Is there a maximum energy for cosmic rays?
There is a predicted maximum energy 6 x 1019 eV, which was calculated by Kenneth Greisen in the United States and G.T. Zatsepin and V.A. Kuz’min in the Soviet Union in 1965. It is called the GZK cutoff after the three scientists who discovered it. Space isof filled with microwave radiation, called the cosmic microwave background, which is leftover radiation from the Big Bang. While a microwave photon doesn’t have much energy, a sufficently energetic cosmic ray would see the photon’s wavelength to be compressed due to the Doppler effect. From the cosmic ray’s perspective, the microwave photon would appear to be a gamma ray. Collisions between protons (cosmic rays) and gamma rays have been studied in accelerators, and these collisions often result in the production of particles called pions, which cause the proton to lose energy. A collision in space between a cosmic ray proton and a microwave photon would result in the same production of pions. With each collision, the proton would lose
