Black Crunch

TL;DR

This work investigates the fate of fluctuations in contracting cosmologies and proposes that generic Big Crunch endpoints are dense black hole fluids with the stiff equation of state $p=\rho$, described by a collapsing $p=\rho$ FRW geometry. Building on the Lifshitz–Khalatnikov analysis, the authors extend to improved fluctuations via scalar fields with nonminimal (improvement) terms and analyze conformal coupling, finding that fluctuations generically grow toward the crunch. They argue that scattering among fluctuations leads to a dense gas of black holes which merges into a BH fluid that saturates the holographic bound, effectively removing observable singular behavior and rendering the end state stationary under the conformal Killing symmetry of the $p=\rho$ FRW metric. The proposed Black Crunch provides a potential mechanism for singularity resolution and ties together gravitational instability, black hole gas dynamics, and holography, with implications for duality-based perspectives in string/M-theory.

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 $p=ρ$ 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.