From Quantum Relative Entropy to the Semiclassical Einstein Equations

Researchers Dorau and Much demonstrate that the semiclassical Einstein equations can be derived from quantum relative entropy and its relationship to changes in horizon surface area, using modular theory applied to quantum fields on bifurcate Killing horizons. Their approach generalizes Jacobson's thermodynamic derivation of Einstein's equations by replacing classical entropy with quantum relative entropy, suggesting that quantum information is fundamental to understanding curved spacetime quantum field theory. The work was published in Physical Review Letters in 2026.