Research on Gravity and Quantum Fluctuation Effects

Tufts University, Medford MA

Investigators

Abstract

Many of the deepest problems in theoretical physics revolve around combining Einstein's theory of general relativity with quantum theory. The resulting theory is called "quantum gravity" and is needed to better understand the origin of the universe, the nature of space and time on small scales, and what happens inside black holes. The research supported by this award will use the latest techniques and tools to try to study quantum fluctuations and their effects, especially rare but large spontaneous fluctuations of energy density. These are subtle effects which are not well understood. The results of this research may have applications to other areas of science and possibly to technology. The large fluctuations to be studied may play a role in nonlinear optics and quantum tunneling, two areas which have broad applications. The project will also have educational benefits. Students will participate in the research and gain valuable experience from doing so. The project should also produce examples which can be used to explain some of the concepts of quantum theory and relativity to students on a variety of educational levels. The project will investigate the probability distributions for quantum stress tensor fluctuations and their applications to gravity theory and other areas of physics. Particular attention will be paid to the asymptotic form of the distribution which governs the probability for large fluctuations. One approach to be used is the calculation of the large moments of the distribution. Preliminary studies indicate that this asymptotic form falls rather slowly compared to that for a thermal distribution. This indicates that quantum vacuum effects could dominate over thermal effects for large fluctuations, and suggests that new physical effects might be discovered in this line of research. Several models will be examined to look for such effects. One will be the effects of radiation pressure fluctuations on quantum tunneling of electrons and other particles. Another model will examine the effects of electric field fluctuations on the propagation of light in a nonlinear material. This study is of interest both for optical physics, and as an analog model for the quantum lightcone fluctuations expected in a quantum theory of gravity. The project will also examine the role of quantum stress tensor fluctuations in the early universe, especially in inflationary models.