We have a concept of time going forward in a particular way.

我们有着时间以特定方式,向前流动的概念。

麻省理工公开课 - 热力学与动力学课程节选

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