Before the Bang: Wormholes at the Dawn of the Universe

TL;DR

This paper explores Euclidean wormholes as potential initial states of the universe, highlighting their advantages over traditional proposals and their relevance for early-universe cosmology within quantum gravity frameworks.

Contribution

It advances the understanding of Euclidean wormholes as initial conditions, broadening the class of relevant saddle points and integrating them into early-universe models.

Findings

Wormholes retain relevance of Euclidean-saddles in cosmological wavefunctions.

They broaden the class of regular saddles for inflating universes.

Wormholes help resolve issues in the no-boundary proposal.

Abstract

This essay discusses recent progress on Euclidean wormholes as candidate contributions to the Universe's initial quantum state. The comparison with the Hartle-Hawking no-boundary proposal highlights both a conceptual affinity and genuine advance: wormholes retain the relevance of Euclidean-saddles as encoders of properties of cosmological wavefunctions, while they broaden the class of regular saddles that are physically relevant for inflating universes and are capable of resolving issues that plague the no-boundary proposal. The principal achievement of the wormhole program is to enlarge the semiclassical initial-condition land-scape in a way that is physically rich, conforms with Holographic expectations and as such becomes increasingly relevant for early-universe model building, within UV complete theories of quantum gravity.