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One of the goals of current cosmological studies is the determination of theexpansion and acceleration rates of the universe as functions of redshift, andthe determination of the properties of the dark energy that can explain theseobservations. Here the expansion and acceleration rates are determined directlyfrom the data, without the need for the specification of a theory of gravity,and without adopting an a priori parameterization of the form or redshiftevolution of the dark energy. We use the latest set of distances to SN standardcandles from Riess et al. (2004), supplemented by data on radio galaxy standardruler sizes, as described by Daly and Djorgovski (2003, 2004). We find that theuniverse transitions from acceleration to deceleration at a redshift of about0.4. The standard "concordance model" provides a reasonably good fit to thedimensionless expansion rate as a function of redshift, though it fits thedimensionless acceleration rate as a function of redshift less well. Theexpansion and acceleration rates are then combined with a theory of gravity todetermine the pressure, energy density, and equation of state of the darkenergy as functions of redshift. Adopting General Relativity as the correcttheory of gravity, the redshift trends for the pressure, energy density, andequation of state of the dark energy out to redshifts of about one aredetermined, and are found to be generally consistent with the concordancemodel.Comment: 8 pages, 5 figures. Invited presentation at Coral Gables 200

international journal of modern physics a

DIRECT DETERMINATIONS OF THE REDSHIFT BEHAVIOR OF THE PRESSURE, ENERGY DENSITY, AND EQUATION OF STATE OF THE DARK ENERGY AND THE ACCELERATION OF THE UNIVERSE