  The search for purely virtual quanta has attracted interest in the past. We
consider various proposals and compare them to the concept of fake particle, or
"fakeon". In particular, the Feynman-Wheeler propagator, which amounts to using
the Cauchy principal value inside Feynman diagrams, violates renormalizability,
unitarity and stability, due to the coexistence of the prescriptions $\pm
i\epsilon $. We contrast the Feynman, fakeon and Feynman-Wheeler prescriptions
in ordinary as well as cut diagrams. The fakeon does not have the problems of
the Feynman-Wheeler propagator and emerges as the correct concept of purely
virtual quantum. It allows us to make sense of quantum gravity at the
fundamental level, and places it on an equal footing with the standard model.
The resulting theory of quantum gravity is perturbative up to an incredibly
high energy.
