origin":35bda54o said:Just a point of clarification here - a photon does not have mass. Just because you can define a photon as a particle - for example with the photoelectric effect, that does not mean that the particle has mass. You should look at a photon as a massless particle.
A photon should be considered as information. Only information can travel at light speed, mass or particles can not.
A photon contains the information, that a physical particle changed it's energetic state. Somewhere a electron shifted into higher orbit and sent a photon as a result to inform another physical particle about the change of energetic state.
Without something or somebody to receive and interact with the information, information does not exist. It keeps moving on. If the information is received, it instructs the receiving matter to change it's energetic state.
Mass is not transferred when information is sent or received. Also, sending information costs for the sender (shifting electron into higher atomic orbit requires energy), but the receiver can profit from the same information. Energy was lost somewhere and gained elsewhere. Net energy in the universe remained the same, as per 1st law of thermodynamics suggest.
Energy can not be created or make vanish, but it can be sent elsewhere in the universe using information. A photon is a carrier of that information.