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From the infinitely small to the infinitely large, covering more than sixty orders of magnitude of spatial dimension, quantum theory is invoked, both to describe the still largely mysterious vibrations of the microscopic strings which could be the elementary constituents of the Universe, that to account for the fluctuations of the microwave radiation which reaches us from the outer reaches of the cosmos. Serge Haroche presents in this lesson the scientific theory that has revolutionized our understanding of nature and extraordinarily enriched our means of action and information on the world.

Physics --- Physical Sciences & Mathematics --- Atomic Physics --- physique atomique --- physique quantique --- atome --- optique

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Dans les années 1920, une théorie mathématique (la diagonalisation des matrices) et une question physique (la détermination du spectre des atomes), nées indépendamment, se sont rejointes pour donner naissance à la mécanique quantique et à la branche des mathématiques appelée « théorie spectrale ». Celle-ci intervient dans toute équation d’évolution linéaire, dont elle décompose les solutions en une superposition de solutions stationnaires dites « modes propres », qui vibrent à des « fréquences propres » : ces fréquences constituent le « spectre ». Située à l’intersection de plusieurs communautés mathématiques, la géométrie spectrale vise à comprendre le lien entre la géométrie initiale d’un objet et son spectre de vibration. L’auteure entreprend de retracer l’histoire de ce domaine très actif à travers quelques grands thèmes de recherche passés et actuels.

History & Philosophy Of Science --- mathématiques --- géométrie spectrale --- physique quantique --- sciences --- spectre

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When physicists began to explore the world of the atom more precisely in an attempt to understand its structure and the laws which govern its behaviour, they soon encountered serious difficulties. Our intuitive concepts, based on our daily experience of the macroscopic world around us, turned out to be totally wrong on the atomic scale; the atom was incomprehensible in classical physics. To unravel these new mysteries, it was therefore necessary, after long trial and error, to develop entirely new concepts, the concepts of quantum mechanics. What are the main steps that led us to this modern vision of the atom? Where is atomic physics currently? What is its contribution to the development of our knowledge and where is it heading?

Physics --- Physical Sciences & Mathematics --- Atomic Physics --- physique atomique --- physique moléculaire --- théorie physique --- physique quantique