The article deals with the competition of scientific and pseudoscientific trends in informal knowledge of the social networks. The author obtains new data on the mechanisms of introduction of scientific knowledge into the space of network communication in the post-truth era. She examines the ordinary knowledge, explores the processes of its formalization within the framework of the institutes of professional production of knowledge and deformalization in the conditions of informal Internet communication. Informal knowledge of social networks is subject to post-truth algorithms. The post-truth based on the representation of personal subjective experience of knowledge of the world. The author interprets the post-truth as a specific strategy of orientation in superdense arrays of digital communication, a strategy that involves the full activation of all cognitive abilities of a person, implemented in the digital media environment of our time. The post-truth also creates additional competitive advantages for the replication of pseudoscience in the media environment and complicates the popularization of scientific knowledge. The study of informal social knowledge generated in social networks and the determination of dynamics in the development of forms of dialogue between science and society will not only expand the understanding of the modern social role of science and pseudoscientific knowledge, but also optimize the training of scientists and improve the quality of popularization of science in the country.