Clocks, correlations and interactions in timeless quantum theory

Thesis

The notion of time as an external parameter regulating the dynamics of physical systems is unsatisfactory from an explanatory point of view. It also clashes with the background-independent character of general relativity. These issues, which constitute part of the so-called “problem of time”, can be solved via a relational approach, that is, by recovering a notion of time from the relations between different physical systems. Quantum relational approaches to time are the most promising as they would be compatible with a hypothetical quantum theory of gravity. These approaches share many similarities and find a natural explanation if quantum theory is understood as a universal physical theory, so we gather them under the term “timeless quantum theory”. Timeless quantum theory recovers an emergent notion of time from the correlations between different subsystems of a stationary quantum Universe. Some of these systems play a special role by acting as clocks. Clocks are usually entangled with the rest of the Universe but do not interact with it. In this thesis, we study the role of clocks, correlations and interactions in timeless quantum theory. We clarify the interpretation of the time instants of the theory and show that the clocks can interact with the rest of the Universe. We also discuss how different correlations with the clocks affect the theory. Finally, we examine the role of interactions and their effect on the relational dynamics and the timekeeping qualities of the clocks. Our results elucidate crucial explanatory aspects of timeless quantum theory and improve its robustness. They also point to several exciting avenues for future research, such as the generalisation to more realistic clocks, the prediction of novel physical effects, and the design of new experiments that could test quantum aspects of time. These lines of inquiry promise to advance our understanding of the interface between quantum theory and relativity.

Authors: Rijavec, S

• DOI: 10.5287/ora-dpgv2epq5
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: relational; quantum theory; quantum gravity; time
• Subjects: Quantum theory; Physics