Quantum Mechanics And Gravity
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Quantum Mechanics and Gravity
Author: Mendel Sachs
language: en
Publisher: Springer Science & Business Media
Release Date: 2013-06-29
Theoretical physics is presently at a very exciting time in the history of scientific discovery. For we are at a precipice facing two conflicting 20th century revolutionary movements in physics, each purporting to be basic truths of nature - the quantum theory and the theory of relativity. In the 20th century the mathematical expression of the quantum theory yielded correct predictions of a great deal of the data on the behavior of the molecular, atomic, nuelear and elementary partiele domains of matter. In the same period, the theory of relativity suc cessfully described new features of material systems. In special rela tivity, the relativistic Doppler effects (transverse and longitudinal) of electromagnetic radiation, and the mechanics of matter that moves at speeds elose to the speed of light, revealing, for example, the en 2 ergy mass relation, E = mc , revolutionized our thinking. In its form of general relativity, it has yielded a formalism that successfully pre dicted features of the phenomenon of gravity, also predicted by the elassical Newtonian theory, but in addition, features not predicted by the elassical theory, thereby superceding Newton's theory of universal gravitation. The problem we are now faced with, in these early decades of the 21st century, is that in their precise mathematical forms and their conceptual bases, the theory of relativity and the quantum theory are both logically and mathematically incompatible.
The Problem of Time
This book is a treatise on time and on background independence in physics. It first considers how time is conceived of in each accepted paradigm of physics: Newtonian, special relativity, quantum mechanics (QM) and general relativity (GR). Substantial differences are moreover uncovered between what is meant by time in QM and in GR. These differences jointly source the Problem of Time: Nine interlinked facets which arise upon attempting concurrent treatment of the QM and GR paradigms, as is required in particular for a background independent theory of quantum gravity. A sizeable proportion of current quantum gravity programs - e.g. geometrodynamical and loop quantum gravity approaches to quantum GR, quantum cosmology, supergravity and M-theory - are background independent in this sense. This book's foundational topic is thus furthermore of practical relevance in the ongoing development of quantum gravity programs. This book shows moreover that eight of the nine facets of the Problem of Time already occur upon entertaining background independence in classical (rather than quantum) physics. By this development, and interpreting shape theory as modelling background independence, this book further establishes background independence as a field of study. Background independent mechanics, as well as minisuperspace (spatially homogeneous) models of GR and perturbations thereabout are used to illustrate these points. As hitherto formulated, the different facets of the Problem of Time greatly interfere with each others' attempted resolutions. This book explains how, none the less, a local resolution of the Problem of Time can be arrived at after various reconceptualizations of the facets and reformulations of their mathematical implementation. Self-contained appendices on mathematical methods for basic and foundational quantum gravity are included. Finally, this book outlines how supergravity is refreshingly different from GR as a realization of background independence, and what background independence entails at the topological level and beyond.
Quantum Space
Author: Jim Baggott
language: en
Publisher: Oxford University Press
Release Date: 2018-11-08
Today we are blessed with two extraordinarily successful theories of physics. The first is Albert Einstein's general theory of relativity, which describes the large-scale behaviour of matter in a curved spacetime. This theory is the basis for the standard model of big bang cosmology. The discovery of gravitational waves at the LIGO observatory in the US (and then Virgo, in Italy) is only the most recent of this theory's many triumphs. The second is quantum mechanics. This theory describes the properties and behaviour of matter and radiation at their smallest scales. It is the basis for the standard model of particle physics, which builds up all the visible constituents of the universe out of collections of quarks, electrons and force-carrying particles such as photons. The discovery of the Higgs boson at CERN in Geneva is only the most recent of this theory's many triumphs. But, while they are both highly successful, these two structures leave a lot of important questions unanswered. They are also based on two different interpretations of space and time, and are therefore fundamentally incompatible. We have two descriptions but, as far as we know, we've only ever had one universe. What we need is a quantum theory of gravity. Approaches to formulating such a theory have primarily followed two paths. One leads to String Theory, which has for long been fashionable, and about which much has been written. But String Theory has become mired in problems. In this book, Jim Baggott describes