Below we will evaluate in detail the decoherence process and its alleged ability to solve foundational questions. However, before doing so, it is important to say a few words regarding the usage of density matrices within quantum theory.

Density matrices
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A density matrix is an operator that encodes information about a quantum mechanical system. However, density matrices are used for different purposes and, in different situations, they contain different amounts and kinds of information regarding the quantum mechanical system (or systems) in question (see e.g., [@Sch; @despagnat]).

To begin with, we point out that, according to the standard interpretation of quantum mechanics, all closed or isolated quantum systems possess, at all times, well-defined quantum states. These states are refereed to as *pure* and are usually represented by vectors on an appropriate Hilbert space. However, as is well known, pure states can also be represented by density matrices. In particular, if the pure state of a system is given by $| \psi \rangle$, then one can define its associated density matrix by $\rho_p = | \psi \rangle \langle \psi|$, which satisfies $\rho_p^2=\rho_p$ and $Tr(\rho_p)=1$.[^3] It is clear that, in this pure state case, the density matrix $\rho_p$ contains exactly the 