Question

What is the speed of a photon with respect to another photon if (a) the two photons are going in the same direction and (b) they are going in opposite directions?

Answer 1

Answer:

Relative velocity of a photon with respect to another photon will be 0, when they are going in the same direction. Thus, the relative velocity of a photon with respect to another photon will be equal to the speed of light when they are going in opposite directions.