The term multiverse refers to a theory that there are many universes besides our own. What is the universe? Think of our universe as a bubble. Inside the bubble is our planet; in fact, all planets, stars, nebulas... all matter, even light and space itself! How big is it? No one knows because we can't see the end of it.
This raises an interesting question. If the universe has an end, then what lies beyond it? This is where the idea of a multiverse comes into play. What lies at the end of the universe? Hmm... maybe another universe? And what would be at the end of that one? Another universe? And after that? More universes? Are we in a universe full of universes? And would these universes be like ours, or different in very striking ways?
This is a tough question – one universe or many? We simply don't have the technology to answer that question right now. You may have read books or watched movies that proposed an idea of an alternate or parallel universe. In a universe such as this, there could be a planet Earth like ours. There might even be another you, but is the other you a good person? Or more like an evil twin?
We can't prove or disprove the existence of these universes yet. What we can do is have a lot of fun dreaming up stories about them. Who knows, perhaps somewhere in a parallel universe, another you is reading these same words right now, pondering the multiverse, just like you are.
Image source: "Multiverse" by kevin dooley is licensed under CC BY 2.0.