  Evaluation of gravitational theories by means of cosmological data suffers
from the fact that galaxies are biased tracers of dark matter. Current bias
models focus primarily on high-density regions, whereas low-density regions
carry significant amounts of information relevant to the constraint of dark
energy and alternative gravity theories. Thus, proper treatment of both high
and low densities is important for future surveys. Accordingly, we here present
an interactionless Ising model for this bias, and we demonstrate that it
exhibits a remarkably good fit to both Millennium Simulation and Sloan Digital
Sky Survey data, at both density extremes. The quality of the fit indicates
that galaxy formation is (to first order) an essentially local process
determined by initial conditions.
