The old quantum theory is a collection of results from the years 1900–1925 which predate modern quantum mechanics.
The theory was never complete or self-consistent, was rather a set of heuristic corrections to classical mechanics.
The theory is now understood as the semi-classical approximation to modern quantum mechanics.
Some Main Ideas about Old Quantum Theory:
In 1926 Erwin Schrödinger found a completely quantum mechanical wave-equation, which reproduced all the successes of the old quantum theory without ambiguities and inconsistencies.
😊Throughout the 1910s and well into the 1920s, numerous problems were attacked using the old quantum theory with mixed results.
😊In 1924, Louis de Broglie introduced the wave theory of matter, which was extended to a semiclassical equation in support of matter waves by Albert Einstein a short time later.
😊Sommerfeld made a crucial contribution by quantizing the z-part of the angular momentum, which in the old quantum era was called space quantization.
😊Molecular rotation and vibration spectra were understood and the electron’s spin was discovered, leading to the confusion of half-integer quantum numbers.
😊Einstein, followed by Debye, applied quantum principles to the motion of atoms, explaining the specific heat anomaly.
😊Schrödinger’s wave mechanics developed separately from matrix mechanics until Schrödinger and others proved the two methods predicted the same experimental consequences.
😊Sommerfeld’s model was much closer to the modern quantum mechanical picture than Bohr’s.
😊Bose and Einstein gave the correct quantum statistics in support of photons.
😊In 1913, Niels Bohr identified the correspondence principle and usual it to formulate a model of the hydrogen atom which explained the line spectrum.
😊Max Planck introduced the zero point energy and Arnold Sommerfeld semiclassically quantized the relativistic hydrogen atom.
😊In the 1950s Joseph Keller updated Bohr-Sommerfeld quantization using Einstein’s interpretation of 1917, now familiar as Einstein–Brillouin–Keller method.
😊Hendrik Kramers explained the Stark effect.
Source:
[1] Wikipedia Contributors. “Old Quantum Theory.” Wikipedia, Wikimedia Foundation, 9 Oct. 2020, en.wikipedia.org/wiki/Old_quantum_theory. Accessed 8 Nov. 2020.
[2] pixy.org. “Nano Technology Quantum Image.” Pixy.org, 13 July 2020, pixy.org/5945129/. Accessed 8 Nov. 2020.