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Analogue Gravity

Carlos Barcelo, Stefano Liberati, Matt Visser

TL;DR

The paper surveys analogue gravity as a framework to study curved spacetime physics using non-gravitational systems, highlighting the acoustic metric as the simplest instantiation. It traces the field from early optical and acoustic ideas through the classical era of dumb holes and BECs to contemporary experiments with hydrodynamic vortices, meta-materials, and quantum fluids of light. Core contributions include a detailed derivation of the acoustic metric, a comprehensive catalogue of models, and a thorough discussion of Hawking radiation, horizon stability, and dispersion effects within analogue contexts. The review emphasizes the cross-disciplinary fertilization between fluid dynamics, condensed matter, optics, and gravity, and it outlines future experimental prospects and foundational questions in emergent spacetime paradigms.

Abstract

Analogue gravity is a research programme that explores analogues of general relativistic gravitational fields within other physical systems, particularly but not exclusively in condensed matter systems, with the aim of gaining new insights into related problems. Analogue models of gravity boast a long and distinguished history, dating back to the early years of general relativity. This review article delves into the history, aims, results, and future prospects of various analogue models. We begin by presenting a particularly simple example of an analogue model, then traverse the rich history and complex array of models discussed in the literature. The last decade has witnessed significant and sustained advances in analogue gravity, resulting in hundreds of published articles, workshops, and books. The future of the analogue gravity programme looks promising, with rapid technological advances on the experimental front and the potential for analogue models to inspire innovative approaches to the problem of quantum gravity on the theoretical front. Most of all, these recent years have seen the rise of an unprecedented collaboration and interplay between different communities that we believe will set a new standard for interdisciplinary research in the years to come.

Analogue Gravity

TL;DR

The paper surveys analogue gravity as a framework to study curved spacetime physics using non-gravitational systems, highlighting the acoustic metric as the simplest instantiation. It traces the field from early optical and acoustic ideas through the classical era of dumb holes and BECs to contemporary experiments with hydrodynamic vortices, meta-materials, and quantum fluids of light. Core contributions include a detailed derivation of the acoustic metric, a comprehensive catalogue of models, and a thorough discussion of Hawking radiation, horizon stability, and dispersion effects within analogue contexts. The review emphasizes the cross-disciplinary fertilization between fluid dynamics, condensed matter, optics, and gravity, and it outlines future experimental prospects and foundational questions in emergent spacetime paradigms.

Abstract

Analogue gravity is a research programme that explores analogues of general relativistic gravitational fields within other physical systems, particularly but not exclusively in condensed matter systems, with the aim of gaining new insights into related problems. Analogue models of gravity boast a long and distinguished history, dating back to the early years of general relativity. This review article delves into the history, aims, results, and future prospects of various analogue models. We begin by presenting a particularly simple example of an analogue model, then traverse the rich history and complex array of models discussed in the literature. The last decade has witnessed significant and sustained advances in analogue gravity, resulting in hundreds of published articles, workshops, and books. The future of the analogue gravity programme looks promising, with rapid technological advances on the experimental front and the potential for analogue models to inspire innovative approaches to the problem of quantum gravity on the theoretical front. Most of all, these recent years have seen the rise of an unprecedented collaboration and interplay between different communities that we believe will set a new standard for interdisciplinary research in the years to come.

Paper Structure

This paper contains 167 sections, 1 theorem, 278 equations, 19 figures, 1 table.

Table of Contents

  1. Introduction
  2. Overview
  3. Motivations
  4. Going further
  5. Acoustics: The Simplest Example of an Analogue Spacetime
  6. Background
  7. Geometrical acoustics
  8. Physical acoustics
  9. General features of the acoustic metric
  10. Horizons and ergo-regions
  11. Surface gravity
  12. Regaining geometric acoustics
  13. Example: Vortex geometry
  14. Example: Slab geometry
  15. Example: Conformal Schwarzschild geometry
  16. ...and 152 more sections

Key Result

theorem 1

If a fluid is barotropic and inviscid, and the flow is irrotational (though possibly time dependent) then the equation of motion for the velocity potential describing a linearized acoustic disturbance $\phi_1$ around some assumed background flow $\phi_0$ is identical to the d'Alembertian equation of Under these conditions, the propagation of sound is governed by an acoustic metric -- $[g_0]_{\mu\n

Figures (19)

  • Figure 1: Artistic impression of cascading sound cones (in the geometrical acoustics limit) forming an acoustic black hole when supersonic flow tips the sound cones past the vertical.
  • Figure 2: Artistic impression of trapped waves (in the physical acoustics limit) forming an acoustic black hole when supersonic flow forces the waves to move downstream.
  • Figure 3: A moving fluid will drag sound pulses along with it.
  • Figure 4: A moving fluid will tip the "sound cones" as it moves. Supersonic flow will tip the sound cones past the vertical.
  • Figure 5: A moving fluid can form "trapped surfaces" when supersonic flow tips the sound cones past the vertical.
  • ...and 14 more figures

Theorems & Definitions (3)

  • theorem 1
  • remark thmcounterremark
  • proof