Magdalena Zych, University of Queensland
Mass-superselection rule (MSR) is a statement that in the non-relativistic quantum mechanics superpositions of states with different masses are unphysical. While MSR features in most quantum physics textbooks, its status and the physical meaning are still open questions: On one hand, its original derivation is formally inconsistent, on the other, a consistent approach does not yield any superselection rule... The modern view on this puzzle is that MSR arises dynamically, as a result of a yet to be understood decoherence mechanism. In this talk I will present the resolution of the MSR puzzle -- fully within the standard formalism, and without postulating any new mechanisms. In fact, the resolution will come for free once we understand two issues: what is the operational meaning of the non-relativistic regime for composite systems, and how the notion of mass parameter arises in that regime.