Roberto Emparan

Title: Holography of Chronology Protection
Abstract: After an introduction to time-machine spacetimes and simple models of them, I will discuss recent work with M. Tomasevic where we use holography to study quantum effects when closed timelike curves (CTCs) are developed. We address the question of whether it is possible to send a signal across the chronology horizon, passing into the region where CTCs are present. We find that the self-interaction of quantum fields manages to banish the passage of field excitations into the non-chronal region. Going further, we compute the gravitational backreaction of the quantum fields, and show that the null chronology horizon turns into a strong, spacelike curvature singularity. This is one of the few controlled, explicit examples where we can see quantum effects change a Cauchy horizon into a spacelike singularity.