Photons which constitute X-rays and gamma rays have a significantly higher energy than those which constitute the visible light. If they have so much more energy, why do they travel at the same speed as photons of visible light. If we add energy to particles such as electrons, we can make them move faster. For example, if we give energy of the order of 220,000 eV to an electron, we can make the electron attain speeds of 90% the speed of light. Why does the same rule not apply to photons?