Quantum creation and inflationary universes: a critical appraisal

TL;DR

This paper critically examines the scenarios of inflation beginning at the universe's inception versus from a prior non-inflationary phase, highlighting conceptual and theoretical challenges in each case.

Contribution

It provides a comparative analysis of inflationary origins, emphasizing the limitations and conditions necessary for each scenario to address the horizon problem.

Findings

Inflation from the universe's inception faces quantum mechanical applicability issues.

Starting from a non-inflationary phase requires a singularity and specific equation of state conditions.

Only certain non-inflationary phases can solve the horizon problem.

Abstract

We contrast the possibility of inflation starting a) from the universe's inception or b) from an earlier non-inflationary state. Neither case is ideal since a) assumes quantum mechanical reasoning is straightforwardly applicable to the early universe; while case b) requires that a singularity still be present. Further, in agreement with Vachaspati and Trodden [1] case b) can only solve the horizon problem if the non-inflationary phase has equation of state $\gamma<4/3$.