• There are two types of molecule: red and blue.
• A red molecule has potential energy \( (\text{num blue neighbors})/2 - height \)
• A blue molecule has potential energy \( (\text{num red neighbors})/2 \)
• Each molecule has some kinetic energy; higher KE is displayed in a darker color.
• At each time step, each molecule:
  • attempts to swap places with a randomly chosen neighbor, failing if they don't have enough kinetic energy to feed the potential energy difference; then
  • gives 1/3 of its energy to a randomly chosen neighbor