Physics of Complex Systems: Criticality in nature

Physical, geophysical, chemical, living and human­-made systems often show behaviours that cannot be understood by studying their building blocks or constituents to ever finer detail but that are emergent. The concept of emergence can be summarized by the statement that there exists an entity (e.g. an organism) which is more than the sum of its parts. This is often used as the defining property of a complex system. Hallmarks of criticality, such as power-laws and self-similarity typical for order-disorder phase transitions in statistical physics, have been found in many complex systems in nature ranging from fault networks to biological networks. In particular, biological neuronal systems are often thought to be organized in such a way that they optimize their information processing and storage capabilities. This is supported by studies, which have indicated that neuronal networks in vivo and in vitro can self-organize to a critical state. In this talk, I will discuss what complex systems are, why they are interesting and how we try to describe and understand their emergent characteristics such as criticality including the self­-organization processes leading to them. The focus will be on information processing and memory consolidation in neuronal systems and the spreading of zoonotic diseases as well as the failure of rock samples and fluid-induced seismicity, such as encountered in enhanced geothermal systems and hydraulic fracturing.

Prof. Joern Davidsen is a Professor in the Department of Physics & Astronomy at the University of Calgary working in the transdisciplinary field of Complexity Science. Starting with his PhD research in Theoretical Physics at the University of Kiel, Germany, and at Imperial College London, UK, he has worked on applications ranging from neurosciences to earthquakes using tools from statistical physics, complex network theory and nonlinear dynamics. This includes studies of chemical reaction-diffusion systems in collaboration with Nobel Laureate Gerhard Ertl’s group at the Fritz-Haber Institute in Berlin, Germany, as well as studies of the climate system while being a research associate at the British Antarctic Survey. Recently, Prof. Davidsen was named 2025 Killam Annual Professors and also awarded a prestigious Alexander von Humboldt Research Fellowship. The latter has allowed him to spend extended periods of time as Visiting Research Professor at the GFZ German Research Centre for Geosciences in Potsdam. He currently leads the Computational Neuroscience Platform at the University of Calgary under its Brain and Mental Health Strategy. Together with his students, postdocs and collaborators, he has published over 100 peer-reviewed papers in international journals with well over 3500 citations.