It is proposed that an event that constitutes a quantum measurement corresponds to the spontaneous breaking of a symmetry in the measuring device over time.
Since the mechanism of spontaneous symmetry breaking has such a relevant impact for the description of physical systems, its explanation should be based on physical considerations with a direct operational meaning. To this purpose, it is useful to recognize that the operational/experimental description of a physical system (not necessarily quantum!) involves the following elements: the set A of its measurable quantities, briefly called observables ; the measurement of the time evolution of the observables; the set ∑ of configurations or states in which the system may be prepared, according to well defined protocols of experimental preparations; the measurement of an observable A , when the system is in the state ω is operationally defined by the experimental expectation 〈A〉 ω