Observer Access as a Boundary Condition: A Foundational Test of the Born Rule

This paper proposes an operational and falsifiable test of whether verified observer access to quantum measurement outcomes correlates with systematic deviations from the Born rule. We introduce a phenomenological indexical weighting factor Φ(I) and a new consistency axiom (NRU – No Retroactive Update) while preserving unitary dynamics. The design uses a clean Access vs. No-access toggle with rigorous controls (including yoked replays and sham-human baselines) and is feasible with existing photonic platforms. Abstract We propose an operational and falsifiable test of whether observer access to quantum measurement outcomes correlates with systematic deviations from the Born rule. The design implements a preregistered toggle between two physically isomorphic conditions: (Access) a live photon stream reaches a human retina and attention is verified via signal-detection measures, versus (No-access) the identical stream is generated and routed but optically blocked at the final millimeter. We formalize a phenomenological weighting of probabilities by an indexical factor Φ(I) over observer frames, derive an observer-access–weighted Born rule that reduces to standard quantum mechanics for uniform Φ, and show that non-signalling holds under locality of Φ̂ together with a no-retroactive-update (NRU) constraint. NRU is introduced axiomatically as a new postulate, and Φ(I) is treated as a phenomenological placeholder rather than a constructive model, with the aim of enabling direct empirical test. This is a preprint version (June 2026). A journal submission is in preparation.