Maxwell's Demon

The Idea :   

    Created by a physicist James Clerk Maxwell, Maxwell’s Demon is an imaginary creature that was theorized to contradict the second law of thermodynamics. This law states that the total entropy of any system will not decrease other than by increasing the entropy of some other system. In an isolated system, its entropy in the system will tend not to decrease. The concept similarly follows that heat will not flow from a colder body to a hotter body due to thermodynamic equilibrium. Basically, heat is only permitted to flow from hot areas to cold, not the other way. Additional energy is required to allow the flow from cold to hot. Heat is also conserved when energy transfer occurs. Thus, the systems at the beginning of the reaction and at the end, the total energy amounts are equal where energy can move from one area to another, yet the total remains the same.

    The concept behind Maxwell’s Demon is described to have a closed system filled with gas at a given temperature. The average speed of the molecules is a certain amount depending on the temperature. Some of the molecules will be going faster than average and some will be going slower than average. A divider is placed in the middle of the closed system that separate the two sides, left and right. On the divider has a trap door that allows molecule to enter from both sides which an existing demon inside the system can open and close the trap door. If it allows fast molecules to enter at the left side and slow molecules to enter at the right, we end up with a hot, high pressure and a slow, low pressure at the other. This model is a common application to heat engines.

This imaginary situation seemed to contradict the second law of thermodynamics :

    1. Since the demon and the gas are interacting, we must consider the total entropy of the gas and the demon combined. The expenditure of energy by the demon will cause an increase in the entropy of the demon, which will be larger than the lowering of the entropy of the gas.

    2. Also, a real demon will have to acquire information about the world through physical interaction with it - on the atomic and molecular scale we cannot ignore the quantum mechanical nature of the world. For example, to be able to see the molecules, the demon will have to absorb whole photons at a time, and any detailed version of the thought experiment will run into the uncertainty principle and the fact that an interacting demon will acquire the same temperature as the rest of the system.

Our Game : 

You control the demon! Your goal is to separate the higher energy (red) particles all into one compartment, and the lower energy (blue) particles to the other side. You accomplish this by moving the trap door up and down, and opening and closing it at opportune times. The levels start off very easy, but get progressively more difficult. Don't take too long to beat the level, there is a time limit for each level.

Controls :

  • Mouse (up/down) - controls the position of the trap door
  • Left click - press down to open the door, let go to close it

Note : A standalone (non-browser) version of the game can be downloaded here, just run the file MaxDemon.jar (requires Java runtime)





Created by Joel Duggan, Kunal Khaladkar, and William Leung

Mentors Prof. Craig Martens and Prof. Peter Krapp