Relativity Reframed: Quantum Reference Frames and Gravity

Quantum reference frames (QRFs) have emerged as a powerful and rapidly developing framework in fundamental physics, providing a systematic approach to formulating theories without fixed classical backgrounds. By making explicit the relational structure of physical laws, QRFs supply concrete tools to define subsystems, observables, and quantum information in diffeomorphism-invariant and dynamically fluctuating spacetimes. Their applications span quantum gravity, algebraic and curved-spacetime quantum field theory, quantum information, cosmology, and phenomenology, refining our understanding of locality, causality, symmetry, and measurement beyond semiclassical regimes. In gravitational settin