This article asks what an adequate philosophical response to the certainty of heat death would be: the moment in the timeline of the universe when all possible energy transformations have been actualized and life, thought, and action cease to be possible. Through a reading of Hans Jonas’s existential work on Gnosticism, the article begins by defining what is meant by the notions cosmotheoretical and cosmoethical as well as offering a description of what Jonas calls “cosmic nihilism.” After this, the article (...) looks at two extreme philosophical responses to heat death. The first response examined is by Friedrich Nietzsche, whose eternal return is shown to be a reactive philosophical response to the linear entropic finitude that heat death implies. The second response is by Ray Brassier. Different from Nietzsche, Brassier is shown to affirm the extinction that heat death promises. However, his insistence that heat death partakes of the transcendental and the real, but not the ideal, is demonstrated to be amphibolous. In the final part of the article, I offer what could be called a thermodynamic architectonic response to the heat death of the universe, arguing that heat death should be understood as a guiding transcendental Idea in the Kantian sense of the term. (shrink)