The universe as a brane

If string theory is on the right track as a description of nature, then our observable universe may be a 3-dimensional membrane surface in a higher-dimensional spacetime. The brane-world picture of the universe, as inspired by string theory, opens up new vistas in cosmology. The extra polarizations of the higher-dimensional graviton, and the additional fields arising from the extra dimensions, bring new features that may leave detectable signatures. Moreover, the hope is that these new ingredients will shed light on the major puzzles associated with the standard cosmological model - in particular, the problem of explaining inflation and the dark energy problem.