Consider a hypothetical state of the universe such that it coincides with its CPT “mirror-image”. I.e., let us reflect positions of all objects by some plane (parity inversion), reverse all momenta (time inversion), replace all matter with antimatter (charge inversion), and get exactly the same state as it was before these transformations. Let this state occur at t = 0. According to the CPT theorem, the universe evolution for t < 0 would be exact mirror image of the universe evolution for t > 0. Therefore, the universe for t < 0 would contain mostly antimatter and its arrow of time (the direction of entropy increase) would be directed backwards compared to the time axis t. Curiously, the universe for t < 0 would be inhabited by people made of antimatter who would observe antimatter world around. For them antimatter would be the “normal” mater. In fact, the universe for t < 0 would be indistinguishable from the universe for t > 0 by means of any physical experiment. Therefore, the universe for t < 0 would not have separate physical reality. Rather two mirror copies of the word (i.e. the universe for t < 0 and t > 0) would constitute physical reality.
The described CPT-symmetric initial state has extremely low entropy. It could be used to explain the second law of thermodynamics and the direction of the arrow of time. It also answers the question: “What was before?” The CPT “mirror-image” world was before, but it did not have separate physical reality.
Is this hypothesis about CPT-symmetric initial state plausible?