Viscosity in Strongly Interacting Quantum Field Theories from Black Hole Physics

TL;DR

This paper demonstrates that a universal ratio of shear viscosity to entropy density, derived from black hole physics via string theory, acts as a lower bound for strongly interacting quantum fluids, indicating black holes are dual to nearly perfect fluids.

Contribution

It establishes a universal lower bound for shear viscosity to entropy density ratio in strongly interacting quantum field theories using holographic duality.

Findings

The ratio is universally equal to 7/477k_B for a large class of theories.

This ratio may serve as a lower bound for various physical systems.

Black hole horizons are dual to the most ideal, nearly perfect fluids.

Abstract

The ratio of shear viscosity to volume density of entropy can be used to characterize how close a given fluid is to being perfect. Using string theory methods, we show that this ratio is equal to a universal value of $\hbar/4\pi k_B$ for a large class of strongly interacting quantum field theories whose dual description involves black holes in anti--de Sitter space. We provide evidence that this value may serve as a lower bound for a wide class of systems, thus suggesting that black hole horizons are dual to the most ideal fluids.