Analogue simulations of quantum gravity with fluids (2402.16136v1)

Abstract: The recent technological advances in controlling and manipulating fluids have enabled the experimental realization of acoustic analogues of gravitational black holes. A flowing fluid provides an effective curved spacetime on which sound waves can propagate, allowing the simulation of gravitational geometries and related phenomena. The last decade has witnessed a variety of hydrodynamic experiments testing disparate aspects of black hole physics culminating in the recent experimental evidence of Hawking radiation and Penrose superradiance. In this Perspective, we discuss the potential use of analogue hydrodynamic systems beyond classical general relativity towards the exploration of quantum gravitational effects. These include possible insights into the information-loss paradox, black hole physics with Planck-scale quantum corrections, emergent gravity scenarios and the regularization of curvature singularities. We aim at bridging the gap between the non-overlapping communities of experimentalists working with classical and quantum fluids and quantum-gravity theorists, illustrating the opportunities made possible by the latest experimental and theoretical developments in these important areas of research

• The paper demonstrates that fluid dynamics can simulate quantum gravity by replicating phenomena such as acoustic horizons and Hawking radiation.
• It outlines experimental techniques that use sound waves in fluids to mimic curved spacetime and validate theoretical gravity models.
• Findings suggest that controlled fluid analogues offer valuable insights into backreaction effects and the emergence of gravitational dynamics.

Analogue Simulations of Quantum Gravity with Fluids

The paper "Analogue simulations of quantum gravity with fluids" explores the intriguing intersection of fluid dynamics and theoretical physics, particularly in the context of simulating quantum gravity phenomena. The authors propose that the recent technological advancements in controlling fluid systems offer a novel experimental platform to paper gravitational analogues, a concept traditionally dominated by complex and often empirically inaccessible models within astrophysics and cosmology.

Background and Motivation

Traditional explorations of quantum gravity phenomena, such as Hawking radiation from black holes, have largely relied on observational astrophysics and theoretical constructs which are not easily subjected to direct experimentation. Fluid-based analogue gravity systems provide a scalable and controlled environment to investigate these quantum mechanical effects in laboratory settings. These systems exploit the dynamics of sound waves in flowing fluids, which can mimic various aspects of gravitational geometries seen in cosmic structures like black holes.

Key Concepts and Experimental Evidence

The paper reviews several key concepts:

• Acoustic Horizons: Just as light cones delineate causal structures in spacetime around massive bodies, sound waves in an inhomogeneous fluid can simulate curved spacetime geometries. An acoustic event horizon forms in regions where the flow velocity exceeds the local speed of sound, preventing sound waves from escaping, akin to a black hole's event horizon.
• Phenomena Observed: The paper discusses how certain emergent phenomena, such as Hawking radiation, which were traditionally theoretical, have been experimentally observed in fluid systems. Key experiments have confirmed Hawking-like radiation and Penrose superradiance in analogue systems, underscoring the robustness of these phenomena across different physical implementations.

Quantum Gravity Implications

The authors delve into the potential implications of these hydrodynamic simulations for understanding quantum gravitational effects:

• Backreaction and Information Paradox: Discussing the possibility of gaining insights into the information paradox, the paper highlights how analogue systems can simulate backreaction effects, where fluctuations affect the background geometry, leading to unitary evolution despite apparent classical inconsistencies.
• Emergent Geometries: The complex behavior within fluids suggests a scenario where spacetime curvature and gravity emerge from underlying microscopic quantum dynamics. This mirrors many emergent gravity theories, challenging the notion of spacetime as a fundamental structure.

Future Directions

The work points towards future research directions that could exploit these analogue systems to tackle outstanding questions in quantum gravity:

• Modified Dispersion Relations: Analogue systems inherently possess modified dispersion relations with natural length scales breaking Lorentz symmetry, offering insights into potential high-energy modifications in gravitational theories.
• Emergent Gravity and Holography: These systems allow experimental investigations into concepts such as the holographic principle, where gravitational dynamics in a bulk spacetime can be related to quantum field theories on a boundary.

Conclusions

The use of fluid systems as analogue models offers a compelling framework for exploring foundational issues in gravity and quantum mechanics. As experimental capabilities continue to evolve, these systems could unlock new pathways for validating theories that remain beyond the reach of direct celestial observations. Further research could elucidate the extent to which analogue gravity can inform us about the nature of quantum gravity, including potential insights into spacetime's emergence from more primal quantum informational units. As such, this interdisciplinary approach not only bridges theoretical and experimental physics but also promises to deepen our understanding of quantum gravity's underlying principles.