In this position paper we present a novel mathematical framework for building metaverses, which is a potential way to unify reality and virtuality to create a cohesive whole universe. We argue that the nature of metaverses is inherently mathematical, and propose that the system of complex numbers could play a key role in constructing them. Specifically, we provide context for our argument and offer a supporting example, the analytic signal, to demonstrate how to construct its imaginary counterpart with the Hilbert transform to a given real signal and how to unify them to form a cohesive complex signal that facilitates the analysis of local dynamic behaviors of the signal. This framework has significant potential for building a metaverse. By leveraging the power of complex numbers, one can create a unified mathematical system that merges the physical and virtual worlds. We believe that this proposal will inspire further research and development of metaverses in this field and that our framework will contribute to the construction of a metaverse that offers unprecedented levels of interactivity and immersion.