UW-Milwaukee Department of Mathematical Sciences presents,

Dr. John Friedman;
Distinguished Professor Emeritus
Department of Physics
University of Wisconsin-Milwaukee

Friday October 9, 2015
2:00pm in EMS E495

**Light Refreshments will be served beginning at 1:30pm in EMS E424A**

Title:
The topological censorship theorem

Description/Abstract:
Every three-dimensional manifold occurs as the spatial topology of a vacuum spacetime (a Ricci flat 4-manifold) and of a spacetime with positive energy. Despite this fact and the common occurrence of wormholes in science fiction, there is no observational evidence for noneuclidean topology in our own spacetime. The topological censorship theorem provides one reason for this: In a spacetime with positive energy, no isolated topological structure can persist long enough for a light ray to traverse it. An implication of the
theorem is that the event horizon of any stationary black hole has the spatial topology of a 3-sphere.