  A coherent picture of the quantum mechanics of a collapse-formed, evaporating
black hole is presented. In a distant frame, semiclassical theory in the zone
describes microscopic dynamics of only the "hard modes," the modes that are
hard enough to be discriminated in the timescale of Hawking emission. The
thermal nature of these modes arises from microcanonical typicality of the full
black hole degrees of freedom, mostly composed of the "soft modes," the modes
that cannot be discriminated at the semiclassical level. The hard modes are
purified by a combined system of the soft modes and early Hawking radiation,
but not by either of them separately. This intrinsically tripartite structure
of entanglement is general, regardless of the age of the black hole. The
interior spacetime emerges only at a coarse-grained level. To describe it, an
effective theory can be erected at each time, which applies only to a limited
spacetime region determined by the time at which the theory is erected. The
entire interior of the black hole can be described only using multiple
effective theories erected at different times, realizing the idea of
complementarity. We analyze implications of the entanglement structure
described here for various phenomena, including Hawking evaporation and general
information retrieval. For multiple entangled black holes, it implies that
semiclassical objects dropped into different black holes cannot meet in the
interior, although each object smoothly enters the horizon of the black hole to
which it is falling. We also discuss physics in Rindler space, elucidating how
it is obtained as a smooth limit of the black hole physics.
