A bizarre new theory suggests there may be a parallel universe where time travels backwards. According to the paper, physical interactions in nature preserve fundamental symmetry, which could be applied to the universe as a whole.
Dark matter may be explained using this mirror-image universe.
In this theory, the early universe would have been tiny and hot and dense, and it would have been so uniform that time would appear symmetrical in both directions.
In the 'anti-universe' theory, charge, parity, and time are symmetrical, and any physical interaction will behave in precisely the same way if they are flipped. This fundamental symmetry is called the CPT symmetry.
The existence of this universe could help explain dark matter This mirror-image universe would be off limits for us because it exists before the Big Bang.