  Contrary to the conventional wisdom that deviations from standard
thermodynamics originate from the strong coupling to the bath, it is shown that
in quantum mechanics, these deviations originate from the uncertainty principle
and are supported by the non-Markovian character of the dynamics. Specifically,
it is shown that the lower bound of the dispersion of the total energy of the
system, imposed by the uncertainty principle, is dominated by the bath power
spectrum and therefore, quantum mechanics inhibits the system
thermal-equilibrium-state from being described by the canonical Boltzmann's
distribution. We show that for a wide class of systems, systems interacting via
central forces with pairwise-self-interacting environments, this general
observation is in sharp contrast to the classical case, for which the thermal
equilibrium distribution, irrespective of the interaction strength, is
\emph{exactly} characterized by the canonical Boltzmann distribution and
therefore, no dependence on the bath power spectrum is present. We define an
\emph{effective coupling} to the environment that depends on all energy scales
in the system and reservoir interaction. Sample computations in regimes
predicted by this effective coupling are demonstrated. For example, for the
case of strong effective coupling, deviations from standard thermodynamics are
present and, for the case of weak effective coupling, quantum features such as
stationary entanglement are possible at high temperatures.
