Spacetime and Universal Soft Modes --- Black Holes and Beyond

TL;DR

This work presents a unified UV/IR framework in which chaotic string-scale dynamics mix hard and soft low-energy modes to produce emergent spacetime behind horizons while preserving quantum unitarity. By coarse-graining soft and far modes, the authors derive a thermofield-double–like interior and construct mirror operators that realize infalling physics within a finite causal domain, reconciling horizon smoothness with information conservation. The analysis highlights an $O(1)$ breaking of global symmetries at the string scale and a self-repair mechanism for horizons, and it extends the picture consistently to Rindler, de Sitter, and asymptotically flat spacetimes, linking interior structure to Born-rule–driven observables. The results connect black hole interiors to broader spacetime contexts, including the BMS symmetry in flat space and holographic descriptions, and propose a principled selection of observables through the quantum-to-classical transition. Overall, the paper offers a microscopic mechanism for interior emergence, horizon regularity, and information retrieval across diverse spacetimes.

Abstract

Recently, a coherent picture of the quantum mechanics of an evaporating black hole has been presented which reconciles unitarity with the predictions of the equivalence principle. The thermal nature of a black hole as viewed in a distant reference frame arises from entanglement between the hard and soft modes, generated by the chaotic dynamics at the string scale. In this paper, we elaborate on this picture, particularly emphasizing the importance of the chaotic nature of the string (UV) dynamics across all low energy species in generating large (IR) spacetime behind the horizon. Implications of this UV/IR relation include O(1) breaking of global symmetries at the string scale and a self-repair mechanism of black holes restoring the smoothness of their horizons. We also generalize the framework to other systems, including Rindler, de Sitter, and asymptotically flat spacetimes, and find a consistent picture in each case. Finally, we discuss the origin of the particular construction adopted in describing the black hole interior as well as the outside of a de Sitter horizon. We argue that the construction is selected by the quantum-to-classical transition, in particular the applicability of the Born rule in a quantum mechanical world.

Figures (2)

• Figure 1: A schematic depiction illustrating the idea that a single branch of a quantum state describes only the spacetime region accessible by a single observer. The global spacetime of general relativity (the entire region including those represented by lighter colors) arises only as a "pictorial depiction" obtained by patching possible spacetime histories represented by various branches.
• Figure 2: For a branch having spacetime that appears approximately as a static patch of a de Sitter spacetime, an effective theory can be erected by coarse-graining the soft modes at time $t = t_*$. The resulting theory contains a spatial section of an emergent full de Sitter spacetime, including the other side of the horizon. This theory allows for describing any future development of the branch.