Thermodynamic Split Conjecture and an Observational Test for Cosmological Entropy (2509.13689v1)

Abstract: We revisit string theoretic derivations of black hole entropy and argue that their enabling structures do not persist in realistic cosmologies. We formalize this as the Thermodynamic Split Conjecture (TSC) which is the statement that in any UV complete quantum gravity, black hole and cosmological horizon thermodynamics are generically inequivalent. The BKE criterion is then formulated to formalize this approach while we also discuss ways to falsify the conjecture. Finally, we propose an observational scaling test which is centered around comparisons of data native entropy proxies from tomographic maps to the Bekenstein Hawking prediction. The framework both sharpens when and why the area law holds and provides a roadmap towards a UV complete description of cosmological horizon entropy.