THEORETICAL EVIDENCE
The concept of the multiverse arises in a few areas of physics – and philosophy – but the most prominent example comes from something called inflation theory. Inflation theory describes a hypothetical event that occurred when our universe was very young – less than a second old. In an incredibly brief amount of time, the universe underwent a period of rapid expansion, ‘inflating’ to become many orders of magnitude larger than its previous size.
The inflation of our universe is thought to have ended about 13.8 billion years ago, but doesn’t end everywhere at the same time. While inflation ended in our universe, there may have been other, much more distant regions where inflation continued – and continues even today. Individual universes can likely ‘pinch off’ from larger inflating, expanding universes, creating an infinite sea of eternal inflation filled with numerous individual universes.