Looking back in time beyond the big bang

TL;DR

This paper explores how string theory's duality symmetries could allow us to observe traces of a pre-big bang phase, emphasizing the role of classical radiation back reaction in connecting this phase to current cosmological observations.

Contribution

It proposes a cosmological model where string theory dualities enable looking beyond the big bang, highlighting the importance of radiation back reaction in smoothing the transition.

Findings

Radiation back reaction isotropizes the universe after pre-big bang contraction.

String dualities suggest observable imprints of pre-big bang phases.

Classical effects can connect pre-big bang to current cosmology.

Abstract

String theory can (in principle) describe gravity at all curvature scales, and can be applied to cosmology to look back in time beyond the Planck epoch. The duality symmetries of string theory suggest a cosmological picture in which the imprint of a primordial, pre-big bang phase could still be accessible to present observations. The predictive power of such a scenario relies, however, on our ability to connect in a smooth way the pre-big bang to the present cosmological regime. Classical radiation back reaction seems to play a key role to this purpose, by isotropizing and turning into a final expansion any state of anisotropic contraction possibly emerging from the pre-big bang at the string scale.