  We show that states of macroscopic systems with purported absolute negative
temperatures are not stable under small, yet arbitrary, perturbations. We prove
the previous statement using the fact that, in equilibrium, the entropy takes
its maximum value. We discuss that, while Ramsey theoretical reformulation of
the Second Law for systems with negative temperatures is logically correct, it
must be a priori assumed that those states are in thermodynamic equilibrium.
Since we argue that those states cannot occur, reversible processes are
impossible and, thus, Ramsey identification of negative absolute temperatures
is untenable.
