Physikalische BlätterVolume 42, Issue 3 p. 80-81 Aus der WissenschaftOpen Access Die Suche nach dem Urzeitpfeil H. D. Zeh, H. D. Zeh Heidelberg Search for more papers by this author H. D. Zeh, H. D. Zeh Heidelberg Search for more papers by this author First published: März 1986 https://doi.org/10.1002/phbl.19860420307Citations: 1 Prof. Dr. H. D. Zeh, Institut für Theoretische Physik Universität Heidelberg, Philosophenweg 19, 6900 Heidelberg. AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume42, Issue3März 1986Pages 80-81 RelatedInformation

Conceptual problems regarding the arrow of time in classical physics, quantum physics, cosmology, and quantum gravity are discussed. Particular attention is paid to the dynamical role of the quantum indeterminism, and to various concepts of timelessness.

A historically important but little known debate regarding the necessity and meaning of macroscopic superpositions, in particular those containing different gravitational fields, is reviewed and discussed from a modern perspective.

I argue that opposite arrows of time, while being logically possible, cannot realistically be assumed to exist during one and the same epoch of our universe.

The existence of spacetime singularities is irrelevant for the irreversible appearance of black holes. However, confirmation of the latter’s unitary dynamics would require the preparation of a coherent superposition of a tremendous number of appropriate “Everett worlds”.

The existence of spacetime singularities is irrelevant for the irreversible appearance of black holes. However, confirmation of the latter's unitary dynamics would require the preparation of a coherent superposition of a tremendous number of appropriate “Everett worlds”.

Limites de la connaissance (Les) Ce livre dresse un panorama de la physique des années 1950 jusqu’aux découvertes les plus récentes, à travers 130 sujets, chacun traité avec la plus grande clarté sur une double page illustrée. Research EU: The Magazine of the European Research Area M. Feuer nous apprend par le détail, documents pertinents à l'appui, que la relativité surgit entretissée aux courants politiques, idéologiques, socialistes en un mot, représentés par ces dériveux. (L'élément juif est important et ...

The introduction of spinor and other massive fields by ``quantizing'' particles (corpuscles) is conceptually misleading. Only spatial fields must be postulated to form the fundamental objects to be quantized (that is, to define a formal basis for all quantum states), while apparent ``particles'' are a mere consequence of decoherence. This conclusion is also supported by the nature of gauge fields.

Introduction to the theory of decoherence. Contents: 1. The phenomenon of decoherence: superpositions, superselection rules, decoherence by "measurements". 2. Observables as a derivable concept. 3. The measurement problem. 4. Density matrix, coarse graining, and "events". 5. Conclusions.

Schroedinger'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 as represented by a wave function) define individual physical states ("it"). This conceptual dilemma may have its origin in the conventional operational foundation of physical concepts, successful in classical physics, but inappropriate in quantum theory because of the existence of mutually exclusive operations (used for the definition of concepts). In contrast, a hypothetical realism, based on concepts that are justified only by their universal and consistent applicability, favors the wave function as a description of (thus nonlocal) physical reality. The (conceptually local) classical world then appears as an illusion, facilitated by the phenomenon of decoherence, which is consistently explained by the very entanglement that must dynamically arise in a universal wave function.

Epistemological consequences of quantum nonlocality (entanglement) are discussed under the assumption of a universally valid Schrödinger equation and the absence of hidden variables. This leads inevitably to a many-minds interpretation . The recent foundation of quasi-classical neuronal states in the brain (based on environmental decoherence) permits in principle a formal description of the whole chain of measurement interactions, including the behavior of a conscious observer, without introducing any intermediate classical concepts (for macroscopic “pointer states”) or “observables” (for microscopic particle positions and the like)—thus consistently formalizing Einstein's ganzer langer Weg from the observed to the observer in quantum mechanical terms.

The conceptual and dynamical aspects of decoherence are analyzed, while their consequences on several fundamental applications are discussed. This mechanism, which is based on a universal Schrodinger equation, is furthermore compared with the phenomenological description of open systems by means of 'quantum dynamical maps'.

Rohrlich's recent claim that the equation of motion for a point charge is symmetric under time reversal is shown to be the result of an inappropriate definition. The equation of motion for a charged sphere of finite size, which is claimed, in contrast, to be asymmetric because of the finite propagation time of its (retarded) self-forces, is shown to possess the same asymmetry (or the same symmetry, depending on the definition) as that for a point charge. The arguments apply similarly to other equations of motion.

This is a brief reply to S. Goldstein's article “Quantum theory without observers” in Physics Today. It is pointed out that Bohm's pilot wave theory is successful only because it keeps Schrödinger's (exact) wave mechanics unchanged, while the rest of it is observationally meaningless and solely based on classical prejudice.

A short critical review of the concept of decoherence, its consequences, and its possible implications for the interpretation of quantum mechanics is given.

It is argued that Hawking's `greatest mistake' may not have been a mistake at all. According to the canonical quantum theory of gravity for Friedmann type universes, any time arrows of general nature can only be correlated with that of the expansion. For recollapsing universes this seems to be facilitated in part by quantum effects close to their maximum size. Because of the resulting thermodynamical symmetry between expansion and (formal) collapse, black holes must formally become `white' during the collapse phase (while physically only expansion of the universe and black holes can be observed). It is conjectured that the quantum universe remains completely singularity-free in this way (except for the homogeneous singularity) if an appropriate boundary condition for the wave function is able to exclude {\it past} singularities (as is often assumed).

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 Schrodinger equation for interacting systems, while the observer's ''increase of information'' is appropriately represented by the resulting dynamical decoupling of the corresponding components of the global wave function.

The physical asymmetry of nature under time reversal is analysed in this essay. The author investigates the most important classes of phenomena that characterize a direction of time: radiation, thermodynamics, quantum phenomena, and the structure of spacetime. Their relations and the search for a cosmological common root of these "arrows of time" and of the traditional concept of causality are discussed. Particular emphasis is placed on quantum indeterminism. It is argued that a common root may be found in the properties of the time-independent wave function of the universe that arises from the quantization of general relativity. This requires that the physical concept of time is reduced to a correlation between physical states, including those characterizing clocks and observers. The description of irreversible phenomena is shown to be fundamentally "observer-related" in a way that can be formalized following Zwanzig. The book is aimed mainly at the student or scientist seeking an overview of the whole issue. Compared to the German version the book has been widely revised and extended.