  Recent measurements of the cosmological constant or cosmic vacuum in Type Ia
SN observations (Riess et al.1998, Perlmutter et al. 1999) imply that $\Omega
(t)$ is exactly unity or nearly unity at any epoch of cosmic evolution. No fine
tuning is needed to describe this phenomenon with the standard cosmological
model based on the Type Ia SN data. A time-independent symmetry relation
between vacuum and matter is basically behind the observed near-parabolic
expansion.
