OBSERVATIONS IN QUANTUM MECHANICS AND THE “COLLAPSE OF THE WAVE FUNCTION”

The paper analyses the measurement process on the basis of the interpretation of the wave function, or more generally the density matrix, as describing our knowledge of the system observed. There has to be a division between the system, as described, and the observer, but usually there is wide flexibility in placing this division within the chain of correlations involved in the measurement. This chain must, in particular, involve three steps: (1) a correlation between the quantity to be observed and the apparatus, (2) and uncontrolled interaction which leads to the loss of information required by the uncertainty principle, and (3) the recognition of the result by the observer.