It can be measured by 1, for example, 0.5 can be said to be half of 1.

The vector (1, 2) in the xoy rectangular coordinate system can be formed by adding one (1, 0) and two (0, 1), but (1, 0) and (0, 1) cannot represent each other. So it can be said that all the vectors in this space can be expressed as the combination of these two vectors, that is, this space is composed of two elements, and this space is two-dimensional. The new understanding of space-time in physics, especially the theory of relativity, is based on some concepts in mathematics, which come from some experiences in life and production. According to rational mathematical deduction, we can draw some conclusions, which are unimaginable under the cover of various illusions, so we always feel very profound.