Stephen Feeney at University College London and colleagues say they’ve found tentative evidence of four collisions with other universes in the form of circular patterns in the cosmic microwave background.
In their model of the universe, called “eternal inflation,” the universe we see is merely a bubble in a much larger cosmos. This cosmos is filled with other bubbles, all of which are other universes where the laws of physics may be dramatically different from ours.
Ref.: http://arxiv.org/abs/1012.1995: First Observational Tests of Eternal Inflation