Why Does Inflation Start at the Top of the Hill?

TL;DR

This paper explains why the universe likely began in an unstable de Sitter state, using quantum cosmology and the no boundary proposal, with implications for theories like M-Theory.

Contribution

It introduces a top down quantum cosmological approach to explain the universe's initial state, emphasizing the role of Hawking-Moss instantons in tunneling.

Findings

Most probable initial state is an unstable de Sitter space.

Quantum tunneling via Hawking-Moss instanton explains universe's emergence.

Approach applicable to M-Theory frameworks.

Abstract

We show why the universe started in an unstable de Sitter state. The quantum origin of our universe implies one must take a `top down' approach to the problem of initial conditions in cosmology, in which the histories that contribute to the path integral, depend on the observable being measured. Using the no boundary proposal to specify the class of histories, we study the quantum cosmological origin of an inflationary universe in theories like trace anomaly driven inflation in which the effective potential has a local maximum. We find that an expanding universe is most likely to emerge in an unstable de Sitter state, by semiclassical tunneling via a Hawking-Moss instanton. Since the top down view is forced upon us by the quantum nature of the universe, we argue that the approach developed here should still apply when the framework of quantum cosmology will be based on M-Theory.