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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?

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  • $\begingroup$ What would create the inversion? Why would the inversion happen only at one point in time ($t=0$) and not very often at random times? It does not seem to have any observable consequences, so I am inclined to think about this as philosophy, not physics. $\endgroup$ – user126422 May 12 '17 at 13:21
  • $\begingroup$ What would create the inversion? It’s an interesting question, but it is beyond the scope of this discussion like the question “What Triggered the Big Bang?” Therefore, let us think that such a symmetric initial condition just happened. I am curious whether it could be theoretically possible or it contradicts some quantum dynamics law like Pauli exclusion principle. $\endgroup$ – Misha Kriachkov May 12 '17 at 14:05
  • $\begingroup$ Answering the second question, I say that CPT-symmetric state cannot happen at random times. There are two possibilities: either a single CPT-symmetric state or an infinite periodic sequence of such states. Indeed, if there were two CPT-symmetric states, let say at t = 0 and t = 1 in an appropriate time scale, then there would be a CPT-symmetric state at t = -1 (as a mirror image of the state t = 1 with reflection at t = 0), also there would be a CPT-symmetric state at t = 2 (as a mirror image of the state t = 0 with reflection at t = 1) and so forth. $\endgroup$ – Misha Kriachkov May 12 '17 at 14:06
  • $\begingroup$ The reversal will violate, at least, conservation of momentum and charge. So you must introduce some new law to allow for it. That the laws are reversible does not mean that a given estate can reverse spontaneously. $\endgroup$ – user126422 May 12 '17 at 14:45
  • $\begingroup$ I am not talking about the reversal of some arbitrary state. In this case, undoubtedly there would be violations mentioned by you. I consider the special case when the state does not change after such a reversal. It is very rare symmetrical state. $\endgroup$ – Misha Kriachkov May 12 '17 at 15:22
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The current quite successful model of the creation and evolution of the universe is the Big Bang model. There the initial fuzzy point of the emergence of the universe is postulated to be quantum mechanical, with the known quantum mechanical probabilistic format.

You are postulating that the existing CPT value of the universe is due to that original point, so that the CP violating component implied by the state of our present universe and our theoretical modeling of particle interactions is due to an original CP violation which is balanced by a coexisting negative time evolution mirror universe.

In the present BB model particles with their CPT properties appear after the inflaton quantum mechanical state.

So my answer is that for such a model to be viable within the existing modeling of the universe, it should assign a CP value to the parent fields from the fuzzy creation point, up to the generation of real particles and the present excess of matter over antimatter. A mathematical model is needed. It is not enough to say that the CP violating part is taken away by a coexisting mirror universe.

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