When an electron and positron collides, they annihilate and produce photons, right? No massive particle can travel faster than light, So here is my confusion... Electrons and Positrons have mass and hence can never reach the Speed of light But When they collide they create photons. Which means When photons are born, they must have some initial acceleration to reach the speed of light... This means photons can actually travel at a speed lesser than c even in vaccuum? (Assume the collision happens in vaccuum) Analogy for the above question: Imagine two race cars(e- & e+) accelerating towards each other and finally collides, and when they does, a tire(photon) is thrown off of the collision. Lets say the tire travels at speed c, but the collision accelerated the tire to reach speed c.. Which means the tire had an initial acceleration.. So My real question is - Does a photon has initial acceleration?