Stochastic stabilization of chaos and the cosmic microwave background

The cosmic microwave background (CMB) is a contemporary echo of the Big Bang. The recently announced WMAP 1-year sky maps(1) provide exceptionally accurate data for the CMB, making it possible to probe the physics of the early Universe down to an unprecedented level of detail. Fluctuations in the CMB have a distribution that is close to Gaussian (i.e. normal).(2) There has been considerable interest in identifying physical mechanisms that might lead to deviations from the Gaussian distribution.(2,3) One class of cosmological models that have been much studied are those in which the Universe has constant negative curvature; all photon trajectories are then exponentially unstable and the Gaussian distribution of the CMB fluctuations, has been related to general properties of quantum wave-functions in chaotic systems.(4-6) Inhomogeneities in the distribution of matter imply a non-constant curvature. Here we show that, surprisingly, random perturbations in the curvature can stabilize photon trajectories. We argue that this leads to quantifiable non-Gaussian fluctuations in the CMB, as well as having other potentially important cosmological consequences.