Dartmouth Events

ABSTRACT: Quantum Mechanics and General Relativity are both well developed, well tested theories that help us understand nature at a more fundamental level. Each are very good at explaining their respective domains: Quantum Mechanics for the micro world and General Relativity for the macro. However, a tension arises between the two famous theories when Quantum Mechanics is assumed to extend into the macroscopic domain. According to General Relativity, massive particles distort spacetime. If such particles also obey the rules of Quantum Mechanics, then they can be put in a superposition of two macroscopically different states, distorting spacetime in an unclassical way. How can we reconcile this with General Relativity as a classical theory given that it describes a unique curvature of spacetime caused by classical mass distributions?

This question has occupied physicists’ and philosophers’ minds since at least the mid 20^th century; theorists have tried to harmonize the two theories mathematically while experimentalists have been looking for ways to create a massive superposition state, and philosophers have explored how the quantum world impacts our everyday notions about reality. In this thesis, I will be looking into some of the key literature surrounding the macro quantum matter-classical gravity tension and its implications for our understanding of the nature of reality. I will also be interviewing several scientists and philosophers working in the field in order to describe the current active debates concerning this tension. An integral third component of this thesis will be a theoretical analysis of a simple model of a massive quantum particle interacting with a fluctuating gravitational field. This model will serve to illustrate how gravity can rapidly destroy quantum superpositions of massive quantum particles, thereby possibly removing the tension by enforcing macroscopic, classical reality.