The short wave signals bounce off the ionosphere that surrounds the Earth,back to the ground and then back to the ionosphere.

VOA: special.2010.12.08

Right, this makes a lot of sense because if the entire atom was made up of nuclei, then we would have 100% probability of hitting one of these nuclei and having things bounce back.

因为如果整个原子,都是原子核，那我们就有100%概率,撞到一个原子核并被弹回来,所以如果我们。

麻省理工公开课 - 化学原理课程节选