Depuis des siècles la plupart des religions enseignent que l’univers a été crée par Dieu à partir de rien. Mais elles sont généralement muettes sur la question de savoir ce que deviendra l’univers. Redisparaitra-t-il en se fondant dans le royaume de Dieu ?
Deux chercheurs américains,Anna Ijjas et Paul Steinhard,, ont publié des articles sur arXiv faisant intervenir un champ comme celui du boson de Higgs, et des équations gouvernant une interaction entre ce champ et l’expansion du cosmos observable. Ce champ scalaire, parfois dit de quintessence, peut servir à décrire la nature de l’énergie dite noire qui autorise l’accélération de l’expansion du cosmos jusqu’à se changer en décélération avec contraction.
Mais deux autres cosmologistes de l’université de Buffalo aux États-Unis, William Kinney et Nina K. Stein, ne partagent pas ce point de vue. Comme ils l’expliquent dans une publication sur arXiv reprise ici, même l’univers cyclique de Ijjas et Steinhardt doit avoir un début dans le temps à partir d’une singularité initiale. Il ne s’agit pas de cycles ininterrompus
Référence 1
Entropy, Black holes, and the New Cyclic Universe
Anna Ijjas, Paul J. Steinhardt
. We track the evolution of entropy and black holes in a cyclic universe that undergoes repeated intervals of expansion followed by slow contraction and a smooth (non-singular) bounce. In this kind of cyclic scenario, there is no big crunch and no chaotic mixmaster behavior. We explain why the entropy following each bounce is naturally partitioned into near-maximal entropy in the matter-radiation sector and near-minimal in the gravitational sector, satisfying the Weyl curvature conditions conjectured to be essential for a cosmology consistent with observations. As a result, this kind of cyclic universe can undergo an unbounded number of cycles in the past and/or the future.
| Comments: | v2: minor amendments |
| Subjects: | General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics – Theory (hep-th) |
| Cite as: | arXiv:2108.07101 [gr-qc] |
| (or arXiv:2108.07101v2 [gr-qc] for this version) | |
| https://doi.org/10.48550/arXiv.2108.07101 Focus to learn more | |
| Related DOI: | https://doi.org/10.1016/j.physletb.2021.136823 Focus to learn more |
Référence 2
Cyclic Cosmology and Geodesic Completeness
William H. Kinney, Nina K. Stein (Univ. at Buffalo, SUNY)
We consider recently proposed bouncing cosmological models for which the Hubble parameter is periodic in time, but the scale factor grows from one cycle to the next as a mechanism for shedding entropy. Since the scale factor for a flat universe is equivalent to an overall conformal factor, it has been argued that this growth corresponds to a physically irrelevant rescaling, and such bouncing universes can be made perfectly cyclic, extending infinitely into the past and future. We show that any bouncing universe which uses growth of the scale factor to dissipate entropy must necessarily be geodesically past-incomplete, and therefore cannot be truly cyclic in time.
| Comments: | 4 pages, 3 figures (V4: Version accepted by JCAP) |
| Subjects: | General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO) |
| Cite as: | arXiv:2110.15380 [gr-qc] |
| (or arXiv:2110.15380v4 [gr-qc] for this version) | |
| https://doi.org/10.48550/arXiv.2110.15380 Focus to learn more |
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