  All entropy is entanglement entropy. This appears as the result of the
existence of black holes. The origin of entropy and the way in which it defines
the perceived time direction in macroscopic systems has been discussed and can
be debated as long as one ignores black holes. In such a case, thermodynamic
entropy may define the arrow of time and entanglement entropy defines some
special globally defined entropy encoding information in a non-local sense.
With black holes however, if we accept that in-falling objects must have their
information encoded outside, for example through non-local fluctuations away
from thermalisation of the Hawking radiation, and that the horizon of a black
hole cuts all classical information from the outside, then all the entropy that
can be added to the black hole, which is basically any form of entropy, must be
translated into some form of entanglement entropy to be detected outside. A
discussion about the nature of information channels shows that spacetime may
not be a correlation-insensitive channel as usually employed in the engineering
of quantum computing. Time may emerge as a property of the complexity of
entanglement spreading.
