  In this paper we investigate whether the holographic principle proposed in
string theory has a classical counterpart in general relativity theory. We show
that there is a partial correspondence: at least in the case of vacuum Petrov
type D spacetimes that admit a non-trivial Killing tensor, which encompass all
the astrophysical black hole spacetimes, there exists a one to one
correspondence between gravity in bulk and a two dimensional classical
conformal scalar field on a null boundary.
