Maxwell's Demon: A Thought Experiment on Entropy and Information

What is Maxwell's Demon?

Maxwell's demon is a thought experiment proposed by James Clerk Maxwell to challenge the second law of thermodynamics. The demon acts as a gatekeeper between two chambers of gas, allowing faster molecules to pass from one chamber to another while blocking slower ones.

This selective action theoretically allows the demon to create a temperature difference without expending energy, seemingly violating the principle that entropy must always increase in an isolated system.

How Does It Work?

In the simulation, Maxwell's demon is represented by a sorting mechanism that can open and close a door between two chambers of gas at different temperatures.

By selectively allowing faster molecules to pass from the hotter chamber to the cooler one, while blocking slower ones, the demon creates an imbalance in temperature without expending energy directly.

Entropy and Information

The concept of entropy is crucial here. Entropy measures disorder or randomness in a system, and the second law states that it must increase over time.

Maxwell's demon uses information to sort molecules, but the question arises: where does this information come from? And what happens when we account for the energy required to store and erase this information?

Landauer's Principle

To address these questions, Rolf Landauer proposed that erasing one bit of information requires a minimum amount of energy, typically 1 joule at room temperature.

This principle suggests that the demon must expend energy to erase its memory after each sorting action, thus maintaining the second law of thermodynamics.

Frequently asked questions

Try it live

Everything above runs in your browser — open Maxwell Demon: 2D Gas and Entropy Ledger and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.