EMERGENCE OF CLASSICALITY FOR PRIMORDIAL FLUCTUATIONS - CONCEPTS AND ANALOGIES

We clarify the way in which cosmological perturbations of quantum orig in, produced during inflation, assume classical properties. Two featur es play an important role in this process: First, the dynamics of fluc tuations which are presently on large cosmological scales leads to a v ery peculiar state (highly squeezed) that is indistinguishable, in a p recise sense, from a classical stochastic process. This holds for almo st all initial quantum states. Second, the process of decoherence by i nteraction with the environment distinguishes the field amplitude basi s as the robust pointer basis. We discuss in detail the interplay betw een these features and use simple analogies such as the foe quantum pa rticle to illustrate the main conceptual issues.