= History of quantum mechanics
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The discovery of the <photon> was one of the major initiators of quantum mechanics.
Light was very well known to be a wave through <diffraction> experiments. So how could it also be a particle???
This was a key development for people to eventually notice that the <electron> is also a wave.
This process "started" in 1900 with <Planck's law> which was based on discrete energy packets being exchanged as exposed at <On the Theory of the Energy Distribution Law of the Normal Spectrum by Max Planck (1900)>.
This ideas was reinforced by <Einstein>'s explanation of the <photoelectric effect> in 1905 in terms of <photon>.
In the next big development was the <Bohr model> in 1913, which supposed non-<classical physics> new quantization rules for the <electron> which explained the <hydrogen emission spectrum>. The quantization rule used made use of the <Planck constant>, and so served an initial link between the emerging quantized nature of <light>, and that of the <electron>.
The final phase started in 1923, when <Louis de Broglie> proposed that in analogy to photons, <electrons> might also be waves, a statement made more precise through the <de Broglie relations>.
This event opened the floodgates, and soon <matrix mechanics> was published in <quantum mechanical re-interpretation of kinematic and mechanical relations by Heisenberg (1925)>, as the first coherent formulation of <quantum mechanics>.
It was followed by the <Schrödinger equation> in 1926, which proposed an equivalent <partial differential equation> formulation to <matrix mechanics>, a mathematical formulation that was more familiar to <physicists> than the matrix ideas of Heisenberg.
<Inward Bound by Abraham Pais (1988)> summarizes his views of the main developments of the subjectit:
\Q[
* Planck's on the discovery of the quantum theory (1900);
* Einstein's on the light-quantum (1905);
* <Bohr model>[Bohr's on the hydrogen atom] (1913);
* Bose's on what came to be called quantum statistics (1924);
* Heisenberg's on what came to be known as <matrix mechanics> (1925);
* and Schroedinger's on wave mechanics (1926).
]
Bibliography:
* https://physics.stackexchange.com/questions/18632/good-book-on-the-history-of-quantum-mechanics on <Physics Stack Exchange>
* https://www.youtube.com/watch?v=5hVmeOCJjOU A Brief History of Quantum Mechanics by <Sean Carroll> (2020) Given at the <Royal Institution>.