Acoustic analog of gravitational wave

We explore nonlinear perturbations in different static fluid systems. We find that the equations, corresponding to the perturbation of the integrals of motion, i.e., Bernoulli’s constant and the mass flow rate, satisfy the massless scalar field equation in a time dependent acoustic metric. When one is interested up to the second order behavior of the perturbations, the emergent time dependent acoustic metric of the system, derived from the massless scalar field equations of the perturbations of the integrals of motion, has some astounding similarities with the metric describing gravitational wave in Minkowski spacetime.

Figure 1

Demonstrating the ring torus region of space (the blue region in the figure) within which all the BEC atoms are effectively trapped (left) and the Thomas-Fermi number density distribution (right).