Branches of the Black Hole Wave Function Need Not Contain Firewalls

Understand

We discuss the branching structure of the quantum-gravitational wave function that describes the evaporation of a black hole.

• A global wave function which initially describes a classical Schwarzschild geometry is continually decohered into distinct semiclassical branches by the emission of Hawking radiation.
• The laws of quantum mechanics dictate that the wave function evolves unitarily, but this unitary evolution is only manifest when considering the global description of the wave function; it is not implemented by time evolution on a single semiclassical branch.
• Conversely, geometric notions like the position or smoothness of a horizon only make sense on the level of individual branches.