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**UNC-CH Physics and Astronomy Dissertation Defense**

Dillon Morse

**“Semi-Classical Backreaction of Quantum Scalar Fields on an Evolving Spacetime”**

The formalism required to extend quantum field theory to curved spacetimes has been studied extensively for the last 40 years. In all treatments of the subject the quantum field is heavily influenced by the spacetime curvature; the geometry, however, is assumed to evolve subject only to classical matter and independently of the energies and pressures of the quantum field. The primary obstacle to solving the fully self-consistent backreaction problem lies in the complexity of the (formally divergent) energy momentum tensor of the quantum field. We explore a number of new approaches towards understanding the underlying mathematics in hopes of determining a physically realistic, finite expression for the energy momentum tensor which describes the quantum field in a particular vacuum state while also influencing the evolution of the spacetime geometry itself.