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"e; entanglement"e; 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 "e;early"e; 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.