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Understanding of the nature of dark energy, which appears to drive the expansion of the universe, is one of the central problems of physical cosmology today. In an earlier paper Daly & Djorgovski (2003) we proposed a novel method to determine the expansion rate and the deceleration parameter in a largely model-independent way, directly from the data on coordinate distances. Here we expand this methodology to include measurements of the pressure of dark energy, its normalized energy density, and the equation of state parameter as functions of redshift. We then apply this methodology to a new, combined data set of distances to supernovae and radio galaxies.
Daly et al. (Fri,) studied this question.