Ernst held a temporary professorship at the Department of Media Studies at the Bauhaus Universität Weimar ("Geschichte und Theorie künstlicher Welten" / History and Theory of Artificial Worlds), at the Institute for Film and Television Studies at the Ruhr-Universität Bochum ("Theorie, Geschichte und Ästhetik der Medien / Theory, History and Media Aesthetics), at the University of Paderborn ("Medienwissenschaft: Schwerpunkt gesellschaftliche und historische Bezüge"/ Media Studies: Specialization in Social and History-Related Topics ), as well as at the Humboldt-Universität Berlin ("Ästhetik und Geschichte der Medien"/ Aesthetics and Media History).

His main research focus covers the use of media in visual recollection, non-discursive places of recollection and remembrance, cultural transmission techniques, time-specific technical aesthetics, and critical media.