One way to mark time is to imagine it carries a clock as it moves, and put markers every second.

标记时间的一种方法是,想像它带着时钟运动,并且每秒做一次标记

耶鲁公开课 - 基础物理课程节选

If that's all it knows, then in that scenario there is no building or anything else; it continues a trajectory both forward in time and backward in time, and it says that whatever seconds, one second before you set your clock to 0, it would've been on the ground.

如果是这样,在那种模式下,没有楼房或者别的什么,物体的运动轨迹可以沿时间可以向后延伸,也可以向前延伸,不管时间取什么值,在零点前一秒时,物体就在地面上

耶鲁公开课 - 基础物理课程节选