Quantum many-systems, such superfluids, are difficult to study in equilibrium, and thus understanding their dynamics poses a particular challenge. When the strength of interactions was suddenly changed in a two-dimensional gas of cesium atoms, Hung et al. (p. 1213, published online 1 August; see the Perspective by Schmiedmayer and Berges) observed oscillations in the time and space domains analogous to the peaks in the spectrum of the cosmic microwave background.
