Four-dimensional space needs four basic coordinates (x, y, z, w), unit vectors (1, 0,0), (0, 1, 0), (0,0, 1, 0), (0,0,0,0,0).

Generally speaking, n straight lines passing through the same point can be found in n-dimensional space, and they are perpendicular to each other. But in reality, we can find at most three straight lines to meet the requirements, so we live in a three-dimensional space.