Uncertainty Principle

Uncertainty Principle, in quantum mechanics, theory stating that it is impossible to specify simultaneously the position and momentum of a particle, such as an electron, with precision. Also called the indeterminacy principle, the theory further states that a more accurate determination of one quantity will result in a less precise measurement of the other, and that the product of both uncertainties is never less than Planck's constant, named after the German physicist Max Planck. Of very small magnitude, the uncertainty results from the fundamental nature of the particles being observed. In quantum mechanics, probability calculations therefore replace the exact calculations of classical mechanics.

Formulated in 1927 by the German physicist Werner Heisenberg, the uncertainty principle was of great significance in the development of quantum mechanics. Its philosophic implications of indeterminacy created a strong trend of mysticism among scientists who interpreted the concept as a violation of the fundamental law of cause and effect. Other scientists, including Albert Einstein, believed that the uncertainty involved in observation in no way contradicted the existence of laws governing the behavior of the particles or the ability of scientists to discover these laws.