With the rapid evolution of metaverse technologies, numerous metaverse applications have arisen for various purposes and scenarios. This makes interoperability across metaverses becomes one of the fundamental technology enablers in the metaverse space. The aim of interoperability is to provide a seamless experience for users to interact with metaverses. However, the development of cross-metaverse interoperability is still in its initial stage in both industry and academia. In this paper, we review the state-of-the-art cross-metaverse interoperability schemes. These schemes are designed for specific interoperating scenarios and do not generalize for all types of metaverses. To this end, we propose MetaOpera, a generalized cross-metaverse interoperability protocol. By connecting to the MetaOpera, users, and objects in metaverses that rely on centralized servers or decentralized blockchains are able to interoperate with each other. We also develop a proof-of-concept implementation for MetaOpera, evaluate its performance, and compare it with a state-of-the-art cross-metaverse scheme based on Sidechains. Simulation results demonstrate that the size of cross-metaverse proof and the average time of cross-metaverse transactions using the proposed solution are respectively about eight times and three times smaller than the Sidechains scheme. This paper also suggests a number of open issues and challenges faced by cross-metaverse interoperability that may inspire future research.

翻译：随着元宇宙技术的快速发展，围绕不同目的与场景涌现出大量元宇宙应用。这使得元宇宙间的互操作性成为该领域的基础技术支撑之一。互操作性的目标是为用户提供跨元宇宙交互的无缝体验。然而，目前跨元宇宙互操作的发展在学术界和工业界均仍处于初期阶段。本文综述了当前最先进的跨元宇宙互操作方案，这些方案针对特定互操作场景设计，未能泛化适用于所有类型的元宇宙。为此，我们提出MetaOpera——一种通用化的跨元宇宙互操作协议。通过连接MetaOpera，依赖中心化服务器或去中心化区块链的元宇宙中的用户与对象能够彼此互操作。我们还开发了MetaOpera的概念验证实现，评估其性能，并与基于侧链的最先进跨元宇宙方案进行对比。仿真结果表明，与侧链方案相比，所提方案的跨元宇宙证明大小和跨元宇宙交易平均时间分别降低了约8倍和3倍。本文还指出了跨元宇宙互操作面临的若干公开问题与挑战，以期为未来研究提供启示。