Disheartened by the cancelation of the Superconducting Super Collider, Weinberg turns his attention to the cosmological constant. It must behave like a vacuum energy density, and can be adjusted to cancel the energy in fluctuating fields. Today the effective vacuum energy density, including the cosmological constant, has come to be called “dark energy.”

The famously controversial 1935 paper by Einstein, Podolsky, and Rosen (EPR) took aim at the heart of quantum mechanics. The paper provoked responses from leading theoretical physicists of the day, and brought entanglement and nonlocality to the forefront of discussion. This book looks back at when the EPR paper was published and explores those intense. conversations in print and in private correspondence. These offer significant insight into the minds of pioneering quantum physicists, including Bohr, Schrödinger and Einstein himself. Offering the most complete collection of sources to date – many published or translated here for the first time – this text brings a rich new context to this pivotal moment in physics history.

Schrödinger’s reaction to the EPR paper is less widely known than, say, Bohr’s, and yet our analysis shows that it fits rather nicely with contemporary concerns in foundations of quantum mechanics. Taking the lead both from the EPR paper and from Pauli’s remarks in their correspondence, Schrödinger shows that EPR’s locality considerations lead to the assignment of values to all quantum mechanical observables, but that under apparently mild assumptions this then leads to contradictions of the von Neumann type. This dilemma (as he explicitly calls it) is thus similar to more recent debates between nonlocality on the one hand and no-go results on the other (whether through violation of the Bell inequalities, the Kochen–Specker theorem, or what you will). We shall first look at Schrödinger’s fundamental worries in the years leading up to 1935. The chapter then discusses in detail the direct reaction by Schrödinger to EPR. It will, however, not exhaust our discussion of Schrödinger, who is a recurring character in the book, having poked and prodded his peers on EPR during the whole summer and autumn of 1935.

This is a reprinting of Margenau’s response to EPR (and to some extent, his evaluation of previous responses to EPR by Bohr, Kemble and Ruark). Margenau’s contribution to the EPR debate is certainly one of the most original, no doubt at least in part due to the meaty correspondence he had with Einstein while producing it. Margenau’s main strategy in this paper is to argue against the standard collapse postulate of quantum mechanics, suggesting that the EPR argument only applies to quantum mechanics with this postulate added. He also argues against the statistical interpretation of the collapse postulate suggested by Kemble and others.

This is a translation of an anonymous report published about Einstein’s seminar in Berlin in November of 1931 dicussed in detail in Chapter 1. The report describes Einstein discussing the meaning of Heisenberg’s uncertainty relations and describing his famous photon-box thought experiment.

This chapter presents a collection of letters between the main protagonists in the EPR debate as analysed in the present volume. Among many other letters, it includes the first ever complete English translation of the correspondence Schrödinger held concerning the EPR paper with, e.g., Einstein, Bohr, Pauli, Born and Teller. He kept these letters in a special folder labelled ‘The Einstein Paradox’, only a small portion of which has previously been discussed in the foundations literature. These historical documents, many of which are published here for the first time, form the basis of our analysis in the beginning chapters of this book.

This is a reprinting of the famous May 1935 paper in Physical Review by Einstein, Podolsky and Rosen. In this paper, the authors argued that the wavefunction fails to provide a complete description of reality unleashing the debate analysed in this volume.

This chapter details not only the prehistory of EPR but also examines the structure and logic of the EPR paper – including Einstein’s own preferred version of the argument for incompleteness. We here attempt a seamless interweaving of the excellent extant literature with additional details that have emerged from our work and the recent work of others. Some examples of new aspects in this prehistory of EPR include evidence of a ‘proto’ photon-box thought experiment Einstein had developed in connection with his ill-starred collaboration with Emil Rupp in 1926. We also describe the potential importance to this prehistory of Einstein’s paper with Tolman and Podolsky and of Einstein’s seminar and discussions with Schrödinger in Berlin in the early 1930s.

This is a translation of notes by Schrödinger wherein he draws the implications of Einstein’s photon-box thought experiment.

This is a reprinting of Einstein, Podolsky and Tolman’s 1931 letter to the editor of Physical Review. In this letter, the authors demonstrate that the principles of quantum mechanics give rise to an uncertainty in the description of past events which is analogous to the uncertainty quantum mechanics assigns to the prediction of future events.

This is the first ever printing of a short unpublished note by Schrödinger discussing canonical conjugates, which he included among his correspondence in the folder he labelled ‘The Einstein Paradox’. The note references Flint’s response to EPR and contains ideas appearing also in a letter to Einstein in July 1935.

This is a transcription of a typescript Kemble had appended to a letter to Margenau in 1935. In this paragraph, Kemble admits that his initial published response to EPR missed the point of their argument.

In this chapter, we dive deeply into Bohr’s views on (in)completeness and (non)locality. Perhaps the most outspoken and famous respondent to EPR, Bohr is generally thought to be obscure in his reply. We analyse it afresh (at least to our satisfaction), in particular in regard to its argumentative structure, the role of Bohr's examples and that of his 'non-mechanical disturbance'. We also assess its limitations as a reply to Einstein's wider concerns.

The topic of this chapter is the wave function – what it is, how it is to be interpreted and how information can be extracted from it. To this end, the notion of operators in quantum physics is introduced. And the statistical interpretation called the Born interpretation is discussed. This discussion also involves terms such as expectation values and standard deviations. The first part, however, is dedicated to a brief outline of how quantum theory came about – who were the key people involved, and how the theory grew out of a need for understanding certain natural phenomena. Parallels are drawn to the historical development of our understanding of light. At a time when it was generally understood that light is to be explained in terms of travelling waves, an additional understanding of light consisting of small quanta turned out to be required. It was in this context that Louis de Broglie introduced the idea that matter, which finally was known to consist of particles – atoms – must be perceived as waves as well. Finally, formal aspects such as Dirac notation and inner products are briefly addressed. And units are introduced which allow for convenient implementations in the following chapters.

This chapter examines the rich and complicated relationship between Pirandello and Germany, beginning with his formation in Bonn and with German intellectual sources that were important for his worldview. It then examines the important role of the German stage and German director Max Reinhardt in influencing his mature theatre. At the same time, Pirandello’s own views of Germany also shifted over time, from his cultural affiliation with German thinkers to criticism of Austria and Germany in the period of the Great War. Spanning from inspiration to reception, Germany held an important if shifting and ambiguous place in Pirandello’s work and life.

Chapter 3 summarizes major equations of statistical and stochastic mechanics, important for description of molecular transport.

One important area where radio astronomers confirmed theoretical predictions was in tests of General Relativity. Radio interferometer measurements made during the 1970s were able to confirm Einstein’s prediction of the gravitational bending of light to an accuracy better than 1 percent, or an order of magnitude better than the controversial classical optical tests made during the time of a solar eclipse. In 1965, MIT Professor Irwin Shapiro suggested and subsequently confirmed a new fourth test of General Relativity resulting from the excess delay of the reflected radar signal from a planet as the signal passes close to the Sun. Radio observations have also found Einstein’s “gravitational lensing” by which a massive cluster of galaxies can form multiple radio images of a background galaxy or quasar. Observations of small periodic deviations in the time of arrival of pulsar pulses at the Arecibo Observatory led Princeton University graduate student Russell Hulse and his supervisor Joe Taylor to the 1993 Nobel Prize in Physics for the first experimental evidence for the predicted existence of gravitational radiation.