Why Firewalls Need Not Exist

Understand

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.