Ultrahigh energy cosmic rays

This is a review of the most resent results from the investigation of the ultrahigh energy cosmic rays, particles of energy exceeding 10¹⁸eV. After a general introduction to the topic and a brief review of the lower energy cosmic rays and the detection methods, the two most recent experiments, the High Resolution Fly’s Eye and the Southern Auger Observatory, are described. Results from these two experiments on the cosmic ray energy spectrum, the chemical composition of these cosmic rays, and searches for their sources are presented. An analysis of the controversies in these results and the projects in development and construction that can help solve the remaining problems with these particles is also presented.