What did we learn from studying acoustic black holes ?

TL;DR

This paper reviews how studying acoustic black holes helps understand the robustness of Hawking radiation against high-frequency physics and explores their implications for black hole evaporation and experimental verification.

Contribution

It demonstrates that the properties of Hawking phonons are insensitive to high-frequency modifications, supporting the universality of Hawking radiation.

Findings

Hawking phonons are insensitive to high-frequency physics.

Acoustic black holes provide insights into black hole evaporation.

Analogy aids in experimental and theoretical studies of Hawking radiation.

Abstract

The study of acoustic black holes has been undertaken to provide new insights about the role of high frequencies in black hole evaporation. Because of the infinite gravitational redshift from the event horizon, Hawking quanta emerge from configurations which possessed ultra high (trans-Planckian) frequencies. Therefore Hawking radiation cannot be derived within the framework of a low energy effective theory; and in all derivations there are some assumptions concerning Planck scale physics. The analogy with condensed matter physics was thus introduced to see if the asymptotic properties of the Hawking phonons emitted by an acoustic black hole, namely stationarity and thermality, are sensitive to the high frequency physics which stems from the granular character of matter and which is governed by a non-linear dispersion relation. In 1995 Unruh showed that they are not sensitive in this respect, in spite of the fact that phonon propagation near the (acoustic) horizon drastically differs from that of photons. In 2000 the same analogy was used to establish the robustness of the spectrum of primordial density fluctuations in inflationary models. This analogy is currently stimulating research for experimenting Hawking radiation. Finally it could also be a useful guide for going beyond the semi-classical description of black hole evaporation.