Why Firewalls Need Not Exist

TL;DR

This paper argues that the firewall paradox arises from limitations of semiclassical theory rather than fundamental physics, suggesting firewalls are unnecessary and proposing a new view of Hawking radiation.

Contribution

It clarifies how the paradox stems from semiclassical approximations and introduces a revised understanding of black hole radiation without firewalls.

Findings

Semiclassical Hilbert space is exponentially smaller than the fundamental one.

Semiclassical theory includes an unphysical large Fock space.

Eliminates the need for firewalls and offers a new perspective on Hawking emission.

Abstract

The firewall paradox for black holes is often viewed as indicating a conflict between unitarity and the equivalence principle. We elucidate how the paradox manifests as a limitation of semiclassical theory, rather than presents a conflict between fundamental principles. Two principal features of the fundamental and semiclassical theories address two versions of the paradox: the entanglement and typicality arguments. First, the physical Hilbert space describing excitations on a fixed black hole background in the semiclassical theory is exponentially smaller than the number of physical states in the fundamental theory of quantum gravity. Second, in addition to the Hilbert space for physical excitations, the semiclassical theory possesses an unphysically large Fock space built by creation and annihilation operators on the fixed black hole background. Understanding these features not only eliminates the necessity of firewalls but also leads to a new picture of Hawking emission contrasting pair creation at the horizon.