Dimensional reduction in the sky?

Abstract: I review the popular idea that at high energies space-time becomes 2 dimensional, thereby simplifying the task of quantum gravity. This seems to be a common prediction in several approaches to quantum gravity, from Horava-Lifshitz to CDTs (causal dynamical triangulations). I then present some recent work on the cosmological implications of this phenomenon, specifically with regards to implications for the CMB. It turns out that near scale-invariant fluctuations can be obtained even without inflation in *all* of these scenarios (with or without violations of Lorentz invariance). The specific departures from exact scale-invariance, the bispectrum, and the level of gravitational waves could then be discriminators among the many different scenarios.