  The Schrodinger equation for a macroscopic number of particles is linear in
the wave function, deterministic, and invariant under time reversal. In
contrast, the concepts used and calculations done in statistical physics and
condensed matter physics involve stochasticity, nonlinearities,
irreversibility, top-down effects, and elements from classical physics. This
paper analyzes several methods used in condensed matter physics and statistical
physics and explains how they are in fundamental ways incompatible with the
above properties of the Schrodinger equation. The problems posed by reconciling
these approaches to unitary quantum mechanics are of a similar type as the
quantum measurement problem. This paper therefore argues that rather than
aiming at reconciling these contrasts one should use them to identify the
limits of quantum mechanics. The thermal wave length and thermal time indicate
where these limits are for (quasi-)particles that constitute the thermal
degrees of freedom.
