What if? Exploring the multiverse through Euclidean wormholes

9 pags., 4 figs., app. -- Open Access funded by Creative Commons Atribution Licence 4.0We present Euclidean wormhole solutions describing possible bridges within the multiverse. The study is carried out in the framework of third quantisation. The matter content is modelled through a scalar field which supports the existence of a whole collection of universes. The instanton solutions describe Euclidean solutions that connect baby universes with asymptotically de Sitter universes. We compute the tunnelling probability of these processes. Considering the current bounds on the energy scale of inflation and assuming that all the baby universes are nucleated with the same probability, we draw some conclusions about which universes are more likely to tunnel and therefore undergo a standard inflationary era.This article is based upon work from COST Action CA15117 “Cosmology and Astrophysics Network for Theoretical Advances and Training Actions (CANTATA)”, supported by COST(European Cooperation in Science and Technology). The work of M.B.-L. is supported by the Basque Foundation of Science Ikerbasque. She and J.M. also wish to acknowledge the partial support from the Basque government GrantNo. IT956-16 (Spain) and FONDOS FEDER under grant FIS2014-57956-P (Spanish government). The research of M.K. was financed by the Polish National Science Center Grant DEC- 2012/06/A/ST2/00395 and by a grant for the Short Term Scientific Mission (STSM) “Multiverse impact onto the cosmic microwave background and its relation to modified gravity” (COST-STSM-CA15117- 36137) awarded by the above-mentioned COST Action. M.K. and J.M. would like to thank the Centro de Matemática e Aplicações of the Universidade da Beira Interior in Covilhã, Portugal for kind hospitality while part of this work was done.M.K. also thanks M.P. Da˛browski for fruitful discussions. J.M. is thankful to UPV/EHU for a Ph.D. fellowship.Peer Reviewe