Firewalls From Double Purity

TL;DR

This paper argues that the firewall paradox stems from the concept of double purity rather than double entanglement, challenging traditional views on black hole horizons and complementarity.

Contribution

It introduces a new perspective that the paradox arises from double purity and critiques existing complementarity models, proposing that local horizon detection is key to understanding firewalls.

Findings

The paradox is rooted in double purity, not entanglement.

Hilbert space identifications cannot resolve the paradox.

Local horizon detection, not violence probability, is crucial for firewalls.

Abstract

The firewall paradox is often presented as arising from double entanglement, but I argue that more generally the paradox is double purity. Near-horizon modes are purified by the interior, in the infalling vacuum. Hence they cannot also be pure alone, or in combination with any third system, as demanded by unitarity. This conflict arises independently of the Page time, for entangled and for pure states. It implies that identifications of Hilbert spaces cannot resolve the paradox. Traditional complementarity requires the unitary identification of infalling matter with a scrambled subsystem of the Hawking radiation. Extending this map to the infalling vacuum overdetermines the out-state. More general complementarity maps ("A=R_B", "ER=EPR") founder when the near-horizon zone is pure. I argue that pure-zone states span the microcanonical ensemble, and that this suffices to make the horizon a special place. I advocate that the ability to detect the horizon locally, rather than the degree or probability of violence, is what makes firewalls problematic. Conversely, if the production of matter at the horizon can be dynamically understood and shown to be consistent, then firewalls do not constitute a violation of the equivalence principle.