Beyond entropic content: photon absorption as causal conjunction and a three-level taxonomy of physical causality

We demonstrate that the standard two-level taxonomy of physical causality — propagative causality bounded by c (Special Relativity) and statistical non-locality (Bell correlations) — is formally incomplete. A photon is not merely a carrier of entropic content S(σ): it constitutes a structured causal block B(σ) encoding, via quantum Fisher information, the complete causal history acquired from emission onwards. Upon absorption, the causal information borne by this block is discharged instantaneously into the receiving system, bringing into permanent causal contact two histories that had no prior causal relation. This constitutes a genuinely new causal level (Level 3: causal conjunction) irreducible to propagation or pre-existing entanglement. We establish this irreducibility mathematically (photon absorption is a push-out in the bicategory Cbl of causal blocks, with a non-faithful forgetful functor U: Cbl → Q_CPTP), operationally (the same channel produces G(|g⟩) = 1.000 bit, G(|+⟩) = 0.601 bit, G(I/2) = 0.189 bit depending on the absorber state — a Bloch sphere hierarchy no channel property predicts), and experimentally (three falsifiable predictions in circuit-QED: φ-scan contrast 0.971 bit at 97σ; the Bloch sphere hierarchy at >40σ; double ratio R₂ = 3.81 at φ = π, derived from the full Schrieffer–Wolff integral with the causal block form factor, verified non-perturbatively). Reproducible Python scripts (experiments 01–12) are available at github.com/ARTUS10/causal-block-photon.