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**1 - 4**of**4**### Nonsingular bouncing cosmology

, 2013

"... This thesis studies the cosmological theory in which the universe transitions from a contraction phase into an expansion phase through a big bounce. Primordial fluc-tuations that seed structure formation in the expansion phase arise from adiabatic perturbations in the preceding contraction phase. Th ..."

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This thesis studies the cosmological theory in which the universe transitions from a contraction phase into an expansion phase through a big bounce. Primordial fluc-tuations that seed structure formation in the expansion phase arise from adiabatic perturbations in the preceding contraction phase. The purpose of this study is to un-derstand how the properties of the adiabatic perturbations are affected by the bounce. In particular, a nonsingular type of bounce is considered in which the universe ceases contraction and reverses to expansion at a finite size, fully described by known the-ories of classical gravity and effective field theory. Two major aspects of such a nonsingular bounce are studied – the stability of the bounce against inhomogeneities, and the power spectrum of adiabatic perturbations after the bounce. Results show that a class of bouncing models based on ghost condensation are subject to unsta-ble growth of curvature and anisotropy, which alters the adiabatic perturbations and disrupts the nonsingular bounce. Another class of models with a ghost field are shown to have limited instability, though the contraction phase requires fine-tuning;

### Recurrence of Space-Time Events

"... Abstract A causal-directed graphical space-time model has been suggested in which the recurrence phenomena that happen in history and science can be naturally explained. In this Ramsey theorem inspired model, the regular and repeated patterns are interpreted as identical or semi-identical space-tim ..."

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Abstract A causal-directed graphical space-time model has been suggested in which the recurrence phenomena that happen in history and science can be naturally explained. In this Ramsey theorem inspired model, the regular and repeated patterns are interpreted as identical or semi-identical space-time causal chains. The "same colored paths and subgraphs" in the classical Ramsey theorem are interpreted as identical or semi-identical causal chains. In the framework of the model, Poincare recurrence and the cosmological recurrence arise naturally. We use Ramsey theorem to prove that there's always a possibility of predictability no matter how chaotic the system is.