Rebbe Nachman teaches: People say that there are two worlds, this world and the World to Come. We all believe that there is a World to Come. This world may also exist somewhere. However, with all the suffering that we see in the world and what people must endure, where we are now must be Gehinnom! (Likutey Moharan II, 119).
Reb Noson told one of his followers, “If you were constantly happy, you wouldn’t see Gehinnom” (Kokhavey Or, p. 78).