Universe... or Multiverse

  A fantastic idea that everyone has thought about since the recognition of the there being a universe is if there is another one along side ours.  Many ideas have come up and been thought up but only three are scientifically recognized.  The first being that the Multiverse has Nine dimensions, if this is true it would let our Three dimensional universe only be a single plane of existence. In this Nine dimensional Multiverse, our universe would be like a page of a book, in that in our three dimensional world, a page of a book is two dimensional.To look at this Hypothesis in lamens terms, the Multiverse is everything, and in that everything there are universes, but like a page from a book there would be many of them.
  The second idea is that there are Infinite numbers of universes.  The way this works is that anything that could have happened has happened.  To look at this through text think of it this way, just by choosing to read this you made a new universe.  The difference between this one and that one is that you didn't read this in that universe.  So in this model, every time any thing ever did something a new universe was made where that thing didn't happen.  This is my favorite theory as it was proposed by the logic of quantum mechanic, the thing I would like to study.
  The third proposed idea is that there are universes in our universe but are so distant that we would never have a chance to see them, or that they only exist inside black holes, and we would thus never see them. By the logic of this theory we could be inside a black hole that was part of a second (any number really.) universe.  This is the most strait forward idea.
  Or we are the only universe in existence and there is no other.  We could be alone, but I don't think that is true.
Minutphysics has more on his channel on YouTube, i highly suggest you watch his stuff.