Universe Preceded by an Antiuniverse?

From a certain vantage point, our Universe looks lopsided. Time runs forward as space expands, and there’s more matter than antimatter. This seems to violate a fundamental symmetry, called CPT symmetry, that says physics is unchanged when time, space, and matter-antimatter are all flipped. To balance out the cosmos, Latham Boyle, Kieran Finn, and Neil Turok from the Perimeter Institute for Theoretical Physics in Canada propose that the big bang was also the starting point of an antiuniverse, where time runs in the opposite direction and antimatter dominates. They show that such a CPT-symmetric model is not only consistent with the known cosmic expansion history but also provides a straightforward explanation for dark matter.