# Industrial Metaverse: A Comprehensive Review, Environmental Impact, and Challenges
## 3 Industrial Metavere's Architecture, Roadmap, and Core Technologies Overview
### Digital Twins  
The Digital Twin (DT) is one of the most promising enabling technologies for Industry 4.0 and smart manufacturing. The seamless integration of the online and physical realm is a defining characteristic of DTs [37]. DTs are defined in [38] as virtual duplicates of any physical object (a physical twin), connected by real-time data exchange. Practically, DTs have a wide range of applications in varying domains including, among other things, designing/planning, optimization, upkeep, safety, decision-making, remote access, and training. For businesses looking to increase their efficiency, productivity, and competitiveness, it can be a very useful tool. These applications are motivated by the advantages of DTs including fast prototyping, as well as product re-designing, cost-effectiveness, predicting problems/System Planning, optimizing solutions and improved maintenance, accessibility, being safer than the physical counterpart, waste reduction, documentation and communication, and training. In general, rapid prototyping is a process that allows de signers to quickly transform their concepts into tangible prototypes. Practically, this enables them to validate, test, and refine their ideas while ensuring the best possible product design. Additionally, it opens up the possibility of customizing each product according to the requirements and usage patterns of users. Because the DT is connected to its physical twin throughout its life, it is possible to compare the performance of the product to what was anticipated, which enables engineers and product designers to re-evaluate the assumptions of the design. In terms of cost-effectiveness, enterprises that have leveraged DT technology have reported an average increase of 15% in efficiency and a 13% reduction in maintenance costs. Consequently, with the creation of virtual replicas of their physical systems, these companies are saving time and money while improving their overall performance [39]. DT technology also enables the prediction of issues and mistakes for its physical twin's future situations, giving planners the chance to adjust systems appropriately. Given the data flowing in real time between the DT and the physical asset, problems can be predicted at various stages of the product lifecycle. Examples in this category include items like automobiles, aircraft, factory equipment, etc., that have complicated structures consisting of several different elements. Ultimately, it becomes more difficult to predict component failures using traditional methods as a product's complexity increases. Another added advantage is that of optimizing solutions and improved maintenance. This is in contrast to classical maintenance methods, which are reactive, rather than proactive due to their reliance on worst case situations and heuristic experience concerning the particular substance, structural layout, and use of a single product. Through the use of several simulations, the DT offers the most optimal solution or maintenance plan, hence simplifying the process of maintaining the system or product. Furthermore, the continuous feedback loop that exists between the DT and its physical equivalent continuously validates and improves the system's operation. Another benefit of a DT is its accessibility, since it allows for remote control and monitoring of the physical device through the DT's usage. Virtual systems, like DTs, are more widely distributed and accessible remotely than physical systems, which are limited by their location. Remote monitoring and control of equipment and systems becomes vital in cases where local access is banned, as was the case during the COVID-19 pandemic, when governments enforced lockdowns and operating remotely or non-contact methods were the only realistic alternative. Furthermore, it is safer than its physical counterpart, particularly when used in dangerous and harsh industries like mining or oil and gas.