If a rocket stage crashes into the moon and no one sees it, did it really crash? 如果一枚火箭的某一级撞上月球却没有人观测到，那它真的撞上月球了吗？ A discarded upper stage of a SpaceX Falcon 9 rocket slammed into the surface of the moon around 2:35 a.m. Eastern time on Wednesday at a speed…