Physics

The physical (of the Greek gr. φυσικη, nature) is étymologiquement the “Science of the Nature”. In a general and old direction, physics indicates the knowledge of all the material nature; it is the direction of Rene Descartes and its pupils Jacques Rohault and Régis. It corresponds then to the Natural science or to the natural Philosophie. In XXIe century, its significance is nevertheless more restricted: it describes in order to it quantitative and conceptual time the basic components of the universe, the force S which are exerted there and their effects. It develops Théorie S by using the tool of the Mathématiques to describe and envisage the evolution of systems. The old significance of physics gathers current physics, chemistry and the natural science current.

Physics accepts as result only what is measurable and Reproductible by experiment. This method makes it possible to confirm or cancel the Hypothèse S based on a Théorie given.

Etymology and significance with the courses of the centuries

The “physical” term comes from the Greek gr. φυσικη, meaning “Nature”.

For Plato, physics is one of the three parts of the teaching of the Philosophie, at the sides of the ethical and the Logique. For Aristote, philosophy is divided into theoretic Philosophie, Philosophie practices and poetic Philosophie; physics is one of the three parts of theoretic philosophy, at the sides of the Mathématique and the Théologie.

At the 12th century, when the word appeared in old French, physics had a double direction: Medicine (example: an English doctor is a physician ), and, as an adjective, “what refers to nature”.

Starting from the end of the 15th century, the physical word indicated “knowledge concerning the natural causes” and one indicated his study by the expression “natural Philosophie” according to a university corpus which rested on the philosophy of Aristote (examples: Physics of Aristote and mathematical Principles of natural philosophy of Newton).

Pulpits of natural philosophy were established in certain Université S, in particular in the United Kingdom (Oxford, Edinburgh, etc) In Paris, one counted for example a pulpit of natural philosophy to the Collège of Clermont, occupied in particular by Ignace-Gaston Pardies.

The physical word taken its modern direction, which is more restricted than the original direction, as from the 17th century (with Galileo and Descartes), and especially of the traditional physics which was born with Newton. With the University of Paris, the Aristotélisme dominated the courses of natural philosophy until in the years 1690, from which it progessivement was progessivement replaced by the Cartésianisme, in particular thanks to the opening of the Collège of the Four-Nations and the courses of Edme Pourchot.

In the first edition of the Dictionary of the French Academy , going back to 1694, the “physical” name is indicated as the “science which has as an aim the knowledge of the natural things, ex: physics belongs to philosophy ; physics is necessary to a doctor .”. The “physical” adjective is defined moreover like meaning “natural, ex: physical impossibility is opposed to moral impossibility ”. It is only in its sixth edition (1832-1835) that the modern direction of “physics” appears, the term is defined as “science which has as an aim the accidental or permanent properties of the material bodies, when one studies them without breaking up them chemically. ”. Finally in its eighth edition (1932-1935), physics is defined as the “science which observes and groups the phenomena of the material world, in order to release the laws which govern them.”

Littré gives more precise definitions. As an adjective, it defines the phenomena physique as “those which take place between the visible bodies, at appreciable distances, and which do not change them PS the characters” and the physical properties, as “natural qualities of the bodies which are perceptible with the directions, such as the solid or gas state, the form, the color, the odor, savor, the density, etc”. Physical sciences are defined as “those which study the natural characters of the bodies, the forces which act on them and the phenomena which result from it”. As a name, physics is defined like “science of the movement and the reciprocal actions of the bodies, as these actions are not composition and of decomposition, which is clean chemistry”.

The current concept of science as “a unit or system of knowledge on a matter” dates only from the 18th century. Before this time, the word “science” meant “knowledge simply that one has something” (science and knowledge have the same etymology) and the concept of scientist did not exist. Contrary, the term “philosophy” indicates in its old direction “the study of the principles and the causes, or the system of the general notions on the unit of the things. ”, the natural science was thus the result of natural philosophy (see the example of the title of the review Philosophical Transactions ).

The expression “physical sciences” currently indicates the unit formed by physics (in its modern direction) and chemistry, this expression takes its current direction in France at the beginning of the XIXe century, at the same time as the word “science” takes the direction of “unit formed by sciences mathematical, physical and natural”. Previously, the expression “physical sciences” was a simple synonym of the expression “natural science”.

Theory and experiment

The Physicien S observe, measure and model the behavior and the interactions of the Matière through the space and the Temps (definite like “physical phenomena”).

A Theory or a Modèle is a mathematically formalized conceptual unit, in which physical parameters that one supposes independent (load, energy and time, for example) are expressed in the form of variables ( Q , E and T ) and are measured with suitable units (Coulomb, Joule and second). The theory connects these variables by one or more equations (for example, E=mc ²). These relations make it possible to predict in a quantitative way the result of Expérience S.

A Expérience is a material protocol making it possible to measure certain phenomena of which the theory gives a conceptual representation. It is illusory to isolate an experiment from the associated theory. The physicist does not measure obviously things randomly; it is necessary that it has with the spirit the conceptual universe of a theory. Aristote forever thought of calculating time that a stone released puts to reach the ground, simply because its design of the sublunary world did not consider such a quantification. This experiment had to await Galileo to be made. Another example of experiment dictated clearly by a theoretical conceptual framework is the discovery of the Quark S within the framework of the Physique of the particles. The physicist of the particles Freezing-Mann noticed that the particles subjected to the strong Force were distributed according to an elegant mathematical structure, but that three fundamental positions (with the mathematical direction of the theory of the representations) of this structure were not carried out. He thus postulated the existence of more fundamental particles (with the physical direction) that the Proton S and the Neutron S. Of the experiments allowed thereafter, while following this theory, to highlight their existence.

Conversely, of the fine or new experiments not coinciding with the theory can, or to call into question the theory - as it of the problem of the black Corps was the case which caused the advent of the quantum Mécanique and the disappearance of the Vitalisme or the thermodynamic Atomisme - or to push the theory and the model to integrate new elements. The example of discovered Neptune is edifying for this reason. The astronomers could make a first experiment, that to measure the trajectory of Uranus. However the theory of Newton gave a trajectory different from that noted. To maintain the theory, Urbain the Glassmaker and, independently, John Adams postulated the existence of a new planet, and according to this assumption predicted its position, which was proven after one second experiment which consisted in directing a telescope at the announced place. It is clear that the interpretation of the first experiment is dependant on the theory, and the second could never have taken place without this same theory and its calculation. Another example is the existence of the Neutrino, supposed by Pauli to explain the continuous spectrum of the Beta decay, as well as the apparent not-conservation of the kinetic Moment.

Modeling and reality

The Histoire of physics seems to show that it is illusory to think that one will end up finding a corpus finished of equations which one will be able to never contradict by experiment. Each theory accepted at one time ends up revealing its limits, and is integrated in a broader theory. The Newtonian theory of the gravitation is valid under conditions where the Speed S are small and which the concerned Masse S are weak, but when speeds approach the Speed of light or that the masses (or in an equivalent way in relativity, energies) become important, it must yield the place to the General relativity. In addition, this one is incompatible with the quantum Mécanique when the scale of study is Microscopique and under conditions of very large energy (for example at the time of the Big Bang or in the vicinity of a Singularité inside a Black hole).

The theoretical physics thus find its limits in measurement and its permanent revival is born in obvious impossibility to reach a perfect state of knowledge and without fault of the Réel. Many philosophers, whose Emmanuel Kant, warned against any belief that the human knowledge of the phenomena can coincide with reality, if there exists. Physics does not describe the world, its conclusions do not carry on the world itself, but on the model which one deduces from some studied parameters. It is an exact science in what the base of the assumptions and parameters considered lead in an exact way to the drawn conclusions.

The modern design of physics, in particular since the discovery of quantum mechanics, is not given generally more like ultimate objective to determine the main causes physical laws, but only to explain of it the how in an approach positivist. One will be able to also retain the idea of Albert Einstein on the work of the physicist: to make physics, it is like emitting theories on the operation of a clock without never being able to open it .

Esthetics, pragmatism and simplicity

Physics has a dimension Esthétique. Indeed, the theorists almost systematically seek to simplify, to unify and to symmetrize the theories. That is made by the reduction of the number of fundamental Constantes (constant G of the gravitation integrated under the same gravitational universe the worlds sublunary and supralunaire), by the meeting of conceptual frameworks before distinct (the theory of Maxwell unified magnetism and electricity, the électrofaible Interaction unified the quantum electrodynamic with the weak Interaction and so on until the construction of the standard Modèle of the Physique of the particles). The research of the symmetry S in the theory, in addition to the fact that by the theorem of Noether they produce constants of the movement spontaneously (as the energy preserves when the equations of the system are invariant temporally), is a vector of beauty of the equations and motivation of the physicists and, since the 20th century, the principal engine of the developments in Theoretical physics.

From the experimental point of view, simplification is a principle of pragmatism. Indeed the development of an experiment requires to control a great number of physical parameters in order to create precisely fixed experimental conditions. The majority of the situations arising spontaneously in nature are very confused and irregular. In addition to exceptional figures like the rainbow, which causes a strong astonishment at the layman, the world on our scale Miss of many principles and theories belonging to disjoined fields of the corpus. The concepts of physics are long to acquire by the physicists themselves. A certain preparation of the experimental device thus allows the demonstration of a phenomenon as purified as possible. All in all, a well contrasted rainbow and Net, to take a poetic image. This experimental requirement malheuresement gives an artificial aspect to physics, in particular during its teaching to a young public. Paradoxically nothing seems as far away from the course of nature as an experiment of physics, only simplification is however required there.

During the history, complex and not very elegant theories from a mathematical point of view can be very effective and dominate of the theories much simpler. The Almageste of Ptolémée, based on a simple geometrical figure, the circle, comprised a great number of constants on which the theory depended, while having made it possible with little error to include/understand the sky during more than thousand years. The standard Modèle describing the Elementary particles also comprises about thirty arbitrary parameters, and yet never no theory was checked in experiments also precisely. However, everyone agrees in the physicists to think that this theory will be sublimated and integrated one day in a simpler and more elegant theory, as the Ptolemaic system disappeared with the profit from the Keplerian theory, then Newtonian.

Technique and physics

History of the Humanity watch that the thought Technique developed well before the physical theories, and with stronger reason mathematized. The Wheel and the lever, the work of materials, in particular the Metallurgy, could be realized without what is called physics. It is by the effort of Rationalité of the Greek thinkers then Arab and, thereafter, the improvement of mathematics, that physics could reveal its conceptual depth. The physical theories then often allowed the improvement of Outil S and Machine S, as well as theirs use.

The 19th century should be waited so that theories give rise to techniques which could not have been born without them. The case of the Laser is exemplary: its invention rests basically on comprehension, by the quantum Mécanique, of the luminous Onde S and the Linéarité their equations. One can obviously quote the Bombe has and the Bombe H like technical creations depending entirely on the physics of their time. GPS functions only by the restricted integration of relativities and general in calculations.

Physics and other sciences

Physics being written in Mathematical terms, it has since its birth have relations more than major with these. Until the 20th century, the mathematicians were most of the time physicists besides (and often philosophers). Of this fact physics was very often the source of major developments in mathematics. For example, the differential Calculus, was invented independently by Leibniz and Newton to in general include/understand dynamics, and the universal gravitation with regard to the second. The development in Fourier series, who became a branch with whole share of the analyzes, was invented by Joseph Fourier to include/understand the diffusion of the Chaleur.

Physical sciences are in relation to other sciences, in particular the Chimie, science of the Molécule S and compounds chemical. They share many fields, such as the quantum Mécanique, the Thermochimie and the electromagnetism. This interdisciplinary field is called the physical Chimie. However, the chemical phenomena sufficiently vast and are varied so that chemistry is generally regarded as a discipline with whole share.

Many other interdisciplinary fields exist in physics. One can mention for example the Astrophysique at the border with the Astronomie, the Biophysique which is with the interface between the Biologie and the Physique statistics inter alia, and more recently the Nanotechnologie S.

Physics and religions

It arrived in the Histoire that the results obtained by physics, and by some other sciences also, enter in conflict with the Religion S. Those indeed define a whole of Croyance S which, in general, include a Représentation world, Univers and of its components.

The prototype of this problem was, at the 17th century, the controversy ptolemeo-copernician, and the judgment of Galileo (1633) which more particularly involved a certain movement of rejection of the Christian religion (Catholique), judged “Obscurantiste” by certain philosophers of the Age of Enlightenment. One of the stakes of this problem was that certain passages of the Bible, for example psalm 93 (92) on God king of the universe, that one could qualify “Cosmologique S”, were written in a direction Géocentrique, or at the very least ambiguous, so that, taken with the letter, they entered in conflict with the theories of physics defined by Galileo, Kepler and Newton. In addition Giordano Bruno was burned in Rome to have affirmed, inter alia, that the universe infinite and was defended the copernicism.

See also: Revolution copernician, Purification of the memory

Initially, the scientists of the 17th century reacted either by rejecting the Philosophie first of the Scolastique, based on the Métaphysique of Aristote (Descartes in Méditations on philosophy first ), or by adhering to dissenting movements Christianisme (case of Pascal, which gave its guarantee to Port-Royal to write a Traduction of the French Bible according to sights Janséniste S). This version was the only elaborate one at the 17th century, and no catholic Théologien was with the height to produce a more consequent version at and the 18th centuries, so that this Bible was used as reference to good number of intellectuals, of which writers, until the 19th century.

Actually, the Église, in the person of the Pape Benoît XIV, authorized the theory of the Héliocentrisme as of the 18th century (in 1741 and 1757), rehabilitating Galileo implicitly, which passed relatively unperceived in the context of the Age of Enlightenment.

The situation started to be clarified at the 19th century, once passed the French revolution and as soon as Christianity could reorganize, when the Christian (Protestant and catholic) realized that the controversy posed of the problems of Exégèse (to return to the texts of origin in Greek or Hebrew) and of Herméneutique (to define rules of interpretation which is not literal). This led to Encyclique S on the study of the biblical texts (by Leon XIII, then Pie XII), defining the relationship between science and the religion, then with translations canonical S of the Bible as from the 20th century (Bible of Jerusalem). After two centuries when there were only three translations of the French Bible, the 19th century thus provides 19 Traductions of the Bible in French, and the 20th century, 22 translations.

More than one rehabilitation of Galileo ( that all the modern Pape S regarded as a large scientist ), the work group wanted by Jean-Paul II was the occasion to clarify the reciprocal relations between the Religion and the Science. Today, the Roman Catholic church is not worried questions of physical structure of the universe. The questions of Foi intervene rather during the application of the theories in the daily life.

Many were the physicists who were either very religious, or ordered themselves. For example, Nicolas Copernic was monk, Edme Mariotte was priest and Georges Lemaître abbot. The explanation is due undoubtedly to the fact that the monks of these times were practically the only well-read men.

In addition, certain religions encouraged the development of the scientific research, as it was the case of the Islam between and the 15th century, which did it besides for religious reasons (see Islamic Sciences and technology), while benefitting very largely from the contribution of the civilizations subjected by Islam (Persian, chaldéenne, Byzantine and Indian, inter alia).

See also: Science of the Middle Ages, Rebirth of XIIe century

In XXIe century, a great number of physicists, and scientists more generally, readily admit to have religious convictions.

It is noted that, in the United States, as in Europe, one realized that should not be taken literally biblical descriptions, which is the joint position of the catholics and the Protestants, taken since the 19th century.

Research

The culture of the research in physics presents a notable difference with that of other sciences with regard to separation between Théorie and Expérience. Since the 20th century, the majority of the physicists are specialized either in Theoretical physics, or in experimental Physique. On the other hand, almost all the famous theorists in Chemistry or Biologie are also experimenters.

The Digital simulation occupies a very important place in research in physics and this since the beginnings of the Informatique. It indeed allows the approximate resolution of mathematical problems which cannot be treated analytically. Many theorists are also numericians.

Principal theories

Although physics is interested in a large variety of systems, certain theories can be attached only to physics as a whole and not with the one of its fields. Each one is supposed just, in a certain field of validity or applicability. For example, the theory of the traditional mechanical accurately describes the movement of an object, provided that (1) its dimensions are much larger than those of a Atome, (2) that its Speed is quite lower than the Speed of light, (3) that it is not too close to an important mass, and (4) that this one is deprived of load. The old theories, such as for example Newtonian mechanics, are still subjects of research in particular in the study of the complex phenomena (example: the Theory of chaos). They constitute the base of any research in physics and very studying in physics, whatever its speciality, is supposed to acquire the bases of each one of them.

Disciplines

Research in contemporary physics is divided into various disciplines which study aspects different from the physical world.

Related disciplines

Many fields of research combine physics with other disciplines.

Close fields

History and philosophy

Tools and methods

Tables and data banks

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