The inflationary universe scenario is the current paradigm of early-universe cosmology. Inflation has been successful phenomenologically: It not only provides answers to several questions that cannot be addressed in the standard Big Bang (SBB) cosmology, but it also led to the first quantitative and predictive theory for the origin of structure in the universe, a theory whose predictions have been verified to great accuracy by cosmic microwave background (CMB) anisotropy experiments. At present, however, models of inflation suffer from serious conceptual problems that have driven attempts to find alternative paradigms.
Inflationary cosmology is based on the assumption that there was a period in the very early universe during which space underwent accelerated, exponential expansion. 1 The paradigm provides explanations for several puzzles of SBB cosmology. For example, during the period of accelerated expansion, the size of the region that could have been in causal contact increased exponentially. (Causal contact means...
