Greisen–Zatsepin–Kuzmin limit

The Greisen–Zatsepin–Kuzmin (GZK) limit refers to a fundamental limit on the energy of cosmic rays, particularly protons, due to interactions with the cosmic microwave background (CMB) radiation. This limit is named after three physicists: Kenneth Greisen, Georgiy Zatsepin, and Vitaly Kuzmin, who independently identified this phenomenon in the early 1960s.