2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/213983We review realistic models that reproduce quantum theory in some limit and yield potentially new physics outside that limit. In particular, we consider deterministic hidden-variables theories (such as the pilot-wave model) and their extension to 'quantum nonequilibrium', and we consider the continuous spontaneous localization model of wave function collapse. Other models are briefly discussed.15 pages. Minor changes. To be published in: Encyclopaedia of Mathematical Physics, eds. J.-P. Francoise, G. Naber and T. S. Tsun (Elsevier, 2006)Quantum PhysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext