This is a simulation of two gases separated by a wall with a small opening.
The gases are initially separate, and will tend to evolve into a
state of being perfectly mixed.
What differentiates “the past” from “the future?”
No direction of time is special to the motion of the particles. The equations governing
their behavior work equally well in reverse.
It is the evolution of the system from low-entropy initial conditions
into the high-entropy equilibrium state that gives time its arrow.
Inspired by From Eternity to Here.