"Yuan" in Chinese word "yuandan" means beginning, while "dan" refers to dawn, so "yuandan" is the first day of a new year on the Gregorian calendar. In the past, people all over the world celebrated the arrival of the New Year with distinctive customs, cleaning away the dirt and the old of the past year and ushering in the new. With times changing rapidly, science is significantly changing our life. The originally abstruse physical concepts in relativity and quantum mechanics are now creeping into our life. In this new era, what should we do on the New Year's Eve?

On December 30, 2019, the New Year's Eve Scientific Speech of "Understand Physics in the New Year"—"What Is Quantum Mechanics" was held in the Institute of Physics (IOP) of the Chinese Academy of Sciences (CAS), organized by the Yangtze River Delta Physics Research Center and the Science Popularization Committee of Chinese Physical Society. The keynote speaker was Cao Zexian, a researcher from IOP.

The Speech was greatly welcomed as soon as it was announced, and the audience was very enthusiastic. It was also live broadcasted on the app of People's Daily, the app of Xinhuanet, Yangshipin, Guangming Online, Broadcast Media Center of Hunan Broadcasting System, the microblog of Science Museums of China, bilibili, Toutiao and Sina Tech.

Li Jie from Beijing TV was the host of the event. At the interactive session, the host carefully chose some interesting questions the audience raised on the online platforms for Cao Zexian to answer. There were no empty seats on the site, and more than 1 million people watched the speech on more than 10 live-broadcasting platforms.

At the end of the event, Zhou Dejin, director of Bureau of Science Communication, CAS, highly appraised the content of the speech, regarding it as a speech that makes students change the attitude toward quantum mechanics and even fall in love with it. He also said that this was the first time CAS did science communication by scientific speech on the New Year's Eve. Since the effect was very good, he hoped that IOP would insist on doing it and build it into an influential brand for popular science.

The organizer said that it was just a start for a series of scientific speeches of "Understand Physics in the New Year", and they said, "We hope spending the New Year's Eve by hearing a scientific speech will arouse more and more attention and affection among people, as well as help to improve the scientific literacy of Chinese citizens."

Playback website: https://b23.tv/av81368705