This volume contains the lectures of the third and fourth Poincaré Seminar, both held in 2003. The third one is devoted to Bose-Einstein Condensation: it covers the physics of superfluid liquid helium as well as the recently discovered atomic Bose-Einstein condensates. Major experimental results are presented, together with relevant theoretical approaches and remaining open questions. The fourth one concentrates on Entropy, giving a comprehensive account of the history and various realizations of this concept, from thermodynamics to black holes, and including theoretical and experimental discussions of the corresponding fluctuations for mesoscopic systems near equilibrium.

The book addresses graduates and researchers in mathematical, experimental and theoretical physics alike, serving both as introduction to the subjects and as guide to the frontiers of experiments and research.

The Poincaré Seminar is held twice a year at the Institut Henri Poincaré in Paris The goal of this Seminar is to provide up-to-date information about general topics of great interest in physics Both theoretical and experimental aspects are covered, with some historical background Particular care is devoted to the pedagogical nature of the presentation so as to fulfill the goal of being accessible to a broad audience of scientists

Inhalt
I: Bose-Einstein Condensation.- Claude COHEN-TANNOUDJI Bose-Einstein Condensation: An Introduction.- Sébastien BALIBAR Looking Back at Superfluid Helium 17.- Gora V. SHLYAPNIKOV Condensed Matter Approaches to Quantum Gases.- Jean DALIBARD and Christophe SALOMON Experiments with Cold Atoms.- Philippe NOZIÈRES Bose-Einstein Condensation and Quantum Coherence:From Superfluidity to Localization,from Fermi Liquids to Superconductors.- II: Entropy.- Olivier DARRIGOL The Origins of the Entropy Concept.- Roger BALIAN Entropy, a Protean Concept.- Christian MAES On the Origin and Use of Fluctuation Relationsfor the Entropy.- Félix RITORT Work Fluctuations, Transient Violations of the Second Law and Free-Energy Recovery Methods: Perspectives in Theory and Experiments.- Thibault DAMOUR The Entropy of Black Holes: A Primer.