As many people here will know, particles have wave-particle duality. A American scientist, Richard Feyman, suggested that when a particle move from a point to another, the particle can move through every possible route, not only one route (or history) as described in classical theory. The route we observed is the only possible route. The question is, if more than one route is possible will we observed more than one route? p/s: I am still learning quantum mechanic, please correct me if I am wrong.