Big bounce universe
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The Big Bounce Universe: A Comprehensive Overview
Introduction to the Big Bounce Universe
The concept of the Big Bounce universe offers an alternative to the traditional Big Bang theory, suggesting that the universe undergoes a cyclic process of contraction and expansion. This model replaces the singularity at the beginning of the universe with a "bounce," where the universe transitions from a contracting phase to an expanding phase.
Genericness of the Big Bounce in Loop Quantum Cosmology
In isotropic loop quantum cosmology, the Big Bounce is a generic feature, meaning it occurs regardless of specific quantization methods or the dynamics of scalar fields. The volume of the universe at the bounce point is determined by a single parameter, which also acts as a cutoff for density perturbation calculations, influencing their amplitudes1.
Inhomogeneities and the Big Bounce
The dynamics of an inhomogeneous universe, studied through hybrid quantization in loop quantum cosmology, reveal that the Big Bounce replaces the initial Big Bang singularity. This model shows that the universe at the bounce is comparable in size to the background homogeneous universe. Additionally, the amplitude of gravitational wave modes varies depending on the dominance of inhomogeneities during the bounce2.
Dark Matter and the Big Bounce Genesis
Dark matter plays a crucial role in the Big Bounce scenario. Studies suggest that the interaction cross-section and mass of dark matter could serve as indicators of a Big Bounce. This model-independent approach to dark matter production during the contraction and expansion phases provides a new pathway to achieve the observed relic abundance, offering a potential signature of the Big Bounce universe3 8.
Spin, Torsion, and the Big Bounce
The Einstein-Cartan theory of gravity, which incorporates spin and torsion, prevents gravitational singularities and replaces the Big Bang with a nonsingular Big Bounce. This theory posits that the coupling between spin and torsion induces gravitational repulsion at high densities, leading to a bounce. The existence of a closed universe is contingent on the product of the scale factor and temperature exceeding a specific threshold4 7 9.
Modified Dispersion Relations and the Big Bounce
Employing modified dispersion relations, researchers have derived modified Friedmann equations and entropy relations for the Friedmann-Robertson-Walker (FRW) universe. The energy scale and entropy behavior at the Big Bounce are sensitive to the curvature parameter ( k ). For a closed universe (( k=1 )), the bounce occurs at a normal energy limit, with zero modified entropy, while for an open universe (( k=-1 )), the bounce is absent10.
The Big Bounce in the Very Early Universe
A cosmological model replacing the Friedmann singularity with a de Sitter solution suggests that the universe contracts to a minimum radius before re-expanding. This transition requires a phase change that converts the quantum vacuum into primordial relativistic matter, shifting from exponential de Sitter expansion to a Friedmann-Lemaitre model5.
The Double Bang Hypothesis
Contrary to the orthodox interpretation of bounce cosmologies, some argue for a "double bang" scenario, where the interface between universes represents the birth of two expanding universes. However, defenders of the orthodox view maintain that features of one universe explain those of the other, supporting a continuous thermodynamic arrow of time through the bounce6.
Conclusion
The Big Bounce universe presents a compelling alternative to the Big Bang theory, offering solutions to the singularity problem and providing new insights into the early universe's dynamics. Through various theoretical frameworks, including loop quantum cosmology, Einstein-Cartan theory, and modified dispersion relations, researchers continue to explore the implications and potential experimental signatures of this fascinating cosmological model.
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Most relevant research papers on this topic
Genericness of a big bounce in isotropic loop quantum cosmology.
The big bounce in loop quantum cosmology is a generic phenomenon, independent of quantization ambiguities and scalar field dynamics, and can be parametrized by a single parameter.
Highly CitedBig Bounce and inhomogeneities
The Big Bounce replaces the initial Big Bang singularity, with a universe size at the bounce being of the same order of magnitude as the background homogeneous universe, and inhomogeneities are amplified in near-vacuum regimes.
Highly CitedBig Bounce Genesis
Big Bounce genesis can be confirmed by using dark matter mass and interaction cross section as a smoking gun signal for the existence of a big bounce at the early stage in our observed universe.
Big Bounce and Closed Universe from Spin and Torsion
The Einstein-Cartan theory of gravity predicts a nonsingular big bounce and closed universe when the product of scale factor and temperature exceeds a certain threshold, preventing gravitational singularities and allowing dark-energy acceleration.
Big bounce in the very early universe
The Big Bounce model replaces the Friedmann singularity in the very early universe with a de Sitter solution and a quantum vacuum, resulting in a phase transition from quantum vacuum to primordial relativistic matter.
Big Bounce or Double Bang? A Reply to Craig and Sinclair on the Interpretation of Bounce Cosmologies
The orthodox interpretation of bounce cosmologies is correct, as features of one universe explain features of the other, and the thermodynamic arrow of time is continuous through the bounce, despite entropy being reset.
Big bounce from spin and torsion
The big bang is replaced by a bounce at a lower energy and larger scale factor, preventing matter in the contracting Universe from reaching conditions for a quantum bounce.
Highly CitedBig Bounce Genesis and Possible Experimental Tests: A Brief Review
Big bounce genesis, a model-independent approach, could potentially test the existence of a bounce universe at the early stage of evolution, impacting our understanding of early universe physics.
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