  The gravitational metric tensor implies a variable dielectric tensor of
vacuum around gravitational matter. The curved spacetime in general relativity
is then associated with a polarizable vacuum. It is found that the number
density of the virtual dipoles in vacuum decreases with the distance from the
gravitational centre. This result offers a polarizable vacuum interpretation of
the gravitational force. Also, the anisotropy of vacuum polarization is briefly
discussed, which appeals for observational proof of anisotropic light
propagation in a vacuum altered by gravitational or electromagnetic field.
