Can the thermodynamic arrow of time in a single universe temporarily reverse in semiclassical gravity? In a unified spacetime where quantum field theory meets classical general relativity, black holes, traversable wormholes, and retrocausal formalisms (absorber, two-vector) create the appearance of exporting entropy. By distinguishing types of gravitational entropy and introducing a cosmological coarse-grained measure, these processes are analyzed on an information-theoretic basis. Within "Global Entropy Transport" (GET), a sectoral inequality is derived: the net decrease in matter-radiation entropy is bounded above by changes in horizon area and mutual information under a generalized second law, focusing conditions, and energy conditions. The bottom line: black holes, wormholes, and retrocausal protocols merely redistribute entropy, locally altering production but never reversing the universal thermodynamic arrow in a connected universe.
Time is a one-way road: events race forward with no U-turn allowed. The arrow of direction is governed by entropy — a measure of disorder, which only grows in the Universe, like a traffic jam at rush hour. You can clear one intersection, but the overall congestion only gets worse.
Even the wildest “detours” — black holes and wormholes in curved spacetime — won’t let you drive the wrong way. Scientists applied the method of global entropy accounting (Global Entropy Transport) and proved: these objects just shuffle disorder from one pocket to another, like tidying one closet but leaving the whole house a mess, while the total chaos in the Universe keeps growing.
The striking conclusion: the entropy of a typical black hole is billions of times greater than that of an ordinary star — these monsters are veritable warehouses of disorder. The arrow of time is as solid as asphalt: even fanciful wormholes can’t make it show the way to the past.
🎯 The entropy of a black hole depends on the area of its surface (event horizon), not its volume — this discovery by [scientist:Jacob Bekenstein]Jacob Bekenstein[/scientist] gave rise to the idea of a holographic Universe.
🎬 In Greg Egan’s novel ‘Schild’s Ladder,’ the characters try to cheat thermodynamics, but the arrow of time remains relentless.