Robustness of the Page-Wootters construction across different pictures, states of the universe and system-clock interactions

Understand

In quantum theory, the concept of time rests on shaky ground.

• One way to address this problem is to remove the usual background time parameter as a primitive entity and explain its emergence via correlations between physical systems.
• This approach was adopted by Page and Wootters (1983), who showed how time can emerge in a stationary quantum universe from the correlations between two of its subsystems, one of them acting as a clock for the other.
• In this work, I study the robustness of the Page-Wootters construction across different pictures, states of the universe and clock interactions, clarifying the role and the nature of the correlations between the subsystems of the universe.