A Groundwork for Perspectival Quantum Mechanics
MetadataShow full item record
There has recently been a renewed focus on ‘perspectival’ quantum theories. which simultaneously maintain the existence of single measurement outcomes and the universality of unitary evolution. At the same time, these theories have come under attack with results by Frauchiger and Renner, Baumann and Wolf, and others. This dissertation aims to respond to a number of these attacks by providing a groundwork for these types of theories. To lay this groundwork I focus on encapsulated measurements, which involve an isolated observer and a superobserver (who measures the observer). I first distinguish between invasive and non-invasive measurements. Each leads to a possible inconsistency: In non-invasive measurements, the observer is certain of the superobserver’s measurement outcome while the superobserver’s physics predicts multiple possible outcomes. In invasive measurements the superobserver can be certain of his measurement outcome while the observer predicts non-zero probabilities for all possible outcomes. I argue that in the case of non-invasive measurements, the perspectivalist avoids diffculty by denying that the observer’s result has any impact on the physics experienced by the superobserver. Consistency is then maintained between them by looking to the unitary evolution of the superobserver’s measurement. This response leads to a detailed discussion about the metaphysical commitments of the perspectival approach. Here I argue the perspectivalist must accept one surprising result – there is a significant divorce of fundamental ontological states from physical dynamics. Turning to invasive measurements, I argue that the concern here is entirely misplaced. Arguments that raise worries about invasive measurements assume the observer should describe herself to be in a quantum state of having observed her measurement outcome when predicting the superobserver’s measurement results. I argue that this is incorrect. Rather, I explain that it is impossible for any observer to know her quantum state and so she should never describe herself as being in any quantum state at all, let alone use such a description to make predictions about a superobserver’s measurement. To conclude, I explain how the perspectivalist responds to concerns raised about entanglement and the possibility of action at a distance. Combining this with the results above brings into focus how the perspectivalist may develop a consistent, single-world picture of quantum mechanics.