Black Holes and Beyond

TL;DR

This paper discusses how string theory's fuzzball concept resolves the black hole information paradox by replacing the classical horizon with a quantum structure, allowing information to escape and challenging traditional semiclassical views.

Contribution

It introduces the fuzzball paradigm as a solution to the information paradox, showing how extended objects in string theory alter black hole interiors and enable information retrieval.

Findings

Fuzzballs replace classical horizons in black holes.

Information escapes via radiation from fuzzball microstates.

Semiclassical approximation breaks at macroscopic scales due to entropy.

Abstract

The black hole information paradox forces us into a strange situation: we must find a way to break the semiclassical approximation in a domain where no quantum gravity effects would normally be expected. Traditional quantizations of gravity do not exhibit any such breakdown, and this forces us into a difficult corner: either we must give up quantum mechanics or we must accept the existence of troublesome `remnants'. In string theory, however, the fundamental quanta are extended objects, and it turns out that the bound states of such objects acquire a size that grows with the number of quanta in the bound state. The interior of the black hole gets completely altered to a `fuzzball' structure, and information is able to escape in radiation from the hole. The semiclassical approximation can break at macroscopic scales due to the large entropy of the hole: the measure in the path integral competes with the classical action, instead of giving a subleading correction. Putting this picture of black hole microstates together with ideas about entangled states leads to a natural set of conjectures on many long-standing questions in gravity: the significance of Rindler and de Sitter entropies, the notion of black hole complementarity, and the fate of an observer falling into a black hole.