There is a lot of research showing how difficult it is to change happiness based on external factors.

很多研究表明,基于外在因素改变快乐很难。

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I could change my external pressure through the whole process, and that's the path.

事实上外界压强,也不必固定。

麻省理工公开课 - 热力学与动力学课程节选

OK, we're going to do this reversibly, which means we're going to slowly change the external pressure very, very slightly at a time, so that at every point we're basically in equilibrium, p2/ until the pressure reaches a new smaller pressure p2.

整个过程保持可逆，外界压强,变化得很慢，每一个瞬间,都保持平衡，直到压强减小到末态值。

麻省理工公开课 - 热力学与动力学课程节选

We're going to change the pressure above, Pext right now there's a p external, which is equal to p on the inside.

来改变外界条件，可以改变外界的压强，它将与气体压强p相等。

麻省理工公开课 - 热力学与动力学课程节选