How Fast Is Cosmic Ray Proton?

The highest-energy cosmic ray ever detected — nicknamed the 'Oh-My-God Particle' — had 99.999999999999999999998% the speed of light. When it hit the atmosphere it carried the kinetic energy of a 145 km/h baseball, all in a single proton.

The 'Oh-My-God' particle had so much energy in a single proton that physicists initially doubted the measurement — only later confirming it with multiple detectors.

• One proton with the energy of a baseball pitch
• Origin still unknown — the 'Oh-My-God particle' was detected in 1991