Well, the theory is quite old, but with evidence...
Yeah, multiverse and quantum-physics, I'm glad I don't get headache while thinking of that stuff, actually I use to explain some of the basics to people quite often. The possibilities of what is, was, and will be are endless.
Too bad, this knowledge is worth nothing. Transdimensional/-universal travel would need so much energy (if it is possible), I think we would destroy our own universe in an attempt to travel. I mean, we only have a few million years before we can not longer exist and then a few trillion until the universe collapses.
But hope dies last. Let's build an interuniversal/-dimensional gate!