Main approaches to the solution of the paradox 

Information is irretrievably lost

• Advantage: Seems to be a direct consequence of relatively non-controversial calculation based on semiclassical gravity.
• Disadvantage: Violates unitarity, as well as energy conservation or causality.
  

  Information gradually leaks out during the black-hole evaporation

  
  
  • Advantage: Intuitively appealing because it qualitatively resembles information recovery in a classical process of burning.
  • Disadvantage: Requires a large deviation from classical and semiclassical gravity (which do not allow information to leak out from the black hole) even for macroscopic black holes for which classical and semiclassical approximations are expected to be good approximations.
    

    Information that suddenly escapes out during the final stage of black-hole evaporation

    
    
    • Advantage: A significant deviation from classical and semiclassical gravity is needed only in the regime in which the effects of quantum gravity are expected to dominate.
    • Disadvantage: Just before the sudden escape of information, a very small black hole must be able to store an arbitrary amount of information, which violates the Bekenstein bound.
      

      Information is stored in a Planck-sized remnant

      
      
      • Advantage: No mechanism for information escape is needed.
      • Disadvantage: To contain the information from any evaporated black hole, the remnants would need to have an infinite number of internal states. It has been argued that it would be possible to produce an infinite amount of pairs of these remnants since they are small and indistinguishable from the perspective of the low-energy effective theory.
        

        Information is stored in a baby universe that separates from our own universe

        
        
        • Advantage: No violation of known general principles of physics is needed.
        • Disadvantage: It is difficult to find an appealing concrete theory that would predict such a scenario.
          

          Information is encoded in the correlations between future and past

          
          

          • Advantage: Semiclassical gravity is sufficient, i.e., the solution does not depend on details of (still not well understood) quantum gravity.
          • Disadvantage: Contradicts the intuitive view of nature as an entity that evolves with time