Emergent Universe

An emergent Universe scenario is a cosmological model that features the Universe being in a low-entropy "dormant" state before the Big Bang or the beginning of the cosmic inflation. Several such scenarios have been proposed in the literature.

"Cosmic egg" scenarios

A popular version proposed by George Ellis and others involves the Universe shaped like a 3-dimensional sphere (or another compact manifold) until a rolling scalar field begins inflating it. These models are notable as potentially avoiding both a Big Bang singularity and a quantum gravity era.[1]

Criticism

This proposal has been criticised by Vilenkin and Mithani[2] and on different grounds by Aguirre and Kehayias[3] as inconsistent if quantum-mechanical effects are taken into account, however it has been suggested that in more exotic scenarios one or both of these issues might be circumvented.[4]

"Rube Goldberg cosmology" scenario

One of such more exotic emergent Universe scenarios, nicknamed "Rube Goldberg cosmology", features the pre-inflationary Universe shaped like a corridor with two finite (compactified) dimensions and two waves traveling along the third dimension towards each other from past-eternity with the speed of light (likened by the author to two trains loaded with explosives headed for a collision on the same railroad track) that initiate inflation or Big Bang upon colliding.[5][6][7]

References
  1. Ellis, George; Maartens, Roy (January 7, 2004). "The Emergent Universe: inflationary cosmology with no singularity". Classical and Quantum Gravity. 21 (1): 223–232. arXiv:gr-qc/0211082. Bibcode:2004CQGra..21..223E. doi:10.1088/0264-9381/21/1/015. S2CID 250819315.
  2. Mithani, Audrey T.; Vilenkin, Alexander (January 10, 2012). "Collapse of simple harmonic universe". Journal of Cosmology and Astroparticle Physics. 2012 (1): 28. arXiv:1110.4096. Bibcode:2012JCAP...01..028M. doi:10.1088/1475-7516/2012/01/028. S2CID 250740037.
  3. Aguirre, Anthony; Kehayias, John (November 7, 2013). "Quantum Instability of the Emergent Universe". Physical Review D. 88 (10): 103504. arXiv:1306.3232. Bibcode:2013PhRvD..88j3504A. doi:10.1103/PhysRevD.88.103504. S2CID 118348623.
  4. see e.g. the collection of references in https://callidusphilo.blogspot.com/2021/04/cosmology.html
  5. https://callidusphilo.blogspot.com/2021/04/cosmology.html
  6. Veklych, Bogdan (October 3, 2023). "Is a Quantum Gravity Era Necessary?". International Journal of Modern Theoretical Physics. 12 (1): 1–8. arXiv:2310.02338. https://inspirehep.net/literature/2706047
  7. https://www.youtube.com/watch?v=r7txEy8708I
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