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An inflationary explanation to the universe's low initial gravitational entropy
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1  Australian National University


The early universe was markedly close to thermal equilibrium, as observed in the homogeneity of CMB photons with temperature deviations of ΔT/T~10-5. Yet, the 2nd Law ensures total entropy will increase. These two facts suggest that this state of thermal equilibrium is one of low entropy, at odds with the current understanding of the high entropic content of equilibrium states. Low initial gravitational entropy may be the cause of low entropy in the early universe. Penrose’s reliance on the fortunate initial value of the Weyl curvature tensor is insufficient in explaining low initial gravitational entropy. Rather, an inflationary model explains how an arbitrary universe could be driven to the ‘specialness’ of low initial gravitational entropy. We suggest that the rapid expansion of false vacuum energy, and its decay during reheating, deposited matter and radiation into the universe homogenously and ‘unclumped’, hence in a state of low gravitational entropy. This puts the early universe in a low entropy state.

Keywords: entropy of the universe; inflation; gravity