"Before there was thought, there was this place. One Earth. With a single history. But with the coming of man, came the illusion of free will. And with that illusion, came chaos. With every choice we make, we literally create a world. History branches in two, creating one Earth where we made the choice, and a second where we didn't. That's the secret of the universe, you know. Billions of people, making billions of choices, creating infinite Earths. Some so similar to each other that you could spend a lifetime searching for any difference. Others so radically different, they defy comprehension."
— Owlman, Justice League: Crisis on Two Earths
"Like you, I recently learned that ours is but a single dimension in a multiverse of dimensions. Intrigued, I used this very portal to survey them all. Which is when I made a startling, horrible discovery. There are not simply eight of you, but...SCORES of you! BEHOLD: a multiverse of accursed Teenage Mutant Ninja Turtles!"
— Shredder / Ch'rell, Turtles Forever
Penny: What's a Multiverse?
"There is not one universe. There are many: A multiverse. We have the technology to travel between universes, but travel is highly restricted and policed. There is not one you. There are many. Each of us exists in present time, in parallel universes. There was balance in the system, but now a force exists who seeks to destroy the balance so he can become The One."
— Narrator, The One
"And a multiverse is... Like, imagine the world you come from. Now imagine that there's a ton of others out there that differ in ways as simple as you being green, to ways so complex you wouldn't believe me if I told you. That's the Multiverse."
—Noble Six, We Are Our Adventuring Avatars