Read more at: http://phys.org/news/2014-05-cosmologists-lost-minds-multiverse.html#jCp
The recent BICEP2 observations – of swirls in the polarisation of the cosmic microwave background – have been proclaimed as many things, from evidence of the Big Bang and gravitational waves to something strange called the multiverse.
The multiverse theory is that our universe is but one of a vast, variegated ensemble of other universes. We don't know how many pieces there are to the multiverse but estimates suggest there many be squillions of them.
But (if they exist) there has not been enough time since our cosmic beginning for light from these other universes to reach us. They are beyond our cosmic horizon and thus in principle unobservable.
How, then, can cosmologists say they have seen evidence of them?