Lets say I got a photon, travelling at light speed, in a completley empty region of space. No stars, no plants, nothing.
From Einstein theory, light always travel at the speed of light, no matter who measures it, but in an empty region of space, it’s impossible to measure this speed because the speed of an object is something which is relative to other objects.
How will this photon behave? what will it look like?
My English is not so good so I hope I made myself clear