GIVEN ASSUMPTIONS. “Although a fully‐satisfactory quantum description of black holes is still missing, it is reasonably clear that they represent the states in a Hilbert space of quantized fields. We shall not question this statement.”
https://onlinelibrary.wiley.com/doi/full/10.1002/prop.201800007?casa_token=GdPRXs_tGLEAAAAA%3Ag-pxPMtkcleTYDUNK3mYGfpEzKRyc2LqQknTgFFB7dkYFDL8rDe2s0f4_0Q0oKjXD4_AEgFPGWolVTQ