Suppose B is a celestial body in the universe, B is called the microcosm, if and only if: (i) B contains the metagalaxy; (ii) all celestial bodies in B do not contain the metagalaxy. Based on the hypothesis that the microcosm exists, a model of the microcosm is established by axiomatic method. The results show that: (i) the microcosm is spherical, and it is constantly shrinking and rotating; (ii) the force which causes the microcosm to shrink is a kind of new fundamental force. The model is simple and natural. It not only can explain some important observed facts, such as redshifts of extragalactic galaxies and dipole anisotropy of spiral galaxy rotation direction distribution, but also can be consistent with other existing astronomical observations. This shows that: (i) the microcosm is most likely existent; (ii) the model is most likely correct.