generalized second law of thermodynamics     physics,
mathematical physics, philosophy of physics  Surveys, textbooks
and lecture notes  theory (physics), model (physics)
experiment, measurement, computable physics    The standard
second law of theormodynamics? states that in a closed system of
classical mechanics or quantum mechanics the (coarse-grained)
entropy is non-decreasing with time.  This is statement is to be
tacitly understood as applying to dynamics taking place on an
a-priori fixed spacetime (a fixed “background”). If however one
takes also gravity into account as part of the “system”, then
the statement of the second law becomes much more subtle.  The
generalized second law of theoremodynamics is an attempt to
generalize the naive second law to general relativity. A central
idea is that the Bekenstein-Hawking entropy of horizons (such as
of black holes) has to be added to the naive entropy of the
matter in the “universe”.   A detailed discussion is in    •
Aron Wall, Ten proofs of the generaliz