Wave-particle duality is a term used to describe the modeling of nature by both wave theory and particle theory. In essence, physical phenomena (e.g. electrons, photons, etc.) can exhibit varying degrees (sometimes determined by the experiment performed) of wave-like behavior and/or particle-like behavior (i.e., the phenomena can best be described by wave related equations or equations that treat phenomena as particles).

In its most usual form, particle-wave duality is a concept generally related to microscopic particles, more specifically their behavior as both particles and waves. This seems like a contradiction in terms because waves and particles are mutually exclusive. This seemingly contradictory statement arises because the concepts of particles and waves were developed from observations of macroscopic objects.

In 1905, German-American physicist Albert Einstein was concerned with explaining the photoelectric effect by extending German physicist Maxwell Planck's concept of energy quantization to electromagnetic radiation...