  In previous works, we suggested considering a (3+1)D quantum gravitational
field as an evolution of a (2+1)D renormalized quantum gravitational field
along the direction of the gravitational force. The starting point of the
suggestion is a derivation of a unique hypersurface which looks effectively
like (2+1)D from the point of view of Einstein equations in (3+1)D. In this
paper, we derive such unique hypersurfaces for different kinds of stationary
spherical metrics. We find that these hypersurfaces exist whenever all the
components of the gravitational force field vanish on the hypersurface. We
discuss the implication of this result and the necessary further work.
