A physicist found a brand new particle nobody needed, and reacted with three words

In 1936, Carl Anderson and Seth Neddermeyer found a particle in cosmic-ray tracks with a mass between the electron's and the proton's: the muon. It behaved almost exactly like a heavier electron and answered no outstanding question in physics; it wasn't even the particle Hideki Yukawa had predicted to carry the nuclear force. Physicist Isidor Rabi reportedly responded to the news by asking, 'Who ordered that?'

— Carl D. Anderson and Seth Neddermeyer, Muon — Physical Review, 1936-1937