  The early cosmic inflation, when taken along with the recent observations
that the universe is currently dominated by a low density vacuum energy, leads
to at least two potential problems which modern cosmology must address. First,
there is the old cosmological constant problem, with a new twist: the
coincidence problem. Secondly, cosmology still lacks a model to predict the
observed current cosmic acceleration and to determine whether or not there is a
future exit out of this state (as previously in the inflationary case). This
constitutes (what is called here) a dynamical problem. In this article a
framework is proposed to address these two problems, based on treating the
cosmic background vacuum (dark) energy as both dynamical and interacting. The
universe behaves as a vacuum-driven cosmic engine which, in search of
equilibrium, always back-reacts to vacuum-induced accelerations by increasing
its inertia (internal energy) through vacuum energy dissipation. The process
couples cosmic vacuum (dark) energy to matter to produce future-directed
increasingly comparable amplitudes in these fields by setting up oscillations
in the decaying vacuum energy density and corresponding sympathetic ones in the
matter fields. By putting bounds on the relative magnitudes of these coupled
oscillations the model offers a natural and conceptually simple channel to
discuss the coincidence problem, while also suggesting a way to deal with the
dynamical problem. A result with useful observational implications is an
equation of state w(t) which specifically predicts a variable, quasi-periodic,
acceleration for the current universe. This result can be directly tested by
future observational techniques such as SNAP.
