Quantum Superpositions of Black Holes

          @misc{ pirsa_23050123,
            doi = {10.48660/23050123},
            url = {https://pirsa.org/23050123},
            author = {Mann, Robert},
            keywords = {Quantum Gravity, Cosmology},
            language = {en},
            title = {Quantum Superpositions of Black Holes},
            publisher = {Perimeter Institute},
            year = {2023},
            month = {may},
            note = {PIRSA:23050123 see, \url{https://pirsa.org}}
          }
          

Abstract

If relativistic gravitation has a quantum description, it must be meaningful to consider a spacetime metric in a genuine quantum superposition. Here I present a new operational framework for studying “superpositions of spacetimes” via model particle detectors. After presenting the general approach, I show how it can be applied to describe a spacetime generated by a BTZ black hole in a superposition of masses and how such detectors would respond. The detector exhibits signatures of quantum-gravitational effects reminiscent of Bekenstein’s seminal conjecture concerning the quantized mass spectrum of black holes in quantum gravity. I provide further remarks in distinguishing spacetime superpositions that are genuinely quantum-gravitational, notably with reference to recent proposals to test gravitationally-induced entanglement, and those in which a putative superposition can be re-expressed in terms of dynamics on a single, fixed spacetime background.