Abstract
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.
Highlights
Inflationary scenarios [1,2] have solved solved the flatness, horizon, and monopole problems, and provide explanations of the origin of structure
Davies has suggested that low initial gravitational entropy may be the explanation of low entropy in the early universe
In addition to the flatness, horizon, and monopole problems, inflation naturally solves the initial low entropy problem if the low initial gravitational entropy dominates the maximal entropy in other degrees of freedom
Summary
Inflationary scenarios [1,2] have solved solved the flatness, horizon, and monopole problems, and provide explanations of the origin of structure. Why did the universe not begin as thermodynamically homogeneous radiation and matter, if this was statistically likely?. What’s missing in our picture of entropy that leads to the conclusion that homogenous and isotropic matter and radiation at thermal equilibrium is somehow far enough from equilibrium to produce stars, life and other entropy-generating structures?. Davies has suggested that during inflation, the universe was ‘wound up’ to a low-entropy state, with the proceeding evolution a subsequent winding down through free energy dissipation and gravitational clumping. He and Penrose make use of gravitational entropy as critical answers to (2). We improve Davies’ model in clarifying the openness of the universe ‘system’ and implications for which Davies claims to ‘decrease’ during inflation
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