Black Crunch

TL;DR

This paper investigates the growth of fluctuations in collapsing cosmologies, proposing that scattering processes lead to a dense black hole gas, culminating in a stationary black hole fluid state in a Big Crunch scenario.

Contribution

It extends classical work on cosmological fluctuations to include scalar fields with improvement terms and hypothesizes a universal black hole fluid final state for Big Crunches.

Findings

Fluctuations grow and can dominate the background.

Scattering leads to a dense black hole gas.

Final state may be a stationary black hole fluid.

Abstract

We study the growth of fluctuations in collapsing cosmologies, extending old work of Lifshitz and Khalatnikov. As examples of systems where the fluctuations have a different composition than the background we study scalar fields with general improvement terms. Fluctuations always grow, and often dominate the homogeneous background. We argue that even for very dilute fluctuations, scattering processes inevitably lead to a dense gas of black holes. This leads us to hypothesize that the generic final state of a Big Crunch is described by a collapsing $p=\rho$ FRW cosmology. We conjecture that the black hole fluid is invariant under the conformal Killing symmetry of this metric, so that the final state is in fact stationary.