I don't believe the game says that per se; rather, a man at Chronopolis says that infinite dimensions are possible, but they are only stabilized from the point of observers within them. In this way, there might be thousands of different dimensions in which Serge lived or died, each with a small, changed detail. This would negate the entire meaning of the Chrono Cross, which is meant to unify the split dimensions -- which are exactly that; split, and not possibilities. The fact that an Angelus Errare point exists between the worlds signifies this. Another and Home split from one identifiable thread and are connected at the point of the split.