Cosmic rays typically travel...at 99.999999 % of the speed of light (b). They get accelerated to super high energies and move super fast. How come they don't move at the speed of light (a) or faster than the speed of light (c)? First of all, nothing moves faster than the speed of light in a vacuum, absolutely nothing. To do so would mean to go backwards in time along with a whole host of other issues. Second, to move at the speed of light in a vacuum would mean that the object would have no mass, and would thus be a photon. Since protons and nuclei have mass, this cannot be. However, for all practical purposes, we assume that cosmic rays travel at the speed of light.
Although people on airplanes are more exposed to cosmic rays than the average person on the ground, cosmic rays do not use airplanes for travel and hence do not typically travel in first class (d)
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