Page "Copenhagen interpretation" Paragraph 21

Some argue that the concept of the collapse of a " real " wave function was introduced by Heisenberg and later developed by John Von Neumann in 1932.

Heisenberg never used the term collapse, preferring to speak of the wavefunction representing our knowledge of a system, and collapse as the " jumping " of the wavefunction to a new state, representing a " jump " in our knowledge which occurs once a particular phenomenon is registered by the experimenter ( i. e. when an observation takes place ).