  Weak gravitational lensing provides a means of testing the long-range
properties of gravity. Current measurements are consistent with standard
Newtonian gravity and inconsistent with substantial modifications on Mpc
scales. The data allows long range gravity to deviate from a 1/r potential only
on scales where standard cosmology would use normal gravity but be dominated by
dark matter. Thus, abnormal gravity theories must introduce two fine-tuning
scales -- an inner scale to explain flat rotation curves and an outer scale to
force a return to Newtonian gravity on large scales -- and these scales must
coincidently match the scales produced by the dark matter theory after evolving
the universe for 10 billion years starting from initial conditions which are
exquisitely determined from the cosmic microwave background.
