Aetherizing Lambda: Barotropic fluids as dark energy

We examine the class of barotropic fluid models of dark energy, in which the pressure is an explicit function of the density, p=f(rho). Through general physical considerations we constrain the asymptotic past and future behaviors and show that this class is equivalent to the sum of a cosmological constant and a decelerating perfect fluid, or aether, with w(AE)>= 0. Barotropic models give substantially disjoint predictions from quintessence, except in the limit of Lambda CDM. They are also interesting in that they simultaneously can ameliorate the coincidence problem and yet predict a value of w approximate to-1.