A brief thought and some minor HP spoilers beneath the fold.
Seriously, though, this is probably one of the most amazing examples of an expert’s name being abused to support some crank’s pet theory that I’ve ever seen. As far as I know, Einstein said very little, if anything, about the probability of "other dimensions" or alternate universes; the idea hasn’t been taken very seriously in science for very long, and is mostly a theoretical framework for understanding certain elements of quantum theory than a notion that physicists will seriously follow up on. Einstein did not dabble in quantum theory.
And the idea of "mirror universes" with evil twins of ourselves who want to wreak havoc in our dimension is pure science fiction. I mean come on; can you even for a moment conceive of the notion of a universe where Bush is a competent president? Someone decided to write up a wacky theory about why things are so screwy here on Earth, and borrowed Einstein’s name to add a ring of authenticity to it.