A Giant Air Shower Array in Nord Rhein Westfalen

The energy spectrum of cosmic rays appears to extend unattenuated beyond 5 · 10 eV although photoproduction of pions by collisions of the primary protons with the universal 2.7◦ K microwave background should have cut off the cosmic ray energy spectrum. The assumption that the highest energy particles of cosmic rays are protons is a most natural one and is also in accord with the observed features of the giant air showers. If the astrophysical sources of the cosmic rays are on average far enough away, that is 100 Mpc or more and with protons as the primary particles, the cut off of the spectrum is unavoidable. Then we have the classical controversy about distances of sources, near of far, that played a fundamental role in many astrophysical phenomena, like recently for the gamma ray bursts (GRB). Only observations decide. Two questions need to find a definite answer experimentally