The first serious attack by Einstein on the "orthodox" conception took place during the Fifth Solvay International Conference on " Electrons and Photons " in 1927. Einstein pointed out how it was possible to take advantage of the (universally accepted) laws of conservation of energy and of impulse (momentum) in order to obtain information on the state of a particle in a process of interference which, according to the principle of indeterminacy or that of complementarity, should not be accessible.