Robert Geroch, University of Chicago 
Faster than light?

It is widely believed that relativity -- both special and general -- requires that no physical signal travel at a speed faster than that of light.  For instance, the assumption that there could be superluminal signals in relativity gives rise to well-known paradoxes.  We suggest that this situation is not nearly as dire as it appears at first sight.  Indeed, we shall argue that relativity in the presence of superluminal signals is virtually as viable and self-consistent as that without.