The classical evolution of the universe can be seen as a parametrised worldline of the minisuperspace, with the time variable $t$ the parameter that parametrises the worldline. The time reversal symmetry of the field equations implies that for any positive oriented solution there can be a symmetric negative oriented one that, in terms of the same time variable, represent an expanding and a contracting universe, respectively. However, the choice of the time variable induced by the correct value of the Schrodinger equation in the two universes makes that their physical time variables could be reversely related. In that case, the two universes would be both expanding universes from the point of view of their internal inhabitants, who identify matter with the particles that move in their spacetimes and antimatter with the particles that move in the time reversely symmetric universe. If the assumptions considered are consistent with a realistic scenario of our universe, the creation of a universe-antiuniverse pair might explain two main and related problems in cosmology: the time asymmetry and the primordial matter-antimatter asymmetry of our universe.
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