Well, I am not a master of science and my knowledge of quantum physics isn't that large but like Gorman (as far as I understood him) I don't think anything happens by accident. Accident is a word humans use to describe something they can't predict because of their lack of understanding physics.
I was going to continue with why and how the hell something would happen by accident but in the best case that would lead to some people posting links to some theories trying to prove the concept of accident and some others would post links to disprove them. It leads nowhere. This is all theory, nothing is proven. It's like asking if god exists (with the difference that eventually one of the physics theories may be proven).
Since I don't know any proven theory I'll just say 'I don't know.' I tend to say that there is no accident and therefore no alternate dimensions/universes/whatever. But who knows?

It is stupid to ponder this multiple dimension theory -_-, It would be nice to know what would happen if we made a different decision long ago but there is no other dimension where this actually occured. We cannot prove there are other dimensions because other dimensions have to exist outside our realm of existance. And as we know, we cannot measure things that do not exist.