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Noise induced inflation

We consider a closed Friedmann-Robertson-Walker Universe driven by the back reaction from a massless, non-conformally coupled quantum scalar field. We show that the back-reaction of the quantum field is able to drive the cosmological scale factor over the barrier of the classical potential so that if the universe starts near zero scale factor (initial singularity) it can make the transition to an exponentially expanding de Sitter phase, with a probability comparable to that from quantum tunneling processes. The emphasis throughout is on the stochastic nature of back reaction, which comes from the quantum fluctuations of the fundamental fields.