What implications do the relative velocity of photons have ?

What implications do the relative velocity of photons have ?

 

What do you mean?

 

If you mean the fact that the speed of light is invariant, the the implication is the theory of special relativity.

Not enough information to proceed. "Relative velocity" can simply mean a difference in direction. You need to clarify.

Is the fact that light is a transverse wave a result of the fact that all photons travel with the same speed ?

What implications do the relative velocity of photons have ?

This is a very open ended question.

 

Basically, it means that you can use light as a 'probe of the causal structure of space-time'.