The idea of another universe that parallels our own, or a collection of multiverses, is one that I have given thought to. So here is my take on it.
Every day, we make decisions. Perhaps hundreds in a single day. Every time we make a decision, or we make a choice, our life as we know it continues on in a way the results from that choice. But perhaps another universe, entire unto itself, is spawned from the opposite choice you make. Say if I have to decide between pizza and chineese, I choose pizza. My life as I know it moves on as I eat the pizza, and whatever follows until I die. But another universe is created the moment I make that decision, a universe in which is based upon me choosing chineese.
This might sound somewhat self-centered at first, but if you think about it, it really is not. Because I being in the position to choose between pizza and chineese food is only a result of someone else's decision in their life, which spawned a universe in which I am now in. This being so, it would mean that at any given moment, not only are there an infinite amount of universes, but that also there are versions of myself in every single one of those universes. This has some other interesting implications.
First, it could explain the sense of deja vu. At any given moment, you get this intense feeling that you have been here, or done that, or seen this, before. Like you have already lived this moment. Well, imagine that all of these parallel universes are being built much like a tree with an infinite number of branches. An ever expanding and growing tree. Well, considering the shape of this tree and its ever expanding branches, there would be many instances that the branches would intersect each other. Of course, each branch represents the foward movement of time in another universe, which you of course inhabit. So when the branches intersect, you feel a sense of deja vu, like you have been here before. Because, in reality, you HAVE been here before. In another universe, from someone else's decision and track, you have lived this exact moment before.
Second, chaos theory. One aspect of it says that a man lighting a cigarette in China will have a direct effect on you here in Maryland. As crazy as this might sound, if the universe were in fact built and moving in this way, this would make sense. Because his decision to light that cigarette, as opposed to not light it, spawned an entirely new universe, that you are in and interact with. So such a far away and insignificant event has a direct effect on you and your life.
So...thats my idea.