  The standard cosmological model, based on general relativity with an
inflationary era, is very effective in accounting for a broad range of observed
features of the universe. However, the ongoing puzzles about the nature of dark
matter and dark energy, together with the problem of a fundamental theoretical
framework for inflation, indicate that cosmology may be probing the limits of
validity of general relativity. The early universe provides a testing ground
for theories of gravity, since gravitational dynamics can lead to
characteristic imprints on the CMB and other cosmological observations.
Precision cosmology is in principle a means to constrain and possibly falsify
candidate quantum gravity theories like M theory. Generalized Randall-Sundrum
brane-worlds provide a phenomenological means to test aspects of M theory. I
outline the 1+3-covariant approach to cosmological perturbations in these
brane-worlds, and its application to CMB anisotropies.
