The Cardinality of Experience Is Underdetermined by the Quantum State: A Constructive Case for a Consciousness-Primitive Interpretation

Version 2 (2026-07-15) — change note. §8 (Empirical Purchase) revised: the Φ ≤ S conjecture is withdrawn. A validated retest — canonical IIT Φ (PyPhi 1.2.0) versus the entanglement entropy of a transverse-field Ising ground state built from the same couplings, N=216, seed 42 — refutes it: the 89% hold rate equals a permutation null (produced entirely by the Φ=0 systems), and every one of the 23 systems with nonzero integrated information violates the bound. The raw Φ–S correlation (r≈+0.65) is a connectivity confound that does not survive a partial-correlation control (partial r=−0.02, p=0.77). Added the Mayner et al. (2018) PyPhi reference; Code Availability updated (repository tag paper-2026-07-15, with an end-to-end reproducibility package). Sections 2–7 are unchanged. Quantum mechanics and the metaphysics of consciousness are usually pursued apart; this paper joins them with a result and an interpretation. The result: the number of unified subjects of experience — the cardinality of experience — is not fixed by anything operationally accessible to a localized perspective in a no-collapse setting; we exhibit this computationally and state it precisely. The significance of the result lies less in the underdetermination itself than in what follows from it: the decombination problem (the standard objection to cosmopsychism) and Everett's how-many-minds problem are the same underdetermination seen from opposite sides, meaning the dialectical cost is shared, not a special liability of consciousness-first views. The non-determination isolates the minimal posit every no-collapse interpretation must add. Taking that posit as ground yields a structural cosmopsychism on which a universal subject's self-relational structure is the Hilbert-space structure. Advaita Vedānta supplies illuminating labels for moves the view defines independently.