Cosmologies, singularities and quantum extremal surfaces

Understand

Following arXiv:2012.07351 [hep-th], we study quantum extremal surfaces in various families of cosmologies with Big-Crunch singularities, by extremizing the generalized entropy in 2-dimensional backgrounds which can be thought of as arising from dimensional reduction.

• Focussing first on the isotropic $AdS$ Kasner case, introducing a spatial regulator enables relating the locations in time of the quantum extremal surface and the observer.
• This shows that the quantum extremal surface lags behind the observer location.
• A potential island-like region, upon analysing more closely near the island boundary, turns out to be inconsistent.