We refine and extend a recent construction of sets of black hole microstates
with semiclassical interiors that span a Hilbert space of dimension $e^S$,
where $S$ is the black hole entropy. We elaborate on the definition and
properties of microstates in statistical and black hole mechanics. The
gravitational description of microstates employs matter shells in the interior
of the black hole, and we argue that in the limit where the shells are very
heavy, the construction acquires universal validity. To this end, we show it
for very wide classes of black holes: we first extend the construction to
rotating and charged black holes, including extremal and near-extremal
solutions, with or without supersymmetry, and we sketch how the construction of
microstates can be embedded in String Theory. We then describe how the approach
can include general quantum corrections, near or far from extremality. For
supersymmetric black holes, the microstates we construct differ from other
recent constructions in that the interior excitations are not confined within
the near-extremal throat.

The Future of Black Hole Microstates: Challenges and Opportunities

In recent years, significant progress has been made in the study of black hole microstates, particularly in understanding their semiclassical interiors. These microstates span a Hilbert space of dimension $e^S$, where $S$ represents the black hole entropy. Building upon this recent construction, it is important to outline a future roadmap that not only refines and extends the existing understanding but also identifies potential challenges and opportunities on the horizon.

Definition and Properties of Microstates

Before delving into the roadmap, it is crucial to first examine the definition and properties of microstates in both statistical and black hole mechanics. Microstates are essentially configurations or arrangements of matter within the interior of a black hole that contribute to its overall entropy. By understanding and characterizing these microstates, we can gain insights into the fundamental nature of black holes.

Universality of the Construction

One key aspect to address in the future roadmap is the claim of universal validity for the construction of microstates. It has been argued that as matter shells within the black hole become increasingly heavy, the construction becomes universally applicable. However, this claim needs further investigation and verification. Future research should focus on refining and strengthening this argument to ensure its validity across various classes of black holes.

Including Rotating and Charged Black Holes

Expanding the construction to include rotating and charged black holes is another important objective outlined in the roadmap. This extension would allow for a more comprehensive understanding of black hole microstates and their behavior in different physical scenarios. Additionally, considering extremal and near-extremal solutions, with or without supersymmetry, would provide valuable insights into the range of possibilities within black hole systems.

Embedding in String Theory

One prominent opportunity on the horizon is the potential for embedding the construction of black hole microstates within String Theory. String Theory offers a powerful framework for studying the quantum nature of black holes. Exploring how the existing construction can be integrated into String Theory would provide a deeper connection between black hole microstates and fundamental physics, opening new avenues for research.

Quantum Corrections and Extremality

Incorporating general quantum corrections, both near and far from extremality, is another crucial challenge that lies ahead. Understanding how quantum effects modify the behavior of black hole microstates would greatly enhance our understanding of the interplay between gravity and quantum physics. It would also shed light on the dynamical properties of black holes in various regimes.

Differences in Supersymmetric Black Holes

A notable aspect of the microstates constructed for supersymmetric black holes is their deviation from other recent constructions. In this roadmap, one potential challenge is to further explore these differences and understand the implications they have for the interior excitations of near-extremal throats. Investigating these deviations could potentially uncover unique properties of supersymmetric black hole microstates.


The future roadmap for black hole microstates is filled with both challenges and opportunities. By refining and extending the existing construction, researchers can strive towards a more comprehensive understanding of black hole interiors. Addressing universal validity, incorporating rotating and charged black holes, exploring embeddings in String Theory, studying quantum corrections, and investigating differences in supersymmetric black holes are all crucial steps in advancing our knowledge of black hole microstates. With each obstacle overcome, new doors will open, revealing deeper insights into the fundamental nature of these enigmatic cosmic entities.

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