Per Bak

Self-organized criticality, the spontaneous development of systems to a critical state, is the first general theory of complex systems with a firm mathematical basis. This theory describes how many seemingly desperate aspects of the world, from stock market crashes to mass extinctions, avalanches to solar flares, all share a set of simple, easily described properties."...a'must read'...Bak writes with such ease and lucidity, and his ideas are so intriguing...essential reading for those interested in complex systems...it will reward a sufficiently skeptical reader." -NATURE"...presents the theory (self-organized criticality) in a form easily absorbed by the non-mathematically inclined reader." -BOSTON BOOK REVIEW"I picture Bak as a kind of scientific musketeer; flamboyant, touchy, full of swagger and ready to join every fray... His book is written with panache. The style is brisk, the content stimulating. I recommend it as a bracing experience." -NEW SCIENTIST

Self-organized criticality, the spontaneous development of systems to a critical state, is the first general theory of complex systems with a firm mathematical basis. This theory describes how many seemingly desperate aspects of the world, from stock market crashes to mass extinctions, avalanches to solar flares, all share a set of simple, easily described properties."...a'must read'...Bak writes with such ease and lucidity, and his ideas are so intriguing...essential reading for those interested in complex systems...it will reward a sufficiently skeptical reader." -NATURE"...presents the theory (self-organized criticality) in a form easily absorbed by the non-mathematically inclined reader." -BOSTON BOOK REVIEW"I picture Bak as a kind of scientific musketeer; flamboyant, touchy, full of swagger and ready to join every fray... His book is written with panache. The style is brisk, the content stimulating. I recommend it as a bracing experience." -NEW SCIENTIST

Un concept nouveau a fait récemment son apparition dans le monde scientifique, celui de criticalité auto-organisée. Un système critique auto-organisé connaît, comme un las de sable auquel on ajouterait de nouveaux grains, des avalanches souvent faibles mais quelquefois importantes. Il est, par nature, instable, et reste dans cet état d'instabilité. Des événements mineurs en eux-mêmes, comme l'ajout de quelques grains, peuvent déclencher des fluctuations de grande amplitude. Per Bak développe hardiment ce modèle pour l'étendre à de nombreux phénomènes dits complexes : les tremblements de terre, les embouteillages sur les routes, les krachs boursiers, l'évolution enfin, à condition d'interpréter les extinctions massives comme de grandes avalanches. Et si le "modèle du tas de sable" ainsi mis en oeuvre constituait la clé de voûte d'une science unique de la complexité, longtemps jugée impossible ?