I still think, when people today talk about the multiverse, they usually mean not just parallel universes, but parallel timelines. Like in the MCU where there are all sorts of different versions of earth, but most are pretty recognizable. I realize the definition doesn’t depend on that, but it seems to be the common usage.
According to some, the idea of infinite worlds was first suggested by the pre-Socratic Greek philosopher Anaximander in the sixth century BCE. However, there is debate as to whether he believed in multiple worlds, and if he did, whether those worlds were co-existent or successive. The first to whom we can definitively attribute the concept of innumerable worlds are the Ancient Greek Atomists, beginning with Leucippus and Democritus in the 5th century BCE, followed by Epicurus (341–270 BCE) and Lucretius (1st century BCE). In the third century BCE, the philosopher Chrysippus suggested that the world eternally expired and regenerated, effectively suggesting the existence of multiple universes across time. The concept of multiple universes became more defined in the Middle Ages.
I still think, when people today talk about the multiverse, they usually mean not just parallel universes, but parallel timelines. Like in the MCU where there are all sorts of different versions of earth, but most are pretty recognizable. I realize the definition doesn’t depend on that, but it seems to be the common usage.
I remember talking about the multiverse while passing around a doobie, way before Marvel’s Cinematic Universe so let’s agree to disagree here.