Quantum mechanics

Quantum mechanics is the physical theory describing matter and energy at atomic and subatomic scales. It predicts measurement outcomes probabilistically and represents some physical quantities as discrete values.

Wave function: A mathematical object encoding a quantum system’s state and the probabilities of measurement outcomes. It represents the state from which quantum predictions are calculated.
Hilbert space: A complete vector space with an inner product, used to represent quantum states and their relationships. Quantum state vectors and operators are defined within this mathematical setting.
Black-body radiation: Electromagnetic radiation emitted by an idealized object in thermal equilibrium. Its spectrum prompted Planck's quantized-energy proposal.
Classical mechanics: The theory describing the motion of macroscopic bodies through forces, positions, and velocities. It predicts definite trajectories where quantum mechanics predicts distributions of outcomes.
Atomic physics: The study of atoms, their structure, and their interactions with radiation and other particles. Quantum mechanics accounts for atomic energy levels and spectra.
Schrödinger equation: A differential equation governing how a nonrelativistic quantum state changes over time. It specifies continuous state evolution between measurements.
Quantum state: A mathematical description of a physical system that determines probabilities for possible measurement outcomes. It is the central object whose evolution and measurement the theory predicts.
Planck's law: A formula describing the spectral distribution of radiation emitted by a black body at a given temperature. It fit the measured spectrum using discrete energy exchanges.
Classical electromagnetism: The classical theory describing electric and magnetic fields and their interaction with charges. Its continuous-field description differs from quantum accounts of light and matter.
Quantum chemistry: The application of quantum theory to molecular structure, bonding, and chemical reactions. It explains chemical bonds through quantum states of electrons.

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