The holographic principle for general backgrounds

We aim to establish the holographic principle as a universal law, rather than a property only of static systems and special spacetimes. Our covariant formalism yields an upper bound on entropy which applies to both open and closed surfaces, independently of shape or location. It reduces to the Bekenstein bound whenever the latter is expected to hold, but complements it with novel bounds when gravity dominates. In particular, it remains valid in closed FRW cosmologies and in the interior of black holes. We give an explicit construction for obtaining holographic screens in arbitrary spacetimes (which need not have a boundary). This may aid the search for non-perturbative definitions of quantum gravity in spacetimes other than AdS. More details, references and examples can be found in papers by Bousso R (1999 J. High Energy Phys. JHEP07(1999)004, JHEP06(1999)028).