The second law is going to define entropy, and is going to tell us about the direction of time, something that conceptually we, clearly, understand but is going to put a mathematical foundation on which way does time go.

第二定律定义了熵，它告诉我们,时间的流向，虽然我们清楚地,知道这个概念,但还是要为时间流动的方向,建立一个数学基础。

麻省理工公开课 - 热力学与动力学课程节选