Stefan Thurner

Stefan Thurner (born 1969) is an Austrian physicist and complexity scientist. He heads the Section for Science of Complex Systems at the Medical University of Vienna and is a co-founder and the president of the Complexity Science Hub (CSH). Thurner also serves as an external professor at the Santa Fe Institute.

His research focuses on extending statistical mechanics to networked complex systems out of equilibrium, with applications to the dynamics and phase transitions of social, biological, and economic systems. Notable contributions include a theory for systems out-of-equilibrium, stress-testing of healthcare systems, agent-based modelling of systemic risk in supply chains and financial networks, and the quantification of resilience. He authored Introduction to the Theory of Complex Systems, a textbook on complex systems.

Thurner has received awards including Austrian Scientist of the Year 2017 and the Paul Watzlawick Ring of Honor (2021).

Career

Early life and education Thurner was born in 1969 in Innsbruck, Austria. He received a PhD in theoretical physics from TU Wien and a second PhD in economics from the University of Vienna. He completed his habilitation in theoretical physics at TU Wien.

Thurner started his academic career in theoretical particle physics before transitioning to research on complex adaptive systems, building on mathematical modelling and quantitative methods.

Research Stefan Thurner's research is grounded in theoretical physics of complex systems and aims at the quantitative characterization of emergent phenomena in high-dimensional, nonlinear, and non-equilibrium systems. Using methods from statistical mechanics, network theory, and agent-based modelling, his research investigates the structural and dynamical properties of economic, biological, and social systems.

Foundations of Complex Systems Thurner has contributed foundational tools for quantifying complexity in non-equilibrium systems, including a derivation of generalized entropy measures for complex systems from first principles. He contributed to the understanding of the statistics of open, driven, out-of-equilibrium systems with the so-called sample space reducing processes that offer an intuitively simple and mathematically tractable explanation of non-Gaussian statistics in complex systems. He co-authored Introduction to the Theory of Complex Systems (2018) (together with Rudolf Hanel and Peter Klimek) that formalizes processes such as fragmentation, aggregation, and adaptive feedback, demonstrating how local interaction rules generate global patterns without centralized control – illustrated empirically by super-linear scaling in urban growth and linguistic evolution. and in an equilibrium setting of DebtRank, a nonlinear metric that quantifies systemic importance of firms, to financial contracts thus making it possible to estimate systemic risk of financial contracts. This opens the possibility to measure the systemic risk of financial contracts by assessing their capacity to distress other institutions beyond direct bilateral exposures. He extended the framework of systemic risk to multilayer financial networks encompassing loans, derivatives, and collateral. Related methods applied to firm-level supply chains showed that rewiring supplier relationships toward lower-risk configurations measurably reduces disruption propagation.

Network Medicine and Healthcare Systems Using large-scale Austrian hospital data, Thurner and collaborators constructed disease comorbidity networks based on ICD-10 diagnosis codes, quantifying co-occurring conditions across patient populations. Agent-based simulations have been applied to model healthcare system resilience, identifying capacity thresholds and failure cascades under varying patient loads. During the COVID-19 pandemic, his group ranked the effectiveness of non-pharmaceutical interventions across 79 territories based on their impact on the effective reproduction number, and co-founded and contributed to Austria's national epidemiological forecasting consortium, which provided weekly projections to health care professionals and government health authorities.

Economics Thurner has applied complex systems thinking to economic modelling, including a linear response theory to quantify sectoral resilience to shocks in the global economy. He conducted early research on supply chain networks at the firm level and has shown that aggregating economic data at the industry level can significantly underestimate the propagation of disruptions through production networks. Related methods have been applied to decarbonization planning, where network-based targeting of firms by systemic relevance achieved substantial emissions reductions while limiting broader economic impact on output and employment.

Social Sciences Thurner applies computational methods to social dynamics, including group formation and opinion polarization. A 2023 study used a spin-glass-inspired self-assembly framework to model how homophily drives the formation of social groups, deriving group-size distributions that match empirical data from online communities. A 2025 study demonstrated mathematically that increasing social connectivity can trigger sudden polarization once a critical societal connectivity threshold is exceeded, linking the rise in close friendships observed since 2000 to measured polarization trends in Western societies. Earlier work includes a 2010 PNAS study of social networks formed by more than 300,000 players in the massive multiplayer online game Pardus including communication, trade, and conflict layers in an online social network, which uncovered gender-specific interaction patterns mirroring offline behavioral asymmetries.

Reception and impact Thurner has published over 300 peer-reviewed articles and holds three patents. Critics Kuśmierz and Toyoizumi countered that linear growth on small-world networks arises only near the critical point (R ≈ 1) and questioned whether the observed patterns require the specific network topology proposed. Thurner and co-authors replied that their model explicitly concerns the near-critical regime and characterized the criticism as a misreading of the paper's scope.

Awards and honors (Selection)

Austrian Scientist of the Year 2017, Austrian Association of Education and Science Journalists Paul Watzlawick Ring of Honor (2021), Vienna Medical Association

Selected publications

Books

2020: S. Thurner: Die Zerbrechlichkeit der Welt. Kollaps oder Wende. Wir haben es in der Hand, edition a, Wien 2020, 2018: S. Thurner, R. Hanel, P. Klimek: Introduction to the Theory of Complex Systems, Oxford University Press, Oxford 2018, 2012: S. Thurner, H. Meyer-Ortmanns: Principles of evolution: from the Planck epoch to complex multicellular life. Springer, Berlin/ Heidelberg 2011, 2012: S. Thurner: Systemic financial risk, Steinbeis/OECD Publishing, Stuttgart/ Paris,

Journal articles and book chapters

Thurner, S., Hofer, M., & Korbel, J. (2025). Why more social interactions lead to more polarization in societies. Proceedings of the National Academy of Sciences, 122(44), e2517530122. https://doi.org/10.1073/pnas.2517530122 Korbel, J., Lindner, S. D., Pham, T. M., Hanel, R., & Thurner, S. (2023). Homophily-Based Social Group Formation in a Spin Glass Self-Assembly Framework. Physical Review Letters, 130(5), 057401. https://doi.org/10.1103/PhysRevLett.130.057401 Thurner, S. (2022). A Complex Systems Perspective on Macroprudential Regulation. Handbook of Financial Stress Testing, pp. 593–634. https://doi.org/10.1017/9781108903011.034 Kaleta, M., Lasser, J., Dervic, E., Yang, L., Sorger, J., Lo Sardo, D. R., Thurner, S., Kautzky-Willer, A., & Klimek, P. (2022). Stress-testing the resilience of the Austrian healthcare system using agent-based simulation. Nature Communications, 13(1), 4259. https://doi.org/10.1038/s41467-022-31766-7 Haug, N., Geyrhofer, L., Londei, A., Dervic, E., Desvars-Larrive, A., Loreto, V., Pinior, B., Thurner, S., & Klimek, P. (2020). Ranking the effectiveness of worldwide COVID-19 government interventions. Nature Human Behaviour, 4(12), pp. 1303–1312. https://doi.org/10.1038/s41562-020-01009-0 Lo Sardo, D. R., Thurner, S., Sorger, J., Duftschmid, G., Endel, G., & Klimek, P. (2019). Quantification of the resilience of primary care networks by stress testing the health care system. Proceedings of the National Academy of Sciences, 116(48), pp. 23930–23935. https://doi.org/10.1073/pnas.1904826116 Corominas-Murtra, B., Hanel, R., & Thurner, S. (2015). Understanding scaling through history-dependent processes with collapsing sample space. Proceedings of the National Academy of Sciences, 112(17), pp. 5348–5353. https://doi.org/10.1073/pnas.1420946112