Anemergent Universe scenario is a cosmological model that features the Universe being in a low-entropy "dormant" state before theBig Bang or the beginning of thecosmic inflation. Several such scenarios have been proposed in the literature.
A popular version proposed byGeorge Ellis and others involves the Universe shaped like a 3-dimensional sphere (or anothercompact manifold) until a rolling scalar field begins inflating it. These models are notable as potentially avoiding both a Big Bangsingularity and aquantum gravity era.[1]
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]
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]
