The newly established {N,n} QM includes the Bohr-QM based part (see in SunQM-1 series, SunQM-2, SunQM-5 series, and SunQM-7), the Schrodinger-equation based part (see in SunQM-3 series and SunQM-4 series), and the {N,n} quantum field part (see in SunQM-6 series). In the SunQM-7 series, I am going to study the relativity under the {N,n} QM. In the current article, first, I used Schrodinger equation/solution (i.e., the wave function) as a tool to study how the space is formed from x-1D to the flat xy-2D, the point-centered rφ-2D, the flat xyz-3D, the point-centered rθφ-3D, and then the point-centered r’rθφ-4D. The orthogonality of the dimensions was discussed. Many examples of the dimension transformation (that were encountered during the {N,n} development, e.g., "opened-space" versus "closed-space", "straight-space" versus "curved-space", larger size 3D space may allow the higher dimension 4D to be effective, etc.) were discussed. Second, based on the Newtonian mechanics (that in the Earth’s orbit that around the Sun, all mass entities (e.g., a H-atom, a space dust, etc.) have the same constant orbital speed as that of the Earth), and also based on that our 3D universe may be a spherical 3D space on the surface of a 4D ball something, I explained the origin of the lightspeed as that "it is the orbital speed in a r’rθφ-4D space". It also automatically explained the origin of the constancy of the lightspeed. These origin explanations may in turn support the correctness of the two axioms in the modern physics: "the lightspeed is the maximum (effective) speed in our universe", and "the speed of light is constant in our universe". Third, I further hypothesized that a group of (large number) random direction/phase "4D thermal oscillators" forms a massed particle that localized in our 3D universe, and a group of (small number) unified direction/phase "4D thermal oscillators" forms a massless photon that un-localized in our 3D universe. This model made me able to further explain several other properties in the general relativity and the special relativity (see in SunQM-7s2). Fourth, because I believed that (in 3D space) a black hole not only stops the light but also stops the gravitational force to escape from its surface, I hypothesized that a black hole may indirectly exert its gravitational force in 3D space (by projecting of its 4D space G-force through the 4th dimension back into the 3D space).