#### Date of Award

8-2013

#### Document Type

Thesis

#### Degree Name

Master of Science (MS)

#### Legacy Department

Physics

#### Advisor

Hartmann, Dieter

#### Committee Member

Tewari , Sumanta

#### Abstract

In this thesis, we consider the implications of solving the quantum measurement problem for the Newtonian description of semiclassical gravity. First we review the formalism of the Newtonian description of semiclassical gravity based on standard quantum mechanics - the Schroedinger-Newton theory - and two well-established predictions that come out of it, namely, gravitational 'cat states' and gravitationally-induced wavepacket collapse. Then we review three quantum theories with 'primitive ontologies' that are well-known known to solve the measurement problem - Schroedinger's many worlds theory, the GRW collapse theory with matter density ontology, and Nelson's stochas- tic mechanics. We extend the formalisms of these three quantum theories to Newtonian models of semiclassical gravity and evaluate their implications for gravitational cat states and gravitational wavepacket collapse. We find that (1) Newtonian semiclassical gravity based on Schroedinger's many worlds theory is mathematically equivalent to the Schroedinger-Newton theory and makes the same predictions; (2) Newtonian semiclassical gravity based on the GRW theory differs from Schroedinger-Newton only in the use of a stochastic collapse law, but this law allows it to suppress gravitational cat states so as not to be in contradiction with experiment, while allowing for gravita- tional wavepacket collapse to happen as well; (3) Newtonian semiclassical gravity based on Nelson's stochastic mechanics differs significantly from Schroedinger-Newton, and does not predict gravita- tional cat states nor gravitational wavepacket collapse. Considering that gravitational cat states are experimentally ruled out, but gravitational wavepacket collapse is testable in the near future, this implies that only the latter two are viable theories of Newtonian semiclassical gravity and that they can be experimentally tested against each other in future molecular interferometry experiments that are anticipated to be capable of testing the gravitational wavepacket collapse prediction.

#### Recommended Citation

Derakhshani, Maaneli, "Newtonian Semiclassical Gravity In Three Ontological Quantum Theories That Solve The Measurement Problem: Formalisms And Empirical Predictions" (2013). *All Theses*. 1764.

https://tigerprints.clemson.edu/all_theses/1764