  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 $ds^2 = (1+\phi)
c^2 dt^2 - dr^2 + (1+\psi) \tau^2 dv^2$, where the coordinates are time $t$,
radial distance $r=\sqrt{x^2 + y^2 + z^2}$ for spatials $x$, $y$ and $z$, and
velocity $v$, with $c$ the speed of light in vacuum and $\tau$ the
Hubble-Carmeli time constant. The metric is accurate to first order in $t/\tau$
and $v/c$. The fields $\phi$ and $\psi$ are general functions of the
coordinates. By showing that $\phi = \psi$, a metric of the form $ds^2 = c^2
dt^2 - dr^2 + \tau^2 dv^2$ is obtained from the general metric, implying that
the universe is flat. For cosmological redshift $z$, the luminosity distance
relation $D_L (z,t) = r (1 + z) / \sqrt{1 - t^2 / \tau^2}$ is used to fit
combined distance moduli from Type Ia Supernovae up to $z < 1.5$ and Gamma-Ray
Bursts up to $z < 7$, from which a value of $\Omega_M = 0.800 \pm 0.080$ is
obtained for the matter density parameter at the present epoch. Assuming a
baryon density of $\Omega_B = 0.038 \pm 0.004$, a rest mass energy of $( 9.79
\pm 0.47 ) \, {\rm GeV}$ is predicted for the anti-baryonic $\bar{Y}$ and the
$\Phi^{*}$ particles which decay from a hypothetical $\bar{X}_1$ particle. The
cosmic aging function $g_1(z,t)= ( 1 + z) ( 1 - t^2 / \tau^2 )$ 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
$\Delta{z} \approx 1$. We determine the multipole of the first acoustic peak of
the Cosmic Microwave Background radiation anisotropy to be $l \approx 224 \pm
5$ and a sound horizon of $\theta_{sh0} \approx (0.805 \pm 0.020 ) {}^{\circ}$
on today's sky.
