A simulator is a world model which can generate rollouts. A simulator embodies the "laws of physics" or transition dynamics for a virtual reality (which may underdetermine rollouts, such as in the case of a probabilistic model). Entities that appear in simulations at runtime are called simulacra. By the progenesis principle, a predictive model dually serves as a simulator of the predicted distribution, and self-supervised learning is a natural (in the sense of "innocent" / ecologically feasible) way to create a simulator.