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How could quantum gravity allow a new space-time region to form?

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Discover the difference between the observable universe and the whole universe — Multiverse Learn about the distinction between the observable universe and the whole universe.

In the context of cosmology, quantum gravity—a hypothetical theory intended to unite general relativity with quantum mechanics—is proposed as a mechanism for the creation of new space-time regions.1

One prominent concept is the "baby universe," where a quantum gravitational process creates a new region of space-time that buds off from a parent universe. This new region may potentially disconnect entirely from the parent, leading to a "tree" of universes that are unlikely to interact after their formation. It has been speculated that this process could occur within the interiors of black holes.1

Additionally, quantum gravity is considered a potential driver for cyclical cosmologies, where the "big crunch" of a collapsing universe might evolve into the big bang of a subsequent expanding universe. Because general relativity alone cannot explain how self-contained space-time is created or destroyed, these quantum gravitational processes are essential to understanding the potential proliferation of space-times within a multiverse.1