Sidney Redner

Sid's research interests primarily lie in non-equilibrium statistical physics and its applications to a wide variety of physical and social systems.  Complex systems typically involve dynamical interactions of many interacting degrees of freedom to give rise to rich emergent collective behavior of the whole.  The tools of statistical mechanics are ideally suited to tackle the broad range of phenomena that fall within this rubric of complex systems

Sid has worked extensively on the structure of complex networks, where he developed new models and methods to elucidate network structures. He also devoted considerable effort to formulate and solve physics-based models of social dynamics, where the goal is to understand the conditions under which either consensus or long-term polarization arises in a socially interacting population.

Sid is inspired by patterns everywhere, including, as examples, the distribution of wealth, the statistics of scientific citations, scoring statistics in basketball, the frequency of record temperature events, optimal parking strategies, and the spatial arrangement of birds on a wire.  For all these phenomena, he was able to obtain profound insights through judicious and simple-minded modeling.

An enduring theme of Sid's research is first-passage processes.  A first-passage process is defined as the event where a random walk, or a diffusing particle, first reaches a specified location.  Such mechanisms underlie, for instance, the triggering of stock options, the initiation of a chemical reaction, or the firing of a neuron in the brain.  One of the amazing features of a first-passage process is that a random walker (or a diffusing particle) is sure to reach any specified location in one dimension, but the average waiting time for this event is infinite.  This dichotomy between certain hitting and a divergent hitting time makes first-passage processes a fascinating subject.  Some of Sid's recent projects in this area include the dynamics of foraging, the dynamics of wealth sharing, and optimization strategies that rely on first-passage resetting.