There was nothing I could do. When you have this kind of a problem, you can only take care of your body.

VOA: special.2010.08.09

You can only do this because it's reversible. What else do I know?

这一步,只对可逆过程成立，还有什么已知条件？

麻省理工公开课 - 热力学与动力学课程节选