This research deals with several aspects of the relationship between quantum theory and gravitation, especially those which are relevant to understanding the origin and evolution of the universe. This work is part of a line of enquiry that seeks to better understand the effects of gravitation on quantum systems and the quantum nature of gravity. The specific research topics include: (1) The problem of the cosmological constant, a fundamental, unsolved problem in cosmology. The problem will be studied in the context of possible dynamical mechanism that force the value of the cosmological "constant" to decay. (2) Quantum violations of classical energy conditions (e.g. generation of negative energy densities) and their effects upon gravitation. This will study the extent to which one can produce exotic gravitational fields with quantum matter and avoid the singularities of classical general relativity. (3) The limits of validity of the semiclassical approximation to quantum gravity. This is of importance both for understanding the early history of the universe and for guiding the development of a more complete quantum gravity theory. (4) Alternative approaches to quantum field theory. This is a search for new ways of studying quantum processes, especially in the presence of gravity.
