The paper by Jonathan Sorce explores the concept of geometric modular flow in quantum field theory, focusing on its implications for understanding energy and entropy in quantum gravity. The Unruh effect, which describes how observers in Minkowski spacetime experience a thermal bath due to their boost motion, is a key example of geometric modular flow. Sorce initiates a general study of settings where geometric modular flow can arise, proving that any such flow must be a conformal symmetry of the background spacetime. Additionally, he shows that in well-behaved "weakly analytic" states, geometric modular flow must be future-directed. The paper also discusses the conditions under which geometric modular flow can be realized in non-conformal theories and provides constructions of states with local modular flow. The author emphasizes that the main results are constraints rather than constructive proofs, aiming to provide a broader understanding of geometric modular flow without treating each case individually.The paper by Jonathan Sorce explores the concept of geometric modular flow in quantum field theory, focusing on its implications for understanding energy and entropy in quantum gravity. The Unruh effect, which describes how observers in Minkowski spacetime experience a thermal bath due to their boost motion, is a key example of geometric modular flow. Sorce initiates a general study of settings where geometric modular flow can arise, proving that any such flow must be a conformal symmetry of the background spacetime. Additionally, he shows that in well-behaved "weakly analytic" states, geometric modular flow must be future-directed. The paper also discusses the conditions under which geometric modular flow can be realized in non-conformal theories and provides constructions of states with local modular flow. The author emphasizes that the main results are constraints rather than constructive proofs, aiming to provide a broader understanding of geometric modular flow without treating each case individually.