In the November 24-30, 2007 Issue of New Scientist there was presentation in an a cover story entitled "Into The Void" of evidence that our universe collided with a 2nd Universe on page 35
Please don't blow off the question by saying "nobody Knows" because we don't know what the dimensionality of our own universe is because of all the rolled-up hidden dimensions - Speculate- give some possibilities, even though you are not certain of their reality.