What is the argument against the hypothesis that information loss in a black hole as initially thought can be the reason for omnipresent increase in entropy of the Universe?

In other words, if we take that information is lost in the black hole (I do not want to argue this assumption), can that increase exactly account for an apparent increase of entropy in the Universe?

This line of thought would imply that entropy of the universe is zero, something similar to idea that the energy of the Universe is zero.

  • $\begingroup$ The question is pretty clear to me. $\endgroup$
    – peterh
    Feb 26, 2017 at 17:37

1 Answer 1


If you believe in the Hawking radiation, which follows pretty clearly from semiclassical assumptions (and via something like 20 different derivations) in a regime where semiclassicality is beyond reasonable (as in, you have microscopic quantum fields, and a stellar-mass black hole, which should preclude regime mixing), then the black hole is literally in a thermodynamic equilibrium with Hawking radiation. If you believe this, then you inevitably have to associate an entropy with the black hole, and then the second law basically becomes "the area of a black hole will increase by at least as much as the entropy of what you threw into the black hole"

If you are going to doubt this picture, then you have to doubt one of the following, in inverse order of likelihood that they're wrong:

  1. Thermodynamics/Stat Mech itself
  2. Quantum Field Theory
  3. General Relativity
  4. The semiclassicality assumption

But they are all pretty good assumptions. Semiclassicality may fail if quantum gravity has some sort of nonlinear effect that trickles all of the way up, though -- say if Hawking radiation is forbidden by some rule of quantum gravity, in the way that the decay of the Hydrogen ground state is forbidden, for example.


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