Worked example - how much energy is 10^15 eV in everyday units? Cosmic-ray energies in electron-volts are hard to picture, so convert to joules. 1 eV = 1.602 x 10^-19 J. Step 1: multiply: 10^15 x 1.602 x 10^-19 J = 1.602 x 10^-4 J, about 0.16 millijoules. Step 2: compare - that is about the energy of a grain of sand falling a millimetre. It sounds tiny, but it is all carried by ONE proton: per particle, it is a quadrillion times the energy of visible-light photons (~2 eV). For the Oh-My-God particle at 3 x 10^20 eV: 3 x 10^20 x 1.602 x 10^-19 = 48 J - like a tennis ball served at 150 km/h, concentrated in a single proton.