Geodesic congruences in acoustic spacetimes and the role of Raychaudhuri equation

TL;DR

This paper investigates how the Raychaudhuri equation describes sound wave propagation in acoustic spacetimes, providing insights into analogue gravity models like black holes and cosmology.

Contribution

It applies the Raychaudhuri equation to acoustic spacetimes, highlighting its robustness and limitations in analogue gravity models.

Findings

Raychaudhuri equation effectively describes sound propagation in acoustic spacetimes

Limits of acoustic analogues are identified and discussed

Insights into black hole and cosmological models via acoustic analogues

Abstract

It has been known that the propagation of sound in fluids can be used to model acoustic spacetimes. These acoustic spacetimes offer analogue models for gravity. We use the Raychaudhuri equation to study the propagation of sound in these fluids, which, via the Eikonal approximation, correspond to null geodesic congruences in the acoustic spacetimes. We explore this within the acoustic analogues of black holes and cosmological spacetimes. The robustness of the Raychaudhuri equation and the limits of the acoustic analogue are emphasised.