H. Dieter Zeh

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In his recent article on "Quantum theory without observers" [1], Sheldon Goldstein raised a number of important questions about quantum theory. Even though I cannot quite understand what a universal physical theory without any concept of observers could mean, I agree with many of his critical remarks. Bell, who once objected "against measurement," also(More)
Schrödinger’s wave function shows many aspects of a state of incomplete knowledge or information (“bit”): (1) it is usually defined on a space of classical configurations, (2) its generic entanglement is, therefore, analogous to statistical correlations, and (3) it determines probabilities of measurement outcomes. Nonetheless, quantum superpositions (such(More)
Quantum theory does not require the existence of discontinuities: neither in time (quantum jumps), nor in space (particles), nor in spacetime (quantum events). These apparent discontinuities are readily described objectively by the continuous process of decoherence occurring locally on a very short time scale according to the Schršdinger equation for(More)
The relation between quantum measurement and thermodynamically irreversible processes is investigated. The reduction of the state vector is fundamentally asymmetric in time and shows an observer-relatedness which may explain the double interpretation of the state vector as a representation of physical states as well as of information about them. The concept(More)
There seems to be some confusion in the literature not only on what may actually be achieved by decoherence, but also on how this concept has to be de ned. I will here \consistently" use it in terms of wave functions (not \histories"), since state vectors represent the established kinematical concept of quantum theory, while events (of which histories are(More)
The concept of decoherence is defined, and discussed in a historical context. This is illustrated by some of its essential consequences which may be relevant for the interpretation of quantum theory. Various aspects of the formalism are also reviewed for this purpose.
The program of a physical concept of information is outlined in the framework of quantum theory. A proposal is made for how to avoid the introduction of axiomatic observables. The conventional (collapse) and the Everett interpretations of quantum theory may in principle lead to different dynamical consequences. Finally, a formal ensemble description not(More)
The conceptual and dynamical aspects of decoherence are analyzed, while their consequences are discussed for several fundamental applications. This mechanism, which is based on a universal Schrödinger equation, is furthermore compared with the phenomenological description of open systems in terms of ‘quantum
The appearance of spinor fields as operators or arguments of field functionals in quantum field theory is often regarded as a second quantization, since fermion wave functions were themselves discovered by quantizing mass points (“particles”). I argue that this language, though reflecting the historical development, is misleading. Field amplitudes always(More)