VIRTUAL SEMINAR - ZOOM MEETING LINK
Link: https://umich.zoom.us/j/99929959678
Passcode: csaaw

Abstract
Virtually anything can be and is ranked; people, institutions, countries, words, genes. Rankings reduce complex systems to ordered lists, reflecting the ability of their elements to perform relevant functions, and are being used from socioeconomic policy to knowledge extraction. A century of research has found regularities when temporal rank data is aggregated. Far less is known, however, about how rankings change in time. We explored the dynamics of 30 rankings in natural, social, economic, and infrastructural systems, comprising millions of elements and timescales from minutes to centuries. We found that the flux of new elements determines the stability of a ranking: for high flux only the top of the list is stable, otherwise top and bottom are equally stable. We show that two basic mechanisms — displacement and replacement of elements — capture empirical ranking dynamics. The model uncovers two regimes of behavior; fast and large rank changes, or slow diffusion. Our results indicate that the balance between robustness and adaptability in ranked systems might be governed by simple random processes irrespective of system details.

Speaker bio
Carlos Gershenson is a tenured, full time research professor at the computer science department of the Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas at the Universidad Nacional Autónoma de México (UNAM), where he leads the Self-organizing Systems Lab. He is also an affiliated researcher at the Center for Complexity Sciences at UNAM and coordinator of the Complexity Sciences National Laboratory. He was a Visiting Professor at MIT and at Northeastern University (2015-2016) and at ITMO University (2015-2019). He was a postdoctoral fellow at the New England Complex Systems Institute (2007-2008). He holds a PhD summa cum laude from the Vrije Universiteit Brussel, Belgium (2002-2007). His thesis was on “Design and Control of Self-organizing Systems”. He holds an MSc degree in Evolutionary and Adaptive Systems, from the University of Sussex (2001-2002), and a BEng degree in Computer Engineering from the Fundación Arturo Rosenblueth, México. (1996-2001). He has a wide variety of academic interests, including complex systems, self-organization, urbanism, artificial life, evolution, cognition, artificial societies, and philosophy.