  Whereas the total energy in zero-point fluctuations of the particle physics
vacuum gives rise to the cosmological constant problem, differences in the
vacuum give rise to real physical phenomena, such as the Casimir effect. Hence
we consider the zero-point energy bound between two parallel conducting plates
-- proxy for a solid slice of cosmological constant -- as a convenient
laboratory in which to investigate the gravitation and inertia of vacuum
energy. We calculate the Casimir effect in a weak gravitational field,
obtaining corrections to the vacuum stress-energy and attractive force on the
plates due to the curvature of spacetime. These results suggest that if the
cosmological constant is due to zero-point energy then it is susceptible to
fluctuations induced by gravitational sources.
