title: Robust dynamic classes revealed by measuring the response function of a social system.
abstract: We study the relaxation response of a social system after endogenous and exogenous bursts of activity using the time series of daily views for nearly 5 million videos on YouTube. We find that most activity can be described accurately as a Poisson process. However, we also find hundreds of thousands of examples in which a burst of activity is followed by an ubiquitous power-law relaxation governing the timing of views. We find that these relaxation exponents cluster into three distinct classes and allow for the classification of collective human dynamics. This is consistent with an epidemic model on a social network containing two ingredients: a power-law distribution of waiting times between cause and action and an epidemic cascade of actions becoming the cause of future actions. This model is a conceptual extension of the fluctuation-dissipation theorem to social systems [Ruelle, D (2004) Phys Today 57:48-53] and [Roehner BM, et al., (2004) Int J Mod Phys C 15:809-834], and provides a unique framework for the investigation of timing in complex systems.
authors.affiliation: Department of Management, Technology, and Economics, Eidgenössische Technische Hochschule Zürich, Kreuzplatz 5, 8001 Zürich, Switzerland. rcrane@ethz.ch
authors.forename: Riley
authors.initials: R
authors.lastname: Crane
authors.forename: Didier
authors.initials: D
authors.lastname: Sornette
mesh_terms: D006801:Humans; D015233:Models, Statistical; D009043:Motor Activity; D016012:Poisson Distribution; D012942:Social Sciences / Q000379:methods*; D013598:Systems Theory; D013997:Time Factors