In quantum mechanics, particles (like atoms and photons)ooze and change their states as they come into and leave contact with other particles. The behavior of a particularly stable subatomic particle, like an electron in an atom, can be predicted only in terms of a probability wave function that describes the likelihood of finding the electron at any particular point.
The Austrian physicist Erwin Schrödinger first proposed the wave equation that underlies quantum mechanics in 1926. The Copenhagen interpretation of his work, developed by Danish physicist Niels Bohr and others in the 1930s, holds that electrons do not have definite positions until they are observed—that is, until they interact with some other form of matter. In 1955, American physicists Eugene Wigner and Hermann Weyl formalized this idea by showing that certain properties (such as spin) of subatomic particles cannot be known for certain until they are measured.