**1. Introduction**

Since Nakamoto published 'Bitcoin: A peer-to-peer electronic cash system' in 2008, the development of Bitcoin has been up and down, but its underlying blockchain technology has received more and more attention in recent years. In 2019, China decided to take blockchain as an important breakthrough for independent innovation of core technologies, and to accelerate the development of blockchain technology and industrial innovation in smart cities with blockchain technology. The main application scenarios could be found in areas like people's livelihood services, urban governance, industrial economy, and ecological livability. The most eye-catching international use of blockchain technology is the rapid development of cryptocurrencies. This study will analyze the development direction of cryptocurrency from the perspective of world political economy, Bitcoin futures ETF, NFT, DAO, Web3.0. At the same time, along with the rising inflation in the United States and the impact of the COVID-19, the American public's attention to encrypted assets has increased and global encrypted assets have reached the level of trillions of dollars. The international application of blockchain is more focused on the financial field and focused on the virtualization industry. This study uses two scenarios of smart city and cryptocurrency to correspond to China's and other countries' concerns, respectively, to describe the development of blockchain technology in China and other countries, and they can get useful inspiration by comparing different development paths to promote the

**Citation:** Liu, F.; Fan, H.-Y.; Qi, J.-Y. Blockchain Technology, Cryptocurrency: Entropy-Based Perspective. *Entropy* **2022**, *24*, 557. https://doi.org/10.3390/e24040557

Academic Editors: Stanisław Drozd˙ z,˙ Jarosław Kwapie ´n and Marcin W ˛atorek

Received: 21 March 2022 Accepted: 13 April 2022 Published: 15 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

development of industry and blockchain technology. This paper uses entropy to analyze the performance of cryptocurrency. The cryptocurrency market and smart city represent a chaotic state, and we introduce Kolmogorov entropy to measure the degree of chaos, which is the direction of our future research. The study is a qualitative study, and we will do more quantitative studies in the future to measure specific monetary entropy, crypto-economic entropy, urban entropy, Kolmogorov entropy etc.

The rest of this article is: Section 2 Entropy in cryptocurrency markets; Section 3 Study of blockchain technology; Section 4 Solutions about blockchain technology; Section 5 Cryptocurrency and entropy; Section 6 Discussion; Finally, Section 7 Concludes this work.
