- History of quantum mechanics
The

**history of**as this interlaces withquantum mechanics **history of**began essentially with the 1838 discovery ofquantum chemistry cathode rays byMichael Faraday , during the 1859-1860 winter statement of theblack body radiation problem byGustav Kirchhoff , the 1877 suggestion byLudwig Boltzmann that the energy states of a physical system could be discrete, and the 1900 quantum hypothesis byMax Planck that any energy radiating atomic system can theoretically be divided into a number of discrete ‘energy elements’ "ε" (epsilon ) such that each of these energy elements is proportional to thefrequency "ν" with which they each individually radiateenergy , as defined by the following formula: :$epsilon\; =\; h\; u\; ,$where "h" is a numerical value called

Planck’s constant . Then, in 1905, to explain thephotoelectric effect (1839), i.e. that shining light on certain materials can function to eject electrons from the material,Albert Einstein postulated, as based on Planck’s quantum hypothesis, thatlight itself consists of individual quantum particles, which later came to be calledphotons (1926). The phrase "quantum mechanics" was first used inMax Born 's 1924 paper "Zur Quantenmechanik". In the years to follow, this theoretical basis slowly began to be applied to chemical structure, reactivity, and bonding.**Overview**In 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 ablack body . In 1905,Einstein explained thephotoelectric effect by postulating that light, or more specifically allelectromagnetic 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:cquote|According to the assumption to be contemplated here, when a light ray is spreading from a point, the energy is not distributed continuously over ever-increasing spaces, but consists of a finite number of "energy quanta" that are localized in points in space, move without dividing, and can be absorbed or generated only as a whole.

This statement has been called the most revolutionary sentence written by a physicist of the twentieth century. [*cite book | last = Folsing | first = Albrecht | title = Albert Einstein: A Biography | publisher = trans. Ewald Osers, Viking | year = 1997*] These "energy quanta" later came to be called "

These theories, though successful, were strictly phenomenological: during this time, there was no rigorous justification for quantization aside, perhaps, for

last =McCormmach

first =Russell

title = Henri Poincaré and the Quantum Theory

journal = Isis

volume = 58

issue = 1

pages = 37-55

date = Spring, 1967] Citation

last =Irons

first =F. E.

title = Poincaré's 1911–12 proof of quantum discontinuity interpreted as applying to atoms

journal = American Journal of Physics

volume = 69

issue = 8

pages = 879-884

date = August, 2001] They are collectively known as the "old quantum theory".

The phrase "quantum physics" was first used in Johnston's "Planck's Universe in Light of Modern Physics" (1931).

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 *Citation last = Hanle first = P.A. title = Erwin Schrodinger's Reaction to Louis de Broglie's Thesis on the Quantum Theory. journal = Isis volume = 68 issue = 4 pages = 606-609 date = December 1977*] . Schrödinger subsequently showed that the two approaches were equivalent.

Heisenberg formulated his

The field of

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

**Timeline**

The following timeline shows the key steps and contributors in the precursory development of

**Founding experiments**

*Thomas Young's

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*The study of

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** [ http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/davger2.html The Davisson-Germer experiment, which demonstrates the wave nature of the electron] *] in the

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*The

*The experimental verification of

**References**

**ee also**

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**External links**

* [*http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/The_Quantum_age_begins.html A History of Quantum Mechanics*]

* [*http://www.oberlin.edu/physics/dstyer/StrangeQM/history.html A Brief History of Quantum Mechanics*]

* [*http://quantum-history.mpiwg-berlin.mpg.de/ Homepage of the Quantum History Project*]

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