  The old cosmological-constant (CC) problem indicates an inconsistency of the
usual formulation of semiclassical gravity. The usual formulation of
semiclassical gravity also seems to be inconsistent with the conventional
interpretation of quantum mechanics based on the discontinuous wave-function
collapse. By reformulating semiclassical gravity in terms of Bohmian
deterministic particle trajectories, the resulting semiclassical theory avoids
both the old CC problem and the discontinuous collapse problem of the usual
semiclassical theory. The relevance to the new CC problem and to particle
creation by classical gravitational fields is also discussed.
