# Quantum physics

The quantum physics is the general name of a whole of Théorie S Physique S born at the 20th century. This denomination is opposed to that traditional Physique, the latter having failed in the description of the infinitely small - Atome S, particle S - and in that of certain properties of the electromagnetic Rayonnement. The quantum physics include/understand:

## History

### Black body and ultraviolet catastrophe

According to the classical theories of physics, a black Corps with thermodynamic balance is supposed to radiate an infinite flow. More precisely, the energy radiated by band wavelength must tend towards the infinite one when the wavelength tends towards zero, in the Ultraviolet for the physicists of the time, since neither the X-rays nor the Gamma rays were then known. It is the ultraviolet Catastrophe.

### Introduction of the quanta in physics

It goes back to the work carried out in 1900 by Planck on the radiation of the black body to thermal balance. A heated cavity emits an electromagnetic radiation (light) at once absorptive by the walls. To give an account of the luminous spectrum by the theoretical calculation of the energy exchanges of emission and absorption (of), Planck had to make the assumption that these exchanges are discontinuous and proportional to the frequencies (ν) of the light radiation: dE=nhν.

• N is an integer

• H is the quantum of action which appeared soon as one of the fundamental constants of nature (constant of Planck)
• v is the frequency of the light

### Quantification of the radiation and the atoms

In 1905, following a thermodynamic reasoning in which it gave to the probabilities a physical direction (that of frequencies of states for a system), Einstein was brought to consider that in fact only the energy exchanges are discontinuous, but the energy of the light radiation itself. It showed that this energy is proportional to the frequency of the light wave: E=hν. That immediately gave the explanation of the photoelectric effect observed 20 years before by Hertz.

### Photoelectric effect

E=hν energy brought by the quantum of light to the electron dependant in an atom makes it possible this one to be released if this energy is higher or equal to the binding energy of the electron W. This effect of threshold was unexplainable in the design continues luminous energy of the traditional electromagnetic theory.

### Limits of the traditional electromagnetic theory

Einstein realized whereas this property of the radiation was in irreducible opposition of manner with the traditional electromagnetic theory (worked out by Maxwell). As of 1906, it announced that this theory should be modified in the atomic field. The way in which this modification should be obtained was not obvious since the theoretical physics rested on the use of differential equations, known as Maxwell's equations, corresponding to sizes with continuous variation.

### The quantum assumption

Although because of its power, few physicists were inclined to imagine that the traditional electromagnetic theory could be invalidated, Einstein then endeavoured to highlight other aspects of the atomic phenomena and radiation which broke with traditional description. It thus extended the quantum assumption, beyond the properties of the radiation, with the energy of the atoms, by its work on the specific heats to the low temperatures. It found the cancellation of the specific heats of the bodies to the absolute zero, phenomenon observed but unexplainable by the classical theory. Other physicists (P. Ehrenfest, W. Nernst, H. - has. Lorentz, H. Poincaré) joined it little by little to conclude with the inescapable character from the quantum assumption that Planck itself hesitated to admit. It however was still accepted generally only for the energy exchanges.

## General panorama

The quantum physics brought a conceptual revolution having repercussions until in Philosophie (called into question of the Déterminisme) and in literature (Science-fiction). It allowed many technological applications: nuclear energy, Medical imagery by nuclear Magnetic resonance, Diode, Transistor, Electron microscope and Laser. One century after its design, it is abundantly used in research in theoretical Chimie (quantum Chimie), in physics (quantum Mécanique, Quantum theory of the fields, Physique of the condensed matter, Nuclear physics, Physique of the particles, Astrophysique), in Mathématiques (formalization of the theory of the fields) and, recently, in Informatique (quantum Ordinateur). She is regarded with the General relativity of Einstein as one of the two major theories of the 20th century.

The quantum physics are known to be against-intuitive, shock the “common direction” and to require a difficult mathematical formalism. Feynman, one of largest the theorists specialists in the quantum physics of second half of the 20th century, thus wrote:

Nobody includes/understands really the quantum physics.

The primary reason of these difficulties is that the world of the infinitely small very differently behaves from macroscopic environment to which we are accustomed. Some basic differences which separate these two worlds are for examples:

• the quantification : a certain number of observable, for example the energy emitted by an atom at the time of a transition between excited states, are quantified, i.e. they can take their value only in a together discrete of results. A contrario , traditional mechanics generally predicts that these observable can take any value continuously.

• the Duality wave-particle : the concept of Wave and particle which is separate in traditional mechanics become two facets of the same phenomenon, described in a mathematical way by its Fonction of wave. In particular, the experiment proves that the light can behave like particles (Photon S, highlighted by the photoelectric Effet) or like a wave (Rayonnement producing Interférence S) according to the experimental context, the electron S and other particles also being able to behave in an undulatory way.
• the Principle of uncertainty of Heisenberg : a fundamental Incertitude prevents the simultaneous exact measurement of two combined sizes. It is in particular impossible to obtain a high degree of accuracy to the measure of the Speed of a particle without obtaining a poor precision on its position, and vice versa . This uncertainty is structural and does not depend on the care which the experimenter takes not “to disturb” the system; it constitutes a limit with the precision of all Measuring instrument.
• the principle of a nature which plays dice : If the evolution of a system is indeed deterministic (e.g., the function of wave governed by the equation of Schrödinger), the measurement of a Observable of a system in a known given state can give by chance a value taken in a whole of possible results.
• the observation influences the system observed: During the measurement of observable, a quantum system sees its modified state. This phenomenon, called Reduction of the package of wave, is inherent in measurement and does not depend on the care which the experimenter takes not “to disturb” the system.
• the not-locality or intrication : Of the systems can be intricate so that an interaction in a place of the system has an immediate repercussion in other places. This phenomenon contradicts seemingly the restricted Relativité for which there exists a speed limit with the propagation of any information, the Speed of light; however, the not-locality does not make it possible to transfer from information.
• the contrafactuality : Of the events which could have occurred, but which did not occur, influential on the results of the experiment.

August 1st

## Complete listing of the articles

: Category: Quantum physics

## References

### Popularizing works

• Sciences and future n°662
• Sven Ortoli and Jean-Pierre Pharabod, the Canticle of quantum the , Collection Tests, Editions the Discovery (2004). ISBN 2-7071-4356-1

• Bruce Hake, the Rabbits of Mr Schrodinger or how multiply the quantum universes Edition the Apple tree

• Serge Haroche, Quantum physics , inaugural Lesson at the Collège de France, co-edition Collège de France/Beech (2004).

• Etienne Klein, Small Voyage in the world of the quanta , Collection Fields 557, Flammarion (2004). ISBN 2-08-080063-9

• Banesh Hoffman and Michel Paty, Strange story of the quanta , Collection Point-Sciences 26, the Threshold (1981). ISBN 2-02-005417-5

• Stephan Deligeorges (ED), quantum Le Monde , Collection Point-Sciences 46, the Threshold (1984). ISBN 2-02-008908-4

• Emile Christmas (ED), Matter today , Collection Point-Sciences 24, the Threshold (1981). ISBN 2-02-005739-5

• quantum physics. Cycle of 3 conferences of Etienne Klein in the City of sciences and industry, France.

• Comment the quantum physics was born?
• Pourquoi the quanta are so disconcerting?
• How “to interpret” the quantum physics?
• Thierry Masson, Quantum physics, 100 years of questions, text published in the rationalist Books, number 569 and 570. (2004)

### Historical development of the concepts

• Jagdish Mehra & Helmut Rechenberg, The Historical Development off Quantum Theory , Springer-Verlag (1982-2002), ISBN 0-387-95262-4. Box of 6 volumes, 9 books, 5889 pages (!) Books available séparéments:
• vol. 1: The Quantum Theory off Planck, Einstein, Bohr & Sommerfeld: It' S Foundations & the Small channel off Its Difficulties (1900-1925) , Share 1: ISBN??.
• vol. 1: The Quantum Theory off Planck, Einstein, Bohr & Sommerfeld: It' S Foundations & the Small channel off Its Difficulties (1900-1925) , Share 2: ISBN 0-387-95175-X.
• vol. 2: The Discovery off Quantum Mechanics , ISBN 0-387-95176-8.
• vol. 3: The Formulation off Matrix Mechanics & It' S Modifications. 1925-1926 , ISBN 0-387-95177-6.
• vol. 4, Share 1: The Fundamentals Equations off Quantum Mechanics (1925-1926) and Part 2: The Reception off the New Quantum Mechanics , ISBN 0-387-95178-4.
• vol. 5: Erwin Schrödinger and the Small channel off Wave Mechanics , Share 1: Schrödinger in Vienna and Zurich (1887-1925), ISBN??
• vol. 5: Erwin Schrödinger & the Small channel off Wave Mechanics , Share 2: The Creation off Wave Mechanics: Early Answers & Applications (1925-1926) , ISBN 0-387-95180-6.
• vol. 6: The Completion off Quantum Mechanics (1926-1941) , Share 1: The Probability Interpretation & the Statistical Theory Transformation, the Physical Interpretation and the Empirical & Mathematical Foundations off Quantum Mechanics (1926-1932) , ISBN 0-387-95181-4
• vol. 6: The Completion off Quantum Mechanics (1926-1941) , Share 2: Conceptual The Completion & the Extensions off Quantum Mechanics (1932-1941) - Epilog: Aspects off the Further Development off Quantum Theory (1942-1999) , ISBN 0-387-95182-2.

### Others

• R. Gilmore, Alice with the country of the quanta , the Apple tree-Beech (2000).
• Sven Ortoli and J. - M. Pelhate, quantum Adventure , Belin, 1993
• Martin Gardner, ambidextrous Universe , Threshold, 1995
• Brian Greene, elegant Universe (supercordes and theory M) , Robert Laffont, 2000
• P. Davies, new physics , Flammarion Sciences, 1993
• Murray Freezing-Mann, the Quark and the jaguar. Travels in the middle of the simple one and the complex , Albin Michel Sciences, 1995
• J. - P. Pharabod and B. Worse, the dream of the physicists , Odile Jacob, 1993
• B. of Espagnat, veiled Reality, analyzes quantum concepts , Fayard, 1994
• R. Forward and J. Davis, the Mysteries of the antimatter , Ed.du Rocher, 1991
• Mr. Duquesne, Matière and antimatter , PUF, coll Which I know? , 767,2000
• Physical of the particles , Forum mégascience of OECD, OECD, 1995
• B. of Espagnat/E.Klein, Glances on the matter , Beech, 1993
• Carlos Calle and Al , Supercordes and other strings: Travel in the middle of physics , Dunod, 2004
• Gordon Kane, Supersymétrie , the Apple tree, 2003
• J. Briggs and D. Peat, a turbulent mirror , InterEditions, 1990
• T. Lombry, One century of physics: 1 - The Quantum physics , Aegeus, 2005

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