Multiverses

Multiverses is a broad term for hypotheses that there exist multiple, causally independent universes beyond the observable cosmos. The concept appears in physics, cosmology, and philosophy and ranges from concrete models intended to explain features of our own universe to speculative metaphysical claims. A multiverse may consist of regions with different physical constants, distinct laws, or divergent histories, and different proposals differ in what constitutes a universe and how it relates to our own.

Physics outlines several families. The cosmological multiverse includes Level I (regions beyond the cosmic horizon with the same laws, different initial conditions) and Level II (universes from eternal inflation with different constants or dimensions). In quantum theory, the Many-Worlds Interpretation posits branching histories for every outcome. Max Tegmark’s Level IV extends this to all mathematically possible structures. Other approaches include the string theory landscape and brane-world or cyclic models.

There is currently no direct empirical evidence for multiverses, and many proposals face questions of falsifiability and testability. Critics argue that some ideas are philosophical or speculative, while proponents contend that multiverse frameworks could address fine-tuning and the origin of cosmic structure. Proposals vary in whether they yield testable predictions or simply reinterpret existing data.

In culture, multiverse concepts appear in science fiction and popular media, while in science they remain debated within cosmology, quantum foundations, and the philosophy of mathematics, with ongoing work to clarify definitions and potential observational consequences.