Asymptotic silence in loop quantum cosmology

TL;DR

This paper explores how asymptotic silence, a state of causal disconnection at high energies, emerges in loop quantum cosmology due to quantum effects, transitioning from Lorentzian to Euclidean space at Planck-scale densities.

Contribution

It provides a quantum gravity perspective on asymptotic silence, linking it to polymerization effects in loop quantum cosmology and identifying a transition at critical energy density.

Findings

Asymptotic silence occurs at half the critical energy density in the model.

Above this density, space becomes Euclidean and causally disconnected.

The transition suggests a phase change from Lorentzian to Euclidean geometry.

Abstract

The state of asymptotic silence, characterized by causal disconnection of the space points, emerges from various approaches aiming to describe gravitational phenomena in the limit of large curvatures. In particular, such behavior was anticipated by Belinsky, Khalatnikov and Lifshitz (BKL) in their famous conjecture put forward in the early seventies of the last century. While the BKL conjecture is based on purely classical considerations, one can expect that asymptotic silence should have its quantum counterpart at the level of a more fundamental theory of quantum gravity, which is the relevant description of gravitational phenomena in the limit of large energy densities. Here, we summarize some recent results which give support to such a possibility. More precisely, we discuss occurrence of the asymptotic silence due to polymerization of space at the Planck scale, in the framework of loop quantum cosmology. In the discussed model, the state of asymptotic silence is realized at the energy density $\rho = \rho_c/2$, where $\rho_c$ is the maximal allowed energy density, being of the order of the Planck energy density. At energy densities $\rho > \rho_c/2$, the universe becomes 4D Euclidean space without causal structure. Therefore, the asymptotic silence appears to be an intermediate state of space between the Lorentzian and Euclidean phases.