156 résultats pour "theory"

• Game Theory I INTRODUCTION Game Theory, mathematical analysis of any situation involving a conflict of interest, with the intent of indicating the optimal choices that, under given conditions, will lead to a desired outcome.

  C Zero-Sum Games A game is said to be a zero-sum game if the total amount of payoffs at the end of the game is zero. Thus, in a zero-sum game the total amount won is exactly equal tothe amount lost. In economic contexts, zero-sum games are equivalent to saying that no production or destruction of goods takes place within the “game economy” inquestion. Von Neumann and Oskar Morgenstern showed in 1944 that any n-person non-zero-sum game can be reduced to an n + 1 zero-sum game, and that such n...

• Quantum Theory I INTRODUCTION Quantum Theory, in physics, description of the particles that make up matter and how they interact with each other and with energy.

  electron in the same way a particle with momentum would: It bumps the electron and changes the electron’s path. The light is also affected by the collision as though itwere a particle, in that its energy and momentum changes. Momentum is a quantity that can be defined for all particles. For light particles, or photons, momentum depends on the frequency, or color, of the photon, which in turndepends on the photon’s energy. The energy of a photon is equal to a constant number, called Planck’s cons...

• Big Bang Theory - astronomy.

  hydrogen atoms. Hydrogen atoms can only absorb and emit specific colors, or wavelengths, of light. The formation of atoms allowed many other wavelengths of light,wavelengths that had been interfering with the free electrons prior to the cooling of the universe, to travel much farther than before. This change set free radiation thatwe can detect today. After billions of years of cooling, this cosmic background radiation is at about 3 K (-270°C/-454°F).The cosmic background radiation was first d...

• Chaos theory

  the tracing out of a path, or trajectory, in state space. It is often possible to study the geometric features of these trajectories, even in actual experimental systems, without explicit knowledge of the solutions they represent. This allows one to characterize trajectories according to their topological features, and the investigation of how those features change as the parameters of the dynamical system are altered. While qualitative questions can be asked about almost any dynamical system, c...

• Relativity I INTRODUCTION Albert Einstein In 1905 German-born American physicist Albert Einstein published his first paper outlining the theory of relativity.

  in calculating very large distances or very large aggregations of matter. As the quantum theory applies to the very small, so the relativity theory applies to the verylarge. Until 1887 no flaw had appeared in the rapidly developing body of classical physics. In that year, the Michelson-Morley experiment, named after the American physicistAlbert Michelson and the American chemist Edward Williams Morley, was performed. It was an attempt to determine the rate of the motion of the earth through t...

• Number Theory I INTRODUCTION Number Theory, branch of mathematics that deals with the properties and relationships of numbers (see Number).

• Matrix Theory and Linear Algebra I INTRODUCTION Matrix Theory and Linear Algebra, interconnected branches of mathematics that serve as fundamental tools in pure and applied mathematics and are becoming increasingly important in the physical, biological, and social sciences.

  vectors and V is called a vector space of dimension m. Two- and three-dimensional Euclidean spaces are vector spaces when their points are regarded as specified by ordered pairs or triples of real numbers. Matrices may be used to describe linear changes from one vector space into another. Contributed By:James Singer Reviewed By:J. Lennart BerggrenMicrosoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

• Theory of Everything.

• Set Theory.

• Nicolaus Copernicus I INTRODUCTION Nicolaus Copernicus (1473-1543), Polish astronomer, best known for his astronomical theory that the sun is at rest near the center of the universe, and that the earth, spinning on its axis once daily, revolves annually around the sun.

• Encyclopedia of Philosophy: THE THEORY OF IDEAS of PLATO

  and that only a concrete individual can be a human being? (D) Classes. Attributes serve as principles according to which objects can be collected into classes: objects whichpossess the attribute of humanity, for instance, can be grouped into the class of human beings. In some waysclasses seem closer than attributes to Platonic Ideas: participation in an Idea can be understood without too muchdifficulty as membership of a class. Classes, like attributes, and unlike paradigms and concrete univers...

• Gravitation I INTRODUCTION Gravitation, the force of attraction between all objects that tends to pull them toward one another.

  precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...

• Gravitation - astronomy.

  precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...

• Relativity - astronomy.

  beta, for example, might be as large as 0.5, and the mass of the electron doubled. The mass of a rapidly moving electron could be easily determined by measuring thecurvature produced in its path by a magnetic field; the heavier the electron, the greater its inertia and the less the curvature produced by a given strength of field ( see Magnetism). Experimentation dramatically confirmed Einstein's prediction; the electron increased in mass by exactly the amount he predicted. Thus, the kinetic ener...

• Cosmology - astronomy.

  In 1917 American scientist Harlow Shapley measured the distance to several groups of stars known as globular clusters. He measured these distances by using amethod developed in 1912 by American astronomer Henrietta Leavitt. Leavitt’s method relates distance to variations in brightness of Cepheid variables, a class of starsthat vary periodically in brightness. Shapley’s distance measurements showed that the clusters were centered around a point far from the Sun. The arrangement of theclusters was...

• Plato I INTRODUCTION Plato (428?

  one of the individuals escapes from the cave into the light of day. With the aid of the sun, that person sees for the first time the real world and returns to the cave withthe message that the only things they have seen heretofore are shadows and appearances and that the real world awaits them if they are willing to struggle free oftheir bonds. The shadowy environment of the cave symbolizes for Plato the physical world of appearances. Escape into the sun-filled setting outside the cave symbolize...

• Plato.

  one of the individuals escapes from the cave into the light of day. With the aid of the sun, that person sees for the first time the real world and returns to the cave withthe message that the only things they have seen heretofore are shadows and appearances and that the real world awaits them if they are willing to struggle free oftheir bonds. The shadowy environment of the cave symbolizes for Plato the physical world of appearances. Escape into the sun-filled setting outside the cave symbolize...

• Albert Einstein I INTRODUCTION Albert Einstein (1879-1955), German-born American physicist and Nobel laureate, best known as the creator of the special and general theories of relativity and for his bold hypothesis concerning the particle nature of light.

  On the basis of the general theory of relativity, Einstein accounted for the previously unexplained variations in the orbital motion of the planets and predicted thebending of starlight in the vicinity of a massive body such as the sun. The confirmation of this latter phenomenon during an eclipse of the sun in 1919 became a mediaevent, and Einstein’s fame spread worldwide. For the rest of his life Einstein devoted considerable time to generalizing his theory even more. His last effort, the unifi...

• Albert Einstein.

  On the basis of the general theory of relativity, Einstein accounted for the previously unexplained variations in the orbital motion of the planets and predicted thebending of starlight in the vicinity of a massive body such as the sun. The confirmation of this latter phenomenon during an eclipse of the sun in 1919 became a mediaevent, and Einstein’s fame spread worldwide. For the rest of his life Einstein devoted considerable time to generalizing his theory even more. His last effort, the unifi...

• Western Philosophy.

  the popular belief in personal deities, but he failed to explain the way in which the familiar objects of experience could develop out of elements that are totally differentfrom them. Anaxagoras therefore suggested that all things are composed of very small particles, or “seeds,” which exist in infinite variety. To explain the way in whichthese particles combine to form the objects that constitute the familiar world, Anaxagoras developed a theory of cosmic evolution. He maintained that the activ...

• History of Chemistry - chemistry.

  even better distillation apparatus than the Arabs had made and to condense the more volatile products of distillation. Among the important products obtained in thisway were alcohol and the mineral acids: nitric, aqua regia (a mixture of nitric and hydrochloric), sulfuric, and hydrochloric. Many new reactions could be carried outusing these powerful reagents. Word of the Chinese discovery of nitrates and the manufacture of gunpowder also came to the West through the Arabs. The Chinese atfirst use...

• Microeconomics.

  changes in any of their underlying determinants. Thus, for example, fairly confident and precise predictions can be made about how changes in consumers' preferencesor in technology are likely to affect demand, supply, and equilibrium output, but only under conditions of perfect competition. Although the model of the firm under conditions of perfect competition is the starting point of the theory of supply in microeconomics, it is generally accepted thatmarkets are not usually characterized by pe...

• Magnetism I INTRODUCTION Magnetism, an aspect of electromagnetism, one of the fundamental forces of nature.

  the French physicist Paul Langevin produced a theory regarding the temperature dependence of the magnetic properties of paramagnets (discussed below), which wasbased on the atomic structure of matter. This theory is an early example of the description of large-scale properties in terms of the properties of electrons and atoms.Langevin's theory was subsequently expanded by the French physicist Pierre Ernst Weiss, who postulated the existence of an internal, “molecular” magnetic field inmaterials...

• Galileo I INTRODUCTION Galileo (1564-1642), Italian physicist and astronomer who, with German astronomer Johannes Kepler, initiated the scientific revolution that flowered in the work of English physicist Sir Isaac Newton.

  V WORK IN ASTRONOMY During most of his time in Padua, Galileo showed little interest in astronomy, although in 1595 he declared in a letter that he preferred the Copernican theory that Earthrevolves around the Sun to the assumptions of Aristotle and Ptolemy that planets circle a fixed Earth ( see Astronomy: The Copernican Theory ; Ptolemaic System). A Observations with the Telescope In 1609 Galileo heard that a telescope had been invented in Holland. In August of that year he constructed a t...

• Galileo.

  V WORK IN ASTRONOMY During most of his time in Padua, Galileo showed little interest in astronomy, although in 1595 he declared in a letter that he preferred the Copernican theory that Earthrevolves around the Sun to the assumptions of Aristotle and Ptolemy that planets circle a fixed Earth ( see Astronomy: The Copernican Theory ; Ptolemaic System). A Observations with the Telescope In 1609 Galileo heard that a telescope had been invented in Holland. In August of that year he constructed a t...

• Macroeconomics.

  IV INFLATION For several decades after World War II (1939-1945) the main inflation theories were demand-pull and cost-push. The cost-push theory basically emphasized the role ofexcessive increases in wages relative to productivity increases as a cause of inflation, whereas the demand-pull theory tended to attribute inflation more to excessdemand in the goods market caused by expansion of the money supply. A central concept in inflationary theory since the mid-1950s has been the Phillips curve...

• Child Development.

  developmental scientists have studied how cultural values guide the skills and attitudes that children acquire as they mature, and how brain maturation influences thedevelopment of thinking and feeling. For a more detailed discussion of child development theories, see the Theories of Child Development section of this article. III BASIC QUESTIONS A Nature and Nurture Scholars have long debated the relative importance of nature (hereditary influences) and nurture (environmental influences) i...

• Psychoanalysis.

  A cornerstone of modern psychoanalytic theory and practice is the concept of anxiety, which institutes appropriate mechanisms of defense against certain dangersituations. These danger situations, as described by Freud, are the fear of abandonment by or the loss of the loved one (the object), the risk of losing the object's love,the danger of retaliation and punishment, and, finally, the hazard of reproach by the superego. Thus, symptom formation, character and impulse disorders, andperversions,...

• History of Astronomy - astronomy.

  Egypt, the Sun was directly overhead at noon. On the same date and time in Alexandria, Egypt, the Sun was about 7 degrees south of zenith. With simple geometryand knowledge of the distance between the two cities, he estimated the circumference of the Earth to be 250,000 stadia. (The stadium was a unit of length, derivedfrom the length of the racetrack in an ancient Greek stadium. We have an approximate idea of how big an ancient Greek stadium was, and based on that approximationEratosthenes was...

• Earthquake.

  III CAUSES Most earthquakes are caused by the sudden slip along geologic faults. The faults slip because of movement of the Earth’s tectonic plates. This concept is called theelastic rebound theory. The rocky tectonic plates move very slowly, floating on top of a weaker rocky layer. As the plates collide with each other or slide past eachother, pressure builds up within the rocky crust. Earthquakes occur when pressure within the crust increases slowly over hundreds of years and finally exceeds...

• Periodic Law - chemistry.

  VI QUANTUM THEORY With the development of the quantum theory and its application to atomic structure by the Danish physicist Niels Bohr and other scientists, most of the detailedfeatures of the periodic table have found a ready explanation. Every electron is characterized by four quantum numbers that designate its orbital motion in space. Bymeans of the selection rules governing these quantum numbers and the exclusion principle of Wolfgang Pauli, which states that two electrons in the same ato...

• Social Psychology.

  During the 1960s, American psychologist Stanley Milgram studied a form of social influence stronger than conformity: obedience to authority. In a famous series ofexperiments that attracted controversy about human research ethics, Milgram put each of 1,000 subjects into a situation in which they were ordered by anexperimenter to administer painful electric shocks to a confederate (who did not actually receive any shocks). The subjects in these studies were led to believe that theywere acting as '...

• english history

  He was a Scottish moral philosopher and a pioneer of political economics. Smith studied social philosophy at the University of Glasgow and the University of Oxford. Smith obtained a professorship at Glasgow teaching moral philosophy. Smith returned home and spent the ten years writing The Wealth of Nations , publishing it in 1776. He became famous for this book, which had a profound influence on modern economics and concepts of individual free...

• HISTOIRE DE KEYNE BRITISH

  He was a Scottish moral philosopher and a pioneer of political economics. Smith studied social philosophy at the University of Glasgow and the University of Oxford. Smith obtained a professorship at Glasgow teaching moral philosophy. Smith returned home and spent the ten years writing The Wealth of Nations , publishing it in 1776. He became famous for this book, which had a profound influence on modern economics and concepts of individual free...

• Physics I INTRODUCTION Physics, major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces.

  Starting about 1665, at the age of 23, Newton enunciated the principles of mechanics, formulated the law of universal gravitation, separated white light into colors,proposed a theory for the propagation of light, and invented differential and integral calculus. Newton's contributions covered an enormous range of naturalphenomena: He was thus able to show that not only Kepler's laws of planetary motion but also Galileo's discoveries of falling bodies follow a combination of his ownsecond law of m...

• Sigmund Freud.

  reminiscences from the past and about her daydreams. Remarkably, as her narrative revisited memories from the past, which were associated with the onset of aparticular symptom, each symptom disappeared when accompanied by an emotional outburst. Breuer made use of this discovery to eliminate her symptoms one at atime. He called the treatment the cathartic technique (from the Greek katharsis meaning “purgation”). The treatment was time consuming and required considerable effort to reach dimly re...

• Shakespeare and Queer Theory

  Book Review Shakespeare and Queer Theory, by Melissa E. Sanchez. Arden Shakespeare and Theory. London: Bloomsbury Arden Shakespeare, 2019. xiv + 228 pp. ISBN: 978-1-474-25667-4. Hardcover $102 Shakespeare and Queer Theory is a guide that aims to bring an understanding of recent and ongoing debates relating to queer methods through an in depth analysis of its convergences with Shakespeare studies and beyond them. In this book, Melissa E. Sanchez expounds on the importance of Shakespeare...

• Modern Art I INTRODUCTION American Gothic American Gothic was painted by the 20th-century American artist Grant Wood in 1930.

  while at the other side a woman in black appears to mourn the end of her participation in the dance. Click on the buttonsto learn more.© Microsoft Corporation. All Rights Reserved. In view of this diversity, it is difficult to define modern art in a way that includes all of 20th-century Western art. For some critics, the most important characteristic ofmodern art is its attempt to make painting and sculpture ends in themselves, thus distinguishing modernism from earlier forms of art that had con...

• Chemistry - chemistry.

  parts of oxygen by weight, which is a ratio of about 1 to 8, regardless of whether the water came from the Mississippi River or the ice of Antarctica. In other words, acompound has a definite, invariable composition, always containing the same elements in the same proportions by weight; this is the law of definite proportions. Many elements combine in more than one ratio, giving different compounds. In addition to forming water, hydrogen and oxygen also form hydrogen peroxide.Hydrogen peroxide h...

• Economics.

  Malthus, nature's check was “positive”: “The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must insome shape or other visit the human race.” The shapes it took included war, epidemics, pestilence and plague, human vices, and famine, all combining to level theworld's population with the world's food supply. The only escape from population pressure and the horrors of the positive check was in voluntary limitation of population, no...

• Geography - Geography.

  Geographers have developed a standard pattern of map symbols for identifying such cultural features as homes, factories, and churches; dams, bridges, and tunnels;railways, highways, and travel routes; and mines, farms, and grazing lands. C Analyzing Geographic Information Techniques that use mathematics or statistics to analyze data are known as quantitative methods. The use of quantitative methods enables geographers to treat a largeamount of data and a large number of variables in an objectiv...

• Ice Ages.

  B Future Ice Ages The record of previous glacial activity is the best indicator for future ice ages. Scientists examine the evidence for the numerous 100,000-year glacial-interglacial cycleswithin the present ice age to attempt a forecast of future ice ages. Since all previous ice ages lasted tens of millions of years, our present ice age will likely continue fora considerable amount of time. Each glaciation begins slowly and may take 80,000 years or more to reach its maximum extent. A rapid me...

• THÉORIE DU SON [Theory of Sound]. Résumé

• Encyclopedia of Philosophy: Albert the Great

  Aristotle seems more Neoplatonic than Aristotelian, it is precisely because it is based as much on the philosophies ofArabic commentators on Aristotle (Alfarabi, Avicenna, the Liber de causis and Averroes) as it is on the philosophy of Aristotle himself. As the principal engineer of the introduction of philosophy to the Latins, Albert tried to portray ashomogeneous a philosophy that is not and cannot be homogeneous in the eyes of the philologist. It is, however,this Arabic-Latin version of Ari...

• Learning.

  B1 Acquisition The acquisition phase is the initial learning of the conditioned response—for example, the dog learning to salivate at the sound of the bell. Several factors can affect the speed of conditioning during the acquisition phase. The most important factors are the order and timing of the stimuli. Conditioning occurs most quickly when theconditioned stimulus (the bell) precedes the unconditioned stimulus (the food) by about half a second. Conditioning takes longer and the response is...

• Ronald Reagan.

  deposed shah of Iran to enter the United States for medical treatment, a group of Iranian revolutionaries stormed the U.S. Embassy in Tehrān and held 53 Americansas hostages. United States media publicized the plight of the hostages and Carter’s failure to win their release. They were eventually released in January 1981, on theday of Reagan’s inauguration. The contrast between the television personalities of the two candidates was also very important. Carter’s stiff, nervous manner had never bee...

• Ronald Reagan - USA History.

  deposed shah of Iran to enter the United States for medical treatment, a group of Iranian revolutionaries stormed the U.S. Embassy in Tehrān and held 53 Americansas hostages. United States media publicized the plight of the hostages and Carter’s failure to win their release. They were eventually released in January 1981, on theday of Reagan’s inauguration. The contrast between the television personalities of the two candidates was also very important. Carter’s stiff, nervous manner had never bee...

• Conceptual analysis

  Kant's important idea that conceptual truths can be either analytic a priori or synthetic a priori is effectively erased by Gottlob Frege in his Foundations of Arithmetic (1884). Frege's overriding philosophical aim is to put mathematical proof on a firm footing by reducing the truths of arithmetic to analytic truths of logic. In view of this, the proper goal of an analysis is the production of non-circular, explanatory, yet meaning-preserving general definitions of fundamental concepts -...

• Encyclopedia of Philosophy: Charles Darwin

  cousins, descended from a common ancestor.The case for Darwin's theory was enormously strengthened in the twentieth century with the discovery of themechanisms of heredity and the development of molecular genetics. It would not be to my purpose, and would bebeyond my competence, to evaluate the scientific evidence for Darwinism. But it is necessary to spend some timeon the philosophical implications of his theory, assuming that it is well established.From Darwin's time until the present, ev...

• Communism.

  In Britain, Robert Owen, a philanthropic Welsh manufacturer, strove against the social problems brought about by the Industrial Revolution and sought to improve thewelfare of workers. As manager of a cotton mill, he enhanced the environment of his workers by improving their housing, modernizing mill equipment for greater safetyand sanitation, and establishing low-priced stores for the workers and schools for their children. Owen believed that workers, rather than governments, should createthe in...