Inherent nonlinearity of fluid motion and acoustic gravitational wave memory

TL;DR

This paper demonstrates that nonlinear sound waves in a perfect fluid can produce an acoustic analogue of gravitational wave memory, highlighting the nonlinear nature of fluid dynamics independent of Einstein's equations.

Contribution

It introduces the concept of acoustic gravitational wave memory arising from nonlinear fluid dynamics and proposes an experimental setup using Bose-Einstein condensates to observe this phenomenon.

Findings

Nonlinear sound waves can produce an acoustic memory effect.

The effect is due to fluid nonlinearity, not Einstein equations.

Experimental protocol with Bose-Einstein condensates is suggested.

Abstract

We consider the propagation of nonlinear sound waves in a perfect fluid at rest. By employing the Riemann wave equation of nonlinear acoustics in one spatial dimension, it is shown that waves carrying a constant density perturbation at their tails produce an acoustic analogue of gravitational wave memory. For the acoustic memory, which is in general $nonlinear$, the nonlinearity of the effective spacetime dynamics is not due to the Einstein equations, but due to the nonlinearity of the perfect fluid equations. For concreteness, we employ a box-trapped Bose-Einstein condensate, and suggest an experimental protocol to observe acoustic gravitational wave memory.