Black-Hole Entropy Bridges in a CPT-Symmetric Cosmology: A falsifiable toy framework for oppositely oriented thermodynamic branches

Abstract

We propose a speculative, falsifiable framework in which black holes act not as entropy sinks but as information-preserving bridges between CPT-conjugate cosmological branches with oppositely oriented thermodynamic arrows. The universe is modeled as two CPT-related sectors emerging from a low-complexity boundary: a matter-dominated branch corresponding to our observable universe and an antimatter-dominated conjugate branch. Observers in either branch experience time as progressing toward increasing entropy, while the complete spacetime may retain an underlying CPT symmetry. Within this geometry, a black hole in one branch may continue through a quantum-gravitational transition region into a white-hole-like, anti-trapped sector associated with the conjugate branch. Information entering the black hole is therefore redistributed among horizons, radiation, bulk degrees of freedom, and cross-branch correlations rather than destroyed. Generalized entropy is defined across the combined system and required to remain compatible with the generalized second law and unitary evolution. We further introduce a conjectural cross-branch extension of quantum-extremal-surface and island reasoning, allowing the entropy of Hawking radiation in one branch to depend on correlations with regions belonging to its CPT partner. This could reconcile apparently inaccessible entropy transfer with globally unitary information conservation. The proposal therefore replaces “entropy dumping” with an information-preserving geometric mechanism. Black holes do not reverse time by removing entropy; instead, they may connect thermodynamic sectors whose arrows point in opposite global directions while remaining locally forward-directed. The framework yields concrete tests involving junction conditions, energy conditions, stability, Page curves, cross-branch quantum extremal surfaces, and consistency with cosmological observations.

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