Imagine a number of finite universes superimposing to realize our apparent physical situation. For us, their many accessible states are expressed by the behavior of corresponding probability waves. Coexisting universes, including even those representing different physics (yet retaining a statistical wavefunction), may influence our every local observable. By their superimposing over all phase to determine the most likely of all states, they manifest our observed neighborhood configuration of states. Consider your immediate environment to be not of one limited cosmos, but an overlay of innumerable such spaces, where interference among them results in the structure of spacetime familiar to us. A large number of universes coinciding would enable the wavefunctions of measurement to select those structures accompanying the greatest relative increase in entropy at every point. We think of superposition usually in the sense of particle probability interaction. Just as possible, though, is the interaction of cosmological probabilities - say, an N dimensional universe and a M dimensional universe resulting in an N + M dimensional universe, a possible mechanism for the compactification of strings (4 + 6) dimensions. Please refer further to "Parallel Universes" by Max Tegmark, in Scientific American, May 2003, p. 40.