Ползунова Обучение коммуникативному чтению 2015

field of science. Today's high-energy particle accelerators can be several kilometres in length, cost hundreds (or even thousands) of millions of dollars, and accelerate particles to enormous energies (trillions of electron volts). Experimental teams, such as those that discovered the W+, W-, and Z quanta of the weak force at the European Laboratory for Particle Physics (CERN) in Geneva can have 100 or more physicists from many countries, along with a larger number of technical workers serving as support personnel. A variety of visual and electronic techniques are used to interpret and sort the huge amounts of data produced by their efforts, and particle-physics laboratories are major users of the most advanced technology, be it superconductive magnets or supercomputers.

Theoretical physicists use mathematics both as a logical tool for the development of theory and for calculating predictions of the theory to be compared with experiment. Newton, for one, invented integral calculus to solve the following problem, which was essential to his formulation of the law of universal gravitation: Assuming that the attractive force between any pair of point particles is inversely proportional to the square of the distance separating them, how does a spherical distribution of particles, such as the Earth, attract another nearby object? Integral calculus, a procedure for summing many small contributions, yields the simple solution that the Earth itself acts as a point particle with all its mass concentrated at the centre. In modern physics, Dirac predicted the existence of the then-unknown positive electron (or positron) by finding an equation for the electron that would combine quantum mechanics and the special theory of relativity.

Relations between physics and other disciplines and society. Influence of physics on related disciplines 2.4 (т.зн.)

Because physics elucidates the simplest fundamental questions in nature on which there can be a consensus, it is hardly surprising that it has had a profound impact on other fields of science, on philosophy, on the worldview of the developed world, and, of course, on technology.

Indeed, whenever a branch of physics has reached such a degree of maturity that its basic elements are comprehended in general principles, it has moved from basic to applied physics and thence to technology. Thus almost all current activity in classical physics consists of applied physics, and its contents form the core of many branches of engineering. Discover-

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ies in modern physics are converted with increasing rapidity into technical innovations and analytical tools for associated disciplines. There are, for example, such nascent fields as nuclear and biomedical engineering, quantum chemistry and quantum optics, and radio, X-ray, and gamma-ray astronomy, as well as such analytic tools as radioisotopes, spectroscopy, and lasers, which all stem directly from basic physics.

Apart from its specific applications, physics—especially Newtonian mechanics–has become the prototype of the scientific method, its experimental and analytic methods sometimes being imitated (and sometimes inappropriately so) in fields far from the related physical sciences. Some of the organizational aspects of physics, based partly on the successes of the radar and atomic-bomb projects of World War II, also have been imitated in large-scale scientific projects, as, for example, in astronomy and space research.

The great influence of physics on the branches of philosophy concerned with the conceptual basis of human perceptions and understanding of nature, such as epistemology, is evidenced by the earlier designation of physics itself as natural philosophy. Present-day philosophy of science deals largely, though not exclusively, with the foundations of physics. Determinism, the philosophical doctrine that the universe is a vast machine operating with strict causality whose future is determined in all detail by its present state, is rooted in Newtonian mechanics, which obeys that principle. Moreover, the schools of materialism, naturalism, and empiricism have in large degree considered physics to be a model for philosophical inquiry. An extreme position is taken by the logical positivists, whose radical distrust of the reality of anything not directly observable leads them to demand that all significant statements must be formulated in the language of physics.

The uncertainty principle of quantum theory has prompted a reexamination of the question of determinism, and its other philosophical implications remain in doubt. Particularly problematic is the matter of the meaning of measurement, for which recent theories and experiments confirm some apparently noncausal predictions of standard quantum theory. It is fair to say that though physicists agree that quantum theory works, they still differ as to what it means.

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Influence of related disciplines on physics 1.0 (т.зн.)

The relationship of physics to its bordering disciplines is a reciprocal one. Just as technology feeds on fundamental science for new practical innovations, so physics appropriates the techniques and instrumentation of modern technology for advancing itself. Thus experimental physicists utilize increasingly refined and precise electronic devices. Moreover, they work closely with engineers in designing basic scientific equipment, such as high-energy particle accelerators. Mathematics has always been the primary tool of the theoretical physicist, and even abstruse fields of mathematics such as group theory and differential geometry have become invaluable to the theoretician classifying subatomic particles or investigating the symmetry characteristics of atoms and molecules. Much of contemporary research in physics depends on the highspeed computer. It allows the theoretician to perform computations that are too lengthy or complicated to be done with paper and pencil. Also, it allows experimentalists to incorporate the computer into their apparatus, so that the results of measurements can be provided nearly instantaneously on-line as summarized data while an experiment is in progress.

The physicist in society 1.4 (т.зн.)

Because of the remoteness of much of contemporary physics from ordinary experience and its reliance on advanced mathematics, physicists have sometimes seemed to the public to be initiates in a latter-day secular priesthood who speak an arcane language and can communicate their findings to laymen only with great difficulty. Yet, the physicist has come to play an increasingly significant role in society, particularly since World War II. Governments have supplied substantial funds for research at academic institutions and at government laboratories through such agencies as the National Science Foundation and the Department of Energy in the United States, which has also established a number of national laboratories, including the Fermi National Accelerator Laboratory in Batavia, Ill., with the world's largest particle accelerator. CERN, mentioned above, is composed of 14 European countries and operates a large accelerator at the Swiss–French border. Physics research is supported in the Federal Republic of Germany by the Max Planck Society for the Advancement of Science and in Japan by the Japan Society for

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the Promotion of Science. In Trieste, Italy, there is the International Center for Theoretical Physics, which has strong ties to developing countries. These are only a few examples of the widespread international interest in fundamental physics.

Basic research in physics is obviously dependent on public support and funding, and with this development has come, albeit slowly, a growing recognition within the physics community of the social responsibility of scientists for the consequences of their work and for the more general problems of science and society.

Atomic physics 3.3 (т.зн.)

The scientific study of the structure of the atom, its energy states, and its interactions with other particles and fields. Atomic physics has proved to be a spectacularly successful application of quantum mechanics, which is one of the cornerstones of modern physics.

The notion that matter is made of fundamental building blocks dates to the ancient Greeks, who speculated that earth, wind, fire, and water might form the essence of the physical world. Little was done, however, to advance the idea that matter might be made of tiny particles until the 17th century. The English physicist Isaac Newton, in his Principia Mathematica (1687), proposed that Boyle's law, which states that the product of the pressure and the volume of a gas is constant at the same temperature, could be explained if one assumes that the gas is composed of particles. In 1808 the English physicist John Dalton suggested that each element consists of identical atoms, and in 1811 the Italian physicist Amedeo Avogadro hypothesized that the particles of elements may consist of two or more atoms stuck together. Avogadro called such conglomerations molecules, and based on experimental work he conjectured that the molecules in a gas of hydrogen or oxygen are formed from pairs of atoms.

During the 19th century, there developed the idea of a limited number of elements, each consisting of a particular type of atom, that could combine in an almost limitless number of ways to form chemical compounds. At mid-century the kinetic theory of gases successfully attributed such phenomena as the pressure and viscosity of a gas to the motions of atomic and molecular particles. By 1895 the growing weight of

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chemical evidence and the success of the kinetic theory left little doubt that atoms and molecules were real.

The internal structure of the atom, however, became clear only in the early 20th century, with the work of the British physicist Ernest Rutherford and his students. Until Rutherford's efforts, a popular model of the atom had been the so-called “plum-pudding” model, advocated by the English physicist J.J. Thomson, which held that each atom consists of a number of electrons (plums) embedded in a gel of positive charge (pudding); the total negative charge of the electrons exactly balances the total positive charge, yielding an atom that is electrically neutral. Rutherford conducted a series of scattering experiments that challenged Thomson's model. Rutherford observed that, when a beam of alpha particles (which are now known to be helium nuclei) struck a thin metal foil, some of the particles were deflected backward. Such large deflections were inconsistent with the plum-pudding model.

Rutherford's work led to the modern understanding of the atom, in which a heavy nucleus of positive charge is surrounded by a cloud of light electrons. The nucleus is composed of positively charged protons and electrically neutral neutrons, each of which is approximately 2,000 times as massive as the electron. The atoms of each chemical element radiate a spectrum with distinctive wavelengths, which reflect the atomic structure. Because atoms are so minute, their properties must be inferred by indirect experimental techniques. Chief among these is spectroscopy, which is used to measure and interpret the electromagnetic radiation emitted or absorbed by atoms as they undergo transitions from one energy state to another. Through the procedures of wave mechanics, the energies and characteristic wavelengths of atoms in various energy states may be computed from certain basic atomic constants, namely, the electron mass and charge, the speed of light, and the fundamental characteristic constant of the quantum theory, Planck's constant. Based on these fundamental constants, the numerical predictions of atomic quantum theory can account for most of the observed properties of different atoms. In particular, quantum mechanics offers a deep understanding of the arrangement of elements in the periodic table, showing, for example, that elements in the same column of the table should have similar properties.

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Physics 1.4 (т.зн.)

During the years 1896–1932 the foundations of physics changed so radically that many observers describe this period as a scientific revolution comparable in depth, if not in scope, to the one that took place during the 16th and 17th centuries. The 20th-century revolution changed many of the ideas about space, time, mass, energy, atoms, light, force, determinism, and causality that had apparently been firmly established by Newtonian physics during the 18th and 19th centuries. Moreover, according to some interpretations, the new theories demolished the basic metaphysical assumption of earlier science that the entire physical world has a real existence and objective properties independent of human observation.

Closer examination of 19th-century physics shows that Newtonian ideas were already being undermined in many areas and that the program of mechanical explanation was openly challenged by several influential physicists toward the end of the century. Yet, there was no agreement as to what the foundations of a new physics might be. Modern textbook writers and popularizers often try to identify specific paradoxes or puzzling experimental results–e.g., the failure to detect the Earth's absolute motion in the Michelson–Morley experiment–as anomalies that led physicists to propose new fundamental theories such as relativity. Historians of science have shown, however, that most of these anomalies did not directly cause the introduction of the theories that later resolved them. As with Copernicus' introduction of heliocentric astronomy, the motivation seems to have been a desire to satisfy aesthetic principles of theory structure rooted in earlier views of the world rather than a need to account for the latest experiment or calculation.

Radioactivity and the transmutation of elements 2.2 (т.зн.)

The discovery of radioactivity by the French physicist Henri Becquerel in 1896 is generally taken to mark the beginning of 20th-century physics. The successful isolation of radium and other intensely radioactive substances by Marie and Pierre Curie focused the attention of scientists and the public on this remarkable phenomenon and promoted a wide range of experiments.

Ernest Rutherford soon took the lead in studying the nature of radioactivity. He found that there are two distinct kinds of radiation emitted

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in radioactivity called alpha and beta rays. The alpha rays proved to be positively charged particles identical to ionized helium atoms. Beta rays are much less massive negatively charged particles; they were shown to be the same as the electrons discovered by J.J. Thomson in cathode rays in 1897. A third kind of ray, designated gamma, consists of highfrequency electromagnetic radiation.

Rutherford proposed that radioactivity involves a transmutation of one element into another. This proposal called into question one of the basic assumptions of 19th-century chemistry: that the elements consist of qualitatively different substances–92 of them by the end of the century. It implied a return to the ideas of Prout and the ancient atomists– namely, that everything in the world is composed of only one or a few basic substances.

Transmutation, according to Rutherford and his colleagues, was governed by certain empirical rules. For example, in alpha decay the atomic number of the «daughter» element is two less than that of the “mother” element, and its atomic weight is four less; this seems consistent with the fact that the alpha ray, identified as helium, has atomic number 2 and atomic weight 4, so that total atomic number and total atomic weight are conserved in the decay reaction.

Using these rules, Rutherford and his colleagues could determine the atomic numbers and atomic weights of many substances formed by radioactive decay, even though the substances decayed so quickly into others that these properties could not be measured directly. The atomic number of an element determines its place in Mendeleyev's periodic table (and thus its chemical properties; see above). It was found that substances of different atomic weight could have the same atomic number; such substances were called isotopes of an element.

Although the products of radioactive decay are determined by simple rules, the decay process itself seems to occur at random. All one can say is that there is a certain probability that an atom of a radioactive substance will decay during a certain time interval, or, equivalently, that half of the atoms of the sample will have decayed after a certain time– i.e., the half life of the material.

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The nucleus 2.2 (т.зн.)

At the University of Manchester (England), Rutherford led a group that rapidly developed new ideas about atomic structure. On the basis of an experiment conducted by Hans Geiger and Ernest Marsden in which alpha particles were scattered by a thin film of metal, Rutherford proposed a nuclear model of the atom (1911). In this model, the atom consists mostly of empty space, with a tiny, positively charged nucleus that contains most of the mass, surrounded by one or more negatively charged electrons. Henry G.J. Moseley, an English physicist, showed by an analysis of X-ray spectra that the electric charge on the nucleus is simply proportional to the atomic number of the element.

During the 1920s physicists thought that the nucleus was composed of two particles: the proton (the positively charged nucleus of hydrogen) and the electron. In 1932 the English physicist James Chadwick discovered the neutron, a particle with about the same mass as the proton but no electric charge. Since there were technical difficulties with the pro- ton–electron model of the nucleus, physicists were willing to accept Heisenberg's hypothesis that it consists instead of protons and neutrons. The atomic number is then simply the number of protons in the nucleus, while the mass number, the integer closest to the atomic weight, is equal to the total number of neutrons and protons. As mentioned above, this simple model of nuclear structure provided the basis for Hans Bethe's theory of the formation of elements from hydrogen in stars.

In 1938 the German physicists Otto Hahn and Fritz Strassmann found that, when uranium is bombarded by neutrons, lighter elements such as barium and krypton are produced. This phenomenon was interpreted by Lise Meitner and her nephew Otto Frisch as a breakup, or fission, of the uranium nucleus into smaller nuclei. Other physicists soon realized that since fission produces more neutrons, a chain reaction could result in a powerful explosion. World War II was about to begin, and physicists who had emigrated from Germany, Italy, and Hungary to the United States and Great Britain feared that Germany might develop an atomic bomb that could determine the outcome of the war. They persuaded the U.S. and British governments to undertake a major project to develop such a weapon first. The U.S. Manhattan Project did eventually produce atomic bombs based on the fission of uranium or of plutonium, a new artificially created element, and these were used against Japan in

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August 1945. Later, an even more powerful bomb based on the fusion of hydrogen atoms was developed and tested by both the United States and the Soviet Union. Thus nuclear physics began to play a major role in world history.

Einstein's 1905 trilogy 3.65 (т.зн.)

In a few months during the years 1665–66, Newton discovered the composite nature of light, analyzed the action of gravity, and invented the mathematical technique now known as calculus–or so he recalled in his old age. The only person who has ever matched Newton's amazing burst of scientific creativity–three revolutionary discoveries within a year–was Albert Einstein, who in 1905 published the special theory of relativity, the quantum theory of radiation, and a theory of Brownian movement that led directly to the final acceptance of the atomic structure of matter.

Relativity theory has already been mentioned several times in this article, an indication of its close connection with several areas of physical science. There is no room here to discuss the subtle line of reasoning that Einstein followed in arriving at his amazing conclusions; a brief summary of his starting point and some of the consequences will have to suffice.

In his 1905 paper on the electrodynamics of moving bodies, Einstein called attention to an apparent inconsistency in the usual presentation of Maxwell's electromagnetic theory as applied to the reciprocal action of a magnet and a conductor. The equations are different depending on which is «at rest» and which is «moving», yet the results must be the same. Einstein located the difficulty in the assumption that absolute space exists; he postulated instead that the laws of nature are the same for observers in any inertial frame of reference and that the speed of light is the same for all such observers.

From these postulates Einstein inferred: (1) an observer in one frame would find from his own measurements that lengths of objects in another frame are contracted by an amount given by the Lorentz–FitzGerald formula; (2) each observer would find that clocks in the other frame run more slowly; (3) there is no absolute time–events that are simultaneous in one frame of reference may not be so in another; and (4) the observable mass of any object increases as it goes faster.

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Closely connected with the mass-increase effect is Einstein's famous formula E = mc2: mass and energy are no longer conserved but can be interconverted. The explosive power of the atomic and hydrogen bombs derives from the conversion of mass to energy.

In a paper on the creation and conversion of light (usually called the «photoelectric effect paper»), published earlier in 1905, Einstein proposed the hypothesis that electromagnetic radiation consists of discrete energy quanta that can be absorbed or emitted only as a whole. Although this hypothesis would not replace the wave theory of light, which gives a perfectly satisfactory description of the phenomena of diffraction, reflection, refraction, and dispersion, it would supplement it by also ascribing particle properties to light.

Until recently the invention of the quantum theory of radiation was generally credited to another German physicist, Max Planck, who in 1900 discussed the statistical distribution of radiation energy in connection with the theory of blackbody radiation. Although Planck did propose the basic hypothesis that the energy of a quantum of radiation is proportional to its frequency of vibration, it is not clear whether he used this hypothesis merely for mathematical convenience or intended it to have a broader physical significance. In any case, he did not explicitly advocate a particle theory of light before 1905. Historians of physics still disagree on whether Planck or Einstein should be considered the originator of the quantum theory.

Einstein's paper on Brownian movement seems less revolutionary than the other 1905 papers because most modern readers assume that the atomic structure of matter was well established at that time. Such was not the case, however. In spite of the development of the chemical atomic theory and of the kinetic theory of gases in the 19th century, which allowed quantitative estimates of such atomic properties as mass and diameter, it was still fashionable in 1900 to question the reality of atoms. This skepticism, which does not seem to have been particularly helpful to the progress of science, was promoted by the empiricist, or «positivist», philosophy advocated by Auguste Comte, Ernst Mach, Wilhelm Ostwald, Pierre Duhem, Henri Poincaré, and others. It was the French physicist Jean Perrin who, using Einstein's theory of Brownian movement, finally convinced the scientific community to accept the atom as a valid scientific concept.

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