Abstract: Ivan Karamazov's nightmare reflects his deep ideological crisis. In the story of Ivan Karamazov's "rebellion" against God, his arguments about recently discovered non-Euclidean geometries play a major role. Confessing that he cannot understand and accept the idea of non-Euclidean geometry and the idea of worlds arranged according to different laws than our world, Ivan therefore denies the possibility for himself to sincerely believe in God. The strange connection between non-Euclidean geometry and belief in God is confirmed by an episode in The Brothers Karamazov, in which Ivan has a vision of the devil. In describing paradise, the devil uses the latest scientific concepts and non-Euclidean geometry, clearly demonstrating that new scientific theories can help a person find faith. This connection, important for the story of Ivan Karamazov, can be explained by the fact that in Dostoevsky's philosophical worldview the existence of "other worlds" plays a very important role as an expression of an unusual interpretation of the idea of immortality. If we accept the idea of people's existence after death in "other worlds", then scientific theories about "other worlds" can be seen as revealing those dimensions of being, where man will visibly understand the existence of God and the possibility of immortality.