  It has been demonstrated that quantum vacuum energy gravitates according to
the equivalence principle, at least for the finite Casimir energies associated
with perfectly conducting parallel plates. We here add further support to this
conclusion by considering parallel semitransparent plates, that is,
delta-function potentials, acting on a massless scalar field, in a spacetime
defined by Rindler coordinates (tau,x,y,xi). Fixed xi in such a spacetime
represents uniform acceleration. We calculate the force on systems consisting
of one or two such plates at fixed values of xi. In the limit of large Rindler
coordinate xi (small acceleration), we recover (via the equivalence principle)
the situation of weak gravity, and find that the gravitational force on the
system is just Mg, where g is the gravitational acceleration and M is the total
mass of the system, consisting of the mass of the plates renormalized by the
Casimir energy of each plate separately, plus the energy of the Casimir
interaction between the plates. This reproduces the previous result in the
limit as the coupling to the delta-function potential approaches infinity.
