Pisin Chen, Po-Shen Hsin, Yuezhen Niu
There exists the entropy problem of the early universe, that is, why did the universe begin with an extremely low entropy and how did it evolve into such high entropy at late times? To address this problem, we invoke the nonlinear generalized Chaplygin gas (GCG) as a toy model to compute the evolution of the cosmological entanglement entropy in the early universe before the matter dominant era. GCG has the advantage of providing a smooth and unitary transition between the inflation epoch and the radiation dominant era, which makes the effective calculation possible. We found that soon after the onset of the inflation, the total entanglement entropy rapidly decreases to a minimum, and after that it rises monotonically throughout the remainder of the inflation and the radiation epochs. This indicates that the universe does not need to begin with an extremely low entropy; its smallness can be naturally induced by the dynamics of inflation itself. We believe that our computation largely captures the essential feature of entropy evolution and can provide us insights beyond the toy model.
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http://arxiv.org/abs/1212.1087
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