  Using the final version of the VLA FIRST survey (Becker et al. 2003), the
optical Sloan Digital Sky Survey Data Release 3 (DR3) quasar list and a series
of carefully selected criteria, we have defined the largest homogeneous
population of double-lobed sources. With the precise sample definition, the
increased depth and sensitivity of the survey data, the large size of the
dataset, and our self-consistent method of analysis, which addresses many of
the problems associated with previous work in the area, we are able to: a)
explore the correlations between the intrinsic properties of the double-lobed
radio sources (the results are also confirmed by a non-parametric analysis) and
study their evolution, b) place more interesting and tighter constraints on the
cosmological parameters, distinguish among the different cosmology models, and
determine the impact of the angular size-redshift studies in cosmology, c)
further our understanding of the behavior of the intergalactic medium (IGM)
density as a function of redshift and shed more light to the quasar-radio
galaxy unification issue.
