Two photons travel along the x-axis of S, with a constant distance L between them.
Find the distance between them as observed in S' (standard config - i.e. moving with speed v in x direction wrt S)
How is this result connected to the Doppler effect?
The Attempt at a Solution
So normally the distance would be lorentz contracted - right? So it would be L/gamma
but i guess it is not here? and how is it related to doppler? any hints would be great ! thanks