How big is the Universe and if there are many, what would happen if they collided? Not a new question and several answers have been proposed (here is one). Another interesting question is why does time move in a single direction? Why does entropy increase? Laura Mersini-Houghton proposes an idea that answers both questions saying that bubble universes form with different arrows of time, eventually adding up to no preferred direction. She even claims to have a way to test this by looking our into the dark for boundaries.
Some have proposed that the Dark Flow may be one of these collisions, and the (now controversial) Great Void may be another. Where bubble universes are pulling and pushing on ours in places. FQXi has given her a grant to pursue the idea.