Decoherence and the Appearance of a Classical World in Quantum Theory

When we were preparing the first edition of this book, the concept of de­ coherence was known only to a minority of physicists. In the meantime, a wealth of contributions has appeared in the literature - important ones as well as serious misunderstandings. The phenomenon itself is now experimen­ tally clearly established and theoretically well understood in principle. New fields of application, discussed in the revised book, are chaos theory, informa­ tion theory, quantum computers, neuroscience, primordial cosmology, some aspects of black holes and strings, and others. While the first edition arose from regular discussions between the authors, thus leading to a clear" entanglement" of their otherwise quite different chap­ ters, the latter have thereafter evolved more or less independently. While this may broaden the book's scope as far as applications and methods are con­ cerned, it may also appear confusing to the reader wherever basic assumptions and intentions differ (as they do). For this reason we have rearranged the or­ der of the authors: they now appear in the same order as the chapters, such that those most closely related to the "early" and most ambitious concept of decoherence are listed first. The first three authors (Joos, Zeh, Kiefer) agree with one another that decoherence (in contradistinction to the Copen­ hagen interpretation) allows one to eliminate primary classical concepts, thus neither relying on an axiomatic concept of observables nor on a probability interpretation of the wave function in terms of classical concepts.

This book describes the phenomena that arise from the interaction between quantum systems and their environment. Since the first edition appeared in 1996, the concepts of decoherence have become firmly established experimentally and are now widely used in the literature. Its major consequences are the emergence of "classicality", superselection rules, the border line between microscopic and macroscopic behavior, the emergence of classical spacetime, and the appearance of quantum jumps.

Most of the new developments in this rapidly evolving field are discussed in this second edition: chaos theory, quantum information, neuroscience, primordial fluctuations in cosmology, black holes and string theory, experimental tests, and interpretational issues. While the major part of the book is concerned with environmental decoherence derived from a universal Schrödinger equation, later chapters address complementary or competing approaches, such as consistent histories, open system dynamics, algebraic methods, and collapse models.