Remnants, Fuzzballs or Wormholes?

TL;DR

This paper reviews three main theoretical resolutions to the black hole information paradox, including remnants, fuzzballs, and wormholes, highlighting recent developments and their implications for black hole physics.

Contribution

It categorizes and compares three sharp theoretical approaches to resolving the black hole information paradox based on quantum strong-subadditivity.

Findings

Remnants imply information loss or a baby universe.

Fuzzballs provide a unitary evaporation mechanism.

Wormholes suggest extreme nonlocality connecting radiation and interior.

Abstract

The black hole information paradox has caused enormous confusion over four decades. But in recent years, the theorem of quantum strong-subaddditivity has sorted out the possible resolutions into three sharp categories: (A) No new physics at $r\gg l_p$; this necessarily implies remnants/information loss. A realization of remnants is given by a baby Universe attached near $r\sim 0$. (B) Violation of the `no-hair' theorem by nontrivial effects at the horizon $r\sim M$. This possibility is realized by fuzzballs in string theory, and gives unitary evaporation. (C) Having the vacuum at the horizon, but requiring that Hawking quanta at $r\sim M^3$ be somehow identified with degrees of freedom inside the black hole. A model for this `extreme nonlocality' is realized by conjecturing that wormholes connect the radiation quanta to the hole.