Tacet is a research publication dedicated to sound arts and experimental music. Tacet, as John Cage showed so well in 4’33“, designates a moment of silence observed by an instrumentalist during the whole period of a movement. By extension, it becomes, as the title of this publication, a moment of introspection, of reflectivity and reflection, where music interrupts itself to give way to research and theoretical questioning. The fourth issue is on the theme of utopias. Mixing science-fiction short stories, theoretical analysis and artists’ writings, this issue addresses utopian and dystopian futures of our sound cultures. Issue edited by Matthieu Saladin, with texts by Cornelius Cardew, J. G. Ballard, François J. Bonnet, Pali Meursault, Em’kal Eyongakpa & Amal Alhaag, Scott Gleason, Andy McGraw, Henry Flynt, Christophe Levaux, Francis Heery, Jonathan Sterne, Filipe Barros Beltrao & Andrew Gray, Pascal Broccolichi, Thibault Walter, Anne Zeitz, Loïc Bertrand, Luc Ferrari, Xavier Hug, G Douglas Barrett.