HISTORY OF PHYSICS

Since antiquity, human beings have sought to understand the workings of nature: why unsupported objects drop to the ground, why different materials have different properties, the character of the universe such as the form of the Earth and the behavior of celestial objects such as the Sun and the Moon, and so forth. Typically the behavior and nature of the world was explained by invoking the actions of gods. Eventually explanations were proposed based on philosophical speculation. Rarely verified by systematic experimental testing, many of them were wrong, but this is part of the dialectical nature of scientific enquiry, and even modern theories of quantum mechanics and relativity are merely considered "theories that have not been broken yet".
The growth of 'physics' has brought not only fundamental changes in ideas about the material world, mathematics and philosophy, but also, through technology, a transformation of society. Physics is considered both a body of knowledge and the practice that makes and transmits it. The Scientific Revolution, beginning about year 1543, is a convenient boundary between ancient thought and classical physics. The emergence of physics as a science distinct from natural philosophy began with the scientific revolution of the 16th and 17th centuries, and continued through the dawn of modern physics in the early 20th century. The year 1900 marks the beginnings of a more modern physics. Today, the science shows no sign of completion, as more issues are raised, with questions rising from the age of the universe, to the nature of the vacuum, to the ultimate nature of the properties of subatomic particles. Partial theories are currently the best that physics has to offer, at the present time. The list of unsolved problems in physics is large.

Early cultures

Aristotle

Babylonian contributions

Babylonian astronomy was the basis for much of what was done in Greece, in India, in Sassanian Iran, in Byzantium, in Syria, in Islam, in Central Asia, and in Western Europe.
The first evidence of recognition that astronomical phenomena are periodic and of the application of mathematics to their prediction is Babylonian. Tablets dating back to the Old Babylonian period document the application of mathematics to the variation in the length of daylight over a solar year. Centuries of Babylonian observations of celestial phenomena are recorded in the series of cuneiform tablets known as the ''Enūma Anu Enlil''. The oldest significant astronomical text that we possess is Tablet 63 of the ''Enūma Anu Enlil'', the Venus tablet of Ammi-saduqa, which lists the first and last visible risings of Venus over a period of about 21 years and is the earliest evidence that the phenomena of a planet were recognized as periodic. The MUL.APIN, contains catalogues of stars and constellations as well as schemes for predicting heliacal risings and the settings of the planets, lengths of daylight measured by a water-clock, gnomon, shadows, and intercalations. The Babylonian GU text arranges stars in 'strings' that lie along declination circles and thus measure right-ascensions or time-intervals, and also employs the stars of the zenith, which are also separated by given right-ascensional differences.^[1]

Egyptian contributions

An early Egyptian interest in astronomy is demonstrated by the development of a stellar-based calendar than can be traced back as far as 4236 BCE.^[2]

Greek and Hellenistic contributions

Main articles: History of science in Classical Antiquity

Western physics began with eminent Greek pre-Socratic philosophers such as Thales, Anaximander, possibly Pythagoras, Heraclitus, Anaxagoras, Empedocles and Philolaus, many of whom were involved in various schools. For example, Anaximander and Thales belonged to the Milesian school.
Plato, briefly and Aristotle at length, continued these studies of nature in their works, the earliest surviving complete treatises dealing with natural philosophy. Democritus, a contemporary, was of the school of Atomists who attempted to characterize the nature of matter.
Due to the absence of advanced experimental equipment such as telescopes and accurate time-keeping devices, experimental testing of physical hypotheses was impossible or impractical. There were exceptions and there are anachronisms. Greek thinkers like Archimedes proposed calculating the volume of objects like spheres and cones by dividing them into very thin disks and adding up the volume of each disk, using methods resembling integral calculus. It was also Archimedes who derived many correct quantitative descriptions of mechanics and also hydrostatics when, so the story goes, he noticed that his own body displaced a volume of water while he was getting into a bath one day. Another remarkable example was that of Eratosthenes, who deduced that the Earth was a sphere, and accurately calculated its circumference using the shadows of vertical sticks to measure the angle between two widely separated points on the Earth's surface.
Modern knowledge of many early ideas in physics, and the extent to which they were experimentally tested, is sketchy. Almost all direct record of these ideas was lost when the Library of Alexandria was destroyed, around 400 AD. Perhaps the most remarkable idea we know of from this era was the deduction by Aristarchus of Samos that the Earth was a planet that traveled around the Sun once a year, and rotated on its axis once a day (accounting for the seasons and the cycle of day and night), and that the stars were other, very distant suns which also had their own accompanying planets (and possibly, lifeforms upon those planets).
The discovery of the Antikythera mechanism points to a detailed understanding of movements of these astronomical objects, as well as a use of gear-trains that pre-dates any other known civilization's use of gears, except that of ancient China.
An early version of the steam engine, Hero's aeolipile was only a curiosity which did not solve the problem of transforming its rotational energy into a more usable form, not even by gears. The Archimedes screw is still in use today, to lift water from rivers onto irrigated farmland. The simple machines were unremarked, with the exception (at least) of Archimedes' elegant proof of the law of the lever. Ramps were in use several millennia before Archimedes, to build the Pyramids.
This period of inquiry into the nature of the world was eventually stifled by a tendency to accept the ideas of eminent philosophers, rather than to question and test those ideas. Pythagoras himself is said to have tried to suppress knowledge of the existence of irrational numbers, discovered by his own school, because they did not fit his number mysticism. For one thousand years following the destruction of the Library of Alexandria, Ptolemy's (not to be confused with the Egyptian Ptolemies) model of an Earth-centred universe in which the planets are assumed to each move in a small circle, called an epicycle, which in turn moves along a larger circle called a deferent, was accepted as absolute truth.

Indian contributions

Main articles: Science and technology in ancient India

In Lothal (c. 2400 BC), the ancient port city of the Harappan civilization, shell objects served as compasses to measure the angles of the 8–12 fold divisions of the horizon and sky in multiples of 40–360 degrees, and the positions of stars. ^[3] In the late Vedic era (c. 9th–6th century BC), the astronomer Yajnavalkya, in his ''Shatapatha Brahmana'', referred to an early concept of heliocentrism with the Earth being round and the Sun being the "centre of spheres". He measured the distances of the Moon and the Sun from the Earth as 108 times the diameters of these heavenly bodies, which were close to the modern values of 110.6 for the Moon and 107.6 for the Sun. Indic Studies Foundation
Indians in the Vedic era classified the material world into five basic elements: earth, fire, air, water and ether/space. Appendix A. Ayurveda's History, Beliefs and Practices From the 6th century BC, they formulated systematic atomic theories, beginning with Kanada and Pakudha Katyayana. Indian atomists believed that an atom could be one of up to 9 elements, with each element having up to 24 properties. They developed detailed theories of how atoms could combine, react, vibrate, move and perform other actions, as well as elaborate theories of how atoms can form binary molecules that combine further to form larger molecules, and how particles first combine in pairs, and then group into trios of pairs, which are the smallest visible units of matter. This parallels with the structure of modern atomic theory, in which pairs or triplets of supposedly fundamental quarks combine to create most typical forms of matter. They had also suggested the possibility of splitting an atom, which as we know today, is the source of atomic energy.
The principle of relativity (not to be confused with Einstein's theory of relativity) was available in an embryonic form since the 6th century BC in the ancient Indian philosophical concept of "''sapekshavad''", literally "''theory of relativity''" in Sanskrit.
The Samkhya and Vaisheshika schools developed theories on light from the 6th–5th century BC. According to the Samkhya school, light is one of the five fundamental "subtle" elements out of which emerge the gross elements, which were taken to be continuous. The Vaisheshika school defined motion in terms of the non-instantaneous movement of the physical atoms. Light rays were taken to be a stream of high velocity ''fire'' atoms, which can exhibit different characteristics depending on the speed and the arrangements of these particles. The Buddhists Dignāga (5th century) and Dharmakirti (7th century) developed a theory of light being composed of energy particles, similar to the modern concept of photons.
Veteran Australian indologist A. L. Basham concluded that "they were brilliant imaginative explanations of the physical structure of the world, and in a large measure, agreed with the discoveries of modern physics."
In 499, the mathematician- Aryabhata propounded a detailed model of the heliocentric solar system of gravitation, where the planets rotate on their axes causing day & night and follow elliptical orbits around the Sun causing year, and where the planets and the Moon do not have their own light but reflect the light of the Sun. Aryabhata also correctly explained the causes of the solar and lunar eclipses and predicted their times, gave the radii of planetary orbits around the Sun, and accurately measured the lengths of the day, sidereal year, and the Earth's diameter and circumference. Brahmagupta, in his ''Brahma Sputa Siddhanta'' in 628, recognized gravity as a force of attraction and understood the law of gravitation.
A particularly important Indian contribution was the Hindu-Arabic numerals. Modern physics can hardly be imagined without a system of arithmetic in which simple calculation is easy enough to make large calculations even possible. The modern positional numeral system (the Hindu-Arabic numeral system) and the number zero were first developed in India, along with the trigonometric functions of sine and cosine. These mathematical developments, along with the Indian developments in physics, were adopted by the Islamic Caliphate, from where they spread to Europe and other parts of the world.
In most of the Indian languages, Physics is known as Bhoutikasastra.

Chinese contributions

Main articles: Science and technology in China

A theory very similar to Newton's first law of motion is found in the ''Mo Ching'' of the 3rd or 4th century BC:^[2]

The cessation of motion is due to the opposing force....If there is no opposing force...the motion will never stop. This is as true as that an ox is not a horse.

Contemporary documentation of the 3rd century AD makes reference to the South Pointing Chariot, a mechanical compass which made early use of the differential gear.^[2]

Physics in the Middle Ages

Islamic world

Main articles: Islamic science

Like the later Scientific revolution in the West, Islamic science was built on a foundation laid in antiquity, in this case, the intellectual patrimony of the Greeks, Byzantines, Persians and Indians they conquered. The Arab and Persian scholars of the Islamic Golden Age made advances by building on previous work in astronomy, mathematics, and physics while developing new fields like alchemy.

Ibn al-Haytham (Alhazen)

The most important scientific development during the Middle Ages was the pioneering development of the experimental scientific method by Ibn al-Haytham (commonly Latinized ''Alhazen'', ''ca.'' 965–1040), as recorded in his ''Book of Optics''.^[6]
Alhazen, who is regarded as the father of optics and the pioneer of the scientific method, developed a broad theory that explained vision, using geometry and anatomy, which 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 built a camera obscura and used the example of the pinhole camera, which produces an inverted image, to support his argument. This contradicted Ptolemy's emission theory of vision that objects are seen by rays of light emanating from the eyes. Alhazen held light rays to be streams of minute particles that travelled at a finite speed. He improved Ptolemy's theory of the refraction of light, and went on to discover the laws of refraction.
He also carried out the first experiments on the dispersion of light into its constituent colors. His major work ''Book of Optics'' 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 father of modern optics.
Alhazen 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.
In the mechanics field of physics, the eldest Banū Mūsā brother, Muhammad ibn Musa, in his ''Astral Motion'' and ''The Force of Attraction'', discovered that there was a force of attraction between heavenly bodies in the 9th century,^[7] foreshadowing Newton's law of universal gravitation.^[8]
In the early 11th century, Ibn al-Haytham discussed the theory of attraction between masses, and it seems that he was aware of the magnitude of acceleration due to gravity. Ibn al-Haytham also discovered Galileo Galilei's law of inertia, 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.Dr. Nader El-Bizri, "Ibn al-Haytham or Alhazen", in Josef W. Meri (2006), ''Medieval Islamic Civilization: An Encyclopaedia'', Vol. II, p. 343-345, Routledge, New York, London. Ibn al-Haytham's contemporary, Avicenna, discovered the concept of momentum, when he referred to impetus as being proportional to weight times velocity, a precursor to the concept of momentum in Newton's second law of motion.A. 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:
He is thus considered the father of the fundamental concept of momentum in physics.^[9] His theory of motion was also consistent with the concept of inertia in Newton's first law of motion.
In the early 12th century, Ibn Bajjah (Avempace) was the first to state that there is always a reaction force for every force exerted, a precursor to Gottfried Leibniz's idea of force which underlies Newton's third law of motion.^[10] His theory of motion had an important influence on later physicists like Galileo Galilei.^[11] Avempace's contemporary, Hibat Allah Abu'l-Barakat al-Baghdaadi, was the first to negate Aristotle's idea that a constant force produces uniform motion, and he instead argued that a force applied continuously produces acceleration, a fundamental law of classical mechanics.^[12] He described acceleration as the rate of change of velocity, an early yet incomplete concept of acceleration in Newton's second law of motion.^[13] 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 vary depending on their distances from the centre of the Earth. This phenomenon was not proven until Newton's law of universal gravitation in the 18th century. Al-Khazini was also one of the first to clearly differentiate between force, mass, and weight.^[14]
gave his name to what we now call an algorithm, and developed modern algebra, which was derived from the Arabic word ''al-jabr'' from the title of his treatise ''Hisab al-jabr w’al-muqabala''.
Significant progress in methodology was made, in particular using experiments to distinguish between competing scientific theories set within a generally empirical orientation.

Medieval Europe

Main articles: History of science in the Middle Ages

Following the collapse of the Western Roman Empire, the knowledge of classical antiquity was preserved in its monasteries, in the Byzantine Empire, and in the Islamic world.^[2] Works lost in Western Christendom but preserved in the Islamic world led clerical scholars such as Michael the Scot to learn Arabic in order to study them. Their translations made available to medieval Europe not only the works of the ancient philosophers, but the advances of Arab, Persian, and Indian ones as well. Works both ancient and contemporary also became known in medieval Europe through such points of contact as the Republic of Venice, al-Andalus, and returning Crusaders. By providing a locus for the exchange of ideas and scholarly collaboration, the birth of the medieval university was key to the intellectual revitalization of Europe.
By the 13th century, precursors of the modern scientific method can be seen on Robert Grosseteste's emphasis on mathematics as a way to understand nature and on the empirical approach admired by Roger Bacon.
Bacon conducted experiments into optics, although much of it was similar to what had been done and was being done at the time by Arab scholars. He did make a major contribution to the development of science in medieval Europe by writing to the Pope to encourage the study of natural science in university courses and compiling several volumes recording the state of scientific knowledge in many fields at the time. He described the possible construction of a telescope, but there is no strong evidence of his having made one. He recorded the manner in which he conducted his experiments in precise detail so that others could reproduce and independently test his results - a cornerstone of the scientific method, and a continuation of the work of researchers like Al Battani.
In the 14th century, some scholars, such as Jean Buridan and Nicole Oresme, started to question the received wisdom of Aristotle's mechanics. In particular, Buridan developed the theory of impetus which was the first step towards the modern concept of inertia.
In his turn, Oresme showed that the reasons proposed by the physics of Aristotle against the movement of the earth were not valid and adduced the argument of simplicity for the theory that the earth moves, and ''not'' the heavens. In the whole of his argument in favor of the earth's motion Oresme is both more explicit and much clearer than that given two centuries later by Copernicus. He was also the first to assume that color and light are of the same nature and the discoverer of the curvature of light through atmospheric refraction; even though, up to now, the credit for this latter achievement has been given to Hooke.
In the 14th century Europe was rocked by the Black Death which led to much social upheaval. In spite of this pause, the 15th century saw the artistic flourishing of the Renaissance. The rediscovery of ancient texts was improved when many Byzantine scholars had to seek refuge in the West after the fall of Constantinople in 1453. Meanwhile, the invention of printing was to make learning more accessible and allow a faster propagation of new ideas. All that paved the way to the Scientific Revolution, which may also be understood as a resumption of the process of scientific change halted around the middle of the 14th century.

Early modern physics

Nicolaus Copernicus 1473-1543, considered the "Father of Modern Astronomy"

Main articles: Scientific Revolution

The early modern period is seen as a flowering of the Renaissance, in what is often known as the "Scientific Revolution", viewed as a foundation of modern science. Historians like Howard Margolis hold that the Scientific Revolution began in 1543, when Nicolaus Copernicus received the first copy of his ''De Revolutionibus'', printed in Nuremberg (Nürnberg) by Johannes Petreius. Most of its contents had been written years prior, but the publication had been delayed. Copernicus died soon after receiving the copy.

Galileo Galilei considered the "Father of Modern Physics"

Further significant advances were made over the following century by Galileo Galilei, Christiaan Huygens, Johannes Kepler, and Blaise Pascal. During the early seventeenth century, Galileo made extensive use of experimentation to validate physical theories, which is the key idea in the modern scientific method. Galileo formulated and successfully tested several results in dynamics, in particular the Law of Inertia. In Galileo's ''Two New Sciences'', a dialogue between the characters Simplicio and Salviati discuss the motion of a ship (as a moving frame) and how that ship's cargo is indifferent to its motion. Huygens used the motion of a boat along a Dutch canal to illustrate an early form of the conservation of momentum.

Sir Isaac Newton

The scientific revolution is considered to have culminated with the publication of the ''Philosophiae Naturalis Principia Mathematica'' in 1687 by the mathematician, physicist, alchemist and inventor Sir Isaac Newton (1643-1727).In 1687, Newton published the ''Principia'', detailing two comprehensive and successful physical theories: Newton's laws of motion, from which arise classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity. Both theories agreed well with experiment. The Principia also included several theories in fluid dynamics.
From the late seventeenth century onward, thermodynamics was developed by physicist and chemist Boyle, Young, and many others. In 1733, Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of statistical mechanics. In 1798, Thompson demonstrated the conversion of mechanical work into heat, and in 1847 Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy. Ludwig Boltzmann, in the nineteenth century, is responsible for the modern form of statistical mechanics.
Classical mechanics was re-formulated and extended by Leonhard Euler, French mathematician Joseph-Louis Comte de Lagrange, Irish mathematical physicist William Rowan Hamilton, and others, who produced new results in mathematical physics. The law of universal gravitation initiated the field of astrophysics, which describes astronomical phenomena using physical theories.
After Newton defined classical mechanics, the next great field of inquiry within physics was the nature of electricity. Observations in the seventeenth and eighteenth century by scientists such as Robert Boyle, Stephen Gray, and Benjamin Franklin created a foundation for later work. These observations also established our basic understanding of electrical charge and current.
By 1808 John Dalton had discovered that atoms of different elements have different weights and proposed the modern theory of the atom.
It was Hans Christian Ørsted who first proposed the connection between electricity and magnetism after observing the deflection of a compass needle by a nearby electric current. By the early 1830s Michael Faraday had demonstrated that magnetic fields and electricity could generate each other. In 1864 James Clerk Maxwell presented to the Royal Society a set of equations that described this relationship between electricity and magnetism. Maxwell's equations also predicted correctly that light is an electromagnetic wave.
The Scientific Revolution began in the late 16th century with only a few researchers, and evolved into an enterprise which continues to the present day. Starting with astronomy, the principles of natural philosophy crystallized into fundamental laws of physics which were enunciated and improved in the succeeding centuries. By the 19th century, the sciences had segmented into multiple fields with specialized researchers and the field of physics, although logically pre-eminent, no longer could claim sole ownership of the entire field of scientific research.

16th century

In the 16th century Nicolaus Copernicus revived Aristarchus' heliocentric model of the solar system in Europe (which survived primarily in a passing mention in ''The Sand Reckoner'' of Archimedes). When this model was published at the end of his life, it was with a preface by Andreas Osiander that piously represented it as only a mathematical convenience for calculating the positions of planets, and not an account of the true nature of the planetary orbits.
In England William Gilbert (1544-1603) studied magnetism and published a seminal work, ''De Magnete'' (1600), in which he thoroughly presented his numerous experimental results.

17th century

In the early 17th century Johannes Kepler formulated a model of the solar system based upon the five Platonic solids, in an attempt to explain why the orbits of the planets had the relative sizes they did. His access to extremely accurate astronomical observations by Tycho Brahe enabled him to determine that his model was inconsistent with the observed orbits. After a heroic seven-year effort to more accurately model the motion
of the planet Mars (during which he laid the foundations of modern integral calculus) he concluded that the planets follow not circular orbits, but elliptical orbits with the Sun at one focus of the ellipse. This breakthrough overturned a millennium of dogma based on Ptolemy's idea of "perfect" circular orbits for the "perfect" heavenly bodies. Kepler then went on to formulate his three laws of planetary motion. He also proposed the first known model of planetary motion in which a force emanating from the Sun deflects the planets from their "natural" motion, causing them to follow curved orbits.
An important device, the vernier, which allows the accurate mechanical measurement of angles and distances was invented by a Frenchman, Pierre Vernier in 1631. It is in widespread use in scientific laboratories and machine shops to this day.
Otto von Guericke constructed the first air pump in 1650 and demonstrated the physics of the vacuum and atmospheric pressure using the Magdeburg hemispheres. Later, he turned his interests to static electricity, and he invented a mechanical device consisting of a sphere of sulfur that could be turned on a crank and repeatedly charged and discharged to produce electric sparks.
In 1656 the Dutch physicist and astronomer, Christian Huygens invented a mechanical clock using a pendulum that swung through an elliptical arc, powered by a falling counterweight, to usher in the era of accurate timekeeping.
The first quantitative estimate of the speed of light was made in 1676 by Ole Rømer, by timing the motions of Jupiter's satellite Io with a telescope.
During the early 17th century, Galileo Galilei made extensive use of experimentation to validate physical theories, which is the key idea in the scientific method. Galileo's use of experiment, and the insistence of Galileo and Kepler that observational results must always take precedence over theoretical results (in which they followed the precepts of Aristotle if not his practice), brushed away the acceptance of dogma, and gave birth to an era where scientific ideas were openly discussed and rigorously tested. Galileo formulated and successfully tested several results in dynamics, including the correct law of accelerated motion, the parabolic trajectory, the relativity of unaccelerated motion, and an early form of the Law of Inertia.
René Descartes, French mathematician, philosopher, and natural scientist, invented analytic geometry, and discovered the law of conservation of momentum. He outlined his views on the universe in his Principles of Philosophy.
In 1687, Isaac Newton published the ''Philosophiae Naturalis Principia Mathematica,'' detailing two comprehensive and successful physical theories: Newton's laws of motion, from which arise classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity. Both theories agreed well with experiment. The Law of Gravitation initiated the field of astrophysics, which describes astronomical phenomena using physical theories.

18th century

''Table of Mechanicks'', 1728 ''Cyclopaedia''.

From the 18th century onwards, thermodynamic concepts were developed by Robert Boyle, Thomas Young, and many others, concurrently with the development of the steam engine, onward into the next century. In 1733, Daniel Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of statistical mechanics. Benjamin Thompson demonstrated the conversion of unlimited mechanical work into heat.Asimov, p. 243
In 1746 an important step in the development of electricity was taken in the invention of the Leyden jar, a capacitor, that could store and discharge electrical charge in a controlled way. Benjamin Franklin effectively used them (together with von Guericke's generator) in his researches into the nature of electricity in 1752Asimov, p. 178
In about 1788, Joseph Louis Lagrange elaborated an important new formulation of mechanics using the calculus of variations, the principle of least action and the Euler-Lagrange equations^[16]

Modern physics

19th century

In a letter to the Royal Society in 1800, Alessandro Volta described his invention of the electric battery, thus providing for the first time the means to generate a constant electric current, and opening up a new field of physics for investigation.
By 1808 John Dalton's earlier ideas about the existence of atoms of different weights and the law of multiple proportions had led him to the modern theory of the atom. The convergence of various estimates of Avogadro's number lent decisive evidence for atomic theory.
The behavior of electricity and magnetism was studied by Michael Faraday, Georg Ohm, Hans Christian Ørsted, and others. Faraday, who began his career in chemistry working under Humphry Davy at the Royal Institution, demonstrated that electrostatic phenomena, the action of the newly discovered electric pile or battery, electrochemical phenomena, and lightning were all different manifestations of electrical phenomena.Asimov, p. 315 ff. Faraday further discovered in 1821 that electricity can cause rotational mechanical motion, and in 1831 discovered the principle of electromagnetic induction, by which means a moving magnet induces an electrical current in a conductor. Thus it was Faraday who laid the foundations for both the electric motor and the electric generatorAsimov, p. 315 ff. Faraday also formulated a physical conception of electromagnetic fields.
Classical mechanics was given a new formulation by William Rowan Hamilton, in 1833 with the introduction of what is now called the Hamiltonian, which a century later gave an entry to wave mechanical formulation of quantum mechanics. During its first 1868 meeting, notable oceanographer Matthew F. Maury helped launch the American Association for the Advancement of Science (AAAS) by giving a very influential lecture on Wind and Current Charts which gave rise to one of the first examples of international scientific collaboration.^[17]

James Clerk Maxwell

James Clerk Maxwell built upon Michael Faraday's physical conception of electromagnetic fields with an interlinked set of twenty equations that explained the interactions between electric and magnetic fields and unified the two phenomena into a single theory of electromagnetism. Maxwell's equations were presented to the Royal Society in 1864. These twenty equations were later reduced, using vector calculus, to a set of four equations by Oliver Heaviside. A prediction of Maxwell's equations was that light is an electromagnetic wave. Confirmation of this observation was made with the 1888 discovery of radio by Heinrich Hertz and in 1895 when Wilhelm Roentgen detected X-rays.
In 1847 James Prescott Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy. However, the principle of conservation of energy had been suggested in various forms by perhaps a dozen German, French, British and other scientists during the first half of the 19th century. About the same time, entropy and the second law of thermodynamics were first clearly described in the work of Rudolf Clausius. In 1875 Ludwig Boltzmann made the important connection between the number of possible states that a system could occupy and its entropy. With two installments in 1876 and 1878, Josiah Willard Gibbs developed much of the theoretical formalism for thermodynamics, and a decade later firmly laid the foundation for statistical mechanics — much of which Ludwig Boltzmann had independently invented. In 1881 Gibbs also was very influential in moving much of the notation of physics from Hamilton's quaternions to vectors.^[18] ^[19]
The discovery of the Hall effect in 1879 gave the first direct evidence that the carrier of electricity was negatively charged.
Dimensional analysis was used for the first time in 1878 by Lord Rayleigh who was trying to understand why the sky is blue.^[20]
In 1887 the Michelson-Morley experiment was conducted and it was interpreted as counter to the generally held theory of the day, that the Earth was moving through a "luminiferous aether". Albert Abraham Michelson and Edward Morley were not fully convinced of the non-existence of the aether. Morley conducted further experiments with Dayton Miller with improved interferometers, again giving null results.

Marie Sklodowska-Curie

In 1887, Nikola Tesla investigated X-rays using his own devices as well as Crookes tubes. In 1895, Wilhelm Conrad Röntgen observed and analysed X-rays, which turned out to be high-frequency electromagnetic radiation. Radioactivity was discovered in 1896 by Henri Becquerel, and further studied by Pierre and Marie Curie and others. This initiated the field of nuclear physics.
In 1895, Röntgen discovered X-rays, which turned out to be high-frequency electromagnetic radiation.
Radioactivity was discovered in 1896 by Henri Becquerel, and further studied by Maria Sklodowska-Curie, Pierre Curie, and others. This initiated the field of nuclear physics.
In 1897, J. J. Thomson deduced that cathode rays were composed of negatively charged particles, which he called "''corpuscles''", later realized to be electrons. Philipp Lenard showed that the particles ejected in the photoelectric effect were the same as those in cathode rays, and that their energy was independent of the intensity of the light, but was greater for short wavelengths of the incident light.^[21]
These discoveries revealed that the assumption of many physicists, that atoms were the basic unit of matter, was flawed, and prompted further study into the structure of atoms, such as Ernest Rutherford's in 1911.

20th century

Albert Einstein

The turn of the 20th century brought the start of a revolution in physics.
The Lorentz transformations, the fundamental equations of special relativity, were published in 1897 and 1900 and also by Joseph Larmor and by Hendrik Lorentz in 1899 and 1904. They both showed that Maxwell's equations were invariant under the transformations. The ability to describe light in electromagnetic terms helped serve as a springboard for Albert Einstein's publication of the theory of special relativity in 1905. This theory combined classical mechanics with Maxwell's equations. The theory of special relativity unifies space and time into a single entity, spacetime. Relativity prescribes a different transformation between reference frames than classical mechanics; this necessitated the development of relativistic mechanics as a replacement for classical mechanics. In the regime of low (relative) velocities, the two theories agree.
In 1900, Max Planck published his explanation of blackbody radiation. This equation assumed that radiators are quantized, which proved to be the opening argument in the edifice that would become quantum mechanics. By introducing discrete energy levels, Planck, Einstein, Niels Bohr, and others developed quantum theories to explain other anomalous experimental results like the photoelectric effect.
In 1904, J. J. Thomson proposed the first model of the atom, known as the plum pudding model. In 1911, Ernest Rutherford deduced from scattering experiments the existence of a compact atomic nucleus, with positively charged constituents dubbed protons. The first quantum mechanical model of the atom, the Bohr model, was published in 1913 by Niels Bohr. Sir W. H. Bragg and his son Sir William Lawrence Bragg, also in 1913, began to unravel the arrangement of atoms in crystalline matter by the use of x-ray diffraction. Neutrons, the neutral nuclear constituents, were discovered in 1932 by James Chadwick.

Ernest Rutherford

In 1911, Ernest Rutherford deduced from scattering experiments the existence of a compact atomic nucleus, with positively charged constituents dubbed protons. Neutrons, the neutral nuclear constituents, were discovered in 1932 by Chadwick. The equivalence of mass and energy (Einstein, 1905) was spectacularly demonstrated during World War II, as research was conducted by each side into nuclear physics, for the purpose of creating a nuclear bomb. The German effort, led by Heisenberg, did not succeed, but the Allied Manhattan Project reached its goal. In America, a team led by Fermi achieved the first man-made nuclear chain reaction in 1942, and in 1945 the world's first nuclear explosive was detonated at Trinity site, near Alamogordo, New Mexico.
In 1915, Einstein extended special relativity to describe gravity with the general theory of relativity. One principal result of general relativity is the gravitational collapse into black holes, which was anticipated two centuries earlier, but elucidated by Robert Oppenheimer. Important exact solutions of Einstein's field equation were found by Karl Schwarzschild in 1915 and Roy Kerr only in 1963. One part of the theory of general relativity is Einstein's field equation. This describes how the ''stress-energy tensor'' creates curvature of spacetime and forms the basis of general relativity. Further work on Einstein's field equation produced results which predicted the Big Bang, black holes, and the expanding universe. Einstein believed in a static universe. He tried, and failed, to fix his equation to allow for this. In 1929, however, Edwin Hubble published his discovery that that the universe is expanding at a possibly exponential rate. This is the basis for understanding that the universe is expanding. Thus, the universe must have been smaller and therefore hotter in the past. In 1933 Karl Jansky at Bell Labs discovered the radio emission from the Milky Way, and thereby initiated the science of radio astronomy. By the 1940s, researchers like George Gamow proposed the ''Big Bang'' theory,^[22] evidence for which was discovered in 1964;^[23] Enrico Fermi and Fred Hoyle were among the doubters in the 1940s and 1950s. Hoyle had dubbed Gamow's theory the ''Big Bang'' in order to debunk it. Today, it is one of the principal results of cosmology.
According to Cornelius Lanczos, any physical law which can be expressed as a variational principle describes an expression which is self-adjoint^[24] or Hermitian. Thus such an expression describes an invariant under a Hermitian transformation. Felix Klein's Erlangen program attempted to identify such invariants under a group of transformations. Noether's theorem identified the conditions under which the Poincaré group of transformations (what is now called a gauge group) for general relativity define conservation laws. The relationship of these invariants (the symmetries under a group of transformations) and what are now called conserved currents, depends on a variational principle, or action principle. Noether's papers made the requirements for the conservation laws precise. Noether's theorem remains right in line with current developments in physics to this day.

Erwin Schrödinger

In 1925 Wolfgang Pauli elucidated the Pauli exclusion principle and introduced the notion of quantized spin and fermions. Over the next several years, quantum mechanics would be formulated by Werner Heisenberg, Erwin Schrödinger and Paul Dirac in different ways which both explained the preceding heuristic quantum theories. In quantum mechanics, the outcomes of physical measurements are inherently probabilistic; the theory describes the calculation of these probabilities. It successfully describes the behavior of matter at small distance scales. In 1925 Schrödinger formulated wave mechanics, which provided a consistent mathematical method for describing a wide variety of physical situations such as the particle in a box and the quantum harmonic oscillator which he solved for the first time. That same year Heisenberg described an alternative mathematical method, called matrix mechanics, which proved to be equivalent to wave mechanics. In 1928 Dirac produced a relativistic formulation built on Heisenberg's matrix mechanics, and predicted the existence of the positron and founded quantum electrodynamics. During the 1920s Schrödinger, Heisenberg, and Max Born were able to formulate a consistent picture of the chemical behavior of matter, a complete theory of the electronic structure of the atom, as a byproduct of the quantum theory.
Quantum mechanics also provided the theoretical tools for condensed matter physics, whose largest branch is solid state physics. It studies the physical behavior of solids and liquids, including phenomena such as crystal structures, semiconductivity, and superconductivity. The pioneers of condensed matter physics include Felix Bloch, who created a quantum mechanical description of the behavior of electrons in crystal structures in 1928. Much of the behavior of solids was elucidated within a few years with the discovery of the Fermi surface which was based on the idea of the Pauli exclusion principle applied to systems having many electrons. The understanding of the transport properties in semiconductors as described in William Shockley's ''Electrons and holes in semiconductors, with applications to transistor electronics'' enabled the electronic revolution of the twentieth century through the development of the ubiquitous, ultra-cheap transistor. The transistor was developed by physicists John Bardeen, Walter Houser Brattain, and William Bradford Shockley in 1947 at Bell Laboratories.
In 1934, the Italian physicist Enrico Fermi had discovered strange results when bombarding uranium with neutrons, which he believed at first to have created transuranic elements. In 1939, it was discovered by the chemist Otto Hahn and the physicist Lise Meitner that what was actually happening was the process of nuclear fission, whereby the nucleus of uranium was actually being split into two pieces, releasing a considerable amount of energy in the process. At this point it became clear to a number of scientists independently that this process could potentially be harnessed to produce massive amount of energy, either as a civilian power source or as a weapon. Leó Szilárd actually filed a patent on the idea of a nuclear chain reaction in 1934. In America, a team led by Fermi and Szilárd achieved the first man-made nuclear chain reaction in 1942 in the world's first nuclear reactor, and in 1945 the world's first nuclear explosive was detonated at Trinity Site, north of Alamogordo, New Mexico. After the war, central governments would become the primary sponsors of physics. The scientific leader of the Allied project, theoretical physicist Robert Oppenheimer, noted the change of the imagined role of the physicist when he noted in a speech that:
:"''In some sort of crude sense, which no vulgarity, no humor, no overstatement can quite extinguish, the physicists have known sin, and this is a knowledge which they cannot lose.''"
Though the process had begun with the invention of the cyclotron by Ernest O. Lawrence in the 1930s, nuclear physics in the postwar period entered into a phase of what historians have called "Big Science", requiring costly huge accelerators and particle detectors, and large collaborative laboratories to test open new frontiers. The primary patron of physics became central governments, who recognized that the support of "basic" research could sometimes lead to technologies useful to both military and industrial applications. Toward the end of the twentieth century, a European collaboration of 20 nations, CERN, became the largest particle physics laboratory in the world.
Another "big science" was the science of ionized gases, plasma, which had begun with Crookes tubes late in the 19th century. Large international collaborations over the last half of the twentieth century embarked on a long range effort to produce commercial amounts of electricity through fusion power, which remains a distant goal.
Further understanding of the physics of metals, semiconductors and insulators led a team of three men at Bell labs, William Shockley, Walter Brattain and John Bardeen in 1947 to the first transistor and then to many important variations, especially the bipolar junction transistor. Further developments in the fabrication and miniaturization of integrated circuits in the years to come produced fast, compact computers that came to revolutionize the way physics was done—simulations and complex mathematical calculations became possible that were undreamed of even a few decades previous.
The discovery of nuclear magnetic resonance in 1946 led to many new methods for examining the structures of molecules and became a very widely used tool in analytical chemistry, and it gave rise to an important medical imaging technique, magnetic resonance imaging.
Quantum field theory was formulated in order to extend quantum mechanics to be consistent with special relativity, and was developed in the late 1940s in the work of Richard Feynman, Julian Schwinger, Sin-Itiro Tomonaga, and Freeman Dyson. They formulated the theory of quantum electrodynamics, which describes the electromagnetic interaction, and successfully explained the Lamb shift. This provided the framework for modern particle physics, which studies fundamental forces and elementary particles. Chen Ning Yang and Tsung-Dao Lee, in the 1950s, discovered an unexpected asymmetry in the decay of a subatomic particle. In 1954, Yang and Robert Mills then developed a class of gauge theories which provided the framework for understanding the nuclear forces (Yang, Mills 1954). The theory for the strong nuclear force was first proposed by Murray Gell-Mann. The electroweak force, the unification of the weak nuclear force with electromagnetism, was proposed by Sheldon Lee Glashow, Abdus Salam, and Steven Weinberg and confirmed in 1964 by James Watson Cronin and Val Fitch. This led to the so-called Standard Model of particle physics in the 1970s, which successfully describes all the elementary particles observed to date.
Starting in 1960 the military establishment of the United States began using atomic clocks to construct the global positioning system which in 1984 achieved its full configuration of 24 satellites in low earth orbits. This came to have many important civilian and scientific uses as well.
Superconductivity, discovered in 1911 by Kamerlingh Onnes, was shown to be a quantum effect and was satisfactorily explained in 1957 by Bardeen, Cooper, and Schrieffer. A family of high temperature superconductors, based on cuprate perovskite, were discovered in 1986, and their understanding remains one of the major outstanding challenges for condensed matter theorists.
In 1974 Stephen Hawking discovered the spectrum of radiation emanating during the collapse of matter into black holes. These mysterious objects became of intense interest to astrophysicists and even the general public in the latter part of the twentieth century.
The two themes of the twentieth century, general relativity and quantum mechanics, appear inconsistent with each other. General relativity describes the universe on the scale of planets and solar systems, while quantum mechanics operates on sub-atomic scales. This challenge is being attacked by string theory, which treats spacetime as composed, not of points, but of one-dimensional objects, strings. Strings have properties similar to a common string (e.g., tension and vibration). The theories yield promising, but not yet testable, results. The search for experimental verification of string theory is in progress.
Attempts to unify quantum mechanics and general relativity made significant progress during the 1990s. At the close of the century, a Theory of everything was still not in hand, but some of its characteristics were taking shape. String theory, loop quantum gravity and black hole thermodynamics all predicted quantized spacetime on the Planck scale.
A number of new efforts to understand the physical world arose in the last half of the twentiety century that generated widespread interest: fractals and scaling, self-organized criticality, complexity and chaos, power laws and noise, networks, non-equilibrium thermodynamics, sandpiles, nanotechnology, cellular automata and the anthropic principle were only a few of these important topics.

Future directions

The United Nations declared the year 2005, the centenary of Einstein's annus mirabilis, as the World Year of Physics.

Main articles: Unsolved problems in physics

Research in physics is progressing constantly on a large number of fronts, and is likely to do so for the foreseeable future.
In condensed matter physics, the greatest unsolved theoretical problem is the explanation for high-temperature superconductivity. Strong efforts, largely experimental, are being put into making workable spintronics and quantum computers.
In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost amongst these are indications that neutrinos have non-zero mass. These experimental results appear to have solved the long-standing solar neutrino problem in solar physics. The physics of massive neutrinos is currently an area of active theoretical and experimental research. In the next several years, particle accelerators will begin probing energy scales in the TeV range, in which experimentalists are hoping to find evidence for the Higgs boson and supersymmetric particles.

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

Theoretical attempts to unify quantum mechanics and general relativity into a single theory of quantum gravity, a program ongoing for over half a century, have not yet borne fruit. Currently, the leading candidates are M-theory, superstring theory, and loop quantum gravity.
Many astronomical and cosmological phenomena have yet to be explained satisfactorily, including the existence of ultra-high energy cosmic rays, the baryon asymmetry, the acceleration of the universe, and the anomalous rotation rates of galaxies.
Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena, involving complexity, chaos, or turbulence remain poorly understood. Complex problems that would appear to be soluble by a clever application of dynamics and mechanics, such as the formation of sand piles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, or self-sorting in shaken heterogeneous collections are unsolved.
These complex phenomena have received growing attention since the 1970s for several reasons, not least of which has been the availability of modern mathematical methods and computers, which enabled complex systems to be modeled in new ways. The interdisciplinary relevance of complex physics also has increased, as exemplified by the study of turbulence in aerodynamics, or the observation of pattern formation in biological systems. In 1932, Horace Lamb correctly prophesied the success of the theory of quantum electrodynamics and the near-stagnant progress in the study of turbulence:

''I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.''

Notes

1.

2.
3. Astronomsko društvo JAVORNIK
4.
5.
6. Rosanna Gorini (2003). "Al-Haytham the Man of Experience. First Steps in the Science of Vision", ''International Society for the History of Islamic Medicine''. Institute of Neurosciences, Laboratory of Psychobiology and Psychopharmacology, Rome, Italy:

7. K. A. Waheed (1978). ''Islam and The Origins of Modern Science'', p. 27. Islamic Publication Ltd., Lahore.
8. Robert Briffault (1938). ''The Making of Humanity'', p. 191.
9. Seyyed Hossein Nasr, "Islamic Conception Of Intellectual Life", in Philip P. Wiener (ed.), ''Dictionary of the History of Ideas'', Vol. 2, p. 65, Charles Scribner's Sons, New York, 1973-1974.
10. 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), p. 521-546 [543].)
11. Ernest A. Moody (1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", ''Journal of the History of Ideas'' '12' (2), p. 163-193.
12.

(cf. Abel B. Franco (October 2003). "Avempace, Projectile Motion, and Impetus Theory", ''Journal of the History of Ideas'' '64' (4), p. 521-546 [528].)
13. A. C. Crombie, ''Augustine to Galileo 2'', p. 67.
14. Salah Zaimeche PhD (2005). Merv, p. 5-7. Foundation for Science Technology and Civilization.
15.
16. Dugas, Ch. 11.
17. Hearn, Chester G. ''Tracks in the Sea: Matthew Fontaine Maury and the Mapping of the Oceans'' McGraw-Hill (2002) p 127, ISBN 0-07-136826-4
18. J. W.Gibbs ''Nature'' '48,' 364 (1893).
19. J. W.Gibbs. ''The Scientific Papers of J. Willard Gibbs, Vol. Two,'' Oxbow Press (1994) ISBN 0-881987-06-x
20. Lord Rayleigh. ''Phil. Mag.'' '41', 107 (1871).
21. Biography Lenard's Nobel biography.
22. Alpher, Herman, and Gamow. ''Nature'' '162', 774 (1948).
23. The cosmic microwave background radiation Wilson's Nobel Lecture.
24. The Variational Principles of Mechanics, , Cornelius, Lanczos, Dover Publication, 1986, ISBN 0-486-65067-7

References

★ Asimov, Isaac ''Asimov's Biographical Encyclopedia of Science and Technology: The Lives & Achievements of 1510 Great Scientists from Ancient Times to the Present'' Revised second edition, Doubleday (1982) ISBN 0-385-17771-2.

★ .

★ Byers, Nina, "E. Noether's Discovery of the Deep Connection Between Symmetries and Conservation Laws," ''Israel Mathematical Conference Proceedings'', vol. 12, 1999[1]

★ Dugas, René, ''A History of Mechanics'' Dover, (1988) ISBN 0-486-65632-2

★ .

★ Motz, Lloyd and Waver, Jefferson Hane ''The Story of Physics,'' Plenum (1989) ISBN 0-306-43076-2.

★ .

★ .

★ .

★ .

★ .

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