On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

as quantum engineering. In the past two decades it has become increasingly clear that many (perhaps all) of the symptoms of classicality can be induced in quantum systems by their environments. Thus decoherence is caused by the interaction in which the environment in effect monitors certain observables of the system, destroying coherence between the pointer states corresponding to their eigenvalues. This leads to environment-induced superselection or einselection, a quantum process associated with selective loss of information. Einselected pointer states are stable. They can retain correlations with the rest of the universe in spite of the environment. Einselection enforces classicality by imposing an effective ban on the vast majority of the Hilbert space, eliminating especially the flagrantly nonlocal ''Schrodinger-cat states.'' The classical structure of phase space emerges from the quantum Hilbert space in the appropriate macroscopic limit. Combination of einselection with dynamics leads to the idealizations of a point and of a classical trajectory. In measurements, einselection replaces quantum entanglement between the apparatus and the measured system with the classical correlation. Only the preferred pointer observable of the apparatus can store information that has predictive power. When the measured quantum system is microscopic and isolated, this restriction on the predictive utility of its correlations with the macroscopic apparatus results in the effective ''collapse of the wave packet.'' The existential interpretation implied by einselection regards observers as open quantum systems, distinguished only by their ability to acquire, store, and process information. Spreading of the correlations with the effectively classical pointer states throughout the environment allows one to understand ''classical reality'' as a property based on the relatively objective existence of the einselected states. Effectively classical pointer states can be ''found out'' without being re-prepared, e.g, by intercepting the information already present in the environment. The redundancy of the records of pointer states in the environment (which can be thought of as their ''fitness'' in the Darwinian sense) is a measure of their classicality. A new symmetry appears in this setting. Environment-assisted invariance or envariance sheds new light on the nature of ignorance of the state of the system due to quantum correlations with the environment and leads to Born's rules and to reduced density matrices, ultimately justifying basic principles of the program of decoherence and einselection.

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Decoherence, einselection, and the quantum origins of the classical

Two classically identical expressions for the mutual information generally differ when the systems involved are quantum. This difference defines the quantum discord. It can be used as a measure of the quantumness of correlations. Separability of the density matrix describing a pair of systems does not guarantee vanishing of the discord, thus showing that absence of entanglement does not imply classicality. We relate this to the quantum superposition principle, and consider the vanishing of discord as a criterion for the preferred effectively classical states of a system, i.e., the pointer states.

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Quantum discord: a measure of the quantumness of correlations.

Extended Theories of Gravity

Superstring theoryをめぐって(放談室)

1 Introduction.- 2 Basic Concepts and Their Interpretation.- 3 Decoherence Through Interaction with the Environment.- 4 Decoherence in Quantum Field Theory and Quantum Gravity.- 5 Consistent Histories and Decoherence.- 6 Superselection Rules and Symmetries.- 7 Open Quantum Systems.- 8 Stochastic Collapse Models.- 9 Related Concepts and Methods.- A1 Equation of Motion of a Mass Point.- A2 Solutions for the Equation of Motion.- A3 Elementary Properties of Composite Systems in Quantum Mechanics.- A4 Quantum Correlations.- A5 Hamiltonian Formulation of Quantum Mechanics.- A6 Galilean Symmetry of Non-Relativistic Quantum Mechanics.- A7 Stochastic Processes.- References.

Decoherence and the Appearance of a Classical World in Quantum Theory

This is the fifth edition of H Dieter Zeh's classic text on the physical foundations of time-irreversibility in the phenomena. A forerunner of this book was the 1984 German text 'Die Physik der Zeitrichtung' of about 80 pages, which appeared as volume 200 in the Springer series Lecture Notes in Physics. It was soon followed by a largely revised and extended English edition of about twice the length. Since then each new edition has been thoroughly revised and, edition by edition, new topics and chapters have been added. As the author says in the introduction: 'The prime intention of this book is to discuss the relations between various arrows of time, and to search for a universal master arrow'. Correspondingly, after a short chapter on 'the physical concept of time', the author systematically discusses in the remaining five chapters the time arrows in electromagnetic radiation theory, in thermodynamics, in quantum mechanics, in black-hole physics and cosmology, and in quantum cosmology. The chapters on thermodynamics and quantum mechanics slightly outweigh the others in terms of length. The fifth edition now includes two new section on 'cosmic probabilities and history' and 'quantum computers', and the section on the 'expansion of the universe' has been restructured and extended. Other changes concentrate on the sections on radiation damping, decoherence, interpretation of quantum theory, and quantum cosmology. It should also be mentioned that the author maintains a regularly updated website for the book at www.time-direction.de. The reading is always highly stimulating and uses results and ideas from a very broad range of physics, with interspersed historical and philosophical comments. Somehow outstanding and of particular interest is the chapter on quantum cosmology, which raises novel interpretational issues that cannot be found in any other textbook I know of on time asymmetry. As regards the mathematical prerequisites, the reader is assumed to have some knowledge on Green functions, special-relativistic electrodynamics, Hamiltonian mechanics, the formalisms of phenomenological and statistical thermodynamics, quantum mechanics, and general relativity. At some rare places the author avowedly shows a certain impatience with mathematical details, in particular if they do not fit with his expectations based on personal intuition. This stands in peculiar contrast to the conceptual depth and thoroughness that otherwise characterizes most of the book. Quite generally, the reader should be prepared to encounter provoking and partially controversial statements, but this should not be too surprising in such a complex and partially highly speculative field. All this certainly sets high standards for the reader's intellectual independence and maturity, but this is definitely in accord with the philosophy of Springer's 'Frontiers Collection'. On the other hand, from personal experience I can say that already the original German text has been very popular with beginning graduate students who had a serious interest in foundational issues. (I obtained my first personal copy as a birthday present from a fellow student.) This is essentially due to the fact that the author's genuine urge to understand, rather than just describe, gives the text a characteristic flair of freshness and authenticity to which beginning researchers are particularly susceptible. Being provocative at places is just part of that. This spirit has essentially survived the various editions, thanks to the author's constant efforts to improve the existing presentation, and also by adding modern topics. However, the negative side of this constant streamlining of presentation according to the author's evolving understanding is that it tends to amplify the already existing idiosyncratic tendencies, sometimes resulting in cryptic remarks which fail their intended clarifying purpose. This already applies to the fairly steep introduction, where the author attempts to clarify in a few lines the central issue of what it means (structurally) to say that a particular dynamical law is (a)symmetric under time reversal. Here I think it would definitely be necessary to give more detailed explanations, e.g., by elaborating on the author's own discussion in 'Note on the time reversal asymmetry of equations of motion' (1999 Found. Phys. Lett. 12 193?96). Also, the structural relations between the operation of time reversal and other space-time symmetries are hardly mentioned. This may be excused insofar as T symmetry in quantum-field theory is not generally addressed in this book (which itself may be regretted), but as part of a structural characterization of the operation of time reversal it would certainly have been useful. The books provides an extensive bibliography which seems (as far as I can tell) fairly complete, though sometimes and for no obvious reason, preprints posted on web-archives are cited instead of the corresponding journal articles. Each reference comes with the page numbers of where it is cited in the text, which is very useful indeed. The positive aspects by far outweigh the critical ones. The new edition of H Dieter Zeh's classic text is highly recommended to anybody interested in foundational issues and ready to take the challenge to follow the sometimes intuitive approach of someone who has spent much time and effort to understand the conceptual intricacies and variations of this indisputably difficult and demanding subject.

https://iopscience.iop.org/article/10.1088/0264-9381/25/20/209003/pdf

The Physical Basis of the Direction of Time

https://commons.erau.edu/cgi/viewcontent.cgi?article=1696&context=publication

Quantum tests of the Einstein Equivalence Principle with the STE–QUEST space mission

Attempts to estimate the influence of global cosmological expansion on local systems are reviewed. Here ``local'' is taken to mean that the sizes of the considered systems are much smaller than cosmologically relevant scales. For example, such influences can affect orbital motions as well as configurations of compact objects, like black holes. Also discussed are how measurements based on the exchange of electromagnetic signals of distances, velocities, etc. of moving objects are influenced. As an application, orders of magnitude of such effects are compared with the scale set by the apparently anomalous acceleration of the Pioneer 10 and 11 spacecrafts, which is ${10}^{\ensuremath{-}9}\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕{\mathrm{s}}^{2}$. There is no reason to believe that the latter is of cosmological origin. However, the general problem of gaining a qualitative and quantitative understanding of how the cosmological dynamics influences local systems remains challenging, with only partial clues being so far provided by exact solutions to the field equations of general relativity.

Domenico Giulini

Papers

Decoherence and the Appearance of a Classical World in Quantum Theory

The Physical Basis of the Direction of Time

Quantum tests of the Einstein Equivalence Principle with the STE–QUEST space mission

Influence of global cosmological expansion on local dynamics and kinematics

"Decoherence: Theoretical, Experimental, and Conceptual Problems"