Quantum mechanics was formulated on the basis of the existence of an ideal classical clock external to the system. The rate of the universal loss of unitarity was estimated using optimal realistic clocks. The loss of unitarity is universal thus affecting all physical phenomena. It is observed that the rate is enough to eliminate the black hole information puzzle.
Publication Source (Journal or Book title)
Physical Review Letters
Gambini, R., Porto, R., & Pullin, J. (2004). Realistic clocks, universal decoherence, and the black hole information paradox. Physical Review Letters, 93 (24) https://doi.org/10.1103/PhysRevLett.93.240401