Quantum Entropy Bridges to Einstein's Equations
From Quantum Relative Entropy to the Semiclassical Einstein Equations
A new paper argues that the semiclassical Einstein equations emerge from quantum relative entropy, offering a quantum field-theoretic twist on Jacobson's thermodynamic derivation. By linking relative entropy between vacuum and coherent excitations on a Killing horizon to energy flux, and assuming the Bekenstein-Hawking entropy-area law, the authors show how gravity's equations follow naturally. This suggests quantum information underpins even the semiclassical approximation of quantum gravity.
This suggests that quantum information plays a central role in what is often seen as a zeroth order approximation of a theory of quantum gravity, namely quantum field theory in curved spacetimes.