The first observation of a cosmic ray with an energy exceeding 1020 electronvolts was made by John Linsley at the Volcanic Ranch experiment in New Mexico in 1962.[1][2] Cosmic rays with even higher energies have since been observed. Among them was the Oh-My-God particle (a play on the nickname "God particle" for the Higgs boson) observed on the evening of 15 October 1991 over Dugway Proving Grounds, Utah. Its observation was a shock to astrophysicists, who estimated its energy to be approximately 3 × 1020 electronvolts (50 joules)-- in other words, a subatomic particle with macroscopic kinetic energy equal to that of a baseball (142 g or 5 ounces) at 96 km/h (60 mph). It was most probably a proton with a velocity only very slightly below the speed of light. To a static observer, such a proton, traveling at [1 − (5×10−24)] times c, would travel only 47 nanometers (5×10−24 light-years) less than a light-year in one year.[3] (the proton would only be 47 nm behind a photon traveling the same path from the same point over the past year).
The first observation of a cosmic ray with an energy exceeding 1020 electronvolts was made by John Linsley at the Volcanic Ranch experiment in New Mexico in 1962.[1][2]
Cosmic rays with even higher energies have since been observed. Among them was the Oh-My-God particle (a play on the nickname "God particle" for the Higgs boson) observed on the evening of 15 October 1991 over Dugway Proving Grounds, Utah. Its observation was a shock to astrophysicists, who estimated its energy to be approximately 3 × 1020 electronvolts (50 joules)-- in other words, a subatomic particle with macroscopic kinetic energy equal to that of a baseball (142 g or 5 ounces) at 96 km/h (60 mph).
It was most probably a proton with a velocity only very slightly below the speed of light. To a static observer, such a proton, traveling at [1 − (5×10−24)] times c, would travel only 47 nanometers (5×10−24 light-years) less than a light-year in one year.[3] (the proton would only be 47 nm behind a photon traveling the same path from the same point over the past year).
Greisen-Zatsepin-Kuzmin limit - Wikipedia, the free encyclopedia
This limit was computed in 1966 by Kenneth Greisen[1] and Vadim Kuzmin and Georgiy Zatsepin[2] independently; based on interactions predicted between the cosmic ray and the photons of the cosmic microwave background radiation. They predicted that cosmic rays with energies over the threshold energy of 5×1019 eV would interact with cosmic microwave background photons to produce pions. This would continue until their energy fell below the pion production threshold. ... Because of the mean path associated with the interaction, extragalactic cosmic rays with distances more than 50 Mpc (163 Mly) from the Earth with energies greater than this threshold energy should never be observed on Earth, and there are no known sources within this distance that could produce them. A number of observations have been made by the AGASA experiment that appeared to show cosmic rays from distant sources with energies above this limit (called ultra-high-energy cosmic rays, or UHECRs). The observed existence of these particles was the so-called GZK paradox or cosmic ray paradox.
...
Because of the mean path associated with the interaction, extragalactic cosmic rays with distances more than 50 Mpc (163 Mly) from the Earth with energies greater than this threshold energy should never be observed on Earth, and there are no known sources within this distance that could produce them.
A number of observations have been made by the AGASA experiment that appeared to show cosmic rays from distant sources with energies above this limit (called ultra-high-energy cosmic rays, or UHECRs). The observed existence of these particles was the so-called GZK paradox or cosmic ray paradox.
A number of exotic theories have been advanced to explain the AGASA observations. The most notable is the theory of doubly-special relativity. However, it is now established that standard doubly special relativity does not predict any suppression of the GZK cutoff, contrary to the pattern explored since 1997 by Luis Gonzalez-Mestres where an absolute local rest frame (the "vacuum rest frame") exists.[citation needed] Other possible theories involve a relation with dark matter.
The most notable is the theory of doubly-special relativity. However, it is now established that standard doubly special relativity does not predict any suppression of the GZK cutoff, contrary to the pattern explored since 1997 by Luis Gonzalez-Mestres where an absolute local rest frame (the "vacuum rest frame") exists.[citation needed]
Other possible theories involve a relation with dark matter.
Apparently not...
In July 2007, during the 30th International Cosmic Ray Conference in Mérida, Yucatán, México, the High Resolution Fly's Eye Experiment (HiRes) and the Auger International Collaboration presented their results on ultra-high-energy cosmic rays. HiRes has observed a suppression in the UHECR spectrum at just the right energy, observing only 13 events with an energy above the threshold, while expecting 43 with no suppression. This result has been published in the Physical Review Letters in 2008 and as such is the first observation of the GZK Suppression.[3] The Auger Observatory has confirmed this result: instead of the 30 events necessary to confirm the AGASA results, Auger saw only two, which are believed to be heavy nuclei events. According to Alan Watson, spokesperson for the Auger Collaboration, AGASA results have been shown to be incorrect.
According to the analysis made by the AUGER collaboration the existence of the GZK cutoff seems to be confirmed, but it has been pointed out that the consequences of this result for models of Lorentz symmetry violation may depend crucially on the composition of the UHECR spectrum,[7] and that a delayed suppression of the GZK cutoff cannot yet be excluded.
