Analysts of international security employ notions of the subject or object of security that draw on a Newtonian cosmology. This view of the world, which treats objects as independent of observation and existing before they interact, arose alongside the changes in forms of political community that led to the modern sovereign state. Michael Frayn's play "Copenhagen' examines competing narratives of a meeting in Copenhagen in 1941 between nuclear physicist Niels Bohr, his former student Werner Heisenberg, and Bohr's wife, Margrethe. This article uses a reading of Frayn's play to explore the discontinuities between the cosmology of Bohr and Heisenberg, which takes as accepted the impossibility of independent observation and pre-existing objects, and the picture of security still common in international relations. It asks in what way ideas of security would be changed if a cosmology that recognized the "final core of uncertainty at the heart of things' were taken seriously.