**5.1 Artificial intelligence and blockchain**

Through the cognitive revolution, the agricultural revolution, and the scientific revolution, humans have entered the stage of connected intelligence, which uses the combined intelligence of humans and machines. As in the movie The Matrix, a symbiotic relationship between humans and machines has begun, and artificial intelligence and blockchain technology are accelerating this.

Artificial intelligence is reaching a stage where prediction and creation are possible through pattern recognition and learning using large amounts of data. And artificial intelligence is helping people to reduce repetitive tasks and human errors. Blockchain technology has deeply entered our society as a digital asset and is developing into a safe and reliable transaction through decentralization. Artificial intelligence is the core of the Forth industrial revolution, and it can be integrated with blockchain technology to make both artificial intelligence and blockchain more powerful [13]. Artificial intelligence and blockchain can change business models and have a transformative impact on society.

#### **5.2 Blockchain for artificial intelligence**

Artificial intelligence has a centralized nature where data is centrally managed and stored, making it a target for hacking and manipulation, which can lead to data tampering. In addition, since the source and reliability of the source for generating data are not guaranteed, there are many errors and risks. The blockchain capabilities of immutability, origin and control mechanisms have the potential to address the shortcomings of artificial intelligence and improve the accountability of trust, privacy issues and decisions. The combination of blockchain and artificial intelligence can help enable trusted digital analysis and decision-making on vast amounts of data. And it can be used to create secure data sharing and make artificial intelligence explainable, as well as regulating trust between devices that cannot trust each other [13].

#### **5.3 Artificial intelligence for blockchain**

Integrity of blockchain data is guaranteed. However, the security of applications built on top of the blockchain platform is not secure. Also, when a new block is added to the blockchain and consensus of all nodes is required, a problem arises that it cannot be used efficiently in fields that require high speed. When an error or vulnerability is found in the script of a smart contract and needs to be corrected, the irreversibility of the blockchain can hinder it. The case of hacking tens of millions of dollars in crypto currencies using vulnerabilities in smart contract algorithms reminds us of the need for agents that can immediately compensate for imperfect algorithms [14]. In such cases, machine learning systems of artificial intelligence can improve the security of blockchain applications, adjust dynamic parameters for scalability, and provide effective personalization and governance mechanisms.

Netflix provides a list of related movies related to your favorite movies, but this is the result of Netflix's central server analyzing personal information. If you do not provide personal information to Netflix, your personal information will be protected, but you will not be provided with personal taste analysis. Instead of collecting data on a central server, you might consider making use of data stored on a decentralized blockchain. However, in the case of a public blockchain, anyone can look into the transaction ledger, so there may be a risk of invasion of privacy as well. Although it is possible to allow individuals to directly control personal information in the blockchain, there is a risk of incurring a lot of cost. Artificial intelligence can provide customized services to individuals without violating personal information. Artificial intelligence can perform analysis on the user's local device and not perform analysis that is not permitted in advance. Artificial intelligence can realize decentralization so that real individuals have control over personal information [15, 16].

#### **6. Blockchain and artificial intelligence encounter in the Metaverse**

Blockchain plays an important role in implementing the economic system in Metaverse. The economy of Metaverse without blockchain will eventually be controlled by someone. If the blockchain is not supported, it is difficult for resources or goods used in the Metaverse world to be recognized for their value or to have economic interactions equivalent to the real economy. NFT-based blockchain technology further activated the Metaverse. With the advent of WEB 3.0 and Blockchain 3.0, Metaverse becomes the world to realize it.

In the Metaverse, people appear by scanning themselves in 3D or transforming them into avatar characters. Characters in the Metaverse are recognized as beings

like clones in real life, not just game characters. In the Metaverse, besides their own avatars, they create things that can express their uniqueness. And to prove this, the NFT technology of the blockchain is used.
