The systems we can directly see are composed of huge numbers of particles. So, the properties of these systems are obtained as statistical averages of the effects of their particles. This casts a conceptual bridge between the macroscopic world wherein we observe systems with their overall properties and the microscopic world where particles with their own properties dominate the scene. Statistical mechanics shows that the former world is determined by what happens in the latter, and this approach provides a better, finer understanding of what’s going on at the macroscopic level and why.
Keywords: Accessible microstates, Boltzmann entropy, Constraints, Equilibration, Gibbs entropy, Inertness, Macroscopically stable equilibrium, Maximum entropy, Maxwell-Boltzmann distribution, Microstates, Microscopically dynamic equilibrium, Phase space, Second law, Spreading function, Stability, Statistical mechanics, Thermodynamic ensemble, Trajectory.