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## History of quantum mechanics
The where ## Additional recommended knowledge
## OverviewIn short, in 1900, German physicist Max Planck introduced the idea that energy is quantized, in order to derive a formula for the observed frequency dependence of the energy emitted by a black body. In 1905, Einstein explained the photoelectric effect by postulating that light, or more specifically all electromagnetic radiation, can be divided into a finite number of "energy quanta" that are localized points in space. From the introduction section of his March 1905 quantum paper, “On a heuristic viewpoint concerning the emission and transformation of light”, Einstein states:
This statement has been called the most revolutionary sentence written by a physicist of the twentieth century. These theories, though successful, were strictly phenomenological: there was no rigorous justification for quantization (aside, perhaps, for Henri Poincaré's discussion of Planck's theory in his 1912 paper The phrase "quantum physics" was first used in Johnston's In 1924, the French physicist Louis de Broglie put forward his theory of matter waves by stating that particles can exhibit wave characteristics and vice versa. This theory was for a single particle and derived from special relativity theory. Building on de Broglie's approach, modern quantum mechanics was born in 1925, when the German physicists Werner Heisenberg and Max Born developed matrix mechanics and the Austrian physicist Erwin Schrödinger invented wave mechanics and the non-relativistic Schrödinger equation as an approximation to the generalised case of de Broglie's theory (see Hanle (1977)). Schrödinger subsequently showed that the two approaches were equivalent. Heisenberg formulated his uncertainty principle in 1927, and the Copenhagen interpretation started to take shape at about the same time. Starting around 1927, Paul Dirac began the process of unifying quantum mechanics with special relativity by proposing the Dirac equation for the electron. The Dirac equation achieves the relativistic description of the wavefunction of an electron that Schrödinger failed to obtain. It predicts electron spin and led Dirac to predict the existence of the positron. He also pioneered the use of operator theory, including the influential bra-ket notation, as described in his famous 1930 textbook. During the same period, Hungarian polymath John von Neumann formulated the rigorous mathematical basis for quantum mechanics as the theory of linear operators on Hilbert spaces, as described in his likewise famous 1932 textbook. These, like many other works from the founding period still stand, and remain widely used. The field of quantum chemistry was pioneered by physicists Walter Heitler and Fritz London, who published a study of the covalent bond of the hydrogen molecule in 1927. Quantum chemistry was subsequently developed by a large number of workers, including the American theoretical chemist Linus Pauling at Cal Tech, and John C. Slater into various theories such as Molecular Orbital Theory or Valence Theory. Beginning in 1927, attempts were made to apply quantum mechanics to fields rather than single particles, resulting in what are known as quantum field theories. Early workers in this area included P.A.M. Dirac, W. Pauli, V. Weisskopf, and P. Jordan. This area of research culminated in the formulation of quantum electrodynamics by R.P. Feynman, F. Dyson, J. Schwinger, and S.I. Tomonaga during the 1940s. Quantum electrodynamics is a quantum theory of electrons, positrons, and the electromagnetic field, and served as a role model for subsequent quantum field theories. The theory of quantum chromodynamics was formulated beginning in the early 1960s. The theory as we know it today was formulated by Politzer, Gross and Wilzcek in 1975. Building on pioneering work by Schwinger, Higgs, Goldstone, Glashow, Weinberg and Salam independently showed how the weak nuclear force and quantum electrodynamics could be merged into a single electroweak force. ## TimelineThe following timeline shows the key steps and contributors in the precursory development of quantum mechanics and quantum chemistry:
## Founding experiments- Thomas Young's double-slit experiment demonstrating the wave nature of light (c1805)
- Henri Becquerel discovers radioactivity (1896)
- Joseph John Thomson's cathode ray tube experiments (discovers the electron and its negative charge) (1897)
- The study of black body radiation between 1850 and 1900, which could not be explained without quantum concepts.
- The photoelectric effect: Einstein explained this in 1905 (and later received a Nobel prize for it) using the concept of photons, particles of light with quantized energy
- Robert Millikan's oil-drop experiment, which showed that electric charge occurs as
*quanta*(whole units), (1909) - Ernest Rutherford's gold foil experiment disproved the plum pudding model of the atom which suggested that the mass and positive charge of the atom are almost uniformly distributed. (1911)
- Otto Stern and Walther Gerlach conduct the Stern-Gerlach experiment, which demonstrates the quantized nature of particle spin (1920)
- Clinton Davisson and Lester Germer demonstrate the wave nature of the electron
^{[2]}in the Electron diffraction experiment (1927) - Clyde L. Cowan and Frederick Reines confirm the existence of the neutrino in the neutrino experiment (1955)
- Claus Jönsson`s double-slit experiment with electrons (1961)
- The Quantum Hall effect, discovered in 1980 by Klaus von Klitzing. The quantized version of the Hall effect has allowed for the definition of a new practical standard for electrical resistance and for an extremely precise independent determination of the fine structure constant.
- The experimental verification of quantum entanglement by Alain Aspect in 1982.
## References**^**Folsing, Albrecht (1997).*Albert Einstein: A Biography*. trans. Ewald Osers, Viking.**^**The Davisson-Germer experiment, which demonstrates the wave nature of the electron
- Hanle, P.A. (1977) Erwin Schrodinger's Reaction to Louis de Broglie's Thesis on the Quantum Theory. Isis, Vol. 68, No. 4 (Dec., 1977), pp. 606-609
## See also |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "History_of_quantum_mechanics". A list of authors is available in Wikipedia. |