Is there really a parallel universe?
As of now, the answer is not final. There are different ideas and explanation given on parallel universes. Some say if parallel universe are far away from us, whereas others say that they are very close to us.
String theorists say that there are actually 11 dimensions. They’d come to the conclusion that our Universe is just one bubble among an infinite number of membranous bubbles which ripple as they wobble through the eleventh dimension.
If we think on probability also, we cannot just be selfish to say that we are alone. There is an equal probability of many such universes with life too.
I feel the space is not sufficient to explain all these thing here. The following links will help you know further.