Energy conditions allow eternal inflation

TL;DR

This paper demonstrates that eternal inflation can occur without violating energy conditions by considering the quantum state selection process, challenging previous assumptions about energy condition violations.

Contribution

It introduces a framework showing eternal inflation is compatible with energy conditions by focusing on quantum state selection rather than single-state violations.

Findings

Eternal inflation does not require violation of energy conditions.

Quantum state selection allows for upward fluctuations without violating energy conditions.

Energy conditions restrict state evolution, not the process of eternal inflation.

Abstract

Eternal inflation requires upward fluctuations of the energy in a Hubble volume, which appear to violate the energy conditions. In particular, a scalar field in an inflating spacetime should obey the averaged null energy condition, which seems to rule out eternal inflation. Here we show how eternal inflation is possible when energy conditions (even the null energy condition) are obeyed. The critical point is that energy conditions restrict the evolution of any single quantum state, while the process of eternal inflation involves repeatedly selecting a subsector of the previous state, so there is no single state where the conditions are violated.