History of quantum mechanics

The development of quantum mechanics from early proposals about quantized energy to the modern theory of matter and radiation, including its mathematical formulations and later interpretations.

Black-body radiation: Electromagnetic radiation emitted by an ideal absorber whose spectrum depends on its temperature. Its measured spectrum exposed the failure of classical predictions at high frequencies.
Max Planck: German physicist who introduced energy quantization to explain black-body radiation. His 1900 work marks the starting point of quantum theory.
Old quantum theory: A collection of pre-1925 models applying quantization to atoms and radiation without a consistent general framework. It bridges Planck's hypothesis and the more systematic quantum mechanics.
Copenhagen interpretation: A family of interpretations emphasizing quantum probabilities and the role of measurement. It became the influential account associated with Bohr and Heisenberg.
Quantum electrodynamics: The quantum field theory describing interactions between electrically charged particles and electromagnetic radiation. Its development in the 1940s resolved infinities and produced highly precise predictions.
Planck's law: A formula describing the spectrum of black-body radiation through energy quantization. Max Planck introduced it in 1900, beginning the quantum hypothesis.
Albert Einstein: Theoretical physicist who developed relativity and made foundational contributions to quantum theory. His light-quantum proposal explained the photoelectric effect.
Matrix mechanics: A formulation of quantum mechanics based on arrays of quantities and their noncommuting multiplication. Heisenberg, Born, and Jordan developed it as the first modern formulation.
Many-worlds interpretation: An interpretation in which quantum evolution branches into noninteracting outcomes rather than collapsing. Everett proposed it as an alternative to collapse-centered accounts.
Quantum field theory: A framework combining quantum principles with fields and, typically, special relativity. It became the broader language for particle physics beyond nonrelativistic quantum mechanics.

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Robert MillikanNarrower topic: Millikan’s photoelectric measurements helped establish a key empirical relation in early quantum theory.