The relativity of cosmic time is developed within the framework of Cosmological Relativity in five dimensions of space, time and velocity. A general linearized metric element is defined to have the form
, where the coordinates are time
, radial distance
for spatials x, y and z, and velocity v, with c the speed of light in vacuum and t the Hubble-Carmeli time constant. The metric is accurate to first order in
and v/c . The fields
and
are general functions of the coordinates. By showing that
=
, a metric of the form
is obtained from the general metric, implying that the universe is flat. For cosmological redshift z, the luminosity distance relation
is used to fit combined distance moduli from Type 1a supernovae up to z<1.5 and Gamma-Ray Bursts up to z<7, from which a value of
is obtained for the matter density parameter at the present epoch. Assuming a baryon density of
, a rest mass energy of (9.79
+ 0.47) GeV is predicted for the anti-baryonic
and
the particles which decay from a hypothetical
particle. The cosmic aging function
makes good fits to light curve data from two reports of Type 1a supernovae and in fitting to simulated quasar like light curve power spectra separated by redshift
. We determine the multipole of the first acoustic peak of the Cosmic Microwave Background radiation anisotropy to be
and a sound horizon of
on today’s sky.