  Drawing from a thought experiment that we conduct, we propose that a virtual
graviton gives rise to a black hole geometry when its momentum surpasses a
certain threshold value on the Planck scale. This hypothesis implies that the
propagator of a virtual graviton, that possesses momentum surpassing this
threshold, vanishes. Consequently, a Feynman diagram containing this type of
graviton propagator does not add to the overall amplitude. This mechanism
suggests the feasibility of formulating an ultraviolet-finite four-dimensional
quantum gravitational theory. The elementary particles including the gravitons
are treated as point particles in this formulation.
