Astronomy and Astrophysics – Astrophysics – General Relativity and Quantum Cosmology
Scientific paper
2002-02-28
Int.J.Mod.Phys. D12 (2003) 963-976
Astronomy and Astrophysics
Astrophysics
General Relativity and Quantum Cosmology
brief discussion on Poincare recurrence included
Scientific paper
10.1142/S0218271803003530
Penrose [1] has emphasized how the initial big bang singularity requires a special low entropy state. We address how recent brane cosmological schemes address this problem and whether they offer any apparent resolution. Pushing the start time back to $t=-\infty$ or utilizing maximally symmetric AdS spaces simply exacerbates or transfers the problem. Because the entropy of de Sitter space is $S\leq 1/\Lambda$, using the present acceleration of the universe as a low energy $(\Lambda\sim 10^{-120}$) inflationary stage, as in cyclic ekpyrotic models, produces a gravitational heat death after one cycle. Only higher energy driven inflation, together with a suitable, quantum gravity holography style, restriction on {\em ab initio} degrees of freedom, gives a suitable low entropy initial state. We question the suggestion that a high energy inflationary stage could be naturally reentered by Poincare recurrence within a finite causal region of an accelerating universe. We further give a heuristic argument that so-called eternal inflation is not consistent with the 2nd law of thermodynamics within a causal patch.
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