Pierre Auger on Cosmic Rays
"In his excellent paper, Louis LePrince-Ringuet, citing a remark of Powell's at the Conference of Bagneres-de-Bigorre in 1953, declared that from that date on, particle accelerators took the place of cosmic rays, which more or less faded into the background. And yet, even today accelerators have not caught up with cosmic rays. For in 1938, I showed the presence in primary cosmic rays of particles of a million Gigavolts -- a million times more energetic than accelerators of that day could produce. Even now, when accelerators have far surpassed the Gigavolt mark, they still have not attained the energy of 1020 eV, the highest observed energy for cosmic rays. Thus, cosmic rays have not been dethroned as far as energy goes, and the study of cosmic rays has a bright future, if only to learn where these particles come from and how they are accelerated. You know that Fermi made a very interesting proposal that particles are progressively accelerated by bouncing off moving magnetic fields, gaining a little energy each time. In this way, given a certain number of "kicks," one could perhaps account for particles of 1018 - 1020 electron volts. As yet, however, we have no good theory to explain the production of the very-high-energy particles that make the air showers that my students and I discovered in 1938 at Jean Perrin's laboratory on a ridge of the Jungfrau."
— Pierre Auger, Journal de Physique, 43, 12, 1982