In the periodic table of the elements, this regularity shows up as the famous "period eight": chemical elements can be arranged in eight columns, in each of which elements with comparable chemical properties are grouped together. The number eight follows directly from the rotational symmetry in three-dimensional space. In other dimensions that number would be different. If we did not know that we live in three-space, we would be able to deduce that fact from the eightfold period in the table of the elements This notion is echoed by , who observed that the structure of atomic theory, particularly the four quantum numbers associated with an electron, is intrinsically linked to the dimensions of space-time. They wrote: "It becomes quite clear why there are four quantum numbers associated with an electron: boundary conditions and mathematical symmetries must be associated with the four dimensions of space-time." This insight underlines the fundamental relationship between the physical laws of the universe and the organizational structure of the elements.