The 6th IOPP Colloquium was held in the Institute of Particle Physics (IOPP) at Central China Normal University on the morning of December 8, 2025.  Professor Xiaosong Chen from the Institute for Advanced Study in Physics at Zhejiang University, who also holds a professorship at the School of Systems Science of Beijing Normal University, delivered a talk titled "Statistical Physics of Eigen Microstates and Its Applications" to faculty and students of IOPP. 

Professor Chen's presentation began with the fundamental theoretical framework of statistical physics, systematically introducing the new paradigm of eigen microstate statistical physics established by his research team. He first reviewed the significance of Gibbs' ensemble theory, then pointed out the limitations of traditional equilibrium statistical mechanics, which relies on the system's Hamiltonian and microscopic state probability distributions. Building on this foundation, he proposed constructing an ensemble matrix composed of microscopic states of many-particle systems to extract eigen microstates with statistical weights, thereby breaking through the constraints of equilibrium states and achieving a unified description of both equilibrium and non-equilibrium complex systems.

In the theoretical methodology, Professor Chen emphasized the connection between eigen microstate condensation and phase transition in critical phenomena. He explained that when the probability of a certain eigen microstate reaches a finite value, the system undergoes a phase transition analogous to Bose-Einstein condensation, where the probability can directly serve as an order parameter to characterize the phase transition behavior. Through typical examples such as the two-dimensional Ising model and the Vicsek flocking model, he demonstrated the universality of this method in identifying both continuous and discontinuous phase transitions.

In the application outlook, Professor Chen further showcased breakthrough achievements of this method in interdisciplinary fields such as Earth system science and ecology. For instance, through eigen microstate analysis of sea surface temperatures, key modes affecting the El Niño-Southern Oscillation phenomenon were revealed; studies on ecosystems like the Heihe River Basin and the Tibetan Plateau accurately identified the crucial driving force of soil moisture in vegetation growth. These results highlight the unique advantages of eigen microstate statistical physics in analyzing the evolutionary patterns of multi-scale complex systems.

During the discussion session with PhD students, Professor Chen engaged in in-depth exchanges with young researchers on issues such as the critical early-warning mechanism of eigen microstate entropy and the application of renormalization group theory in fluid systems. He particularly stressed that "statistical physics research based on big data from complex systems that requires breaking down disciplinary barriers and promoting deep integration of experimentation, simulation, and theory."

The IOPP Colloquium is a series of high-end academic events hosted by the Institute of Particle Physics. This talk, through the deep integration of statistical physics with Earth science and ecology, demonstrated China's original breakthroughs in the field of complex systems research. It provided a platform for attendees to discuss interdisciplinary methodologies with top scholars, further strengthening Central China Normal University's academic research with an "international perspective and interdisciplinary integration."

Professor Xin-nian Wang, Director of C3NT and IOPP, presented
Professor Xiaosong Chen with the 6th IOPP Colloquium Commemorative plaque

Xiaosong CHEN is a Professor at the Institute for Advanced Study in Physics, Zhejiang University, and the School of Systems Science, Beijing Normal University. He earned his B.S. in Physics (1982) and M.S. in Theoretical Physics (1984) from Central China Normal University, and his Ph.D. in Natural Sciences (1992) from Freie Universität Berlin, Germany. In 1999, he was selected for the “Hundred Talents Program” of the Chinese Academy of Sciences, and in 2003, he received the National Science Fund for Distinguished Young Scholars.

He has held research and teaching positions at several institutions, including Freie Universität Berlin, RWTH Aachen University, the Institute of Theoretical Physics (Chinese Academy of Sciences), and the University of Chinese Academy of Sciences. In October 2018, he joined the School of Systems Science at Beijing Normal University, and in September 2024, he was appointed as a Professor at the Institute for Advanced Study in Physics, Zhejiang University.

His research focuses on statistical physics of liquids, fundamental theories of phase transitions and critical phenomena, as well as statistical physics and phase transition behavior in complex systems and Earth systems.

Group Photo of the 6th IOPP Colloquium

Correspondent: Xiangyu Shui
Proof-reader: Wei Li, Xin-Nian Wang