This book is devoted to an extensive and systematic study on unitary representations of the Poincaré group. The Poincaré group plays an important role in understanding the relativistic picture of particles in quantum mechanics. Complete knowledge of every free particle states and their behaviour can be obtained once all the unitary irreducible representations of the Poincaré group are found. It is a surprising fact that a simple framework such as the Poincaré group, when unified with quantum theory, fixes our possible picture of particles severely and without exception. In this connection, the theory of unitary representations of the Poincaré group provides a fundamental concept of relativistic quantum mechanics and field theory.

This book is devoted to an extensive and systematic study on unitary representations of the Poincaré group. The Poincaré group plays an important role in understanding the relativistic picture of particles in quantum mechanics. Complete knowledge of every free particle states and their behaviour can be obtained once all the unitary irreducible representations of the Poincaré group are found. It is a surprising fact that a simple framework such as the Poincaré group, when unified with quantum theory, fixes our possible picture of particles severely and without exception. In this connection, the theory of unitary representations of the Poincaré group provides a fundamental concept of relativistic quantum mechanics and field theory.

Special relativity and quantum mechanics, formulated early in the twentieth century, are the two most important scientific languages and are likely to remain so for many years to come. In the 1920's, when quantum mechanics was developed, the most pressing theoretical problem was how to make it consistent with special relativity. In the 1980's, this is still the most pressing problem. The only difference is that the situation is more urgent now than before, because of the significant quantity of experimental data which need to be explained in terms of both quantum mechanics and special relativity. In unifying the concepts and algorithms of quantum mechanics and special relativity, it is important to realize that the underlying scientific language for both disciplines is that of group theory. The role of group theory in quantum mechanics is well known. The same is true for special relativity. Therefore, the most effective approach to the problem of unifying these two important theories is to develop a group theory which can accommodate both special relativity and quantum mechanics. As is well known, Eugene P. Wigner is one of the pioneers in developing group theoretical approaches to relativistic quantum mechanics. His 1939 paper on the inhomogeneous Lorentz group laid the foundation for this important research line. It is generally agreed that this paper was somewhat ahead of its time in 1939, and that contemporary physicists must continue to make real efforts to appreciate fully the content of this classic work.

This is the first of two volumes containing papers submitted by the invited speakers to the 11th International Congress of Logic, Methodology and Philosophy of Science, held in Cracow in 1999, under the auspices of the International Union of History and Philosophy of Science, Division of Logic, Methodology and Philosophy of Science. The invited speakers are the leading researchers and accordingly the book presents the current state of the intellectual discourse in the respective fields. The papers delivered at the congress were divided into 17 sections. Thus the structure of the volume corresponds to the very schedule of the congress. Volume one contains the opening lecture by Andrzej K. Wróblewski as well as invited papers in sections of Proof Theory, Model Theory, Recursion Theory, Axiomatic Set Theory, Logic and Computation, Logic, Language and Cognition, Methodology, Probability, Induction, and Decision Theory, Philosophy of Logic, Mathematics, and Computer Science, and Philosophy of the Physical Sciences.

Today, quantum field theory (QFT)—the mathematical and conceptual framework for contemporary elementary particle physics—is the best starting point for analysing the fundamental building blocks of the material world. QFT if taken seriously in its metaphysical implications yields a picture of the world that is at variance with central classical conceptions. The core of Kuhlmann’s investigation consists in the analysis of various ontological interpretations of QFT, e.g. substance ontologies as well as a process-ontological approach. Eventually, Kuhlmann proposes a dispositional trope ontology, according to which particularized properties and not things are the most basic entities, in terms of which all other entities are to be analysed, e.g as bundles of properties. This book was chosen for the 2009 ontos-Award for research on analytical ontology and metaphysics by the German Society for Analytical Philosophy.

This book covers advanced topics in quantum mechanics, including nonrelativistic multi-particle systems, relativistic wave equations, and relativistic fields. Numerous examples for application help readers gain a thorough understanding of the subject. The presentation of relativistic wave equations and their symmetries, and the fundamentals of quantum field theory lay the foundations for advanced studies in solid-state physics, nuclear, and elementary particle physics. The authors earlier book, Quantum Mechanics, was praised for its unsurpassed clarity.