In physics, a quantum leap or jump is the change of an electron from one energy state to another within an atom. It is discontinuous; electrons jump from one energy level to another instantaneously, with no intervening or intermediary condition. The phenomenon contradicts classical theories, which expect energy levels to be continuous. Quantum leaps are the sole cause of the emission of electromagnetic radiation, including light, which occurs in the form of quantized units called photons. Ironically, when laymen use the term colloquially, they use it to describe large jumps in progress, when in reality a quantum leap is a very small change of state.