Entropy

Why time has a direction

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Entropy counts the number of microscopic arrangements behind a large-scale state.
• Second law: the total entropy of an isolated system never decreases.
• It explains mixing, the direction of heat flow, and the arrow of time.

Steps

1. Backwards video
2. Count the arrangements
3. The second law
4. Heat flow
5. Counting arrangements
6. Refrigerators