The Reality of the Quantum State


Quantum mechanics is one of the most prominent theories of physics to date. However, since its conception, there have been disputes about the interpretation of its main object: the quantum state of a system. Are quantum states aspects of the world (ontic interpretation), or do they represent our knowledge about a system (epistemic interpretation)?

For some eighty years, this has been mainly a philosophical question. However, in 2012, Pusey, Barrett and Rudolph (PBR) showed that, given some intuitive assumptions, an epistemic interpretation is in conflict with quantum mechanical predictions. Specifically, their theorem demonstrates that, in any model that is able to reproduce the predictions of quantum mechanics, and in which states give a direct description of reality, the quantum state must be part of this description of reality. Obviously, such a result requires that the notion of an ontic interpretation of quantum states is formalized within the language of mathematics. In this project this step will be severely scrutinized to assess the precise philosophical import of the PBR theorem and other so-called ψ-ontology theorems. In addition, there are two sub-projects on the implications of ψ-ontology theorems.

The first concerns the implications for the quantum mechanical description of macroscopic systems. Quantum mechanics allows for the possibility of superposition states which, on an ontic interpretation, leads to the famous paradox of Schrödinger's cat. This sub-project explicates the possibilities for reconciling the quantum description of macroscopic systems with our every day experience.

The second focuses on the role of quantum states as generators for probability functions. Does an ontic interpretation of quantum states directly imply that these probabilities are also intrinsic properties of the world? And if not, what do ψ-ontology theorems tell us about the nature of quantum probabilities? These questions will be answered in the second sub-project.





Dr. R. Hermens

Verbonden aan

Rijksuniversiteit Groningen


Dr. R. Hermens


16/01/2018 tot 31/08/2020