylinder 'Monobloc' pump, invented in 1551, could also create a partial vacuum, which was formed "as the lead weight moves upwards, it pulls the piston with it, creating vacuum which sucks the water through a non return clack valve into the piston cylinder."

The measurement of viscosity appears for the first time in an Arabic military treatise dating back to the early 14th century. The viscosity (qawam) of distillated oils is gauged by the number of "words", ranging from ten and thirty "words" for various oils. This is similar to the modern method, where viscosity is gauged by the number of seconds needed for a certain volume of oil to fall through a calibrated orifice.


In aeronautics, Abbas Ibn Firnas (Armen Firman, 810-887) invented a primitive version of the parachute. John H. Lienhard described it in The Engines of Our Ingenuity as follows: "In 852, a new Caliph and a bizarre experiment: A daredevil named Armen Firman decided to fly off a tower in Cordova. He glided back to earth, using a huge winglike cloak to break his fall."

Abbas Ibn Firnas was also the first to make an attempt at controlled flight in a hang glider in 875, as opposed to earlier manned kite flights in ancient China which were not controllable. Ibn Firnas manuipulated the flight controls of his hang glider using two sets of artificial wings to adjust his altitude and to change his direction. He successfully returned to where he had lifted off from, but his landing was unsuccessful. According to Philip Hitti in History of the Arabs: "Ibn Firnas was the first man in history to make a scientific attempt at flying."

Theoretical physics

Theory of impetus

Avicenna (980-1037) developed an elaborate theory of motion, in which he made a distinction between the inclination and force of a projectile, and concluded that motion was a result of an inclination (mayl) transferred to the projectile by the thrower, and that projectile motion in a vacuum would not cease. He viewed inclination as a permanent force whose effect is dissipated by external forces such as air resistance. He also developed the concept of momentum, referring to impetus as being proportional to weight times velocity, for which he is considered a pioneer of the concept of momentum. His theory of motion was also consistent with the concept of inertia in classical mechanics, and later formed the basis of Jean Buridan's theory of impetus and exerted an influence on the work of Galileo Galilei.

Hibat Allah Abu'l-Barakat al-Baghdaadi (1080-1165) wrote a critique of Aristotelian physics entitled al-Mu'tabar, where he was the first to negate Aristotle's idea that a constant force produces uniform motion, as he realized that a force applied continuously produces acceleration, considered "the fundamental law of classical mechanics" and an early foreshadowing of Newton's second law of motion.

Abel B.

Franco (October 2003).

"Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4), p.

521-546 [528].) He also described acceleration as the rate of change of velocity. The 14th-century philosophers Jean Buridan and Albert of Saxony later refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus. Abu'l-Barakat also modified Avicenna's view on projectile motion, and stated that the mover imparts a violent inclination (mayl qasri) on the moved and that this diminishes as the moving object distances itself from the mover. Abu'l-Barakat also suggested that motion is relative, writing that "there is motion only if the relative positions of the bodies in question change."

Biruni verses Avicenna debate

Abū Rayhān al-Bīrūnī and Avicenna (Ibn Sina), who are regarded as two of the greatest polymaths in Persian history, were both colleagues and knew each other since the turn of the millennium. Biruni later engaged in a written debate with Avicenna, with Biruni criticizing the Peripatetic school for its adherence to Aristotelian physics and natural philosophy, while Avicenna and his student Ahmad ibn 'Ali al-Ma'sumi respond to Biruni's criticisms in writing.

This debate has been preserved in a book entitled al-As'ila wal-Ajwiba (Questions and Answers), in which al-Biruni attacks Aristotle's theories on physics and cosmology, and questions almost all of the fundamental Aristotelian physical axioms. For example, he rejects the notion that heavenly bodies have an inherent nature and asserts that their "motion could very well be compulsory"; maintains that "there is no observable evidence that rules out the possibility of vacuum"; and states that there is no inherent reason why planetary orbits must be circular and cannot be elliptical. He also argues that "the metaphysical axioms on which philosophers build their physical theories do not constitute valid evidence for the mathematical astronomer." This marks the first real distinction between the vocations of the philosopher-metaphysician (which he labelled Aristotle and Avicenna as) and that of the mathematician-scientist (which al-Biruni viewed himself as). In contrast to the philosophers, the only evidence that al-Biruni considered reliable were either mathematical or empirical evidence, and his systematic application of rigorous mathematical reasoning later led to the mathematization of Islamic astronomy and the mathematization of nature.

Biruni began the debate by asking Avicenna eighteen questions, ten of which were criticisms of Aristotle's On the Heavens, with his first question criticizing the Aristotelian theory of gravity for denying the existence of levity or gravity in the celestial spheres, and the Aristotelian notion of circular motion being an innate property of the heavenly bodies. Biruni's second question criticizes Aristotle's over-reliance on more ancient views concerning the heavens, while the third criticizes the Aristotelian view that space has only six directions. The fourth question deals with the continuity and discontinuity of physical bodies, while the fifth criticizes the Peripatetic denial of the possibility of there existing another world completely different from the world known to them.In his sixth question, Biruni rejects Aristotle's view on the celestial spheres having circular orbits rather than elliptic orbits. In his seventh question, he rejects Aristotle's notion that the motion of the heavens begins from the right side and from the east, while his eighth question concerns Aristotle's view on the fire element being spherical. The ninth question concerns the movement of heat, and the tenth question concerns the transformation of elements.

The eleventh question concerns the burning of bodies by radiation reflecting off a flask filled with water, and the twelfth concerns the natural tendency of the classical elements in their upward and downward movements. The thirteenth question deals with vision, while the fourteenth concerns habitation on different parts of Earth. His fifteenth question asks how two opposite squares in a square divided into four can be tangential, while the sixteenth question concerns vacuum. His seventeenth question asks "if things expand upon heating and contract upon cooling, why does a flask filled with water break when water freezes in it?" His eighteenth and final question concerns the observable phenomenon of ice floating on water.

After Avicenna responded to the questions, Biruni was unsatisfied with some of the answers and wrote back commenting on them, after which Avicenna's student Ahmad ibn 'Ali al-Ma'sumi wrote back on behalf of Avicenna.

Other theories on dynamics and kinematics

Ja'far Muhammad ibn Mūsā ibn Shākir (800-873) of the Banū Mūsā hypothesized that heavenly bodies and celestial spheres were subject to the same laws of physics as Earth, unlike the ancients who believed that the celestial spheres followed their own set of physical laws different from that of Earth. In his Astral Motion and The Force of Attraction, he also hypothesized that there was a force of attraction between heavenly bodies, which Robert Briffault views as a precursor to Newton's law of universal gravitation. Thābit ibn Qurra (836-901) rejected the Peripatetic and Aristotelian notions of a "natural place" for each element. He instead proposed a theory of motion in which both the upward and downward motions are caused by weight, and that the order of the universe is a result of two competing attractions (jadhb): one of these being "between the sublunar and celestial elements", and the other being "between all parts of each element separately".

Ibn al-Haytham (965-1039) discussed the theory of attraction between masses, and it seems that he was aware of the magnitude of acceleration due to gravity and he stated that the heavenly bodies "were accountable to the laws of physics". Ibn al-Haytham also enunciated the law of inertia, later known as Newton's first law of motion, when he stated that a body moves perpetually unless an external force stops it or changes its direction of motion. He also developed the concept of momentum, though he did not quantify this concept mathematically.

Nobel Prize winning physicist Abdus Salam wrote the following on Ibn al-Haytham:

Abū Rayhān Bīrūnī (973-1048) appears to be the earliest to cite movement and friction as the cause of heat, which in turn produces the element of fire, and a lack of movement as the cause of cold near the geographical poles:

Ibn Bajjah (Avempace) (d. 1138) argued that there is always a reaction force for every force exerted, which Shlomo Pines views as "a precursor to the Leibnizian idea of force" which "underlies Newton's third law of motion",Shlomo Pines (1964), "La dynamique d’Ibn Bajja", in Mélanges Alexandre Koyré, I, 442-468 [462, 468], Paris

Abel B.

Franco (October 2003), "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4): 521-546 [543]) though he did not refer to the reaction force as being equal to the exerted force. His theory of motion had an important influence on later physicists like Galileo.

Averroes (1126–1198) defined and measured force as "the rate at which work is done in changing the kinetic condition of a material body" and correctly argued "that the effect and measure of force is change in the kinetic condition of a materially resistant mass." In the 13th century, ʻAbd Allah Baydawi hypothesized that heat is due to either one of two possibilities:

In 1253, a Latin text entitled Speculum Tripartitum stated the following regarding Avicenna's theory on heat:

In the 13th century, Nasīr al-Dīn al-Tūsī stated an early version of the law of conservation of mass, noting that a body of matter is able to change, but is not able to disappear. In the early 16th century, al-Birjandi developed a hypothesis similar to Galileo's notion of "circular inertia." The Muslim developments in mechanics laid the foundations for the later development of classical mechanics in early modern Europe.


Ibn al-Haytham's Maqala fi daw al-qamar (On the Light of the Moon), which he wrote some time before his famous Book of Optics (1021), was the first successful attempt at combining mathematical astronomy with physics, and the earliest attempt at applying the experimental method to astronomy and astrophysics. Regarding moonlight, he disproved the universally held opinion that the moon reflects sunlight like a mirror and correctly concluded that it "emits light from those portions of its surface which the sun's light strikes." In order to prove that "light is emitted from every point of the moon's illuminated surface," he built an "ingenious experimental device." Ibn al-Haytham had "formulated a clear conception of the relationship between an ideal mathematical model and the complex of observable phenomena; in particular, he was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment showing that the intensity of the light-spot formed by the projection of the moonlight through two small apertures onto a screen diminishes constantly as one of the apertures is gradually blocked up."

In 1574, al-Din used astrophysics to explain the intromission model of vision. He stated since the stars are millions of kilometres away from the Earth and that the speed of light is constant, that if light had come from the eye, it would take too long for light "to travel to the star and come back to the eye. But this is not the case, since we see the star as soon as we open our eyes. Therefore the light must emerge from the object not from the eyes."

Celestial mechanics

In astrophysics and celestial mechanics, the eldest Banū Mūsā brother, Ja'far Muhammad ibn Mūsā ibn Shākir (9th century), made significant contributions. He was the first to hypothesize that the heavenly bodies and celestial spheres are subject to the same laws of physics as Earth, unlike the ancients who believed that the celestial spheres followed their own set of physical laws different from that of Earth. In his Astral Motion and The Force of Attraction, Muhammad ibn Musa proposed that there is a force of attraction between heavenly bodies, foreshadowing Newton's law of universal gravitation.

Ibn al-Haytham (Alhazen), in his Book of Optics (1021), 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 and Tychonic systems of astronomy. In his Epitome of Astronomy, he also insisted that the heavenly bodies "were accountable to the laws of physics."

Abū Rayhān al-Bīrūnī was also one of the first to conduct elaborate experiments related to astronomical phenomena. He supposed the Milky Way galaxy to be a collection of numerous nebulous stars, and in Khorasan, he observed and described the solar eclipse on April 8, 1019, and the lunar eclipse on September 17, 1019, in detail, and gave the exact latitudes of the stars during the lunar eclipse. Al-Biruni also theorized that gravity exists within the heavenly bodies and celestial spheres, and he criticized the Aristotelian views of them not having any levity or gravity and of circular motion being an innate property of the heavenly bodies. He also described the Earth's gravitation as:

In 1121, al-Khazini, in his treatise The Book of the Balance of Wisdom, was the first to propose the theory that the "gravities" of bodies, or their gravitational potential energy, vary depending on their distances from the centre of the Earth. This phenomenon was not proven until the 18th century. He states:

Maragha Revolution

In Islamic astronomy, some have described the achievements of the Maragha schoolmarker in the 13th and 14th centuries as a "Maragha Revolution", "Maragha School Revolution", or "Scientific Revolution before the Renaissance". An important aspect of this revolution included the realization that astronomy should aim to describe the behaviour of physical bodies in mathematical language, and should not remain a mathematical hypothesis, which would only save the phenomena. The Maragha astronomers also realized that the Aristotelian view of motion in the universe being only circular or linear was not true, as the Tusi-couple developed by Nasīr al-Dīn al-Tūsī showed that linear motion could also be produced by applying circular motions only.

Unlike the ancient Greek and Hellenistic astronomers who were not concerned with the coherence between the mathematical and physical principles of a planetary theory, Islamic astronomers insisted on the need to match the mathematics with the real world surrounding them, which gradually evolved from a reality based on Aristotelian physics to one based on an empirical and mathematical physics after the work of Ibn al-Shatir. The Maragha Revolution was thus characterized by a shift away from the philosophical foundations of Aristotelian cosmology and Ptolemaic astronomy and towards a greater emphasis on the empirical observation and mathematization of astronomy and of nature in general, as exemplified in the works of Ibn al-Shatir, Ali al-Qushji, al-Birjandi and Shams al-Din al-Khafri.

Ibn al-Shatir (13041375) of Damascusmarker, in A Final Inquiry Concerning the Rectification of Planetary Theory, incorporated the Urdi lemma, and eliminated the need for an equant by introducing an extra epicycle (the Tusi-couple), departing from the Ptolemaic system in a way that was mathematically identical to what Nicolaus Copernicus did in the 16th century. Unlike previous astronomers before him, Ibn al-Shatir was not concerned with adhering to the theoretical principles of natural philosophy or Aristotelian cosmology, but rather to produce a model that was more consistent with empirical observations. His model was thus in better agreement with empirical observations than any previous model, and was also the first that permitted empirical testing. His work thus marked a turning point in astronomy, which may be considered a "Scientific Revolution before the Renaissance". His rectified model was later adapted into a heliocentric model by Copernicus, which was mathematically achieved by reversing the direction of the last vector connecting the Earth to the Sun.

Earth's motion

In the 9th century, Ja'far ibn Muhammad Abu Ma'shar al-Balkhi (Albumasar) developed a planetary model which some have interpreted as a heliocentric model. This is due to his orbital revolutions of the planets being given as heliocentric revolutions rather than geocentric revolutions, and the only known planetary theory in which this occurs is in the heliocentric theory. His work on planetary theory has not survived, but his astronomical data was later recorded by al-Hashimi and al-Biruni.

In the 11th century, Abū Rayhān al-Bīrūnī, in response to al-Sijzi and Indian astronomers who believed in heliocentrism and/or the Earth's rotation, wrote in his Indica:

The work of Ali al-Qushji (d. 1474), who worked at Samarkandmarker and then Istanbulmarker, is seen as a late example of innovation in Islamic theoretical astronomy and it is believed he may have had an influence on Nicolaus Copernicus due to similar arguments concerning the Earth's rotation. Before al-Qushji, the only astronomer to present an empirical argument for the Earth's rotation was Nasīr al-Dīn al-Tūsī (d. 1274), who used the phenomena of comets to refute Ptolemy's claim that a stationery Earth can be determined through observation alone. Al-Tusi, however, accepted that the Earth was stationery on the basis of natural philosophy instead, particularly Aristotelian cosmology. In the 15th century, the influence of Aristotelian physics and natural philosophy was declining due to religious opposition. Al-Qushji, in his Concerning the Supposed Dependence of Astronomy upon Philosophy, thus rejected Aristotelian physics and completely separated natural philosophy from astronomy, allowing astrophysics to become a purely empirical and mathematical science. This allowed him to explore alternatives to the Aristotelian notion of a stationery Earth, as he explored the idea of a moving Earth. He elaborated on al-Tusi's argument and concluded, on the basis of empiricism rather than speculative philosophy, that the moving Earth theory is just as likely to be true as the stationary Earth theory and that it is not possible to empirically deduce which theory is true.

In the 16th century, the debate on the Earth's motion was continued by al-Birjandi (d. 1528), who in his analysis of what might occur if the Earth were rotating, develops a hypothesis similar to Galileo Galilei's notion of "circular inertia", which he described in the following observational test (as a response to one of Qutb al-Din al-Shirazi's arguments):

Apparatus and instruments

Optical instruments

Ibn al-Haytham (Alhazen) gave the first clear description and correct analysis of the camera obscura and pinhole camera in his Book of Optics (1021). In his earlier Maqala fi daw al-qamar (On the Light of the Moon), in order to prove that "light is emitted from every point of the moon's illuminated surface," he built an "ingenious experimental device." The first optical research to describe a magnifying lens used in an instrument was also found in the Book of Optics written by Ibn al-Haytham. His work in light refraction, parabolic mirrors, as well as the creation of other instruments such as the camera obscura, also helped spark the Scientific Revolution.

Laboratory apparatus

During his experiments on physics, Abū Rayhān al-Bīrūnī invented the conical measure, in order to find the ratio between the weight of a substance in air and the weight of water displaced, and to accurately measure the specific weights of the gemstones and their corresponding metals, which are very close to modern measurements.

Abū Rayhān al-Bīrūnī also invented the laboratory flask and pycnometer in the early 11th century, and the hydrostatic balance and steelyardmarker were invented by al-Khazini in the early 12th century. The earliest known descriptions for these instruments are found in al-Khazini's The Book of the Balance of Wisdom (1121).

Also in the 11th century, Avicenna (Ibn Sina) was the employed a rudimentary air thermometer to gauge the relative hotness or coldness of dry air.Robert Briffault (1938), The Making of Humanity, p. 191 He also invented the refrigerated coil, which condenses aromatic vapours, in order to produce essential oils through steam distillation.

Other devices

The first suction pump, was invented in 1206 by the Arabian engineer and inventor, Al-Jazari. The suction pump later appeared in Europe from the 15th century. Taqi al-Din's six-cylinder 'Monobloc' pump, invented in 1551, could also create a partial vacuum, which was formed "as the lead weight moves upwards, it pulls the piston with it, creating vacuum which sucks the water through a non return clack valve into the piston cylinder." He also invented an early practical steam turbine as a prime mover for the first steam-powered and self-rotating spit, as described in his book, Al-Turuq al-samiyya fi al-alat al-ruhaniyya (The Sublime Methods of Spiritual Machines), completed in 1551 AD (959 AH).

In the 14th century, Ibn al-Shatir invented the compass dial, a timekeeping device incorporating both a universal sundial and a magnetic compass. He invented it for the purpose of finding the times of Salah prayers. The Arabs also invented the 32-point compass rose during the Middle Ages. A cartographic Qibla instrument with a sundial and compass attached to itDavid A. King (1997), "Two Iranian World Maps for Finding the Direction and Distance to Mecca", Imago Mundi 49: 62-82 [62] was created by Muhammad Husayn in the 17th century.Muzaffar Iqbal, "David A. King, World-Maps for Finding the Direction and Distance to Mecca: Innovation and Tradition in Islamic Science", Islam & Science, June 2003.

Other experiments

Other experiments related to physics include Abbas Ibn Firnas' invention of "some sort of metronome", and his attempt at creating an artificial weather simulation room, in which spectators saw stars and clouds, and were astonished by artificial thunder and lightning, which were produced by mechanisms hidden in his basement laboratory. Possibly the earliest and nearest approach to the discovery of the identity of lightning, and electricity from any other source, is to be attributed to the Arabs, who before the 15th century had the Arabic word for lightning (raad) applied to the electric ray.


Arabic writers were aware of magnetism since the ---------- 9th century, when Muhammad ibn Zakarīya Rāzi (Rhazes) wrote a treatise on the subject. In the 12th century, Ibn Bajjah (Avempace) described the properties of magnets and its attraction towards iron. Like some of the ancient Greek philosophers, the early Islamic philosophers were also aware of the properties of natural plastic amber, and they observed that it can draw up small bits of paper.

After the arrival of an early compass from Chinamarker around the 12th or 13th century, Islamic geography and navigational sciences became highly developed with the use of the magnetic compass. The first astronomical uses of the magnetic compass is also found in a treatise on astronomical instruments written by the Yemenimarker sultan al-Ashraf (d. 1296 AD) in 1282 AD (681 AH). This was the first reference to the compass in astronomical literature.

Al-Ashraf's compass used a steel needle magnetized by rubbing with a magnetic stone, due to steel needles keeping their magnetic property longer than iron needles. Al-Ashraf also provides detailed explanations on the magnetic properties of the needle. He was aware that when the end rubbed with the magnetic stone, that each head retains its attraction to turn north or south, referring to the fact that the head of the needle which is not rubbed has also changed its behavior. He also described two flaws of the early magnetic compass: "loss of magnetic properties and attrition of the cone", and wrote that these were the reasons why it was neglected by “the early scholars”. Al-Ashraf then develops an improved compass for use as a "Qibla indicator" instrument in order to find the direction to Meccamarker. Al-Ashraf's instrument was one of the earliest dry compasses, and appears to have been invented independently of Peter Peregrinus.

In the 14th century, Ibn al-Shatir invented the compass dial, a timekeeping device incorporating both a universal sundial and a magnetic compass. He invented it for the purpose of finding the direction of Qibla and the times of Salah prayers. The Arabs also invented the 32-point compass rose during the Middle Ages.

Muslim astronomers were aware of magnetic declination by the 15th century, when the Egyptian astronomer 'Izz al-Din al-Wafa'i (d. 1469/1471) measured it as 7 degrees from Cairomarker. A cartographic Qibla instrument with a sundial and compass attached to it was created by Muhammad Husayn in the 17th century.


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