Thought experiment: without the second law

Problem

What would happen in a universe where the second law did not hold? Discuss in five lines.

Solution

The arrow of time would disappear: processes would run equally in either direction. Heat could flow spontaneously from cold to hot, a gas could recompress itself into a corner of its container, the shards of a vase could spontaneously reassemble. There would no longer be any distinction between past and future, and heat engines would have no limit on their efficiency. Above all, evolution would not exist: life exploits entropy gradients to organise itself, and without the second law those gradients would no longer exist. $\ev{\text{no arrow of time}}$

Links

Topics: Entropy and the second law Concepts: Entropy · Second law of thermodynamics Skills: Limiting-case and thought-experiment analysis