Why are black holes hot?  Eugenio Bianchi, Perimeter Institute
March 5, 2013, 3:30 pm  Black holes are perhaps the most
perfectly thermal objects in the universe. Identifying the
physical mechanism that explains their entropy is a long-
standing problem in theoretical physics. In this talk I discuss
a recent result on entanglement and thermalization that resolves
this puzzle and can have far-reaching implications. The
mechanism was first found in the context of loop quantum
gravity, but it survives in the perturbative regime. I consider
the entanglement entropy of gravitons and matter across the
horizon of a black hole. Remarkably, in low-energy physical
processes, the change in the entanglement entropy reproduces the
Bekenstein-Hawking area law: causal horizons are hot and have an
entropy because of entanglement. The universality of the result
relies on a quantum version of Einstein's equivalence principle.