Where do they exist?
Parallel universes, or "multiverses," are a theoretical concept in modern physics. They're like alternate realities, but not quite like that. Think of them as neighboring branches on the grand tree of existence.
Some theories suggest they're created through quantum fluctuations, like a cosmic game of "what if." Others propose they're the result of our universe's own chaotic evolution. Either way, it's enough to make your head spin.
But here's the thing: we're not entirely sure how to get there. That's right; it's like trying to find a needle in a haystack, except the haystack is infinite and the needle is probably hiding under a different haystack altogether.