History of physics

2008/9 Schools Wikipedia Selection. Related subjects: History; Physics

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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 behaviour of celestial objects such as the Sun and the Moon, and so forth. Typically the behaviour 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 inquiry, 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 transformed society, through the development of technology by the engineering profession. Physics is considered both a body of knowledge and the practice that makes and transmits it. Experimental physics began in the Middle Ages with experimental investigations into optics, statics and dynamics. The Scientific Revolution, beginning around 1543, is considered a convenient boundary between ancient thought and classical mechanics. 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. The list of unsolved problems in physics is large.

Antiquity

The first records of the 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 ( 2nd millennium BC) 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.. 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.

Further investigations into early ideas in 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. Similar atomic philosophy would develop in ancient India. 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. In doing so Archimedes would be the first to uncover a law of nature. 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 unknown. 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, which is considered to be the earliest analog computer, 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. The discovery of the Baghdad Battery also suggests that a primitive form of electricity may have been known in Mesopotamia during the Parthian or Sassanid periods.

A primitive steam-powered device, 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.

A particularly important ancient contribution that would allow physics to develop into a science came from India. It was the introduction of 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.

Physics in the Middle Ages

Islamic world

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 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 modern optics, experimental physics, and hydrodynamics.

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. Alhazen, who is regarded as the "father of modern optics", and a pioneer of the scientific method and experimental physics, 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 travelling at a finite speed. He improved Ptolemy's theory of the refraction of light, and went on to discover the law 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 spherical aberration.

Avicenna (980-1037) agreed that the speed of light is finite, as he "observed that if the perception of light is due to the emission of some sort of particles by a luminous source, the speed of light must be finite." Abū Rayhān al-Bīrūnī (973-1048) also agreed that light has a finite speed, and he was the first to discover that the speed of light is much faster than the speed of sound. Qutb al-Din al-Shirazi (1236-1311) and Kamāl al-Dīn al-Fārisī (1260-1320) gave the first correct explanations for the rainbow phenomenon.

In mechanics, the eldest Banū Mūsā brother, Muhammad ibn Musa, in his Astral Motion and The Force of Attraction, hypothesized that there was a force of attraction between heavenly bodies in the 9th century. Abū Rayhān al-Bīrūnī (973-1048), and later al-Khazini, developed experimental scientific methods for mechanics, especially the fields of statics and dynamics, particularly for determining specific weights, such as those based on the theory of balances and weighing. Muslim physicists unified statics and dynamics into the science of mechanics, and they combined the fields of hydrostatics with dynamics to give birth to hydrodynamics. They applied the mathematical theories of ratios and infinitesimal techniques, and introduced algebraic and fine calculation techniques into the field of statics. They were also generalized the theory of the centre of gravity and applied it to three-dimensional bodies. They also founded the theory of the ponderable lever and created the "science of gravity" which was later further developed in medieval Europe. Al-Biruni also theorized that acceleration is connected with non-uniform motion.

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, and he stated that the heavenly bodies "were accountable to the laws of physics". also enunciated the law of inertia when he stated that a body moves perpetually unless an external force stops it or changes its direction of motion. He also developed the concept of momentum, though he did not quantify this concept mathematically. His contemporary Avicenna also developed the concept of momentum, referring to impetus as being proportional to weight times velocity, for which he is considered a pioneer of the concept of momentum. His theory of motion was also consistent with the concept of inertia in classical mechanics.

In 1121, al-Khazini, in his treatise The Book of the Balance of Wisdom, further elaborated an idea proposed by the Greeks that all bodies are attracted towards the centre of the earth. Al-Khazini also developed the concept of gravitational potential energy and was one of the first to clearly differentiate between force, mass, and weight. Avempace (d. 1138) argued that there is always a reaction force for every force exerted, though he did not refer to the reaction force as being equal to the exerted force. His theory of motion had an influence on later physicists like Galileo Galilei. His 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, an important concept in classical mechanics. He also described acceleration as the rate of change of velocity. Averroes (1126–1198) defined and measured force as "the rate at which work is done in changing the kinetic condition of a material body" and correctly argued "that the effect and measure of force is change in the kinetic condition of a materially resistant mass." In the early 16th century, al-Birjandi developed a hypothesis similar to "circular inertia." The Muslim developments in mechanics laid the foundations for the later development of classical mechanics in early modern Europe.

Medieval Europe

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. 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 ancients, but also contemporary work. 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 an important 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 favour 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 colour 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

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.

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.

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 universal gravitation, which describes the fundamental force of gravity. 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. Newton's Law of gravitation also helped put celestial mechanics on proper scientific and mathematical footing.

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 electricity, and published a seminal work, De Magnete (1600), in which he thoroughly presented his numerous experimental results. Gilbert who designed the versorium: a device that detected the presence of statically charged objects.

17th century

In the early 17th century, the invention of the telescope and microscope, which is claimed to have been invented by three individuals ( Hans Lippershey, Jacob Metius, and Zacharias Jansen) would have profound implications on the history of science, in particular astronomy and physics. 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.

In 1643, Evangelista Torricelli invented the barometer, which arose from solving an important practical problem. Torricelli discovered Torricelli's Law, regarding the speed of a fluid flowing out of an opening, which was later shown to be a particular case of Bernoulli's principle. Torricelli also devised an equation sometimes called Torricelli's equation, which is used in the study of kinematics.

In 1660, Robert Hooke, an English scientist, formulated Hooke's law of elasticity, which describes the linear variation of tension with extension in an elastic spring.

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. Huygens also formulated Newton's second law of motion, but in quadratic form. Huygens greatest contribution comes from his early theory that light travels in waves (Wave–particle duality), and for his development of Huygens–Fresnel principle, along with French physicist Augustin-Jean Fresnel. This mathematical principle provided a method of analysis that could be applied to problems of wave propagation, and it would have applications in the later development of quantum mechanics.

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.

A French mathematician and scientist Blaise Pascal invented the hydraulic press, and an early calculator. Pascal also formulated Pascal's law, which states that for all points at the same absolute height in a connected body of an incompressible fluid at rest, the fluid pressure is the same, even if additional pressure is applied on the fluid at some place. Pascal also wrote many important papers on the scientific method.

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. Newton's theory of gravity would be so successful that it would be used by William Herschel a century later to discover a new planet in the solar system, Uranus. The Law of Gravitation initiated the field of astrophysics and celestial mechanics, which describes astronomical phenomena using physical theories. In the Principia Mathematica Newton also enunciated the principles of conservation of momentum and the conservation of angular momentum. Later on in life Newton would move on to formulate the law of cooling and developed a theory of light based on his experiments with decomposing light through a prism. Newton would also invent a reflecting telescope and along with Gottfried Leibniz would move on to independently of one another invent calculus, which has many important applications in physics.

The 17th century would also witness the beginning of the metric system, which would result in the formation of set of standards for weight and measurements. Early work in developing the metric system were pioneered by John Wilkins, Gabriel Mouton, and Antoine Lavoisier among others.

18th century

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. Bernoulli would also lay the foundation of kinetic molecular theory in 1738, with the publication of Hydrodynamica. In Hydrodynamica, Bernoulli would state that all gases consist of molecules that are constantly in motion, moving in all directions, and impacting on surfaces. It was these movements and impacts that resulted in pressure, and that heat is the kinetic energy of these moving molecules. Another pioneer of kinetic molecular theory during the 18th century was Mikhail Lomonosov. Kinetic molecular theory would have wide ranging applications in physics, in particular thermodynamics, and chemistry. Bernoulli would also move on to develop what become known as Bernoulli's principle. It states that when an ideal fluid that has no work acting on it, an increase in velocity will result in a simultaneous decrease in pressure or a change in the fluids gravitational potential energy. The principle plays a central role in fluid dynamics and would have considerable impact on the development of aerodynamics in the 19th and 20th century. During the beginning of the 18th century methods were slowly taking shape in order to provide a standard set of measures to determine temperature. One set of measure was put forward by Anders Celsius in 1742. A peculiarity of Celsius scale was that melting point of an object was set at 0 degrees Celsius and was not until a famous botanist, Carl Linnaeus, would have the scale inverted to read boiling point being at 100 degrees Celsius. Another method for determining temperature was put forward by Gabriel Fahrenheit, in 1724. Both methods are named after their respective originators and both are used interchangeably by scientists all over the world to the present date.

In 1729 the English Astronomer Royal James Bradley gave the first empirical proof of heliocentrism, by explaining stellar aberration from the hypotheses of the finite speed of light and the Earth annually orbiting the Sun, after which the prevailing geoheliocentric planetary models were abandoned in favour of heliocentrism.

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. In the 18th century many of the fundamental concepts about the nature of electricity were discovered. In 1733, C. F. du Fay, discovered the existence of two types of electricity and named them "vitreous" and "resinous" (later known as positive and negative charge respectively). William Watson, in 1747 discovered that a discharge of static electricity was equivalent to an electric current. Charles Augustin de Coulomb formulated Coulomb law, which gives the definition of the electrostatic force of attraction and repulsion. Nearing the 18th century André-Marie Ampère discovered the relationship that relates the circulating magnetic field in a closed loop to the electric current passing through the loop.