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]