All physical quantities in the natural world can be expressed by complex numbers, in which the real part and virtual part together form an entity of contradiction. In detail, the real part is not only opposite but also interlinked to the virtual part and they can achieve mutual transformation. In a complex mass, the real part (real mass) embodies the particle (fermion) property of a substance, while the virtual part (virtual mass) embodies the wave (boson) property. Furthermore, the virtual

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... erty and entity property of mass lay a foundation for the theory of wave-particle duality. In addition, virtual substance is a main source to produce dark matter. The real part presents with a Riemann geometric space when expanded, which reflects the curvature property of the space-time, while the virtual part presents with a Roche geometric space when expanded, which reflects the torsion property of the space-time. Roche space takes speed as radius and its limited radius is the speed of light.