Professor Kim Christensen, Professor of Theoretical Physics, presents his Inaugural Lecture; ‘Why do we need a theory of non-elephants?’ 

Abstract: A car is complicated because it consists of many components, but nevertheless the components with known properties work together in a predictable way and the car does what it is designed to do. A complex system is different in the sense that the behaviour of the system cannot be predicted from knowing the properties of the constituent parts alone.

For example, the behaviour of the brain cannot be deduced from studying a single neuron in isolation nor can the behaviour of an ant colony be deduced from studying a single ant. These complex systems display emergent behaviour due to the interactions of the constituent parts that cannot be predicted or forecasted with present theories. This matters a great deal because complex systems are ubiquitous in the natural and man-made world. The society is facing increasingly complex problems since the plentitude of interactions make standard modelling inadequate, hindering forecasting and control. Therefore, it is of paramount importance to develop new appropriate approaches and theories to real-world challenges and a proper understanding of design, management, uncertainty and risk at systems level is necessary.

Complexity science is attempting to find a theory of complex systems or, equivalently, a theory of non-equilibrium systems which the Hungarian mathematician John von Neumann refereed to as a “theory of non-elephants”. In the lecture, I will embark on the quest of a theory of non-elephants, looking for signs of the mere existence of such a theory. The quest is only in its infancy, so it seems appropriate we start with a pile of sand before moving on to discuss other non-equilibrium systems like the crust of the earth and the atmosphere. This will take us into the realm of self-regulating systems and an ant colony is an ideal model system for studying the principles of how biological social self-regulatory systems work as they represent the pinnacle of social evolution in animals. In fact, we are merely following the advice of King Solomon: “Go to the ant, thou sluggard, consider her ways and be wise” (Book of Proverbs, Chapter Six).

Biography: Kim Christensen graduated from University of Aarhus in 1990. He undertook his PhD study at Brookhaven National Laboratory, co-inventing a simple model for earthquakes. He joined University of Oslo in 1993, where experimental and theoretical studies of granular flow led to the so-called Oslo model for avalanches in granular media that plays a pivotal role in slowly driven non-equilibrium systems. After studying evolution of networks at the Federal University of Rio de Janeiro, he joined Imperial as an EU-fellow in 1997 and he was appointed a lecturer at Dept. of Physics in 1999. At Imperial, he co-invented a model of biological evolution capable of reproducing the macro-evolutionary phenomenon of punctuated equilibrium. He continued his work on relaxational systems and analysis of real earthquake data revealed that there is no unique way of distinguishing main- and aftershocks and a new way of measuring rain events showed that they are analogous to earthquakes and avalanches. Recently, he co-authored a pedagogical textbook entitled Complexity and Criticality, and in 2007, he moved to the Institute for Mathematical Sciences, aiming to create a focus for complexity science at Imperial and beyond in collaboration with Prof. Henrik J. Jensen.

Chair: Professor Donal Bradley FRS, Department of Physics

Vote of Thanks: Professor Hans C. Frogedby, Institute of Physics and Astronomy, University of Aarhus, Denmark

A pre lecture tea reception will be served in the Physics Common Room, Level 8 Blackett Building


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