Some theoretical physicists are committed to unifying four basic forces, such as gravity, electromagnetic force, strong force and weak force, into one force. 1 force: The nucleus consists of positively charged protons and neutrons. Why doesn't Coulomb repulsion between proton positive charges scatter the nucleus? That's because there is a strong interaction between nucleons, which can overwhelm Coulomb repulsion (nuclear force). On the scale of the nucleus, the intensity is much greater than that of coulomb force, but it is a short-range force. When the distance between nuclei is too large, the intensity drops rapidly and disappears. Weak force: There is also a short-range interaction between elementary particles. The distance of weak force is shorter than that of strong force, and the strength of force is much smaller than that of strong force. Weak force plays an important role in β decay, which releases electrons and neutrinos, and there is only weak force between electrons and neutrinos. There are also weak forces between other elementary particles. Electromagnetic force: electricity is the interaction between two charged particles or objects, and there is a magnetic force between two moving charges. Gravity: it is the mutual attraction between any objects. In contrast, for ordinary objects, gravity is very weak. But it is a kind of remote force, which plays a decisive role in the formation of the universe and celestial bodies. For example, the formation of the solar system and the Milky Way depends on gravity, and cosmology cannot be separated from the theory of gravity.