What Does GZK Stand For?

GZK stands for Greisen Zatsepin Kuzmin Cut Off Cosmic Ray Energies

GZK, or Greisen Zatsepin Kuzmin Cut Off, refers to a theoretical limit on the energy of cosmic rays originating from extragalactic sources. Proposed in the 1960s by physicists Georgiy Greisen, Vitaly Zatsepin, and Alexander Kuzmin, the GZK cutoff arises from the interaction of high-energy cosmic rays with the cosmic microwave background radiation. This phenomenon results in the attenuation of cosmic rays beyond an energy threshold of approximately 5 x 10^19 electron volts, effectively reducing the number of detectable ultra-high-energy cosmic rays and influencing our understanding of the sources and mechanisms of cosmic radiation.