" Poincare took Laplace’s argument to its logical conclusion. He proved, using the full rigour of mathematics, that if you have a box of gas containing a definite number of particles (as many as you like, as long as it is not actually infinite) and the particles strictly obey Newton’s laws of motion, then after a sufficiently long interval of time the distribution of the particles in the box must return to its original state, with each particle moving in the same direction and at the same speed that it was moving to start with. "

― John Gribbin , Deep Simplicity: Bringing Order to Chaos and Complexity