Investigations of Quantum Effects Related to Black Holes and the Early Universe

Wake Forest University, Winston Salem NC

Investigators

Abstract

This award will study black hole evaporation during an inflationary phase in the very early universe. A particular focus will be to determine possible effects that black hole radiation from that time period could have on the cosmic background radiation. If there are potentially observable effects, then these could provide information about the existence of primordial black holes during inflation. Hawking’s original calculation of black hole evaporation gave information about how black holes evaporate at late times after the black hole forms. A detailed study will be made of quantum effects that occur at early and intermediate times in the black hole formation process in a simple model of black hole formation. The results may provide insight into the important question of what happens to the information when a black hole is created. Analog black holes are systems that can be studied in the laboratory and mimic one or more aspects of real black holes. Analog black holes have been made from Bose-Einstein condensates that consist of Rubidium atoms that have been cooled to very low temperatures. Theoretical calculations, similar in nature to those for real black holes, will be made and used to predict the values for certain quantities for these analog black holes that have been measured in the laboratory. If the agreement is found with the experimental data, then that will provide evidence that predictions made by Hawking and others relating to quantum effects in real black holes are correct. The semiclassical approximation in gravity provides a bridge between Einstein’s theory of gravity, general relativity, and a fully quantum theory of gravity. It has been used to study particle production in the early universe as well as black hole evaporation. The validity of the semiclassical approximation will be investigated for two different early universe scenarios. One is for simple models in which the Universe first contracts to a minimum size and then begins expanding. The other is particle production in an important model of inflation called Starobinsky inflation. The particle production occurs after inflation is over and fills the Universe back up with matter and radiation. Two or three graduate students will participate in various aspects of the research. The project will include undergraduate students, continuing a long history of the training of both undergraduate and graduate students in numerical and analytical research techniques and co-authorship on publications. Results will be disseminated to the research community through publications and presentations at national and/or international meetings. The research will address black hole evaporation, observable effects in Bose-Einstein condensates which can serve as black hole analogs, and early universe cosmology. Specifically, it will investigate questions related to whether observable effects could arise from primordial black hole evaporation during inflation, the information about how a black hole forms, the correspondence between theoretical and experimental results related to quantum effects in analog black hole systems, and the validity of the semi-classical approximation in the early universe. For black hole evaporation during inflation, one goal is to determine the effects it could have on the cosmic background radiation. Other quantum effects related to primordial black holes will also be investigated. Black hole evaporation will also be studied in the case that a spherically symmetric shell of radiation collapses to form a black hole. Objectives include gaining insight into the question of what happens to the information about how a black hole forms and to check the accuracy of similar calculations in two dimensional dilaton theories of gravity. Bose-Einstein condensates that can serve as analog black holes have been studied in the laboratory. The goal of the research in this area is to determine whether certain experimental results for Bose-Einstein condensates which can serve as analog black holes are in quantitative agreement with predictions resulting from quantum field theory in curved space calculations in the analog spacetimes. The semiclassical approximation has been used to study important effects in the early universe such as reheating after inflation. One goal of the research is to determine whether the semiclassical approximation is valid in certain models in which the universe contracts to a minimum size and then expands and in the post-inflation era of a well-known model of inflation, sometimes called Starobinsky inflation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.