  We present a case that current observations may already indicate new
gravitational physics on cosmological scales. The excess of power seen in the
Lyman-alpha forest and small-scale CMB experiments, the anomalously large bulk
flows seen both in peculiar velocity surveys and in kinetic SZ, and the higher
ISW cross-correlation all indicate that structure may be more evolved than
expected from LCDM. We argue that these observations find a natural explanation
in models with infinite-volume (or, at least, cosmological-size) extra
dimensions, where the graviton is a resonance with a tiny width. The
longitudinal mode of the graviton mediates an extra scalar force which speeds
up structure formation at late times, thereby accounting for the above
anomalies. The required graviton Compton wavelength is relatively small
compared to the present Hubble radius, of order 300-600 Mpc. Moreover, with
certain assumptions about the behavior of the longitudinal mode on super-Hubble
scales, our modified gravity framework can also alleviate the tension with the
low quadrupole and the peculiar vanishing of the CMB correlation function on
large angular scales, seen both in COBE and WMAP. This relies on a novel
mechanism that cancels a late-time ISW contribution against the primordial
Sachs-Wolfe amplitude.
