On the Discovery Channel's Through the Wormhole (I think that's the name of it), two scientists came to a similar conclusion from two different starting points. One was researching string theory and the other, dark flow.

I'll spare the technical details, as I wouldn't do them justice anyway. In a nutshell, the string theory researcher says that string theory allows for a ridiculous amount of possible configurations of the 10 or 11 dimensions and so raises the possibility of multiverses. While you couldn't travel from one to another due to the differences in physics from one to the other, they could still effect each other. She predicted that two adjacent universes would each exhibit a "cold spot" in the area where they were closest.

Dark flow, which not everyone has been sold on at this point, is the observation that galaxy clusters are all moving toward a common, very massive object, outside our universe. The direction also seems to coincide with a unique "cold spot" on the cosmic map.

The two scientists were not aware of each others work until fairly recently, but are now collaborating. Both believe that there may be a universe adjacent to ours and that matter in each is being drawn toward the other.

This is an interesting line of thought, in that I would imagine a multiverse situation to be dynamic and that while we may have one adjacent universe now, in the future perhaps another will come within our proximity and create new effects on the motion of matter within our universe and others. This might also explain how a closed system could remain so dynamic. Forces outside our system could be constantly stirring up the pot.