  With the simplest proof ever, we justify the significance of quantum-gravity
in non-relativistic quantum mechanics together with the related theories and
experiments. Since the de Broglie wave length is inverse proportional to the
mass, it would descend towards and below the Planck scale 10^{-33} cm for large
masses even at slow non-relativistic motion. The tricky relationship between
gravity and quantum mechanics ---well-known in the relativistic case--- shows
up in non-relativistic motion of massive objects. Hence the gravity-related
modification of their Schr\"odinger equation is m a n d a t o r y. We also
recall the option of an autonomous Newtonian quantum-gravity, a theory
parametrized by hbar and G. On cancellation of c from the Newtonian limit of
Planck scale metric fluctuations is given a new hint.

Quantum Physics;General Relativity and Quantum Cosmology