The success of Newtonian mechanics, especially the success of predicting Neptune, has caused misunderstanding to some extent, equating certainty with predictability, and holding that deterministic motion must be predictable. The research after 1970s shows that although the system is deterministic, the chaotic motion which is extremely sensitive to the initial value of the motion state, seemingly random and unpredictable generally exists in a large number of nonlinear systems. Chaos refers to a seemingly irregular and complex form of motion that exists in the real world. * * * Homologous is an orderly movement form that originally followed simple physical laws. Under certain conditions, it suddenly deviates from the expected regularity and becomes a disorderly form. Chaos can appear in many deterministic dynamic systems. Chaos is similar to stochastic process in statistical characteristics, and it is considered to be inherent randomness in deterministic systems.