Increase the flow of water, and strange things will happen. The waterwheel will revolve in one direction as before, and then suddenly jerk about and revolve in the other direction. The explanation for the irregular movement of the gas lies at the molecular level. While the box sides may seem smooth and thus the flow of the gas should always be regular, at molecular levels the sides of the box are quite irregular due to the motion of atoms and molecules. After all, in any solid not at absolute zero, total entropy is positive and there must be some irregularity in the molecular structure of the sides of the box.
Molecular interactions are tiny, however.
The theory behind how small deviations can lead to large deviations lies at the heart of chaos theory. The explanation is simple and, in retrospect, obvious explanation commonly known as sensitive dependence on initial conditions . He could print out graphs of fluctuating temperatures or other conditions, and his program captured the fancy of his fellow meteorologists. However, when he ran the program again, his results were different from the initial run. In the program, all values were calculated to six significant digits.