The study of black holes has revealed a deep connection between
quantum information and spacetime geometry. Its origin must lie
in the quantum theory of gravity, which offers a valuable hint in
our search for a unified theory. Precise formulations of this relation
recently led to new insights in Quantum Field Theory, some of which
have been rigorously proven. An important example is our discovery
of the first universal lower bound on the local energy density. The
energy near a point can be negative but it is bounded below by a
quantity related to the information flowing past the point.