# A Survey of the Real-Time Metaverse: Challenges and Opportunities +
## 6 Metaverse Engine
### Digital Twin  
The integration of digital twin (DT) technology into the metaverse is transformative, serving as a crucial bridge between the physical and virtual worlds [59]. By creating a real-time digital replica of physical entities, DTs enable an immersive and interactive metaverse experience. This constant synchronization ensures that changes in the physical world are instantly reflected in the virtual environment, allowing users to engage with highly accurate and dynamic digital representations of objects, environments, and even people [177]. Inthis way, DTs elevate the realism and functionality of the metaverse, making it a more practical and engaging platform for users.  
One of the most significant challenges in this integration is achieving real-time synchronization between the physical and digital realms [75]. Digital twins must continually update as real-world changes occur, ensuring that the metaverse remains a faithful and current representation [36]. By distributing the metaverse into smaller, localized sub-metaverses, these systems can process data closer to the source, reducing delays and enhancing the responsiveness of the digital twin environment [178]. This decentralized approach is particularly valuable in applications like autonomous vehicles [179], healthcare [180], and smart cities [181], where real-time accuracy is critical. In smart city ecosystems, the combination of DTs and the metaverse offers new dimensions for urban management and citizen interaction. Digital twins can mirror real-time city infrastructures, providing an immersive way for users to interact with urban spaces as though they are physically present. This not only improves user experience but also enhances urban planning, resource management, and disaster response through real-time simulations and predictive modeling [182]. As cities grow more complex, the ability to manage them in real-time through a metaverse-driven interface becomes increasingly valuable, offering more efficient ways to allocate resources and address challenges.  
In sectors like healthcare and manufacturing, DTs integrated into the metaverse offer powerful tools for decision-making and efficiency [183]. For instance, in healthcare, digital twins can monitor patient health in real-time, allowing healthcare providers to predict potential issues and intervene before conditions worsen [180]. Similarly, in manufacturing, DTs simulate production processes, helping companies optimize performance, predict equipment failures, and reduce operational downtime [184]. By enabling these real-time simulations, the metaverse enhances decision-making capabilities and operational efficiency in critical industries. Security and trust are also essential aspects of the metaverse, where DTs play a pivotal role [185]. The decentralized nature of the metaverse, combined with blockchain technology, offers a secure and transparent framework for transactions and interactions. Blockchain ensures that all transactions are immutable, decentralized, and verifiable, making it ideal for safeguarding the integrity of digital twins and their data within the metaverse [186]. This decentralized trust mechanism is crucial as the metaverse becomes more integrated into everyday life, supporting interactions that are both secure and reliable.