For most of human history, the idea of parallel universes belonged to the realm of myth, mysticism, and—much later—science fiction. It appeared in folk tales about mirrored worlds, in ancient philosophical speculation, and eventually in comic books and blockbuster movies. But today, the multiverse has evolved from a narrative device into something far more serious: a concept many physicists now consider not only plausible, but mathematically unavoidable. The shift didn’t happen overnight. It em...