2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/8628Inflationary cosmology has provided a predictive and phenomenologically very successful scenario for early universe cosmology. Attempts to implement inflation using scalar fields, however, lead to models with serious conceptual problems. I will discuss some of the problems, explain why string theory could provide solutions to a subset of these problems, and give a brief overview of ``string gas cosmology'', one of the approaches to merge string theory and early universe cosmology.Plenary talk at PASCOS-04/NathFest, August 2004, to be published in the proceedings (2 minor comments added to this second version)AstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - PhenomenologyHigh Energy Physics - Theorytext