# Alternative Decohering Histories in Quantum Mechanics. (arXiv:1905.05859v1 [quant-ph])

We continue our efforts to understand, within the framework of the quantum

mechanics of the universe as a whole, the quasiclassical realm of familiar

experience as a feature emergent from the Hamiltonian of the elementary

particles and the initial condition of the universe. Quantum mechanics assigns

probabilities to exhaustive sets of alternative decoherent histories of the

universe. We introduce and define the notion of strong decoherence. We replace

the notion of maximal sets of alternative decohering histories by defining the

more useful concept of "full" sets of alternative strongly decohering

histories. These full sets fall into equivalence classes each of which is

characterized by a basis in Hilbert space. Finally we describe our continuing

efforts to find measures of classicality --- measures that could be applied to

such full sets of alternative strongly decohering so as to characterize a

quasiclassical realm.