How about this.. Photons exists everywhere in universe.. And i mean everywhere..Think the universe is an aquarium filled with water to its limit..Thats what i mean.. It has a mass.. The question is how we couldn't find it yet? Answer is quite simple, its equally spreaded so it has no gravitational effect in universe..No positive or negative charge..And photons are only used by heat, in the form of light.So that heat transfer occurs via these photons.And we see it as light.. Oh and black mater anyone? A copper wire carrying electricity is a good example for this..The wire never moves or goes to lightspeed its there and standing still..Its the electricity that moves using the wire and unleashing its energy at the end..Good example of what i am trying to tell here.. Just thinking loudly, so any phsycian here wanna tell me why i am wrong in a technical manner?