P. Busch
Abstract
The quantum measurement problem is formulated in the form of an insolubility theorem that states the impossibility of obtaining, for all available object preparations, a mixture of states of the compound object and apparatus system that would represent definite pointer positions. A proof is given that comprises arbitrary object observables, whether sharp or unsharp, and besides sharp pointer observables a certain class of unsharp pointers, namely, those allowing for the property of pointer value definiteness. A recent result of H. Stein is applied to allow for the possibility that a given measurement may not be applicable to all possible object states but only to a subset of them. The question is raised whether the statement of the insolubility theorem remains true for genuinely unsharp observables. This gives rise to a precise notion of unsharp objectification.