Holography of time machines

Abstract

We use holography to examine the response of interacting quantum fields to the appearance of closed timelike curves in a dynamically evolving background that initially does not contain them. For this purpose, we study a family of two-dimensional spacetimes that model very broad classes of wormhole time machines. The behavior of strongly coupled conformal theories in these spacetimes is then holographically described by three-dimensional AdS bulk geometries that we explicitly construct. The dual bulk spacetime is free from any divergences, but splits into two disconnected components, without and with CTCs, which are joined only through the boundary; then, passages across the chronology horizon are impossible for any field excitations. In dual terms, the strong self-interaction of the CFT decouples the pathological part from the rest of the spacetime. We also find that entangling the CFTs in two separate time machines connects them through a traversable bulk wormhole. Nevertheless, any entanglement-assisted chronology violations will be prevented by quantum bulk corrections, i.e., subleading 1/N effects, again without needing any gravitational backreaction of the CFT. We are led to speculate that chronology may be protected without involving Planck scale physics.

The correspondence between rotating black holes and fundamental strings

“…In [49,50] it was found that the size of static strings agrees with the random-walk estimate in (4.4) [47]. In a companion paper [51] we compute the size of rotating strings; in particular we find agreement with the random-walk expectation (4.24).…”

“…If the black ring managed to reach this coupling intact, we would expect it to become a ring-shaped string state very unstable to breaking apart into multiple string balls, i.e., not a very different outcome than if the black ring had fragmented in the first place. The existence of this instability can indeed be verified using the formalism in [13] for self-gravitating string states [61].…”

Black hole-wormhole collisions and the emergence of islands

“…In particular, we chose to connect the two mouths with a zero length bridge which effectively provides a shortcut in spacetime. Imposing the physically-relevant achronal averaged null energy condition amounts to making the length through the wormhole longer than the direct path without crossing the wormhole [13,34,37]. In practice, this will move down the green cone in Fig.…”

“…Unfortunately, in this setting a similar definition using retarded time appears to be out of reach. 6 It should be noted that imposing the AANEC amounts to requiring that L > d, so that the wormhole is 'long' [13,34,37]. Eq.…”

Unruh-DeWitt detector in dimensionally-reduced static spherically symmetric spacetimes

“…In this case, the boundary conditions will be captured by the Wightman function W (x, x ) with respect to the truncated metric, similar to the Vaidya and star scenarios, and then one takes the proper time derivative on both arguments. Some aspects of QFT on AdS 2 and its topological identification (e.g., those that produce time machines) were recently investigated [44][45][46][47][48][49] and they are readily extended to the derivative coupling variant [50].…”