Midisuperspace foam and the cosmological constant

TL;DR

This paper investigates how quantum spacetime foam in a spherically symmetric model might naturally suppress the observable effects of a large cosmological constant, offering insights into the smallness of dark energy.

Contribution

It introduces a midisuperspace model demonstrating classical cancellations and quantum stationary states that could explain the small effective cosmological constant.

Findings

Classical foamy initial data lead to small average expansion.

Quantum stationary states exhibit near-zero probability current.

Model suggests spacetime foam can hide a large cosmological constant.

Abstract

Wheeler's conjectured "spacetime foam" -- large quantum fluctuations of spacetime at the Planck scale -- could have important implications for quantum gravity, perhaps even explaining why the cosmological constant seems so small. Here I explore this problem in a midisuperspace model consisting of metrics with local spherical symmetry. Classically, an infinite class of ``foamy'' initial data can be constructed, in which cancellations between expanding and contracting regions lead to a small average expansion even if $\Lambda$ is large. Quantum mechanically, the model admits corresponding stationary states, for which the probability current is also nearly zero. These states appear to describe a self-reproducing spacetime foam with very small average expansion, effectively hiding the cosmological constant.