AMPS Firewall
In 2012, Almheiri, Marolf, Polchinski, and Sully (AMPS) argued that complementarity fails. They used entanglement monogamy: a particle near the horizon cannot be maximally entangled with both the outgoing Hawking radiation AND the infalling partner mode. To preserve unitarity (entanglement with radiation), the entanglement across the horizon must be broken.
Breaking Entanglement
Breaking the entanglement across the horizon releases a huge amount of energy. This creates a 'firewall'—a wall of high-energy particles—at the event horizon. An infalling observer would be incinerated instantly, violating the Equivalence Principle.
Complementarity vs. Firewall
Complementarity
- Horizon is smooth (Equivalence Principle holds)
- Information is duplicated globally but not locally
- Relies on observer-dependent reality
Firewall
- Horizon is a high-energy barrier
- Unitarity is strictly preserved
- Equivalence Principle is violated at the horizon