  A generic prediction of the standard cosmology, based on general relativity
(GR), dark matter and the cosmological constant (and more generally, smooth
dark energy), is that, the two gravitational potentials describing the spatial
and temporal scalar perturbations of the universe are equivalent. Modifications
in GR or dark energy clustering in general violate this relation. Thus this
ratio serves as a smoking gun of the dark universe. We propose a method to
extract this ratio at various cosmological scales and redshifts from a set of
measurements, in a model independent way. The ratio measured by future surveys
has strong discriminating power for a variety of dark universe scenarios.
