Cauchy horizon

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In physics, a Cauchy horizon is a light-like boundary of the domain of validity of a Cauchy problem (a particular boundary value problem of the theory of partial differential equations). One side of the horizon contains closed space-like geodesics and the other side contains closed time-like geodesics. The concept is named after Augustin-Louis Cauchy. The simplest example is the internal horizon of a Reissner–Nordström black hole. Under the averaged weak energy condition (AWEC), Cauchy horizons are inherently unstable and severely susceptible to time-dependent perturbations. The smallest perturbation to the horizon would cause a contraction of proper time and an increase of energy density that would grow exponentially for an observer approaching the horizon. Such an observer would see the entire future history of the universe pass by as they approached the horizon until they suddenly hit a wall of infinite energy: a curvature singularity at the Cauchy horizon. However, since the region...

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