## Review of J.A. Wheeler and W.H. Zurek (editors), Quantum Theory and Measurement, Princeton University Press 1983.

**Summary:**

Wheeler and Zurek have assembled a reprint compilation of 49 physics papers (in English translation where appropriate) relevant to quantum measurement, dating from 1926 to 1981, many of which are seminal contributions. The collection begins with an introductory overview and ends with an extensive annotated bibliography of the related literature up to 1982.

The organization is divided into sections, with contributions covering: Commentaries, Questions of Principle, Interpretations of the Act of Measurement, “Hidden Variables” Versus “Phenomenon” and Complementarity, Field Measurements, Irreversibility and Quantum Theory, and Accuracy of Measurements: Quantum Limitations.

In the Preface, the editors state:

A textbook on quantum theory and measurement does not exist, nor is this intended to be one. This is a reference book, containing key papers on quantum theory as it relates to measurement. They are arranged in such a way, and accompanied by such supplementary references, that the collection can be used as a source book for university course or seminar on the subject. It was so used by us in 1979-1980 and in 1980-1981 at the University of Texas.

**Strengths:**

As an indication of the pivotal importance of many of these works, they include the original papers presenting Born’s probability interpretation, Heisenberg’s uncertainty principle, Bohr’s quantum postulate and complementarity, Szilard’s entropic analysis of Maxwell’s demon, Mott’s analysis of alpha-wave tracks, the Bohr-Einstein debates, Schrödinger’s cat paradox, the Einstein-Podolsky-Rosen paradox along with Bohr’s response, von Neumann’s projection postulate, Bohr and Rosenfeld’s analysis of E&M field measurement, Bohm’s hidden-variable theory, Everett’s many-worlds theory, Wigner’s remarks on consciousness, and Bell’s theorem along with its consequences in the key experimental papers of Clauser, Freedman, Fry, and Aspect.

The full table of contents can be seen at (click the ‘Look inside’ feature): Contents.

To have all of these and several dozen more collected within one source will be invaluable to a wide range of researchers. In particular, those involved in the quantum measurement problem will find this an essential resource. Although many of these papers can now be accessed digitally by those at universities and research institutes, this volume is a convenient resource for those without such access and still a handy compendium for those that have it. It also contains papers that are less well-known but are historically important. For example, the paper J. A. Wheeler, “Polyelectrons” (1946) discusses an idea for using electron-positron pair production to produce correlated photon states and which led in the 1950’s to the first realization of polarization-entangled photons; i.e. the first EPR correlated states. Another example is Braginsky, Vorontsov, and Thorne (1980), “Quantum nondemolition measurements”, a technique which became important in quantum information and recently for the first interferometric detection of gravitational waves.

Altogether, in this volume there are many important papers along with some brief historical commentaries by Werner Heisenberg, Léon Rosenfeld, Hendrik Casimir and Aage Petersen, and an extended guide by the editors to the literature at the time of publication.

**Weaknesses: **

This book was produced at a time before a physically-based definition of the quantum measurement problem had been formulated. This is evident in the Preface, where the editors state:

Why there is not a textbook on the measurement side of quantum theory is clear to anyone who participates in a seminar on the subject, and even clearer to one who gives a course on it: puzzlement! Beyond the probability interpretation of quantum mechanics, beyond all the standard analysis of idealized experiments, beyond the principle of indeterminacy and the limits it imposes, the deep issues on which full agreement has not yet been reached in the physics community. They include questions like these: Does observation demand an irreversible act of amplification such as takes place in a grain of photographic emulsion or in th electron avalanche of a Geiger counter? And if so, what does one mean by “amplification”? And by “irreversibility”? Does the quantum theory of observation apply in any meaningful way to the “whole universe”? Or is it restricted, even in principle, to the light cone?

Although most of the above questions have still not reached a consensus today, at least a precise formulation of the measurement problem can be stated, which largely is the identification of particular configurations of matter that are most efficient in constituting a bona fide measurement device. This is at the heart of the physical measurement problem as defined in [1, Chapter 4].

Readers of the Wheeler-Zurek book will find little guidance on how these reprinted papers fit into the many arguments and controversies in current discussions of the quantum measurement problem. There are also no commentaries by Wheeler and Zurek on the individual papers, a decision likely taken so as not to expand the already 809 pages of this volume. There are only a few brief commentaries by Werner Heisenberg, Léon Rosenfeld, Hendrik Casimir and Aage Petersen which are reprints from other sources.

**Conclusions:**

Quantum Theory and Measurement is an excellent single source for many important papers relevant to quantum measurement that were published up to the year 1982. Although the editors stated at that time that “A textbook on quantum theory and measurement does not exist”, we recommend our own recent text [1], combined with Wheeler-Zurek, as an excellent starting point for anybody interested in performing research in this area.

Quantum Theory and Measurement had been out of print for many years and could only be obtained at high prices on the secondary market. Princeton University Press now has a print-on-demand paperback version so that it is readily available with the result that affordable used copies can also now be easily found.

[1] M. J. Steiner, R. W. Rendell, The Quantum Measurement Problem, Inspire Institute (2018).