I believe... Particles without mass are required to travel at the speed of light. Particles traveling at the speed of light don't experience time in their own

I believe... Particles without mass are required to travel at the speed of light. Particles traveling at the speed of light don't experience time in their own frame of reference. For instance a photon is emitted and absorbed at the same instance from its point of view. So they have no time to do anything like change properties.