Parallel UniversesThe subject of parallel universes used to belong to the realm of science fictions. Some cosmologists propose that our Universe might be just one of many in an ever-multiplying network of parallel universes, which they call the multiverse . Recent observational data open up the possibility that it is conceivable scientifically with some creative imagination.
The theory of eternal inflation posits that the entire eternally inflating spacetime (false vacuum) originated as a minuscule closed multiverse. The multiverse is eternal, but it did have a beginning. Inflation rapidly blows the universe up to an enormous size. It stopped where we are, producing our own island universe, and many others. But due to the peculiar structure of inflationary spacetime, it continues in other areas of the multiverse at large.
The multiverse contains an unlimited number of island universes. We live in one of them, and our observable region is one of the infinite numbers of observable regions (at different locations) that it contains .
We may be able to travel to the other observable regions, but we are forever confined to our own island universe. Constants of nature that shape the character of our world take different values in other island universes. Most of these universes are drastically different from ours, and only a tiny fraction of them are hospitable to life.