Wormholes and islands

This thesis explores the topic of spacetime wormholes and islands. Wormholes can be thought of as smooth bridges between two far away, disconnected points in spacetime. A wormhole that allows information to travel through it is called traversable. For a wormhole to be traversable it needs to be supported by negative energy, which is not easily produced. In recent developments, a non-local coupling connecting two sides of a double sided black hole was constructed by Gao, Jafferis and Wall, which allows holographic wormholes to become traversable. In this thesis, we investigate various features of this geometry, such as the amount of information that can be sent through. We also construct a new wormhole geometry in higher dimensions.
Additionally, we study islands, a much newer concept in physics. Recently, the Page curve of Hawking radiation was recovered within semi-classical gravity, using the island formula. Essentially, what was realized is that in order to correctly calculate the fine grained entropy of the radiation we need to include in the computation a disconnected region that usually lies inside the black hole, called the island. The island formula naturally has been applied mostly to black holes, where we have a clear notion of the information paradox. Moreover, there have been found some conditions that are necessary in order to have an island. In this thesis, we apply these conditions to open and closed sliced FRW cosmologies and investigate in which cases it is possible to have an island.