High Energy Theory Seminar

In 1975 Hawking showed that the evaporation of black holes creates a problem for unitarity. This argument can be made rigorous through the small corrections theorem, and implies that there must be a fundamental change in our picture of semiclassical gravity. In string theory it appears that black hole microstates are horizon sized quantum objects called fuzzballs. We argue that virtual fuzzballs are an important component of the vacuum; their resistance to compression is needed to maintain causality in the semiclassical approximation. This component of the vacuum is also likely to be relevant to understanding cosmology.