An emergent Universe scenario is a cosmological model that features the Universe being in a low-entropy "dormant" state before the
Big Bang
The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including th ...
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
In mathematics, a closed manifold is a manifold Manifold with boundary, without boundary that is Compact space, compact.
In comparison, an open manifold is a manifold without boundary that has only ''non-compact'' components.
Examples
The onl ...
) until a rolling scalar field begins inflating it. These models are notable as potentially avoiding both a Big Bang
singularity and a
quantum gravity
Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the v ...
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 (
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.
[https://www.youtube.com/watch?v=r7txEy8708I]
References
{{Reflist
Physical cosmology