Patterns in the sand

The formation of patterns and its underlining mechanism in granular systems are discussed from a physicist's point of view. These findings may help us understand the patterns formed in other more complex non-equilibrium systems. It is found that the randomization and dissipation properties of non-equilibrium systems are the underlining mechanisms for pattern formation. The symmetry of the system and the ratio of the weight factors of the above two mechanisms determine the pattern shapes. A final and key factor for pattern formation is the 2nd law of maximization of the entropy, which determines if a system is organized orderly or disorderly. Examples in granular systems are given to illustrate the above view points.