Origin of the highest energy cosmic rays

Abstract

After briefly recalling the history of discovery of cosmic rays, the present statns of the subject is discussed. Cosmic-ray particles with energy exceeding 1020 eV have been detected. The origin of cosmic rays remains an unsolved problem in physics and astrophysics. The nature of the source(s) as well as the physical mechanism(s) responsible for endowing the cosmic-ray particles with extremely high energies are not known with certainty. We discuss some recent ideas in this context with special emphasis on the problem of origin of the highest-energy cosmic rays.