Venzo De Sabbata – författare

The Ninth Course of the International School of Cosmology and Gravita­ tion of the Ettore Majorana Centre for Scientific Culture is concerned with "Topological Properties and Global Structure of Space-Time." We consider this topic to possess great importance. Our choice has also been influenced by the fact that there are many quest ions as yet unre­ solved. Standard general relativity describes space-time as a four-dimensional pseudo-Riemannian manifold, but it does not prescribe its large-scale structure. Inorderto attempt answers to some topological questions, such as whether our universe is open or closed, whether it is orientable, and whether it is complete or possesses singularities, various theoretical approaches to global aspects of gravitational physics are presented here. As topological questions playa role in non-standard theories as weIl, it will be found that some of the lectures and seminar talks in this volume adopt the point of view of standard relativity, whereas others are based on different theories, such as Kaluza-Klein theories, bimetric theories, and supergravity. We have found it difficult to organize these papers into classes, say standard and non-standard theory, or models with and without singularities. One paper, by R. Reasenberg, is experimental. Its purpose was to give the theorists present an inkling of the opportunities, as weIl as the pitfalls, of experimental research in gravitational physics. Accordingly, we have arranged all contributions alphabetically, by ~first-named) author.

Peter Gabriel Bergmann started his work on general relativity in 1936 when he moved from Prague to the Institute for Advanced Study in Princeton. Bergmann collaborated with Einstein in an attempt to provide a geometrical unified field theory of gravitation and electromagnetism. Within this program they wrote two articles together: A. Einstein and P. G. Bergmann, Ann. Math. 39, 685 (1938) ; and A. Einstein, V. Bargmann and P. G. Bergmann, Th. von Karman Anniversary Volume 212 (1941). The search for such a theory was intense in the ten years following the birth of general relativity. In recent years, some of the geometrical ideas proposed in these publications have proved essential in contemporary attempts towards the unification of all interactions including gravity, Kaluza-Klein type theories and supergravity theories. In 1942, Bergmann published the book "Introduction to the Theory of Relativity" which included a foreword by Albert Einstein. This book is a reference for the subject, either as a textbook for classroom use or for individual study. A second corrected and enlarged edition of the book was published in 1976. Einstein said in his foreword to the first edition: "Bergmann's book seems to me to satisfy a definite need. . . Much effort has gone into making this book logically and pedagogically satisfactory and Bergmann has spent many hours with me which were devoted to this end.

Bringing geometric algebra to the mainstream of physics pedagogy, Geometric Algebra and Applications to Physics not only presents geometric algebra as a discipline within mathematical physics, but the book also shows how geometric algebra can be applied to numerous fundamental problems in physics, especially in experimental situations.This reference begins with several chapters that present the mathematical fundamentals of geometric algebra. It introduces the essential features of postulates and their underlying framework; bivectors, multivectors, and their operators; spinor and Lorentz rotations; and Clifford algebra. The book also extends some of these topics into three dimensions. Subsequent chapters apply these fundamentals to various common physical scenarios. The authors show how Maxwell's equations can be expressed and manipulated via space-time algebra and how geometric algebra reveals electromagnetic waves' states of polarization. In addition, they connect geometric algebra and quantum theory, discussing the Dirac equation, wave functions, and fiber bundles. The final chapter focuses on the application of geometric algebra to problems of the quantization of gravity.By covering the powerful methodology of applying geometric algebra to all branches of physics, this book provides a pioneering text for undergraduate and graduate students as well as a useful reference for researchers in the field.

For the Sixth Course of the International School of Cosmology and Gravitation of the "Ettore Maj orana" Centre for Scientific Cul- ture we choose as the principal topics torsion and supergravity, because in our opinion it is one of the principal tasks of today's theoretical physics to attempt to link together the theory of ele- mentary particles and general relativity. Our aim was to delineate the present status of the principal efforts directed toward this end, and to explore possible directions of work in the near future. Efforts to incorporate spin as a dynamic variable into the foundations of the theory of gravitation were poineered by E. Cartan, whose contributions to this problem go back half a century. Accord- ing to A. Trautman this so-called Einstein-Cartan theory is the sim- plest and most natural modification of Einstein's 1916 theory. F. Hehl has contributed a very detailed and comprehensive analysis of this topic, original view of non-Riemannian space-time. Characteristic of Einstein-Cartan theories is the enrichment of Riemannian geometry by torsion, the non-symmetric part of the otherwise metric-compatible affine connection.Torsion has a impact on the theory of elementary particles. According to V. de Sabbata, weak interactions can be based on the Einstein-Cartan geometry, in that the Lagrangian describing weak interactions and torsion inter-- action possess analogous structures, leading to a unification of weak and gravitational forces.

The Ninth Course of the International School of Cosmology and Gravita­ tion of the Ettore Majorana Centre for Scientific Culture is concerned with "Topological Properties and Global Structure of Space-Time." We consider this topic to possess great importance. Our choice has also been influenced by the fact that there are many quest ions as yet unre­ solved. Standard general relativity describes space-time as a four-dimensional pseudo-Riemannian manifold, but it does not prescribe its large-scale structure. Inorderto attempt answers to some topological questions, such as whether our universe is open or closed, whether it is orientable, and whether it is complete or possesses singularities, various theoretical approaches to global aspects of gravitational physics are presented here. As topological questions playa role in non-standard theories as weIl, it will be found that some of the lectures and seminar talks in this volume adopt the point of view of standard relativity, whereas others are based on different theories, such as Kaluza-Klein theories, bimetric theories, and supergravity. We have found it difficult to organize these papers into classes, say standard and non-standard theory, or models with and without singularities. One paper, by R. Reasenberg, is experimental. Its purpose was to give the theorists present an inkling of the opportunities, as weIl as the pitfalls, of experimental research in gravitational physics. Accordingly, we have arranged all contributions alphabetically, by ~first-named) author.

Bringing geometric algebra to the mainstream of physics pedagogy, Geometric Algebra and Applications to Physics not only presents geometric algebra as a discipline within mathematical physics, but the book also shows how geometric algebra can be applied to numerous fundamental problems in physics, especially in experimental situations.This reference begins with several chapters that present the mathematical fundamentals of geometric algebra. It introduces the essential features of postulates and their underlying framework; bivectors, multivectors, and their operators; spinor and Lorentz rotations; and Clifford algebra. The book also extends some of these topics into three dimensions. Subsequent chapters apply these fundamentals to various common physical scenarios. The authors show how Maxwell's equations can be expressed and manipulated via space-time algebra and how geometric algebra reveals electromagnetic waves' states of polarization. In addition, they connect geometric algebra and quantum theory, discussing the Dirac equation, wave functions, and fiber bundles. The final chapter focuses on the application of geometric algebra to problems of the quantization of gravity.By covering the powerful methodology of applying geometric algebra to all branches of physics, this book provides a pioneering text for undergraduate and graduate students as well as a useful reference for researchers in the field.

This book gives an exposition of both the old and new results of spin and torsion effects on gravitational interactions with implications for particle physics, cosmology etc. Physical aspects are stressed and measurable effects in relation to other areas of physics are discussed.Among the topics discussed are: alternative ways of unifying gravity with electroweak and strong interactions by an energy dependent spin torsion coupling constant; the idea that all interactions can be understood as originating from spin curvature coupling; the possibility of cosmological models with torsion providing a solution to the cosmological constant problem; and a demonstration that torsion can lead directly to the quantization of space-time itself.

This volume contains the Proceedings of "Quantum Gravity": a series of qualified lectures of most outstanding scientists given during the XIV Course of the International School of Cosmology and Gravitation. As usual of that School, the Course was conceived for researchers at different levels of scientific maturity ranging from post-doctorate research students to well established research workers: then in every lecture you can find an introduction where a review and analysis of the main mathematical, physical and epistemological difficulties encountered at the formulations of relativistic quantum theories are expounded, ranging from relativistic quantum mechanics and quantum field theory in Minkowski and in curved space-time to the various canonical and covariant approaches to quantum gravity.

The introduction of spin is believed to be a necessary tool if one wishes to quantize general relativity. Then the main problem is to see if the introduction of spin generalizing the general relativity from a geometric point of view, i.e. through the concept of torsion, can be experimentally verified.The reader can find in this book both theoretical and experimental arguments which show the necessity for the introduction of spin, and then of torsion, in gravity. In fact, torsion constitutes the more natural and simple way to introduce spin in general relativity. For that reason it is of fundamental importance to see if there are some experiences that indicate — if not directly, then at least indirectly — the presence of torsion. This book presents a discussion on experiments with a polarized-mass torsion pendulum, the search for galactic dark matter interacting with a spin pendulum, a description of a space-based method for determination of the gravitational constant and space-based measurements of spin in gravity, as well as a discussion on theoretical arguments, for instance the nature of torsion and nonmetricity, the viability of gravitational theories with spin-torsion and spin-spin interaction, many-dimensional gravitational theories with torsion, spinors on curved spaces, the spinors in real space-time, etc.We know that until now there has been no evidence for torsion, but this fact cannot prevent us from considering in some detail this implement of research that seems to be important from both a geometrical and a physical point of view.