In Liu Cixin's science fiction novel," The Three Bodies," the order of magnitude and the cosmic unit were two important concepts. The order of magnitude refers to the difference between one quantity and another. It can be used to describe the difference in the quantity of two objects or the importance of an object in the universe. In " Three-Body ", the order of magnitude was usually used to describe the number or size of objects. For example, the distance between the three-body galaxy and the Earth was an order of magnitude, indicating that the distance between them far exceeded the speed of light in the universe. Cosmic units referred to a specific object in the universe, usually a star or a planet. In " The Three-Body Problem ", cosmic units were usually used to indicate the position or importance of an object in the universe. For example, the " three-body " in the " three-body person " was a cosmic unit that represented its specific position and importance in the universe. The order of magnitude and cosmic units were very important concepts in " The Three Bodies " to help readers better understand the plot and setting in the novel.