The primary cosmic-ray spectrum has been measured up to an energy of 10²⁰ eV, and several groups have described projects under development or in mind to investigate the spectrum further, into the energy range 10²¹-10²² eV. This note predicts that above 10²⁰ eV the primary spectrum will steepen abruptly, and the experiments in preparation will at last observe it to have a cosmologically meaningful termination.
No takes yet. Share an insight, caveat, or question.
K. Greisen (1966) studied this question.