Quantum Epistemology Beyond Quantum Measurement

It is well known that quantum mechanics does not, in general, predict any one outcome of a given experiment with certainty, but instead predicts a distribution of probability values for possible outcomes. One enduring question in the interpretation of quantum mechanics is: just what do these probabilities signify? Many believe quantum probabilities represent something objective, such as frequencies of measurement outcomes in repeated trials. Others suggest a perhaps more radical view that quantum probabilities only represent a person's subjective personal beliefs. On this subjective view, different people making predictions with quantum mechanics might even reasonably disagree about the probabilities of experimental outcomes. These objective and subjective interpretations of quantum probability present starkly different philosophical viewpoints. And understanding quantum probabilities is not only important for making sense of the theory itself; it also has implications for the fields of quantum information and quantum computing, which aim to use quantum theory to develop new technologies. The goal of this project is to investigate the status of quantum probability by developing a view that does not require quantum probabilities to be only objective or only subjective, but instead allows for both possibilities. The project will analyze the relationships among objective and subjective probabilities in quantum mechanics to yield important insights about how they both figure into the nature of physical probability.

The current project approaches the interpretation of quantum probability in a novel way by separating questions about probability from other controversial topics in the interpretation of quantum mechanics. The question of whether probabilities are objective frequencies or subjective beliefs has been addressed in existing work by tying an answer to more contentious views about the status of measurements in quantum theory. For example, some investigators reach an understanding of probability based on a view of quantum measurement that implies the existence of a 'multiverse' of many worlds. This project will develop methods for analyzing the relationship between objective and subjective probabilities, methods which do not depend on such highly debated issues. As such, the project aims to make a lasting impact by establishing tools for understanding quantum probability that will apply, regardless of the ultimate interpretation of quantum mechanics. The project will thus lay the foundation for further research and understanding, which will be aided by disseminating the developed methods in a workshop to train early career interdisciplinary researchers, as well as public lectures to engage the broader community in these deep questions about fundamental physics and the nature of probability.

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.