  We consider a linearized, effective quantum theory of gravitation in which
gravity weakens at energies higher than ~10^-3 eV in order to accommodate the
apparent smallness of the cosmological constant. Such a theory predicts
departures from the static Newtonian inverse-square force law on distances
below ~0.05 mm. However, we show that such a modification also leads to changes
in the long-range behavior of gravity and is inconsistent with observed
gravitational lenses.
