Emergent Locality from Depth-Restricted Quantum Dynamics

We introduce a framework in which spacetime locality and geometric causal structure are not assumed as fundamental, but instead emerge conditionally from quantum dynamics under restricted observational access. We define depth as a restriction on the set of observables accessible to an observer and show that, un- der appropriate conditions of redundancy and decoherence, effective locality and finite propagation speed arise from intrinsically nonlocal quantum systems. Con- versely, locality degrades when these conditions fail. Using simple toy models, we demonstrate threshold behavior separating regimes with and without stable causal structure. This approach reframes spacetime geometry as an emergent description rather than a primitive input, while remaining compatible with standard quantum mechanics and general relativity within their respective domains of validity.