Time Fisher information associated with fluctuations in quantum geometry

• Published in: Europhysics letters 2022-09, Vol.139 (6), p.62002
• Main Authors: Wani, Salman Sajad, Quach, James Q., Faizal, Mir
• Format: Article
• Language: English
• Subjects: Constraints; Fisher information; Quantum gravity
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/0295-5075/ac8caf

As time is not an observable, we use Fisher information (FI) to address the problem of time. We demonstrate that although the Hamiltonian operator is the generator of time, the Hamiltonian constraint operator cannot observe the change that arises through the passage of time. This is because the Hamiltonian constraint does not contain time FI. As we also identify an alternative operator on the world-sheet which does contain time FI, we argue that the timelessness of quantum gravity occurs due to the use of an inappropriate operator. We propose that a criterion for a physically meaningful operator in any quantum gravitational process is that it should contain non-vanishing time FI. Although we explicitly derive these results on the world-sheet of bosonic strings, we argue that it holds for any quantum geometry associated with time-reparametrization–invariant classical geometry.