Editing History of physics (section)

===Quantum mechanics===
{{further|History of quantum mechanics}}
[[File:Max Planck 1878.GIF|thumb|left|upright|[[Max Planck]] (1858–1947)]]
Although relativity resolved the electromagnetic phenomena conflict demonstrated by Michelson and Morley, a second theoretical problem was the explanation of the distribution of electromagnetic radiation emitted by a [[black body]]; experiment showed that at shorter wavelengths, toward the ultraviolet end of the spectrum, the energy approached zero, but classical theory predicted it should become infinite. This glaring discrepancy, known as the [[ultraviolet catastrophe]], was solved by the new theory of [[quantum mechanics]]. Quantum mechanics is the theory of [[atom]]s and subatomic systems. Approximately the first 30 years of the 20th century represent the time of the conception and evolution of the theory. The basic ideas of quantum theory were introduced in 1900 by Max Planck (1858–1947), who was awarded the [[Nobel Prize for Physics]] in 1918 for his discovery of the quantified nature of energy. The quantum theory (which previously relied in the "correspondence" at large scales between the quantized world of the atom and the continuities of the "[[Physics in the Classical Limit|classical]]" world) was accepted when the [[Compton Effect]] established that light carries momentum and can scatter off particles, and when [[Louis de Broglie]] asserted that matter can be seen as behaving as a wave in much the same way as electromagnetic waves behave like particles ([[wave–particle duality]]).

[[File:Heisenberg 10.jpg|thumb|upright|left|[[Werner Heisenberg]] (1901–1976)]]

In 1905, Einstein used the quantum theory to explain the photoelectric effect, and in 1913 the Danish physicist [[Niels Bohr]] used the same constant to explain the stability of [[Rutherford model|Rutherford's atom]] as well as the frequencies of light emitted by hydrogen gas. The quantized theory of the atom gave way to a full-scale quantum mechanics in the 1920s. New principles of a "quantum" rather than a "classical" mechanics, formulated in [[Matrix mechanics|matrix-form]] by [[Werner Heisenberg]], [[Max Born]], and [[Pascual Jordan]] in 1925, were based on the probabilistic relationship between discrete "states" and denied the possibility of [[causality]]. Quantum mechanics was extensively developed by Heisenberg, [[Wolfgang Pauli]], [[Paul Dirac]], and [[Erwin Schrödinger]], who established an equivalent theory based on waves in 1926; but Heisenberg's 1927 "[[uncertainty principle]]" (indicating the impossibility of precisely and simultaneously measuring position and momentum) and the "[[Copenhagen interpretation]]" of quantum mechanics (named after Bohr's home city) continued to deny the possibility of fundamental causality, though opponents such as Einstein would metaphorically assert that "God does not play dice with the universe".<ref name="Harvtxt|Kragh|1999">{{Harvtxt|Kragh|1999}}</ref> The new quantum mechanics became an indispensable tool in the investigation and explanation of phenomena at the atomic level. Also in the 1920s, the Indian scientist [[Satyendra Nath Bose]]'s work on [[photon]]s and quantum mechanics provided the foundation for [[Bose–Einstein statistics]], the theory of the [[Bose–Einstein condensate]].

{{anchor|spin–statistics}} The [[spin–statistics theorem]] established that any particle in quantum mechanics may be either a [[boson]] (statistically Bose–Einstein) or a [[fermion]] (statistically [[Fermi–Dirac statistics|Fermi–Dirac]]). It was later found that all [[Elementary particle|fundamental]] bosons transmit forces, such as the photon that transmits electromagnetism.

Fermions are particles "like electrons and nucleons" and are the usual constituents of [[matter]]. Fermi–Dirac statistics later found numerous other uses, from astrophysics (see [[Degenerate matter]]) to [[semiconductor]] design.

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