The idea of a multiverse consisting of "parallel universes" is a popular science fiction trope, recently explored in the Oscar-winning movie "Everything Everywhere All At Once." However, it is within the realm of scientific possibility.
It is important to state from the start that the existence (or not) of the multiverse is a consequence of our present understanding of the fundamental laws of physics—it didn't come from the minds of whimsical physicists reading too many sci-fi books.
There are different versions of the multiverse. The first and perhaps most popular version comes from quantum mechanics, which governs the world of atoms and particles. It suggests a particle can be in many possible states simultaneously—until we measure the system and it picks one. According to one interpretation, all quantum possibilities that we didn't measure are realized in other universes.
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