Assuming that the universe we currently experience is finite, that would imply a finite number of elementary particles. If we extend the concept of quantum numbers to all particles (not just electrons) then purely theoretically it may be possible for quantum numbers beyond the fourth to define (for example) alternative spacetime coordinates for the same particle in another phase. Since phase is on a 360 degree continuum and thus (presumably) has a potentially infinite number of possible states, this could account for an infinite number of universes - or more probably an infinite number of states simultaneously existing in the same spacetime.