wave-particle duality: a standalone construct

Louis de Broglie's 1924 doctoral thesis, published in 1925 as Recherches sur la théorie des quanta, minted wave-particle duality as a general principle: he proposed that every material particle, such as an electron, is accompanied by a wave whose length is set by the particle's momentum, extending to all matter the dual behaviour Albert Einstein had shown for light in 1905, when Einstein treated a light wave as a stream of energy quanta to explain the photoelectric effect. The principle holds that a single quantum entity displays wave-like properties, such as interference and diffraction, or particle-like properties, such as a localised impact carrying definite energy and momentum, according to how it is observed, and never both aspects in one measurement. Arthur Compton's 1923 X-ray scattering experiments gave the light quantum a measurable momentum, and Clinton Davisson and Lester Germer's 1927 diffraction of electrons from a nickel crystal confirmed de Broglie's matter waves directly. What makes the principle a landmark is its universality: it applies to photons, electrons, atoms, and larger particles alike, and it underlies the wavelength-momentum relation and the quantum-mechanical formalism that describes both behaviours with one wave function.[1][2][3][4]

Unit

A foundational principle of quantum physics governing the behaviour of quantum entities

Recovery means

Not applicable

Measured by

Shown experimentally: wave behaviour by interference and diffraction patterns, particle behaviour by discrete localised detection events, with the de Broglie wavelength given by the relation lambda = h/p