WHAT IS WAVE-FUNCTION COLLAPSE BY MEASUREMENT

On the basis of the many-Hilbert-space approach to quantum measurements, we reformulate the notion of wave-function collapse as a dephasing process, without making use of von Neumann's projection postulate. A ''detector'' is described as an open quantum system, characterized by thermodynamical properties, and endowed with a many-Hilbert-space structure: These features enable us to provoke decoherence and to perform quantum measurements. Our approach is compared to other Copenhagen-based theories in some detail