Do we really understand quantum mechanics?
Résumé
This article presents a general discussion of several aspects of our presentunderstanding of quantum mechanics. The emphasis is put on the very specialcorrelations that this theory makes possible: they are forbidden by verygeneral arguments based on realism and local causality. In fact, thesecorrelations are completely impossible in any circumstance, except the veryspecial situations designed by physicists especially to observe these purelyquantum effects. Another general point that is emphasized is the necessity forthe theory to predict the emergence of a single result in a single realizationof an experiment. For this purpose, orthodox quantum mechanics introduces aspecial postulate: the reduction of the state vector, which comes in additionto the Schrödinger evolution postulate. Nevertheless, the presence inparallel of two evolution processes of the same object (the state vector) maybe a potential source for conflicts; various attitudes that are possible toavoid this problem are discussed in this text. After a brief historicalintroduction, recalling how the very special status of the state vector hasemerged in quantum mechanics, various conceptual difficulties are introducedand discussed. The Einstein Podolsky Rosen (EPR) theorem is presented withthe help of a botanical parable, in a way that emphasizes how deeply the EPRreasoning is rooted into what is often called "scientific method''. Inanother section the GHZ argument, the Hardy impossibilities, as well as theBKS theorem are introduced in simple terms.
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