New research has broken an important ‘barrier’ in neutrino physics which is relevant for both particle physics and cosmology. A new upper limit of 0.8 electronvolt (eV) for the mass of the neutrino has been obtained. This first push into the sub-eV mass scale of neutrinos by a model-independent laboratory method allows KATRIN to constrain the mass of these ‘lightweights of the universe’ with unprecedented precision.