Quintessence cosmology and the cosmic coincidence

Abstract
Within present constraints on the observed smooth energy and its equation of state parameter wQ=P/ρQ, it is important to find out whether the smooth energy is static (cosmological constant) or dynamic (quintessence). The most dynamical quintessence fields observationally allowed are now still fast rolling and no longer satisfy the tracker approximation if the equation of state parameter varies moderately with cosmic scale a=1/1+z. We are optimistic about distinguishing between a cosmological constant and appreciably dynamic quintessence by measuring average values for the effective equation of state parameter wQ(a). However, reconstructing the quintessence potential from observations of any scale dependence wQ(a) appears problematic in the near future. For our flat universe, at present dominated by smooth energy in the form of either a cosmological constant (LCDM) or quintessence (QCDM), we calculate the asymptotic collapsed mass fraction to be maximal at the observed smooth energy-matter ratio R02. Identifying this collapsed fraction as a conditional probability for habitable galaxies, we infer that the prior distribution is flat in R0 or Ωm0. Interpreting this prior as a distribution over theories, rather than as a distribution over unobservable subuniverses, leads us to heuristic predictions about the class of future quasistatic quintessence potentials.