The metaverse is a vast virtual environment composed of numerous distinct virtual worlds, each designed for specific purposes and characterized by unique features. Among these virtual worlds, there are certain virtual worlds that incorporate digital twins—virtual representations of physical entities that act as interfaces between the physical and virtual domains. These digital twins enable bidirectional interactions, allowing information from physical objects to be transmitted to their virtual counterparts, thereby achieving synchronization. Conversely, actions performed on virtual objects can influence or control the corresponding physical objects. This Recommendation explores service scenarios and defines the requirements for integrating virtual and physical worlds through digital twins in the metaverse.