The Oh-My-God Particle
The University of Utah operates a cosmic ray detector called the Fly's Eye II, situated at the Dugway Proving Ground about an hour's drive from Salt Lake City. The Fly's Eye consists of an array of telescopes which stare into the night sky and record the blue flashes which result when very high energy cosmic rays slam into the atmosphere. From the height and intensity of the flash, one can calculate the nature of the particle and its energy.
On the night of October 15, 1991, the Fly's Eye detected a proton with an energy of 3.2±0.9×1020 electron volts.[1,2] By comparison, the recently-canceled Superconducting Super Collider (SSC) would have accelerated protons to an energy of 20 TeV, or 2×1013 electron volts—ten million times less. The energy of the Oh My God particle seen by the Fly's Eye is equivalent to 51 joules—enough to light a 40 watt light bulb for more than a second—equivalent, in the words of Utah physicist Pierre Sokolsky, to “a brick falling on your toe.” The particle's energy is equivalent to an American baseball travelling fifty-five miles an hour.
All evidence points to these extremely high energy particles being protons—the nuclei of hydrogen atoms. Recalling that the rest mass of the proton is 938.28 MeV—roughly 1 GeV, 1×109 eV, all of the rest of the particle's energy results from the kinetic energy resulting from its motion, which we can calculate according to basic formulæ of special relativity. So let's crunch a few numbers.
