Quantum Causality

There is no sharp dividing line between the foundations of physics and philosophy of physics. This is especially true for quantum mechanics. The debate on the interpretation of quantum mechanics has raged in both the scientific and philosophical communities since the 1920s and continues to this day. (We shall understand the unqualified term ‘quantum mechanics’ to mean the mathematical formalism, i. e. laws and rules by which empirical predictions and theoretical advances are made. ) There is a popular rendering of quantum mechanics which has been publicly endorsed by some well known physicists which says that quantum mechanics is not only 1 more weird than we imagine but is weirder than we can imagine. Although it is readily granted that quantum mechanics has produced some strange and counter-intuitive results, the case will be presented in this book that quantum mechanics is not as weird as we might have been led to believe! The prevailing theory of quantum mechanics is called Orthodox Quantum Theory (also known as the Copenhagen Interpretation). Orthodox Quantum Theory endows a special status on measurement processes by requiring an intervention of an observer or an observer’s proxy (e. g. a measuring apparatus). The placement of the observer (or proxy) is somewhat arbitrary which introduces a degree of subjectivity. Orthodox Quantum Theory only predicts probabilities for measured values of physical quantities. It is essentially an instrumental theory, i. e.

In this paper we consider two entangled particles and study all the possibilities: when both are immobile, or one of them is immobile, or both are moving in different directions, or one of them is moving in a different direction.

An intermittent but mentally quite disabling illness prevented Henry Mehlberg from becoming recognized more widely as the formidable scholar he was, when at his best. During World War II, he had lived in hiding under the false identity of an egg farmer, when the Nazis occupied his native Poland. After relatively short academic appointments at the University of Toronto and at Princeton University, he taught at the University of Chicago until reaching the age of normal retirement. But partly at the initiative of his Chicago colleague Charles Morris, who had preceded him to a 'post-retirement' profes sorship at the University of Florida in Gainesville, and with the support of Eugene Wigner, he then received an appointment at that University, where he remained until his death in 1979. In Chicago, he organized a discussion group of scholars from that area as a kind of small scale model of the Vienna Circle, which met at his apart ment, where he lived with his first wife Janina, a mathematician. It was during this Chicago period that the functional disturbances from his illness were pronounced and not infrequent. The very unfortunate result was that colleagues who had no prior knowledge of the caliber of his writings in Polish and French or of his very considerable intellectual powers, had little incentive to read his published work, which he had begun to write in English.

In July 2006, a major international conference was held at the Perimeter Institute for Theoretical Physics, Canada, to celebrate the career and work of a remarkable man of letters. Abner Shimony, who is well known for his pioneering contributions to foundations of quantum mechanics, is a physicist as well as a philosopher, and is highly respected among the intellectuals of both communities. In line with Shimony’s conviction that philosophical investigation is not to be divorced from theoretical and empirical work in the sciences, the conference brought together leading theoretical physicists, experimentalists, as well as philosophers. This book collects twenty-three original essays stemming from the conference, on topics including history and methodology of science, Bell's theorem, probability theory, the uncertainty principle, stochastic modifications of quantum mechanics, and relativity theory. It ends with a transcript of a fascinating discussion between Lee Smolin and Shimony, ranging over the entire spectrum of Shimony's wide-ranging contributions to philosophy, science, and philosophy of science.

Causality is central to understanding the mechanisms of nature: some event "A" is the cause of another event “B”. Surprisingly, causality does not follow this simple rule in quantum physics: due to to quantum superposition we might be led to believe that "A causes B” and that "B causes A”. This idea is not only important to the foundations of physics but also leads to practical advantages: a quantum circuit with such indefinite causality performs computationally better than one with definite causality. This thesis provides one of the first comprehensive introductions to quantum causality, and presents a number of advances. It provides an extension and generalization of a framework that enables us to study causality within quantum mechanics, thereby setting the stage for the rest of the work. This comprises: mathematical tools to define causality in terms of probabilities; computational tools to prove indefinite causality in an experiment; means to experimentally test particular causal structures; and finally an algorithm that detects the exact causal structure in an quantum experiment.

​This book summarizes the results of research the authors have pursued in the past years on the problem of implementing Bell's notion of local causality in local physical theories and relating it to other important concepts and principles in the foundations of physics such as the Common Cause Principle, Bell's inequalities, the EPR (Einstein-Podolsky-Rosen) scenario, and various other locality and causality concepts. The book is intended for philosophers of science with an interest in the formal background of sciences, philosophers of physics and physicists working in foundation of physics.