I have told you how far up is, and how far down is.

VOA: special.2009.03.28

What I just spent many lectures discussing is the fact that we can not know how far away an electron is from the nucleus, so we can't actually know the radius of a certain atom.

我花了这么多课时所讨论的正是我们,不可能知道电子离原子核有多远这一事实，因此我们不可能知道某个原子的半径。

麻省理工公开课 - 化学原理课程节选