  By considering (non-relativistic) quantum mechanics as it is done in practice
in particular in condensed-matter physics, it is argued that a deterministic,
unitary time evolution within a chosen Hilbert space always has a limited
scope, leaving a lot of room for embedding the quantum-classical transition
into our current theories without recurring to difficult-to-accept
interpretations of quantum mechanics. Nonunitary projections to initial and
final states, the breaking of time-reversal symmetry, a change of Hilbert
space, and the introduction of classical concepts such as external potentials
or localized atomic nuclei are widespread in quantum mechanical calculations.
Furthermore, quantum systems require classical environments that enable the
symmetry breaking that is necessary for creating the atomic configurations of
molecules and crystals. This paper argues that such classical environments are
provided by finite-temperature macroscopic systems in which the range of
quantum correlations and entanglement is limited. This leads to classical
behavior on larger scales, and to collapse-like events in all dynamical
processes that become coupled to the thermalized degrees of freedom.
