  We propose to include gravity in quantum field theory non-perturbatively, by
modifying the propagators so that each virtual particle in a Feynman graph move
in the space-time determined by the four-momenta of the other particles in the
same graph. By making additional working assumptions, we are able to put this
idea at work in a simplified context, and obtain a modified Feynman propagator
for the massless neutral scalar field. Our expression shows a suppression at
high momentum, strong enough to entail finite results, to all loop orders, for
processes involving at least two virtual particles.
