Can the universe afford inflation?

TL;DR

This paper compares different methods for evaluating the likelihood of cosmic inflation, finding that traditional semiclassical approaches favor inflation, while newer frameworks disfavor it, highlighting fundamental challenges in early universe modeling.

Contribution

It introduces an alternative semiclassical calculation that favors inflation, contrasting with previous methods that disfavor it, and discusses the fundamental challenges in reconciling these approaches.

Findings

Traditional semiclassical methods favor inflation.

Newer frameworks strongly disfavor inflation.

Reconciling different approaches poses fundamental challenges.

Abstract

Cosmic inflation is envisioned as the ``most likely'' start for the observed universe. To give substance to this claim, a framework is needed in which inflation can compete with other scenarios and the relative likelihood of all scenarios can be quantified. The most concrete scheme to date for performing such a comparison shows inflation to be strongly disfavored. We analyze the source of this failure for inflation and present an alternative calculation, based on more traditional semiclassical methods, that results in inflation being exponentially favored. We argue that reconciling the two contrasting approaches presents interesting fundamental challenges, and is likely to have a major impact on ideas about the early universe.