14735 2007.16091 10.1007/JHEP02(2021)009 9 9 Bra-ket wormholes in gravitationally prepared states Regular Article - Theoretical Physics 1 61 2021 2 1 2020 9 15 2020 12 17 2021 2 1 The Author(s) 2021 Open Access. This article is distributed under the terms of the Creative Commons Attribution License ( CC-BY 4.0 ), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited. 13130 2021 2021 2 2 Yiming Chen ymchen.phys@gmail.com Victor Gorbenko vitya@stanford.edu Juan Maldacena malda@ias.edu grid.16750.35 0000 0001 2097 5006 Jadwin Hall Princeton University Princeton New Jersey USA grid.168010.e 0000000419368956 SITP Stanford University Palo Alto California USA grid.78989.37 0000 0001 2160 7918 Institute for Advanced Study Princeton New Jersey USA Abstract We consider two dimensional CFT states that are produced by a gravitational path integral. As a first case, we consider a state produced by Euclidean AdS2 evolution followed by flat space evolution. We use the fine grained entropy formula to explore the nature of the state. We find that the naive hyperbolic space geometry leads to a paradox. This is solved if we include a geometry that connects the bra with the ket, a bra-ket wormhole. The semiclassical Lorentzian interpretation leads to CFT state entangled with an expanding and collapsing Friedmann cosmology. As a second case, we consider a state produced by Lorentzian dS2 evolution, again followed by flat space evolution. The most naive geometry also leads to a similar paradox. We explore several possible bra-ket wormholes. The most obvious one leads to a badly divergent temperature. The most promising one also leads to a divergent temperature but by making a projection onto low energy states we find that it has features that look similar to the previous Euclidean case. In particular, the maximum entropy of an interval in the future is set by the de Sitter entropy. Keywords 2D Gravity Models of Quantum Gravity ArXiv ePrint: 2007.16091