Principle that subatomic particles possess some wavelike characteristics, and that electromagnetic waves , such as light, possess some particlelike characteristics.
In 1905, by demonstrating the photoelectric effect , Albert Einstein showed that light, which until then had been thought of as a form of electromagnetic wave (see electromagnetic radiation ), must also be thought of as localized in packets of discrete energy (see photon ). In 1924 Louis-Victor Broglie proposed that electrons have wave properties such as wavelength and frequency ; their wavelike nature was experimentally established in 1927 by the demonstration of their diffraction . The theory of quantum electrodynamics combines the wave theory and the particle theory of electromagnetic radiation.