  This note is to bring to the reader's attention the fact that general
relativity and quantum mechanics differ from each other in one main aspect.
General relativity is based on the diffeomorphism covariant formulation of the
laws of physics while quantum mechanics is constructed such that its
fundamental laws remain invariant to a change of topology. It is the goal of
this paper to show that in order to obtain a complete description of quantum
gravity one has to extend the principle of diffeomorphism invariance from
general relativity in the sense of quantum mechanics i.e. the laws of physics
must be covariant to a change in the topology of spacetime.
