AdS/CFT Correspondence
The Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence is a duality in string theory. It states that a gravitational theory in a higher-dimensional space (AdS) is mathematically equivalent to a quantum field theory without gravity on its lower-dimensional boundary (CFT).
Implication for Information
Since the boundary CFT is a standard quantum theory, it is unitary and conserves information. Therefore, the dual gravitational theory (including black holes) must also be unitary. This strongly suggests that information is NOT lost during black hole evaporation, even if we don't yet know exactly how it escapes.
Open Questions
While AdS/CFT works in idealized universes, our universe is not Anti-de Sitter. How these insights apply to real-world asymptotically flat spacetimes remains an active area of research.