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What Is Entropy?

PhysicsThermodynamics

Quick Answer

Entropy is a measure of disorder or randomness in a system; the second law of thermodynamics states that entropy in an isolated system always increases.

The Full Story

In thermodynamics, entropy (S) quantifies the number of microscopic arrangements (microstates) that correspond to a system macroscopic state. A system with high entropy has many possible microstates — it is more disordered. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time; it either increases or stays the same. This is why heat flows from hot to cold (never the reverse without work input), ice melts in a warm room, and a dropped egg splatters but never reassembles. Entropy also governs the arrow of time: the future is the direction in which entropy increases.

Key Facts

1.Ludwig Boltzmann formulated the statistical interpretation of entropy; his famous equation S = k ln W is engraved on his tombstone.
2.The heat death of the universe — a state of maximum entropy where no energy gradients exist — is one predicted fate of the cosmos.
3.Living organisms locally decrease entropy by consuming energy, but they increase the entropy of their surroundings by more than they decrease their own.

YouTube Angle

Suggested video title for this topic:

"Entropy — Why Everything Falls Apart"