Complementarity Endures: No Firewall for an Infalling Observer

TL;DR

The paper argues that the complementarity framework in quantum gravity remains consistent with the equivalence principle, resolving the firewall paradox by emphasizing the role of quantum state evolution and classical emergence.

Contribution

It demonstrates that the complementarity interpretation avoids the firewall paradox through a detailed analysis of quantum state evolution and classical emergence.

Findings

Quantum states evolve unitarily without firewalls.

Classical world arises consistently within quantum mechanics.

Complementarity remains valid in the context of black hole horizons.

Abstract

We argue that the complementarity picture, as interpreted as a reference frame change represented in quantum gravitational Hilbert space, does not suffer from the "firewall paradox" recently discussed by Almheiri, Marolf, Polchinski, and Sully. A quantum state described by a distant observer evolves unitarily, with the evolution law well approximated by semi-classical field equations in the region away from the (stretched) horizon. And yet, a classical infalling observer does not see a violation of the equivalence principle, and thus a firewall, at the horizon. The resolution of the paradox lies in careful considerations on how a (semi-)classical world arises in unitary quantum mechanics describing the whole universe/multiverse.