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 (). 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 w₀₄0. Barotropic models give substantially disjoint predictions from quintessence, except in the limit of. They are also interesting in that they simultaneously can ameliorate the coincidence problem and yet ``predict'' a value of w-1.