The Quest for a Fundamental Theory of Physics - Rise and Demise of the Field Paradigm

Abstract

Quite remarkably, the two physical theories that describe extremely well physical phenomena on the largest and smallest distance scales in our universe, viz. general relativity and quantum theory, respectively, are radically disparate. Both theories are now almost a century old and have passed with flying colours every test to which they have been put, but they seem to be telling us completely different stories about the nature of physical reality. Loosely formulated, general relativity is a local, deterministic, background independent theory, while quantum theory is fundamentally nonlocal, indeterministic and background dependent, with experiments moreover putting very strong constraints on any interpretation of the quantum world that is more akin to general relativity in the first two respects. This thesis is essentially a detailed and critical review of both these fundamental theories, as well as the further developments they spawned. Regarding the first aspect, issues such as the historical emergence and conceptual foundations of both theories are crucially dealt with, while notions such as black holes, the thermodynamic arrow of time, applications of quantum theory to field systems, renormalization theory and the standard models of modern cosmology and particle physics are key to the second aspect. Two other equally important and related, but so far critically unresolved issues in this latter regard revolve around the question of how to interpret the quantum formalism and the problem of how to integrate both theories into an overall unified framework a so called theory of quantum gravity. In dealing with these issues, the discussion includes fairly comprehensive and critical treatments of constructs as esoteric as string M-theory, the anthropic landscape and parallel quantum universes, as well as apparently somewhat more worldly ideas, such as loop quantum gravity, Bohmian beables, and the quantum-classical cut. Although the upshot of these discussions is that there are good reasons to think that both quantum theory and general relativity will have to undergo subtle, but profound revisions before a successful, even-handed quantum gravity scheme can be formulated, the status of quantum theory is specifically focussed upon here. Indeed, one of the main conclusions of the present work is that quantum theory, in spite of all its triumphant empirical confirmations, is most presumably an approximate theory.