Before Inflation

Abstract

Observations of the cosmic microwave sky are revealing the primordial non-uniformities from which all structure in the Universe grew. The only known physical mechanism for generating the inhomogeneities we see involves the amplification of quantum fluctuations during a period of inflation. Developing the theory further will require progress in quantum cosmology, connecting inflation to a theory of the initial state of the Universe. I discuss recent work within the framework of the Euclidean no boundary proposal, specifically classical instanton solutions and the computation of fluctuations around them. Within this framework, and for a generic inflationary theory, it appears that an additional anthropic constraint is required to explain the observed Universe. I outline an attempt to impose such a constraint in a precise mathematical manner.