  In this paper, we derive an expression for the grand canonical partition
function for a fluid of hot, rotating massless scalar field particles in the
Einstein universe. We consider the number of states with a given energy as one
increases the angular momentum so that the fluid rotates with an increasing
angular velocity. We find that at the critical value when the velocity of the
particles furthest from the origin reaches the speed of light, the number of
states tends to zero. We illustrate how one can also interpret this partition
function as the effective action for a boosted scalar field configuration in
the product of three dimensional de Sitter space and $S^1$. In this case, we
consider the number of states with a fixed linear momentum around the $S^1$ as
the particles are given more and more boost momentum. At the critical point
when the spacetime is about to develop closed timelike curves, the number of
states again tends to zero. Thus it seems that quantum mechanics naturally
enforces the chronology protection conjecture by superselecting the causality
violating field configurations from the quantum mechanical phase space.
