Time for M in my Sci-Fi themed A-to-Z Challenge!
One of the earliest uses of the word multiverse in science fiction is in The Sundered Worlds, by Michael Moorcock, published in 1963. It is the hypothetical set of all universes, the many possible realities that may co-exist. Certain aspects of quantum physics might be explained if every possible outcome of an event is equally valid (whatever can happen does happen; reality is constantly branching off into alternate, independent parallels). You have probably heard of the Schrödinger’s Cat thought experiment used to explain this (actually, the whole thing was a bit of a parody – Schrödinger wanted to point out what he saw as absurd assumptions of quantum physics).
What Could Have Been
In science-fiction, the idea is taken to some interesting extremes. Authors imagine realities where the Axis won WW2, where the Roman Empire never fell, or where the dinosaur-killing asteroid missed the Earth. Some stories have characters traveling between alternate universes as a sort of “sideways” time travel that lets them check out other possibilities.
Sliding through realities, cast members, network mix-ups, cancellation …
In reality? It’s hard to say. There are scientists who support and those who criticize multiverse theory. We might be in a multiverse and be unable to prove it because we don’t know what to look for! One thing’s for sure, though – we have at least this one, enormous, wonderful universe to play around in, as well as the fantastic multiverses of our minds.
More about the possibility of a multiverse: