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As forms of science historically developed out of philosophy, physics (Greek: φύσις physis "nature") was originally referred to as natural philosophy, a term describing a field of study concerned with "the workings of nature".

Physics is a branch of science that was referred to as natural philosophy until the late 19th century. Currently, physics is traditionally defined as the study of matter, energy, and the relation between them. Physics is, in some senses, the oldest and most basic pure science; its discoveries find applications throughout the natural sciences, since matter and energy are the basic constituents of the natural world. The other sciences are generally more limited in their scope and may be considered branches that have split off from physics to become sciences in their own right. Physics today may be divided loosely into classical physics and modern physics.


Physics (from Greek φυσική (ἐπιστήμη), i.e. "knowledge of nature", from φύσις, physis, i.e. "nature"[1][2][3][4][5]) is the natural science that involves the study of matter[6] and its motion through space and time, along with related concepts such as energy and force.[7] More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.[8][9][10]

Early history in Middle East and Mediterranean[]

Elements of what became physics were drawn primarily from the fields of astronomy, optics, and mechanics, which were methodologically united through the study of geometry. These mathematical disciplines began in Antiquity with the Babylonians and with Hellenistic writers such as Archimedes and Ptolemy. Meanwhile, philosophy, including what was called “physics”, focused on explanatory (rather than descriptive) schemes, largely developed around the Aristotelian idea of the four types of “causes”.

Ancient Mesopotamia[]

The origins of Western astronomy can be found in Mesopotamia (Iraq).[11] In the course of the last few decades it has become increasingly clear that all Western efforts in the exact sciences are descendants in direct line from the work of the late Babylonian astronomers.[11] Our knowledge of Sumerian astronomy is indirect, via the earliest Babylonian star catalogues dating from about 1200 BCE. The fact that many star names appear in Sumerian suggests a continuity reaching into the early Bronze Age.

Early attempts at philosophically explaining nature date back to the 8th and 7th centuries BC, when Babylonian astronomers developed an empirical approach to astronomy. They began studying natural philosophy dealing with the ideal nature of the universe, and began employing an internal logic within their predictive planetary systems.[12]

In the 2nd century BC, the Babylonian astronomer Seleucus of Seleucia proposed a heliocentric model where the Earth rotated around its own axis, which in turn revolved around the Sun. Though the arguments he used were lost, Plutarch stated that Seleucus was the first to prove the heliocentric system through reasoning.

Ancient Mediterranean[]

This move towards a more rational understanding of nature later influenced the Eastern Medierranean, particularly the Greeks and Phoenicians, at least since the Archaic Period (650 BC – 480 BC), with the Presocratics.

The Phoenician philosopher Thales (7th and 6th centuries BCE), sometimes anachronistically dubbed a "father of science" (in the philosophical sense) for refusing to accept various supernatural, religious or mythological explanations for natural phenomena, proclaimed that every event had a natural cause.[13] Thales also made advancements in 580 BCE, suggesting that water is the basic element, experimenting with magnets and attraction to rubbed amber, and formulating cosmologies.

Accordingly, Leucippus (Greek: Λεύκιππος, first half of 5th century BC), refusing to accept various supernatural, religious or mythological explanations for natural phenomena, proclaimed that every event had a natural cause. He went on to develop the theory of atomism — the idea that everything is composed entirely of various imperishable, indivisible elements called atoms. This was elaborated in great detail by Democritus.

Aristotle (Greek: Ἀριστοτέλης, Aristotélēs) (384 BC – 322 BC), a student of Plato, promoted the concept that observation of physical phenomena could ultimately lead to the discovery of the natural laws governing them. He wrote the first work which refers to that line of study as "Physics" (Aristotle's Physics). During the classical period (6th, 5th and 4th centuries BC) and in Hellenistic times, natural philosophy slowly developed into an exciting and contentious field of study.

Early in classical antiquity, that the earth is a sphere ("round"), was generally known by all, and around 240 BCE, the Libyan astronomer Eratosthenes (276 BCE - 194 BCE) accurately estimated its circumference in Egypt. In contrast to Aristotle's geocentric views, Aristarchus of Samos (Greek: Ἀρίσταρχος; 310 BC – ca. 230 BC) presented a heliocentric view of the solar system, placing the Sun, not the Earth, at the centre.

Many contributions were made by many thinkers, including the mathematician Archimedes (Greek: Ἀρχιμήδης) (c. 287 BC – c. 212 BC) of "Eureka!" fame, who defined the concept of the centre of gravity and created the field of statics, and the Egyptian astronomer Ptolemy (Claudius Ptolemaeus), who wrote scientific treatises in Alexandria that were later used as the basis of much later science.

Much of the accumulated knowledge of the ancient world was lost. Even of the works of the better known thinkers, few fragments survived. Although he wrote at least fourteen books, almost nothing of Hipparchus' direct work survived. Of the 150 reputed Aristotelian works, only 30 exist, and some of those are "little more than lecture notes". Though reinterpreted to fit theological concerns, both Jewish and Islamic scholarship preserved and developed some of the ancient knowledge that would otherwise have been lost. (See Judeo-Islamic philosophies (800 - 1400).)

Awareness of ancient works re-entered the West through translations from Arabic to Latin. Their re-introduction, combined with Judeo-Islamic theological commentaries, had a great influence on Medieval philosophers such as Thomas AquinasScholastic European scholars, who sought to reconcile the philosophy of the ancient classical philosophers with Judeo-Christian theology, proclaimed Aristotle the greatest thinker of the ancient world. In cases where they didn't directly contradict the Bible, Aristotelian physics became the foundation for the physical explanations of the European Churches.

Medieval Islamic physics[]

During the period of time known as the European Dark Ages (5th to 15th centuries), much scientific progress occurred in the Muslim world during what is known as the Islamic Golden Age. The scientific research of the Islamic scientists is often overlooked due to the conflict of the Crusades and "it's possible, too, that many scholars in the Renaissance later downplayed or even disguised their connection to the Middle East for both political and religious reasons."[14]

The Islamic Abbasid caliphs gathered many classic works of antiquity and had them translated into Arabic. Islamic philosophers such as Al-Kindi (Alkindus), Al-Farabi (Alpharabius), Avicenna (Ibn Sina) and Averroes (Ibn Rushd) reinterpreted Hellenistic thought in the context of their religion. Important contributions were made by Ibn al-Haytham and Abū Rayhān al-Bīrūnī[15][16] before eventually passing on to Western Europe where they were studied by scholars such as Roger Bacon and WiteloIbn Sina (980 – 1037), known by the Latin name Avicenna, was a medical researcher from Bukhara, Uzbekistan responsible for important contributions to the disciplines of physics, optics, philosophy and medicine. He is most famous for writing The Canon of Medicine, a text used to teach student doctors in Europe until the 1600s.

Important contributions were made by Ibn al-Haytham (965 – 1040), a mathematician from Basra, Iraq considered one of the founders of modern optics. Ptolemy and Aristotle theorised that light either shone from the eye to illuminate objects or that light emanated from objects themselves, whereas al-Haytham (known by the Latin name Alhazen) suggested that light travels to the eye in rays from different points on an object. The works of Ibn al-Haytham and Abū Rayhān al-Bīrūnī eventually passed on to Western Europe where they were studied by scholars such as Roger Bacon and Witelo.[15][16] Omar Khayyám (1048–1131), an Iraqi scientist, calculated the length of a solar year to 10 decimal places and was only out by a fraction of a second when compared to our modern day calculations. He used this to compose a calendar considered more accurate than the Gregorian calendar that came along 500 years later. He is classified as one of the world's first great science communicators – he is said to have convinced a Sufi theologist that the world turns on an axis. Muḥammad ibn Jābir al-Ḥarrānī al-Battānī (858 – 929), from Harran, Turkey, further developed trigonometry (first conceptualised in Ancient Greece) as an independent branch of mathematics, developing relationships such as tanθ = sinθ / cosθ. His driving force was to obtain the ability to locate Mecca from any given geographical point – aiding in Muslim rituals such as burial and prayer, which require participants to face the holy city, as well as making the pilgrimage to Mecca (known as the hajj).

Jābir ibn Hayyān (721 – 815) was a chemist and alchemist who, in his quest to make gold from other metals, discovered strong acids such as sulphuric, hydrochloric and nitric acids. He was the also first person to identify the only substance that can dissolve gold – aqua regis (royal water) – a volatile mix of hydrochloric and nitric acid. It is disputed whether Jabir was the first to use or describe distillation, but he was definitely the first to perform it in the lab using an alembic (from 'al-inbiq'). The most famous Persian mathematician is considered to be Muḥammad ibn Mūsā al-Khwārizmī (780 – 850), who produced a comprehensive guide to the numbering system developed from the Brahmi system in India, using only 10 digits (0-9, the so-called "Arabic numerals"). Al-Khwarizmi also used the word algebra ('al-jabr') to describe the mathematical operations he introduced, such as balancing equations, which helped in several problems.

Furthermore, Nasir al-Din al-Tusi (1201–1274), an astronomer and mathematician from Baghdad, authored the Treasury of Astronomy, a remarkably accurate table of planetary movements that reformed the existing planetary model of Roman astronomer Ptolemy by describing a uniform circular motion of all planets in their orbits. This work led to the later discovery, by one of his students, that planets actually have an elliptical orbit. Copernicus later drew heavily on the work of al-Din al-Tusi and his students, but without acknowledgment.[14] The gradual chipping away of the Ptolemaic system paved the way for the revolutionary idea that the Earth actually orbited the Sun (heliocentrism). Nasīr al-Dīn al-Tūsī also 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.[17] This is a fundamental concept underlying the laws of thermodynamics.

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",[18] though he did not necessarily refer to the reaction force as being equal to the exerted force.[19] His theory of motion had an important influence on later physicists like Galileo.[20]

It has been noted that Al-Ghazali's atomic theory of physical reality circa 1100 (related to atomism and occasionalism) anticipates some of the core principles of contemporary quantum physics (also known as quantum mechanics) by almost a millennium. In her 1993 paper, Causality Then and Now: Al Ghazali and Quantum Theory, the scholar Karen Harding stated:[21]

"The extent of the commonalities is striking. For example, both deny that the regularities in the behavior of objects should be attributed to the existence of causal laws. Further, they agree that events in the world ate not strictly predictable. Both accept the idea that unexpected, unpredictable things can and do occur. According to al Ghazali's explanation, God is omnipotent and involved in the world at every moment and can, therefore, cause anything to happen. The Copenhagen Interpretation of quantum theory says that it is impossible to predict the exact behavior of an object based on physical laws. As a result, while one might expect a lead ball to fall when it is dropped, there is a definite possibility that the ball will rise instead."

In a 2003 paper, Ümit Yoksuloglu Devji and Eric L. Ormsby further elaborated on Harding's comparative analysis between Al-Ghazali's theory and contemporary quantum physics.[22]

Hibat Allah Abu'l-Barakat al-Baghdadi (1080–1165) also suggested that motion is relative, writing that "there is motion only if the relative positions of the bodies in question change."[23] This anticipates some of the core principles of the theory of relativity.

Theory of impetus[]

Based on Aristotelian physics, Scholastic physics described things as moving according to their essential nature. Celestial objects were described as moving in circles, because perfect circular motion was considered an innate property of objects that existed in the uncorrupted realm of the celestial spheres. The theory of impetus, the ancestor to the concepts of inertia and momentum, was developed along similar lines by medieval philosophers, such as the Egyptian John Philoponus, the Persian Avicenna, and the French Jean Buridan. Motions below the lunar sphere were seen as imperfect, and thus could not be expected to exhibit consistent motion. More idealized motion in the “sublunary” realm could only be achieved through artifice, and prior to the 17th century, many did not view artificial experiments as a valid means of learning about the natural world. Physical explanations in the sublunary realm revolved around tendencies. Stones contained the element earth, and earthy objects tended to move in a straight line toward the centre of the earth (and the universe in the Aristotelian geocentric view) unless otherwise prevented from doing so.

In the 11th century, Avicenna developed an elaborate theory of motion in The Book of Healing, 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.[24] The violent inclination he conceived was non-self-consuming, a permanent force whose effect is dissipated only as a result of external forces such as air resistance,[24][25] making him "the first to conceive such a permanent type of impressed virtue for non-natural motion."[26] Avicenna's concept of mayl is almost the opposite of the Aristotelian conception of violent motion and is reminiscent of the concept of inertia, known as Newton's first law of motion, roughly equivalent to Jean Buridan's concept of impetus.[27] Avicenna's theory of mayl also attempted to provide a quantitive relation between the weight and velocity of a moving body, resembling the concept of momentum.[28] Avicenna's theory also holds that the object is pushed along by the air it displaces.[29]

In the 12th century, Hibat Allah Abu'l-Barakat al-Baghdadi adopted and modified Avicenna's theory on projectile motion. In his Kitab al-Mu'tabar, Abu'l-Barakat 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.[30] He was also the first to reject Aristotle's law that a constant force produces uniform motion, as he realized that a force applied continuously produces acceleration, which is now considered "the fundamental law of classical mechanics."[31] He also described acceleration as the rate of change of velocity.[32] 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.[30]

In the 14th century, Jean Buridan rejected the Philoponan notion that the motive force, which he named impetus, dissipated spontaneously, and adopted the Avicennan impetus theory in which (i) it is only corrupted by the resistances of the medium and of gravity in the case of anti-gravitational motion, but would otherwise be permanently conserved in the absence of any resistances to motion, and in which (ii) gravity is also a downward projector and creator of downward impetus, unlike in the radically different Philoponan theory in which gravity neither creates not destroys impetus. The assimilation of the role of gravity in natural motion to the role of a projector that creates impetus just as it is created by a thrower in anti-gravitational violent motion was explicitly stated by Buridan's pupil Dominicus de Clavasio in his 1357 De Caelo.

Early history in Far East[]

Important physical and mathematical traditions also existed in ancient Chinese and Indian sciences.



The Hindu-Arabic numeral system. The inscriptions on the edicts of Ashoka (3rd century BCE) display this number system being used by the Imperial Mauryas.

In Indian philosophy, Kanada was the first to systematically develop a theory of atomism during the 6th century BCE,[33][34] and it was further elaborated by the Buddhist atomists Dharmakirti and Dignāga during the 1st millennium CE.[35] Pakudha Kaccayana, a 6th-century BCE Indian philosopher and contemporary of Gautama Buddha, had also propounded ideas about the atomic constitution of the material world. These philosophers believed that other elements (except ether) were physically palpable and hence comprised minuscule particles of matter. The last minuscule particle of matter that could not be subdivided further was termed Parmanu. The Indian concept of the atom was developed independently and prior to the development of the idea in the Greco-Roman world. These philosophers considered the atom to be indestructible and hence eternal. The Buddhists thought atoms to be minute objects unable to be seen to the naked eye that come into being and vanish in an instant. The Vaisheshika school of philosophers believed that an atom was a mere point in space. Indian theories about the atom are greatly abstract and enmeshed in philosophy as they were based on logic and not on personal experience or experimentation.

In Indian astronomy, Aryabhata's Aryabhatiya (499 CE) proposed the Earth's rotation, while Nilakantha Somayaji (1444–1544) of the Kerala school of astronomy and mathematics proposed a semi-heliocentric model resembling the Tychonic system.


File:Su Song Star Map 1.JPG

A star map with a cylindrical projection. Su Song's star maps represent the oldest existent ones in printed form.

The study of magnetism in Ancient China dates back to the 4th century BCE. (in the Book of the Devil Valley Master),[36] A main contributor to this field was Shen Kuo (1031–1095), a polymath scientist and statesman who was the first to describe the magnetic-needle compass used for navigation, as well as discovering the concept of true north. In optics, Shen Kuo independently developed a camera obscura.[37] The study of magnetism in China dates back to the 4th century BCE (in the Book of the Devil Valley Master),[38] eventually leading to the invention of the compass.

Emergence of experimental method and mathematical physics[]

See also: Physics in medieval Islam, Experimental physics, Mathematical physics, History of optics, and Science in the Middle Ages

The use of empirical experiments [39] in geometrical optics dates back to second century Roman Egypt, where the Egyptian astronomer Ptolemy carried out several experiments on reflection, refraction and binocular vision.[40] However, he either discarded or rationalized any empirical data that did not support his Platonic paradigm.[41] Experiments did not hold any importance at the time, and empirical evidence was thus seen as secondary to general theory.[42] The incorrect emission theory of vision thus continued to dominate optics through to the 10th century.

Ibn al-Haytham's mathematical physics and physical optics[]

See also: Alhazen and Book of Optics

The turn of the second millennium saw the development of an experimental method emphasizing the role of experimentation as a form of proof for scientific inquiry together with the development of physical optics where mathematics and geometry were combined with the philosophical field of physics. The Iraqi physicist, Ibn al-Haytham (Alhazen), is considered a central figure in this shift in physics from a philosophical activity to an experimental and mathematical one, and the shift in optics from a mathematical discipline to a physical and experimental one.[43][44][45][46][47][48]

Due to his positivist approach,[49] his Doubts Concerning Ptolemy insisted on scientific demonstration and criticized Ptolemy's confirmation bias and conjectural undemonstrated theories.[50] His Book of Optics (1021) was the earliest successful attempt at unifying a mathematical discipline (geometrical optics) with the philosophical field of physics, to create the modern science of physical optics. An important part of this was the intromission theory of vision, which in order to prove, he developed an experimental method to test his hypothesis.[43][44][45][46][48][51] He conducted various experiments to prove his intromission theory[52] and other hypotheses on light and vision.[53] The Book of Optics established experimentation as the norm of proof in optics,[51] and gave optics a physico-mathematical conception at a much earlier date than the other mathematical disciplines.[54] His On the Light of the Moon also attempted to combine mathematical astronomy with physics, a field now known as astrophysics, to formulate several astronomical hypotheses which he proved through experimentation.[45] Ibn al-Haytham is today considered to be the "first theoretical physicist".[55]

Scientific methodology[]

See also: History of 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),[56][57] which was due to the emphasis on empirical observation found in the Qur'an and Sunnah,[58][59][60][61] and the rigorous historical methods established in the science of hadith.[58] Muslim scientists thus combined precise observation, controlled experiment and careful records[57] with a new[56] approach to scientific inquiry which led to the development of the scientific method.[51] 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,[62] which he first introduced to optics and astrophysics.[45][51][63]

Other early experimental methods were developed by Geber for alchemy and chemistry,[64] by al-Kindi for the Earth sciences,[65] and by Abū Rayhān al-Bīrūnī for astrophysics[66] and mechanics.[16] 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.[56][67][68][69][70][71][72][73][74]

Alhazenian method[]

Ibn al-Haytham, considered the "father of modern optics",[75] 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.[76] 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.[77] Ibn al-Haytham's scientific method was similar to the modern scientific method in that it consisted of the following procedures:[78]

  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).[79][80]

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.[81]

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.[82]

The Book of Optics was the first book to emphasize the role of experimentation as a form of proof in scientific inquiry.[83] 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.[49]

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."[84] 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.[85]

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

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...[46]

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

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.[46]

Birunian and Avicennian methods[]

See also: Abū Rayhān al-Bīrūnī and Avicenna

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.[86] He was also responsible for introducing the experimental method into mechanics,[16] and was one of the first to conduct elaborate experiments related to astronomical phenomena.[87]

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."[88] He also introduced the method of checking tests during experiments.[89]

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."[90]

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.[86] 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.[91]

Classical physics[]

See also: Classical physics and Scientific revolution

Galileo Galilei and the rise of physico-mathematics[]

In the 17th century, natural philosophers began to mount a sustained attack on the Scholastic philosophical program, and supposed that mathematical descriptive schemes adopted from such fields as mechanics and astronomy could actually yield universally valid characterizations of motion. The Tuscan mathematician Galileo Galilei was the central figure in the shift to this perspective. As a mathematician, Galileo’s role in the university culture of his era was subordinated to the three major topics of study: law, medicine, and theology (which was closely allied to philosophy). Galileo, however, felt that the descriptive content of the technical disciplines warranted philosophical interest, particularly because mathematical analysis of astronomical observations—notably the radical analysis offered by astronomer Nicolaus Copernicus concerning the relative motions of the sun, earth, moon, and planets—indicated that philosophers’ statements about the nature of the universe could be shown to be in error. Galileo also performed mechanical experiments, and insisted that motion itself—regardless of whether that motion was natural or artificial—had universally consistent characteristics that could be described mathematically.

Galileo used his 1609 telescopic discovery of the moons of Jupiter, as published in his Sidereus Nuncius in 1610, to procure a position in the Medici court with the dual title of mathematician and philosopher. As a court philosopher, he was expected to engage in debates with philosophers in the Aristotelian tradition, and received a large audience for his own publications, such as The Assayer and Discourses and Mathematical Demonstrations Concerning Two New Sciences, which was published abroad after he was placed under house arrest for his publication of Dialogue Concerning the Two Chief World Systems in 1632.[92][93]

Galileo’s interest in the mechanical experimentation and mathematical description in motion established a new natural philosophical tradition focused on experimentation. This tradition, combining with the non-mathematical emphasis on the collection of "experimental histories" by philosophical reformists such as William Gilbert and Francis Bacon, drew a significant following in the years leading up to and following Galileo’s death, including Evangelista Torricelli and the participants in the Accademia del Cimento in Italy; Marin Mersenne and Blaise Pascal in France; Christiaan Huygens in the Netherlands; and Robert Hooke and Robert Boyle in England.

The Cartesian philosophy of motion[]

The French philosopher René Descartes was well-connected to, and influential within, the experimental philosophy networks. Descartes had a more ambitious agenda, however, which was geared toward replacing the Scholastic philosophical tradition altogether. Questioning the reality interpreted through the senses, Descartes sought to re-establish philosophical explanatory schemes by reducing all perceived phenomena to being attributable to the motion of an invisible sea of “corpuscles”. (Notably, he reserved human thought and God from his scheme, holding these to be separate from the physical universe). In proposing this philosophical framework, Descartes supposed that different kinds of motion, such as that of planets versus that of terrestrial objects, were not fundamentally different, but were merely different manifestations of an endless chain of corpuscular motions obeying universal principles. Particularly influential were his explanation for circular astronomical motions in terms of the vortex motion of corpuscles in space (Descartes argued, in accord with the beliefs, if not the methods, of the Scholastics, that a vacuum could not exist), and his explanation of gravity in terms of corpuscles pushing objects downward.[94][95][96]

Descartes, like Galileo, was convinced of the importance of mathematical explanation, and he and his followers were key figures in the development of mathematics and geometry in the 17th century. Cartesian mathematical descriptions of motion held that all mathematical formulations had to be justifiable in terms of direct physical action, a position held by Huygens and the German philosopher Gottfried Leibniz, who, while following in the Cartesian tradition, developed his own philosophical alternative to Scholasticism, which he outlined in his 1714 work, The Monadology.

Newtonian motion versus Cartesian motion[]

In the late 17th and early 18th centuries, the Cartesian mechanical tradition was challenged by another philosophical tradition established by the Cambridge University mathematician Isaac Newton. Where Descartes held that all motions should be explained with respect to the immediate force exerted by corpuscles, Newton chose to describe universal motion with reference to a set of fundamental mathematical principles: his three laws of motion and the law of gravitation, which he introduced in his 1687 work Mathematical Principles of Natural Philosophy. Using these principles, Newton removed the idea that objects followed paths determined by natural shapes (such as Kepler’s idea that planets moved naturally in ellipses), and instead demonstrated that not only regularly observed paths, but all the future motions of any body could be deduced mathematically based on knowledge of their existing motion, their mass, and the forces acting upon them. However, observed celestial motions did not precisely conform to a Newtonian treatment, and Newton, who was also deeply interested in theology, imagined that God intervened to ensure the continued stability of the solar system.

Newton’s principles (but not his mathematical treatments) proved controversial with Continental philosophers, who found his lack of metaphysical explanation for movement and gravitation philosophically unacceptable. Beginning around 1700, a bitter rift opened between the Continental and British philosophical traditions, which were stoked by heated, ongoing, and viciously personal disputes between the followers of Newton and Leibniz concerning priority over the analytical techniques of calculus, which each had developed independently. Initially, the Cartesian and Leibnizian traditions prevailed on the Continent (leading to the dominance of the Leibnizian calculus notation everywhere except Britain). Newton himself remained privately disturbed at the lack of a philosophical understanding of gravitation, while insisting in his writings that none was necessary to infer its reality. As the 18th century progressed, Continental natural philosophers increasingly accepted the Newtonians’ willingness to forgo ontological metaphysical explanations for mathematically described motions.[97][98][99]

Rational mechanics in the 18th century[]

The mathematical analytical traditions established by Newton and Leibniz flourished during the 18th century as more mathematicians learned calculus and elaborated upon its initial formulation. The application of mathematical analysis to problems of motion was known as rational mechanics, or mixed mathematics (and was later termed classical mechanics). This work primarily revolved around celestial mechanics, although other applications were also developed, such as the Swiss mathematician Daniel Bernoulli’s treatment of fluid dynamics, which he introduced in his 1738 work Hydrodynamica.[100]

Rational mechanics dealt primarily with the development of elaborate mathematical treatments of observed motions, using Newtonian principles as a basis, and emphasized improving the tractability of complex calculations and developing of legitimate means of analytical approximation. A representative contemporary textbook was published by Johann Baptiste Horvath. By the end of the century analytical treatments were rigorous enough to verify the stability of the solar system solely on the basis of Newton’s laws without reference to divine intervention—even as deterministic treatments of systems as simple as the three body problem in gravitation remained intractable.[101]

British work, carried on by mathematicians such as Brook Taylor and Colin Maclaurin, fell behind Continental developments as the century progressed. Meanwhile, work flourished at scientific academies on the Continent, led by such mathematicians as Daniel Bernoulli, Leonhard Euler, Joseph-Louis Lagrange, Pierre-Simon Laplace, and Adrien-Marie Legendre. At the end of the century, the members of the French Academy of Sciences had attained clear dominance in the field.[102][103][104][105]

Physical experimentation in the 18th and early 19th centuries[]

At the same time, the experimental tradition established by Galileo and his followers persisted. The Royal Society and the French Academy of Sciences were major centers for the performance and reporting of experimental work, and Newton was himself an influential experimenter, particularly in the field of optics, where he was recognized for his prism experiments dividing white light into its constituent spectrum of colors, as published in his 1704 book Opticks (which also advocated a particulate interpretation of light). Experiments in mechanics, optics, magnetism, static electricity, chemistry, and physiology were not clearly distinguished from each other during the 18th century, but significant differences in explanatory schemes and, thus, experiment design were emerging. Chemical experimenters, for instance, defied attempts to enforce a scheme of abstract Newtonian forces onto chemical affiliations, and instead focused on the isolation and classification of chemical substances and reactions.[106]

Nevertheless, the separate fields remained tied together, most clearly through the theories of weightless “imponderable fluids", such as heat (“caloric”), electricity, and phlogiston (which was rapidly overthrown as a concept following Lavoisier’s identification of oxygen gas late in the century). Assuming that these concepts were real fluids, their flow could be traced through a mechanical apparatus or chemical reactions. This tradition of experimentation led to the development of new kinds of experimental apparatus, such as the Leyden Jar and the Voltaic Pile; and new kinds of measuring instruments, such as the calorimeter, and improved versions of old ones, such as the thermometer. Experiments also produced new concepts, such as the University of Glasgow experimenter Joseph Black’s notion of latent heat and Philadelphia intellectual Benjamin Franklin’s characterization of electrical fluid as flowing between places of excess and deficit (a concept later reinterpreted in terms of positive and negative charges).

While it was recognized early in the 18th century that finding absolute theories of electrostatic and magnetic force akin to Newton’s principles of motion would be an important achievement, none were forthcoming. This impossibility only slowly disappeared as experimental practice became more widespread and more refined in the early years of the 19th century in places such as the newly established Royal Institution in London, where John Dalton argued for an atomistic interpretation of chemistry, Thomas Young argued for the interpretation of light as a wave, and Michael Faraday established the phenomenon of electromagnetic induction. Meanwhile, the analytical methods of rational mechanics began to be applied to experimental phenomena, most influentially with the French mathematician Joseph Fourier’s analytical treatment of the flow of heat, as published in 1822.[107][108][109]

Thermodynamics, statistical mechanics, and electromagnetic theory[]

The establishment of a mathematical physics of energy between the 1850s and the 1870s expanded substantially on the physics of prior eras and challenged traditional ideas about how the physical world worked. While Pierre-Simon Laplace’s work on celestial mechanics solidified a deterministically mechanistic view of objects obeying fundamental and totally reversible laws, the study of energy and particularly the flow of heat, threw this view of the universe into question. Drawing upon the engineering theory of Lazare and Sadi Carnot, and Émile Clapeyron; the experimentation of James Prescott Joule on the interchangeability of mechanical, chemical, thermal, and electrical forms of work; and his own Cambridge mathematical tripos training in mathematical analysis; the Glasgow physicist William Thomson and his circle of associates established a new mathematical physics relating to the exchange of different forms of energy and energy’s overall conservation (what is still accepted as the “first law of thermodynamics”). Their work was soon allied with the theories of similar but less-known work by the German physician Julius Robert von Mayer and physicist and physiologist Hermann von Helmholtz on the conservation of forces.

Taking his mathematical cues from the heat flow work of Joseph Fourier (and his own religious and geological convictions), Thomson believed that the dissipation of energy with time (what is accepted as the “second law of thermodynamics”) represented a fundamental principle of physics, which was expounded in Thomson and Peter Guthrie Tait’s influential work Treatise on Natural Philosophy. However, other interpretations of what Thomson called thermodynamics were established through the work of the German physicist Rudolf Clausius. His statistical mechanics, which was elaborated upon by Ludwig Boltzmann and the British physicist James Clerk Maxwell, held that energy (including heat) was a measure of the speed of particles. Interrelating the statistical likelihood of certain states of organization of these particles with the energy of those states, Clausius reinterpreted the dissipation of energy to be the statistical tendency of molecular configurations to pass toward increasingly likely, increasingly disorganized states (coining the term “entropy” to describe the disorganization of a state). The statistical versus absolute interpretations of the second law of thermodynamics set up a dispute that would last for several decades (producing arguments such as “Maxwell's demon”), and that would not be held to be definitively resolved until the behavior of atoms was firmly established in the early 20th century.[110][111]

Meanwhile, the new physics of energy transformed the analysis of electromagnetic phenomena, particularly through the introduction of the concept of the field and the publication of Maxwell’s 1873 Treatise on Electricity and Magnetism, which also drew upon theoretical work by German theoreticians such as Carl Friedrich Gauss and Wilhelm Weber. The encapsulation of heat in particulate motion, and the addition of electromagnetic forces to Newtonian dynamics established an enormously robust theoretical underpinning to physical observations. The prediction that light represented a transmission of energy in wave form through a “luminiferous ether”, and the seeming confirmation of that prediction with Helmholtz student Heinrich Hertz’s 1888 detection of electromagnetic radiation, was a major triumph for physical theory and raised the possibility that even more fundamental theories based on the field could soon be developed.[112][113][114][115] Research on the transmission of electromagnetic waves began soon after, with the experiments conducted by physicists such as Nikola Tesla, Jagadish Chandra Bose and Guglielmo Marconi during the 1890s leading to the invention of radio.

Modern physics[]

The emergence of a new physics circa 1900[]

The triumph of Maxwell’s theories was undermined by inadequacies that had already begun to appear. The Michelson-Morley experiment failed to detect a shift in the speed of light, which would have been expected as the earth moved at different angles with respect to the ether. The possibility explored by Hendrik Lorentz, that the ether could compress matter, thereby rendering it undetectable, presented problems of its own as a compressed electron (detected in 1897 by British experimentalist J. J. Thomson) would prove unstable. Meanwhile, other experimenters began to detect unexpected forms of radiation: Wilhelm Röntgen caused a sensation with his discovery of x-rays in 1895; in 1896 Henri Becquerel discovered that certain kinds of matter emit radiation on their own accord. Marie and Pierre Curie coined the term “radioactivity” to describe this property of matter, and isolated the radioactive elements radium and polonium. Ernest Rutherford and Frederick Soddy identified two of Becquerel’s forms of radiation with electrons and the element helium. In 1911 Rutherford established that the bulk of mass in atoms are concentrated in positively-charged nuclei with orbiting electrons, which was a theoretically unstable configuration. Studies of radiation and radioactive decay continued to be a preeminent focus for physical and chemical research through the 1930s, when the discovery of nuclear fission opened the way to the practical exploitation of what came to be called “atomic” energy.

Radical new physical theories also began to emerge in this same period. In 1905 Albert Einstein, then a Bern patent clerk, argued that the speed of light was a constant in all inertial reference frames and that electromagnetic laws should remain valid independent of reference frame—assertions which rendered the ether “superfluous” to physical theory, and that held that observations of time and length varied relative to how the observer was moving with respect to the object being measured (what came to be called the “special theory of relativity”). It also followed that mass and energy were interchangeable quantities according to the equation E=mc2. In another paper published the same year, Einstein asserted that electromagnetic radiation was transmitted in discrete quantities (“quanta”), according to a constant that the theoretical physicist Max Planck had posited in 1900 to arrive at an accurate theory for the distribution of blackbody radiation—an assumption that explained the strange properties of the photoelectric effect. The Danish physicist Niels Bohr used this same constant in 1913 to explain the stability of Rutherford’s atom as well as the frequencies of light emitted by hydrogen gas.

The radical years: general relativity and quantum mechanics[]

The gradual acceptance of Einstein’s theories of relativity and the quantized nature of light transmission, and of Niels Bohr’s model of the atom created as many problems as they solved, leading to a full-scale effort to reestablish physics on new fundamental principles. Expanding relativity to cases of accelerating reference frames (the “general theory of relativity”) in the 1910s, Einstein posited an equivalence between the inertial force of acceleration and the force of gravity, leading to the conclusion that space is curved and finite in size, and the prediction of such phenomena as gravitational lensing and the distortion of time in gravitational fields.

The quantized theory of the atom gave way to a full-scale quantum mechanics in the 1920s. The quantum theory (which previously relied in the “correspondence” at large scales between the quantized world of the atom and the continuities of the “classical” world) was accepted when the Compton Effect established that light carries momentum and can scatter off particles, and when Louis de Broglie asserted that matter can be seen as behaving as a wave in much the same way as electromagnetic waves behave like particles (wave-particle duality). New principles of a “quantum” rather than a “classical” mechanics, formulated in matrix-form by Werner Heisenberg, Max Born, and Pascual Jordan in 1925, were based on the probabilistic relationship between discrete “states” and denied the possibility of causality. Erwin Schrödinger established an equivalent theory based on waves in 1926; but Heisenberg’s 1927 “uncertainty principle” (indicating the impossibility of precisely and simultaneously measuring position and momentum) and the “Copenhagen interpretation” of quantum mechanics (named after Bohr’s home city) continued to deny the possibility of fundamental causality, though opponents such as Einstein would assert that “God does not play dice with the universe”.[116] Also in the 1920s, Satyendra Nath Bose's work on photons and quantum mechanics provided the foundation for Bose-Einstein statistics, the theory of the Bose-Einstein condensate, and the discovery of the boson.

Constructing a new fundamental physics[]


A “Feynman diagram” of a renormalized vertex in quantum electrodynamics.

As the philosophically inclined continued to debate the fundamental nature of the universe, quantum theories continued to be produced, beginning with Paul Dirac’s formulation of a relativistic quantum theory in 1928. However, attempts to quantize electromagnetic theory entirely were stymied throughout the 1930s by theoretical formulations yielding infinite energies. This situation was not considered adequately resolved until after World War II ended, when Julian Schwinger, Richard Feynman, and Sin-Itiro Tomonaga independently posited the technique of “renormalization”, which allowed for an establishment of a robust quantum electrodynamics (Q.E.D.).[117]

Meanwhile, new theories of fundamental particles proliferated with the rise of the idea of the quantization of fields through “exchange forces” regulated by an exchange of short-lived “virtual” particles, which were allowed to exist according to the laws governing the uncertainties inherent in the quantum world. Notably, Hideki Yukawa proposed that the positive charges of the nucleus were kept together courtesy of a powerful but short-range force mediated by a particle intermediate in mass between the size of an electron and a proton. This particle, called the “pion”, was identified in 1947, but it was part of a slew of particle discoveries beginning with the neutron, the “positron” (a positively-charged “antimatter” version of the electron), and the “muon” (a heavier relative to the electron) in the 1930s, and continuing after the war with a wide variety of other particles detected in various kinds of apparatus: cloud chambers, nuclear emulsions, bubble chambers, and coincidence counters. At first these particles were found primarily by the ionized trails left by cosmic rays, but were increasingly produced in newer and more powerful particle accelerators.[118]

File:First Gold Beam-Beam Collision Events at RHIC at 100 100 GeV c per beam recorded by STAR.jpg

Thousands of particles explode from the collision point of two relativistic (100 GeV per ion) gold ions in the STAR detector of the Relativistic Heavy Ion Collider; an experiment done in order to investigate the properties of a quark gluon plasma such as the one thought to exist in the ultrahot first few microseconds after the big bang

The interaction of these particles by “scattering” and “decay” provided a key to new fundamental quantum theories. Murray Gell-Mann and Yuval Ne'eman brought some order to these new particles by classifying them according to certain qualities, beginning with what Gell-Mann referred to as the “Eightfold Way”, but proceeding into several different “octets” and “decuplets” which could predict new particles, most famously the Error no link defined, which was detected at Brookhaven National Laboratory in 1964, and which gave rise to the “quark” model of hadron composition. While the quark model at first seemed inadequate to describe strong nuclear forces, allowing the temporary rise of competing theories such as the S-Matrix, the establishment of quantum chromodynamics in the 1970s finalized a set of fundamental and exchange particles, which allowed for the establishment of a “standard model” based on the mathematics of gauge invariance, which successfully described all forces except for gravity, and which remains generally accepted within the domain to which it is designed to be applied.[116]

The “standard model” groups the electroweak interaction theory and quantum chromodynamics into a structure denoted by the gauge group SU(3)×SU(2)×U(1). The formulation of the unification of the electromagnetic and weak interactions in the standard model is due to Abdus Salam, Steven Weinberg and, subsequently, Sheldon Glashow. After the discovery, made at CERN, of the existence of neutral weak currents,[119][120][121][122] mediated by the Error no symbol defined boson foreseen in the standard model, the physicists Salam, Glashow and Weinberg received the 1979 Nobel Prize in Physics for their electroweak theory.[123]

While accelerators have confirmed most aspects of the standard model by detecting expected particle interactions at various collision energies, no theory reconciling the general theory of relativity with the standard model has yet been found, although “string theory” has provided one promising avenue forward. Since the 1970s, fundamental particle physics has provided insights into early universe cosmology, particularly the “big bang” theory proposed as a consequence of Einstein’s general theory. However, starting from the 1990s, astronomical observations have also provided new challenges, such as the need for new explanations of galactic stability (the problem of dark matter), and accelerating expansion of the universe (the problem of dark energy).

The physical sciences[]

With increased accessibility to and elaboration upon advanced analytical techniques in the 19th century, physics was defined as much, if not more, by those techniques than by the search for universal principles of motion and energy, and the fundamental nature of matter. Fields such as acoustics, geophysics, astrophysics, aerodynamics, plasma physics, low-temperature physics, and solid-state physics joined optics, fluid dynamics, electromagnetism, and mechanics as areas of physical research. In the 20th century, physics also became closely allied with such fields as electrical, aerospace, and materials engineering, and physicists began to work in government and industrial laboratories as much as in academic settings. Following World War II, the population of physicists increased dramatically, and came to be centered on the United States, while, in more recent decades, physics has become a more international pursuit than at any time in its previous history.


Name Living time Contribution(s) Location
Babylonian astronomers BC 800-600 Babylonian astronomy Iraq
Kanada BC 600-500 Vaiśeṣika Sūtra India
Aristotle BC 384-322 Physicae Auscultationes Greece
Archimedes BC 287-212 BC 250, On Floating Bodies Sicily
Ptolemaeus (Ptolemy) AD 90-168 AD 150, Almagest, Geography, Apotelesmatika Alexandria, Egypt
Aryabhata 476-550 499, Aryabhatiya India
Ibn al-Haytham (Alhazen) 965-1040 1020, 1021, 1025, 1038, On the Light of the Moon, Book of Optics, Doubts Concerning Ptolemy, The Model of the Motions Iraq & Egypt
Ibn Sina (Avicenna) 980-1037 1025, 1027, The Canon of Medicine, The Book of Healing Persia
Abū Rayhān al-Bīrūnī 973-1048 1031, Masudic Canon, Book of Coordinates, Indica Persia
Shen Kuo 1031–1095 1088, Dream Pool Essays China
Copernicus 1473–1543 1543, On the Revolutions of the Celestial Spheres Poland
Galileo 1564–1642 1632, Dialogue Concerning the Two Chief World Systems Italy
Descartes 1596-1650 1641, Meditations on First Philosophy France
Isaac Newton 1643-1727 1687, Mathematical Principles of Natural Philosophy England
Michael Faraday 1791-1867 1839, 1844, Experimental Researches in Electricity, vols. i. and ii. England
Maxwell 1831–1879 1873, Treatise on Electricity and Magnetism United Kingdom
Einstein 1879-1955 1905, On the Electrodynamics of Moving Bodies Germany

See also[]


  1. "physics". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=physics&allowed_in_frame=0. 
  2. "physic". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=physic&allowed_in_frame=0. 
  3. φύσις. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  4. φυσική. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  5. ἐπιστήμη. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  6. Richard Feynman begins his Lectures with the atomic hypothesis, as his most compact statement of all scientific knowledge: "If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations ..., what statement would contain the most information in the fewest words? I believe it is ... that all things are made up of atoms – little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. ..." R.P. Feynman, R.B. Leighton, M. Sands (1963). The Feynman Lectures on Physics. 1. p. I-2. ISBN 0-201-02116-1. 
  7. J.C. Maxwell (1878). Matter and Motion. D. Van Nostrand. p. 9. ISBN 0-486-66895-9. http://books.google.com/?id=noRgWP0_UZ8C&printsec=titlepage&dq=matter+and+motion. "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events." 
  8. H.D. Young, R.A. Freedman (2004). University Physics with Modern Physics (11th ed.). Addison Wesley. p. 2. "Physics is an experimental science. Physicists observe the phenomena of nature and try to find patterns and principles that relate these phenomena. These patterns are called physical theories or, when they are very well established and of broad use, physical laws or principles." 
  9. S. Holzner (2006). Physics for Dummies. Wiley. p. 7. ISBN 0-470-61841-8. http://www.amazon.com/gp/reader/0764554336. "Physics is the study of your world and the world and universe around you." 
  10. Note: The term 'universe' is defined as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the term 'universe' may also be used in slightly different contextual senses, denoting concepts such as the cosmos or the philosophical world.
  11. 11.0 11.1 Aaboe, Asger. "The culture of Babylonia: Babylonian mathematics, astrology, and astronomy." The Assyrian and Babylonian Empires and other States of the Near East, from the Eighth to the Sixth Centuries B.C.E Eds. John Boardman, I. E. S. Edwards, N. G. L. Hammond, E. Sollberger and C. B. F. Walker. Cambridge University Press, (1991)
  12. D. Brown (2000), Mesopotamian Planetary Astronomy-Astrology , Styx Publications, ISBN 9056930362.
  13. Singer, C. A Short History of Science to the 19th Century. Streeter Press, 2008. p. 35.
  14. 14.0 14.1 "Top 10 ancient Arabic scientists". COSMOS magazine. 2011-01-06. http://www.cosmosmagazine.com/news/3924/ancient-arabic-scientists?page=0%2C1. Retrieved on 2013-04-20. 
  15. 15.0 15.1 Glick, Livesey & Wallis (2005, pp. 89–90)
  16. 16.0 16.1 16.2 16.3 Mariam Rozhanskaya and I. S. Levinova (1996), "Statics", p. 642, in Rashed & Morelon (1996, pp. 614–642):
    "Using a whole body of mathematical methods (not only those inherited from the antique theory of ratios and infinitesimal techniques, but also the methods of the contemporary algebra and fine calculation techniques), Arabic scientists raised statics to a new, higher level. The classical results of Archimedes in the theory of the centre of gravity were generalized and applied to three-dimensional bodies, the theory of ponderable lever was founded and the 'science of gravity' was created and later further developed in medieval Europe. The phenomena of statics were studied by using the dynamic approach so that two trends - statics and dynamics - turned out to be inter-related within a single science, mechanics."
    "The combination of the dynamic approach with Archimedean hydrostatics gave birth to a direction in science which may be called medieval hydrodynamics."
    "Archimedean statics formed the basis for creating the fundamentals of the science on specific weight. Numerous fine experimental methods were developed for determining the specific weight, which were based, in particular, on the theory of balances and weighing. The classical works of al-Biruni and al-Khazini can by right be considered as the beginning of the application of experimental methods in medieval science."
    "Arabic statics was an essential link in the progress of world science. It played an important part in the prehistory of classical mechanics in medieval Europe. Without it classical mechanics proper could probably not have been created."
    Cite error: Invalid <ref> tag; name "Rozhanskaya-642" defined multiple times with different content
  17. Farid Alakbarov (Summer 2001). A 13th-Century Darwin? Tusi's Views on Evolution, Azerbaijan International 9 (2).
  18. Shlomo Pines (1964), "La dynamique d’Ibn Bajja", in Mélanges Alexandre Koyré, I, 442-468 [462, 468], Paris
    (cf. Abel B. Franco (October 2003), "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4): 521-546 [543])
  19. Abel B. Franco (October 2003), "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4):521-546 [543])
  20. Ernest A. Moody (1951), "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", Journal of the History of Ideas 12 (2): 163-193
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  23. Langermann, Y. Tzvi (1998), "al-Baghdadi, Abu 'l-Barakat (fl. c.1200-50)", Islamic Philosophy, Routledge Encyclopedia of Philosophy, http://www.muslimphilosophy.com/ip/rep/J008.htm, retrieved on 3 February 2008 
  24. 24.0 24.1 Fernando Espinoza (2005). "An analysis of the historical development of ideas about motion and its implications for teaching", Physics Education 40 (2), p. 141.
  25. Aydin Sayili (1987), "Ibn Sīnā and Buridan on the Motion of the Projectile", Annals of the New York Academy of Sciences 500 (1), p. 477–482 [477]:
    "It was a permanent force whose effect got dissipated only as a result of external agents such as air resistance. He is apparently the first to conceive such a permanent type of impressed virtue for non-natural motion."
  26. Aydin Sayili (1987), "Ibn Sīnā and Buridan on the Motion of the Projectile", Annals of the New York Academy of Sciences 500 (1), p. 477–482 [477]
  27. Aydin Sayili (1987), "Ibn Sīnā and Buridan on the Motion of the Projectile", Annals of the New York Academy of Sciences 500 (1): 477–482 [477]:
    "Indeed, self-motion of the type conceived by Ibn Sina is almost the opposite of the Aristotelian conception of violent motion of the projectile type, and it is rather reminiscent of the principle of inertia, i.e., Newton's first law of motion."
  28. Seyyed Hossein Nasr & Mehdi Amin Razavi (1996), The Islamic intellectual tradition in Persia, Routledge, p. 72, ISBN 0700703144 
  29. Classical Arabic philosophy: an anthology of sources Jon McGinnis, David C. Reisman Hackett Publishing, 2007 ISBN 0872208710, 9780872208711
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  31. Shlomo Pines (1970). "Abu'l-Barakāt al-Baghdādī , Hibat Allah". Dictionary of Scientific Biography. 1. New York: Charles Scribner's Sons. pp. 26–28. ISBN 0684101149. 
    (cf. Abel B. Franco (October 2003), "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4): 521-546 [528])
  32. A. C. Crombie, Augustine to Galileo 2, p. 67.
  33. Chattopadhyaya 1986, pp. 169–70
  34. Radhakrishnan 2006, p. 202
  35. (Stcherbatsky 1962 (1930). Vol. 1. P. 19)
  36. Li Shu-hua, "Origine de la Boussole 11. Aimant et Boussole," Isis, Vol. 45, No. 2. (Jul., 1954), p.175
  37. Joseph Needham, Volume 4, Part 1, 98.
  38. Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” Isis, Vol. 45, No. 2. (Jul., 1954), p.175
  39. Smith (1996, p. x)
  40. Smith (1996, p. 18)
  41. Smith (1996, p. 19)
  42. Tybjerg (2002, p. 350)
  43. 43.0 43.1 Thiele (2005a):
    “Through a closer examination of Ibn al-Haytham's conceptions of mathematical models and of the role they play in his theory of sense perception, it becomes evident that he was the true founder of physics in the modern sense of the word; in fact he anticipated by six centuries the fertile ideas that were to mark the beginning of this new branch of science.”
  44. 44.0 44.1 Thiele (2005b):
    "Schramm showed that already some centuries before Galileo, experimental physics had its roots in Ibn al-Haytham."
  45. 45.0 45.1 45.2 45.3 Toomer (1964)
  46. 46.0 46.1 46.2 46.3 Sabra (2003, pp. 91–2) Cite error: Invalid <ref> tag; name "Sabra" defined multiple times with different content
  47. Rashed & Armstrong (1994, pp. 345–6)
  48. 48.0 48.1 Smith (1996, p. 57)
  49. 49.0 49.1 Rashed (2007, p. 19):
    "In reforming optics he as it were adopted ‘‘positivism’’ (before the term was invented): we do not go beyond experience, and we cannot be content to use pure concepts in investigating natural phenomena. Understanding of these cannot be acquired without mathematics. Thus, once he has assumed light is a material substance, Ibn al-Haytham does not discuss its nature further, but confines himself to considering its propagation and diffusion. In his optics ‘‘the smallest parts of light’’, as he calls them, retain only properties that can be treated by geometry and verified by experiment; they lack all sensible qualities except energy."
    Cite error: Invalid <ref> tag; name "Rashed" defined multiple times with different content
  50. Sabra (1998, p. 300)
  51. 51.0 51.1 51.2 51.3 Gorini (2003):
    "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."
  52. G. A. Russell, "Emergence of Physiological Optics", pp. 686-7, in Rashed & Morelon (1996)
  53. Sabra (1989)
  54. (Dijksterhuis 2004, pp. 113–5):
    "Through the influential work of Alhacen the onset of a physico-mathematical conception of optics was established at a much earlier time than would be the case in the other mathematical sciences."
  55. http://news.bbc.co.uk/2/hi/science/nature/7810846.stm
  56. 56.0 56.1 56.2 Robert Briffault (1928). The Making of Humanity, p. 191. G. Allen & Unwin Ltd.
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  59. Observe nature and reflect over it.
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  60. “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.”[Quran 17:36]
  61. “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.”[Quran 2:164]
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    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.
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  67. Robert Briffault wrote in The Making of Humanity:
    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 the Greeks were a foreign importation never thoroughly acclimatized in Greek culture. The Greeks systematized, generalized and theorized, but the patient ways of investigation, the accumulation of positive knowledge, the minute methods of science, detailed and prolonged observation, experimental inquiry, were altogether alien to the Greek temperament. [...] What we call science arose in Europe as a result of a new spirit of inquiry, of new methods of investigation, of the method 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.
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    Science is the most momentous contribution of Arab civilization to the modern world, but its fruits were slow in ripening. Not until long after 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.
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    The main, as well as the least obvious, achievement of the Middle Ages was the creation of the experimental spirit and this was primarily due to the Muslims down to the 12th century.
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    The only effective link between the old and the new science is afforded by the Arabs. The dark ages come as an utter gap in the scientific history of Europe, and for more than a thousand years there was not a scientific man of note except in Arabia.
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Further reading[]