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See Link for Math calculations...etc...
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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.
First of all, noting that mass and energy are equivalent, we can calculate the rest mass equivalent of a 3×1020 eV particle to be about 5×10−13 grams. That doesn't sound like much until you recall that this is about 3×1011 daltons (chemists measure molecular mass in daltons, where 1 dalton is the mass of a hydrogen atom), just about the same as a single cell of the intestinal bacterium E. coli (5×1011 daltons). Thus this single subatomic particle had a mass-energy equivalent to a bacterium.
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After traveling one light year, the particle would be only 0.15 femtoseconds—46 nanometres—behind a photon that left at the same time.
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These calculations involve some elementary but easy to mess up algebra and some very demanding numerical calculations for which regular IEEE double precision is insufficient. If you'd like to double-check these results, be sure to use a multiple precision calculator with at least 30 significant digits of accuracy. I generally use Mathematica for symbolic work and Mark Hopkins' package C-BC for number crunching. It's entirely possible I've made one or more mistakes of order-of-magnitude or greater significance. But even so, (and please correct me!), this is, particle physics wise, a genuine Oh Wow event.