  One of the goals of current cosmological studies is the determination of the
expansion and acceleration rates of the universe as functions of redshift, and
the determination of the properties of the dark energy that can explain these
observations. Here the expansion and acceleration rates are determined directly
from the data, without the need for the specification of a theory of gravity,
and without adopting an a priori parameterization of the form or redshift
evolution of the dark energy. We use the latest set of distances to SN standard
candles from Riess et al. (2004), supplemented by data on radio galaxy standard
ruler sizes, as described by Daly and Djorgovski (2003, 2004). We find that the
universe transitions from acceleration to deceleration at a redshift of about
0.4. The standard "concordance model" provides a reasonably good fit to the
dimensionless expansion rate as a function of redshift, though it fits the
dimensionless acceleration rate as a function of redshift less well. The
expansion and acceleration rates are then combined with a theory of gravity to
determine the pressure, energy density, and equation of state of the dark
energy as functions of redshift. Adopting General Relativity as the correct
theory of gravity, the redshift trends for the pressure, energy density, and
equation of state of the dark energy out to redshifts of about one are
determined, and are found to be generally consistent with the concordance
model.
