Does entanglement change a photon's local behaviour at fixed reduced state? A proposal for an exploratory test

Exploratory test proposal (version 2, 5 November 2026). It compares, for an observable measured on the signal photon only, a photon from an entangled pair and a photon from a separable pair with the same reduced state. Standard quantum mechanics predicts strict equality; the author's hypothesis (the "flucton") allows a difference whose sign and size are not predicted. The document specifies the two preparations, separability and local-state checks, a main observable fixed in advance (fringe visibility), a blind 5-sigma decision rule and an ideal statistical sensitivity. It is a proposal to be adapted by experimental groups, not the quantitative prediction of a new theory; no experiment has been carried out. English text with full French translation. Prepared with AI assistance (Claude, Anthropic); the author is responsible for the scientific content.