### Approach to equilibrium

Introduction

The following three simulations explore some of the qualitative properties of macroscopic systems. Before you actually do the simulations, think about what you believe the results will be. In many cases, the most valuable part of the simulation is not the simulation itself, but the act of thinking about a concrete model and its behavior.

Questions to ponder as you do these simulations include the following:

1. Do macroscopic systems exhibit a direction of time? If so, why?
2. What is the nature of equilibrium?

Simulations

- Particles in a box. A simple Monte Carlo simulation of particles initially confined to one half of the box. The simulation shows the approach to a more random state from a specially prepared state and the importance of fluctuations in equilibrium.
- Three partitions. A molecular dynamics simulation of a Lennard-Jones liquid in two dimensions. The particles are initially restricted to the middle third of the simulation cell.
- Two partitions. A molecular dynamics simulation of a box divided into two partitions. The particles are initially restricted to the left half of the simulation cell.

Updated 12 May 2008.