Wormholes and entropies in de sitter space-time

In this thesis, we explore the feasibility of creating wormholes connecting between regions of spacetime. We start by discussing the recent progress using black holes anti-de Sitter (AdS), where the amount of negative required for preventing its collapse can be produced by (artificially) coupling the 2 asymptotic boundaries together. The amount of information that can be transferred is bounded by (the absolute value of) the energy. We then continue the discussion in de Sitter (dS), where the energy requirement for opening wormholes carries the opposite sign. However, increasing the energy content to open larger wormholes in dS drastically modifies its spacetime structure to Schwarzschild-de Sitter (SdS). We therefore study the SdS geometry in more detail and highlight the importance of special observers. The observers situated at the right distance of the black hole, will neither fall into it nor getting pulled away by the cosmic expansion, thus defining the (inertial) static observers. For completeness, we analyzed charged black holes in dS. We then conclude by studying the causal structure of SdS, before introducing the double wormhole that forms as the positive energetic Hawking radiation emitted from the black holes reaches the cosmological horizon.