Alternatives to cosmological inflation from quantum gravity

Robert Brandenberger

February 17, 2011

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Abstract: I will argue that in spite of its phenomenological success, inflationary cosmology suffers from serious conceptual problems which motivate a search for alternatives. I will then outline two alternatives – “string gas cosmology’ and the “matter bounce scenario’. I will show how one can obtain a scale-invariant spectrum of cosmological perturbations in these scenarios, and discuss how the scenarios might arise from different approaches to quantum gravity, e.g. superstring theory.