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 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.

Criticism

This proposal has been criticised by Vilenkin and Mithani and on different grounds by Aguirre and Kehayias 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.

"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 dimensions and two waves traveling along the third dimension towards each other from past-eternity with the speed of light that initiate inflation or Big Bang upon colliding.