  In this paper, we try to construct black hole thermodynamics based on the
fact that, the formation and evaporation of a black hole can be described by
quantum unitary evolutions. First, we show that the Bekenstein-Hawking entropy
$S_{BH}$ may not be a Boltzmann or thermal entropy. To confirm this statement,
we show that the original black hole's "first law" may not simply be treated as
the first law of thermodynamics formally, due to some missing metric
perturbations caused by matter. Then, by including those (quantum) metric
perturbations, we show that the black hole formation and evaporation can be
described in a unitary manner effectively, through a quantum channel between
the exterior and interior of the event horizon. In this way, the paradoxes of
information loss and firewall can be resolved effectively. Finally, we show
that black hole thermodynamics can be constructed in an ordinary way, by
constructing statistical mechanics.
