: : Massless particles are referred to as having 0 rest mass. Meaning that if they ever come to a stop, theory predicts they would have no mass. In a practical sense, massless particles, such as photons, never stop or slow down and always travel at the speed of light. Having 0 rest mass means they can zip away at the speed of light without suffering relativistic effects.

: : if E = mc2 then how can you have massless particles? : : it how can the speed of light squared, times zero, : : equal anything else other than zero?

: : feel free to email me as well as post the answer!

: : tate@aapi.co.uk

Thinking about it... Surely photons must loose speed or energy as they change direction/reflect off of surfaces? What is it that keeps them always traveling at 186k mps? Why do we never see "slow" photons? What is it that "governs" them?