Parallel universes are possible universes. They are the ways things could have been if the past had been different or if the laws were different. They are useful ways of thinking about things, but I think their only advantage is utility. I don't think they exist; certainly they don't exist in our Universe. They would have no relation whatsoever to us. I have a question for you, Woodstock-Hippie. Do you believe in determinism, that everything is caused? Do you think that everything is a product of the past and the laws of nature? I say this because neither the past nor the laws of nature seem like they could be "up to us." If neither of these things are up to us, then how do we have free will or free action? This is known as the Consequence Argument. I think the only way to salvage free will is to say that free will is just the desires you have about what your desires should be.